PROTEC-12068,No.of Pages 12 ARTICLE IN PRESS JOURNAL OF MATERIALS PROCESSING TECHNOLOGY XXX (2008)XXX-XXX ELSEVIER journal homepage:www.elsevier.com/locate/imatprotec Review Review of warm forming of aluminum-magnesium alloys Serkan Toros,Fahrettin Ozturk',Ilyas Kacar Department of Mechanical Engineering,Nigde University,51245 Nigde,Turkey ARTICLE INFO ABSTRACT ived 31 Octobe r200 ellent high-s ance abilit 112 nrevisedform er,the tor olity and the ality of the final product alloys ar Accepted 31 March 2008 tive body materials recen esults show that the formability of these alloys is increased at temperature range from 20 product has been a f Al-Mg Warm forming 2008 Elsevier B.V.All rights reserved Aluminum-magnesium(Al-Mg) 5XXx series Contents 12 Introduction agnesium sheets S55 The effects of blankholder force and drawbead geometry 33 888 Conclusion cnowl dgements 888 Introduction industry.The advantages of these alloys are lightweight and very good therm roduced and used in many forms such fact tha as casting.sheet plate.bar.rod channels and foreines in some of these alloys can be formed in a soft condition and various areas of industry and especially in the aerospace heat treated to a temper comparable to structural steel make Coe sponding author.Tel:252254. 16/j.jmatprote i68spd,aro,t,Rieowofvam6mingodalminm-nigetmaor1htePoces.Tehpm
Please cite this article in press as: Toros, S., et al., Review of warm forming of aluminum–magnesium alloys, J. Mater. Process. Tech. (2008), doi:10.1016/j.jmatprotec.2008.03.057 PROTEC-12068; No. of Pages 12 ARTICLE IN PRESS journal of materials processing technology xxx (2008) xxx–xxx journal homepage: www.elsevier.com/locate/jmatprotec Review Review of warm forming of aluminum–magnesium alloys Serkan Toros, Fahrettin Ozturk∗, Ilyas Kacar Department of Mechanical Engineering, Nigde University, 51245 Nigde, Turkey article info Article history: Received 31 October 2007 Received in revised form 11 March 2008 Accepted 31 March 2008 Keywords: Warm forming Aluminum–magnesium (Al–Mg) alloys 5XXX series abstract Aluminum–magnesium (Al–Mg) alloys (5000 series) are desirable for the automotive industry due to their excellent high-strength to weight ratio, corrosion resistance, and weldability. However, the formability and the surface quality of the final product of these alloys are not good if processing is performed at room temperature. Numerous studies have been conducted on these alloys to make their use possible as automotive body materials. Recent results show that the formability of these alloys is increased at temperature range from 200 to 300 ◦C and better surface quality of the final product has been achieved. The purpose of this paper is to review and discuss recent developments on warm forming of Al–Mg alloys. © 2008 Elsevier B.V. All rights reserved. Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00 2. Aluminum for passenger vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00 3. Formability of aluminum–magnesium sheets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00 3.1. The effects of blankholder force and drawbead geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00 3.2. The effects of temperatures and strain rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00 3.3. The effects of lubrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00 4. Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00 1. Introduction Aluminum alloys are produced and used in many forms such as casting, sheet, plate, bar, rod, channels and forgings in various areas of industry and especially in the aerospace ∗ Corresponding author. Tel.: +90 388 225 2254. E-mail address: fahrettin@nigde.edu.tr (F. Ozturk). industry. The advantages of these alloys are lightweight, corrosion resistance, and very good thermal and electrical conductivity. The aforementioned factors plus the fact that some of these alloys can be formed in a soft condition and heat treated to a temper comparable to structural steel make 0924-0136/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2008.03.057
PROTEC-12068:No.of Pages 12 ARTICLE IN PRESS JOURNAL OF MATERIALS PROCESSING TECHNOLOGY XXX (2008)XXX-XX) /15073 four digit system.Themajor al USA 2x1 hat c Manganese fo 20253035 uused series for 9XXx are main alloving elements. use ong Fig.1-Av nun application of the aluminum and its alloys this Khare 2000:sch warz et al,2001). use or .For expanding use ofalu u Aluminum alloys are effective materials for the reduction s in many areas of vehicle weight and are expanding their applications.Fig. o overcome.The formability of the aluminum alloys at ratesthe usage of a on to and A emperatures is generally lower than at both cryogenic has recently increased their aluminum alloy usage. xpect that m alloys usage in Japan A alloys especially 5xXX series alloys and is related to the cle production holds steady at around 10 million units.the due o ng.wh at ele ve age around () ing at crvogenic temperatur nging th at high ot forr Ihe dema num a uch as creep mechanisms which m eformation and cavitations at grain boundaries which may nduce premature the by casting such as engines.wheels.exhaust decor how Aluminum for pass nge vehicles ightweight vehicles have become a key targ get for car mar including bumper beams ou and in forgings including suspension parts Fig 2. 5 g the vehicle nerforma the most e comfort and r abil s that minun ty (Cole and S erman, 1995).Aluminum will prob 2kg of stee can lead to a net reduction me ve the ns in the utomotiv industry (Carle ents on co emissions a shown coa emission is uts in arious allo elements n area can also have a big influence on the sustainabilit of a ca ome of the important sign aspects of a ca t and T ates the material has big infl car eight un (300.000km).although i would about 30%mo 0201202020302094·2003 de while incr asing the employment in the short term (Fuhrmann,1979). Miller et al.,2000;Turkish Statistical Institute,2004). s.S.et al..Review of warm forming of aluminum-magnesium alloys.I.Mater.Process.Tech.(2008
Please cite this article in press as: Toros, S., et al., Review of warm forming of aluminum–magnesium alloys, J. Mater. Process. Tech. (2008), doi:10.1016/j.jmatprotec.2008.03.057 PROTEC-12068; No. of Pages 12 ARTICLE IN PRESS 2 journal of materials processing technology xxx (2008) xxx–xxx it very attractive for fabricating various aircraft and missile parts. The present system utilized to identify aluminum alloys is the four digit designation system. The major alloy element for each type is indicated by the first digit, i.e., 1XXX indicates aluminum of 99.00% minimum; 2XXX indicates that copper is the main alloying element. Manganese for 3XXX, silicon for 4XXX, magnesium for 5XXX, magnesium and silicon for 6XXX, zinc for 7XXX, lithium for 8XXX, and unused series for 9XXX are main alloying elements. In industry, low carbon steels have been commonly used for a long time due to their excellent formability at room temperature, strength, good surface finish, and low cost. However application of the aluminum and its alloys in this field were ranked far behind steels because of cost and formability issues, despite their high-strength-to-weight ratio and excellent corrosion resistance. For expanding use of aluminum alloys or replacing steels in many areas, however, there have been challenging formability problems for aluminum alloys to overcome. The formability of the aluminum alloys at room temperatures is generally lower than at both cryogenic and elevated temperatures. At cryogenic temperatures, the tensile elongation is significantly increased for many aluminum alloys especially 5XXX series alloys and is related to the enhancement of work hardening, while at elevated temperatures it is mainly due to the increased strain rate hardening. Forming at cryogenic temperatures is technologically more challenging than at high temperatures. At hot forming temperatures, other issues should also be taken into consideration such as creep mechanisms which may affect the forming deformation and cavitations at grain boundaries which may induce premature failure at low strain rates. 2. Aluminum for passenger vehicles Lightweight vehicles have become a key target for car manufacturers due to increasing concerns about minimizing environmental impact and maximizing fuel economy without sacrificing the vehicle performance, comfort, and marketability (Cole and Sherman, 1995). Aluminum will probably play an important role in the future car generations. Its material properties give some advantages and open the way for new applications in the automotive industry (Carle and Blount, 1999). As a result of the developments in the aluminum industry, improving the mechanical properties of the aluminum alloys by adding various alloying elements increased the application area of these alloys in automotive and aerospace industries (Richards, 1900). Design of aluminum structures can also have a big influence on the sustainability of a car. Some of the important design aspects of a car which influence the environment are weight, aerodynamic and roll-resistance. DHV Environment and Transportation Final Report indicates that the material has a big influence on the car weight. (DHV Environment and Transportation Final Report, 2005). Lightweight car consumes less material resources in the long run (300,000 km), although it would cost about 30% more than the conventional car. Therefore, its production would decrease employment in the car industry by about 4% over a decade while increasing the employment in the short term (Fuhrmann, 1979). Fig. 1 – Average use of aluminum (International Aluminum Institute (IAI), 2002; Martchek, 2006; Mildenberger and Khare, 2000; Schwarz et al., 2001). Aluminum alloys are effective materials for the reduction of vehicle weight and are expanding their applications. Fig. 1 illustrates the usage of aluminum for European and American vehicles over years. In addition to USA and Europe, Japan has recently increased their aluminum alloy usage. Analysts expect that the aluminum alloys usage in Japan Automotive Industry will reach 1.5 million tons by 2010. Assuming vehicle production holds steady at around 10 million units, the average yearly growth will be around 2.5% (McCormick, 2002). As shown in Fig. 1, the amount of aluminum used in 1960 is substantially low. The main reasons are forming difficulties of aluminum alloys at that time and the smaller range of alloys available. The demand for aluminum alloys as light weight materials has increased in recent years. Fig. 2 demonstrates the amount of produced aluminum products in the world. In the past, the main aluminum products were produced by casting such as engines, wheels, exhaust decor; however nowadays wrought aluminum products are finding more applications in sheets including exterior panels such as hoods and heat insulators, in extrusions including bumper beams, and in forgings including suspension parts Fig. 2. One of the most important benefits of using aluminum alloys in automotive industry is that every kg of aluminum, which replaces 2 kg of steel, can lead to a net reduction of 10 kg of CO2 equivalents over the average lifetime of a vehicle (Ungureanu et al., 2007). In Fig. 3, the effects of the car components on CO2 emissions are shown. CO2 emission is Fig. 2 – Aluminum products for automobile over years (Cole and Sherman, 1995; Inaba et al., 2005; Patterson, 1980; Miller et al., 2000; Turkish Statistical Institute, 2004)
PROTEC-12068 No.of Pages1 ARTICLE IN PRESS JOURNAL OF MATERIALS PROCESSING TECHNOLOGY XXX (2008)XXX-XXX P9tao8Rgent1gegon oengine ico Motorheating Fuel Quality <%1-3 Meogeagnt<%tio Woton te Loses<%10 Fig.3-Effect of technical measures on the CO2 emission(Mordike and Ebert,2001). Table 1-Saving in fuel consumption(Mordike and Ebert,2001) Measure taken Potential saving (%fuel Importance innovative materials Short-medium term Long term 35 10-15 Motor\gear control 5 Resistance to rolling Motor preheating +士士 Equipment critical in terms of environmental pollution.Schwarz et al. alloy 5017.In their study,they focused on changes in the d that the change in the iron content does not lead to a dramatic degen- by using lightweight materials such as aluminum in new eration in the performance of the material. transportation designs.Weight reduction of the car's compo- Aluminum alloy sheets are widely used in the car,ship nents influences fuel consumption considerably.In Table 1 building and aerospace industries as substitutes for steel the effect of weight reduction on fuel savings is s sheets and fiber reinforced plastic(FRP)pa nels,due to their econom ents of aro 16-8%or as exeper gallon can be realized for every1weigh s high- tyCaka et al 2001)T atur of suc on resis we reduction(Mordike and Ebert,2001). the most used aluminum-magnesium alloys in automotive Recyclability of alloys has also become an important issue application were summarized in Table 2.Figs.4 and 5 illus- in view of energy and resource conservation.For example trates aluminum and other materials usages in automotive recycling potential of the aluminum products is much bet and aerospace industry,respectively. ter than the ferrous metals.Martchek (200)and Mildenb of the mo st effective and widely used and Khare (2000)investigated the recycling potential essary energy to reproduce the aluminum products.According in the 5XXX series alloys.These alloys often contain smal to Martchek(2006),increasing the recycled metal usage in the additions of transition elements such as chromium or man- aluminum production consumes less energy and emits less ganese,and less frequently zirconium to control the grain or greenhouse gas to produce the aluminum ingots.Sillekens et subgrain structure and iron and silicon impurities that are al.(1997)investigated the formability of recy cled aluminum usually present in the form of intermetallic particles(ASM Table 2-Comparison of several Al-Mg alloys Strength Formability Resistance to corrosion Weldability Excellen 5454,5652 5454,5652 545e 5083.5456 5154,5254 5005,5050,5083 5005,5050.5083,5254,5652 5154,5254,5557
Please cite this article in press as: Toros, S., et al., Review of warm forming of aluminum–magnesium alloys, J. Mater. Process. Tech. (2008), doi:10.1016/j.jmatprotec.2008.03.057 PROTEC-12068; No. of Pages 12 ARTICLE IN PRESS journal of materials processing technology xxx (2008) xxx–xxx 3 Fig. 3 – Effect of technical measures on the CO2 emission (Mordike and Ebert, 2001). Table 1 – Saving in fuel consumption (Mordike and Ebert, 2001) Measure taken Potential saving (%) fuel Importance innovative materials Short-medium term Long term Light constructions 3–5 10–15 ++ Cw value 2 4–6 + Motor\gear control 5 10 ± Resistance to rolling 1–2 3 + Motor preheating 2 4–6 ± Equipment 2 4 ± critical in terms of environmental pollution. Schwarz et al. (2001) inspected that the relationship between the usage of the aluminum products in new designs and the CO2 emission and emphasized that the CO2 emission ratio could be reduced by using lightweight materials such as aluminum in new transportation designs. Weight reduction of the car’s components influences fuel consumption considerably. In Table 1, the effect of weight reduction on fuel savings is seen. Fuel economy improvements of around 6–8% or as much as 2.5 extra miles per gallon can be realized for every 10% in weight reduction (Mordike and Ebert, 2001). Recyclability of alloys has also become an important issue in view of energy and resource conservation. For example, recycling potential of the aluminum products is much better than the ferrous metals. Martchek (2006) and Mildenberger and Khare (2000) investigated the recycling potential and necessary energy to reproduce the aluminum products. According to Martchek (2006), increasing the recycled metal usage in the aluminum production consumes less energy and emits less greenhouse gas to produce the aluminum ingots. Sillekens et al. (1997) investigated the formability of recycled aluminum alloy 5017. In their study, they focused on changes in the amounts of alloying elements (particularly iron) to see how they affect the formability of products. It is observed that the change in the iron content does not lead to a dramatic degeneration in the performance of the material. Aluminum alloy sheets are widely used in the car, shipbuilding and aerospace industries as substitutes for steel sheets and fiber reinforced plastic (FRP) panels, due to their excellent properties such as high-strength, corrosion resistance, and weldability (Naka et al., 2001). The features of the most used aluminum–magnesium alloys in automotive application were summarized in Table 2. Figs. 4 and 5 illustrates aluminum and other materials usages in automotive and aerospace industry, respectively. Magnesium is one of the most effective and widely used alloying elements for aluminum, and is the principal element in the 5XXX series alloys. These alloys often contain small additions of transition elements such as chromium or manganese, and less frequently zirconium to control the grain or subgrain structure and iron and silicon impurities that are usually present in the form of intermetallic particles (ASM Table 2 – Comparison of several Al–Mg alloys Strength Formability Resistance to corrosion Weldability Excellent 5454, 5652 – – 5454, 5652 Highest 5052 – – – High 5456 – 5456 5083, 5456 Good 5154, 5254 5005, 5050, 5083 5005, 5050, 5083, 5254, 5652 5154, 5254, 5557
le 3-Prop of Al-Mg alloysi 99:Boyd et materials (IMUA,2006;Wendt and Weis,2004;Beer and Johnston,1992;Talbot and Talbot,1998; p (kg/m o-(Mra E(GPa) G(GPa) CTE (20C) Hardness Appic Prices 009 124 45925.9 25.9 23.8 BS:28 148 5051 72014.9 25.9 23.8 8547 or panels an No.of Pages 12 5182 103773.6 69.6 23.9 8574 s,load floors (sheet 线 tanks 23.8 OF MATERIALS PROCESSING TECHNOLOGY XXX (2008 ARTICLE IN PRESS 340 567 1200 8 AM6OB- WES4-T S:8 ZK60A- 85792.3 1140 6578g.5 28 595
doi: Please cite this article in press as: Toros, S., et al., Review of warm forming of aluminum–magnesium alloys, J. Mater. Process. Tech. (2008), 10.1016/j.jmatprotec.2008.03.057 ARTICLE IN PRESS 4 PROTEC-12068; No. of Pages 12 journal of materials processing technology xxx (2008) xxx–xxx Table 3 – Properties of Al–Mg alloys in automotive structures and other materials (IMUA, 2006; Wendt and Weiß, 2004; Beer and Johnston, 1992; Talbot and Talbot, 1998; Material Property Data, 1996–2007; Shernaz, 1991; Boyd et al., 1995) Material (kg/m3) a (MPa) Strenght/density (Pa/(kgm3)) E (GPa) G (GPa) CTE (20 ◦C) εb Hardness Applications in automotive Prices Aluminium 5005 2700 124 45925, 9 68, 9 25, 9 23, 8 25 BS: 28 Trim, nameplates, appliques´ 1486 5052 2680 193 72014, 9 70, 3 25, 9 23, 8 25 BS: 47 Interior panels and components, truck bumpers and body panels 5182 2650 275 103773, 6 69, 6 26 23, 9 21 BS: 74 Inner body panels, splash guards, heat shields, air cleaner trays and covers, structural and weldable parts, load floors (sheet) 5252 2670 180 67455, 7 69 26 23, 8 23 BS: 46 Trim 5454 2690 248 92193, 3 70, 3 26 23, 6 22 BS: 62 Various components, wheels, engine accessory brackets and mounts, welded structures (i.e. dump bodies, tank trucks, trailer tanks) 5457 2690 131 48698, 9 68, 9 26 23, 8 22 BS: 32 Trim 5657 2690 110 40892, 2 69 26 23, 8 25 BS: 28 Trim 5754 2670 230 86142, 3 68 22.6 HV: 55 Inner body panels, splash guards, heat shields, air cleaner trays and covers, structural and weldable parts, load floors Magnesium AZ80A-F 1800 340 188888, 8 45 17 26 7 BS: 67 Headlight housing, wheels and tires 1200 AZ31B-F 1770 260 146892, 7 45 17 26 15 BS: 49 Seats, passenger restraints instruments and controls, case of seat belt AZ91D-F 1810 230 127071, 8 45 17 26 3 BS: 63 Treadle of Bicycle AM50A-F 1770 228 128813, 5 45 17 26 15 BS: 60 Exhaust decor, exhaust system AM60B-F 1800 241 133888, 9 45 17 26 13 BS: 65 transmission or transaxle, clutch (if manual), drive line (rear-wheel drive) WE54-T6 1850 280 151351, 4 45 17 26 4 BS: 85 Differential, transfer case subframes, engine block ZK60A-F 1830 340 185792, 3 45 17 26 11 BS: 75 Fuel storage system Plastics Nylon 6/6 1140 75 65789, 5 2, 8 – 144 50 BS: 95 320
PROTEC-12068.No.of Pages 12 ARTICLE IN PRESS JOURNAL OF MATERIALS PROCESSING TECHNOLOGY XXX (2008)XXX-X 景属8另88宝8：1 Fig.4-Alalloys and its application for automotive industry (Sherman,2000;White,2006). 0%5-cunetmtealuagesfcBoing7S7AMosconih 的始88始兽片3设8：总8 Metal Handbook.1988).When magnesium is used as the maio ength,no y.Aloy tance even in marine applications.Selection of g所g8 alloys,for several primarily,mechanical properties.Table 3summarizes feature 首程窗 Formability of aluminum-magnesium sheets 8份好份导9景尽员于的员可 The effects of blankholder force and drawbead 8星品品品品品 made from a metal sheet,the deep drawing process or the suitable pre mal to the sheet are us ted.Two important failure modes limit the applicabil of thec p dra wing and s tretching process:necking and to accurately predict the occurrence of wrinkling is critical 8i5pd5,ao,stl,ioawofvamfomingodahmnum-mgneumaoys1ateocsTdhpocgl
Please cite this article in press as: Toros, S., et al., Review of warm forming of aluminum–magnesium alloys, J. Mater. Process. Tech. (2008), doi:10.1016/j.jmatprotec.2008.03.057 PROTEC-12068; No. of Pages 12 ARTICLE IN PRESS journal of materials processing technology xxx (2008) xxx–xxx 5 Polycarbonate 1200 65 54166, 7 2, 4 – 122 110 BS: 115 400 Polyester, PBT 1340 55 41044, 8 2, 4 – 135 150 Shore D:65 380 Polyester elastomer 1200 45 37500, 0 0, 2 – 130 500 Shore D: 30–82 520 Adhesives 1030 55 53398, 1 3, 1 – 125 2 – 250 Rubber, PVC 1440 40 27777, 8 3, 1 – 135 40 Shore D: 74–88 120 Rubber 910 15 16483, 6 0, 5 – 162 600 Shore A: 30–90 130 Ti–6Al–4Vc 4730 900 190274, 8 120 235 9, 5 10 BS: 334 5845 Cu extruted 8910 390 43771, 1 120 44 16.9 4 BS: 90 2323 Epoxy/glass SMC 1600 260 162500, 0 – – 3, 65 – – – H254 polyester laminate 1600 41 25625, 0 – – 0, 29 – Barcol:30 – Thermoset polyester 1820 55 30219, 8 – – 1, 2 – Barcol:32 – Epoxy/glass SMC 1600 260 162500, 0 – – 3, 65 – – – H254 polyester laminate 1600 41 25625, 0 – – 0, 29 – Barcol:30 – a Yield point. b Elongation at break %. c Heat-treatment. Fig. 4 – Al alloys and its application for automotive industry (Sherman, 2000; White, 2006). Fig. 5 – Current material usages for Boing 757 (Moscovitch, 2005). Metal Handbook, 1988). When magnesium is used as the major alloying element or combined with manganese, the result is a moderate to high-strength, non-heat-treatable alloy. Alloys in this series are readily weldable and have excellent resistance to corrosion, even in marine applications. Selection of suitable aluminum alloys, for several applications, requires a basic knowledge of heat treatment, corrosion resistance, and primarily, mechanical properties. Table 3 summarizes features and applications of Al–Mg alloys. Three different material groups, their properties and applications were compared for material selection. 3. Formability of aluminum–magnesium sheets 3.1. The effects of blankholder force and drawbead geometry Typical sheet metal forming processes are bending, deep drawing, and stretching. If a doubly curved product must be made from a metal sheet, the deep drawing process or the stretching process is used. The deep drawing process can reach production cycles of less than 10 s, and is hence a suitable process for mass production. In deep drawing and stretching, the stresses normal to the sheet are usually very small compared to the in-plane stresses and are therefore neglected. Two important failure modes limit the applicability of the deep drawing and stretching process: necking and wrinkling. Both are closely related to the material properties. The ability to accurately predict the occurrence of wrinkling is critical in the design of tooling and processing parameters (Xi and Jian, 2000) like sheet thickness, blankholder force
PROTEC-12068:No.of Pages 12 ARTICLE IN PRESS JOURNAL OF MATERIALS PROCESSING TECHNOLOGY XXX (2008)XXX-XXX nd the sheet(Hutchi Cooled Punch e limits an de oped blank holding force (BHF)contro Water Cooling Heat Blank Holder these d part qu Electric Heater Pin Thermocoupl trol afo esaid p meters.Jinta et al (2000) (XX and results indicate that aluminum allo ally forms rinkles then steel,especially 6xxx series alu n allo a 、Drawing Die n deep drawing of square cup in order i Wire Thermocouple tearing,and thickn material to be drawn into the die cavity without line at the straight sides which cause tearing.Lin e 00 Shehata et al.,1978).Schmoeckel (1994)and Schmoeckel et rmined the drawing limit under cor ant 1(1995)investigated the drawability of 5xxx series alloys into the die cavity during the stretch forming of larg pa de that they redu orming showed that the formability with a partial heating ir the 100 ler or matrices are a was mucr ls ts er when co 1994 f dr wbead and the amo ount of force on it are very s of part quality.Samu 2002 investigated the force (DBRP)and BHF numerically and experimentally forau rated hydromechanical stamp.Modeling of the deep draw minum alloy.In his study.two kinds of drawbead geom e bead are higher than those for the rounded femal It was demonstrated that the formability is improved by He emph ncy are o re increase. but the ts ent plastic strain and von Mises stresse on the con mposition of the aluminum afsquarefemaled have a relativ ely goo stretcher lines,which givesan uneven surface after deform The effects of temperatures and strain rates Althoueh the aluminum alloys have hieh-streneth to v eigh at the elevate ratio and good corros esistance.the low formability luminum shee some prod intended to over come this 2002).Yamashita et al.(2007)numer ally si ulated circu levated formingtem cups cal warm forming experimental set-up is shown in Fig6.in waomingset-updies andbl oders are he ated t of the rigid punch.Browne and Battikha(199 eating rods that are located in these narts are used hut ther is a risk of necking during heating and cooling.Warm form o ac urately simulate warm forming of alumi m shee ars,e.g the 1970s and 198 the t d an nk,2004).Because of this, on very impo a出 al for the aluminum alloys such as 5082 the formability of the Al-Mg alloy sheets can be improved by ncreasing the temperature in some parts of the sheet an os.s.et al..Review of warm forming of aluminun magnesium alloys.I.Mater.Process.Tech.(2008)
Please cite this article in press as: Toros, S., et al., Review of warm forming of aluminum–magnesium alloys, J. Mater. Process. Tech. (2008), doi:10.1016/j.jmatprotec.2008.03.057 PROTEC-12068; No. of Pages 12 ARTICLE IN PRESS 6 journal of materials processing technology xxx (2008) xxx–xxx and the local curvature of the sheet (Hutchinson and Neale, 1985). Ahmetoglu et al. (1997) determined wrinkling and fracture limits and developed blank holding force (BHF) control to eliminate these defects, improve part quality and increase the formability. A computer simulation model was developed to control aforesaid parameters. Jinta et al. (2000) examined wrinkle behavior in 5XXX and 6XXX series aluminum alloys and compared the results with wrinkle behavior of steel. Their results indicate that aluminum alloys generally forms more wrinkles then steel, especially 6XXX series aluminum alloy has a tendency to more wrinkles than 5XXX series. Gavas and Izciler (2007) examined the effect of blank holder gap (BHG) on deep drawing of square cup in order to investigate wrinkling, tearing, and thickness distribution. As a result of their study, they observed that increasing of the BHG allows more material to be drawn into the die cavity without tearing or shape distortions. It is also noticed that it was impossible to use too large BHG because of excessive wrinkling and buckling at the straight sides which cause tearing. Lin et al. (2007) determined the drawing limit under constant and variable BHF. Drawbeads are directly related with wrinkling behavior of the materials. They are used to control the flow of sheet metal into the die cavity during the stretch forming of large panels. Beside that they reduce the BHF and minimize the blank size needed to make a part (Demeri, 1993). The shape and position of drawbead and the amount of force on it are very important in terms of part quality. Samuel (2002) investigated the influence of drawbead geometry on the drawbead restraining force (DBRF) and BHF numerically and experimentally for aluminum alloy. In his study, two kinds of drawbead geometry which are square female and round female were investigated. As a result, it is obtained that the DBRF and BHF for the square female bead are higher than those for the rounded female bead. He emphasized that this discrepancy are occurred due to the sharp corners. It is also observed that the total equivalent plastic strain and von Mises stresses at upper and lower surfaces of square female drawbead are higher than those for the round female drawbead. 3.2. The effects of temperatures and strain rates Although the aluminum alloys have high-strength to weight ratio and good corrosion resistance, the low formability of aluminum sheets limits their use in some products with complex shapes, such as automotive body parts. The warm forming process is intended to overcome this problem by using an elevated forming temperature which is below the recrystallization temperature (Tebbe and Kridli, 2004). A typical warm forming experimental set-up is shown in Fig. 6. In the warm forming set-up, dies and blank holders are heated to 200–300 ◦C. In order to heat dies and blank holders, electrical heating rods that are located in these parts are used but there is a risk of necking during heating and cooling. Warm forming was studied for many years, e.g. in the 1970s and 1980s by Shehata et al. (1978) and Wilson (1988) with increasing attention being dedicated to the subject in the last decade. The warm forming method improves the formability of the aluminum alloys. This improvement at the elevated temperatures is principal for the aluminum alloys such as 5082 and 5005 alloys due to the increased strain rate hardening Fig. 6 – A typical warm forming set-up (Palumbo and Tricarico, 2007). (Shehata et al., 1978). Schmoeckel (1994) and Schmoeckel et al. (1995) investigated the drawability of 5XXX series alloys at the elevated temperatures. Temperature has a significant influence on the stamping process. Further investigation on forming showed that the formability with a partial heating in the holder or matrices area was much better when compared with the homogeneously heated tools (Schmoeckel, 1994). Schmoeckel et al. (1995) showed that a significant increase in the limiting drawing ratio (LDR) for the aluminum alloy AlMg4.5 Mn0.4 can be achieved by a heated and lower strain rated hydromechanical stamp. Modeling of the deep drawing with a rotationally symmetrical tool (stamp diameter: 100mm) which was cooled from the stamp side by additional air ensured an increase in LDR. It was demonstrated that the formability is improved by a uniform temperature increase, but the best results are obtained by applying temperature gradients. The formability depends strongly on the composition of the aluminum alloy. Aluminum–magnesium alloys have a relatively good formability. A disadvantage is that these alloys suffer from stretcher lines, which gives an uneven surface after deformation. Because of this reason, 5XXX series aluminum is used for inner panels of vehicles. These undesired surface defects can be eliminated by the forming processes at the elevated temperatures (Van Den Boogaard et al., 2001). The aluminum which contains 6% magnesium could give a 300% total elongation at about 250 ◦C, finds more application in industry (Altan, 2002). Yamashita et al. (2007) numerically simulated circular cups drawing process by using Maslennikov’s technique (Maslennikov, 1957) which is also called “punchless drawing”. In this production technique, a rubber ring is used instead of the rigid punch. Browne and Battikha (1995) optimized the formability process by using a flexible die and optimized the process parameters to ensure a defect-free product. To accurately simulate warm forming of aluminum sheet, a material model is required that incorporates the temperature and strain-rate dependency (Van Den Boogaard and Huetink, 2004 ´ ). Because of this, the effect of temperature distribution on warm forming performance is very important. Van Den Boogaard and Huetink (2006) ´ observed that the formability of the Al–Mg alloy sheets can be improved by increasing the temperature in some parts of the sheet and
PROTEC-12068;No.of Pages 12 ARTICLE IN PRESS JOURNAL OF MATERIALS PROCESSING TECHNOLOGY XXX(2008)XXX-XXX cooling the other parts when simulated by the cylindrical cup minum alloy AA5182-0.The dynamic strain aging effect was deep drawing at the different temperature gradients of the observed at all temperature between-80 and 110C and at tools and the blanks.Chen et al.(2006)investigated combined strain rates lower than 10-1s-1.In addition,the strain rate isothermal/non-isothermal finite element analysis(FEA)with sensitivity parameter was also determined as a function of design ofexperiments tools to predict appropriate warm form- temperature and plastic strain.Abedrabbo et al.(2007)devel- ing temperature conditions for 5083-0(Al-Mg)sheet metal oped a temperature-dependent anisotropic material model for blanks,deep drawing and two-dimensional stamping cases. FEA and formability simulation for two automotive aluminum To achieve increased degrees of forming,different tempera- alloys,AA5182-0 and AA5754-0.Multiple temperatures to ture levels should be assigned to the corner and body of the simulate the formability of more complex automotive parts, die and punch.25-250%elongation ranges were seen.They where the temperatures of the different sections will be deter- found that the formability of Al-5083 alloy is greatly depen- mined automatically,can be found by this model.In addition dent on the temperature distribution of the die and punch. to the temperature,the forming speed controlling the strain It is also observed that the optimal temperature distributions rate,the die and stamp comner radii and other geometric for warm deep drawing and warm two-dimensional stamping parameters of the die set-up determine the forming charac- were not identical. teristics of aluminum alloy sheets. Naka et al.(2003)investigated the effects of temperature In the finite element simulations,material models are quite on yield locus for 5083 aluminum alloy sheet.In their study, important in order to evaluate accurately the formability of they have tried to determine the optimum condition of press aluminum alloy sheets.Barlat models are commonly used to forming for an aluminum alloy sheet,the effect of form- define aluminum alloy behaviors. ing temperature on the yield locus.They obtained the yield Barlat and Lian (1989)developed a yield function that locus for a fine grain Al-Mg alloy(5083-O)sheet by performing described the behavior of orthortropic sheets and metals biaxial tensile tests,using cruciform specimens,at temper- exhibiting a planar anisotropy and subjected to plane stress atures of 30,100,170,250,and 300C at 10s-1 strain rate conditions.This yield function showed similar results cal- As expected,the size of the yield locus drastically decreased culated by the Taylor/Bishop and Hill models.Barlat et al. with increasing temperature.This can be exploited to improve (1991)extended this method to triaxial loading conditions press operations.Naka and Yoshida (1999)investigated the by using a six-component yield function.Lian et al.(1989) effects of temperature and forming rates on deep drawabil- used this yield function to study the influence of the yield ity of 5083 Al-Mg alloy.In their study,different temperature surface shape on failure behavior of sheet metals.Yu et al. gradients from room temperature to 180C and the form- (2007)developed a ductile fracture criterion which is intro- ing speeds between 0.2 and 500mm/min were performed. duced by a finite element simulation.They carried out the Results show that LDR increases mostly with increasing the simulations of aluminum alloy sheet forming based on Bar- die temperature because the deformation resistance in flange at's yield function (Barlat and Lian,1989)and Hollomon's shrinkage decreases with an increase in temperature.Beside hardening equation.In their study,the critical punch strokes that the LDR becomes smaller with increasing the forming of the aluminum alloy sheets of X611-T4,6111-T4 and 5754- speed at all temperatures since the flow stress of the heated o in a cylindrical complex forming in which deep drawing blank(at the flange)increases with increasing the strain rate. and stretching modes were calculated by the ductile fracture Moreover,the cooled blank at the punch corner becomes less criterion.The results showed good agreements with the exper- ductile.Another comprehensive study for 5XXX series alu- imental results.Barlat et al.(1997)measured the yield surfaces minum alloys was done by Bolt et al.(2001).In that study, for binary aluminum-magnesium sheet samples with differ- the formability was compared for 1050,5754 and 6016 type ent microstructures.A generalized plastic behavior of any aluminum alloys from 100 to 250C by using the both box aluminum alloy sheet yield description was proposed to pre- shaped and conical rectangular products.They observed that dict the behavior of the solute strengthened (precipitation the minimum die temperature of 6016 alloy on the die pro- hardened)aluminum alloy sheets.Barlat et al.(2003)proposed cess limits was lower than that of the 5754 alloy.Smerda et a plane stress yield function that describes the anisotropic al.(2005)investigated the strain rate sensitivity of 5754 and behavior of the sheet metals,in particular,for aluminum 5182 type aluminum alloy sheets at room temperature and alloy sheets.The anisotropy of the function was introduced elevated temperatures.In their study,the split Hopkinson bar in the formulation using two linear transformations on the apparatus was used to identify the constitutive response and Cauchy stress tensor.For the Al-5 wt.%Mg and 6016-T4 alloy the damage evolution in the aluminum alloys at high strain sheet samples,yield surface shapes,yield stress and r-value rates of 600,1100 and 1500s-1.It was observed that the qua- directionalities were compared with those of previously sug- sistatic and dynamic stress strain responses in the range of gested yield functions by Yoon et al.(2004).Barlat et al.(2005) strain rates and temperatures were low for both alloys.AA5754 proposed anisotropic yield functions based on linear transfor- exhibited a mild increase in flow stress with strain rate,while mations of the stress deviator in general terms.Two specific AA5182 appeared to be strain rate insensitive.The ductility convex formulations were given to describe the anisotropic of the materials showed little differences in the tempera- behavior of metals and alloys for a full stress state(3D).Choi ture range between 23 and 150C at a strain rate of 1500s-1. et al.(2007)developed analytical models for hydro-mechanical However,the final elongation was decreased for both alu- deep drawing tests to investigate the effects of process con- minum alloys at 300C and a strain rate of 1500s-1 when ditions such as temperature,hydraulic pressure,BHF and compared to that at lower temperatures.Picu et al.(2005) forming speed.According to their models,the experimental investigated the mechanical behavior of the commercial alu- results show good agreement with the FE models.One of the Please cite this article in press as:Toros,S.,et al.,Review of warm forming of aluminum-magnesium alloys,J.Mater.Process.Tech.(2008) doi:10.1016/j.jmatprotec.2008.03.057
Please cite this article in press as: Toros, S., et al., Review of warm forming of aluminum–magnesium alloys, J. Mater. Process. Tech. (2008), doi:10.1016/j.jmatprotec.2008.03.057 PROTEC-12068; No. of Pages 12 ARTICLE IN PRESS journal of materials processing technology xxx (2008) xxx–xxx 7 cooling the other parts when simulated by the cylindrical cup deep drawing at the different temperature gradients of the tools and the blanks. Chen et al. (2006) investigated combined isothermal/non-isothermal finite element analysis (FEA) with design of experiments tools to predict appropriate warm forming temperature conditions for 5083-O (Al–Mg) sheet metal blanks, deep drawing and two-dimensional stamping cases. To achieve increased degrees of forming, different temperature levels should be assigned to the corner and body of the die and punch. 25–250% elongation ranges were seen. They found that the formability of Al-5083 alloy is greatly dependent on the temperature distribution of the die and punch. It is also observed that the optimal temperature distributions for warm deep drawing and warm two-dimensional stamping were not identical. Naka et al. (2003) investigated the effects of temperature on yield locus for 5083 aluminum alloy sheet. In their study, they have tried to determine the optimum condition of press forming for an aluminum alloy sheet, the effect of forming temperature on the yield locus. They obtained the yield locus for a fine grain Al–Mg alloy (5083-O) sheet by performing biaxial tensile tests, using cruciform specimens, at temperatures of 30, 100, 170, 250, and 300 ◦C at 10 s−1 strain rate. As expected, the size of the yield locus drastically decreased with increasing temperature. This can be exploited to improve press operations. Naka and Yoshida (1999) investigated the effects of temperature and forming rates on deep drawability of 5083 Al–Mg alloy. In their study, different temperature gradients from room temperature to 180 ◦C and the forming speeds between 0.2 and 500mm/min were performed. Results show that LDR increases mostly with increasing the die temperature because the deformation resistance in flange shrinkage decreases with an increase in temperature. Beside that the LDR becomes smaller with increasing the forming speed at all temperatures since the flow stress of the heated blank (at the flange) increases with increasing the strain rate. Moreover, the cooled blank at the punch corner becomes less ductile. Another comprehensive study for 5XXX series aluminum alloys was done by Bolt et al. (2001). In that study, the formability was compared for 1050, 5754 and 6016 type aluminum alloys from 100 to 250 ◦C by using the both box shaped and conical rectangular products. They observed that the minimum die temperature of 6016 alloy on the die process limits was lower than that of the 5754 alloy. Smerda et al. (2005) investigated the strain rate sensitivity of 5754 and 5182 type aluminum alloy sheets at room temperature and elevated temperatures. In their study, the split Hopkinson bar apparatus was used to identify the constitutive response and the damage evolution in the aluminum alloys at high strain rates of 600, 1100 and 1500 s−1. It was observed that the quasistatic and dynamic stress strain responses in the range of strain rates and temperatures were low for both alloys. AA5754 exhibited a mild increase in flow stress with strain rate, while AA5182 appeared to be strain rate insensitive. The ductility of the materials showed little differences in the temperature range between 23 and 150 ◦C at a strain rate of 1500 s−1. However, the final elongation was decreased for both aluminum alloys at 300 ◦C and a strain rate of 1500 s−1 when compared to that at lower temperatures. Picu et al. (2005) investigated the mechanical behavior of the commercial aluminum alloy AA5182-O. The dynamic strain aging effect was observed at all temperature between −80 and 110 ◦C and at strain rates lower than 10−1 s−1. In addition, the strain rate sensitivity parameter was also determined as a function of temperature and plastic strain. Abedrabbo et al. (2007) developed a temperature-dependent anisotropic material model for FEA and formability simulation for two automotive aluminum alloys, AA5182-O and AA5754-O. Multiple temperatures to simulate the formability of more complex automotive parts, where the temperatures of the different sections will be determined automatically, can be found by this model. In addition to the temperature, the forming speed controlling the strain rate, the die and stamp corner radii and other geometric parameters of the die set-up determine the forming characteristics of aluminum alloy sheets. In the finite element simulations, material models are quite important in order to evaluate accurately the formability of aluminum alloy sheets. Barlat models are commonly used to define aluminum alloy behaviors. Barlat and Lian (1989) developed a yield function that described the behavior of orthortropic sheets and metals exhibiting a planar anisotropy and subjected to plane stress conditions. This yield function showed similar results calculated by the Taylor/Bishop and Hill models. Barlat et al. (1991) extended this method to triaxial loading conditions by using a six-component yield function. Lian et al. (1989) used this yield function to study the influence of the yield surface shape on failure behavior of sheet metals. Yu et al. (2007) developed a ductile fracture criterion which is introduced by a finite element simulation. They carried out the simulations of aluminum alloy sheet forming based on Barlat’s yield function (Barlat and Lian, 1989) and Hollomon’s hardening equation. In their study, the critical punch strokes of the aluminum alloy sheets of X611-T4, 6111-T4 and 5754- O in a cylindrical complex forming in which deep drawing and stretching modes were calculated by the ductile fracture criterion. The results showed good agreements with the experimental results. Barlat et al. (1997) measured the yield surfaces for binary aluminum–magnesium sheet samples with different microstructures. A generalized plastic behavior of any aluminum alloy sheet yield description was proposed to predict the behavior of the solute strengthened (precipitation hardened) aluminum alloy sheets. Barlat et al. (2003) proposed a plane stress yield function that describes the anisotropic behavior of the sheet metals, in particular, for aluminum alloy sheets. The anisotropy of the function was introduced in the formulation using two linear transformations on the Cauchy stress tensor. For the Al–5 wt.% Mg and 6016-T4 alloy sheet samples, yield surface shapes, yield stress and r-value directionalities were compared with those of previously suggested yield functions by Yoon et al. (2004). Barlat et al. (2005) proposed anisotropic yield functions based on linear transformations of the stress deviator in general terms. Two specific convex formulations were given to describe the anisotropic behavior of metals and alloys for a full stress state (3D). Choi et al. (2007) developed analytical models for hydro-mechanical deep drawing tests to investigate the effects of process conditions such as temperature, hydraulic pressure, BHF and forming speed. According to their models, the experimental results show good agreement with the FE models. One of the
PROTEC-12068;No.of Pages 12 ARTICLE IN PRESS 8 JOURNAL OF MATERIALS PROCESSING TECHNOLOGY XXX (2008)XXX-XXX most important problems in forming simulation programs is as a screening test for ranking the relative formability among the method by which the defects are analyzed during the different sheet alloys.The strain hardened 5XXX alloys (Al simulation.Forming conditions of the sheet metals were also 5182+Mn and Al 5754)have shown better formability than investigated in implicit and explicit finite element simulations the precipitation hardened alloy(Al 6111-T4).Li and Ghosh by Van Den Boogaard et al.(2003).The study showed that the (2004)also investigated biaxial warm forming behavior in the computation time for implicit finite element analyses tended temperature range 200-350C for three automotive aluminum to increase disproportionally with increasing problem size. sheet alloys:Al 5754,Al 5182 containing 1%Mn and Al 6111- Sheet metal deformation is considered biaxial rather than T4.Formability was studied by forming rectangular parts at a tensile deformation.For this reason,biaxial data in material rapid rate of 1s-1using internally heated punch and die for model should be evaluated.Li and Ghosh(2003)studied uni- both isothermal and non-isothermal conditions.It is observed axial tensile deformation behavior of three aluminum sheet that the formability for all the three alloys improves at ele- alloys,Al 5182+1%Mn,Al 5754 and Al 6111-T4 in the warm vated temperatures,the strain hardened alloys Al 5754 and Al forming temperature range of 200-350C and in the strain 5182+Mn show considerably greater improvement than the rate range of 0.015-1.5s-1.It is found that the total elonga- precipitation hardened alloy Al 6111-T4.Results show that tion in uniaxial tension increased with increasing temperature temperature effects on drawing of the sheet have a large and decreased with increasing strain rate.They contributed effect on formability.Setting die temperature slightly higher to the enhanced ductility at elevated temperatures primarily than punch temperature was favorable in promoting forma- from the post-uniform elongation which becomes dominant bility.They also determined the forming limit diagram(FLD) at elevated temperatures and/or at slow strain rates.The under warm forming conditions which showed results con- enhancement of strain rate sensitivity with increasing tem- sistent with the evaluation of part depth.Fig.7 shows that perature accounts for the ductility improvement at elevated the effects of temperature on FLDs of type 5754,5182 and temperatures.In their study,the uniaxial tensile test is used 6111-T4 aluminum alloy.As seen in the figures,the formabil- (a)200 (b)200 A15754 A15182+Mn Forming Temperature 350℃ 1501 Forming Temperature 150 350℃ 100 300℃ 100 300℃ 0 250℃≤ 250℃ -10 5 10 0 5 10 15 Minor Strain,e2% Minor Strain,e2% (c)200 A6111-T4 150 Forming Temperature 100 300℃ 350℃ 250℃ 0 -10 .5 0 15 Minor Strain,e2% Fig.7-The effect of warm temperatures on FLDs(Li and Ghosh,2004). Please cite this article in press as:Toros,S.,et al.,Review of warm forming of aluminum-magnesium alloys,J.Mater.Process.Tech.(2008), doi10.1016/.jmatprotec..2008.03.057
Please cite this article in press as: Toros, S., et al., Review of warm forming of aluminum–magnesium alloys, J. Mater. Process. Tech. (2008), doi:10.1016/j.jmatprotec.2008.03.057 PROTEC-12068; No. of Pages 12 ARTICLE IN PRESS 8 journal of materials processing technology xxx (2008) xxx–xxx most important problems in forming simulation programs is the method by which the defects are analyzed during the simulation. Forming conditions of the sheet metals were also investigated in implicit and explicit finite element simulations by Van Den Boogaard et al. (2003). The study showed that the computation time for implicit finite element analyses tended to increase disproportionally with increasing problem size. Sheet metal deformation is considered biaxial rather than tensile deformation. For this reason, biaxial data in material model should be evaluated. Li and Ghosh (2003) studied uniaxial tensile deformation behavior of three aluminum sheet alloys, Al 5182 + 1%Mn, Al 5754 and Al 6111-T4 in the warm forming temperature range of 200–350 ◦C and in the strain rate range of 0.015–1.5 s−1. It is found that the total elongation in uniaxial tension increased with increasing temperature and decreased with increasing strain rate. They contributed to the enhanced ductility at elevated temperatures primarily from the post-uniform elongation which becomes dominant at elevated temperatures and/or at slow strain rates. The enhancement of strain rate sensitivity with increasing temperature accounts for the ductility improvement at elevated temperatures. In their study, the uniaxial tensile test is used as a screening test for ranking the relative formability among different sheet alloys. The strain hardened 5XXX alloys (Al 5182 + Mn and Al 5754) have shown better formability than the precipitation hardened alloy (Al 6111-T4). Li and Ghosh (2004) also investigated biaxial warm forming behavior in the temperature range 200–350 ◦C for three automotive aluminum sheet alloys: Al 5754, Al 5182 containing 1%Mn and Al 6111- T4. Formability was studied by forming rectangular parts at a rapid rate of 1 s−1 using internally heated punch and die for both isothermal and non-isothermal conditions. It is observed that the formability for all the three alloys improves at elevated temperatures, the strain hardened alloys Al 5754 and Al 5182 + Mn show considerably greater improvement than the precipitation hardened alloy Al 6111-T4. Results show that temperature effects on drawing of the sheet have a large effect on formability. Setting die temperature slightly higher than punch temperature was favorable in promoting formability. They also determined the forming limit diagram (FLD) under warm forming conditions which showed results consistent with the evaluation of part depth. Fig. 7 shows that the effects of temperature on FLDs of type 5754, 5182 and 6111-T4 aluminum alloy. As seen in the figures, the formabilFig. 7 – The effect of warm temperatures on FLDs (Li and Ghosh, 2004)
PROTEC-12068;No.of Pages 12 ARTICLE IN PRESS JOURNAL OF MATERIALS PROCESSING TECHNOLOGY XXX (2008)XXX-XXX ity of aluminum alloys increases with increasing the forming enhanced using the appropriate temperature distribution for temperature.It is also determined that Al 5754 forming tem- the local heating and cooling technique and with variable perature sensitivity is greater than other type aluminums blank holder pressure control.Kim et al.(2006)investigated Takuda et al.(2002)studied the deformation behavior and thermomechanically coupled FEA which was performed for the temperature change in cylindrical deep drawing of an forming of aluminum rectangular cups at elevated tempera- aluminum alloy sheet at elevated temperatures by the com- tures.They examined applicability,accuracy and repeatability bination of the rigid-plastic and the heat conduction finite of three different failure criteria (maximum load,minimum element methods.It was clarified that the appropriate distri- load,and thickness ratio)to identify the onset of failure dur- bution of flow stress depending on temperature must exist ing FEA.They selected the thickness ratio criterion since it in the sheet for the higher LDR.In their study,the numeri- resulted in accurate prediction of necking-type failure when cal results as well as the experimental show that the LDR in compared with experimental measurements obtained under the warm deep drawing increases with the die profile radius. a variety of warm forming conditions.They also compared Jain et al.(1998)investigated experimentally and numerically predicted part depth values from FEA at various die-punch the limiting draw ratios (LDRs)and other axisymmetric deep temperature combinations and blank holder pressures con- drawing characteristics of AA5754-O and AA6111-T4 automo- ditions with experiments.Results indicate that they were in tive aluminum sheet materials as a function of die profile radii. good agreement.They established forming limit diagrams at Other deep drawing characteristics such as punch load versus three different warm forming temperature levels(250,300 displacement traces,flange draw-in,strain distribution along and 350C).It is concluded that limit strain increases with the cup profile,flange wrinkling,wall ironing and fracture increasing forming temperatures.In addition,strain distribu- characteristics are experimentally assessed for the two sheet tions on the formed part obtained under different die-punch materials as a function of the die profile radius.They observed temperature combinations were also compared to further that the deep drawability of AA5754-0 as measured by cup validate the accuracy of FEA.A high temperature gradient depth at fracture and LDR is superior to that of AA6111-T4. between die and punch (Tdie>Tpunch)was found critical to They explained the differences in the deep drawing behav- increase formability.Naka and Yoshida (1999)investigated ior of the two materials in terms of the competition in work the effects of forming speed and temperature on the deep hardening between the material in the flange at the die profile drawability for a fine grain Al-Mg alloy(5083-O)sheet by per- region versus the material at the punch profile region,bend- forming cylindrical deep drawing tests at various forming ability of the two materials,and fracture characteristics.They speeds(0.2-500 mm/min)at die temperatures of 20-180C(the also observed that a decrease in LDR and flange draw-in as a die was heated,while the punch was water cooled during function of the die profile radius.Namoco et al.(2007)stud- the tests).They observed that the LDR mostly increases with ied embossing and restoration process of A5052 and A6061 to increasing die temperature,because the deformation resis- reduce the deformation force,the drawing resistance and to tance in flange shrinkage decreases with temperature rise and increase the drawability of the sheet and LDR.Palumbo and the LDR also becomes lower with increasing forming speed at Tricarico(2007)investigated warm deep drawing process of all temperatures because of the flow stress of the heated blank AA5754-0 aluminum alloy.In this experimental work,they at the flange increases with increasing strain rate.Moreover, took into account the parameters which were temperature the cooled blank at the punch comner becomes less ductile. level of the blank in the centre of the specimen and the Naka et al.(2001)investigated the effects of forming speed forming speed;in addition they used grease lubricant.They and temperature on the FLD experimentally for a fine grain observed that the temperature in the blank centre had a strong Al-Mg alloy(5083-O)sheet by performing stretch-forming test influence on the process feasibility and thus on the material at various forming speeds(0.2-200mm/min)at several tem- formability.Spigarelli et al.(2004)investigated the deforma- peratures from 20 to 300C.It is found that the forming tion behavior of an Al alloy between 120 and 180C by means limit strain increased drastically with decreasing speed for of uniaxial compression tests to identify possible differences any strain paths at a high temperature ranging from 150 to in the deformation response compared with uniaxial tensile 300C.It is known that the FLD was not sensitive to speed at data.They found that the strength of the alloy was slightly room temperature.The improvement in formability at 300C greater in compression than in tension and this difference at low forming speed is specifically due to the high strain gradually disappearing as strain rate decreased.Yoshihara et rate hardening characteristic of the material,but below 200C al.(2004)demonstrated spin formability of Al-Mg alloy using the formability is also affected strongly by strain harden- an NC control machine at 300C with a main shaft rotational ing.The number of available 5XXX series Al-based alloys for frequency of 300rpm and feed per revolution of 180 mm/min. passenger vehicles is very limited.At the present time,5052 By spin forming,it is possible to form a domed shape similar and 5456 are the most commonly used alloys.Although 5052 to a pressure vessel at the end of a pressurized gas cylinder offers a good combination of mechanical properties,corro- for passenger and aeronautical vehicles.Their study presents sion resistance,and formability,it is unsuitable for use at the finite element simulation of the spin forming of Al-Mg temperatures above 120C due to its poor creep resistance alloys.This model was constructed based on the material and its low strength at elevated temperatures.In order to properties at 300C as recorded in the real forming process. get a better overall understanding of alloys and to identify They also developed a new deep drawing process (Yoshihara the most promising compositions,most researchers examine et al.,2003a,b)and localized heating and cooling technique and evaluate the micro structural features,tensile properties (Yoshihara et al.,2003a,b)to improve formability.The con- and creep resistance.Zhang et al.(1998)presented some new clusion is deep drawing performance of the alloy would be Al-Mg alloys with good creep resistance,acceptable formabil- Please cite this article in press as:Toros,S.,et al.,Review of warm forming of aluminum-magnesium alloys,J.Mater.Process.Tech.(2008) doi:10.1016/j.jmatprotec.2008.03.057
Please cite this article in press as: Toros, S., et al., Review of warm forming of aluminum–magnesium alloys, J. Mater. Process. Tech. (2008), doi:10.1016/j.jmatprotec.2008.03.057 PROTEC-12068; No. of Pages 12 ARTICLE IN PRESS journal of materials processing technology xxx (2008) xxx–xxx 9 ity of aluminum alloys increases with increasing the forming temperature. It is also determined that Al 5754 forming temperature sensitivity is greater than other type aluminums. Takuda et al. (2002) studied the deformation behavior and the temperature change in cylindrical deep drawing of an aluminum alloy sheet at elevated temperatures by the combination of the rigid-plastic and the heat conduction finite element methods. It was clarified that the appropriate distribution of flow stress depending on temperature must exist in the sheet for the higher LDR. In their study, the numerical results as well as the experimental show that the LDR in the warm deep drawing increases with the die profile radius. Jain et al. (1998) investigated experimentally and numerically the limiting draw ratios (LDRs) and other axisymmetric deep drawing characteristics of AA5754-O and AA6111-T4 automotive aluminum sheet materials as a function of die profile radii. Other deep drawing characteristics such as punch load versus displacement traces, flange draw-in, strain distribution along the cup profile, flange wrinkling, wall ironing and fracture characteristics are experimentally assessed for the two sheet materials as a function of the die profile radius. They observed that the deep drawability of AA5754-O as measured by cup depth at fracture and LDR is superior to that of AA6111-T4. They explained the differences in the deep drawing behavior of the two materials in terms of the competition in work hardening between the material in the flange at the die profile region versus the material at the punch profile region, bendability of the two materials, and fracture characteristics. They also observed that a decrease in LDR and flange draw-in as a function of the die profile radius. Namoco et al. (2007) studied embossing and restoration process of A5052 and A6061 to reduce the deformation force, the drawing resistance and to increase the drawability of the sheet and LDR. Palumbo and Tricarico (2007) investigated warm deep drawing process of AA5754-O aluminum alloy. In this experimental work, they took into account the parameters which were temperature level of the blank in the centre of the specimen and the forming speed; in addition they used grease lubricant. They observed that the temperature in the blank centre had a strong influence on the process feasibility and thus on the material formability. Spigarelli et al. (2004) investigated the deformation behavior of an Al alloy between 120 and 180 ◦C by means of uniaxial compression tests to identify possible differences in the deformation response compared with uniaxial tensile data. They found that the strength of the alloy was slightly greater in compression than in tension and this difference gradually disappearing as strain rate decreased. Yoshihara et al. (2004) demonstrated spin formability of Al–Mg alloy using an NC control machine at 300 ◦C with a main shaft rotational frequency of 300 rpm and feed per revolution of 180mm/min. By spin forming, it is possible to form a domed shape similar to a pressure vessel at the end of a pressurized gas cylinder for passenger and aeronautical vehicles. Their study presents the finite element simulation of the spin forming of Al–Mg alloys. This model was constructed based on the material properties at 300 ◦C as recorded in the real forming process. They also developed a new deep drawing process (Yoshihara et al., 2003a,b) and localized heating and cooling technique (Yoshihara et al., 2003a,b) to improve formability. The conclusion is deep drawing performance of the alloy would be enhanced using the appropriate temperature distribution for the local heating and cooling technique and with variable blank holder pressure control. Kim et al. (2006) investigated thermomechanically coupled FEA which was performed for forming of aluminum rectangular cups at elevated temperatures. They examined applicability, accuracy and repeatability of three different failure criteria (maximum load, minimum load, and thickness ratio) to identify the onset of failure during FEA. They selected the thickness ratio criterion since it resulted in accurate prediction of necking-type failure when compared with experimental measurements obtained under a variety of warm forming conditions. They also compared predicted part depth values from FEA at various die-punch temperature combinations and blank holder pressures conditions with experiments. Results indicate that they were in good agreement. They established forming limit diagrams at three different warm forming temperature levels (250, 300 and 350 ◦C). It is concluded that limit strain increases with increasing forming temperatures. In addition, strain distributions on the formed part obtained under different die-punch temperature combinations were also compared to further validate the accuracy of FEA. A high temperature gradient between die and punch (Tdie > Tpunch) was found critical to increase formability. Naka and Yoshida (1999) investigated the effects of forming speed and temperature on the deep drawability for a fine grain Al–Mg alloy (5083-O) sheet by performing cylindrical deep drawing tests at various forming speeds (0.2–500mm/min) at die temperatures of 20–180 ◦C (the die was heated, while the punch was water cooled during the tests). They observed that the LDR mostly increases with increasing die temperature, because the deformation resistance in flange shrinkage decreases with temperature rise and the LDR also becomes lower with increasing forming speed at all temperatures because of the flow stress of the heated blank at the flange increases with increasing strain rate. Moreover, the cooled blank at the punch corner becomes less ductile. Naka et al. (2001) investigated the effects of forming speed and temperature on the FLD experimentally for a fine grain Al–Mg alloy (5083-O) sheet by performing stretch-forming test at various forming speeds (0.2–200mm/min) at several temperatures from 20 to 300 ◦C. It is found that the forming limit strain increased drastically with decreasing speed for any strain paths at a high temperature ranging from 150 to 300 ◦C. It is known that the FLD was not sensitive to speed at room temperature. The improvement in formability at 300 ◦C at low forming speed is specifically due to the high strain rate hardening characteristic of the material, but below 200 ◦C the formability is also affected strongly by strain hardening. The number of available 5XXX series Al-based alloys for passenger vehicles is very limited. At the present time, 5052 and 5456 are the most commonly used alloys. Although 5052 offers a good combination of mechanical properties, corrosion resistance, and formability, it is unsuitable for use at temperatures above 120 ◦C due to its poor creep resistance and its low strength at elevated temperatures. In order to get a better overall understanding of alloys and to identify the most promising compositions, most researchers examine and evaluate the micro structural features, tensile properties and creep resistance. Zhang et al. (1998) presented some new Al–Mg alloys with good creep resistance, acceptable formabil-
PROTEC-12068;No.of Pages 12 ARTICLE IN PRESS 0 JOURNAL OF MATERIALS PROCESSING TECHNOLOGY XXX (2008)XXX-XXX ity,and low cost.They also investigated the influence of small world.Many of these researchers have used material prop- additions of Ca and Sr on the tensile and creep properties. erties which are obtained from tensile test results in their Another room temperature formability testing was performed investigations.However,information on properties obtained on an Al-Mg6.8 type alloy sheet with a fully recrystallized at elevated temperatures under a biaxial state of stress is structure (average grain diameter ~18um)and after partial limited.Mostly,they are not available for finite element sim- annealing with a retained deformed structure by Romhanji ulation.This area needs to be studied extensively. et al.(1998).The yield strengths attained after full recrystal- In terms of numerical simulations,there are no well lization and after partial annealing,were 175 and 283MPa, defined material models includingtemperature and strain rate respectively.Such an increase in strength is followed by forma- effects for aluminum alloy.Further investigations on material bility degradation,maximized around the plain strain state to models are required.In future study,material models should either 42%,as obtained using the limiting dome height test be developed and the effect of process parameters should be (LDH),or 35%after using forming limit curves(FLC).A com- investigated for process optimization. parison with known high-strength formable alloys has shown that the tested alloy in the recrystallized condition has a bet- ter stretch formability (at the same or even higher yield stress Acknowledgements level),while in the unrecrystallized-partially annealed con- dition it has a lower formability,limiting its application to This work is supported by The Scientific and Technologi- moderate forming requirements for very high-strength parts. cal Research Council of Turkey (TUBITAK).Project Number: 106M058,Title:"Experimental and Theoretical Investigations of The Effects of Temperature and Deformation Speed on 3.3. The effects of lubrication Formability".TUBITAK support is profoundly acknowledged. One of the important parameter for the forming of aluminum sheets is lubrication.It is used during the forming process REFERENCES to get better surface quality and to decrease the friction of die surfaces.This contributes to increasing the die life- time by reducing wear.Meiler et al.(2003)investigated the Abedrabbo,N.,Pourboghrat,F.,Carsley,J.,2007.Forming of effects of dry film lubricants on aluminum sheet metal form- AA5182-O and AA5754-O at elevated temperatures using ing and compared the results with other type lubricants.They coupled thermo-mechanical finite element models.Int.J Plast.23,841-875. observed that dry film lubricants showed advantages over con- Ahmetoglu,M.A.,Kinzel,G.,Altan,T.,1997.Forming of aluminum ventional oil lubricants because of their high deep drawing alloys-application of computer simulation and blank holding performance,especially on complex shaped body panels.They force control.J.Mater.Process.Technol.71,147-151. also emphasized in their study the formability is increased as Altan,T.,2002.Warm forming of aluminum alloys-academic a consequence of reduced friction and it is possible to get more exercise or practical opportunity?Stamping J.14,58-59. homogeneous sheet thickness distributions.Wu et al.(2006) ASM Metal Handbook,1988.Volume 14 Forming and Forging.9th studied a super plastic 5083 Al alloy under biaxial deformation ed.ASM International,Metals Park,Ohio,pp.791-804. Barlat,F.,Lian,J.,1989.Plastic behavior and stretchability of sheet by deforming the sheet into a rectangular die cavity with and metals.Part I.A yield function for orthotropic sheets under without lubrication.Results indicate that reducing the inter- plane stress conditions.Int.J.Plast.5,51-66 facial friction by use of a lubricant altered the metal flow after Barlat,F.,Lege,D.J.,Brem,J.C.,1991.A six-component yield the deformed sheet had made contact with the die surface. function for anisotropic materials.Int.J.Plast.7,693-712 Besides,they observed that changes of the metal flow dur- Barlat,F.,Maeda,Y.,Chung,K.,Yanagawa,M.,Brem,J.C. ing forming not only developed a better thickness distribution Hayashida,Y.,Lege,D.J.,Matsui,K.,Murtha,S.J.,Hattori,S. of the formed part,but also improved cavitations distribution Becker,R.C.,Makosey,S.,1997.Yield function development for aluminum alloy sheets.J.Mech.Phys.Solids 45(11/12), (Kelly and Cotterell,2002). 1727-1763 Barlat,F.,Brem,J.C.,Yoon,J.W.,Chung,K.,Dick,R.E.,Lege,D.J. Pourboghrat,F.,Choi,S.H.,Chu,E.,2003.Plane stress yield Conclusion function for aluminum alloy sheets.Part 1.Theory.Int.J.Plast 19,1297-1319. In this paper,formability of Al-Mg alloys at warm temperature Barlat,E.,Aretz,H.,Yoon,J.W.,Karabin,M.E.,Brem,J.C.,Dick,R.E., is presented.In general,at temperatures above 225C the flow 2005.Linear transformation-based anisotropic yield stress becomes strain rate dependent. functions.Int.J.Plast.21(5),1009-1039. Beer,F.P.,Johnston,E.R.,1992.Mechanics of Materials,Second ed The warm forming process is beneficial in terms of forma- McGraw-Hill,Inc,International ed. bility.Researchers have been conducted their studies at lab Bolt,P.J.,Lamboo,N.A.P.M.,Rozier,P.J.C.M.,2001.Feasibility of environment for years.No well-know procedure have been warm drawing of aluminum products.J.Mater.Process developed for press shop.It is very important to transfer warm Technol..115,118-121. forming from lab to press shop.As known sheet metal part Boyd,R.G.,Jung,C.,Seldon,B.J.,1995.The market structure of the manufacturing is a mass production process.It is necessary to US aluminum industry.J.Econ.Bus.47,293-301. develop the procedure for successful warm forming operation Browne,DJ.,Battikha,E.,1995.Optimization of aluminum sheet forming using a flexible die.J.Mater.Process.Technol.55, in press shop. 218-223. The properties of aluminum alloys at elevated tempera- Carle,D.,Blount,G.,1999.The suitability of aluminum as an tures have been determined by various researchers around the alternative material for car bodies.Mater.Des.20,267-272 Please cite this article in press as:Toros,S.,et al.,Review of warm forming of aluminum-magnesium alloys,J.Mater.Process.Tech.(2008), doi10.1016/.jmatprotec..2008.03.057
Please cite this article in press as: Toros, S., et al., Review of warm forming of aluminum–magnesium alloys, J. Mater. Process. Tech. (2008), doi:10.1016/j.jmatprotec.2008.03.057 PROTEC-12068; No. of Pages 12 ARTICLE IN PRESS 10 journal of materials processing technology xxx (2008) xxx–xxx ity, and low cost. They also investigated the influence of small additions of Ca and Sr on the tensile and creep properties. Another room temperature formability testing was performed on an Al–Mg6.8 type alloy sheet with a fully recrystallized structure (average grain diameter ∼18m) and after partial annealing with a retained deformed structure by Romhanji et al. (1998). The yield strengths attained after full recrystallization and after partial annealing, were 175 and 283 MPa, respectively. Such an increase in strength is followed by formability degradation, maximized around the plain strain state to either 42%, as obtained using the limiting dome height test (LDH), or 35% after using forming limit curves (FLC). A comparison with known high-strength formable alloys has shown that the tested alloy in the recrystallized condition has a better stretch formability (at the same or even higher yield stress level), while in the unrecrystallized-partially annealed condition it has a lower formability, limiting its application to moderate forming requirements for very high-strength parts. 3.3. The effects of lubrication One of the important parameter for the forming of aluminum sheets is lubrication. It is used during the forming process to get better surface quality and to decrease the friction of die surfaces. This contributes to increasing the die lifetime by reducing wear. Meiler et al. (2003) investigated the effects of dry film lubricants on aluminum sheet metal forming and compared the results with other type lubricants. They observed that dry film lubricants showed advantages over conventional oil lubricants because of their high deep drawing performance, especially on complex shaped body panels. They also emphasized in their study the formability is increased as a consequence of reduced friction and it is possible to get more homogeneous sheet thickness distributions. Wu et al. (2006) studied a super plastic 5083 Al alloy under biaxial deformation by deforming the sheet into a rectangular die cavity with and without lubrication. Results indicate that reducing the interfacial friction by use of a lubricant altered the metal flow after the deformed sheet had made contact with the die surface. Besides, they observed that changes of the metal flow during forming not only developed a better thickness distribution of the formed part, but also improved cavitations distribution (Kelly and Cotterell, 2002). 4. Conclusion In this paper, formability of Al–Mg alloys at warm temperature is presented. In general, at temperatures above 225 ◦C the flow stress becomes strain rate dependent. The warm forming process is beneficial in terms of formability. Researchers have been conducted their studies at lab environment for years. No well-know procedure have been developed for press shop. It is very important to transfer warm forming from lab to press shop. As known sheet metal part manufacturing is a mass production process. It is necessary to develop the procedure for successful warm forming operation in press shop. The properties of aluminum alloys at elevated temperatures have been determined by various researchers around the world. Many of these researchers have used material properties which are obtained from tensile test results in their investigations. However, information on properties obtained at elevated temperatures under a biaxial state of stress is limited. Mostly, they are not available for finite element simulation. This area needs to be studied extensively. In terms of numerical simulations, there are no well defined material models including temperature and strain rate effects for aluminum alloy. Further investigations on material models are required. In future study, material models should be developed and the effect of process parameters should be investigated for process optimization. Acknowledgements This work is supported by The Scientific and Technological Research Council of Turkey (TUB¨ ˙ ITAK). Project Number: 106M058, Title: “Experimental and Theoretical Investigations of The Effects of Temperature and Deformation Speed on Formability”. TUB¨ ˙ ITAK support is profoundly acknowledged. references Abedrabbo, N., Pourboghrat, F., Carsley, J., 2007. Forming of AA5182-O and AA5754-O at elevated temperatures using coupled thermo-mechanical finite element models. Int. J. Plast. 23, 841–875. Ahmetoglu, M.A., Kinzel, G., Altan, T., 1997. Forming of aluminum alloys-application of computer simulation and blank holding force control. J. Mater. Process. Technol. 71, 147–151. Altan, T., 2002. Warm forming of aluminum alloys-academic exercise or practical opportunity? Stamping J. 14, 58–59. ASM Metal Handbook, 1988. Volume 14 Forming and Forging. 9th ed. ASM International, Metals Park, Ohio, pp. 791–804. Barlat, F., Lian, J., 1989. Plastic behavior and stretchability of sheet metals. Part I. A yield function for orthotropic sheets under plane stress conditions. Int. J. Plast. 5, 51–66. Barlat, F., Lege, D.J., Brem, J.C., 1991. A six-component yield function for anisotropic materials. Int. J. Plast. 7, 693–712. Barlat, F., Maeda, Y., Chung, K., Yanagawa, M., Brem, J.C., Hayashida, Y., Lege, D.J., Matsui, K., Murtha, S.J., Hattori, S., Becker, R.C., Makosey, S., 1997. Yield function development for aluminum alloy sheets. J. Mech. Phys. Solids 45 (11/12), 1727–1763. Barlat, F., Brem, J.C., Yoon, J.W., Chung, K., Dick, R.E., Lege, D.J., Pourboghrat, F., Choi, S.H., Chu, E., 2003. Plane stress yield function for aluminum alloy sheets. Part 1. Theory. Int. J. Plast. 19, 1297–1319. Barlat, F., Aretz, H., Yoon, J.W., Karabin, M.E., Brem, J.C., Dick, R.E., 2005. Linear transformation-based anisotropic yield functions. Int. J. Plast. 21 (5), 1009–1039. Beer, F.P., Johnston, E.R., 1992. Mechanics of Materials, Second ed. McGraw-Hill, Inc, International ed. Bolt, P.J., Lamboo, N.A.P.M., Rozier, P.J.C.M., 2001. Feasibility of warm drawing of aluminum products. J. Mater. Process. Technol. 115, 118–121. Boyd, R.G., Jung, C., Seldon, B.J., 1995. The market structure of the US aluminum industry. J. Econ. Bus. 47, 293–301. Browne, D.J., Battikha, E., 1995. Optimization of aluminum sheet forming using a flexible die. J. Mater. Process. Technol. 55, 218–223. Carle, D., Blount, G., 1999. The suitability of aluminum as an alternative material for car bodies. Mater. Des. 20, 267–272.
