1s79_s83.1999 Published by Elsevier Science Ltd.All rights reserved Printed in Great Britain PⅡ：S1359-645498)00365-6 1359-6454/99S19.00+0.00 PERGAMON NOVEL ULTRA-HIGH STRAINING PROCESS FOR BULK MATERIALS-DEVELOPMENT OF THE ACCUMULATIVE ROLL-BONDING (ARB)PROCESS Y.SAITO,H.UTSUNOMIYA,N.TSUJI and T.SAKAI Division of Materials Science and Engineering,Graduate School of Engineering,Osaka University, 2-1 Yamada-oka.Suita 565-0871.Japan Received 19 August 1998:accepted 9 October 1998) Abstract-A novel intense plastic straining process named accumulative roll-bonding (ARB)is proposed. First,a strip is neatly placed on top of another strip.The two layers of material are joined together by roll- ing like a roll-bonding process.Then,the length of rolled material is sectioned into two halves.The sec- tioned strips are again stacked and roll-bonded.The whole process is repeated again and again.The process can introduce ultra-high plastic strain without any geometrical change if the reduction in thickness is maintained to 50%every rolling pass.The process has been applied to commercial aluminum (1100), Al-Mg alloy (5083)and interstitial free (IF)steel.Well-bonded bulk materials were successfully obtained. After several cycles of ARB,ultra-fine (sub-micron)grain structure with large misorientations,i.e.polycrys- tal,was formed and the materials were strengthened dramatically.C1999 Acta Metallurgica Inc.Published by Elsevier Science Ltd.All rights reserved. 1.INTRODUCTION principle of the ARB process and some convincing It has been reported that materials with ultra-fine experimental results are presented. (sub-micron)grains show outstanding high strength at ambient temperatures,high-speed superplastic 2.ACCUMULATIVE ROLL-BONDING (ARB) deformation at elevated temperatures,and high cor- Figure I schematically represents the proposed rosion resistance.These materials,known as super metals,have given rise to much interest.They have ARB process.Stacking of materials and conven- been produced by various uncommon techniques tional roll-bonding are repeated in the process. such as rapid solidification,vapor deposition,mech- First,a strip is neatly placed on top of another anical alloying,cryogenic metalforming and intense strip.The interfaces of the two strips are surface- treated in advance in order to enhance bond plastic straining.Intense plastic straining is con- sidered the most appropriate process for industrial strength,if required.The two layers of material are application.Special processes such as cyclic extru- joined together by rolling,as in a conventional roll- sion compression (CEC)[1],equal channel angular bonding process.Then,the length of rolled material is sectioned into two halves.The sectioned strips press (ECAP)[2]and torsion straining under high pressure (TS)[3]have already been proposed as are again surface-treated,stacked and roll-bonded. intense plastic straining and successfully applied to The whole process is repeated again and again.The various materials.However,these processes have process should be conducted at elevated tempera- two main drawbacks.Firstly,forming machines ture below recrystallization temperature because recrystallization cancels out the accumulated strain. with large load capacities and expensive dies are Low temperature would result in insufficient duct- indispensable for these processes.Secondly,the pro- ility and bond strength.There exists a minimum ductivity is relatively low and the amount of ma- terials produced is very limited.These processes are limit of reduction in thickness,i.e.threshold defor- mation to attain sufficient bonding.It is well known thought to be inappropriate for practical appli- cation,especially for large-sized structural materials that the threshold deformation decreases with tem- perature.If the homologous temperature of the such as sheets. roll-bonding is less than 0.5,a sound joining can be The authors now propose an alternative novel intense plastic straining process named accumulat- achieved by reduction >50%[5].This means that materials can be bonded together without recrystal- ive roll-bonding (ARB)[4]for bulk-material manu- lization. facturing at high productivity.In this paper,the The process can introduce ultra-high plastic strain without any geometrical change,if the re- +To whom all correspondence should be addressed duction in thickness is maintained to 50%in every 579
NOVEL ULTRA-HIGH STRAINING PROCESS FOR BULK MATERIALSÐDEVELOPMENT OF THE ACCUMULATIVE ROLL-BONDING (ARB) PROCESS Y. SAITO, H. UTSUNOMIYA{, N. TSUJI and T. SAKAI Division of Materials Science and Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita 565-0871, Japan (Received 19 August 1998; accepted 9 October 1998) AbstractÐA novel intense plastic straining process named accumulative roll-bonding (ARB) is proposed. First, a strip is neatly placed on top of another strip. The two layers of material are joined together by rolling like a roll-bonding process. Then, the length of rolled material is sectioned into two halves. The sectioned strips are again stacked and roll-bonded. The whole process is repeated again and again. The process can introduce ultra-high plastic strain without any geometrical change if the reduction in thickness is maintained to 50% every rolling pass. The process has been applied to commercial aluminum (1100), Al±Mg alloy (5083) and interstitial free (IF) steel. Well-bonded bulk materials were successfully obtained. After several cycles of ARB, ultra-®ne (sub-micron) grain structure with large misorientations, i.e. polycrystal, was formed and the materials were strengthened dramatically. # 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved. 1. INTRODUCTION It has been reported that materials with ultra-®ne (sub-micron) grains show outstanding high strength at ambient temperatures, high-speed superplastic deformation at elevated temperatures, and high corrosion resistance. These materials, known as super metals, have given rise to much interest. They have been produced by various uncommon techniques such as rapid solidi®cation, vapor deposition, mechanical alloying, cryogenic metalforming and intense plastic straining. Intense plastic straining is considered the most appropriate process for industrial application. Special processes such as cyclic extrusion compression (CEC) [1], equal channel angular press (ECAP) [2] and torsion straining under high pressure (TS) [3] have already been proposed as intense plastic straining and successfully applied to various materials. However, these processes have two main drawbacks. Firstly, forming machines with large load capacities and expensive dies are indispensable for these processes. Secondly, the productivity is relatively low and the amount of materials produced is very limited. These processes are thought to be inappropriate for practical application, especially for large-sized structural materials such as sheets. The authors now propose an alternative novel intense plastic straining process named accumulative roll-bonding (ARB) [4] for bulk-material manufacturing at high productivity. In this paper, the principle of the ARB process and some convincing experimental results are presented. 2. ACCUMULATIVE ROLL-BONDING (ARB) Figure 1 schematically represents the proposed ARB process. Stacking of materials and conventional roll-bonding are repeated in the process. First, a strip is neatly placed on top of another strip. The interfaces of the two strips are surfacetreated in advance in order to enhance bond strength, if required. The two layers of material are joined together by rolling, as in a conventional rollbonding process. Then, the length of rolled material is sectioned into two halves. The sectioned strips are again surface-treated, stacked and roll-bonded. The whole process is repeated again and again. The process should be conducted at elevated temperature below recrystallization temperature because recrystallization cancels out the accumulated strain. Low temperature would result in insucient ductility and bond strength. There exists a minimum limit of reduction in thickness, i.e. threshold deformation to attain sucient bonding. It is well known that the threshold deformation decreases with temperature. If the homologous temperature of the roll-bonding is less than 0.5, a sound joining can be achieved by reduction >50% [5]. This means that materials can be bonded together without recrystallization. The process can introduce ultra-high plastic strain without any geometrical change, if the reduction in thickness is maintained to 50% in every Acta mater. Vol. 47, No. 2, pp. 579±583, 1999 # 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain PII: S1359-6454(98)00365-6 1359-6454/99 $19.00 + 0.00 {To whom all correspondence should be addressed. 579
580 SAITO et al:ACCUMULATIVE ROLL-BONDING Surface treatment Cutting greasing. Wire brushing Roll bonding Stacking Heating Fig.1.Diagrammatic representation of the accumulative roll-bonding (ARB)process. rolling pass.because the increase in width is negli-materials were fully annealed before the ARB pro- gible in sheet rolling.The achieved strain is unlim-cess.The mean grain sizes were 37,18 and 27 um ited since repetition times are endless in principle.for 1100,5083 and IF steel,respectively.The width Arbitrarily large deformation is possible by the was limited by the load capacity of rolling mills ARB process.When the reduction is 50%per cycle, used.The interface between two strips was the thickness of the initial strip after n cycles is degreased by acetone and scratch-brushed.A 304 lo stainless-wire bevel brush driven by a hand grinder 1 (1) was used for this purpose.Two strips were layered to set brushed surfaces in contact and fixed to each where to is the initial thickness of strips other closely.For this purpose,four holes,which The total reduction r after n cycles is had been drilled in the vicinity of the four corners of strips were bound firmly by wires as shown in (2) Fig.2(a). The layered strips were heated in a box-type elec- Assuming von Mises yield criterion and plane strain tric furnace before roll-bonding.The roll-bonding condition,i.e.no lateral spreading,the equivalent was performed by 50%-reduction rolling under dry plastic strain is expressed by ={房() n=0.80n. (3) a For example,if the process is repeated seven times, the initial thickness is reduced to 1/128.The 1.0 mm thickness reduces to 7.8 um.The achieved total re- duction is 99.2%and the total equivalent plastic strain is 5.6.In case of 10 cycles,the final thickness (b) is 1.0 um.the total reduction is 99.9%and the strain is 8.0.It is easy to introduce ultra-high strain into materials by the ARB process. 3.EXPERIMENTAL In order to study the feasibility of the ARB pro- RD 50mm cess,three kinds of materials [i.e.commercial alumi- num (1100).Al-Mg alloy (5083)and Ti-added interstitial free (IF)steel],were chosen.The initial dimensions of the materials were 1.0 mm in thick- Fig.2.Appearance of initial and ARB processed 5083 ness,20 mm in width and 300 mm in length.All strips at 473 K:(a)initial;(b)and (c)after three cycles
rolling pass, because the increase in width is negligible in sheet rolling. The achieved strain is unlimited since repetition times are endless in principle. Arbitrarily large deformation is possible by the ARB process. When the reduction is 50% per cycle, the thickness of the initial strip after n cycles is t t0 2n 1 where t0 is the initial thickness of strips. The total reduction rt after n cycles is rt 1 ÿ t t0 1 ÿ 1 2n : 2 Assuming von Mises yield criterion and plane strain condition, i.e. no lateral spreading, the equivalent plastic strain e is expressed by e 2 3 p ln 1 2 n 0:80n: 3 For example, if the process is repeated seven times, the initial thickness is reduced to 1/128. The 1.0 mm thickness reduces to 7.8 mm. The achieved total reduction is 99.2% and the total equivalent plastic strain is 5.6. In case of 10 cycles, the ®nal thickness is 1.0 mm, the total reduction is 99.9% and the strain is 8.0. It is easy to introduce ultra-high strain into materials by the ARB process. 3. EXPERIMENTAL In order to study the feasibility of the ARB process, three kinds of materials [i.e. commercial aluminum (1100), Al±Mg alloy (5083) and Ti-added interstitial free (IF) steel], were chosen. The initial dimensions of the materials were 1.0 mm in thickness, 20 mm in width and 300 mm in length. All materials were fully annealed before the ARB process. The mean grain sizes were 37, 18 and 27 mm for 1100, 5083 and IF steel, respectively. The width was limited by the load capacity of rolling mills used. The interface between two strips was degreased by acetone and scratch-brushed. A 304 stainless-wire bevel brush driven by a hand grinder was used for this purpose. Two strips were layered to set brushed surfaces in contact and ®xed to each other closely. For this purpose, four holes, which had been drilled in the vicinity of the four corners of strips were bound ®rmly by wires as shown in Fig. 2(a). The layered strips were heated in a box-type electric furnace before roll-bonding. The roll-bonding was performed by 50%-reduction rolling under dry Fig. 1. Diagrammatic representation of the accumulative roll-bonding (ARB) process. Fig. 2. Appearance of initial and ARB processed 5083 strips at 473 K: (a) initial; (b) and (c) after three cycles. 580 SAITO et al.: ACCUMULATIVE ROLL-BONDING
SAITO et al.:ACCUMULATIVE ROLL-BONDING 581 Table 1.Roll-bonding conditions Material Heating Roll diameter(mm) Roll speed (m/min) Mean strain rate (/s) A1(1100 473K×5min )59 0 A-Mg(083) 473K×5min 310 4 IF steel 773K×10min 310 46 conditions.The heating and other conditions are gauge width was 5 mm.The cross-head speed was listed in Table 1.Well-bonded bulk materials were 0.5mm/min so that the initial strain rate was successfully obtained.However,excessively high 8.3×10-4/s total reduction,i.e.repetition times,sometimes resulted in edge cracks or center fracture as shown 4.RESULTS in Figs 2(b)and (c).It may be due to tensile stress caused by lateral spreading near the edges.The lat- Optical micrographs of ARB processed IF steel eral spreading cannot be neglected when the aspect are shown in Fig.3.In the case of two-cycle pro- ratio (width/thickness)is less than 10 [6].In order cessed material [Fig.3(c)],the interface introduced to avoid propagation of edge cracks in following in the second cycle is seen clearly.It is difficult to cycles,both edges of the roll-bonded strip were find the interfaces of the first pass at a quarter of trimmed by shearing.The leading and trailing ends the thickness.This meant that the subsequent roll- of strips were cropped.These edge cracks may not ing sufficiently improves the bonding of interfaces occur in the case of industrial materials with high introduced in a previous cycle.The severely sheared aspect ratio. structure can be observed just below the surface. The longitudinal cross sections normal to the After five cycles,the whole thickness is covered by transverse direction were observed by an optical very thin and elongated grains and it is very diffi- microscope.Transmission electron microscopy cult to observe individual grains as shown in (TEM)studies were also conducted using a Fig.3(d).Figure 4 shows TEM micrographs of sev- HITACHI H-800 microscope operated at 200 kV. eral-cycle ARB processed materials.The associated For this purpose,thin foils parallel to the rolling selected area diffraction (SAD)patterns taken from plane were prepared by twin-jet polishing.The the center of the field by use of an aperture (1.8 um mechanical properties of initial and several-cycle in diameter)are also shown in the figure.The struc- processed strips were measured by tensile test at ture is of a granular type with equiaxed grains.The ambient temperature by an Instron-type testing ma- grain sizes are less than 0.5 um.The SAD patterns chine.Tensile-test specimens were spark-machined have numerous reflections along circles.Such pat- so that the tensile direction was parallel to the roll- terns indicate that large misorientations exis ing direction.The gauge length was 10 mm and the between individual grains.Therefore,it is clear that (a)Initial (b)1 cycle (c)2 cycles (d)5 cycles 300um Fig.3.Longitudinal cross section of initial and ARB processed IF steel strips
conditions. The heating and other conditions are listed in Table 1. Well-bonded bulk materials were successfully obtained. However, excessively high total reduction, i.e. repetition times, sometimes resulted in edge cracks or center fracture as shown in Figs 2(b) and (c). It may be due to tensile stress caused by lateral spreading near the edges. The lateral spreading cannot be neglected when the aspect ratio (width/thickness) is less than 10 [6]. In order to avoid propagation of edge cracks in following cycles, both edges of the roll-bonded strip were trimmed by shearing. The leading and trailing ends of strips were cropped. These edge cracks may not occur in the case of industrial materials with high aspect ratio. The longitudinal cross sections normal to the transverse direction were observed by an optical microscope. Transmission electron microscopy (TEM) studies were also conducted using a HITACHI H-800 microscope operated at 200 kV. For this purpose, thin foils parallel to the rolling plane were prepared by twin-jet polishing. The mechanical properties of initial and several-cycle processed strips were measured by tensile test at ambient temperature by an Instron-type testing machine. Tensile-test specimens were spark-machined so that the tensile direction was parallel to the rolling direction. The gauge length was 10 mm and the gauge width was 5 mm. The cross-head speed was 0.5 mm/min so that the initial strain rate was 8.310ÿ4 /s. 4. RESULTS Optical micrographs of ARB processed IF steel are shown in Fig. 3. In the case of two-cycle processed material [Fig. 3(c)], the interface introduced in the second cycle is seen clearly. It is dicult to ®nd the interfaces of the ®rst pass at a quarter of the thickness. This meant that the subsequent rolling suciently improves the bonding of interfaces introduced in a previous cycle. The severely sheared structure can be observed just below the surface. After ®ve cycles, the whole thickness is covered by very thin and elongated grains and it is very di- cult to observe individual grains as shown in Fig. 3(d). Figure 4 shows TEM micrographs of several-cycle ARB processed materials. The associated selected area diraction (SAD) patterns taken from the center of the ®eld by use of an aperture (1.8 mm in diameter) are also shown in the ®gure. The structure is of a granular type with equiaxed grains. The grain sizes are less than 0.5 mm. The SAD patterns have numerous re¯ections along circles. Such patterns indicate that large misorientations exist between individual grains. Therefore, it is clear that Table 1. Roll-bonding conditions Material Heating Roll diameter (mm) Roll speed (m/min) Mean strain rate (/s) Al (1100) 473 K 5 min 255 10 12 Al±Mg (5083) 473 K 5 min 310 43 46 IF steel 773 K 10 min 310 43 46 Fig. 3. Longitudinal cross section of initial and ARB processed IF steel strips. SAITO et al.: ACCUMULATIVE ROLL-BONDING 581
582 SAITO et al:ACCUMULATIVE ROLL-BONDING 5.DISCUSSIONS It is made clear that the proposed accumulative roll-bonding (ARB)process causes ultra-fine (sub- micron)grains and surprising strength.These effects are confirmed experimentally by three materials: aluminum(1100),Al-Mg alloy(5083)and Ti-added interstitial free steel. There are two possible additional mechanisms in (a)8-cycle processed 1100 the ARB process which differ from other high straining processes.The first possible mechanism is the effect of severe shear deformation just below the surface.It has been reported that severe shear de- formation is introduced by friction between the workpiece and the roll under dry conditions [8]. This shear deformation significantly increases the equivalent strain from the value calculated by equation (3)and promotes grain refinement. Moreover,the ARB process can introduce this (b)7-cycle processed 5083 severely deformed region into the interior of the material by repetition.The whole thickness of ma- terials may be severely strained after several cycles The other mechanism is the introduction of new interfaces.A large number of interfaces are intro- duced by several ARB cycles.These interfaces show a well-developed fiber structure.The oxide films on the surfaces,as well as inclusions,are dispersed uni- formly by repetition.These things contribute to the strength and may act as obstacles for grain growth (c)5-cycle processed IF steel In the case of 1100 aluminum,the variation in structure and mechanical properties in the ARB Fig.4.TEM micrographs and SAD patterns of ARB pro- process were investigated in Ref.[9].However,the cessed strips. general mechanism of the grain refinement during ARB is still unclear at this stage and requires further study an ultra-fine (sub-micron)grain structure with large The advantage of this process against other high misorientations,i.e.polycrystal,was formed. straining processes is its high productivity and the Mechanical properties of initial and ARB pro- feasibility of large-sized material production cessed materials are compared in Table 2.In the Although the experiments have been carried out case of aluminum 1100,the tensile strength of com- with narrow 20 mm wide materials in this study,it mercially available full-hardened material (temper is supposed that application to bulk materials such grade H18)is ~165 MPa [7].The tensile strength of as wide strips in a coil is not difficult.The process the ARB processed 1100(eight cycles)is 1.8 times does not require any special machines because the higher than that of the 1100-H18.The ARB pro- roll-bonding is widely adopted in clad metal cessed 5183 and IF steel also showed extremely production [10].The process can be readily industri- high strength,however,the elongation decreased alized. from 8 to 5%.On the other hand.the material still shows sufficient ductility,despite the fact that the materials were highly strained. 6.CONCLUSIONS Table 2.Mechanical properties of initial and ARB processed ma- A novel ultra-high straining process,the accumu- terials lative roll-bonding (ARB)process is proposed.The No. Tensile ARB process has successfully been applied to Material of cycles strength(MPa) Elongation (% aluminum(1100),Al-Mg alloy (5083)and Ti-added interstitial free steel.All three several-cycle ARB A1(1100) 0(initial） 84 processed materials have structures with sub-micron A11100m 8 30 A-Mg(083) 0(initial) 319 grains and show very high strength.The proposed A-Mg(5083) 351 ARB is a promising process for the manufacture of IF steel 0(initial) 274 IF steel 751 6 high-strength bulk materials at a high level of pro- ductivity
an ultra-®ne (sub-micron) grain structure with large misorientations, i.e. polycrystal, was formed. Mechanical properties of initial and ARB processed materials are compared in Table 2. In the case of aluminum 1100, the tensile strength of commercially available full-hardened material (temper grade H18) is 0165 MPa [7]. The tensile strength of the ARB processed 1100 (eight cycles) is 1.8 times higher than that of the 1100-H18. The ARB processed 5183 and IF steel also showed extremely high strength, however, the elongation decreased from 8 to 5%. On the other hand, the material still shows sucient ductility, despite the fact that the materials were highly strained. 5. DISCUSSIONS It is made clear that the proposed accumulative roll-bonding (ARB) process causes ultra-®ne (submicron) grains and surprising strength. These eects are con®rmed experimentally by three materials: aluminum (1100), Al±Mg alloy (5083) and Ti-added interstitial free steel. There are two possible additional mechanisms in the ARB process which dier from other high straining processes. The ®rst possible mechanism is the eect of severe shear deformation just below the surface. It has been reported that severe shear deformation is introduced by friction between the workpiece and the roll under dry conditions [8]. This shear deformation signi®cantly increases the equivalent strain from the value calculated by equation (3) and promotes grain re®nement. Moreover, the ARB process can introduce this severely deformed region into the interior of the material by repetition. The whole thickness of materials may be severely strained after several cycles. The other mechanism is the introduction of new interfaces. A large number of interfaces are introduced by several ARB cycles. These interfaces show a well-developed ®ber structure. The oxide ®lms on the surfaces, as well as inclusions, are dispersed uniformly by repetition. These things contribute to the strength and may act as obstacles for grain growth. In the case of 1100 aluminum, the variation in structure and mechanical properties in the ARB process were investigated in Ref. [9]. However, the general mechanism of the grain re®nement during ARB is still unclear at this stage and requires further study. The advantage of this process against other high straining processes is its high productivity and the feasibility of large-sized material production. Although the experiments have been carried out with narrow 20 mm wide materials in this study, it is supposed that application to bulk materials such as wide strips in a coil is not dicult. The process does not require any special machines because the roll-bonding is widely adopted in clad metal production [10]. The process can be readily industrialized. 6. CONCLUSIONS A novel ultra-high straining process, the accumulative roll-bonding (ARB) process is proposed. The ARB process has successfully been applied to aluminum (1100), Al±Mg alloy (5083) and Ti-added interstitial free steel. All three several-cycle ARB processed materials have structures with sub-micron grains and show very high strength. The proposed ARB is a promising process for the manufacture of high-strength bulk materials at a high level of productivity. Fig. 4. TEM micrographs and SAD patterns of ARB processed strips. Table 2. Mechanical properties of initial and ARB processed materials Material No. of cycles Tensile strength (MPa) Elongation (%) Al (1100) 0 (initial) 84 42 Al (1100) 8 304 8 Al±Mg (5083) 0 (initial) 319 25 Al±Mg (5083) 7 551 6 IF steel 0 (initial) 274 57 IF steel 5 751 6 582 SAITO et al.: ACCUMULATIVE ROLL-BONDING
SAITO et al:ACCUMULATIVE ROLL-BONDING 583 Acknowledgements-We are grateful to J.Miyamoto,R.- 4.Saito,Y.,Utsunomiya,H.,Tsuji,N.and Sakai,T., G.Hong and S.Tanigawa of Osaka University for exper- imental Japanese Patent applied for. assistance.Nakayama Steel Works,Ltd are thanked for improvements in the rolling mill and 5.Nicholas.M.G.and Milner,D.R.,Br.Weld.J., Sumitomo Light Metal Industries,Ltd and NKK 1961.8.375. Corporation for material supplies.This study was finan- 6.Helmi,A.and Alexander,J.M.,J.Iron Steel Inst., cially supported by the Japan Research and Development 1968.206.1110. Center for Metals (JRCM). 7.Metals Handbook,9th edn,Vol.2.American Society for Metals,Metals Park,OH,1979,pp.65-66. REFERENCES 8.Sakai,T..Saito,Y..Hirano,K.and Kato,K..Trans. 1.Richert,J.and Richert,M.,Aluminium,1986,62,604. IS1J,1988,28.1028. 2.Valiev,R.Z.,Krasilnikov,N.A.and Tsenev,N.K., 9.Saito,Y.,Tsuji,N.,Utsunomiya,H.,Sakai,T.and Mater.Sci.Engng.1991.A137.35. 3.Horita,Z..Smith,D.J..Furukawa,M..Nemoto,M., Hong.R.G.,Scripta mater..1998,39,1221. Valiev,R.Z.and Langdon,T.G..J.Mater.Res., 10.Tylecote,R.F.,The Solid Phase Welding of Metals. 1996.11.1880. Edward Arnold,London,1968
AcknowledgementsÐWe are grateful to J. Miyamoto, R.- G. Hong and S. Tanigawa of Osaka University for experimental assistance. Nakayama Steel Works, Ltd are thanked for improvements in the rolling mill and Sumitomo Light Metal Industries, Ltd and NKK Corporation for material supplies. This study was ®nancially supported by the Japan Research and Development Center for Metals (JRCM). REFERENCES 1. Richert, J. and Richert, M., Aluminium, 1986, 62, 604. 2. Valiev, R. Z., Krasilnikov, N. A. and Tsenev, N. K., Mater. Sci. Engng, 1991, A137, 35. 3. Horita, Z., Smith, D. J., Furukawa, M., Nemoto, M., Valiev, R. Z. and Langdon, T. G., J. Mater. Res., 1996, 11, 1880. 4. Saito, Y., Utsunomiya, H., Tsuji, N. and Sakai, T., Japanese Patent applied for. 5. Nicholas, M. G. and Milner, D. R., Br. Weld. J., 1961, 8, 375. 6. Helmi, A. and Alexander, J. M., J. Iron Steel Inst., 1968, 206, 1110. 7. Metals Handbook, 9th edn, Vol. 2. American Society for Metals, Metals Park, OH, 1979, pp. 65±66. 8. Sakai, T., Saito, Y., Hirano, K. and Kato, K., Trans. ISIJ, 1988, 28, 1028. 9. Saito, Y., Tsuji, N., Utsunomiya, H., Sakai, T. and Hong, R. G., Scripta mater., 1998, 39, 1221. 10. Tylecote, R. F., The Solid Phase Welding of Metals. Edward Arnold, London, 1968. SAITO et al.: ACCUMULATIVE ROLL-BONDING 583