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 579NOVEL 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 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-®ne (sub-micron) grain structure with large misorientations, i.e. polycrys￾tal, 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 cor￾rosion 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, mech￾anical alloying, cryogenic metalforming and intense plastic straining. Intense plastic straining is con￾sidered the most appropriate process for industrial application. Special processes such as cyclic extru￾sion 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 pro￾ductivity is relatively low and the amount of ma￾terials produced is very limited. These processes are thought to be inappropriate for practical appli￾cation, especially for large-sized structural materials such as sheets. The authors now propose an alternative novel intense plastic straining process named accumulat￾ive roll-bonding (ARB) [4] for bulk-material manu￾facturing 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 conven￾tional 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 surface￾treated in advance in order to enhance bond strength, if required. The two layers of material are joined together by rolling, as in a conventional roll￾bonding 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 tempera￾ture below recrystallization temperature because recrystallization cancels out the accumulated strain. Low temperature would result in insucient duct￾ility and bond strength. There exists a minimum limit of reduction in thickness, i.e. threshold defor￾mation to attain sucient bonding. It is well known that the threshold deformation decreases with tem￾perature. 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 recrystal￾lization. The process can introduce ultra-high plastic strain without any geometrical change, if the re￾duction 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