Abstract：The effect of forging pass on the deformation structure of high purity aluminum at room temperature during multi-direction forging process was investigated by experiment. The multi-direction forging process was analyzed by using software of DEFORM-3D. The results show that an X-shape fine grain zone (in the center of the sample) and four coarse grain zones (near the end surface of the sample) are initially formed on the cross section of the sample as forging passes increase to 3. With a further increasing the passes to 9, this X-shape zone tends to spread the whole sample. However, the grain difference between the coarse grain zone and fine grain zone still exists on the sample forged by 9 passes. Limitation in the structural refinement is observed in the center of the sample with the increment of equivalent strain. The grains size in the center is refined to a certain size (about 70μm) as equivalent strain reaches 2.5, and no further grain refinement in the center with increasing the equivalent strain to 6.0. However, the grains size in the area near the surface is continuously refined with the increasing the equivalent strain to 4.0. This indicates that the local deformation state and the equivalent strain are two important factors that affect the grain size.
 RINGEVAL S,PIOT D,DESRAYAUD C,et al.Texture and microtexture development in an Al-3Mg-Sc(Zr) alloy deformed by triaxial forging[J].Acta Materialia,2006,54(11):3095-3105.
 SITDIKOV O,SAKAI T,GOLOBORODKO A,et al.Grain fragmentation in a coarse-grained 7475 Al alloy during hot deformation[J].Scripta Materialia,2004,51(2):175-179.
 LIU W C,CHEN M B,YUAN H.Evolution of microstructures in severely deformed AA 3104 aluminum alloy by multiple constrained compression[J].Materials Science and Engineering:A,2011,528(16-17):5405-5410.
 ZHU Q F,LI L,BAN C Y,et al.Structure uniformity and limits of grain refinement of high purity aluminum during multi-directional forging process at room temperature[J].Transactions of Nonferrous Metals Society of China,2014,24(5):1301-1306.
 VALIVIEV Z,ISLAMGALIEV K,ALEXANDROV V.Bulk nanostructured materials from severe plastic deformation[J].Progress in Materials Science,2000,45(2):103-189.
 IWAHASHI Y,HORITA Z,NEMOTO M,et al.An investigation of microstructural evolution during equal-channel angular pressing[J].Acta Materialia,1997,45(11):4733-4741.
 VALIEV R Z,LANGDON T G.Principles of equal-channel angular pressing as a processing tool for grain refinement[J].Progress in Materials Science,2006,51(7):881-981.
 ZHU R,WU Y J,JI W Q,et al.Cyclic softening of ultrafine-grained AZ31 magnesium alloy processed by equal-channel angular pressing[J].Materials Letters,2011,65(23):3593-3596.
 任国成,赵国群.AZ31镁合金等通道转角挤压应变累积均匀性分析及组织性能研究[J].材料工程,2013,(10):13-18. REN G C,ZHAO G Q.Homogeneous deformation analysis and microstructure properties study of AZ31 magnesium alloy in multi-pass equal channel angular pressing[J].Journal of Materials Engineering,2013,(10):13-18.
 何运斌,潘清林,刘晓艳,等.ECAP 法制备细晶ZK60 镁合金的微观组织与力学性能[J].材料工程,2011,(6):32-38. HE Y B,PAN Q L,LIU X Y,et al.Microstructure and mechanical properties of ZK60 magnesium alloy produced by equal channel angular pressing[J].Journal of Materials Engineering,2011,(6):32-38.
 VALIEV R Z,KRASILNIKOV N A,TSENEV N K.Plastic deformation of alloys with submicron-grained structure[J].Materials Science and Engineering:A,1991,137:35-40.
 MAZILKIN A A,STRAUMAL B B,BORODACHENKOVA M V,et al.Gradual softening of Al-Zn alloys during high-pressure torsion[J].Materials Letters,2012,84(10):63-65.
 SAITO Y,UTSUNOMIYA H,TSUJI N,et al.Novel ultra-high straining process for bulk materials—development of the accumulative roll-bonding (ARB) process[J].Acta Materialia,1999,47(2):579-583.
 TISUJI N,ITO Y,SAITO Y,et al.Strength and ductility of ultrafine grained aluminum and iron produced by ARB and annealing[J].Scripta Materialia,2002,47(12):893-899.
 周蕾,史庆南,王军丽,等.异步累积叠轧纯铜材的取向变化过程与力学性能[J].材料工程,2013,(3):38-41. ZHOU L,SHI Q N,WAMG J L,et al.Texture and mechanical properties of pure copper deformed by asymmetrical accumulative roll-bonding[J].Journal of Materials Engineering,2013,(3):38-41.
 SAKAI T,MIURA H,GOLOBORAODKO A,et al.Continuous dynamic recrystallization during the transient severe deformation of aluminum alloy 7475[J].Acta Materialia,2009,57(1):153-162.
 ANDREW C P,PAUL S C,THOMAS J H.High-purity aluminum sputter targets[P].European Patent:1444376B1,2010-10-06.