Effect of Pass Strain on Grain Refinement in 7475 Al Alloy during Hot Multidirectional Forging
Effect of Pass Strain on Grain Refinement in 7475 Al Alloy during Hot Multidirectional Forging
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DOI：
10.2320/matertrans.45.2232
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发表时间：
2004-07
影响因子：
1.2
通讯作者：
O. Sitdikov;T. Sakai;A. Goloborodko;H. Miura;R. Kaibyshev
中科院分区：
文献类型：
--
作者：
O. Sitdikov;T. Sakai;A. Goloborodko;H. Miura;R. Kaibyshev
在490℃、应变速率为3 ~ 10 ~ 4 s ~ 1的条件下，研究了道次应变对粗晶7475铝合金多向锻造晶粒细化的影响。矩形试样变形至累积应变约为6，随后加载方向随道次变化90°。每次压缩时的孔道应变分别为0.4和0.7。每次压缩积分的累积流动曲线在屈服后表现出明显的功软化，其次是高应变下明显的稳态塑性流动。结构变化的特征是由于变形和/或微剪切带的频繁发展导致晶粒破碎，然后在原始晶粒中充分演化出新的细晶粒。增大的“”显著加速了晶粒细化的动力学，导致在中高应变下流动应力更明显地降低。在3.5以上的应变下，MDF的平均尺寸为7.5 mm左右，而在更高的应变约为6时，MDF的平均尺寸为- ‘ ’¼0:4，晶粒结构略粗。详细讨论了MDF对新晶粒演化的影响和晶粒细化的机理。
Effect of pass strain (�" ) on grain refinement was studied in multidirectional forging (MDF) of a coarse-grained 7475 Al alloy at 490 � C under a strain rate of 3 � 10 � 4 s � 1 . Samples of rectangular shape were deformed up to accumulated strains of around 6 with subsequent changes in loading direction 90 � from pass to pass. The pass strains in each compression (�" ) were 0.4 and 0.7. The cumulative flow curves integrated by each compression exhibit significant work softening just after yielding, followed by apparent steady state plastic flow at high strains. Structural changes were characterized by grain fragmentation due to frequent development of deformation and/or microshear bands followed by full evolution of new fine grains in the original grains. Increasing �" accelerates significantly the kinetics of grain refinement, leading to more clear reduction of flow stresses at moderate to high strains. MDF of �" ¼ 0:7 results finally in formation of a finer grained structure with an average size of around 7.5 mm at strains of above 3.5, while, the processing with �" ¼ 0:4 develops a slightly coarser grain structure at higher strain of about 6. The effect of MDF on new grain evolution and the mechanisms of grain refinement are discussed in details.