大塑性变形镁合金的晶粒细化

摘要

采用电子背散射技术(EBSD)定量研究AZ31镁合金在225~400°C往复挤压大变形过程中的晶粒细化。结果表明：在225°C往复挤压3道次即获得了超细晶AZ31镁合金。随着变形温度的降低，变形组织的平均位相差和大角度晶界的比例逐渐增加。在3道次的AZ31组织中，只发现少量的{1012}孪晶，位错滑移是主要的变形机制。施密特因子计算表明，在225~350°C变形时，锥面滑移系{1011}〈1120〉被大量激活。而在400°C变形时，基面滑移系{0001}〈1120〉被大量激活。亚晶界的详细分析为连续动态再结晶在镁合金大变形过程中晶粒细化的重要作用提供了直接的证据。%Grain refinement of AZ31 Mg alloy during cyclic extrusion compression (CEC) at 225−400 °C was investigated quantitatively by electron backscattering diffraction (EBSD). Results show that an ultrafine grained microstructure of AZ31 alloy is obtained only after 3 passes of CEC at 225 °C. The mean misorientation and the fraction of high angle grain boundaries (HAGBs) increase gradually by lowering extrusion temperature. Only a small fraction of {10 1 2} twinning is observed by EBSD in AZ31 Mg alloys after 3 passes of CEC. Schmid factors calculation shows that the most active slip system is pyramidal slip {10 1 1}〈1120〉and basal slip {0001}〈1120〉 at 225−350 °C and 400 °C, respectively. Direct evidences at subgrain boundaries support the occurrence of continuous dynamic recrystallization (CDRX) mechanism in grain refinement of AZ31 Mg alloy processed by CEC.