镁合金热变形下变形带的形貌和晶体学特征

MORPHOLOGY AND CRYSTALLOGRAPHIC CHARACTERISTICS OF DEFORMATION BANDS IN Mg ALLOY UNDER HOT DEFORMATION

对不同温度单向压缩下AZ31镁合金不均匀形变组织的形貌和晶体学特征进行了研究.结果显示:形变组织具有很强的温度和应变敏感性;250℃时,晶粒内在变形初期出现大量的{1012}拉伸孪晶和少数{1011}压缩孪晶,随着应变量的加大,拉伸孪晶因相同取向孪晶的合并而急剧减少,而压缩孪晶明显变粗,数量也有所增加;300℃以上时,非基面滑移被激活后,出现了与压缩轴基本垂直的扭折带,其晶体学方向垂直于(0001)基面,扭折带两侧的主滑移系都为(0001)基面滑移,变形初期扭折带界面取向差为2°—6°,随着变形量的增加,扭折带密度加大;温度升高至400℃时,扭折界面发生明显的弯曲.对扭折带和其他变形带的特征进行了对比考察.

When metals and alloys are subjected to considerable plastic deformation such as coldor warm-rolling,characteristic inhomogeneities generally appear as a form of deformation or shear bands.Recently much attention has been given to the deformation mechanism and morphology of fcc and bcc materials.It is well known that such inhomogeneities play an essential role in the process of work-hardening,recrystallization,metal fatigue and fracture.Therefore,in order to obtain the guiding principle for controlling those processes in Mg based alloys,it is indispensable to make clear the details of those inhomogeneous deformation structures in hcp materials.In this work,the inhomogeneous deformation and microscopic features of AZ31 Mg based alloy were studied under compression at temperature ranging from 250 to 400℃and at a strain rate of 3×10^（-3） s^（-1）.The analysis of experimental data shows that such inhomogeneities depend on deformation temperature and strain sensitively.At 250℃,the {1012} c-axis extension twins and deformation bands appear at around 45°with the compression axis in grain interior when straining toε=0.1,the {1012} twins continue to grow until they impinge each other and finally most of the original grains are replaced by twinned grains at a strain of aboutε=0.2.The boundaries between {1012} twins and their neighbors disappear during twinning. At 300℃,in contrast,the non-basal slips are activated,the kink bands with low misorientation angles are frequently evolved in grain interior and they are roughly perpendicular to the（0001） basal plane,further deformation leads to an increase in the number and misorientation angle of the kink bands.The initial grains are fragmented by kinking.With temperature increasing,the spacing of kink bands increase rapidly.The difference between kinking and other deformation bands was discussed in some detail.