镁合金温变形过程中的孪生及孪晶交叉

对AZ31镁合金在3种温度(523,573和673 K)下进行了单向压缩变形.在523 K,当真应变ε达到0.22时真应力-真应变曲线出现尖锐的应力峰值,在应力峰值之前先后经历了缓慢加工硬化(0.02≤ε<0.06)和急剧加工硬化(0.06≤ε<0.22)2个阶段.利用SEM/EBSD技术分析了这2个阶段对应的显微组织.结果表明,在缓慢加工硬化阶段(ε=0.03),仅有少量孪晶出现;在急剧加工硬化阶段(ε=0.06),产生了大量{101~-2}孪晶,孪晶间的相互交叉导致材料产生急剧加工硬化.AZ31镁合金{101~-2}孪晶间交叉有5种可能存在的形式,孪晶的形成和交叉与压缩应力方向有密切关系.在基体应力方向分别为近似<112~-0>和<101~-0>方向时确认了(101~-2)-(011~-2)和(101~-2)-(01~-12)2种交叉形式.

TWINNING AND TWIN INTERSECTION IN AZ31 Mg ALLOY DURING WARM DEFORMATION

Though electron backscattering diffraction (EBSD) is widely employed for the ori-entation analysis of deformed microstructures in many metallic materials, its applications to Mg and its alloys are not widespread because of the difficulties involved in sample preparation. In this work, uniaxial compression tests were performed on samples cut along the extrusion direction from AZ31 Mg alloy bars, and then the twins and their intersections were analyzed by SEM/EBSD microscopy. Deformation and deformation mechanisms operating in Mg alloy depend sensitively on temperatures. Flow curve at 523 K shows a sharper and larger stress peak following slow strain hardening and rapid strain hardening. At slow hardening stage (0.02 ≤ε < 0.06) a few of {101~-2} twinning was commonly observed, but at rapid hardening stage (0.06 ≤ε < 0.22) more twins and twin intersections appeared. There are five possible types of twin intersections, which are strongly depended on the stress direction. The two types of (101~-2)-(011~-2) and (101~-2)-(01~-12) twin intersections were observed at stress axis near to <112~-0> and <10~-10> in the samples compressed to a true strain of 0.06.