AZ31镁合金在平面应变压缩过程中的孪生行为研究

STUDY OF TWINNING BEHAVIOR OF AZ31 Mg ALLOY DURING PLANE STRAIN COMPRESSION

采用EBSD技术研究了AZ31镁合金在平面应变压缩过程中的孪生行为.结果表明,当压缩方向为TD,约束方向为RD时,孪生类型主要以{1012}拉伸孪晶为主,孪生变体的选择主要由沿TD的孪生Schmid因子(m)决定,并受RD的影响.可用孪生应变张量来解释不同类型孪生晶粒的差异.对于晶粒内部只发生1个{1012}孪生变体的情况,孪生变体在约束方向上的平均孪生应变张量会使得样品伸长;对于晶粒内部含有2个及以上变体的情况,孪生m较大的变体在约束方向上的平均孪生应变张量使得样品伸长,而m较小的变体使得样品在约束方向缩短,在平面应变压缩变形过程中,不同类型的孪生变体相互协调变形.

Mg alloy has hexagonal structure and exhibits poor workability at room temperature, which is attributed to the difficulty in activating a sufficient number of independent slips to accommodate the deformation. Twinning plays an important role in plastic deformation of Mg alloys during low and medium temperature to accommodate the imposed strain, especially the strain along the c-axis. Therefore, the twinning behavior ofAZ31 Mg alloy during plane strain compression at room temperature was investigated with EBSD in this work. Rectangular specimens with a dimension of 10 mm in length, 9 mm in width and 7 mm in thickness were cut from a hot rolled plate. The results show that { 101^-2} twinning is dominant when the compression and constraint direction are parallel to transverse direction （TD） and rolling direction （RD） of the plate, respectively. The twinning variant selection mechanism is dominated by the Schmid factor （m） along compression direction, and also related to the constraint direction. The differences of twinning behavior can be interpreted by the twinning strain tensor. For the case when single twinning variant occurs within a grain, the average twinning strain tensor of twinning variant in constraint direction will result in spreading; while for the case there are two or more twinning variants taking place within agrain, the average twinning strain tensor of the variant with higher m will induce spreading in the constraint direction, and that with lower m results in size reducing in the constraint direction. During plane strain compression, different twinning variants coordinate with each other, twinning won＇t be suppressed until the micro-strain in the con- straint direction reaches 0.