The Research On Twnning Of AZ31Magnesium Alloy During Plastic Deformation

The HCP structure of magnesium and most of its alloys can not meet the needs ofdeformation for the lack of enough slip systems at room temperature, which greatlylimits its application and development. Twinning as the one of the main deformationmechanesiums can stimulate more systems of slip and twinning by adjusting the grainorientation, which can abtain a large deformation. Therefore，committing to the researchon twinning of magnesium alloy during plastic deformation has a important realisticguiding significance for improving the ability of plastic deformation of magnesiumalloy.In this paper, through DPD compression and extension at room temperature, theinfluence of deformation processing on twinning of magnesium alloys during plasticdeformation, such as strain, grain orientation, strain rate and Pre degeneration, isinvestigated by optical microscopy, EBSD and TEM, and the formation of twinningplane type during deformation is also determined by Matlab software. The mainresearch contests and results are as follows:①The influence of strain, grain orientation, strain rate and pre-deformation ontwinning is researched by uniaxial compression and extension of AZ31magnesiumalloys at room temperature. It results that during uniaxial compression of90°samplewith the high strain rate of500/s,{1012} twinning is the main twinning mode. A largenumber of {1012} twins which have a strong coordination ability are generated in theearly stage of deformation. With the strains increasing, the volume fraction of twingradually increases, on the contrary, the density of boundary is gradually reduced. Whenstrain comes to a certain extent, two different variants meet each other in a same grainand constitute a new interface relationship of60°<1010>, and with the strainsincreasing further, this types of interface relationship increase significantly; When thestrain is given, the twinning behavior of different orientation samples is very differentduring the compression at room temperature. The main deformation mechanism of0°sample is slip and there have a small amount of {1011}-{1012} twin in the grains. Themain deformation mechanism of90°sample is {1012} twinning and there have a largenumber of {1012} twins in the grains.30°and90°are transition types, themicrostructure and properties of which are between0°and90°. The transition of0°to90°corresponds the transformation of slip to twinning;{1012} twining is the main deformation mechanism during uniaxial extension of0°sample at room temperature.The increase of strain rate will increase the occurrence tendency of twinning because ofthe high sensitivity of twinning to strain rate, with the strain rate increasing, the yieldstress and elongation decrease gradually, but there is only a little change of ultimatetensile stress. During uniaxial extension of90°sample at room temperature, slip is themain deformation mechanism, with the strain rate increasing, the elongation decreasesgradually, but the change of ultimate tensile stress is still not significant; The density ofdislocation substructures is so high after DPD6%that the blocking effect of dislocationto twinning is very obvious during the subsequent stretching process, which bring aresult that comparing to no DPD, the yield stress increases significantly, but theelongation is also still decreasing.②Through the TEM image analysis of90°sample with different strains afterDPD at room temperature, the twin morphology and twinning plane type areinvestigated. The research shows that the shape of {1012} twin is like convex lens, andthe density of dislocation near the twin boundary is relatively high. With the strainsincreasing, the size of twin sheet increases gradually. The twinning plane types areidentified as (0112) and (1102) by the analysis of the diffraction spectrum at last.