The Research On Twinning Of Magnesium Alloy During Plastic Deformation

Magnesium alloys are attracting more and more attentions as their advanced properties, but the poor plasticity at room temperature limits their development and extensive applications in industry. The lattice structure of pure magnesium and most magnesium alloys is hexagonal-close-packed (hcp) structure, so the twinning plays an important role in the plastic deformation of Magnesium alloys. In this paper, through compression and extension in room temperature and rolling in high temperature of AM60, AZ31 and ZK60 Magnesium alloys, the influence of deformation processing on twinning of Magnesium alloys during deformation, such as loading mode, deforming rate and deformation degree, is investigated by analyzing microstructure, XRD, mechanical property and fracture plane.Firstly, the influence of the grain orientation, loading mode, deforming rate and deformation degree on twinning is researched by uniaxial compression, uniaxial extension and plane-strain compression of AM60 and AZ31. It results that during uniaxial compression of AM60 casting ingot with the compression rate of 0.2mm/min, the { 101 2} plane twins in primary deformation, and the { 101 1} plane twins with the increasing of compression degree. The main twinning mode during compression at air temperature of AM60 and AZ31 extruded plate is { 101 2} twinning, and it is activated only when the grain is extended paralleling to the C axis or compressed perpendicular to the C axis. { 101 2} twin can block the slipping of dislocation, and it results in the higher compressive resistance of TD and ED than that of ND. The sensitivity of deforming rate to the twinning changes in regard of the twinning mode. During the ND extension of AZ31 in plane-strain compression, with the increasing of deforming rate, the ultimate compressive resistance and ultimate compression degree decrease as there is too little time for the { 101 2} twinning to be activated.Secondly, the influence of reduction per pass on twinning of magnesium alloys during hot rolling and the effect of the twin to the plastic deformation during rolling and anneal is researched through hot rolling of ZK60 and AZ31 extruded plate and anneal of ZK60 rolled plate. The results show that during rolling of ZK60 in 250℃and AZ31 in 300℃, the fraction of twin increases with the increasing of deformation degree, and when the deformation degree is close to the limited, the DRX grains appear in grain boundary, twin boundary or in the...