Unusual texture formation and mechanical property in AZ31 magnesium alloy sheets processed by CVCDE

In order to shorten process flow, improve production efficiency, the continuous variable channel direct extrusion (CVCDE) was used for processing magnesium alloy sheets with high performance, which could control shapes and properties of sheets simultaneously. The results of experimental research showed that, compared with the conventional direct extrusion (CDE) method, the CVCDE method promoted the grain refinement of magnesium alloy sheets, reduced the formation of twins and increased the volume fraction of recrystallized grains. It made the orientation of (0002) basal planes tilt from ND direction by a certain angle, and the angle at which the basal planes tilted from the TD direction was gradually approached to the angle tilted from the ED direction, and the Schmid factor of the basal slip was gradually increased, which made the basal slip easier to be activated. In the magnesium alloy sheets extruded by CVCDE using one interim die, incomplete grain refinement led to uneven microstructure, the dislocation wall was generated in the crystal, the dislocation density was high, and the texture strength was increased. In the magnesium alloy sheets extruded by CVCDE using two interim dies, there were obvious triple grain boundaries, low dislocation density in the crystal and the weaker basal texture. Through the joint effect of grain refinement and texture evolution, the magnesium alloy sheets extruded by CVCDE using two interim dies had lower YS and UTS, and the EI increased by 18% compared with the CDE.