Microstructure Refinement of Magnesium Alloy (AZ31) through a Combination of Extrusion and Room Temperature Equal Channel Angular Process

摘要

It is well known that magnesium alloys have difficulties in room temperature formability because of their HCP (Hexagonal close packed) lattice structure. In order to obtain microstructure refinement of magnesium alloy (AZ31), a new combination process including an extrusion followed by a room temperature equal channel angular pressing (ECAP) was attempted. ECAP die has an inner die corner angle of 135 degree, the fillet angle of 45 degree and thickness of 5mm. A finite element analysis with a three-dimensional thermo-coupled elasto-plastic material model was also carried out to understand the change of stress and strain of the deformed material during a room temperature ECAP. Experiments showed that the AZ31 alloy, which is extruded at a ratio of 20 and heat-treated at 623K, was successful in a room temperature ECAP. From the simulated results, it was found that the effective strain gradually analysis via von Mises criterion. Furthermore, it also matched well with the experiments which showed a uniform shear deformation band. It was also interesting to note that compressive yield strength was drastically increased, which is caused by the occurrence of numerous twins spread across the materials. Finally, the grain refinement to the size of 0.6 μm was obtained.