Effect of ball milling time on microstructure and mechanical properties of ultrafine- grained Mg-3Al-Zn alloy prepared by powder metallurgy

The ultrafine-grained Mg-3Al-Zn alloy was prepared by high energy ball milling,cold vacuum press and warm extrusion. The influence of ball milling time on the microstructure and mechanical properties of the alloy was studied. The results show that Al and Zn elements completely dissolve into the magnesium matrix in the process of ball milling. The single phase solid solution is formed. After the ball-milling for 20 h, the average particle size of the powder particles is about 25 μm, and the average grain size is about 45 nm. After the powder is densified by cold pressing and warm extruded, the average grain size of the alloy milled for 20 h is 600 nm, and the grain shape is regular and equiaxed crystal. All ultrafine-grained alloys show higher mechanical properties. The yield strength, tensile strength and breaking strain of the alloy after ball milling for 20 h are 369 MPa, 401 MPa and 3.5%, respectively. The tensile true stress-true strain curve of ultrafine-grained magnesium alloy shows a characteristic of ideal rigid plasticity. The compression true stress-true strain curve can be divided into three stages: working hardening, working softening and working hardening