Microstructure, mechanical properties and corrosion resistance of as-cast and as-extruded Mg-4Zn-1La magnesium alloy

Microstructure, mechanical properties and corrosion resistance of as-cast and as-extruded Mg-4 wt% Zn-1 wt% La magnesium alloys were investigated. The alloys were produced by low-pressure die casting method and extruded at 350 degrees C after homogenization at 400 degrees C for 24 h. The results show that the as-cast alloy mainly consists of primary alpha-Mg matrix and Mg-Zn-La ternary second phases (also called T-Phase) along grain boundaries and isolated spherical particles inside the grains. After extrusion at 350 degrees C, the average grain size decreases by 81% due to dynamic recrystallization mechanism and T-phase particles are distributed along the extrusion direction. The elongation, yield strength and tensile strength of the as-cast Mg-4Zn-1La alloy increase by 179%, 90% and 40%, respectively, as a result of the extrusion process. The as-extruded Mg-4Zn-1La alloy shows better corrosion resistance than the as-cast alloy due to increased grain boundaries and decreased content of T-phase.