Unraveling the effects of Zn addition and hot extrusion process on the microstructure and mechanical properties of as-cast Mg-2Al magnesium alloy

The effects of zinc addition and hot working via extrusion process on the microstructure and mechanical properties of as-cast Mg-2Al-xZn (x = 0, 0.5, 1, 2, and 5 wt%) magnesium alloys were studied. It was revealed that the simultaneous addition of 2 wt% Al and 0.5 wt% Zn (known as AZ20 alloy) is an effective way for refining of a-Mg in the as-cast condition, which resulted in a significant enhancement of tensile properties and changing the fracture mechanism from brittle cleavage facets to fibrous appearance characterized by ductile dimples. Further addition of Zn had negligible effect on the grain size but resulted in the appearance of Mg-21(Zn,Al)(17) intermetallic known as phi-phase, where the latter resulted in the deterioration of tensile properties of as-cast ingot due to its unfavorable morphology. After extrusion process, fine and recrystallized microstructures were observed along with the fractured and dispersed second phase particles. Besides the effect of fine grain size as verified by the Hall-Petch relationship, the presence of finely dispersed particles in the ZA52 (Mg-5Zn-2Al) alloy was found to be favorable in improving the mechanical properties and tensile toughness of the extruded alloy. Based on these findings, it was recommended to use these alloys in the wrought condition.