Effect of gravity die casting, squeeze casting and extrusion on microstructure, mechanical properties and corrosion behaviour of AZ91 magnesium alloy

In this study, the effect of squeeze casting and extrusion in comparison to gravity casting on microstructure, mechanical properties, and corrosion behaviour of AZ91 Mg alloy has been investigated. With the presence of refined grains and a continuous interdendritic network of β-phase with significantly less porosity, squeeze cast AZ91 showed 93.9 %, 100 %, and 214.3% improvement in UTS, TYS, and % elongation, respectively, in tensile testing and 12.32 % in hardness compared to gravity die cast AZ91. In contrast, the extruded AZ91 showed 184.3 %, 186.2 % and 709.1 % improvement in UTS, TYS, and % elongation, respectively, in tensile testing and 8.89 % in hardness compared to squeeze cast AZ91. The squeeze cast AZ91 and extruded AZ91 exhibited lower weight loss rates of 0.25 mg·cm−2·day−1 and 0.125 mg·cm−2·day−1, respectively, in 3.5 % NaCl solution and showed better corrosion resistance compared to the gravity die-cast AZ91 sample. The extruded AZ91 (at 350 °C) exhibited the highest tensile properties and corrosion resistance among the three alloys due to the negligible porosity, recrystallized grains, and dispersive strengthening effect of the β-phase.