Role of alloyed Al on the microstructure and corrosion behavior of as-cast dilute Mg-2Zn-xAl-0.5Ca alloys

Effect of Al on microstructure and corrosion behaviors of cast Mg-2Zn-xAl-0.5Ca (x = 0, 0.5, 1.0, 2.0 wt%) alloys is investigated. The 0.5Al specimen shows the lowest corrosion rate (4 mm/y) because appropriate Al doping into Ca2Mg6Zn3 decreases cathodic activity of this phase and Al alloying significantly refines intermetallics, both of which contribute to reducing pitting corrosion. Moreover, finer grains enhance barrier effect of continuous net-like phases at grain boundaries, effectively confining the corrosion propagation. The formation of Al2O3 reinforces the surface film. Optimum Al content is determined as 0.5–1.0%, which endows alloy with admirable corrosion resistance and high ultimate tensile strength.