Role of trace additions of Ca and Sn in improving the corrosion resistance of Mg–3Al–1Zn alloy

The limited wide applicability of commercial Mg alloys is mainly attributed to the poor corrosion resistance. Addition of alloying elements is the simplest and effective method to improve the corrosion properties. Based on the low-cost alloy composition design, the corrosion behavior of commercial Mg–3Al–1Zn (AZ31) alloy bearing minor Ca or Sn element was characterized by scanning Kelvin probe force microscopy, hydrogen evolution, electrochemical measurements, and corrosion morphology analysis. Results revealed that the potential difference of Al₂Ca/α-Mg and Mg₂Sn/α-Mg was (230 ± 19) mV and (80 ± 6) mV, respectively, much lower than that of Al₈Mn₅/α-Mg (430 ± 31) mV in AZ31 alloy, which illustrated that AZ31–0.2Sn alloy performed the best corrosion resistance, followed by AZ31–0.2Ca, while AZ31 alloy exhibited the worst corrosion resistance. Moreover, Sn dissolved into matrix obviously increased the potential of α-Mg and participated in the formation of dense SnO₂ film at the interface of matrix, while Ca element was enriched in the corrosion product layer, resulting in the corrosion product layer of AZ31–0.2Ca/Sn alloys more compact, stable, and protective than AZ31 alloy. Therefore, AZ31 alloy bearing 0.2wt% Ca or Sn element exhibited excellent balanced properties, which is potential to be applied in commercial more comprehensively.