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/alpha-Mg and Mg2Sn/alpha-Mg was (230 +/- 19) mV and (80 +/- 6) mV, respectively, much lower than that of Al8Mn5/alpha-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 alpha-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.

Automated summary

The poor corrosion resistance of commercial Mg alloys can be improved by adding minor amounts of Ca or Sn elements. In this study, the corrosion behavior of Mg-3Al-1Zn (AZ31) alloy with Ca or Sn additions was investigated. The results showed that AZ31-0.2Sn alloy exhibited the best corrosion resistance, followed by AZ31-0.2Ca alloy. The addition of Sn increased the potential of alpha-Mg and contributed to the formation of a dense SnO2 film, while Ca enriched in the corrosion product layer, resulting in a more compact, stable, and protective layer.