Effect of Sn on Corrosion Resistance of As-cast AZ91 Magnesium Alloys

The microstructure and corrosion behavior of AZ91+sSn（x =0,0.2,0.5,1wt%） magnesium alloys were investigated by optical microscopy（OM）, X-ray diffractometry（XRD）, scanning electron microscopy（SEM）, collecting gas method and electrochemical test. The results show as following:with Sn addition increasing, the corrosion resistance of tested alloys initially improves and then decreases in 3.5%NaCl solution. The AZ91+0.2Sn alloy has the lowest corrosion rate, which is 54% of AZ91 alloy, is contributed to the fully divorced β-Mg₁₇Al₁₂phase in the alloy replacing the partially divorced β-Mg₁₇Al₁₂ phase in AZ91 alloy. Nevertheless, AZ91+1.0Sn alloy has the highest corrosion rate, which is 118% of AZ91 alloy,is ascribed to the existence of located corrosion in the alloy.