Corrosion behavior of erbium modified Zn-11Al-3Mg cast alloy in stagnant 3.5 wt% NaCl solution

Zn-11Al and Zn-11Al-3Mg-xEr (x=0, 0.05, 0.1, 0.5) alloys were prepared, and the microstructures and corrosion resistance of the alloys were investigated by scanning electron microscopy (SEM), x-ray diffraction (XRD), and electrochemical methods. The results show that the primary Al-rich phase in Zn-11Al alloys is corroded as the main anode. The electronegativity of the primary Al phase in Zn-11Al-3Mg alloys is higher than the primary MgZn2 phase, and the electronegativity of Al-rich and Mg2Zn11 phases is higher than that of the eta-Zn phase in ternary eutectic structure. The primary Al-rich phase and Mg2Zn11 phases in the alloy are corroded as the main anodes. On the other hand, the erbium (Er) reacts with Al to form the AlEr phase, and the AlEr phase has a significant refining and homogenizing effect on the primary Al-rich phase in the Zn-11Al-3Mg alloy. When the content of Er is 0.05%, the primary Al phase transforms into fine discontinuous cellular structure. However, the increase of Er addition promotes the growth of primary Al-rich phase and the reduction of ternary eutectic, which weakens the corrosion resistance of the alloy.