Effects of Ce and Ca Addition on Microstructure and Corrosion Resistance of Mg-9Al-Zn Alloy

The effects of the combined addition of minor Ce and Ca on the microstructure and corrosion resistance of Mg-9Al-Zn alloy were studied by OM, SEM, XRD, scanning Kelvin probe force microscopy (SKPFM) and polarization curve test. The results showed that after adding 0.6%Ce to Mg-9Al-Zn alloy, the morphology of precipitate phases changed from continuous network to discontinuous and dispersive one. Ce reacted with Al to form Al₂Ce phase, which caused the reduction in content of cathodic phase β-Mg₁₇Al₁₂, and the corrosion resistance of the alloy was improved obviously. After further adding 0.3%Ca to Mg-9Al-Zn-0.6Ce, Ca was dissolved in the β-Mg17Al12 phase, reducing the potential difference between the β-Mg₁₇Al₁₂ phase and α-Mg phase. The corrosion rate of Mg-9Al-Zn-0.6Ce-0.3Ca alloy was reduced by 54.14% compared with Mg-9Al-Zn alloy, and the corrosion current density was also significantly reduced, hence the corrosion resistance was further improved. However, when the Ca addition raised to 0.8%, Al₄Ca phase was formed, and the amount of the cathodic phases significantly increased, leading to the reduction of corrosion resistance compared with the Mg-9Al-Zn-0.6Ce-0.3Ca alloy.