Effect of cooling rate on the microstructure and corrosion properties of Zn-5Al-0.1RE-xSi alloys

The effects of cooling rate and Si on the microstructure and corrosion property of the Zn-5Al-0.1 RE alloy were studied by scanning electron microscopy-energy dispersive spectrometry, X-ray diffraction, neutral salt spray test and polarization curves. The results show that Zn-5Al-0.1RE-xSi alloys are composed of primary η-Zn phase and η-Zn + α-Al eutectic structure, and the former is uniformly distributed on the adjacent η-Zn + α-Al entectic cells. The reduction of cooling rate and the addition of Si make the grain size increase and the boundary area per unit alloy area decrease; at the same time, the corrosion resistance is improved. The corrosion resistance of the Zn-5Al-0.1 RE-xSi alloys is dependent on their solidification structure and the relative amount of corrosion products including Zn₅(OH)₈Cl₂·H₂0 and ZnO.