Study of the corrosion product films formed on the surface of Mg–xZn alloys in NaCl solution

•There are compact surface films formed on the Mg–2Zn and Mg–5Zn alloys in NaCl.•The degradation behavior of the corrosion product films is studied.•The protection ability of the film on Mg–2Zn is superior to that on Mg–5Zn.•Chemical composition and microstructure greatly affect the corrosion product films.

The corrosion product films formed on the surface of Mg–2Zn and Mg–5Zn alloys in NaCl solution were investigated by electrochemical measurement, scanning electron microscopy (SEM) observation and X-ray photoelectron spectroscopy (XPS) analysis. It is found that a compact corrosion product film is formed in the initial stage of immersion, and then the film gradually degrades due to dissolution reaction. The product film formed on Mg–2Zn alloy presents better protection property than that on Mg–5Zn alloy, which can be attributed to the different chemical composition and microstructure of the both alloys.