Phosphating process of AZ31 magnesium alloy and corrosion resistance of coatings

Zinc phosphate films were formed on AZ31 magnesium alloy by immersing into a phosphatation bath to enhance the corrosion resistance of AZ31. Different films were prepared by changing the processing parameters such as immersing time and temperature. The corrosion protection of the coatings was studied by electrochemical measurements such as electrochemical impedance spectroscopy, potentiodynamic polarization curves, and the structure of the films were studied by metalloscopy and X-ray diffraction (XRD). The results show that, the film formed at 80 °C, 10 min has the highest corrosion resistance. The XRD patterns show that the film consists of hopeite (Zn₃(PO₄)₂ · xH₂O).