Corrosion properties of AZ31 magnesium alloy and protective effects of chemical conversion layers and anodized coatings

Abstract

The corrosion properties of AZ31 magnesium alloys were studied by potentiodynamic polarization curves and electrochemical impedance spectroscopy(EIS) techniques, meanwhile, the protective properties of two environmentally protective types of chemical conversion layers and anodized coatings of AZ31 magnesium alloys were also discussed. The component of chemical conversion bath is NaH 2O 4 12H 2O 20 g/L, H 3PO 4 7.4 mL/L, NaNO 2 3 g/L, Zn(NO 3) 2·6H 2O 5 g/L and NaF 1g L, and components of the anodization bath is Na 2SiO 3 60 g/L, C 6H 5Na 3O 72H 2O 50 g/L, KOH 100 g/L and Na 2B 4O 7·2H 2O 20 g L. The results show that the corrosion resistance of AZ3 1 magnesium increases with the increase of pH value of the corrosive medium. For the chemical conversion layer acquired at 80 °C, 10 min is the best processing time and the charge transfer resistance of the chemical conversion layer is enhanced nearly by 10 times. The optimum processing time for the anodization of AZ31 is 60 min, the charge transfer resistance value of the anodized sample at the early immersion stage is nearly 26 times of that of the blank sample and the corrosion type of the anodized samples is pitting.