Study on the corrosion resistance of phytic acid conversion coating for magnesium alloys

Chemical conversion treatment is a basic method to improve the corrosion resistance of magnesium and its alloys. In the method of conventional conversion, however, the solution contains hexavalent chromium compounds which are harmful to the environment. The replacement surface treatment has been strongly emphasized in recent years. A chemical conversion treatment solution containing phytic was developed in this study for magnesium alloys. The surface conversion coating was characterized by SEM and EDS. The factors of influence to the corrosion resistance of conversion coating were discussed through hydrogen evolution method and polarization potential. The corrosion resistance of phytic acid conversion coating was comparable with the chromate containing. The experimental results indicate that the phytic acid conversion coating had better corrosion resistance when magnesium alloy was treated with a solution containing 0.5% to 1% phytic acid at temperature 25 to 60 °C and pH value at the range of 3∼5 for 30 to 60 min.