Preparation and Characterization of Phosphate Film for Magnesium Alloy AZ31

An anticorrosion phosphate film with free of chromate, fluorides and nitrite, was successfully prepared on the surface of the magnesium alloy AZ31 via chemical deposition method. The effects of film-forming temperature and free acid on the corrosion resistance of the film were investigated through SEM. The analysis results indicate that the compactness of the film increased with the increase of film-forming temperature, but more residues is brought. While increasing FA in the proper range can decrease the residues. The EDS characterizations of the film confirm that the phosphate film contains only three elements of Mn, P and O. The analysis of the polarization curves further prove that the film has great inhibitive action on anodic dissolution and cathodic hydrogen evolution, and the corrosion resistance is improved with the increase of temperature