Investigation on the Compound Phosphate Film Formed in Bath with Cerium Salts on the Magnesium Aluminum Alloy

A composite phosphate film was formed on magnesium aluminum (Mg-Al) alloy which was impregnated in phosphating solution containing phosphate, cerium salt, organic ammonium and corrosion inhibitor. The sample was examined by scanning electron microscope (SEM), X-ray diffraction (XRD), and Energy Dispersive Spectrometer (EDS) to analyze the organization and structure of the film. Additionally, the corrosion resistance of the film of composite phosphate was also investigated by salt spray test. As a result, it shows that the components of the film formed on Mg-Al alloy contain phosphates and elemental zinc. On the other hand, the composite phosphate film possessing photo-absorption property can be used for protective layer and laser pretreatment of Mg-Al alloy.