Morphology and Corrosion Resistance of Chrome-free Phosphate Film for AZ91D Magnesium Alloy

A chrome-free phosphate film was prepared on the AZ91D magnesium alloy surface via chemical deposition method. The morphology of surface and interface was examined using scanning electron microscopy (SEM). The results show that a uniform phosphate film with thickness of 6~10 μm and some micro-cracks can be prepared. The film hardly ethibited corrosion phenomenon for 72 h in the neutral salt spray test (NSS). The potentiodynamic polarization curves prove that the Ecorr of the alloy with the film was shifted positively by 150 mV (vs. SCE), the Jcorr was decreased at least by three orders compared with that of the bare substrate. The results confirm that the film possesses good corrosion resistance.