Electrochemical oxidation characteristic of AZ91D magnesium alloy under the action of silica sol

Electrochemical oxidation of AZ91D magnesium alloy in silicate electrolyte with and without addition of silica sol was investigated. The effects of silica sol content, anodic current density and electrolyte temperature on the anodic film were also investigated. The anodic films were characterized by optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The corrosion resistance of AZ91D alloys with and without anodic film was evaluated by a fast anti-acid test and anodic polarization curves, as well as by immersion and neutral salt spray tests. The results showed that the addition of silica sol increased the anodic film thickness and improved the uniformity of the anodic film. The addition of silica sol resulted in the increase of Si and the presence of C in the anodic film, possibly since silica sol particles were adsorbed on the anode and encased in the anodic film during the electrochemical oxidation process. The results of corrosion tests showed that AZ91D Mg alloy with the anodic film formed in the electrolyte of silicate with the addition of 10 vol.% silica sol demonstrated higher corrosion resistance than without addition of silica sol.