The effect of DC magnetron sputtering AlN coatings on the corrosion behaviour of magnesium alloys

Magnesium and its alloys are susceptible to corrosion, which has limited their use in the automotive and aerospace industries, where low weight is of significant concern. In this study, AlN films were coated on the magnesium alloys (AZ31, AZ61, AZ63, and AZ91) using physical vapour deposition (PVD) technique of DC magnetron sputtering, and the influence of the coating on the corrosion behaviour of the magnesium alloys was examined. A physical vapour deposition (PVD) system for coating processes, a potentiostat for electrochemical corrosion tests, X-ray difractometer (XRD) for compositional analysis of coating, and scanning electron microscopy (SEM) for surface examinations were used. It was found that DC magnetron sputtering AlN coatings deposited on magnesium alloys increased the corrosion resistance of these alloys. However, the basis factor determining the ability of protection from corrosion was that small structural defects in the coating, e.g., pores, pinholes, cracks that could arise from the coating process or substrate.