Preparation of micro-arc discharge oxidized coating on hot-dip aluminized stainless steel sheet

A new method of surface treatment for austenitic stainless steel sheets was developed to improve their mechanical performance. An aluminium layer was firstly formed on the surface of stainless steel by immersing the sheet into a 760degreesC molten aluminium bath for 8 min. The aluminized stainless steel sheet was then treated by micro-arc discharge oxidation. The structure of the resultant compound coating was analyzed by using X-ray diffraction, scanning electron microscopy with energy dispersive spectrometer and Vickers micro-hardness tester. The results show that a ceramic coating composed mainly of alpha-Al2O3 and gamma-Al2O3 is formed on a medium intermetallic compound layer and the content of gamma-Al2O3 is higher than that of alpha-Al2O3. The micro-hardness of the compound coating shows a gradation from the coating surface (800HV) to the substrate (230HV) through the medium intermetallic compound layer (250similar to600HV).