The Research On Anodizing Processing Of AZ31 Magnesium Alloy

In this paper, a novel anodizing processing based on an environmentally friendly electrolyte bath was developed for the anodizing of AZ31 magnesium alloy. The electrolyte bath contained none of chromate, fluoride or any other poisonous ingredient but could improve the surface properties of AZ31 magnesium alloy significantly, especially corrosion resistance. The anodic films were formed by constant current anodizing method and the properties of the films were fast determined by potentiodynamic polarization method. The effective components of the electrolyte bath and the optimized formula of the bath were determined by selective experiments and orthogonal tests methods. The results of potentiodynamic tests showed that the corrosion resistance of AZ31 magnesium alloy was greatly enhanced. Different components and concentration of the electrolyte bath had different influence on the composition.On the basis of the above study, the effects of all kinds of factors on the formation of anodic films and their properties were investigated. Besides electrolyte solution, the anodization of magnesium and its alloys was also affected by some other factors, including the magnitude of current density, processing time, solution temperature, pretreatment and post-treatment, etc. The investigation revealed that when constant current density was applied, anodic film grew at an almost well-proportioned rate. Its thickness increased with treatment time and applied current density. The corrosion protection provided by anodic film was determined principally by its thickness when the same electrolyte solution was employed. High temperature was not benefit to the development of the film. The behaviors of bath voltage on the anodizing processing were affected primarily by the thickness of anodic film and its compositions and microstructure.The film formation process and mechanism of corrosion resistance of the anodized films were also discussed in the paper. The scanning electron microscopy study combined with the phenomenon of anodizing processing showed that the anodized film were always formed at different area of the alloy surface at the initial anodizing stage. The porous anodizing films grew on the surface in two directions: parallel direction to cover the alloy surface and perpendicular direction to thickening the film. EDS and XRD results showed both the electrolyte solution and the base of the alloy had taken part in the film formation process.Potentiodynamic polarization curves results showed that the free corrosion...