Protection and treatment of surface corrosion of magnesium aluminium alloys

The lack of corrosion resistance of magnesium aluminium alloys has limited their application in a number of fields. To solve the problem of corrosion protection of magnesium aluminium alloy, the purity of magnesium aluminium alloy can be improved from its internal impurity control, the development of new corrosion resistant alloy ion injection into magnesium aluminium alloy or laser surface modification, etc. For large-scale industrial production, protective film and layer treatment can be used to achieve a high degree of economy. At present, the main methods of surface corrosion treatment for magnesium and aluminium alloys include chemical treatment, anodic oxidation and metal plating.

1, chemical treatment

　　Through the chemical treatment can make the magnesium aluminium alloy surface form a layer of oxide protection film, the protection film can form a close combination with the magnesium aluminium alloy, block the external corrosion medium directly erode the magnesium aluminium alloy surface matrix, enhance the corrosion resistance of magnesium aluminium alloy. In industrial production, the common chemical treatment method of magnesium aluminium alloy is to use sodium chromate and magnesium fluoride to form a protective film on the surface of magnesium aluminium alloy for protection, the protective film can also slowly repair itself after erosion, very good protection effect. The addition of rare earth elements can also form a protective film on the surface of magnesium aluminium alloy. According to the relevant research, this protective film can make the corrosion of M-Al alloy slow down significantly in the buffer solution with pH 8.5, but its protective performance will be reduced in the aggressive solution with pH 8.5.

2、Anodic oxidation

　　The anodic oxidation storage energy of magnesium aluminium alloy can make the corrosion resistance of magnesium aluminium alloy to be improved substantially compared to the chemical treatment method. Magnesium aluminum alloy anodic oxidation of the oxide film porosity is high, and the hole shape is irregular, if not to these voids for processing, it is easy to lead to corrosion media more easily through the oxide film directly erode magnesium aluminum alloy surface. The anodic oxidation of magnesium aluminium alloys requires more of a reduction in the density of the voids in the oxide film. Micro-arc oxidation technology is a kind of anodic oxidation technology developed in recent years, by placing the magnesium aluminium alloy in an aqueous solution of electrolyte, and accessing high voltage to make the micro-pores in the magnesium aluminium alloy surface oxide film produce spark discharge spots to enhance the protection ability of the oxide film. Therefore, it is now possible to improve the corrosion resistance of magnesium aluminium alloys compared to the normal anodising method.