Phosphate coatings anodic treatment

These corrosion results suggest that the sealing treatment can significantly improve the corrosion resistance of an anodized Mg alloy. In fact, this sealing technique can also be applied to a phosphated coating (Song, 2009a) to obtain improved corrosion performance. 

One very beneficial chemical pretreatment treatment for aluminum substrates is phosphoric acid anodization (PAA), which provides an oxide coating that is inherently hydration-resistant. Its stability is due to a layer of phosphate incorporated into the outer A1203 surface during anodization. 

Chromatizing is applied to zinc and to aluminum, often after an anodizing pretreatment, in order to reinforce the corrosion protection provided by the oxide film. Unfortunately, chromates are toxic and therefore chromatizing treatments are no longer acceptable, in spite of the fact that they provide excellent corrosion protection. They are replaced by less polluting surface treatments such as phosphatizing or suitably chosen coatings. 

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