Magnesium alloys chromate treatments

Chromates are very effective inhibitors of the corrosion of magnesium alloys by saline and other waters, and many treatments have been developed by means of which substantial hlms containing slightly soluble chromate are formed in the metal surface. Except on parts which are to be exposed only to a rural atmosphere, chromate treatment must be supplemented by paint, for which it provides a good base. 

Post-Treatments. Although many post-treatments have been used over plated metals, chromate conversion coatings remain as the most popular. Chromates are used to improve corrosion resistance, provide good paint and adhesive base properties, or to produce brighter or colored finishes. Formulations are usually proprietary, and variations are marketed for use on zinc, zinc alloys, cadmium, copper and copper alloys, and silver (157). Chromates are also used on aluminum and magnesium alloys (158,159). More recently, chromate passivation has been used to extend salt spray resistance of autocatalytic nickel plated parts. 

Magnesium alloys do not retain a high lustre like the aluminium alloys and cannot be electroplated with the same ease as the zinc alloys. Finishing is usually achieved by painting or lacquering. Chromate treatments are used to protect against corrosion, but have little decorative value. 

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