Effect of Fluoride Ion on the Microstructure and Properties of Permanganate Conversion Coating on AZ91D Magnesium Alloy

摘要

Because of the toxicity of chromate, it is necessary to develop alternatives to chromate conversion coatings. Permanganate conversion coating treatment is one of the methods that are potentially alternative to the chromate treatment on magnesium alloys. This study investigated the effect of fluoride ion in the permanganate solution on the microstructure and corrosion resistance of the conversion coating on AZ91D alloy. Experimental results showed that the presence of fluoride ion impeded the conversion coating reaction and accordingly retarded the formation of the conversion coating, which resulted in a thinner and more uniform coating. Therefore, the permanganate conversion coating formed in the fluoride-containing solution was nearly crack-free and displayed higher corrosion resistance than the coating formed in the solution without fluoride ion.