Properties of Conversion Coating of Magnesium Alloys by a Phosphate-Permanganate Solution
A chromium-free conversion coating for AZ91D magnesium alloys has been obtained by using a phosphate-permanganate solution. Examinations have been carried out on the conversion coating for morphology, composition, adhesion force and corrosion resistance. Results show that the conversion coatings are relatively uniform and continuous, with thickness from 7µm to 10µm. They exhibit good adhesion to matrix and have some non-penetrate tiny holes on the surface. The main elements of the conversion coating of AZ91D alloy are Mg、O、P、K、Al、Mn. Results of corrosion resistance test indicate that the corrosion resistance of the conversion coating by phosphate-permanganate solution is in match to that of the conversion coating formed in a chromate solution, but for the corrosion resistance after painting, the former is better than the later.
W.Ke, E.H.Han, Y.F.Han, K.Kainer and A.A.Luo
S. S. Wu et al., "Properties of Conversion Coating of Magnesium Alloys by a Phosphate-Permanganate Solution", Materials Science Forum, Vols. 488-489, pp. 665-668, 2005