Influence of surface pretreatment on phosphate conversion coating on AZ91 Mg alloy
Chunyan Zhang (Harbin Engineering University, Chinese Academy of Sciences)
Bin Liu (Harbin Engineering University)
Baoxing Yu (Chinese Academy of Sciences)
Xiaopeng Lu (Northeastern University China)
Yong Wei (Harbin Engineering University)
Tao Zhang (Chinese Academy of Sciences, Harbin Engineering University, Northeastern University China)
J. M.C. Mol (TU Delft - (OLD) MSE-6)
Fuhui Wang (Northeastern University China)
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Abstract
Surface pretreatment is generally applied before application of protective coatings on Mg alloys, which influences surface microstructure and electrochemical activity of the substrate and has an effect on the coating properties. The effect of various pretreatment processes (sand-blasting, grinding and polishing) on the microstructure and corrosion protection performance of phosphate conversion coating (PCC) on AZ91D Mg alloy was investigated in the present study. Sand-blasting cleaning significantly increases the surface roughness and electrochemical activity of the substrate, leading to formation of a porous PCC with inferior corrosion protection performance. In the case of ground/polished Mg alloy, the uniformity and corrosion resistance of the resultant conversion coating are mainly related to the surface roughness. Relatively low surface roughness of the substrate facilitates formation of a corrosion protective PCC.