Influence of The KF Concentration on The Coating Process And Properties of Potentiostatic Deposited Fluoride Conversion Film on AZ31 Mg Alloy

Abstract

The dependence of coating process and properties of the fluoride conversion film on AZ31 Mg alloy on the concentration of deaerated KF solutions was studied by anodic potentiostatic deposition, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS). The results show that the film deposited in 0.05 M KF solution is a monolayer consisting of amorphous Mg(OH) 2 and MgF 2 , while amorphous Mg(OH) 2 and MgF 2 and crystallized KMgF 3 as a double layer formed in 0.1 M~0.5 M KF solutions. The composition of inner layer is same as that of the monolayer, while the outer layer is composed of Mg(OH) 2 and MgF 2 and KMgF 3 . Continually increasing KF concentration reduces the content of KMgF 3 in the outer layer, shortens the coating duration, and reduces the film thickness. The corrosion resistance of FCF coatings is closely correlated with the content of KMgF 3 and the film thickness.