Fabrication of phosphate conversion coatings on rolled AZ31 magnesium alloy: Variation of corrosion resistance on different planes induced by the crystallographic texture

In this work, the microstructure and corrosion resistance of phosphate conversion coatings on the cross-sectional surface (CS), the rolled surface (RS) and the slanted surface (SS) of rolled AZ31 magnesium alloy were compared. Results demonstrate that most grains on the rolled surface (RS) conform (0001) orientation, which renders a lowest electrochemical reactivity; while the cross-sectional surface (CS) and the slanted surface (SS) exhibited a preferential orientation of ( 01 1 ‾ 0 ) and ( 1 ‾ 2 1 ‾ 0 ) , which renders a higher electrochemical reactivity. The variation of electrochemical reactivity affects the nucleation rate of crystals, thus altering the compactness and corrosion resistance of phosphate conversion coating on different surfaces. The conversion coating on the RS exhibits the worst corrosion resistance. • Different electrochemical reactivity was observed on the rolled AZ31 Mg alloy. • The better coating corrosion resistance is attributed to the higher electrochemical reactivity. • The enhanced coating corrosion resistance is related to the faster crystal nucleation kinetics. • The electrochemical reactivity alters the supersaturation degree.