Conversion coatings of Mg-alloy AZ91D using trihexyl（tetradecyl） phosphonium bis（trifluoromethanesulfonyl）amide ionic liquid

This work reveals the performance of a trihexyl（tetradecyl）phosphonium bis（trifluoromethanesulfonyl）amide （[P6,6,6,14][NTf2]） ionic liquid （IL） conversion coating upon AZ91D. Such conversion coatings represent a novel avenue for chromate replace- ment. An optimization of coating performance was pursued by careful alloy pretreatment to generate a surface on which the coating performs best, as the AZ91 substrate is distinctly different from pure or dilute Mg alloys. The results reveal that a functional conversion coating can be achieved, retarding anodic dissolution kinetics, causing a significant decrease in corrosion rate. The coating efficacy is closely tied to the pretreatment performed, which dictates both the microstructural and electro- chemical heterogeneity of the surface. The resulting coatings were found to contain MgxFx and phosphonium cation related components, the proportions of which were dependent on the pretreatment.