Corrosion Behavior of AZ91D Magnesium Alloy with a Calcium–Phosphate–Vanadium Composite Conversion Coating

A novel self-healing calcium–phosphate–vanadium (Ca–P–V) composite coating on Mg alloy was successfully fabricated through a chemical conversion method. The effects of the vanadium concentration on the anticorrosion property of the substrate were also tested. The Ca–P–V coating with the main composition of CaHPO4, Ca3(PO4)2, and Mg3(PO4)2, with some hydroxides of V(V) dispersed into it has a similar morphology to the single vanadium coating. The corrosion behaviour of the Ca–P–V coating was studied through the electrochemical tests and the scratch immersion test in 3.5 wt % NaCl solution. The results showed that the Ca–P–V coated samples not only exhibit good corrosion resistance property, but also show self-healing ability. The ions of Ca, P, and V released from the coating can migrate in the corrosion solution and form a new compound layer on the damaged zone.