Novel Green and Ecofriendly Route for Fabricating a Robust Corrosion Protection Coating on AZ91D Magnesium Alloy

Mg is the lightest structural metal on earth; hence, applications of its alloys have attracted attention from researchers. However, these alloys have poor corrosion resistance, which impedes their use in practice. Many researchers have investigated protective coatings for Mg alloys, but current methods consume much energy, use hazardous substances, or are complex (such as anodizing and micro-arc oxidation). This paper proposes a novel method of creating a durable and protective coating on Mg alloy substrates. The AZ91D Mg alloy was selected for investigation, and a Mn-V-P conversion coating treatment in which voltage of only 5 V was applied for 1 min to enhance the alloy’s corrosion resistance. A compact, single-layer film with uniform thickness was created; the average thickness was 1750 nm. The corrosion resistance of alloys treated with the method and through anodizing treatment was compared. For the novel coating, the corroded area fraction after a 168-h salt spray test was less than 5%, superior to that for the coating produced through anodizing treatment. The feasibility and potential applications of the novel process are discussed.