Supercritical-CO2 electroless nickel plating enhanced anti-corrosion properties of micro-arc oxidized AZ31 magnesium alloy

Abstract

Magnesium alloys which perform low density, high strength-to-weight ratio and excellent mechanical properties have received extensive attention especially in the weight-constrained components in aerospace and automotive industries. Nevertheless, magnesium alloys generally exhibit poor corrosion and wear resistance, which seriously limit their lifespan and developments. Regarding the aforementioned issues, we selected an AZ31 magnesium alloy as the controlled specimen, on which a designed multilayer structure was fabricated to be the surface protective coating. The multilayer coating consisted of an oxide layer prepared by micro-arc oxidation (MAO), a sputtered Ag intermedium layer and a Ni-based anti-corrosion coating deposited by supercritical CO 2 assisted electroless deposition (SC-EL-Ni). The Ag/MAO interlayer performed an excellent compatibility between the Ni coating and Mg substrate, leading to a good coating adhesion. Moreover, the as-prepared amorphous SC-EL-Ni layer exhibited a dense and uniform surface, which can effectively prevent the intergranular corrosion and galvanic corrosion. Therefore, the obtained SC-EL-Ni/Ag/MAO sample presented a much better corrosion resistance compared with the Mg alloy and the porous MAO-treated sample. • Surface properties of SC-EL-Ni/Ag/MAO coating have been systematically analyzed. • Sputtered Ag layer performed excellent compatibility between Ni and MAO coating. • Amorphous Ni film with dense and uniform surface was obtained. • SC-EL-Ni exhibited outstanding anti-corrosion property.