A comparative study on the corrosion behaviour of Al, Ti, Zr and Hf metallic coatings deposited on AZ91D magnesium alloys

This paper focuses on the deposition of anti-corrosion, conductive coatings for Mg alloys used in electronics and aerospace industries. Metallic Al, Ti, Zr and Hf coatings were fabricated on an AZ91D Mg alloy surface via magnetron sputtering. Electrochemical system and salt spray tests were performed to investigate the corrosion resistance and the mechanism of corrosion failure of coated samples. The Hf-coated Mg alloy exhibited an extremely low corrosion current density of 0.825 μA/cm2 and a high protective efficiency of 99.49% during the electrochemical test. More importantly, the Hf coating provided superior protection for the Mg alloy against corrosion during the 24 h salt spray test. However, the Al-, Ti- and Zr-coated alloys exhibit poor performances in the above measurements. The low difference in potentials, the excellent corrosion resistance and the good adhesion to the substrate are considered probable causes for the anti-corrosion performance of the Hf coating.