Multilayer Ni‐P Coating for Improving the Corrosion Resistance of AZ91D Magnesium Alloy

The purpose of this paper is to provide a high corrosion resistance multilayer coating on AZ91D magnesium alloy. The multilayer coating having a thickness of about 45 μm and consisting of different Ni‐P alloy layer was prepared by electroless deposition. The composition of the multilayer coating from substrate to surface was designed as the protective layer, a Ni‐P layer with high phosphorus content and a Ni‐P layer with low phosphorus content, respectively. The so‐called protective layer was a direct electroless plating Ni‐P deposits with the thickness of about 10 μm. The electrochemical behavior and the corrosion resistance of this multilayer coating were evaluated by the electrochemical measurement and the acid immersion test, respectively. Being different from the other Ni‐P alloys coatings on the magnesium alloy, this multilayer coating could provide the electrochemical protection for the substrate.