Electroless Deposition Of Ni-w-p Coating On Az91d Magnesium Alloy

With AZ91D magnesium alloy is being increasingly wider range of applications, preparation of electroless Ni-W-P plating with high-hardness, good wear performance and excellent corrosion resisting properties have become hot research topic. In the article, the morphology, microstructure and components of the Ni-W-P plating were characterized by SEM, XRD and EDS. Potentiodynamic polarization curves and EIS were used to characterize the electrochemical properties. Microhardness and the friction and wear tests were adopted to characterize mechanical properties.A one-step pickling-activation process was proposed as an environmental friendly pretreatment method before electroless on magnesium alloys. The Ni-W-P coating is a medium phosphorous coating, and it is a mixture of amorphous and crystal. The Ni-W-P coating contributed to increase the hardness and corrosion-resistance of AZ91D magnesium alloy.The effect of low temperature heat treatment on characteristic of electroless Ni-W-P alloy deposits on AZ91D is studies. The microstructure of the coating had no changed on the heat treatment. But heat treatment contributed to increase the hardness and wear resistance of electroless Ni-W-P coating. The coating heat-treated had the maximum hardness and wear resistance at about 150℃. With anneal temperatures increasing, corrosion resistance increased firstly and decreased then. When the temperature reached 200℃, the maximal corrosion resistance was obtained.The Ni-W-P coating was repeated electroless deposited on AZ91D magnesium alloy. The coating has uniform composition with medium phosphorous content, and it is also a mixture of amorphous and crystal. Compared with the coating deposited directly, it has higher hardness, wear resistance and corrosion-resistance. The repeated electroless deposion, which is the best technique in the article, could acquire a Ni-W-P coating of high performance on AZ91D magnesium alloy.A Ni-W-P coating was successfully deposited on the stannate chemical conversion coating pre-applied to AZ91D alloy. A chemical conversion treatment and an electroless Ni-W-P plating were applied to AZ91D alloy to improve its corrosion resistance and mechanical properties.