Technology for Direct Electroless Nickel Plating of AZ91 Magnesium Alloy and Performance of the Nickel Coating

The technology for direct electroless nickel plating of AZ91 Mg alloy was optimized, and the compactness,hardness,corrosion resistance and adhesion to substrate of the electroless Ni coating were determined. It was found that the optimized Ni electroless plating bath consisted of 5 g/L Ni(CH_3COO)_2,12 mL/L 40%HF,5 g/L C_6H_8O_7 ? H_2O,30 g/L 25%NH,? H_2O,20 g/L Na_2HPO_4·H_2O and 1 mg/L thiourea,while the optimal electroless plating parameters were suggested as pH value of 6.5,temperature of 95℃and time of 1.5 h.Resultant electroless Ni coating was uniform and compact and well bonded with Mg alloy substrate.In the meantime,the Ni coating obtained under the optimized electroless plating conditions had a hardness as high as 146 HV and was free of peeling under 300℃.