Environmental Electroless Nickel Plating Technology on Magnesium Alloy in Solution with NiSO_4 as Main Salt

Using H3PO4+(NH4)6Mo7O24·4H2O as pickling solution and NiSO4·6H2O as main salt,the environmental direct electroless Ni-P plating technology on AZ91D magnesium alloy was investigated.The optimal contents of main compositions in electroless Ni-P plating bath were determined by orthogonal test.The surface and cross-section morphology of the electroless Ni-P coating were observed by using SEM.The structure of the coating was analyzed by X-ray difraction.The results showed that the electroless nickel deposits on magnesium alloys under the optimal technological conditions were amorphous,and compact without obvious defects.The micro-hardness of Ni-P coatings was 546 HV and the deposition rate was about 26 μm/h.The corrosion rate of the Ni-P coating in 3.5% NaCl solution for 14 h was only 0.76 μm/h.