Traditional process of electroless Ni-P plating on AZ91D magnesium alloy was improved, and the poisonous substances of hydrofluoric acid and Cr^6＋ were not used. The mechanism of pretreatment and nickel initial deposition for new process was investigated. Meantime, the process of Ni-P-ZrO2 composite plating was developed, and the microstructure and properties of the composite coating were studied. The results show that the Ni-P coating prepared with new process is more compact and uniform, and the corrosion resistance is superior to that of traditional process Ni-P coating. The potentiodynamic polarization curves in 3.5 % NaCl solution indicate that the Ni-P-ZrO2 composite coating could provide adequate protection to magnesium alloy substrate. The wear mass loss of Ni-P coating is nearly twice more than that of Ni-P-ZrO2 coating, implying that the wear resistance of the composite coating is improved due to the co-deposition of ZrO2 nanometer particles.
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