Process for Electroless Ni-Co-P Plating of Magnesium Alloy and Properties of the Coating

Orthogonal tests were carried out to optimize the process for electroless plating of Ni-Co-P alloy coating on the surface of magnesium alloy, and several factors affecting the plating rate were discussed. Moreover, the properties and chemical composition of the ternary alloy coating were compared to that of electroless Ni-P coating based on measurement of hardness and scanning electron microscopic and energy dispersive spectrometric analyses. It was found that the introduction of Co2+ was beneficial to the electroless plating of the ternary alloy coating but leadsed to decrease in the hardness of the coating. The highest plating rate was recorded at a concentration of 30 g/L of complexing agent sodium citrate, while the introduction of a proper amount of coumarin contributed to increasing the plating rate and improving the brightness of the coating. Moreover, the ternary alloy coating showed better corrosion resistance and adhesion to substrate than the Ni-P binary alloy coating.