Effect of copper content on the properties of electroless Ni-Cu-P coatings prepared on magnesium alloys

The Ni-Cu-P coatings were obtained by electroless plating method on ZK61M magnesium alloys. The effect of copper content on the properties of electroless Ni-Cu-P coatings on magnesium alloys was further studied. The coatings surface and cross-section morphologies were observed with scanning electron microscope. The crystal structure and corrosion resistance of Ni-Cu-P coatings were evaluated by X-ray diffractometer and electrochemical tests. The experimental results showed that the Ni-Cu-P coatings were uniform and compact, and the corrosion resistance of these coatings was superior to Ni-P coatings owing to the introduction of copper. The crystallinity and compactness of the Ni-Cu-P coatings gradually enhanced with the increasing of copper content in the coatings. The introduction of copper element in the Ni-Cu-P coatings contributes to the formation of passivation film. The Ni-Cu-P coatings with higher corrosion resistance were obtained from the solution with a higher CuSO4 concentration.