Electroless Co–P coating was successfully applied on AZ31 magnesium alloy through environmentally friendly cerium–lanthanum–permanganate conversion coating treatment. It is found that application of the conversion coating activates the electroless Co–P plating. Electroless nucleation centres were first formed around the conversion coating pores due to replacement reaction between the cobalt ions and the alloying elements, and then were grown to form cobalt clusters. Low phosphorous, crystalline and compact electroless coating with no obvious pores or cracks in the coating/substrate interface was obtained. The results of open circuit potential and electrochemical impedance spectroscopy measurements showed that the corrosion resistance of the AZ31 alloy was significantly increased by electroless Co–P plating.
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