Galvanic replacement deposited copper layer as an efficient activator to realize electroless Ni-P plating on aluminum

Electroless Ni-P plating is an important process to enhance the corrosion and wear resistance of aluminum. However, due to the presence of an oxide layer on aluminum substrate, achieving a reliable Ni-P coating necessitates complex processes such as double zincate treatment or palladium immersion pretreatment. This study demonstrates that the copper immersion layer on an aluminum substrate can initiate the electroless Ni-P plating process. The copper immersion layer is deposited on the aluminum substrate through a convenient galvanic replacement reaction using an alkaline aqueous solution of copper sulfate and ammonia. This copper immersion layer can form a galvanic cell with the aluminum substrate, thereby initiating electroless Ni-P plating, similar to initiate electroless Ni-P plating by contact activation. It is confirmed that activation ability of the copper immersion layer is comparable to that of a palladium immersion layer by comparing the morphology, structure, deposition kinetics, and performance of Ni-P coatings obtained on copper and palladium immersion layers.