A protocol for fast electroless Ni-P on Al alloy at medium-low temperature accelerated by hierarchically structured Cu immersion layer

Electroless Ni-P coating is helpful to improve the corrosion resistance and mechanical properties of the Al alloys. However, the electroless Ni-P plating is usually operated at higher temperature (above 80 °C, even up to 90 °C) in order to achieve appropriate deposition rate. Herein it is demonstrated that a novel Cu immersion layer on Al alloy with a hierarchical structure can significantly accelerate the electroless Ni-P process in a wide range of temperature. The hierarchically structured Cu layer is deposited on Al alloy through galvanic replacement deposition from an environment-friendly deep eutectic solvent comprising choline chloride and ethylene glycol. The hierarchical structure of Cu immersion layer strongly affects the nucleation and growth of Ni-P, which is beneficial for enhancing the deposition rate of electroless process. This protocol might be of interest in the fast fabrication of electroless Ni-P deposition on Al alloys at medium and low temperature (50 °C ~ 70 °C).