Galvanic deposition of Ni on Al alloy from a choline chloride based ionic liquid for electroless Ni-P pretreatment

A Ni layer on Al alloy was deposited by galvanic replacement reaction in an environmental friendly deep eutectic solvent (DES) comprising choline chloride (ChCl) and ethylene glycol (EG). Thermodynamic feasibility and kinetics of galvanic replacement reaction of Ni on Al alloy were studied by cyclic voltammetry, open circuit potential (OCP) and electrochemical noise (ECN) analysis. The characterization of Ni layer was investigated using scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis. Results showed that the Ni galvanic replacement on Al alloy was thermodynamically feasible and sustained in the ChCl-EG DES solution. The presence of the galvanic replacement Ni layer can serve as pretreatment layer for electroless Ni-P on Al alloy, resulting in obtaining a continuous and uniform Ni-P coating. The Ni-P coatings possessed typical spherical nodules structure and showed well corrosion resistance, which was similar to the result of Ni-P coatings on Al alloy with other pretreatments. The galvanic replacement Ni layer obtained from the deep eutectic solvent provided an alternative pretreatment method for electroless Ni-P coatings on Al alloy.