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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. [ABSTRACT FROM AUTHOR]

Electroless nickel-phosphorus plating is an important surface treatment method for copper due to its good corrosion resistance and nonmagnetic properties. However, a palladium activation procedure is needed owing to the inactiveness of copper to hypophosphite. Herein, nickel film, which could act as an activator, was deposited on copper through abnormal galvanic replacement deposition in the deep eutectic solvent containing nickel chloride in 10 min, which was 1/30 of the deposition time in other report (5 h). The open circuit potential tests proved that the practical potential of pure copper was obviously reduced to be lower than that of nickel in deep eutectic solvent, which made the deposition of nickel on copper through galvanic replacement reaction probable. It was remarkable that electroless nickel-phosphorus plating could be directly initiated by the as-prepared nickel film. The surface morphology, cross-sectional morphology, composition, and corrosion resistance of nickel-phosphorus coatings prepared on nickel and palladium films were characterized and compared. The results showed that the nickel-phosphorus coatings initiated by nickel and palladium films had similar morphology, composition, structure, and corrosion resistance. This result indicated that the nickel film prepared by galvanic replacement deposition possessed good activation ability to electroless nickel-phosphorus plating on copper, which was comparable to palladium film. [ABSTRACT FROM AUTHOR]

Electroless nickel–phosphorus (Ni–P) plating is a widely used surface treatment method due to its excellent corrosion and wear resistance properties. However, the inertness of copper to hypophosphite oxidation necessitates a palladium activation process for the preparation of Ni–P coating on copper. In this study, a convenient approach is presented for the deposition of a cobalt layer on copper using galvanic replacement, facilitated by the special complexing ability of iodide. The results demonstrated that the actual potential of copper could be adjusted to be lower than that of cobalt in a solution containing 8 mol L−1 NaI, enabling the deposition of a cobalt layer on copper in 15 min at 90 °C. Furthermore, the deposition rate of the cobalt layer was found to increase with the concentration of CoCl2 in the NaI solution. Importantly, the Ni–P coating obtained through cobalt layer activation from either acidic or alkaline plating solution exhibited morphology, structure, corrosion resistance, and tribological performance similar to the Ni–P coating obtained using the common palladium activation. The Ni–P coatings obtained through cobalt and palladium layer activation from alkaline plating solution had a larger thickness than the Ni–P coating obtained from acidic plating solution. Therefore, the cobalt layer prepared on copper through galvanic replacement may serve as a viable alternative to palladium for activating electroless Ni–P plating.Graphical abstract: Electroless nickel–phosphorus (Ni–P) plating is a widely used surface treatment method due to its excellent corrosion and wear resistance properties. However, the inertness of copper to hypophosphite oxidation necessitates a palladium activation process for the preparation of Ni–P coating on copper. In this study, a convenient approach is presented for the deposition of a cobalt layer on copper using galvanic replacement, facilitated by the special complexing ability of iodide. The results demonstrated that the actual potential of copper could be adjusted to be lower than that of cobalt in a solution containing 8 mol L−1 NaI, enabling the deposition of a cobalt layer on copper in 15 min at 90 °C. Furthermore, the deposition rate of the cobalt layer was found to increase with the concentration of CoCl2 in the NaI solution. Importantly, the Ni–P coating obtained through cobalt layer activation from either acidic or alkaline plating solution exhibited morphology, structure, corrosion resistance, and tribological performance similar to the Ni–P coating obtained using the common palladium activation. The Ni–P coatings obtained through cobalt and palladium layer activation from alkaline plating solution had a larger thickness than the Ni–P coating obtained from acidic plating solution. Therefore, the cobalt layer prepared on copper through galvanic replacement may serve as a viable alternative to palladium for activating electroless Ni–P plating. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ni was deposited on Cu by an iodide-induced unusual galvanic replacement method. • High iodide concentration was conducive to replacement deposition of Ni on Cu. • The Ni film could replace Pd and act as activator for electroless Ni-P plating. Galvanic replacement provides a convenient route to synthesize metallic films and nanostructures. However, metals commonly reduce more noble metal ions. In this work, nickel film was deposited on copper through an iodide-assisted galvanic replacement method. It was found copper had a lower electrode potential than nickel in high concentration of iodide solution, so nickel film could be obtained through the unusual galvanic replacement. The experimental results revealed increasing iodide concentration was conducive to the galvanic replacement rate between copper and nickel ions, and complete nickel film could be obtained in solution with 1200 g·L−1 sodium iodide in 10 min. The as-prepared nickel film showed good activation ability for electroless nickel-phosphorus plating, for the nickel-phosphorus coatings obtained on the nickel and traditional palladium films possessed similar morphology, structure and corrosion resistance. [ABSTRACT FROM AUTHOR]