New Insight into Adherence of Ni-P Electroless Deposited Coatings on AA6061 Alloy through Al2O3 Ceramic

Abstract

The adhesion quality of Ni-P coatings on aluminum is important for mechanical and anticorrosion properties. In this study, the adhesion of Ni-P coatings on nanoporous Al2O3 ceramic (NAC) was evaluated by impact testing. NAC was fabricated on AA6061 alloy by anodizing in sulfuric acid. The deposition of Ni-P coating was carried out on NAC with and without zincate pretreatment. It was found that zincate activation of Al2O3 accelerates the formation of Ni-P coating. A cross-sectional analysis using energy-dispersive X-ray spectroscopy showed that the mechanical properties and impact resistance of the Ni-P coating are strongly related to the chemical composition in the vicinity of its interface with Al2O3. The course of the formation process of Ni-P coating and its mechanisms are also very important. Although the formation of Ni-P coating was slower without zincate treatment, its stronger adhesion to NAC led to superior impact resistance compared to zincate-treated Al2O3. Improved durability of items with Ni-P coatings can benefit many applications.