Nickel electroplating of 6061-T6 aluminum alloy using anodizing process as the pretreatment

Typically, aluminum and its alloys fail to be coated by the electroplating process due to the existence of an inherent oxide layer on the surface which reduces the adhesion between the coatings and the substrate. In this regard, suitable surface preparation is required before the electroplating process. In this study, the anodizing process is chosen as the surface pretreatment. For this purpose, the soft anodizing process was done in a 0.3 M oxalic acid electrolyte at 25 °C and 90 V for different duration. AAO dissolving process was performed to increase the diameter of the pores. Finally, electroplating of nickel was performed in a Watts bath at 40 °C, pH of 3, and different current densities. Three variable of anodizing and dissolving durations and electroplating current density were optimized by a response surface methodology to form a continuous layer of electroplated nickel on the surface. FE-SEM surface morphology, SEM cross-sectional observations, surface XRD characteristics and Daimler-Benz adhesion test were performed to characterize and evaluate the coatings. The optimization of the three variables led to a sequence process of a 9 min anodizing treatment, followed by a 100 min dissolving stage, then electroplating under a current density of 20 mA/cm2. The formation mechanism of the electroplated layer is thoroughly discussed.