Effects of Hard Surface Grinding and Activation on Electroless-Nickel Plating on Cast Aluminium Alloy Substrates

This work examined effects of hard surface polishing grits and activation on electroless-nickel (EN) plating on cast aluminium alloy substrates in sodium hypophosphite baths. As-received aluminium alloy sample sourced from automobile hydraulic brake master cylinder piston was melted in electric furnace and sand cast into rod. The cast samples were polished using different grits (60？μm–1200？μm) before plating. The effects on adhesion, appearance, and quantity of EN deposits on substrates were studied. Observation shows that the quantity of EN deposit is partly dependent on the alloy type and roughness of the surface of the substrates, whereas the adhesion and brightness are not solely controlled by the degree of surface polishing. The best yield in terms of adhesion and appearance was obtained from the activation in zincate and palladium chloride solutions. Higher plating rates (g/mm2/min) of , , and were obtained from chromate, zincate, and chloride than , , and as obtained from HCl etched, NaOH, and H2O activated surfaces, respectively. 1. Introduction Al alloys are widely used in engineering structures and components where light weight or corrosion resistance is required [1] such as automotive engines. Aluminium-magnesium alloys are found useful in automotive engine cylinder, master brake, and clutch cylinder and so on, but they are subject to wear and corrosion. Ajibola and Jimoh [2] and Ajibola et al. [3] had studied the quality, while Ajibola et al. [4] studied the wear behaviour of Al alloys used in making brake master cylinder pistons used hydraulic brake fluid. The studies were performed to assess the metallurgical properties and wear rates of pistons with the view to improving on the wear resistance and corrosion resistance of the Al alloy substrates in brake fluid. The studies [4, 5] also suggested the application of surface treatment and overlay of durable metallic film as remedy to alleviating wear and corrosion of this useful machine part in brake oil. There are various methods of metal coating. These include processes like hot dipping, anodising, electroplating [6–8], electroless-plating [9–13], autocatalytic plating [13], cladding, Parkerizing, and galvanising. Plating has been done for hundreds of years, but it is also critical for modern technology. Plating is used for decoration, corrosion inhibition, to improve solderability, to increase hardness, to improve wear resistance, to reduce friction, to improve paint adhesion, and to alter conductivity, for radiation shielding, and for other purposes. Electroless-nickel (EN) plating is a