Electro- and Electroless Deposition of Ni/SiC and Co/SiC Composite Coatings on Aluminum

Aluminum and its alloys characterize usually poor superficial properties. To improve hardness and wear resistance, aluminum base materials are covered by protective layers. Deposition of metallic coatings on aluminum is accompanied by some difficulties due to tenacious oxide layer present on the substrate surface. Hence, some additional stages are needed to assure good adhesion of the coating to the substrate. In many cases, electrodeposition and electroless methods are competitive for providing deposits with ceramic particles uniformly incorporated within the metal layer. The most extensive studies were carried out on deposition of Ni/SiC composites, but no attempts on Co/SiC coatings deposition on aluminum have been performed. Experiments presented were conducted to develop simply methods for deposition of Ni/SiC and Co/SiC composite coatings on aluminum substrate. The consecutive stages of the hydrometallurgical route were: zincating of aluminum in alkaline solutions, electroless nickel (cobalt) deposition and electrodeposition or electroless deposition of the composite coating. The influence of deposition time and composition of the baths on thickness and composition of the deposits was studied. Microstructure and microhardness of as-plated individual layers were also determined.