Electroless and electrolytic deposition of Co–SiC composite coatings on aluminum

Hydrometallurgical methods for production of Co–SiC composite coatings on aluminum were developed. The following consecutive stages were proposed: zincating of aluminum substrate in strong alkaline solutions (cementation, compact deposition, double dip), electroless cobalt deposition in an alkaline solution and, finally, electroless deposition or electrodeposition of the composites. All stages and appropriate reductant selection were essential to achieve good adherence of the multilayered system to the aluminum surface. It was found that double zincate treatment of the substrate and subsequent electroless deposition of cobalt layer (for 30 min, in the presence of 0.3 M maleic acid as a bath stabilizer) are essential steps to achieve good adherence of electroless or electrodeposited composites of high SiC contents (25–46 wt%). Microscopic observations showed uniform composition and thickness of the individual layers over the cross-section of the samples. Microhardness of deposits was also determined: it increased from 35 HV for pure substrate to 604 HV for Al/Zn/Coel/Co–SiCel or 312 HV forAl/Zn/Coel/Co–SiCed systems.