Effect of Surface Substrate Roughness and of Chelating Agent on the Microstructure and Mechanical Properties of Electroless Processed Brass Coatings

Brass coatings were deposited by electroless process on zamak-5 alloy substrates with various degrees of polishing and different concentrations of chelating agent in the chemical baths, in which the Cu complexing agent was varied in a wide range of compositions. The effect of Rochelle salt content as well as the substrate roughness on the microstructure and mechanical properties of the prepared coatings was addressed. A two-layer structure is formed during the deposition process having stoichiometric composition corresponding to CuZn and Cu5Zn8 for the top and bottom layer, respectively, and also CuZn5 was detected. The CuZn stoichiometric top layer showed invariably higher hardness. Polishing of the substrate leads to coatings with coarse-grained microstructure and higher surface hardness. It is found that both the chelating agent and the substrate roughness influence the microstructure and mechanical properties of the coatings, and higher chelating agent concentrations and smoother substrates produce higher densities and therefore better mechanical properties.