Corrosion of cyanide copper deposits on zinc diecastings in acid solutions

The corrosion potential and morphology of copper films deposited from a cyanide solution on zinc diecast were studied in acid solutions similar to those employed in industry for the deposition of a second copper layer. Open circuit potential measurements and gravimetric methods were employed to determine the influence of the copper electrodeposition variables on the corrosion potential. The influence of variables such as the presence or absence of additives, the current density and the copper or cyanide concentrations were studied. The corrosion potential decreased with increasing copper film thickness. Less protection was obtained when a thin copper layer was electrodeposited from a solution without additives. Higher protection for the same thickness was obtained from a solution with high cyanide content. This result is related to the strong interaction between cyanides and the metal surface during the electrodeposition. A smooth surface structure was observed by SEM under these conditions.