Corrosion of cyanide copper deposits on zinc diecastings in acid solutions

The corrosion potential and morphology of copper films deposited from a cya nide solution on zinc diecast were studied in acid solutions similar to tho se employed in industry for the deposition of a second copper layer. Open c ircuit potential measurements and gravimetric methods were employed to dete rmine the influence of the copper electrodeposition variables on the corros ion potential. The influence of variables such as the presence or absence o f additives, the current density and the copper or cyanide concentrations w ere studied. The corrosion potential decreased with increasing copper film thickness. Less protection was obtained when a thin copper layer was electr odeposited from a solution without additives. Higher protection for the sam e thickness was obtained from a solution with high cyanide content. This re sult is related to the strong interaction between cyanides and the metal su rface during the electrodeposition. A smooth surface structure was observed by SEM under these conditions.