The electrodeposition of Cu on zinc alloy diecast from a cyanide bath was studied using electrochemical techniques and scanning tunneling microscopy (STM) imaging. As the current density ii) is changed from 1 to 30 mA cm(-2), the root mean square roughness of the deposit (xi) first increases, reaching a maximum value at j = 10 mA cm(-2), and then decreases. This behavior is explained by the strong interference of the hydrogen evolution reaction at the highest current densities. The dynamic scaling theory applied to the STM images for the advanced stages of Cu electrodeposition obtained at j = 10 mA cm(-2) leads to a roughness exponent a = 0.80 and growth exponent beta > 0.5 consistent with an unstable interface evolution. The addition of sodium selenite promotes a leveling effect by hindering the growth of instabilities, leading to an interface evolution consistent with the predictions of thr Edwards-Wilkinson growth model.