Galvanostatic pulse plating of Cu-Al alloy in a room-temperature chloroaluminate molten salt - Rotating ring-disk electrode studies

The galvanostatic plating of Cu-Al alloy was examined at a platinum electro de in solutions of Cu+ in the 60.0-40.0 mol % aluminum chloride-1-ethyl-3-m ethylimidazolium chloride room-temperature molten salt at 28 degreesC using periodic-current plating techniques. The plating techniques that were inve stigated include pulse current, superimposed-pulse current, and reverse-pul se current. The composition of the electrodeposited alloy was determined by using rotating ring-disk anodic linear sweep voltammetry. The electrodepos ition of Cu-Al is complicated by the instability of the alloy in solutions containing Cu+. If alloy electrodeposits are removed from cathodic protecti on while immersed in the plating bath, a condition that occurs during the p ulse plating "off- time,'' t(off), Cu+ in the plating solution oxidizes Al from the electrodeposits. The rate of this displacement reaction is greates t for small values of t(off) but decreases as t(off) becomes longer, sugges ting that a copper-rich layer forms on the electrodeposits that blocks the displacement reaction. The displacement reaction can be minimized by loweri ng the Cu+ concentration at the electrode surface through the application o f a superimposed current during t(off), whose magnitude is comparable to th at of the limiting current for Cu+. (C) 2001 The Electrochemical Society. [ DOI: 10.1149/1.1366624] All rights reserved.