A study was carried out to examine copper immersion deposition on AZ91 magnesium alloy in a hydrofluoric acid-containing bath. The role of fluoride and the effect of bath temperature were investigated. The study was performed by measuring the ac impedance and open-circuit potentials in combination with X-ray photoelectron spectroscopy and scanning electron microscopy surface analysis. Results showed that the effect of both HF concentration and temperature on copper immersion deposition is significant, via affecting the surface film formation on the magnesium surface. A model for understanding the copper immersion deposition process is depicted based on surface characterization and the electrochemical measurements. (c) 2005 The Electrochemical Society. All rights reserved.