Sono-Immersion Deposition on Magnesium Alloy

Abstract

Coating is a viable way to improve the corrosion resistance of magnesium alloys for aerospace and automotive applications. This paper presents the acoustic effect on the copper immersion coating of AZ91 magnesium alloy. Electrochemical impedance spectroscopy and open-circuit potential measurements were conducted to characterize the copper immersion-coating processes. The surface morphology changes of the copper immersion coatings obtained with and without sonication were examined using scanning electron microscopy. All experimental results have clearly demonstrated a significant increase of surface coverage on magnesium alloy. Data analysis indicated that formation of a surface film on the uncoated magnesium area during immersion coating under nonsonicated condition restrained magnesium dissolution which, in turn, limited the deposition process. The application of sonication induced asymmetric cavitations at the interface and efficiently destroyed or prevented the formation of a surface film. As a result, the anodic reaction (magnesium dissolution) was maintained to provide a continuous driving force for cathodic copper reduction and deposition, hence increasing the surface coverage. (c) 2005 The Electrochemical Society. All rights reserved.