Effect of NaCl Concentration on the Galvanic Corrosion Behavior of a Magnesium AZX611/Aluminum A6N01 Alloy Joint
Isao Nakatsugawa, Yasumasa Chino
Abstract
The time variation of galvanic corrosion that occurred in an AZX611 magnesium/A6N01 aluminum alloy in differently concentrated NaCl solutions was evaluated by galvanic potential/current measurements and the Scanning Vibrating Electrode Technique (SVET). The weight loss and surface profile of alloy samples after the test were measured to quantify the degree of galvanic corrosion. The galvanic current showed a maximum at the initial stage and then decreased with time. Higher concentrations of NaCl resulted in higher currents, and the decay proceeded at a slower rate. The weight loss measurement revealed that galvanic corrosion damaged not only AZX611 but also A6N01 due to the surface alkalization caused by the cathode reaction. SVET detected numerous local anodes on the AZX611 surface, which gradually disappeared and were replaced with passive areas. As the NaCl concentration increased, local anodes appeared at the joint, which agrees with the results of previous studies. For the A6N01 counterpart, the entire surface was corroded regardless of NaCl concentration. The analysis of the surface profile supported the SVET results. It was concluded that the galvanic corrosion of the AZX611/A6N01 joint was controlled by the depassivation behavior of the AZX611 anode, in which the NaCl concentration was critical.