The corrosion of Mg alloy Mg-10Gd-3Y-0.4Zr, in the as-cast (F), solution treated (T4) and aged (T6) conditions, was investigated in 5% NaCl solution by immersion tests and potentiodynamic polarization measurements. The as-cast (F) condition had the highest corrosion rate due to micro-galvanic corrosion of the α-Mg matrix by the eutectic. Solution treatment led to the lowest corrosion rate, attributed to the absence of any second phase and a relatively compact protective surface film. Ageing at 250 °C increased the corrosion rate with increasing ageing time to 193 h attributed to increasing micro-galvanic corrosion acceleration of the Mg matrix by increasing amounts of the precipitates. Ageing for longer periods caused a decrease in the corrosion rate attributed to some barrier effect by a nearly continuous second-phase network. Electrochemical measurements did not give accurate evaluation of the corrosion rate in agreement with the immersion tests.
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This work was supported by Postdoctoral foundation of China (No. 20080430657), Program of Shanghai Subject Chief Scientist of China (No. 08XD14020) and National Basic Research Program of China (No. 2007CB613701). The authors would like to thank Dr. Yi-jian Lai of the Center of Analysis and Measurement of Shanghai Jiao Tong University for his help in observation of the corrosion products with Field Emission Scanning Electron Microscope (FE-SEM).
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