Influence of heat treatment and microstructure on the corrosion of magnesium alloy Mg-10Gd-3Y-0.4Zr

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 alpha-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 A degrees 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.