Effects of low temperature aging on microstructure and corrosion behavior of Mg-6.5Gd-0.9Y-0.5Zr alloy

This paper investigates the effects of aging at 175 °C on microstructure and corrosion behavior of the Mg-6.5Gd-0.9Y-0.5Zr (wt.%) alloy. After aging treatment, β′ precipitates are formed within grains and at grain boundaries in the alloy except for the original Zr nucleus, Mg 5 (Gd,Y), and Mg 3 Y 3 Gd 2 second phase particles. Both immersion weight loss testing and electrochemical measurement in 3.5 wt.% NaCl shows that the corrosion resistance of the alloy increases at first and then decrease with the prolonged aging time. The alloy in the peak aging state demonstrates the highest corrosion resistance, with P w of 0.443 mm/y and I corr of 6.79 μA/cm². The aging treatment consumes the high density of dislocations in the as-extruded alloy, resulting in the enhanced localized corrosion resistance. The high corrosion resistance of alloys in the peakaging state can be primarily attributed to the protective effect of the β′ precipitates, which are distributed in a reticulated manner within grains and continuously at the grain boundaries. Additionally, the formation of a dense film of corrosion products contributes to this resistance.