The relation between microstructure and corrosion behavior of Mg-Y-RE-Zr alloys

Corrosion performance of sand cast Mg-Y-RE-Zr alloy after different heat-treatments was investigated in 3.5% NaCl solution saturated with Mg(OH)(2) (pH 10.5) using potentio-dynamic polarization and Auger electron spectroscopy. Microstructure analyses have been carried out on the Mg-Y-RE-Zr alloy after different heat-treatments. It was found that the central zirconium-rich areas within the grains of the alloy were more corrosion resistant than the outer zirconium-depleted areas of the grains. Based on the analyses of the corrosion process, polarization behavior and the microstructure of the alloy, it is concluded that zirconium acts in a number of ways to improve corrosion resistance. Our main results show that when zirconium is added to refine the grain size, the corrosion resistance of the alloy is significantly improved. The microstructure is controlled by different heat-treatments. Due to different aging time two different precipitates: were one located in grain center and the other distributed randomly. Grain centers, rich of zirconium, exhibit a better corrosion resistance than the zirconium-depleted edge areas of the grains. The corrosion rate of the Mg-Y-RE-Zr alloys after 3 h aging in 250 degrees C, to comparison the others aging times, decreasing by more than 100%. (c) 2006 Elsevier B.V. All rights reserved.