Effect of heat-treatment on corrosion behavior of Mg-4Gd-2Nd alloy

Understanding the corrosion behavior of Mg alloys in the Cl− environments is crucial to preventing catastrophic accidents in their facilities due to their poor corrosion. The microstructures and corrosion behaviors of the Mg-4Gd-2Nd alloy under different heat-treatment conditions were investigated. The content of Mg41Nd5 in the alloy decreased significantly with increasing heat-treatment temperature. It was found that the formation of solid solution atomic oxides separates the lamellar Mg(OH)2 during the corrosion process of Mg alloys. With the increase of solid solution atomic oxides, lamellar Mg(OH)2 is no longer clustered and laid flat on the alloy surface. The loose Mg(OH)2 corrosion product film is eroded by Cl− and converted to the rod-like Mg2Cl(OH)3·4H2O, which lead to the detachment of the loose lamellar Mg(OH)2 in pieces. Furthermore, the corrosion products of the as-extruded alloy fall off in large blocks, whereas the corrosion products of the heat-treated alloys fall off in small pieces. Therefore, 540 °C-treated specimen exhibits best corrosion resistance.