Electrochemical corrosion of stir cast and heat-treated magnesium alloy EV31A in different electrolytes: Analysis via X-ray photoelectron spectroscopy

Abstract

The study aims to determine the chemical state of elements in EV31A after electrochemically corroded in four different electrolytic solutions. EV31A, a magnesium alloy containing rare earth elements, was manufactured via stir-casting and heat-treated based on T4 and T6 conditions. Electrochemical corrosion of the as-cast, T4, and T6 EV31A were carried out in 0.6 M NaCl, 0.05 M H2SO4, 0.1 M HNO3, and 0.1 M HF solutions. In addition, the X-ray photoelectron spectroscopy (XPS) examination was performed on the corroded surface of EV31A. During the XPS analysis, the elements such as Magnesium (Mg), Neodymium (Nd), Gadolinium (Gd), Zinc (Zn), Zirconium (Zr), chlorine (Cl), sulphur (S), nitrite (N), fluorine (F), and oxygen (O) were studied, and only the peaks of Mg, O, Nd, and Gd were detected on the surface of corroded alloy. In all test settings, the corrosion resistance of the as-cast alloy is better than that of the heat-treated alloy. Even though the corrosion resistance of the as-cast alloy is high, its corrosion rate of EV31A in H2SO4 and HNO3 is very high. The corrosion resistance of as-cast EV31A in NaCl and HF mainly results from the formation of Nd2O3 and electronegative fluorine, respectively, as determined by XPS.