Mechanical, electrochemical corrosion, and high-temperature oxidation properties of stir-cast and heat-treated AZ80 magnesium alloy

Abstract

This study aims to produce a stir-cast AZ80 magnesium alloy and to correlate the phases and microstructure of the as-cast, T4, and T6 conditions with the alloy's mechanical, corrosion, and oxidation properties. Microstructure was analysed using Field Emission Scanning Electron Microscopy (FE-SEM) with Energy Dispersive Spectroscopy (EDS), Electron Backscatter Diffraction (EBSD), and High-Resolution Transmission Electron Microscopy (HRTEM), and X-ray diffraction (XRD) technique was employed to examine at the alloy’s phases. A Vickers microhardness, tensile, and impact test specimens were meticulously prepared according to ASTM specifications. The electrochemical corrosion was tested in 0.6 M NaCl and 0.05 H2SO4, simulating the salty seawater and low-sulphur air environments. Based on the eutectic temperature of the Mg-Al alloy system, which is 437 ℃, the high-temperature oxidation test was carried out at 400 ℃, 410 ℃, and 420 ℃. Microstructural study confirms that both T4 and T6 alloys undergo grain coarsening with a grain size of 72.64 µm, and the orientation of the grains shifted from the pyramidal plane (2−1-10) to the basal plane (0001). The TEM investigation helps pinpoint the GP zone's genesis in T4 heat-treated AZ80. T4 AZ80 has a maximum ultimate tensile strength of 306 MPa and a ductility of 29.77% because of the dispersion-strengthening effect. The T6 AZ80, on the other hand, has a minimum corrosion rate of 0.158 mm/year in NaCl solution and an oxidation rate constant of 4.19 mg2.cm−4h−1 at 420 ⁰C. Notably, the T6 AZ80 shows significant peaks of Mg2Al3, and the as-cast shows more peaks of Mg17Al12. Magnesium alloy AZ80 is significantly affected by intermetallic phases like Mg17Al12 and Mg2Al3. The Mg2Al3 phase shows the latter tendency to resist corrosion and oxidation.