The corrosion behaviors of Mg–7Gd–5Y–1Nd–0.5Zr alloy under (NH₄)₂SO₄, NaCl and Ca(NO₃)₂ salts spray condition

Abstract

The corrosion behaviors of Mg–7Gd–5Y–1Nd–0.5Zr alloys after T5 treatment under (NH₄)₂SO₄, NaCl and Ca(NO₃)₂ salt spray condition were investigated by weight loss rates, residual mechanical properties, scanning electron microscope (SEM), X-ray Diffraction (XRD) and potentiodynamic polarization tests. The corrosion degree of Mg–7Gd–5Y–1Nd–0.5Zr alloys in Ca(NO₃)₂ salt spray was very shallow by corrosion morphology and the corrosion route was extended along the surface in texture-like shape, while the alloy in NaCl and (NH₄)₂SO₄ salt spray were major local corrosion and there were serious corrosion pits on the surface. The weight loss rates in (NH₄)₂SO₄, NaCl and Ca(NO₃)₂ salt spray was respectively 0.4147, 0.1618 and 0.0725 mg/(cm² d⁻¹). The results of residual mechanical properties indicated that the corrosion order in salts spray of Mg–7Gd–5Y–1Nd–0.5Zr alloys is NH₄SO₄ > NaCl > Ca(NO₃)₂, which was consistent with the results of potentiodynamic polarization tests. The type of the salts will play a vital role in the initiation of the corrosion of EW75 alloy when they are used in the atmosphere environments. Inorganic salts with the smaller PH value after dissolution will have a stronger impact on the corrosion of EW75 magnesium alloys.