Corrosion of Mg Alloy AM60B Micro-Alloyed with As

Abstract.The effect of micro-alloying AM60B (Mg-6Al-0.3Mn) with As (well-known cathodic hydrogen gas (H2) evolution poison) on the reducing corrosion in 3.5 wt.% NaCl (aq) was determined. Custom permanent mold casting AM60B material, with and without, 0.23 wt.% micro-alloyed As was made for this purpose. Microstructure characterization was carried out using light optical microscopy and scanning electron microscopy with associated X-ray energy-dispersive spectroscopy. Corrosion rates were measured using mass loss and volumetric hydrogen gas evolution measurements. Potentiodynamic polarization measurements were made to reveal the global anode and cathode kinetics. Micro-alloying with As is somewhat beneficial in reducing corrosion, but not to the extent reported for unalloyed Mg. More importantly, corrosion involves toxic arsine gas (AsH3) evolution, in addition to H2, consistent with thermodynamic predictions. Alternative micro-alloying routes are proposed for improved corrosion control via micro-alloying with non-toxic cathode poisons.