CORROSION BEHAVIOUR OF UNTREATED AND THERMALLY-TREATED AS21X Mg ALLOY IN SULPHATE AND CHLORIDE MEDIA

摘要

Weight losses, electrochemical techniques (potentiodynamic polarization curve and EIS measurements), optical and SEM microscope examinations were used to investigate the corrosion behaviour of AS21X Mg alloy in 0.1 N and 1N solutions of Na2SO4 or NaCl. AS21X showed a good corrosion resistance (superior to that of other conventional magnesium alloys) both in the sulphate and in the more aggressive chloride solutions. The formation of a passivating film was particularly evident in the concentrated sulphate solution. Chlorides, mainly at high concentrations, interfered with the formation or the maintenance of such a layer. A thermal treatment, carried out to improve the creep resistance at high temperatures, caused a decrease in the corrosion resistance by lowering the tendency to a stable passive behaviour of the base alloy. In this case, after a short time, a grain undermining effect took place.