Effects of Heat Treatments on Corrosion Behavior of Mg AT72 Alloy

Abstract

The effects of heat treatments, including T4, T5, T6 treatments, on corrosion behaviors of Mg-7Al-2Sn (AT72) alloy processed by high vacuum die casting have been investigated. The optical microscope, scanning electron microscope observations were used to analyze the microstructures, especially the distribution of second phase, phase contents and grain size. The hydrogen evolution tests, electrochemical methods including open circuit potential curves and polarization curves were used to describe the corrosion properties as well. The results indicated that different heat treatments had influence on microstructures, especially distribution of second phase, phase contents and grain sizes. The existence of second phase had a relationship with corrosion properties, in which the as-cast samples showed low corrosion rate in hydrogen evolution tests while the heat treatment methods had little impact on improving corrosion resistance. The electrochemical analyses also agreed with this observation. Based on these results, the optimized heat treatment method for corrosion resistant AT72 magnesium alloy has been established.