Effects of grain size and Al-Mn phase on the corrosion performance of hot-rolled AZ31 magnesium alloy

In this paper, the effects of multiple hot rolling on the microstructure and corrosion resistance were studied in detail, and the mechanism of structural evolution on corrosion resistance was explored for hot rolled AZ31 alloy. The multiple hot rolling can effectively refine the grain, thus improving the corrosion resistance of AZ31 alloy. The rolling process can break and refine the bulk Al-Mn phase to granular Al-Mn phase in AZ31 alloy. Employing quasi-in-situ scanning electron microscopy, it has been observed that the granular Al-Mn phase shows a notably decreased propensity to accelerate the corrosion of the proximal α-Mg matrix. Employing quasi-in-situ scanning electron microscopy, it was observed that the granular Al-Mn phase exhibits a significantly reduced tendency to accelerate the corrosion of the proximal α-Mg matrix. This observation is attributed to the reduced size of the Al-Mn phase, which effectively minimizes the potential difference with the matrix. Consequently, the cathodic effect of the Al-Mn phase in galvanic corrosion is diminished, resulting in a lower overall corrosion rate.