Static recrystallisation and corrosion behavior of a hot-rolled AZ31 magnesium alloy

The microstructure and texture of an AZ31 alloy were investigated after hot rolling at 350°C to achieve low, medium and high strain (i.e., 20%, 50% and 85% thickness reduction, respectively) and subsequent annealing at 350°C for 2, 10 and 60 min using electron backscatter diffraction. The effect of hot rolling and subsequent static recrystallisation on corrosion behavior in seawater was also evaluated using electrochemical tests. At low strain, the microstructure was characterised by the absence of twinning, mainly due to the prior deformation state of the as-received alloy. However, various modes of twinning were observed at medium strain. At high strain, the dynamic recrystallisation process resulted in a microstructure with a typical basal texture. The results demonstrate that twins are responsible for the deviation of {0002} basal poles from normal towards the transversal direction. Annealing at 350°C for up to 60 min led to normal grain growth in all the samples. In medium and highly strained samples, the deformation texture was retained, while the low strain sample underwent noticeable changes due to the absence of dynamic recrystallisation. A synergetic effect of grain refinement and texture weakening was responsible for the alloy's enhanced corrosion resistance.