Precipitation and recrystallization in two Al-4.5% Mg-Mn alloys

A study was made of the correlation between the microstructure of Al-Mg with different quantities of the element Mn in the annealing treatment after different amounts of cold working. The results show that the amount of cold working, the annealing temperature, and the content of Mn element in the Al-4.5% Mg-Mn alloys all affect primary recrystallization. From TEM, it can be seen that dispersoid particles of MnAl₄ were precipitated on the intradendrites after homogenization. These dispersoid particles can promote recrystallization by providing a recrystallization nucleation site. In addition, they also have the effect of restricting the growth of recrystallized grains, preventing them from becoming too coarse. However, if the alloys are subjected to protracted annealing at high temperature, the grain will become abnormally coarse. It was also found that the recrystallization rate of these alloys matches the Arrhenius-type law. The activation energy of recrystallization decreases as the quantity of the element Mn and the amount of cold working increase.