On the role of Sc or Er micro-alloying in the microstructure evolution of Al-Mg alloy sheets during annealing

Abstract

Microstructure evolutions of a Sc-containing and an Er-containing Al-Mg alloy during annealing process were investigated comparatively. Microhardness of the Er-containing alloy decreases with the increase of annealing temperature and a dramatic decrease is observed between 300 °C and 400 °C. Electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) results show that the recrystallization process of the Er-containing alloy finishes rapidly between 350 °C and 400 °C, resulting in the formation of large recrystallized grains and the loss of sub-structure strengthening. In comparison, the Sc-containing alloy shows good thermal stability and the dramatic decrease of microhardness occurs between 450 °C and 550 °C. The Sc-containing alloy maintains sub-structures even after annealing at 400 °C for 1 h. The different recrystallization behavior of the two alloys is attributed to the fact that Al3(Scx, Zr1-x) dispersoids have higher thermodynamic stability than Al3(Erx, Zr1-x) dispersoids. Cold-rolled sheets of the two experimental alloys exhibit typical rolling texture, mainly consisting of Brass, Copper, and S orientations. Texture components of the two alloys dramatically change to random orientations once recrystallization completes. In-situ high-temperature XRD results reveal that dislocation density of the Sc-containing and the Er-containing cold-rolled sheets decreases rapidly with the increase of temperature. Sc or Er addition does not exert significant influence on the annihilation of dislocation at low-temperature annealing (below 250 °C).