Phase transformations in mechanically milled and annealed single-phase β-Al3Mg2

Mechanical deformation drastically affects both microstructure and thermal stability of polycrystalline β-Al3Mg2. Upon milling, the β-Al3Mg2 phase transforms into a nanoscale supersaturated Al(Mg) solid solution with 40at.% Mg. Upon heating, the milled powders display a complex thermal behavior characterized by four distinct exothermic events. At low temperatures, an increasing amount of Mg is rejected from the solid solution with increasing temperature. At higher temperatures, the β′-phase, a hexagonal phase with composition Al3Mg2, is formed and no traces of the solid solution can be detected, indicating that the solid solution is metastable and transforms into more stable phase(s). Finally, the subsequent exothermic events reveal the formation and growth of the β-Al3Mg2 phase.