Structural evolution of rapidly solidified Al–Mn and Al–Mn–Sr alloys

In the present paper, microstructure, phase composition and elevated temperature behaviour of two rapidly solidified (RS) Al–5.0 wt.% Mn and Al–4.6 wt.% Mn–2.1 wt.% Sr melt spun ribbons are described. The RS binary alloy was composed of supersaturated α-Al solid solution and finely dispersed spheroids of quasi-crystalline icosahedral I-Al6Mn phase. The Sr-addition led to a reduction of volume fraction of the I-Al6Mn phase. Manganese was more concentrated in stable tetragonal β-Al4Sr phase. DSC measurements revealed exothermal reactions between 400 and 500 °C which were more pronounced in the binary Al–Mn alloy. This proved a higher degree of metastability of the binary alloy. The solid state phase transformations included:1.Decomposition of the supersaturated α-Al solid solution.2.Polymorphous transformation of the quasi-crystalline icosahedral I-Al6Mn phase to a stable orthorhombic O-Al6Mn phase.The decomposition of the supersaturated solid solution produced finely dispersed O-Al6Mn precipitates which induced some hardening of both alloys after pre-annealing at 350 °C/5 h.