Stable and metastable phase equilibria in the Al-Mn system

The aim of the present investigation was resolution of certain obscure features of the Al-Mn phase diagram. The experimental approach was guided by assessment of the previous literature and modeling of the thermodynamics of the system. It has been shown that two phases of approximate stoichiometry “Al₄Mn” (λ and μ) are present in stable equilibrium, λ forming by a peritectoid reaction at 693 ± 2 °C. The liquidus and stable equilibrium invariant reactions as proposed by Goedecke and Koester have been verified. A map has been made of the successive nonequilibrium phase transformations of as-splat-quenched alloys. Finally, the thermodynamic calculation of the phase diagram allows interpretation of complex reaction sequences during cooling in terms of a catalogue of all the metastable invariant reactions involving (Al), Al₆Mn, λ, μ, ϕ, and Al₁₁Mn₄ phases.