Stabilizing the strengthening precipitates in aluminum-manganese alloys by the addition of tungsten

The Al-Mn-W system has considerable potential as a basis for lightweight aluminum alloys that are intended for use at temperatures approaching 350 °C (623 K). In this ternary system, aluminum, manganese, and tungsten co-precipitate to form the meta-stable Al12(Mn(1-x)Wx) phase, which is thermally stable and will not coarsen when held at elevated temperatures for extended periods of time. This enhanced thermal stability of the Al12(Mn(1-x)Wx) phase in comparison to the Al12Mn phase which forms in binary Al-Mn alloys is explained in terms of the Gibbs free energy of the two phases. It is shown that co-precipitating tungsten with aluminum and manganese lowers the Gibbs free energy of the precipitated phase and by so doing, it slows down its coarsening rate and enhances its thermal stability.