The phase transformation of Al9(Mn, Ni)2 eutectic phase in an Al-4Ni-2Mn alloy during heat treatment

The phase transformation of Al9(Mn, Ni)2 eutectic phase has been observed in the Al-4Ni-2Mn alloy during heat treatment at 350 °C, 400 °C, 450 °C, 500 °C and 550 °C for different times, and investigated by scanning electron microscopy and transmission electron microscopy. It has been found, for the first time, that fibrous Al9(Mn, Ni)2 eutectic phase can transform into a ternary hexagonal κ-phase (κ-Al14.4Cr3.4Nil.1-type, hP227, P63/m) during the heat treatment, and the lattice parameters of Al-Ni-Mn κ-phase have been determined to be a = 1.799 nm, c = 1.295 nm, by measuring the selected area electron diffraction patterns. Furthermore, the experimental results also show that Al-Ni-Mn κ-phase prefers to nucleate at the interface between Al matrix and Al9(Mn, Ni)2 eutectic phase and grows into the parent phase, eventually, resulting in the breakup of the eutectic fiber at the nucleation sites.