Age hardening reaction of the Al0.3CrFe1.5MnNi0.5 high entropy alloy

In this study, an Al0.3CrFe1.5MnNi0.5 high entropy alloy (HEA) was synthesized using a well-developed arc-melting and casting method. The as-cast alloy ingot was heat treated for 8 h at 650–750 °C and then quenched in water to investigate the effects of age treatment on the microstructure and microhardness of the alloy. The microstructure of the as-cast Al0.3CrFe1.5MnNi0.5 alloy consisted of the interdendritic rich-Ni FCC phase, rich-Cr BCC phase dendrite matrix, and a small fraction of cross-like rich-Ni FCC phase (β-FCC) within the majority dendritic structure. After aging at 650 °C, a cross-like FCC phase (β-FCC) with dendritic matrix disappeared, and both AlNi phase and Cr5Fe6Mn8 phase precipitated within the matrix dendrites. The interdendritic β1 FCC phases decomposed into matrix structures and transformed into the second-phase (β2 FCC) during aging at 750 °C. In addition, the precipitation of AlNi phase in the matrix dendrites became larger and globular shape inside the grain matrix. These precipitation phases in the grain matrix are the main age hardening mechanism.