Unraveling solid–liquid phase transition and microstructural coarsening of semi-solid Al0.8Co0.5Cr1.5CuFeNi HEA with dual globules for thixoforming application

Abstract

Multi-phase HEAs typically have potential of semi-solid processing due to wide semi-solid range. For thixoforming route of semi-solid processing (SSP), the semi-solid billet preparation by semi-solid isothermal heat treatment (SSIT) is one of the most important process steps. This work focuses on the microstructure evolution during SSIT of a semi-solid Al0.8Co0.5Cr1.5CuFeNi HEA with dual globules for thixoforming application. This semi-solid HEA contains BCC(B2), FCC globules and Cu-rich liquid film. Solidified liquid follows K-S, epitaxial orientation relationship withneighboringBCC(B2) and FCC globules. Solutionizing point for B2 phase is higher than roughly 1175 °C, and complete disordering of BCC(B2) globule occurs at 1225 °C. While, FCC globule persists stable disordered solid solution. Solid-liquid phase transition of globules provides liquid film proliferation. CALPHAD simulation on the “hypothetical” alloy system corresponding to component constitution of individual globule successfully forecasted solid–liquid phase transition. Coupling coarsening inhibition effects, including sluggish diffusion in globules, Cu-rich liquid film as inhibitory barrier, heterogeneous globule as obstacle, account for extremely sluggish microstructural coarsening (coarsening rate is only 2.44–11.25 μm3/s). Finally, through forming ofexemplar component, intriguing potential for SSP application in component manufacturing was verified.