Effect of Reheating in the Solid–Liquid Region on Al-5Fe-4Cu-Based Alloys

Abstract

Two Al-5Fe-4Cu-based alloys, AF1 alloy and AF15 alloy, with a high-volume fraction of second-phase iron-bearing intermetallics (AlFe phases for short) were reheated to a solid–liquid region, and the microstructural evolution of the alloys was investigated. During heating in the solid–liquid region, the high-melting-point solid AlFe phases were demonstrated to stunt grain growth, block liquid convection, restrict diffusion and coalescence, and reduce movement of solids. This mechanical barrier affected semisolid heating and prompted the formation of grains with increased high-angle grain boundaries (HAGBs), resulting in alloys with smaller grain sizes and lower coarsening rate constants. Consequently, the grains from the earlier stage (5–20 min) of isothermal heating were several times larger than those from the later stage (20–60 min), whereas average diameter of the grains increased with elevated heating temperatures and prolonged holding time. The coarsening of Al-5Fe-4Cu-based alloys is predominantly controlled by grain boundary diffusion. The AF15 alloy had a higher fraction of AlFe phases and more complex phase morphologies than the AF1 alloy. Furthermore, it had coarsening rate constants only one-fifth to one tenth those of the AF1 alloy.