The thermal stability of deformed Al-CuAl 2 eutectic

Abstract

The thermal stability of a deformed Al-CuAl₂ eutectic alloy has been studied after both room-temperature and high-temperature rolling. At room temperature, the strain is accommodated by plastic flow of the Al-rich phase and cracking of the CuAl₂ phase. On annealing at 500°C the broken CuAl₂ lamellae spheroidize only where Al has penetrated the cracks during rolling; where the cracked lamellae have not been penetrated by Al, the voids are stable on annealing. Prolonged annealing (> 1 day at 500°C) leads also to the break-up of Al lamellae in these specimens by the migration of triple junctions at sub-boundaries in the Al phase, as previously documented. The strains associated with hot rolling (at temperatures >350°C) are accommodated by plastic flow in both phases with a limited amount of cracking in the CuAl₂ phase. On annealing, a substructure is formed in both phases with associated triple-point migration. The rate of migration is faster for those triple points moving into the CuAl₂ phase; this is found to be due to the higher energy of sub-boundaries in the CuAl₂ phase (for a given misorientation across the sub-boundary), giving a greater driving force for migration. Although the structure can locally reach an equilibrium configuration after short annealing times, both the cold- and hot-rolled specimens are inherently unstable and the microstructure becomes equiaxed on prolonged annealing at 500°C.