Microstructural evolution of aluminum alloy 2618 during homogenization and its kinetic analysis

Abstract

The microstructure evolution of aluminum alloy 2618 and its homogenization kinetics were investigated by optical microscope, scanning electron microscope, energy dispersive spectroscopy and differential scanning calorimeter. The results show that the main constituent phases in as-cast alloy 2618 are α-Al, Al9FeNi phase and non-equilibrium binary θ (Al 2Cu) phase instead of typical S (Al2CuMg) phase. The θ phase was dissolved into α-Al gradually and the continuous dendritic-network structure was broken with the increase of homogenization temperature and time. DSC analysis shows that the overburnt and liquidus temperatures of as-cast alloy 2618 are 506.4 C and 638.0 C, respectively. After the alloy was homogenized at optimized temperature 500 C for 16 h, the θ phase was completely dissolved in matrix. The size and morphology of Al 9FeNi phase had little change, while the liquidus temperature shifted to 641 C. The calculated homogenization time for alloy 2618 at 500 C is 15 h, which is in accordance with that obtained in homogenization experiments. © 2014 by Walter de Gruyter Berlin/Boston 2014.