Impact of microstructural stability on the creep behavior of cast Al–Cu alloys

Creep behavior of three cast Al–Cu alloys at 300 °C was studied by measuring their steady state creep rates as a function of stress. Microalloying additions in two alloys stabilized the θ' (Al2Cu) precipitates to 300 °C, which allowed grain boundary-controlled creep deformation to dominate at low stresses in these alloys. In contrast, the instability of the microstructure at 300 °C in a conventional Al–Cu 206 alloy led to the majority of θ′ precipitates transform to the θ phase. The 206 alloy displayed diminished resistance to dislocation motion and a dislocation creep mechanism dominated from the lowest stresses. A modified Coble creep model was developed to describe the experimental low-stress creep rates in the alloys with thermally stable precipitate structures. It is concluded that increasing the thermal stability of precipitates in Al–Cu alloys can provide significant improvement in their creep performance.