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

摘要

Creep behavior of three cast Al-Cu alloys at 300 ℃ was studied by measuring their steady state creep rates as a function of stress. Microalloying additions in two alloys stabilized the θ' (Al_2Cu) precipitates to 300 ℃, which allowed grain boundary-controlled creep deformation to dominate at low stresses in these alloys. In contrast, the instability of the microstructure at 300 ℃ in a conventional Al-Cu 206 alloy led to the majority of θ' precipitates transform to the 0 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.