The precipitation behavior of Al–Cu–Mg–Ag single crystal during aging under elevated compression stresses

The Al–Cu–Mg–Ag single crystal is prepared to study its precipitation behavior during aging under elevated compression stresses. Transmission electron microscopy (TEM), high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and hardness test are used for this investigation. The results show that a compression stress of 50 MPa leads to more uniform length distribution but slightly lower number density of Ω-phase in the stress-aging sample, as compared to that of the stress-free aging sample. When a higher compressive stress of 200 MPa is applied, the number density of Ω-phase is significantly decreased while a large number density of θ’-phase are precipitated along the dislocation lines introduced by the applied stress. Furthermore, the stress-orientating effect on Ω precipitation can not be observed in Al–Cu–Mg–Ag single crystal during stress aging even under the compressive stress of 200 MPa loading along the [2¯15]Al direction. This result signifies that the applied stress magnitude is not the only critical factor in determining whether the stress-orienting effect of Ω-phase can be generated, as this effect may be also associated with the loading orientation during stress aging.