Effects of segregation, quenching rate, and external stress on precipitation behaviors of Al-Cu-Cd alloys

The addition of Cd to Al–Cu alloys alters their precipitation behaviors and improves their mechanical properties. Previous studies focused primarily on the aging process. However, the inhomogeneous conditions caused by segregation and quenching rate and the external stress during aging affect the precipitation behaviors, which is unavoidable for large-scale components. In this work, the effects of these factors on the precipitation behaviors of Al-Cu-Cd alloys were studied. The obtained results indicated segregation and a low quenching rate delayed the precipitation process, and reduced the 8 h-aged yield strength from 459 MPa to 389 MPa and 312 MPa, respectively. External stress had two opposite effects on the precipitation behavior: (i) trapping Cd atoms and impeding the motion of Cd atoms and (ii) introducing dislocations and accelerating nucleation of the precipitates. The 15 h-aged yield strength subjected to the external stress of 60 MPa was 432 MPa, and the 9 h-aged elongation subjected to the external stress of 130 MPa was 6.7%. Both were lower than those of the stress-free sample. Therefore, minimizing the inhomogeneous conditions caused by segregation and quenching rate and avoiding the external stress during aging was the optimum route of alloy fabrication.