Effect of artificial aging on the Cu-Mg co-clustering and mechanical behavior in a pre-strained Al-Cu-Mg alloy

In the present work, the effect of artificial aging on the Cu-Mg co-clustering and mechanical behavior in a pre-strained Al-Cu-Mg alloy are investigated by tensile and fatigue testing, X-ray diffraction (XRD), transmission electron microscope (TEM) and atom probe tomography (APT). Results show that in the pre-strained samples, sample with artificial aging (170 °C/30 min) possesses unchanged strength and higher elongation in comparison with naturally aged sample. This is due to the greater strengthening effect caused by cluster hardening but the weaker strengthening effect caused by strain hardening in 170 °C/30 min sample. The fatigue crack propagation (FCP) resistance of 170 °C/30 min sample is higher than that of naturally aged sample. APT analysis indicates that artificial aging remarkably increases Cu-Mg co-cluster size, which leads to a greater critical shear stress for dislocation motion. This undoubtedly enhances fatigue crack closure effect and FCP resistance. Meanwhile, artificial aging reduces the dislocation density, which enhances FCP resistance as well. Compared to the sample without pre-strain, the pre-strained samples exhibit a higher FCP rate as a high density dislocation favors a detrimental effect on FCP resistance.