Effects of pre-strain on Cu-Mg co-clustering and mechanical behavior in a naturally aged Al-Cu-Mg alloy

Effects of pre-strain on Cu-Mg co-clusters and mechanical behavior in a naturally aged Al-Cu-Mg alloy were investigated by tensile and fatigue testing, transmission electron microscope (TEM) and atom probe tomography (APT) in present work. Results show that pre-strain contributes to increasing tension strength, not only by increasing dislocation density as previously recognized, but also through enhancing Cu/Mg ratio of Cu-Mg co-cluster and resultant critical shear stress for dislocation slip. Fatigue crack propagation (FCP) resistance is not degraded by further increasing pre-strain from 5% to 10%, in spite of a FCP resistance degradation when a pre-strain of 5% is initially applied. APT analysis indicates, comparing with 5% pre-strain, 10% pre-strain remarkably enhances Cu-Mg co-cluster size and Cu/Mg ratio during natural aging, which leads to a greater critical shear stress for dislocation slip. This undoubtedly enhances fatigue crack closure effect, and retards FCP resistance degradation when a greater pre-strain of 10% is applied.