Effect of natural aging time on tensile and fatigue anisotropy of extruded 7075 Al alloy

Abstract

In this study, 7075 Al alloy was prepared by solution treatment + natural aging. The anisotropic behavior of 7075 Al alloy in extrusion direction (ED), 45° direction (45°) and radial direction (RD) was studied by quasi-static tensile test and strain controlled low cycle fatigue (LCF) test. The specimens of ED, 45° and RD were 0°, 45° and 90° to the extrusion direction of the bar, respectively. The mechanical properties of the specimens in three directions showed strong anisotropy. The yield strength (YS) and ultimate tensile strength (UTS) of ED specimens were better than 45° and RD specimens, but 45° specimens had better plasticity. With the extension of aging time, the YS and UTS increase significantly. In the quasi-static tensile process, the specimens would have dynamic strain aging (DSA), and obvious serrated flow behavior could be observed on the curve. For the fatigue performance of specimens in three directions, when the strain amplitude was low, the fatigue life of ED and 45° specimens was high. When the strain amplitude was high, the fatigue life of RD specimens was high. The experimental results showed that after cyclic loading, the second phase size of solution treatment + cyclic loading specimens was larger than T6 (480 °C × 3 h + 130 °C × 24 h). Therefore, the fatigue fracture mode was multi-source fracture at low strain amplitude.