厚板铝合金搅拌摩擦焊接头沿板厚方向低周疲劳性能不均匀性研究

he low- cycle fatigue tests have been conducted for the base material and friction stir welded (FSW) joints along the thickness direction of 20 mm 2219-T62 aluminum alloy thick plate. The influence of coupled thermal-mechanical and welding parameters on the fatigue deformation behavior of the joint has also been systematically investigated. The results show that stress amplitudes and plastic strain amplitudes present horizontal distribution during cyclic deformation at low strain amplitudes of 0.1% and 0.2%. Moreover, single fatigue crack initiates from the surface or near-surface defects and propagation zone is basically characterized by fatigue striations. While at higher strain amplitudes of 0.4%, 0.6% and 0.8%, the stress amplitude increases and the plastic strain amplitude decreases as cyclic deformation proceeded, indicating that cyclic hardening occurred, and the degree of hardening increases. The fracture surface presents a multi-source initiation and dimple-like features. Based metal (BM) exhibits higher stress amplitude and low hysteresis energy at mid-life which causes less fatigue damage at the same strain amplitude, resulted in a longer fatigue lifetime. Compared to middle and bottom slices, the top has higher stress amplitude and lower plastic strain amplitude corresponding to a lower fatigue life. Moreover, both the propagation zone area in the top and bottom slice are basically the same, fatigue striation in the bottom increases. The higher the rotational rate, the higher the stress amplitude, the lower the plastic strain amplitude and fatigue life, but no strong effect of the welding speed on the fatigue life can be seen.