Study on the mechanical properties and fatigue failure mechanism of 7075-T6 aluminum alloy joints under different joining processes

To obtain the theoretical basis and reference basis for the selection of low ductility aluminum alloy joining methods, three kinds of joints were obtained using 7075-T6 aluminum alloy sheets for clinching, self-piercing riveting (SPR), and resistance spot welding (RSW) joints, and the single-lap shear tests were performed on the three kinds of joints, and fatigue tests were conducted on the clinched joints and SPR joints. The fatigue fracture of the SPR joint was analyzed using scanning electron microscopy (SEM) and X-ray energy-dispersive spectroscopy (EDS). The results showed that the SPR joint demonstrated the best static performance, followed by the clinched joint and the RSW joint. In the case of the fatigue test, the SPR joint showed better fatigue performance than that of the clinched joint. The fatigue failure of the SPR joint and clinched joint is associated with fretting wear. Fretting wear of the SPR joint is more severe than that of the clinched joint. The debris produced by fretting led to microcracking phenomena in the plate. Under the action of alternating load, the microcracks continued to expand and generate macrocracks, and the joint was broken and finally failed. This fretting wear is the root cause of the failure of the SPR joint. Thus, the SPR joints exhibited the best mechanical properties.