Abstract
The microstructure and mechanical properties of friction spot welding (FSpW) 2198-T8 alloy during aging treatment were studied. Whereafter, the fracture process before and after aging treatment was observed by using the in-situ straining transmission electron microscopy method. The results show that fined equiaxed grains remained with predominant T1 phase re-precipitated in the microstrucuture of FSpW 2198-T8 Al-Li alloy after aging treatment. With the extension of holding time (12 h –48 h), grains gradually grew up in the range of 9.2–13.2 μm and the size and volume fraction of T1 phases were also increased. Tensile strengths of thermal-mechanical coupling zone (TMCZ) of FSpW 2198-T8 alloy first increased and then decreased after aging treatment. When aging at 175 °C for 36 h, the strength reached the maximum (435 MPa) with the elongation decreased to 11.4%. Meanwhile, the fracture mode of TMCZ zone transformed from ductile brittle mixed fracture to brittle fracture after aging treatment. And cracks initiated at and propagated along precipitate-free zones (PFZs) after aging treatment.
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