Microstructural evolution and mechanical behavior of friction spot welded 2198-T8 Al-Li alloy during aging treatment

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 T-1 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 mu m and the size and volume fraction of T-1 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 degrees 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. (C) 2016 Elsevier Ltd. All rights reserved.