Measurement of Mechanical Properties of Friction Stir Welding of Al–Li alloy under different environmental conditions

The butt joints of AA2099-T86 alloy were prepared by friction stir welding process under four different environments, i.e. conventional (C-FSW), liquid nitrogen (LN-FSW), ultrasonic vibration welding (U-FSW), and ultrasonic vibration with liquid nitrogen (ULN-FSW). The welding tool rotational speed of 650 rpm and tool traverse speed of 80 mm/min were fixed for all experiments. The microstructural characterization of the welded samples is examined with optical microscopy, SEM, and XRD. Higher tensile strength and microhardness were obtained in the ULW-FSW welded samples. The ultrasonic vibrations promote plastic deformation and material mixing, increasing the dislocation density and improving the weld strength. In addition, liquid nitrogen restricts the grain size and dissolution of strengthening precipitates due to the rapid welding cooling rate, resulting in higher hardness. Comparative analysis of weld joint efficiencies revealed that the ULN-FSW welded sample achieved an impressive efficiency of 87.12%. In contrast, U-FSW, LN-FSW, and C-FSW displayed efficiencies of about 86.17%, 83.01%, and 74%, respectively.