Structure and properties of friction stir welding joint of Al-Li alloy

In order to reduce the welding pressure and meet the demand of robot friction stir welding, the friction stir welding test was carried out with small size shoulder and lower welding load. With the same heat input per unit area as the control principle, the effects of the shoulder size of the stirring head on the pressure, weld shape, joint microstructure and mechanical properties of 2 mm thick 2060-T8 Al-Li alloy during friction stir welding were studied. The results show that with the decrease of the shoulder size of the stirring head, the required welding pressure decreases nonlinearly, and the pressure amplitude decreases in the stable welding process. When the size of the shoulder is 4 mm, a large flying edge is formed on the surface of the weld and there are holes in the joint. When the size of the shoulder is larger than 6 mm, the joint with good surface shape and no internal defects can be obtained. When the shoulder size is 6 mm, the welding pressure is 2 800 N, the average grain size of the welding core zone is 0.52 μm, the maximum tensile strength of the joint is 396 MPa, which is 74.1% of that of the base metal, the microhardness is “U” type distribution, the fracture position is the welding core zone, and the fracture mode is ductile-brittle mixed fracture.