Finite Element Simulation And Formability Of Friction Stir Welded TC4 Titanium Alloy Lap Joints

Titanium alloy, which owns excellent mechanical properties, has becomes one of the materials which are mainly used to fabricate modern aircraft. Generally, the main joining method for titanium alloy is fusion welding. As a new solid-state joining technology, friction stir welding(FSW) can be used to avoid voids and hot cracks, which always appear during conventional fusion welding process. In order to increase structural strength and reduce weight in the aircraft manufacturing industry, the trend that the riveted joints were replaced by lap joints is inevitable. Therefore, the studies of the friction stir lap welding of TC4 titanium alloy were performed in this paper.The temperature fields of friction stir lap welded TC4 titanium alloy were simulated by finite element simulation software Abaqus/CAE, and the temperature distributions at the interface were investigated. The results show that the temperature distributions present ellipse shapes. The temperature gradient at the rear of tool is smaller than at the front of tool. With the increase of rotational velocity, both the temperature gradient between top and bottom surfaces of joint and the peak temperature increase. The peak temperature at the lap interface is lower than that of top surface of joint.The tool with W-Re was used in the friction stir lap welding of TC4 titanium alloy. Results show that at the constant rotational velocity, size and quantity of groove defects increase with increasing the welding speed. Lap joints without any groove defects were produced by the threaded tool. The results indicate that the surface formation of joints using the threaded tool is better than using non-threaded tool. Size of tunnel defects decreases with decreasing the temperature. The oxides at the lap interface are more diffuse when the higher rotational velocity was employed. The threaded tool enhances the material flow along the vertical direction and therefore increases the material exchange between the top and bottom plates. When the rotational velocity varied from 200 rpm to 150 rpm, the breaking load of joint firstly decreases and then increases. The maximum and minimum breaking load are 20.54 KNand 18.30 KN, respectively. The breaking load of the lap joint using the threaded tool is higher than using non-threaded tool. Fracture surface morphology represents the typical ductile fracture.