Study On The Welding Process And Mechanical Properties Of Friction Stir Lap Joints Of2219Aluminum Alloy

Friction stir lap welding (FSLW) is a new type of solid-state connection technology. Comparedwith riveting, FSLW significantly reduces structural weight, lessenes assembling cycle, and avoidscrack nucleation in the riveting. In comparison with resistance spot welding (RSW), FSLW joints arecomposed of fine grains, have no porosity defects and lead to low distortion.In this paper,2219aluminum alloy with3mm+3mm thickness sheet, according to four differenttool pin profiles exerting force on the weld, we can know that the migration interface is formed. Theinfluences of welding process on the migration interface, hardness profiles and tensile strength havebeen discussed specifically. The results show that tunnel defect easily appears in the weld whenrotation speed is too low. With the increase of the rotation speed, vertical migration of interface andsound weld width also increase. But vertical migration of interface and sound weld width tend todecrease if the rotation speed is too large. Under the same rotation speed and welding speed, Weldproduced by using triangular exhibits that vertical migration of interface is the lowest and the ultimatetensile strength is up to201.2MPa. Nucleation and propagation cracks initially are at migrationinterface, which is brittle features; Then, the lap joint fractures finally at the thermo-mechanicallyaffected zone/weld nugget that plastic fracture characteristics have been found.In the double-pass welding，one migration interface in the weld moves upwards, anothermigration interface moves downwards when it is welded by threaded cylindrical tool. Therefore, thejoint efficiency is79.5%because it avoids reducing effective sheet thickness and enhance lap-shearfailure load. Double-pass welding joint is the same as the hardness distribution of single-pass weldingjoint that is "W" shape, however, both heat affected zone and weld nugget zone enlarge.The effect of post-weld heat treatment (PWHT) on microstructures and properties of lap jointsare investigated. The experiment results indicate that the hardness and strength of weld increase as theaging temperature rises. Hardness is similar to the profile of basin-shaped. After aging temperature at200℃for18h, the softening is due to overaging of precipitated phase. The shallow ductile dimplesand torn edges are mainly micro feature of the fracture surface.