Study On Friction Stir Welding Process

Friction stir welding (FSW) is a patented new solid joining process, which was invented at TWI ten years ago. Unlike more conventional fusion welding, the friction stir weld remains solid state during welding, so there is no welding defect such as cracking, porosity and loss of alloying elements etc. There is no requirement for filler wire or shielding gas during welding process. No joint preparation is required before welding. Energy for friction stir welding is lower than conventional fusion welding. There are no radiation hazards, weld fume, splash and high noise during welding process. So friction stir welding is a "green joining process" with excellent mechanical properties of joints, high efficient and lower costs and its application is widely.At present, in developed countries the friction stir welding process is already in commercial use, but it is just beginning in our country. The study on friction stir welding of aluminum alloys sheet was conducted with self-made equipment. The study will provide the bases of theory and practice for wide application of friction stir welding in our country.The design of welding head geometry is the key for friction stir welding. The friction stir welding using cylindrical stir-welding head was conducted, and the effect of welding head on welding process and welding quality by changing the diameter of the shoulder and welding pin was analyzed. The results of experiments show that the optimal size of cylindrical stir-welding head for 3 mm thick aluminum alloys plate is that the diameter of shoulder is 9 mm and the diameter of welding-pin is 3 mm.Proper heat input is important factors on welding quality. In friction stir welding process, the friction heat between welding head and work-pieces is the source of energy. Welding quality depends on the size of welding head, rotating speed, welding speed and pressure. The study results show that heat input depends on the ratio of rotating speed and welding speed(n/v) when other parameters are constant. In this experiment, good quality weld can be achieved when n/v is in the range of 15 ~ 23 .The microscopic examinations reveal that the grain size of FSW weld is fine andthe heat affected zone is narrow than that of fusion weld. So the mechanical properties of FSW joint are good.