Study On Friction Stir Joining Of High-Strength Al Alloy Thin Sheet

As a new solid-state joining technique, friction stir joining provides a new method for traditional difficult-welding materials. This technology is getting more and more practical applications. Friction stir joining devices are usually bulky, expensive and high in use and maintenance costs. The device is used to joining thin or thick materials. There has been no special small or micro friction stir joining devices for welding sheets. In order to solve this problem, this paper used experimental methods on optimization the design of a small milling machine and transformed it into a special friction stir joining device which was used to weld thin pieces. The influences of the parameters and the clamping method to the tensile strength and residual stress of the welded parts were studied. The optimum parameters and the clamping method were concluded.The main work and results in this thesis are as follows:1.The small milling machine through the installation of motor, driver, controller, human-machine interface were optimized and rebuilt, and the automatic control of the table was realized.2.Explored the effect of rotating speed and connection speed on forming properties of the joints.Analysis the microstructure and microhardness on the joint’s different regions.Obtained the reasonable range of the rotational speed and the connection speed.3. Further analysis the influence of the rotating speed and the connection speed on the mechanical properties of the joints.The analysis showed that:With the increase of the stir-welding head spinning velocity and joining speed,the strength to extension decreased before increase;The vertical residual stress of the top surface showed a “M” shape distribution, and that of the bottom surface showed a inverted “V” shape distribution; When the stir-welding head spinning speed reached 1050 rpm, joining speed reached 200mm/min, the strength to extension reached its maximum and the peak residual stress reached its minimum.4. Further analysis the influence of the impact of the clamping on the mechanical properties of the joints.The analysis showed that:The tensile strength decreased significantly without adding side top block; When adding side top block, the advancing side distance 15 mm, the retreating side distance 25 mm,the strength to extension reached its maximum and the peak residual stress reached its minimum.