Research On The Technology And Mechanical Properties Of Joint Of Friction Stir Spot Welding With No Probe Hole

Friction stir spot welding is an efficient, clean, and energy-saving–new spot welding technology based on Friction stir welding (FSW). After using common tool when friction stir spot welding, will leave a defect ---Keyhole. Not only affects the weld surface appearance, but also reduces the mechanical properties of weld. In this paper, 2mm2A12-T4 aluminum alloy sheet being jointed by friction stir spot welding with no probe hole, this friction stir spot welding tool and welding process have been developed.In this paper, the tool materials and the shape of the pin, which is used in friction stir spot welding, have been studied. Manual control retractable pin which is made of 9341 and 35CrMo can be used on the 2mm 2A12-T4 aluminum sheet to test. Then found the appropriate parameters of test to satisfy the request of friction stir spot welding with no probe hole.In this paper, 2mm 2A12-T4 aluminum alloy sheet has been joined by friction stir spot welding with re-filling probe hole and retractable friction stir spot welding with no probe hole. Different parameters affect on mechanical properties by tensile test, micro structural experiment and micro hardness test have been studied.According to the results: On the friction stir spot welding with re-filling probe hole, when other welding parameter is constant and the rotation speed of the tool is 600r/min, shear force on welding joint reaches the maximum value 4707N. The rotation speed changes from 600r/min to 1000 r/min, the shearing force will deteriorate with the increase of the parameters. When changing the distance of shoulder plunged again, the mechanical property of welding joint increase along with the distance and maximizing 4666N when the distance reaches 1.2mm. When changing the extended length of pin, the mechanical property of welding joint increase along with the extended length of pin and maximizing 4666N when the extended length reaches 3.4mm. The metallographic structure shows that the welding spots can be divided into the mixed zone, the stir zone and the parent metal. Among them, the grain size in the mixed zone is minute while in the stir zone there is a coarsening phenomenon. The micro hardness testing shows that, the micro hardness of the welding spots is between 100 and 150. And the Mixed Zone has the highest micro hardness while the Stir Zone has the lowest.On the retractable friction stir spot welding with no probe hole, when rotation speed is 800r/min, retractable distance is 30mm and retractable speed is 45mm/min, the structure of the welding spot was the best. The micro hardness testing shows that compared with the parent material, the hardness of weld zone was lower. The hardness of weld nugget zone was higher, heat affected zone was the minimum. And the micro hardness of forward side was lower than retreat side.After comparison between friction stir spot welding with no probe hole and the traditional friction stir spot welding, it is found that the two methods of friction stir spot welding with no probe hole both finished refilling the probe hole. The welding spots of friction stir spot welding with no probe hole had no defects on the surface, the shapes were good and the probe holes refilled full. The failure loads of friction stir spot welding with no probe hole were higher than the traditional friction stir spot welding. The process of refilling the probe hole made the shearing force of at least a 30% increase.