Study On Friction Stir Repair Welding And Friction Spot Joining Of 2A70 Aluminum Alloy

Friction stir welding (FSW) is a new solid face joining method, unlike the conventional arc welding no air vent or crack remained after FSW. Friction stir repair welding is a high efficiency repair method, which can patch up the weld defects in the MIG weldment and overcome the limits of traditional TIG arc repairing. Friction stir spot welding (FSSW) is a new spot welding method, compare with conventional resistance spot welding, FSSW possess many merits such as energy saving, simple device and very suitable for aluminum alloy joining. These two welding methods are absolutely needful for our factory. In this dissertation, friction stir repair welding and FSSW for 2A70 aluminum alloy was studied.Friction stir repair welding of 2A70 aluminum alloy in 8 mm thickness is applied, the diameter of the shoulder is 24mm and the length of the pin is 7.8mm in the experiments. The repair process was taken after fusion welding before the first X-ray test to the weld line. The second X-ray test, preceded after repair work, manifested no flaws in the weld line that by contrasting the consequence of the two test. In order to inspect the intention of the weld, tensile test will be taken. The tensile results, with parameter r=400rpm and v=100mm/min showed that the tensile strength after repair had increased by 66% of the base metal. Microstructures of friction stir repair welded 2A70 aluminum alloy joints were analyzed. The results showed that there were several typical divided zones on transverse cross section including weld nugget, thermal mechanical affected zone, heat affected zone, and the shoulder affected zone and the fusion weld zone. These zones were affected by different mechanical action and went with plastic flow, which lead to different microstructures. The difference of the different part on the cross section was reflected by the hardness test.The effects of welding parameters of FSSW of 1mm thick and 6mm thick 2A70 Al alloy on weld mechanical properties and microstructure were investigated. The experimental results show that: For 1mm Al alloys, the best welding parameters are: rotation speed 2500rpm, the plunging speed 11mm/s, the loading time 1.7~2.7s; the maximal shear strength is 1.965kN, about 1.56 times of the RSW. For 6mm aluminum alloys, the best welding parameters are: rotation speed 2000rpm, the plunging speed 3mm/s, loading time 4s; the maximum shear strength is 14.53kN.