Study on Eliminating Hook Defect of Lap Joint by Double-Side Friction Stir Welding
For friction stir lap welding joints,Hook defect is formed by the bending of lap interface during welding.Hook always acts as the weak point of the joint when the joint is subjected to external forces,thus it is necessary to eliminate the hook.Based on the principle that plastic material flows vertically and squeezes the surrounding materials during friction stir lap welding,the double-side friction stir welding was used for the lap joining of the aluminum alloy plate to try to eliminate the hook.The effect of welding speed on the structure and mechanical properties of the lap joint was studied.The results show that double-side welding is an effective method to eliminate the hook.When the welding speed is 150,200 mm/min,hook defect can be completely eliminated.The hardness of the weld zone is obviously lower than that of the base meal,and the lowest hardness position of the joint is located at the thermal-mechanically affected zone and heat affected zone formed by the second welding process.The joint failure load first increases and then decreases with the increase of the welding speed.The maximum tensile load of 14.0 kN is obtained when the welding speed is 100 mm/min.Two fracture modes are obtained during tensile test.The joint presents tensile fracture mode when the welding speed is smaller than 100 mm/min,and it shows shear fracture mode when the welding speed is higher than 150 mm/min.
friction stir lap weldinghook defectwelding speedtensile failure load
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