| Summary: | 碩士 === 國立虎尾科技大學 === 創意工程與精密科技研究所在職專班 === 99 === Friction Stir Welding(FSW) is a solid-state joining process. A number of potential advantages of FSW over conventional fusion-welding processes have been identified. such as good mechanical properties、Energy saving, low environmental impact and wide adaptability. Because of the low cost and high quality, the FWS has been widely used in aerospace, high-speed trains, ships, cars and other manufacturing fields.
Thick aluminum-alloy plate is widely being used in the manufacture, to improve the strength of structure, the technology of thick plate welding should be researched. The main problem with thick plate FSW are temperature gradient along with thickness direction、lower temperature of the lower part and plastic flow not enough, so the lower part is the weak portion of the joints. In this paper, 14mm A3003 thick plate being jointed by Friction Stir Welding, the FSW tool and welding process have been developed.
During the test process, the profile of FSW tool being designed with 「screw groove pattern」 and 「whisk screw groove pattern」 which has a whisk pattern at thetop end of the FSW tool. By means of changing the welding speed and rotation speed,the influence of the welding parameters on the joint’s tensile strength isstudied. While 「whisk screw groove pattern」 FSW tool being used with the Rotation speed 1200 rpm and the welding speed changes from 120 mm/min to 190mm/min,the joint’s tensile strength is above 97％ of the base-material. While the Rotation speed changes from 1000 rpm to 1400 rpm with the welding speed 150 mm/min,the joint’s tensile strength is above 96％ of the base-material. But while 「screw groove pattern」 tool being used, the proper parameters range which no-defect joints can obtained is narrower than 「whisk screw groove pattern」. So in order to obtain high quality joints, 「whisk screw groove pattern」 FSW tool should be used.
The FSW joint is made by the synthesis effect friction and stir, to make thewhisk pattern at the top end of FSW tool can reinforce the stir for the plastic metal, promote given off the heat of plastic deformation and temperature gradient along with thickness direction decreased. At the same time, the whisk patter of the tool has an effect to reinforce flow behavior of the plastic metal、to improve dynamic recrystallization course occur in the crystal grain of weld nugget, so the problem thatthe lower part has a weak performance can be solved
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