Study On Friction Stir Tool Optimum Design In FSW Of 2219 Aluminum Alloy And Weld Flaw

Friction stir welding (FSW) invented by The Welding Institute (TWI) in 1991 is a new joining method for Al alloy. Many problems when using traditional fusion welding methods can be resolved by using FSW such as distortion, crack, porosity and slag inclusion. Friction stir tool is the core of in FAW process. In this paper, several kinds of friction stir tools with different probe geometries were designed to weld 2219-T87 Al alloy. Choose the friction stir tools which get best joint mechanical properties, and draw up weld parameters. The material flow during friction stir welding and defects produced by different conditions have been studied.In this paper, 7 friction stir tools with different probe geometries were designed. 8mm 2219-T87 Al alloy were welded under two suits of welding parameter, and joint microstructures and mechanical properties have been studied to choose the better friction stir tools. The results show that the friction stir tool with triplatform is the best choice. The weld surface is good. Refine and even grains in the weld nugget have no certain direction, strengthening phase distributes uniformly. The grains in thermal mechanical affected zone (TMAZ) grow little, and the welding nugget transit smoothly to TMAZ. Mechanical properties of welding joint are good and steady.8mm 2219-T87 Al alloy was welded with friction stir tool with triplatform, the relationship between welding parameter and mechanical properties was researched through designing experiment process by using orthogonal test. The result shows that the ultimate tensile strength of FSW joint can reach up to 82.7% of the base metal acquired at the welding peed of 260mm/min, the rotary speed of 1000r/min and the stop time before welding of 10s.2219-T87 Al alloy and LF6 Al alloy were respectively welded with friction stir tool with triplatform. The remarkable difference of causticity between 2219-T87 and LF6 was used to investigate the material flow. The result shows that the plasticizing materials in welding joint has 3"onion"in the vertical direction , and materials flow is regional flow in small scale. In horizontal direction the scope of materials flow became smaller from the upper part to the lower part of welding joint. The materials in retreating side flowed to advancing side from back of friction stir tool.8mm 2219-T87 Al alloy was welded with friction stir tool with triplatform under different assembly conditions. The welding joint was detected by X-ray, and the section was metallographic analyzed. The result shows that void appeared at the junction of base metal in advancing side and welding line when there is difference of depth or certain gap between lap jointed sheet. Groove appeared at welding line when the size of gap between lap jointed sheet exceeded 2.3mm. The gap between lap jointed sheet and inadequate tool plunge depth resulted in void. Joint line remnant at the junction of base metal in advancing side of upper and middle part and welding line ,as well as crack appeared under the conditions of inadequate tool plunge depth and the existence of serious oxide film.