Research On TA2Friction Stir Welding And The Field Of Weld Temperature

Friction stir welding (FSW) invented by TWI in1990s is a new solid-state weldingtechnique. FSW has the advantage of high degree of automation, good welding environmentand fine welding shaping over traditional welding process, and it can be used to combinesome materials that are difficult to weld with common welding process, such as aluminumalloys, titanium alloys, etc. FSW has been widely applied to many industries.In this paper, the object of the study is commercial pure Ti sheet TA2, which has greatcorrosion resistance, moderate plasticity and strength among pure Ti. With the utility ofFSW, exploring welding experiment is carried out for2mm thick sheet TA2and the optimalparameters were achieved. The microstructure and mechanical property of welding jointwere analyzed. The result of the analyses was that the welding joint of TA2consisted ofbase material, heat affected zone, thermal mechanically affected zone and the weld nugget.The grains of thermal mechanically affected zone and the weld nugget were crushed andrefined, but the refinement degree of nugget zone was higher without obvious phasetransformation. Compared with base metal, part grains of heat affected zone grewsignificantly, resulting in uneven grain sizes. The hardness of stirring zone is higher thanbase material, and only the hardness of heat affected zone is slightly lower than base metal.What’s more, the hardness of retreating side of the tool pin is higher than the advancing side.Friction performance of different regions of welding joint were studied in fluidenvironment, according to TA2in seawater pipeline environment. The results show thatfriction performance of the regional difference is not so much, consistent with the basicmetal.Temperature field is simulated of welding process by ANSYS finite element software.Getting the temperature distribution clouds of the preheat phase and the process of welding,and the temperature distribution clouds on the surface and on the lower surface of the weld.The temperature variation of characteristic points was measured during the process ofwelding with the primer parameters. Due to the different heat production mechanisms ofpreheating stage and welding stage, experiments were conducted to measure the temperaturevariation of characteristic points around tool pin during preheating stage, the temperaturevariation of characteristic points in the position below the plate corresponding to bothsymmetrical sides of weld seam in welding process, as well as the temperature variation of feature points that were perpendicular to weld direction respectively. It was observed thatthe temperature of characteristic points rose slowly first and then increased rapidly inpreheating period. During the process of welding, the peak temperature of characteristicpoints of advancing side of pin was lower than that of retreating side, however it was higherthan the peak temperature of characteristic points in corresponding position below the plate.The peak temperature of measured points vertical to weld direction was delayed. And thecloser to the weld center, the lager temperature gradient it was. The measured results areconsistent with the characteristics of temperature distribution clouds.