Study On Process Of Tungsten Inert Gas Arc Hybrid Friction Stir Welding For Steel

Tungsten inert gas arc hybrid friction stir welding and one electric heating clamping device optimized process lately with the Si3N4friction stir tools were used to weld Q235low carbon steel, to study the role of the composite heat source in improving the welding speed, welding quality and reducing the damage to the friction stir tools.When the tungsten argon arc was in80A preheat current, welds without any surface defect were acquired and the welding speed could be increased by0.3mm/s to0.6mm/s, but it could not be able to avoid the generation of defects yet, while the shape of the internal holes changed and its area reduced; micro-hardness fluctuations heavy in every regional of the joint, reflecting inhomogeneity in microstructure.tensile test shows that the joints still fracture in the junction of the weld nugget zone and the heat-affected zone of the advanced side in the weld seam, and the fracture had obvious at the macro, but the tensile strength of the joint increased to283MPa coMPare with the one of FSW, reaching to75%of the strength of the base metal.When the electric heating clamping device was used additionally and set its temperature of220℃, the tungsten argon arc preheat current of60A,the welding speed could be up to0.95mm/s. Microstructure analysis shown there were no any defects in the weld joint. But the use of the electric heating clamping device extended the weld high temperature residence time, microstructure in the weld nugget zone and the heat affected zone grew up to tend to the same degree; carbon element diffused fully and flaky pearlite structure and acicular proeutectoid ferrite phase are alternately distributed in the ferrite grain boundaries. The micro-hardness shown small difference between the regions of the joint and they were all higher in the weld nugget zone and the heat-affected zone than that in the base metal. Mechanics Performance Testing shown that the fractures were located in the base metal, which proved the strength of the joint under this process can be equal to that of the base metal.When the speed of the material filling the pin cavity and the welding speed satisfied a certain relationship, the generation of the tunnel defect could be avoided. The most seriously worn parts on the friction tool are ends of the should and the stir pin.