Preparation And Effect Of Activating Flux Of Laser Welding On Microstructures And Properties Of Superalloy

As the key stmaterial of spacecraft andaerial craft, high-temperature alloy hasbeen applied to aviation and astronavigation industry, specially to the body ofairplane and the engine which demanded high strength and heat resistance. The jointof high temperature alloy has been an important technique during the application of it.Laserwelding has advantages than the other welding methods, however, the reflectance of the laser of many metallic materials were very high. If no special treatment of itssurface, the laser welding may lose technical advantages. In recent years, activatingflux welding technology as a new welding technique which used to improve the weldshape, weld penetration and productivity. Thus, it will be a new direction for the futuredevelopment of laser welding. The active welding was used to the laser welding ofhigh temperature alloy GH4169, the effect of different activating flux formulation onthe microstructure and mechanical properties of the joint were studied. Themicrostructure and change of compositions of welded joints of high temperature alloywere observed by optical microscope, scanning electron microscopy and X-raydiffraction, etc. Mechanical properties of welded joints of high temperature alloy weremeasured by hardness and tensile tests, the main results were as following:In this paper, the common oxides and halides such as SiO₂, MgO, CaO, TiO₂,MnO₂, A1₂O₃, CaF₂and NaF were selected as the basis of activating fluxes. Theactivating flux formulations of high-temperature alloys on LBW were developed bythe formula uniform design method, so that the times of experiments are greatlyreduced. The results show that: the process of the low power laser weding ofhigh-temperature alloy GH4169added to the resultant formulations F12enables theweld penetration depth up to2times higher than the conventional laser welding.The effect of parameters on penetrations was studied by process experiments, byanalysis of the microstructure and mechanical properties of the joints: the fusion linewas clear, the heat affect zone was narrow. The both sides of fusion line distributecolumnar grain, as to the center of the weld, the grain change to small equiaxed crystal.After the use of activating fluxes, the weld equiaxed crystal region became larger. Underthe same welding conditions, activating flux increase the penetration of weld but thephase composition within the weld was not changed, which includes substrate Niphase, Ni₃Al phase and Ni₈Nb phase. The tensile strength of the joints equal strength to the base metal, the fracture morphology of the joints is dimple fracture. The depth ofpenetration increase of laser welding is mainly due to the use of the active agent,which improving the absorption rate of the specimen of the laser energy.