Research On Microstructure And Properties Of Spray Formed 2195 Al-Li Alloy Welded Joint By TIG Welding

Realizing the reliable connection of 2195 Al-Li alloy has always been the focus of attention in the industry.At present,the conventional fusion welding method is still inferior to the solid-phase welding method.However,flexible fusion welding method is still indispensable when welding the head,melon flap and other parts of the carrier rocket tank.Therefore,from the perspective of ensuring the welded joint strength and plasticity,two different series of filler wires and variable polarity tungsten argon arc welding(VPTIG)were selected to study the welding of spray formed 2195-T6aluminum lithium alloy in this paper.At the same time,the microstructure,element content and distribution,grain orientation and grain boundary structure,mechanical properties and fracture mechanism of the joint were studied by means of optical microscope(OM),scanning electron microscope(SEM),energy dispersive spectrometer(EDS),electron backscatter diffraction(EBSD),micro-hardness tester and tensile equipment.Finally,the automatic welding process of 2195 Al-Li alloy is explored.The main research results of this paper are as follows:(1)The results show that the porosity of welded joint with Al-Si-Cu filler wire was7.989 times higher than that with Al-Cu filler wire.Besides,the results indicated that the average strength and elongation of TIG welding joint can reach 68.6%and 89.9%of the base metal strength and elongation when using Al-Cu filler wire,while the average strength and elongation of the joint only reach 56.8%and 39.9%of the base metal strength and elongation when using Al-Si-Cu filler wire.(2)The distribution rule of the structure and elements near the fracture position of the sample was studied.It was found that when using the Al-Cu filler wire,the Al/Cu eutectic distributed more at the grain boundary,while the Al₂Cu phase distributed more inside the grain,which improved the strength of the joint of the Al-Cu filler wire.However,when using Al-Si-Cu filler wire,more Si,Cu and Ti elements segregate at the grain boundary,forming brittle and hard Al/Cu/Ti network eutectic,reducing the joint performance.(3)The fracture rule of the welded joint with different filler wires were studied.It was found that the main fracture of the weld joint with Al-Cu filler wire was plastic fracture along the grain boundary and mixed fracture around the second phase particles.However,when Al-Si-Cu filler wire was used,the fracture of the weld was mainly quasi-cleavage along the grain boundary and pores.Therefore,regardless of the degree of element segregation or the analysis of the fracture process,the welded joints obtained by using the Al-Cu filler are superior to the joint properties obtained by using the Al-Si-Cu filler wire.(4)The porosity content and distribution of welded joint in TIG automatic welding were studied.The results show that when the welding current was small and the plate was not preheated,more pores were emerged,and they were mainly concentrated in the fusion line and the junction between the bottom and the top layer.In addition,the pore diameter range of single-layer or double-layer welding was mainly within 0.1-0.15mm.