Study On The Effect Of Interlayer,Process Parameters And Magnetic Field On Microstructure And Properties Of Al5052-TC4 Heterogeneous Material TIG Welding-brazing

Due to the low density,high specific strength,and corrosion resistance of titanium alloys,and the high specific strength and low cost of aluminum alloys,titanium alloys and aluminum alloy composite structures have been widely used in aviation,aerospace and other fields.However,because of the huge difference in physical and chemical properties of titanium and aluminum,there are difficulties in welding titanium/aluminum dissimilar alloys.In this paper,an excellent Ti6Al4V/Al5052dissimilar alloy welding-brazing joint was obtained by adding interlayer.Using welding current and welding speed as variables,reasonable welding process parameters were obtained.The effect of welding heat input on the microstructure and properties of the fusion zone and brazing zone of the joint was studied.In addition,the effect of different composition of the interlayer and the magnetic field on the performance and microstructure of Ti6Al4V/Al5052 welding-brazing joint was also studied.Adding a pure Zn interlayer with a thickness of 10?m can increase the wettability and spreadability of the liquid solder on the surface of the titanium alloy base material.When the wire feeding speed is constant at 0.6m/min,changing the welding current and welding speed had a great influence on the weld morphology.When the welding current was too low(such as 70A)or the welding speed was too high(such as 0.25m/min),there were invalid physical connections and unwelded defects at the brazing interface.When the welding current was too high(such as 110A)or the welding speed was too low(such as 0.15m/min),the welded seam was burned through.However,when the welding current was 90A and the welding speed was 0.2m/min,the welded seam was optimal,forming a complete,continuous and smooth welding seam;The average tensile strength of the welded joint was 190MPa,which was 83.3%of the strength of the aluminum alloy base material(228MPa);The fracture occured in the heat-affected zone of aluminum alloy,there were a lot of dimples at the fracture,and the fracture mode was plastic fracture.The microstructure of welded seam zone mainly contained?-Al matrix,Al-Si eutectic phase,Si phase,TiAl₃intermetallic compound and a small amount of Al-Si-Fe impurity phase.The welding heat input had a great influence on microstructure morphology and distribution in the welded seam.As the welding current increasing,the number of TiAl₃intermetallic compounds in the welded seam increased significantly and the morphology of TiAl₃changed from a short rod to a feather.The formation of TiAl₃intermetallic compounds layer at the brazing interface was a key to achieving brazing connection.When the welding heat input was low,the TiAl₃intermetallic compounds layer was thinner and discontinuous;As the welding heat input increasing,the TiAl₃intermetallic compounds layer presented a continuous cell or zigzag shape and extended to the welded seam to grow;However,when the welding heat input was too high,TiAl₃ intermetallic compounds at interface grew up sharply;Due to the effect of arc stirring,TiAl₃ fractured and entered the welded seam.Under welding current of 90A,welding speed of 0.2m/min,and wire feeding speed of 0.6m/min,pure Zn,Cu-38wt.%Zn,and pure Cu interlayers were added respectively to study Ti6Al4V/Al5052 welding-brazing.The results indicated that the joint morphology and mechanical properties obtained by adding pure Cu interlayer were poorer,while joint morphology obtained by adding pure Zn and Cu-38wt.%Zn interlayers was a more continuous,more complete and smoother.Compared with the joint with pure Zn interlayer,the microstructure of fusion zone of the joint with Cu-38wt.%Zn interlayer contained not only?-Al matrix,Al-Si eutectic phase,Si phase,TiAl₃ intermetallic compound and a small amount of Al-Si-Fe but also Al₂Cu phase;In addition,the thickness of TiAl₃ intermetallic compounds layer was reduced;the average microhardness of welded seam zone was higher;The fractures all occurred in the aluminum alloy heat-affected zone and the average tensile strength value was 190MPa.After the magnetic field was added into the welding process,compared with the original welding joint,the wettability and spreading performance of molten liquid metal solder on the surface of titanium alloy were enhanced and the number of pores was reduced;The size of?-Al matrix grain in the welded seam was reduced by about 15%and the distribution of?-Al matrix grain was more uniform;The coarse columnar crystal microstructure in the fusion line zone was obviously was refined and homogenized;In the welded seam,there was no change in the types of phases,but the number of intermittent and flaky TiAl₃ phases was significantly increased and the diffusion of Zn element was more uniform,what is more,the number and size of Al-Si-Fe phase was reduced;The thickness of the TiAl₃ reaction layer at the brazing interface was reduced by 19.8%;The microhardness of the heat-affected zone,fusion line zone,and welded seam zone increased,and the microhardness of the welded seam zone changed more smoothly;The tensile strength of the joint was increased by 13.1%,and the fracture mode of the joint changed from the quasi-cleavage fracture at welded seam to the plastic fracture in the heat-affected zone of aluminum alloy.