Effect Of Heat Treatment On The Uniformity Of Superplastic Deformation Of Laser Welded Joint Of Titanium Alloy

Welding/superplastic forming combination technology has great advantage in the titanium alloy multi-layer hollow lightweight structure.At present,titanium alloy welding/superplasticity application prefer diffusion connection/superplastic forming(SPF/DB)combination technology.However,the application of diffusion bonding /superplastic forming technology on titanium alloy has low production efficiency,poor flexibility of parts design and manufacturing.Laser welding can effectively overcome the difficulty of titanium alloy diffusion connection,ensure the good formation performance joints,But the laser welding / superplastic forming technology could arise necking and tissue uneven phenomenon after deformation,This will seriously affect the performance of the part.So improving the laser welding superplastic joint deformation uniformity and uniformity of the microstructure was the key issue that we should breakthrough.In this paper,TC4 titanium alloy laser welding joints as the research object,The uniformity of the microstructure and tensile uniformity of TC4 titanium alloy laser welding superplastic deformation were studied.The conclusions are as follows:When quenching at 1000 ℃,the area of the joint is β phase,the β phase,s Size ratio of the base material and the welding is 1.2,The difference in microhardness is10 HV,Quenching treatment could improve the TC4 titanium alloy laser welded joint tissue state,Improve the uniformity of welded joints,With the quenching temperature rise,The overall tissue uniformity of the joints is enhanced;When the quenching treatment between 960 ℃~1000 ℃,The peak flow stress of the joint is between 15 MPa and 60 MPa during the superplastic deformation,The elongation is between 178.362%and 581.733%.Under the same deformation conditions,the stress-strain curve of the joint is moved up with the increase of quenching temperature,The peak flow stress of the welded joint increases with the increase of the quenching temperature,and reduced with the deformation temperature increasing,increased With the strain rate increasing;The elongation of the welded joint decreases with the increase of the quenching temperature,which increases with the increase of the deformation temperature and decreases with the increase of the strain rate.It was found that the quenching treatment could improve the deformationcoordination of the welded joints and alleviate the problems of neck shrinkage and unevenness of the joints after superplastic deformation of welded joints.In the early stage of superplastic deformation of welded joints,the microstructure of weld and base metal changed from fine needle-like structure to lamellar microstructure,and the superplastic deformation mechanism was softened and dynamic recrystallization;In the late stage of superplastic deformation,the lamellar microstructure continues to grow and the fractures are formed to form irregular and equiaxed microstructure.The deformation coordination mechanism is dominated by dynamic recrystallization and spheroidization.After the superplastic deformation of the welded joint,the whole microstructure of the joint is irregular and equiaxed,and the microstructural uniformity of the welded joint is enhanced.In this paper,we introduce the uniformity coefficient M and the deformation uniformity coefficient K to characterize the homogenization of the welded joint.With the quenching temperature increasing,the uniformity coefficient M and the deformation uniformity coefficient K and the homogenization imporved;At the same quenching temperature,both increase of the deformation temperature and the decrease of the strain rate would increase the uniformity of the joint.Under the condition of quenching temperature of 1000 ℃,deformation temperature of 940 ℃ and strain rate of 10-4s-1,the tensile uniformity coefficient of the joint is 0.9269 and the microstructural uniformity coefficient is 0.66134.