| TA19 titanium alloy is a typical near-alpha titanium alloy,with excellent welding performance and high specific strength and other excellent properties,widely used in aerospace and other fields.For large ring parts and special-shaped rings with complex cross-sections,the tonnage requirements of the forging equipment are higher and the processing capacity is limited.It is difficult to produce by the traditional forging-rolling process.The combination of welding and post-heat processing can reasonably reduce the consumption of materials in the processing process,reduce the structural quality,and obtain parts with complex cross-sections.Flash welding is a solid-state welding technology.Compared with traditional fusion welding,it has no weld defects formed by as-cast structures such as voids.However,due to the rapid heating and cooling of flash welding,a lamellar Widmansatten structure is formed in the weld,and with the difference between the center of the weld to the base material,the cooling speed and the welding upset stress,different structures are obtained,including lamellar Non-uniform welded structures such as Widmansatten structure,thin lamellar structure and deformed isometric structure.In the later ring rolling and bulging and rounding process,cracks due to uneven plastic deformation and deformation defects in service are easy to occur.Therefore,by studying the structural evolution characteristics of TA19 flash welded joints and the post-weld heat treatment of the non-uniform structure of flash welded joints,the organization is adjusted to reduce the area of joint performance caused by the difference in tissue uniformity and further improve the TA19 flash welded joints Performance.In this paper,the flash welding joint TA19 titanium alloy is taken as the researchobject to study the microstructure evolution law of the flash welding joint,through the effect of the microstructure evolution law and mechanical properties of the joints at different solution temperatures,and the isothermal and constant temperature of the weld layer structure In the strain rate compression test,the law of stress-strain curve of the thermal deformation structure of the weld is studied,and the evolution behavior of the structure at different deformation rates and deformation temperatures of the weld is analyzed.The research results can provide a theoretical basis for the improvement of the control of the non-uniform structure of titanium alloy welding and the hot processing of ring rolling with welded joints.The main research contents are as follows:(1)The microstructure and morphological characteristics of each area of the TA19 flash welding joint are studied,and the phase change process of the welding seam and the heat affected zone and other areas under the heat of welding in the titanium alloy flash welding solid state welding process is analyzed.Using scanning electron microscope and atomic probe,EBSD technology analyzes the structure of each region of the welded joint.The joint is affected by the temperature field and deformation force,and the degree of recrystallization is different.The characteristics of the phase change structure during the rapid heating and cooling of the weld are related to the element diffusion distribution.(2)According to the different solution temperature and aging treatment,it has the characteristics of significant influence on the ? phase morphology in the structure of the flash welding head.The characteristics of structural transformation and elemental distribution of joints in joints under solution temperature aging were studied.The results show that with the increase of solution temperature,the aspect ratio of the lamellar structure in the weld zone decreases,the content of ? transformed structure increases,and the secondary ? precipitated over time increases the strength of the joint.The distortion energy stored in the deformed alpha grains provides the impetus for the static recrystallization of the grains.In the heat treatment process,equiaxing occurs through static recrystallization,the uniformity of the welded joint is improved,the mechanical properties of the joint are improved,and a good strong plasticmatching is achieved.(3)According to different strain,deformation rate and deformation temperature,the hot processing characteristics of the flash welding seam layer structure in the heat deformation process.By taking thermal simulation samples along the longitudinal direction of the weld,the thermal simulation compression deformation experiments were completed under different deformation conditions,to study the characteristics of the structure evolution of TA19 under different thermal deformation parameters,and to obtain the law of hot processing of the weld layer structure.According to the stress-strain curve,the constitutive equations for thermal processing with different parameters of temperature,deformation and strain rate are established to obtain the key parameters of hot rolling with welding seam ring rolling.(4)To study the characteristics of the flow stress curve of TA19 titanium alloy under different deformation parameters during thermal deformation in the two-phase zone,and analyze the effect of different deformation parameters on the degree of spheroidization of the layer.Investigate the influence mechanism of deformation temperature,deformation rate and deformation degree on the spheroidization of lamellar ?.Studies have shown that under the same strain rate,with the increase of thermal deformation temperature,the peak value of the flow stress shows a downward trend.When the deformation temperature is reduced,the deformation rate is increased,the peak stress is increased,and the flow stress curve is obvious during the work hardening stage.Increasing the amount of deformation,increasing the deformation temperature,and reducing the deformation rate are conducive to the recrystallization nucleation of the layer ?,improving the recrystallization grains,and increasing the degree of spheroidization. |
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