CN115821186A - Heat treatment method for improving plasticity and toughness of titanium alloy welded joint - Google Patents
Heat treatment method for improving plasticity and toughness of titanium alloy welded joint Download PDFInfo
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Abstract
The invention discloses a heat treatment method for improving the plasticity and toughness of a titanium alloy welding joint, which comprises the following steps: s100, carrying out laser filler wire welding on a test plate to be welded; s200, heating the welding test plate subjected to laser wire filling welding in a vacuum environment at 800-1200 ℃ for a period of time, and cooling to room temperature along with a furnace. The heat treatment method for improving the plasticity and toughness of the titanium alloy welding joint can improve the plasticity and toughness of the titanium alloy welding joint and can ensure the strength of a welding seam. And technical support is provided for popularization and application of large-scale titanium alloy welding joints.
Description
Technical Field
The invention relates to a heat treatment method for improving the plasticity and toughness of a titanium alloy welding joint, belonging to the technical field of welding processing.
Background
The titanium alloy has the advantages of small density, high specific strength, corrosion resistance, fatigue resistance and the like, and is widely applied to the fields of weaponry and deep sea industry. The TC4 titanium alloy is a typical alpha-beta dual-phase titanium alloy, has the advantages of both alpha type titanium alloy and beta type titanium alloy, and is one of the titanium alloys with the widest application range. Compared with the traditional welding technology, the narrow-gap laser filler wire welding has the advantages of small heat input, narrow heat affected zone, high welding efficiency and the like, and meanwhile, the structure performance of a welding joint can be further optimized by utilizing the supplement of the filler wire to the burning loss alloy and beneficial alloy elements, so that the filler wire welding is widely applied to the field of titanium alloy welding.
The narrow gap laser filler wire welding process is the accumulation of single-channel multilayer filler metal, and multiple thermal cycles in the multilayer welding process inevitably make weld joint tissues extremely complex and uneven, so that stress deformation of a welding joint during superplastic forming is uneven, the service safety performance of titanium alloy welding parts is affected, and the problem is provided for the application of the titanium alloy welding parts in industrial production. The heat conductivity of the titanium alloy is poor, the temperature of a welding seam molten pool of the titanium alloy is high under the condition of laser high-energy beam welding, sufficient conditions are provided for the growth of high-temperature beta-phase crystal grains, and the content of alpha' martensite generated by shear is high due to the high cooling speed after welding, so that the plasticity and toughness of a welded joint are directly influenced. Therefore, the heat treatment method is an ideal method for further regulating and controlling the structure composition, the shape and the distribution of the weld joint and further optimizing the mechanical property of the welded joint.
The tissue structure of the titanium alloy is sensitive to the heat treatment process, and the microstructure distribution of tissues in all regions of the welded joint can be coordinated through changing the tissue composition of the welded joint of the titanium alloy during the heat treatment, so that the stress deformation uniformity of the welded joint is improved. In recent years, heat treatment studies of titanium alloy welded joints have been carried out successively by related researchers at home and abroad. Ma Quan and the like adopt TC4 welding wires to perform TIG on TB8 plates, annealing the welding joints at 500, 550, 600 and 650 ℃ for 1h after welding, cooling the furnace, and testing the structure and strength of the welding joints after heat treatment, wherein the results show that: the welded weld joint is an as-cast structure with uneven component distribution, the [ Mo ] eq of the as-cast structure is 6.5-11, and a matrix consists of a coarse metastable beta phase; after the welding seam is annealed at 500 ℃, alpha' is cancelled out, but no alpha-photo layer structure is formed; after annealing at 550 ℃, superfine alpha phase sheet layers are separated out from the beta phase, and the tensile strength of the joint reaches the maximum value of 1223MPa; after annealing at 600 ℃ and 650 ℃, the alpha-photo layer precipitated from the beta phase is coarsened, the tensile strength of the joint is reduced, and the fracture has the characteristic of complete brittle fracture. Li Rui, etc. to perform linear friction welding on TC17 titanium alloy, and to analyze the structure morphology and mechanical properties of the obtained welded joint in different heat treatment states, the welding seam structure after heat treatment is found to be decomposed due to metastable beta phase and metastable alpha phase, so that the dispersed acicular alpha phase is separated out to greatly improve the joint performance, the tensile test is broken at the base material, and the strengthening effect of the dispersed acicular alpha phase is found to be closely related to the heat treatment temperature. Zhang Jingli, etc., researches the influence of postweld heat treatment process on the structure and mechanical properties of Ti650 alloy electron beam welded joint, and the results show that after 700 ℃/2h AC annealing, the alpha' martensite in the welding seam is subjected to near-equilibrium phase transformation into alpha, and simultaneously a large amount of secondary short acicular alpha phase is precipitated in the welding seam; after 1010 ℃/1.5h WC +650 ℃/2h AC treatment, the alpha phase is obviously coarsened and equiaxial, the short needle-shaped alpha separated out secondarily is combined with the primary coarsened alpha sheet layer to effectively improve the strength of the welding line, hinder the expansion of cracks, and enable the welding joint to have better strength.
The above researchers have focused on the improvement of tensile properties of welded joints by heat treatment, and coordinated the overall microstructure by controlling the size, amount and distribution characteristics of the alpha phase. The welding seam area in the TC4 titanium alloy laser wire-filling welding joint mainly takes alpha 'martensite as a main component phase to participate in service, the alpha' martensite and the alpha phase in a close-packed hexagonal HCP structure have fewer slippage systems and strong anisotropy, so the crystal structure characteristics of the welding seam area specify that the plasticity and toughness of the welding seam area are poorer, and the core of the performance regulation and control of the TC4 dual-phase titanium alloy welding joint through a heat treatment process is the plasticity and toughness.
Disclosure of Invention
The invention provides a heat treatment method for improving the plasticity and toughness of a titanium alloy welded joint, which aims to solve the problems in the prior art.
A heat treatment method for improving the plasticity and toughness of a titanium alloy welding joint comprises the following steps:
s100, carrying out laser filler wire welding on a test plate to be welded;
s200, heating the to-be-welded plate subjected to laser wire filling welding in a vacuum environment at 800-1200 ℃ for a period of time, and then cooling to room temperature along with a furnace.
Further, in S100, the method specifically includes the following steps:
s110, performing groove machining on a test plate to be welded, performing pretreatment after the machining is finished, and then clamping;
s120, under the protection of inert protective gas, filling a groove of the test plate to be welded in a laser beam circular swing mode by adopting a laser wire filling welding method;
and S130, using single laser to perform priming, and filling 6 filling layers in total to complete welding.
Further, in S110, the groove machining specifically includes: and processing the test plate to be welded into a Y-shaped groove.
Further, in S120, the size of the test panel to be welded is 400mm × 200mm × 20mm TC4 titanium alloy plate, the chemical composition is 6.30% Al, 4.11% V, 0.018% Fe, 0.024% C, 0.007% N, 0.001% H, 0.14% O and the balance Ti; the flux-cored wire adopted in the laser wire-filling welding method is a Ti-Al-V metal powder-cored flux-cored wire, and the deposited metal of the flux-cored wire comprises the following chemical components: 6.10% of Al, 4.15% of V, 0.04% of Fe, 0.012% of C0.006% by weight, 0.001% by weight, H, 0.02% by weight, O and the balance Ti.
Further, in S200, specifically, the temperature of heating in the vacuum environment is 990 ℃.
Further, in S200, specifically, the heating time in the vacuum environment is 2h.
The invention has the beneficial effects that: the heat treatment method for improving the ductility and toughness of the titanium alloy welding joint can improve the ductility and toughness of the titanium alloy welding joint, effectively ensure the strength of a welding seam, avoid the appearance of alpha' martensite in the welding seam structure, effectively ensure the ductility and toughness of the welding seam, and provide technical support for the popularization and application of large-scale titanium alloy welding joints.
Drawings
FIG. 1 is a weld joint macro topography;
FIG. 2 is a microstructure of a welded joint;
FIG. 3 is a microstructure of a heat treated weld joint;
FIG. 4 is an EBSD map of the weld metal;
FIG. 5 is a distribution of misorientation between grains;
FIG. 6 is a weld XRD pattern;
FIG. 7 is a weld joint hardness profile;
FIG. 8 is a graph of the texture of a tensile specimen after fracture;
FIG. 9 is the structure of the impact specimen after fracture;
FIG. 10 is a flowchart of a method of a heat treatment method for improving ductility and toughness of a titanium alloy welded joint according to the present invention;
FIG. 11 is an in-situ observation shot profile of a deposited metal sample during heating, wherein FIG. 11 (a) is an in-situ observation shot profile of a deposited metal sample at 890 ℃; FIG. 11 (b) is an in-situ observation shot shape of a deposited metal sample at 990 ℃; FIG. 11 (c) is an in-situ observation shot profile of a deposited metal specimen at 1190 ℃;
FIG. 12 is an in-situ observation shot of a deposited metal specimen during cooling, wherein FIG. 12 (a) is an in-situ observation shot of a deposited metal specimen at 990 ℃; FIG. 12 (b) is an in-situ observation shot pattern of a deposited metal sample at 943.7 ℃; FIG. 12 (c) is an in-situ observation shot profile of a deposited metal sample at 708 ℃;
FIG. 13 is a graph showing the effect of heat treatment time on phase fraction and phase morphology, wherein FIG. 13 (a) is the volume fraction of each tissue; fig. 13 (b) is an average aspect ratio of the striped α phase.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
Referring to fig. 10, the heat treatment method for improving the ductility and toughness of the titanium alloy welded joint comprises the following steps:
s100, carrying out laser filler wire welding on a test plate to be welded;
s200, heating the plate to be welded after laser wire filling welding in a vacuum environment at 800-1200 ℃ for a period of time, and cooling to room temperature along with a furnace.
Further, in S100, the method specifically includes the following steps:
s110, performing groove machining on a test plate to be welded, performing pretreatment after the groove machining is completed, and then clamping;
s120, under the protection of inert protective gas, filling the groove of the to-be-welded test plate in a laser beam circular swing mode by adopting a laser wire filling welding method;
and S130, using single laser to perform priming, and filling 6 filling layers in total to complete welding.
Specifically, in S100, the groove machining specifically includes: processing a test plate to be welded into a Y-shaped groove; the truncated edge of the groove is 2mm, the gap at the root part of the groove is 3.2mm, and the angle of the single-side groove is 1.5 degrees; the pretreatment specifically comprises the following steps: the test panel to be welded is ground and pickled, the pickling solution being 5% by volume of HF +30% by volume of HNO 3 +H 2 And O, removing oil stains and oxides on the surface of the test board to be welded, washing the test board with alcohol and water to remove acid liquor, and drying the test board for later use. In S200, inert shielding gas Ar is adopted to carry out front and back surface protection on the welding seam in the welding process, and the pressure of the shielding gas Ar is 0.5MPa; the welding heat source adopts YLS-6000 fiber laser manufactured by Germany IPG company; the circular oscillation mode is specifically as follows: the swing frequency is 100Hz, and the swing amplitude is 2mm; in S300, the interlayer temperature of the 6 filling layers is controlled within 150 ℃.
Further, in S100, the size of the test panel to be welded is 400mm × 200mm × 20mm TC4 titanium alloy plate, the chemical composition is 6.30% of Al, 4.11% of V, 0.018% of Fe, 0.024% of C, 0.007% of N, 0.001% of H, 0.14% of O and the balance Ti; the flux-cored wire adopted in the laser wire-filling welding method is a Ti-Al-V metal powder-cored flux-cored wire, and the deposited metal of the flux-cored wire comprises the following chemical components: 6.10% Al, 4.15% by weight, 0.04% Fe, 0.012% by weight, C, 0.006% by weight, N, 0.001% by weight, H, 0.02% by weight, O and the balance Ti.
Specifically, the chemical compositions of the base metal and the flux-cored wire deposited metal are shown in table 1:
table 1 chemical compositions (mass fraction,%) of base metal and flux cored wire deposited metal are detailed, and detailed welding process parameters are shown in table 2:
TABLE 2 welding Process parameters
Further, in S200, specifically, the temperature of heating in the vacuum environment is 990 ℃.
Further, in S200, specifically, the heating time in the vacuum environment is 2h.
Specifically, image-Pro software is adopted to quantitatively characterize the phase volume fraction and the phase morphology in the welded tissue. Fig. 13 shows the volume fraction of each tissue and the change of the average aspect ratio of the striped α phase with the heat treatment time, and it can be seen that the volume fraction of the spheroidized α phase slightly increases with the heat treatment time, and after 60min, the increase is not significant, and the average aspect ratio of the striped α phase significantly decreases and reaches a minimum value at 120 min. Therefore, the heat treatment time has great influence on the average length-diameter ratio of the strip alpha phase, and the length-diameter ratio is reduced along with the extension of the heat preservation time; the heat treatment holding time is defined as 2 hours in order to obtain a certain amount of spheroidized alpha phase.
Specifically, the grain structure morphology of the TC4 titanium alloy laser flux-cored welding wire deposited metal sample taken in situ during the heating process is shown in fig. 11. When heated to 890.5 ℃, the primary alpha phase has begun to germinate at the grain boundaries. In the heating process of the TC4 titanium alloy laser flux-cored welding wire deposited metal, the volume change is small during alpha → beta transition, the phase change stress is low, and the beta phase self-diffusion coefficient of a body-centered cubic structure is high, so that the transition process is short and only lasts for about 50 s. From the whole heating process, the beta phase grows in a mode of phase boundary movement, and the beta phase can be considered to grow continuously from the original beta phase boundary epitaxy, but not to generate beta new phase tissue in a nucleation mode. Under the conditions of this test, a transition temperature of the β phase around 990 ℃ was observed.
Therefore, according to the above test results, the heating temperature of the heat treatment is set to 990 ℃, which ensures that the β phase starts to be converted into the α phase in the subsequent heat-insulating process.
FIG. 12 (a) shows that after the heat preservation is finished for 500s, the morphology of the tissue is photographed in situ at the moment of furnace cooling, and the coarse beta-phase grain boundary is clear and obvious; FIG. 12 (b) is the in-situ imaging profile at the moment when the temperature is reduced to 943.7 ℃ and a primary phase appears on a beta-phase crystal boundary, wherein the primary alpha phase preferentially nucleates at the beta-phase crystal boundary to form a continuous crystal boundary alpha gb (graminboundary); FIG. 12 (c) is the characteristic temperature point tissue morphology after the completion of the cooling process, the sample tissue is bundled by primary lamellar alpha phase with aspect ratio close to 50 p And a small amount of grain boundary alpha gb Forming;
namely, no alpha ' martensite appears in the weld joint structure, because the alpha ' martensite is in a close-packed hexagonal HCP structure and has less slip system, the ductility and toughness of the weld joint are poor, and therefore the weld joint structure without the alpha ' martensite can effectively ensure the ductility and toughness of the weld joint.
FIG. 1 shows the macro-morphology of the whole and cross-section of a laser wire-filling welded joint, and no defects such as air holes, cracks, poor side wall fusion and the like are found. The weld zone of the welded joint is composed of columnar crystals, and the columnar crystals grow along the direction of increasing temperature gradient, so that the columnar crystals grow from two sides to the center of the weld and are symmetrically distributed.
FIGS. 2 to 3 are microstructure morphologies of a welded joint and a heat-treated welded joint, respectively, wherein the microstructure composition and morphology feature difference of each region in the two groups of welded joints are large, a welded joint region is formed by long acicular alpha ' martensite penetrating through the whole columnar crystal, fine secondary alpha ' martensite is formed between the alpha ' martensite, continuous grain boundary distribution is found in a weld SEM image, and finally the weld region is in a basket-shaped morphology; the heat affected zone is formed by a small amount of initial alpha p Phase, grain boundary alpha gb Facies and widmannstatten structures.
The weld joint area of the welded joint after heat treatment consists of a large number of crystal boundaries alpha gb Initial alpha of phase, spheroidization p Phase, secondary angle of alpha s Phase and residual beta phase in a dotted distribution; thermal influenceZones almost exclusively of smaller size secondary alpha s Phase, small amount of initial alpha p The phase and the residual beta phase, and the Widmannstatten tissues disappear. The microscopic scales of the regions of the two groups of welding joints are obviously different, and the original beta-phase crystal boundary width in the welding seam region of the heat treatment welding joint is obviously narrower than that in the welding seam region of the welding joint.
Fig. 4 is a grain structure morphology and grain boundary orientation diagram of the weld zones of two sets of welded joints, wherein fig. 4a and 4b are the grain morphology and orientation diagram of the weld zone in as-welded joints, and fig. 4c and 4d are the grain morphology and orientation diagram of the weld zone of heat-treated welded joints. When the structure morphology is observed, two different types of original beta crystal boundaries, namely a continuous crystal boundary and a discontinuous crystal boundary, are found, wherein the discontinuous crystal boundary is generated and grown into a crystal boundary alpha only in the crystal boundary because the cooling speed of a welding seam area is slower and the generated supercooling degree is smaller in the furnace cooling process of a heat treatment state welding joint gb Because the growth speed is also slow, the nucleation driving force is not enough to form continuous grain boundaries; the continuous grain boundary is cooled from a beta phase high temperature region, the temperature is higher, and enough time and nucleation driving force are provided to ensure that alpha is initially generated p The phases nucleate and grow at grain boundaries and grow into continuous grain boundaries. And the lattice distortion is easy to accumulate at the position of the continuous grain boundary, so that the tensile strength can be improved, and therefore, the tensile strength of the heat treatment state welding seam without the continuous grain boundary is slightly lower, and the ductility and toughness are higher.
The different oriented tissues in the two groups of welding seams are mutually interwoven, and the capability of the lath with the anisotropic characteristic for hindering the crack propagation is stronger than that of the lath with the isotropic characteristic, so that the crack propagation is favorably inhibited, and the toughness of the material is improved. The comparison shows that the thickness of the acicular lamellar structure in the welding seam area is obviously increased after heat treatment, and the length-diameter ratio is reduced. The relevant literature indicates that the morphology of the lamellar phase affects the properties of the alloy, and that an increase in the thickness of the lamellar phase results in a decrease in tensile strength and hardness.
The green lines in fig. 4b and 4d represent the low angle grain boundaries of 2-15 °, and the black lines represent the high angle grain boundaries greater than 15 °, it can be seen from the figure that the proportion of the high angle grain boundaries in the heat-treated welding joint is slightly larger, and the statistical distribution result of the grain boundary orientation difference in the welding seam area of the two groups of welding joints is shown in fig. 5.
Calculation results show that the percentage of large-angle grain boundaries with the orientation difference between grains larger than 15 degrees in a welding seam area in the as-welded welding joint is about 81.78 percent, wherein the large-angle grain boundaries are about 70.67 percent distributed between 55.5 degrees and 66.5 degrees; the percentage of large angle grain boundaries with an orientation difference between grains of more than 15 degrees in the weld joint of the welded joint in the heat treatment state is 85.20 percent, wherein the percentage is about 74.27 percent distributed between 55.5 degrees and 66.5 degrees. The impact toughness is closely related to the inter-grain orientation difference distribution of the impact toughness, and the large-angle inter-grain orientation distribution can effectively prevent microcracks from expanding in grains; and the micro-cracks are expanded among the grains with small-angle orientation distribution, and only a slight deflection angle is needed to realize the micro-cracks. Thus, the above test results may indicate that the impact toughness values of the as-heat-treated weld joints may be slightly higher.
In order to determine the phase composition of the weld zones of the two sets of weld joints, the XRD test technique was used to analyze the weld phase composition, and the results are shown in FIG. 6, in which no body centered cubic lattice (BCC) or orthorhombic lattice structure, i.e., no alpha "or omega phase, was found in the weld zones of the two sets of weld joints. Meanwhile, according to the lattice constant ratio c/a and the combination of the microstructure analysis, the welded weld joint is mainly composed of alpha' martensite, main strong peaks are consistent and appear at 2 theta =40.5 degrees, and a small number of weak multi-angle alpha-phase diffraction peaks are also formed. The center angle position of the diffraction peak of the alpha phase in the as-heat treated weld was consistent with that of the alpha 'martensite in the as-welded weld, and a relatively sharp diffraction peak of the beta phase (110) was also found, and the diffraction peak was shifted to the right, because the non-equilibrium alpha' martensite was transformed into the beta phase during the heat treatment and remained during the subsequent furnace cooling.
The rightward shift of the diffraction peak shows that the lattice constant of the welded seam structure after heat treatment is reduced, the interplanar spacing is also reduced, and the alpha phase is nucleated at the beta phase crystal boundary and grows in a certain direction into the beta phase crystal along with the cooling from the beta phase, so that the solid solubility of the welded seam is increased by the heat treatment.
FIG. 7 shows the overall microhardness distribution of two groups of welded joints, and the overall microhardness distribution shows the distribution rule of a weld zone > a heat affected zone > a base material zone. The hardness distribution of the welded joint is closely related to the structure and phase content, and because the alpha 'martensite has high density of dislocation and twin crystal, so that a considerable amount of grain boundaries can be generated, the hardness of the welded joint is obviously higher than that of other phases, so that the hot affected zone and the parent metal zone of the welding joint with the highest alpha' martensite content in the two groups of welded joints have high hardness.
The hardness values of the corresponding areas of the two groups of welding joints are slightly different, and the integral microhardness value of the welding joint after heat treatment is lower than that of the welding joint in a welding state. In the process of loading the hardness load, the load can enable dislocation to slide to a grain boundary to cause dislocation plugging, the grain boundary can have obvious barrier effect on dislocation movement, the density of the dislocation plugging is increased along with the increase of the load, and along with the generation of stress concentration, when the concentrated stress can overcome the barrier effect of the grain boundary, the stress can be released to generate plastic deformation to cause dislocation movement of adjacent grain structures, and the grain boundary between the adjacent grain structures is intersected to harden the material.
Table 3 shows the room temperature tensile and impact properties of the TC4 titanium alloy base metal and the two sets of welded joints, the welded joints after heat treatment have slightly lower tensile strength, and the elongation after fracture and room temperature impact properties have higher values than those of the welded joints and the base metal.
TABLE 3 tensile and impact properties of base metal and welded joint
Fig. 8 shows SEM morphologies of fracture low power and high power of tensile test specimen in welded state and in heat treated state, respectively, where the two groups of welded joints both underwent a relatively significant necking phenomenon before fracture, and the tensile fracture of the welded joint was characterized by microporous polymerization, with deeper and larger pits and relatively significant tearing edges, which also indicates that the welded joint has less deformation during the stretching process, and is consistent with the test result of relatively low elongation after fracture. A large number of uniform and deep dimples surrounded by tearing lips can be observed on the fracture of the welded joint in a heat treatment state, the fracture has typical crystal-crossing fracture characteristics, is in micropore polymerization toughness fracture, has sufficient plastic deformation, and is consistent with a test result of high elongation after fracture.
After the welding joint is subjected to annealing heat treatment, the original widmannstatten structure in the welding joint can be converted into an alpha-phase basket structure, the grain boundary is broken or even disappears, the barrier effect of the grain boundary on sliding is weakened, the sliding distance is increased, and the plasticity is obviously improved; at the same time, the higher strength α' martensite is transformed into a coarsened α + β phase, so that the tensile strength is reduced. In addition, the thick-thin lamellar structure interwoven in a single alpha cluster causes the crack propagation direction to deviate, has obvious barrier effect on the crack propagation, and is beneficial to improving the plasticity of the welding seam.
FIG. 9 shows the macro and micro structure shapes of the room temperature impact specimen at the center of the weld after fracture. FIG. 9a shows a welded joint impact specimen fracture macro morphology with a river-like pattern being evident, belonging to cleavage fracture and poor toughness; and FIG. 9b shows the macroscopic morphology of the fracture of the impact sample of the welded joint in a heat treatment state, and the fracture characteristics of a shear lip and toughness are found, so that the welded joint has better impact toughness.
FIGS. 9c and 9d are microstructure morphologies of the characteristic region of the as-welded and heat-treated impact fracture of the joint, respectively. The fracture in the initiation region of the specimen in FIG. 9c consists primarily of tearing dimples, and the fracture in the impact specimen of the selected area high power microstructure in FIG. 9c consists of a large number of small dimples; the fracture in the fracture initiation region of the test sample in fig. 9d is entirely composed of shear dimples, the fracture initiation region of the impact fracture of the welded joint in the heat treatment state has a larger width than that of the fracture initiation region of the impact fracture of the welded joint in the welding state, and the fracture dimples of the impact test sample with the high-power microstructure in the selected region in fig. 9d are larger and more uniformly distributed.
Impact toughness is closely related to the thickness of the lamellar structure. The weld joint structure after annealing treatment is alpha p And alpha s The photo layer structure is mainly, and a small amount of residual beta phase and grain boundary alpha distributed in a point shape exist between the sheet layers gb And (4) phase(s). During the impact process of a sample, the crack propagation directions of the coarse-fine lamella layer and the alpha/beta interface are easy to deflect, so that the propagation path is bent; at the same time, alpha p /α s The existence of residual beta phase between interfaces can ensure that the two sides of the grain boundary can still carry out sliding transmission under the condition of lower geometric harmony factors. In addition, when the welding joint is heated to 990 ℃ and is kept warm for 2 hours, the formation and the decomposition of metastable phase are caused in the subsequent slow furnace cooling process, a large amount of metastable phase is taken as the mass point of spheroidized alpha phase nucleation, thereby greatly improving the spheroidized alpha phase nucleation rate and producing a large amount of fine secondary alpha phase s Precipitation of phases cuts off nascent alpha p And phase laths, which reduce the length-diameter ratio of alpha laths. At the same time, secondary of alpha s The increased phase content results in more divisions within the grain that reduce the frequency of cross-slip of dislocations and increase the holding capacity of the in-grain dislocations, thereby improving the impact toughness of the welded joint.
Claims (6)
1. The heat treatment method for improving the plasticity and toughness of the titanium alloy welded joint is characterized by comprising the following steps of:
s100, carrying out laser filler wire welding on a test plate to be welded;
s200, heating the test plate subjected to laser wire filling welding in a vacuum environment at 800-1200 ℃ for a period of time, and then cooling the test plate to room temperature along with a furnace.
2. The heat treatment method for improving the ductility and toughness of the titanium alloy welded joint according to claim 1, wherein in S100, the method specifically comprises the following steps:
s110, performing groove machining on a test plate to be welded, performing pretreatment after the machining is finished, and then clamping;
s120, under the protection of inert protective gas, filling the groove of the to-be-welded test plate in a laser beam circular swing mode by adopting a laser wire filling welding method;
and S130, using single laser to perform priming, and filling 6 filling layers in total to complete welding.
3. The heat treatment method for improving the ductility and toughness of the titanium alloy welded joint according to claim 2, wherein in S110, the groove machining specifically comprises: and processing the test plate to be welded into a Y-shaped groove.
4. The heat treatment method for improving the toughness of a titanium alloy welded joint, as recited in claim 3, wherein in S120, the size of the test plate to be welded is 400mm x 200mm x 20mm TC4 titanium alloy plate, the chemical composition is 6.30% Al, 4.11% V, 0.018% Fe, 0.024% C, 0.007% N, 0.001% H, 0.14% O and the balance Ti; the flux-cored wire adopted in the laser wire-filling welding method is a Ti-Al-V metal powder-cored flux-cored wire, and the deposited metal of the flux-cored wire comprises the following chemical components: 6.10% Al, 4.15% by weight, 0.04% Fe, 0.012% by weight C, 0.006% N, 0.001% by weight H, 0.02% O and the balance Ti.
5. The heat treatment method for improving the ductility and toughness of the titanium alloy welded joint as claimed in claim 1, wherein the heating temperature in the vacuum environment in S200 is 990 ℃.
6. The heat treatment method for improving the ductility and toughness of the titanium alloy welded joint according to claim 5, wherein in S200, the heating time in the vacuum environment is 2 hours.
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