Welding method for reducing welding cracks of Ti2AlNb alloy

Abstract

The invention provides a welding method for reducing welding cracks of a Ti2AlNb alloy. The welding method comprises the following steps: preheating the Ti2AlNb alloy to be welded before welding; the preheated Ti2AlNb alloy is subjected to wire filling welding; and after welding is completed, a welding part is rapidly subjected to postweld heat treatment, and the Ti2AlNb alloy welding part without welding cracks is obtained. According to the Ti2AlNb alloy welding method, the cooling rate after welding can be effectively reduced through preheating treatment before welding, thermal stress accumulation of a welding joint is reduced, an intergranular liquid film is prevented from being torn due to the stress effect after welding, and the overall quality of the Ti2AlNb alloy welding joint is greatly improved; according to the method, ultrahigh-frequency pulse welding and the wire filling technology form a synergistic effect, ultrahigh-frequency pulses can precisely refine the structure of a weld joint fusion area, continuous distribution of intergranular finally-solidified residual eutectic liquid phases at the grain boundary is avoided, the wire filling technology can effectively compensate the shrinkage amount in the welding process, and the welding quality is improved. And therefore, the stress concentration phenomenon of the welding joint is avoided, initiation and extension of welding cracks are inhibited, and the quality stability of the Ti2AlNb alloy welding joint is improved.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more specifically, to a welding method for reducing welding cracks in Ti2AlNb alloys. Background Technology

[0002] Ti2AlNb alloy is an intermetallic compound with a typical microstructure consisting of ordered orthorhombic O phase, body-centered cubic B2 phase, and close-packed hexagonal α2 phase. This alloy possesses excellent room-temperature and high-temperature mechanical properties, good corrosion resistance, and low density, making it a promising candidate for applications in the aerospace field. It is expected to replace nickel-based superalloys and become a crucial material for manufacturing key components such as aero-engine casings.

[0003] Although the combination of phases in Ti2AlNb alloys endows them with excellent comprehensive properties, their processing and manufacturing, especially in welding, still present significant challenges. Welding, as one of the key processes in forming complex components, is prone to causing weld cracks and high residual stress in Ti2AlNb alloys due to the high strength and limited plasticity of the intermetallic compounds themselves, often requiring additional process control measures. Therefore, developing an economical, efficient, and flexible welding process is particularly important to address the problems of cracking and stress concentration that easily occur during the welding of this type of alloy.

[0004] During welding, Ti2AlNb alloys are prone to defects such as weld cracks, porosity, and tungsten inclusions, which severely restrict their engineering applications. Among these, weld cracks are primarily crystallization cracks. Their formation mechanism can be attributed to the enrichment of solute atoms (such as Al) into the intergranular residual liquid phase during molten pool solidification, forming a low-melting-point eutectic liquid phase that eventually solidifies at the grain boundaries, causing compositional segregation. As the temperature further decreases, the shrinkage strain of the weld joint acts on the brittle intergranular liquid film, causing it to tear and thus forming crystallization cracks.

[0005] In summary, hot cracking is highly likely to occur in Ti2AlNb alloys during welding, which is a core challenge in the welding application of this material. The root cause lies in the rupture of the low-melting-point eutectic liquid film formed at the grain boundaries under stress. Therefore, developing a welding process that can effectively suppress welding cracks in Ti2AlNb alloys has significant engineering value and application prospects. Summary of the Invention

[0006] To address the problems in the prior art, the purpose of this invention is to provide a welding method that reduces welding cracks in Ti2AlNb alloys, thereby solving the problem of reduced mechanical properties of welded joints due to defects such as welding cracks generated during the welding process of Ti2AlNb alloys.

[0007] The welding method for reducing welding cracks in Ti2AlNb alloy according to the present invention includes the following steps: Step S1: Preheat the Ti2AlNb alloy to be welded before welding; Step S2: Perform filler wire welding on the preheated Ti2AlNb alloy; Step S3: After welding, the welded parts are quickly subjected to post-weld heat treatment to obtain Ti2AlNb alloy welded parts without welding cracks.

[0008] Preferably, the preheating treatment in step S1 is achieved using a constant temperature heating platform, with the preheating temperature controlled at 300~400℃ and the preheating holding time being 0.2~0.5h.

[0009] Preferably, during the preheating process, the temperature of the Ti2AlNb alloy welding area is uniformly distributed, and the maximum temperature difference within the area does not exceed ±10℃.

[0010] Preferably, the filler wire welding in step S2 adopts an ultra-high frequency pulsed AC arc welding method, and the welding current waveform is set to a sine wave.

[0011] Preferably, the pulse frequency of the ultra-high frequency pulsed AC arc welding is 10000-17500Hz, and the welding AC frequency is 10-100Hz.

[0012] Preferably, the peak current of the ultra-high frequency pulsed AC arc welding is 90-180A, and the welding base current is 60A smaller than the welding peak current.

[0013] Preferably, the filler material used in the filler welding in step S2 is consistent with the element types and contents of the Ti2AlNb alloy being welded.

[0014] Preferably, before step S2, a beveling pretreatment process is also included: a 60° V-groove is machined in the Ti2AlNb alloy welding area using wire cutting technology, and the V-groove and surrounding area are pickled and polished.

[0015] Preferably, the post-weld heat treatment in step S3 is a solution treatment plus aging treatment, wherein the solution treatment temperature is 850~900℃ and the holding time is 1~2h, and the aging treatment temperature is 800~850℃ and the holding time is 6~12h.

[0016] Preferably, the equipment corresponding to the ultra-high frequency pulsed AC arc welding includes, but is not limited to, tungsten inert gas welding machine, electron beam welding machine and laser welding machine.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. In this invention, the preheating treatment before welding can effectively slow down the cooling rate after welding, reduce the accumulation of thermal stress in the welded joint, prevent the intergranular liquid film from tearing due to stress after welding, and greatly improve the overall quality of Ti2AlNb alloy welded joints. 2. In this invention, the ultra-high frequency pulse welding and the filler wire process work synergistically. The ultra-high frequency pulse can precisely refine the microstructure of the weld fusion zone and prevent the residual eutectic liquid phase that is finally solidified between grains from forming a continuous distribution at the grain boundaries. The filler wire process can effectively compensate for the shrinkage during the welding process, thereby avoiding stress concentration in the weld joint. Under the dual action, the initiation and propagation of welding cracks can be effectively suppressed, and the quality stability of Ti2AlNb alloy weld joints can be significantly improved. 3. The targeted heat treatment after welding in this invention can further and thoroughly eliminate welding residual stress, prevent the generation of subsequent cold cracks from the root, and at the same time, it can accurately control the phase composition and phase ratio of the fusion zone, significantly enhance the mechanical properties of the welded joint, and ensure the service reliability of the welded parts. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort. Other features, objects, and advantages of the present invention will become more apparent by reading the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a comparison of the welding characteristics of the Ti2AlNb alloy before and after using the method of the present invention during welding in Example 1.

[0019] Figure 2 A flowchart of the welding method for reducing welding cracks in Ti2AlNb alloy in this invention is provided. Detailed Implementation

[0020] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0021] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0022] The technical solution of the present invention will be described in detail below with reference to specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0023] The technical solutions of the present invention and how they solve the above-mentioned technical problems will be described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0024] Example 1 In this embodiment, Ti-24Al-25Nb-0.5Mo alloy (atomic percentage) was selected as the base material for welding, and argon arc welding was used for welding.

[0025] First, a 60° V-groove was machined on the alloy surface using wire cutting technology to form the weld bevel, and the bevel area was then pickled and ground. Next, the base material was placed on a constant-temperature heating platform for preheating at 400℃ for 0.3 hours. Welding was performed using ultra-high frequency pulsed AC tungsten inert gas welding (TIG) with filler wire welding. The current waveform was sinusoidal, with a pulse frequency of 15000Hz, an AC frequency of 10Hz, a base current of 60A, and a peak current of 120A. The welding wire composition was consistent with the base material, both being Ti-24Al-25Nb-0.5Mo alloy. After welding, the welded parts were immediately transferred to a heat treatment furnace for solution treatment and aging. The solution treatment involved holding at 850℃ for 1 hour, followed by aging at 800℃ for 12 hours.

[0026] After all welding processes were completed, the welded parts were left to stand for 48 hours, and X-ray inspection was used to examine the welded area. The results showed that the weld formation was regular and good, no welding cracks were detected, and the welding quality met the usage requirements.

[0027] Example 2 In this embodiment, Ti-22Al-25Nb alloy (atomic percentage) was selected as the base material for welding, and argon arc welding was used for welding.

[0028] First, a 60° V-groove was machined on the alloy surface using wire cutting, followed by pickling and grinding of the grooved area. The sample was then placed on a constant-temperature heating platform and preheated at 300°C for 0.5 hours. The welding process employed ultra-high frequency pulsed AC tungsten inert gas welding with filler wire welding. The current waveform was sinusoidal, with a pulse frequency of 10000Hz, an AC frequency of 20Hz, a base current of 90A, and a peak current of 150A. The welding wire composition was identical to the base material, being a Ti-22Al-25Nb alloy. Immediately after welding, heat treatment was performed: solution treatment at 900°C for 1.5 hours, followed by aging at 820°C for 8 hours.

[0029] After all welding processes were completed, the welded parts were left to stand for 48 hours, and X-ray inspection was used to examine the welded area. The results showed that the weld formation was regular and good, no welding cracks were detected, and the welding quality met the usage requirements.

[0030] Example 3 In this embodiment, Ti-23Al-27Nb alloy (atomic percentage) was selected as the base material for welding, and argon arc welding was used for welding.

[0031] First, a 60° V-groove was machined using wire EDM, followed by pickling and grinding of the groove area. Then, the base material to be welded was placed on a constant-temperature heating platform and preheated at 350°C for 0.4 hours. Welding was performed using ultra-high frequency pulsed AC tungsten inert gas welding (TIG) with filler wire welding. The current waveform was sinusoidal, with a pulse frequency of 13000Hz, an AC frequency of 40Hz, a base current of 120A, and a peak current of 180A. The welding wire composition was consistent with the base material, being a Ti-23Al-27Nb alloy. Immediately after welding, heat treatment was performed: solution treatment at 890°C for 2 hours, followed by aging at 840°C for 6 hours.

[0032] After all welding processes were completed, the welded parts were left to stand for 48 hours, and X-ray inspection was used to examine the welded area. The results showed that the weld formation was regular and good, no welding cracks were detected, and the welding quality met the usage requirements.

[0033] Comparative Example 1 The alloy composition of the base material and welding wire in this comparative example is the same as that in Example 1. The welding process is basically the same as that in Example 1, except that no preheating treatment is performed before welding.

[0034] After the welding process was completed, the welded parts were placed for 48 hours and X-ray inspection was performed on the welded area. It was found that there were obvious welding cracks in the welded area, which could not meet the service performance requirements.

[0035] Analysis revealed that insufficient preheating led to significant stress concentration during welding, causing the intergranular liquid film to tear during the later stages of solidification, thus initiating cracks. Therefore, for Ti2AlNb alloys, insufficient preheating before welding will result in cracks due to liquid film tearing.

[0036] Comparative Example 2 The alloy composition of the base material in this comparative example is the same as that in Example 2. The welding process is basically the same as that in Example 2, except that the filler wire welding process was not used.

[0037] After the welding process was completed, the welded parts were placed for 48 hours and X-ray inspection was performed on the welded area. It was found that there were obvious welding cracks in the welded area, which could not meet the service performance requirements.

[0038] Analysis showed that the lack of filler wire welding resulted in insufficient liquid metal in the fusion zone for feeding, causing the intergranular liquid film formed in the weld to crack under the stress of solidification shrinkage. Therefore, in the welding process of Ti2AlNb alloy, if filler wire is not used, insufficient feeding will lead to welding cracks.

[0039] Comparative Example 3 The alloy composition of the base material and welding wire in this comparative example is the same as that in Example 3. The welding process is basically the same as that in Example 3, except that no post-weld heat treatment is performed on the welded parts after welding.

[0040] After the welding process was completed, the welded parts were placed for 48 hours and the welded area was inspected using X-ray flaw detection. It was found that the welded area was well formed and no welding cracks were detected. However, its tensile strength and elongation decreased by 24% and 60% respectively compared with the welded parts in Example 1 and Example 2.

[0041] Analysis revealed that the lack of post-weld heat treatment resulted in excessively rapid weld cooling, leaving a large amount of residual eutectic structure. Under external forces, microcracks easily initiate and propagate along brittle phase interfaces, severely deteriorating the mechanical properties of the welded joint. Therefore, while the absence of heat treatment after welding Ti2AlNb alloys can prevent macroscopic cracks, it will lead to a significant decrease in the mechanical properties of the joint.

[0042] The various embodiments described in this specification are presented in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0043] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A welding method for reducing welding cracks in Ti2AlNb alloys, characterized in that, Includes the following steps: Step S1: Preheat the Ti2AlNb alloy to be welded before welding; Step S2: Perform filler wire welding on the preheated Ti2AlNb alloy; Step S3: After welding, the welded parts are quickly subjected to post-weld heat treatment to obtain Ti2AlNb alloy welded parts without welding cracks.

2. The welding method for reducing welding cracks in Ti2AlNb alloy according to claim 1, characterized in that, The preheating process in step S1 is achieved using a constant temperature heating platform, with the preheating temperature controlled at 300~400℃ and the preheating holding time being 0.2~0.5h.

3. The welding method for reducing welding cracks in Ti2AlNb alloy according to claim 2, characterized in that, During the preheating process, the temperature of the Ti2AlNb alloy welding area is uniformly distributed, and the maximum temperature difference within the area does not exceed ±10℃.

4. The welding method for reducing welding cracks in Ti2AlNb alloy according to claim 1, characterized in that, The filler wire welding in step S2 adopts an ultra-high frequency pulsed AC arc welding method, and the welding current waveform is set to a sine wave.

5. The welding method for reducing welding cracks in Ti2AlNb alloy according to claim 4, characterized in that, The pulse frequency of the ultra-high frequency pulsed AC arc welding is 10000~17500Hz, and the welding AC frequency is 10~100Hz.

6. The welding method for reducing welding cracks in Ti2AlNb alloy according to claim 4, characterized in that, The peak current of the ultra-high frequency pulsed AC arc welding is 90-180A, and the welding base current is 60A less than the welding peak current.

7. The welding method for reducing welding cracks in Ti2AlNb alloy according to claim 1, characterized in that, The filler material used in the filler welding in step S2 is consistent with the element types and contents of the Ti2AlNb alloy being welded.

8. The welding method for reducing welding cracks in Ti2AlNb alloy according to claim 1, characterized in that, Before step S2, a beveling pretreatment process is also included: a 60° V-groove is machined in the Ti2AlNb alloy welding area using wire cutting technology, and the V-groove and surrounding area are pickled and polished.

9. The welding method for reducing welding cracks in Ti2AlNb alloy according to claim 1, characterized in that, The post-weld heat treatment in step S3 is a combination of solution treatment and aging treatment, wherein the solution treatment temperature is 850~900℃ and the holding time is 1~2h, and the aging treatment temperature is 800~850℃ and the holding time is 6~12h.

10. The welding method for reducing welding cracks in Ti2AlNb alloy according to claim 4, characterized in that, The equipment corresponding to the ultra-high frequency pulsed AC arc welding includes, but is not limited to, tungsten inert gas welding machines, electron beam welding machines, and laser welding machines.

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