Thick-wall titanium alloy electron beam welding joint structure refining method and application

Abstract

The invention discloses a thick-wall titanium alloy electron beam welding joint structure refining method and application. The invention belongs to the field of thick-wall titanium alloy welding. The method aims at solving the technical problem that an existing thick-wall titanium alloy electron beam welding joint is not high in comprehensive performance. The method comprises the following steps: taking a lamellar Ti-6Al-4V-x-y alloy as a welding filler, placing the lamellar Ti-6Al-4V-x-y alloy between plates to be welded, and realizing connection by adopting electron beam welding; wherein x is Cu, Fe, Ni, Mo or Be, y is Si, Y or B, x is equal to 1-10 wt.%, and y is equal to 0.1-1 wt.%. According to the method, the structure of the welded joint is obviously refined, and the comprehensive performance of the welded joint is improved. The obtained joint is applied to the fields of aerospace, weaponry, ocean engineering and the like.

Description

Technical Field

[0001] The invention belongs to the field of thick-wall titanium alloy welding, and in particular relates to a method and application for microstructure refinement of thick-wall titanium alloy electron beam welded joints. Background Art

[0002] Titanium alloys are widely used in aerospace, weapons and equipment, marine engineering and other fields due to their low density, high specific strength, excellent corrosion resistance and good welding performance. In aviation manufacturing, in order to ensure the strength and service life of components, important load-bearing structures often use titanium alloys with a thickness of 10 to 100 mm and are connected by welding technology. At present, the commonly used welding methods of titanium alloys include tungsten inert gas shielded welding (TIG), metal inert gas shielded welding (MIG), laser welding (LBW), plasma arc welding (PAW) and electron beam welding (EBW). TIG welding has difficulty in controlling the weld penetration, large groove requirements and significant deformation, and low welding efficiency. MIG welding often causes spatter, which affects the weld formation and protection effect. Both welding methods require inert gas protection and are easily doped with air, thereby forming oxides and nitrides at high temperatures, reducing the performance of the weld. In contrast, LBW, PAW and EBW, as high-energy beam welding technologies, have high energy density and fast welding speed, but LBW and PAW still require inert gas protection, which may lead to defects such as pores, hydrogen embrittlement and cracks. EBW welding has the advantages of high energy density, controllable beam, stable process, high efficiency, etc., and has narrow weld, large aspect ratio and small deformation, which is very suitable for welding thick-walled titanium alloy components.

[0003] However, the inherent high temperature gradient and high cooling rate of electron beam welding, as well as the small solidification temperature range of titanium alloys (for example, the solidification temperature range of Ti-6Al-4V is less than 5°C), result in the formation of coarse columnar β grains, needle-shaped martensite α′ phase, large α / α′ clusters and continuous grain boundary α / α′ phase in the welded joint, resulting in a significant decrease in performance. Coarse columnar β grains cause anisotropy of properties and low fracture toughness in the weld zone, thus affecting the fracture mode and fatigue resistance of the welded joint. Coarse columnar β grains will produce larger α / α′ clusters, further reducing the strength of the alloy, while the continuously distributed grain boundary α / α′ phase seriously affects the plasticity of the welded joint. Therefore, how to obtain fine structure becomes the key to solving the problem of uniformity of welded joints. Summary of the invention

[0004] The purpose of the present invention is to solve the technical problem that the comprehensive performance of existing thick-walled titanium alloy electron beam welded joints is not high, and to provide a method and application for microstructure refinement of thick-walled titanium alloy electron beam welded joints.

[0005] One of the purposes of the present invention is to provide a method for microstructure refinement of thick-walled titanium alloy electron beam welded joints, the method being carried out in the following steps:

[0006] A thin sheet of Ti-6Al-4V-xy alloy is used as a welding filler, which is placed between the plates to be welded and connected by electron beam welding; wherein x is Cu, Fe, Ni, Mo or Be, y is Si, Y or B, x=1-10wt.%, y=0.1-1wt.%.

[0007] It is further defined that the sheet thickness is 0.5-1.5 mm.

[0008] It is further defined that the Ti-6Al-4V-xy alloy is formed by vacuum non-consumable melting.

[0009] Further defined, the smelting process parameters are: voltage is 10-30V, current is 300-500A.

[0010] The welding process parameters are further defined as follows: acceleration voltage of 50-70 kV, beam current of 60-100 mA, focusing current of 950-1000 mA, welding speed of 300-500 mm / min, and chamber vacuum of less than 5×10 -2 Pa.

[0011] A second object of the present invention is to provide a joint obtained by the above method.

[0012] It is further defined that the average size of β grains in the center of the joint weld is less than 200 μm.

[0013] It is further defined that the average size of β grains in the center of the joint weld is less than 100 μm.

[0014] The third object of the present invention is to provide a joint obtained by the above method for use in the fields of aerospace, weapon equipment and marine engineering.

[0015] A fourth object of the present invention is to provide an application of the above method in electron beam welding of thick-walled titanium alloy.

[0016] Compared with the prior art, the present invention has the following significant effects:

[0017] The present invention proposes a method for refining the structure of thick-walled titanium alloy electron beam welded joints, aiming to improve the microstructure of titanium alloy welded joints. The method uses Ti-6Al-4V (all mass ratios in this patent) alloy plate as a base material, and prepares an alloy with a composition of Ti-6Al-4V-x (Cu, Fe, Ni, Mo, Be) -y (Si, Y, B) by vacuum non-consumable melting technology, wherein the mass fraction of x is 1-10wt.%, and the mass fraction of y is 0.1-1wt.%. The alloy is prepared into a thin sheet as a welding filler by mechanical processing and applied to the welding gap of flat plate butt joints. Finally, a high-quality welded joint is obtained by electron beam welding technology. The key to the method is to effectively increase the component supercooling during the electron beam welding process by introducing the above elements into the weld, promote grain nucleation, and then lead to grain refinement. At the same time, compounds such as TiFe, Ti2Cu, Ti2Ni, Y2O3, TiB, etc. are formed during the solidification process and are evenly distributed at the β grain boundary, thereby inhibiting grain growth. These compounds can not only inhibit grain growth, but also serve as heterogeneous nucleation cores of α / α′ phases, significantly reducing the generation of α / α′ clusters and grain boundary α / α′ phases, thereby promoting the formation of a finer and more evenly distributed α / α′ phase structure. The present invention significantly refines the weld joint structure and improves the comprehensive performance of the weld joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of electron beam welding of thick-walled titanium alloy according to the present invention;

[0019] Figure 2 Schematic diagram of the thinning mechanism of the thick-walled titanium alloy electron beam welded joint of the present invention;

[0020] Figure 3 The microstructure of the weld center of the weld joint obtained in Example 1;

[0021] Figure 4 The microstructure of the weld center of the weld joint obtained in Example 2;

[0022] Figure 5 The microstructure of the weld center of the weld joint obtained in Example 3;

[0023] Figure 6 The microstructure of the weld center of the weld joint obtained in Comparative Example 1;

[0024] Figure 7 The microstructure of the weld center of the weld joint obtained in Comparative Example 2;

[0025] Figure 8 This is the microstructure of the weld center of the weld joint obtained in Comparative Example 3. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0027] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained through commercial channels by those skilled in the art.

[0028] The terms "comprising," "including," "having," "containing," or any other variations thereof, as used in the following examples, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus comprising the listed elements is not necessarily limited to only those elements, but may include other elements not expressly listed or inherent to such composition, step, method, article, or apparatus.

[0029] The "one embodiment" or "embodiment" of the present invention refers to a specific feature, structure or characteristic that can be included in at least one implementation of the present invention. The "in one embodiment" that appears in different places in this specification does not refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.

[0030] The endpoints and any values ​​of the ranges disclosed in the invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article.

[0031] Embodiment 1: The method for microstructure refinement of thick-walled titanium alloy electron beam welded joints of this embodiment is carried out in the following steps:

[0032] Step 1: Use a vacuum non-consumable melting furnace to prepare a Ti-6Al-4V-5Cu-0.5Si alloy ingot. The melting process parameters used are: voltage of 20V, current of 400A, melting 4 times, each melting for 2 minutes, to ensure uniform composition.

[0033] Step 2: The Ti-6Al-4V-5Cu-0.5Si alloy ingot is machined into a sheet of 100 mm × 15 mm × 1 mm, and the surface is ensured to be free of defects and oxide scale.

[0034] Step 3: First, grind the Ti-6Al-4V alloy sheet of 100mm×50mm×15mm to ensure that there is no oxide scale on the surface; then place the prepared Ti-6Al-4V-5Cu-0.5Si alloy sheet between two 100mm×50mm×15mm plates; finally, use electron beam welding equipment to weld to obtain high-quality welded joints. The welding process parameters used are: acceleration voltage of 60kV, beam current of 80mA, focusing current of 980mA, welding speed of 400mm / min, and chamber vacuum of less than 5×10 -2 Pa.

[0035] The microstructure of the weld center was observed using a scanning electron microscope. Figure 3 As shown, the average size of the β grains in the center of the weld with Ti-6Al-4V-5Cu-0.5Si alloy filler is 162μm, which is about 59% lower than the microstructure in the center of the weld without filler, and the grain refinement is significant.

[0036] Embodiment 2: The method for microstructure refinement of thick-walled titanium alloy electron beam welded joints of this embodiment is carried out in the following steps:

[0037] Step 1: Prepare Ti-6Al-4V-5Cu-0.5Y alloy ingot by smelting in a vacuum non-consumable smelting furnace. The smelting process parameters used are: voltage of 20V, current of 400A, smelting 4 times, each smelting for 2 minutes, to ensure uniform composition.

[0038] Step 2: The Ti-6Al-4V-5Cu-0.5Y alloy ingot is machined into a sheet of 100 mm × 15 mm × 1 mm, and the surface is ensured to be free of defects and oxide scale.

[0039] Step 3: First, grind the Ti-6Al-4V alloy sheet of 100mm×50mm×15mm to ensure that there is no oxide scale on the surface; then place the prepared Ti-6Al-4V-5Cu-0.5Y alloy sheet between two 100mm×50mm×15mm plates; finally, use electron beam welding equipment to weld to obtain high-quality welded joints. The welding process parameters used are: acceleration voltage of 60kV, beam current of 80mA, focusing current of 980mA, welding speed of 400mm / min, and chamber vacuum of less than 5×10 -2 Pa.

[0040] The microstructure of the weld center was observed using a scanning electron microscope. Figure 4Shown is the microstructure of the weld center with Ti-6Al-4V-5Cu-0.5Y alloy filler. Compared with the microstructure of the weld center without filler, the average size of the β grains in the weld center with Ti-6Al-4V-5Cu-0.5Y alloy filler is 152μm, which is reduced by about 61%, and the grain refinement is significant.

[0041] Embodiment 3: The method for microstructure refinement of thick-walled titanium alloy electron beam welded joints of this embodiment is carried out in the following steps:

[0042] Step 1: Prepare Ti-6Al-4V-5Cu-0.5B alloy ingot by smelting in a vacuum non-consumable smelting furnace. The smelting process parameters used are: voltage of 20V, current of 400A, smelting 4 times, each smelting for 2 minutes, to ensure uniform composition.

[0043] Step 2: The Ti-6Al-4V-5Cu-0.5B alloy ingot is machined into a sheet of 100 mm × 15 mm × 1 mm, and the surface is ensured to be free of defects and oxide scale.

[0044] Step 3: First, grind the Ti-6Al-4V alloy sheet of 100mm×50mm×15mm to ensure that there is no oxide scale on the surface; then place the prepared Ti-6Al-4V-5Cu-0.5B alloy sheet between two 100mm×50mm×15mm plates; finally, use electron beam welding equipment to weld to obtain high-quality welded joints. The welding process parameters used are: acceleration voltage of 60kV, beam current of 80mA, focusing current of 980mA, welding speed of 400mm / min, and chamber vacuum of less than 5×10 -2 Pa.

[0045] The microstructure of the weld center was observed using a scanning electron microscope. Figure 5 The average size of the β grains in the center of the weld with Ti-6Al-4V-5Cu-0.5B alloy filler is 64μm, which is about 84% lower than the microstructure in the center of the weld without filler, and the grain refinement is significant.

[0046] Comparative Example 1:

[0047] The Ti-6Al-4V alloy plate with a size of 100 mm × 50 mm × 15 mm was polished to ensure that there was no oxide scale on the surface; then, the two plates were butt-jointed along the 100 mm edge; finally, electron beam welding equipment was used to weld the welded joint with excellent quality as a control test. The welding process parameters used were: acceleration voltage of 60 kV, beam current of 80 mA, focusing current of 980 mA, welding speed of 400 mm / min, and chamber vacuum of less than 5×10-2 Pa.

[0048] The microstructure of the weld center was observed using a scanning electron microscope. Figure 6 As shown, the average size of the β grains in the center of the weld without filler is 394μm.

[0049] Comparative Example 2:

[0050] Step 1: Prepare Ti-6Al-4V-5Cu alloy ingot by smelting in a vacuum non-consumable smelting furnace. The smelting process parameters used are: voltage of 20V, current of 400A, smelting 4 times, each smelting for 2 minutes, to ensure uniform composition.

[0051] Step 2: The Ti-6Al-4V-5Cu alloy ingot is machined into a sheet of 100 mm × 15 mm × 1 mm, and the surface is ensured to be free of defects and oxide scale.

[0052] Step 3: First, grind the Ti-6Al-4V alloy sheet of 100mm×50mm×15mm to ensure that there is no oxide scale on the surface; then place the prepared Ti-6Al-4V-5Cu alloy sheet between two 100mm×50mm×15mm plates; finally, use electron beam welding equipment to weld to obtain high-quality welded joints. The welding process parameters used are: acceleration voltage of 60kV, beam current of 80mA, focusing current of 980mA, welding speed of 400mm / min, and chamber vacuum of less than 5×10 -2 Pa.

[0053] The microstructure of the weld center was observed using a scanning electron microscope. Figure 7 As shown, the average size of the β grains in the center of the weld with Ti-6Al-4V-5Cu alloy filler is 193 μm, which is about 51% lower than the microstructure in the center of the weld without filler, and the grain refinement is significant.

[0054] Comparative Example 3:

[0055] Step 1: Use a vacuum non-consumable melting furnace to prepare Ti-6Al-4V-5Ni alloy ingots. The melting process parameters used are: voltage of 20V, current of 400A, melting 4 times, each melting for 2 minutes, to ensure uniform composition.

[0056] Step 2: The Ti-6Al-4V-5Ni alloy ingot is machined into a sheet of 100 mm × 15 mm × 1 mm, and the surface is ensured to be free of defects and oxide scale.

[0057] Step 3: First, grind the Ti-6Al-4V alloy plate of 100mm×50mm×15mm to ensure that there is no oxide scale on the surface; then place the prepared Ti-6Al-4V-5Ni alloy sheet between two 100mm×50mm×15mm plates; finally, use electron beam welding equipment to weld to obtain high-quality welded joints. The welding process parameters used are: acceleration voltage of 60kV, beam current of 80mA, focusing current of 980mA, welding speed of 400mm / min, and chamber vacuum of less than 5×10 -2 Pa.

[0058] The microstructure of the weld center was observed using a scanning electron microscope. Figure 8 As shown, the average size of the β grains in the center of the weld with Ti-6Al-4V-5Ni alloy filler is 266μm, which is about 32% lower than the microstructure in the center of the weld without filler, and the grain refinement is significant.

[0059] Table 1 Mechanical properties of welded joints

[0060]

[0061] The tensile properties of the base material and different embodiments and comparative examples were tested. It can be found that the welding coefficients (defined as the ratio of the tensile strength of the welded joint to the tensile strength of the base material) of the welded joints with Ti-6Al-4V-5Cu-0.5Si (Example 1), Ti-6Al-4V-5Cu-0.5Y (Example 2) and Ti-6Al-4V-5Cu-0.5B (Example 3) fillers were 1.10, 1.06 and 1.09, respectively, all higher than 1.0, indicating that the strength of the welded joint is better than that of the base material. In the tensile test, the final fracture positions of these welded joints all occurred in the base material, further indicating that the welded joints have excellent comprehensive properties and high welding quality.

[0062] In contrast, the welded joint without filler (Comparative Example 1) eventually broke in the fusion zone, indicating that the overall performance of the weld is lower than that of the parent material. Although the welded joint with Ti-6Al-4V-5Cu (Comparative Example 2) broke in the parent material, the welding coefficient was 0.97, which was lower than 1.0, indicating that the overall performance of the weld was still slightly inferior to that of the parent material. The welded joint with Ti-6Al-4V-5Ni (Comparative Example 3) had a welding coefficient of 1.04, and the fracture also occurred in the parent material, indicating that the overall performance of the welded joint was better than that of the parent material.

[0063] It can be seen that in the electron beam welding process of thick plate titanium alloy, the reasonable addition of fillers (especially fillers containing Si, Y or B) can significantly improve the comprehensive performance of the welded joint, making its strength and quality better than the base material and meeting the needs of high-performance applications.

[0064] The above are only preferred specific embodiments of the present invention, which are all different implementations based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for microstructure refinement of thick-walled titanium alloy electron beam welded joints, characterized in that: The method: A thin sheet of Ti-6Al-4V-xy alloy is used as a welding filler, which is placed between the plates to be welded and connected by electron beam welding; wherein x is Cu, Fe, Ni, Mo or Be, y is Si, Y or B, x=1-10wt.%, y=0.1-1wt.%.

2. The method according to claim 1, characterized in that The thickness of the sheet is 0.5-1.5 mm.

3. The method according to claim 1, characterized in that Ti-6Al-4V-xy alloy is made by vacuum non-consumable melting.

4. The method according to claim 3, characterized in that The smelting process parameters are: voltage is 10-30V, current is 300-500A.

5. The method according to claim 1, characterized in that The welding process parameters are as follows: acceleration voltage 50-70 kV, beam current 60-100 mA, focusing current 950-1000 mA, welding speed 300-500 mm / min, and chamber vacuum less than 5×10 -2 Pa.

6. A joint obtained by the method according to any one of claims 1 to 5.

7. The joint according to claim 6, characterized in that The average size of β grains in the center of the weld is less than 200μm.

8. The joint according to claim 7, characterized in that The average size of β grains in the center of the weld is less than 100μm.

9. Application of the joint according to claim 6 in the fields of aerospace, weapon equipment and marine engineering.

10. Use of the method according to any one of claims 1 to 5 in electron beam welding of thick-walled titanium alloys.

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