CN111299795A

CN111299795A - Dissimilar vacuum electron beam welding method for titanium alloy and stainless steel

Info

Publication number: CN111299795A
Application number: CN202010158712.1A
Authority: CN
Inventors: 蒋小松; 张亚丽; 吕星星; 谌金梅; 高奇; 莫德锋; 李雪
Original assignee: Southwest Jiaotong University
Current assignee: Southwest Jiaotong University
Priority date: 2020-03-09
Filing date: 2020-03-09
Publication date: 2020-06-19

Abstract

The invention discloses a dissimilar metal vacuum electron beam welding method of titanium alloy and stainless steel, which belongs to the technical field of metal material welding and mainly comprises the following steps: cleaning the surface to be welded of the sample, assembling the sample, and welding by an electron beam welding technology; according to the invention, the copper-niobium composite interlayer is added between TC4 titanium alloy and 316L stainless steel, the TC4 titanium alloy-niobium foil-copper foil-316L stainless steel or the 316L stainless steel-copper foil-niobium foil-TC 4 titanium alloy is placed in sequence, and a transition solid solution phase can be formed in a weld pool by selecting proper parameters such as electron beam current, accelerating voltage, welding speed, beam offset distance and the like and the interlayer thickness, so that the diffusion reaction among elements such as titanium, iron and chromium is inhibited, the formation of brittle ferrotitanium intermetallic compounds is avoided, and the performance of the weld is damaged.

Description

Dissimilar vacuum electron beam welding method for titanium alloy and stainless steel

Technical Field

The invention relates to the technical field of metal material welding, in particular to a vacuum electron beam welding method for dissimilar metals of titanium alloy and stainless steel.

Background

The normal operation of the infrared focal plane detector requires a micro metal dewar device to provide a good electrical, mechanical, thermal and optical transmission channel for the infrared focal plane detector. The main materials for manufacturing the micro-metal Dewar comprise titanium alloy and stainless steel. Because the titanium alloy has the advantages of high obdurability, high melting point, excellent corrosion performance, low density and the like, the titanium alloy is widely applied to the fields of petrochemical industry, mechanical manufacturing, aviation industry and the like; 316L stainless steel is a structural material with lower corrosion rate, reliability, high strength and low cost, has good corrosion resistance, excellent low-temperature performance, processability and welding performance, and is often applied to industrial manufacturing.

However, dissimilar welding of titanium alloys to stainless steel presents several problems. First, a large residual stress is generated in the welded joint due to the difference in physical properties of the two metal materials. In addition, the chemical compositions of the two are greatly different, so that a great amount of TiFe and TiFe can be easily generated in a weld pool₂And the like, thereby jeopardizing the quality of the welded joint and causing the weldment to be easily broken under the action of external force.

The problem of welding between titanium alloy and stainless steel has become a factor limiting the development of the related welding field, and if the difficult problem of welding between the titanium alloy and the stainless steel is effectively solved, great contribution is made to the development of the related field, and the development of welding of dissimilar metal materials can also be promoted.

In 2018, an article named as 'influence of an electroplating barrier layer on performance of a titanium/steel electron beam welded joint' is published in rare metal materials and engineering journals. Researchers have employed electron beam fusion welding, electron beam barrier welding, and electron beam barrier fusion-brazing, respectively, to weld titanium alloys and stainless steel. As a result, it was found that brittle intermetallic compounds were generated in the weld zone, adversely affecting the properties of the joint. When welding is performed by direct fusion welding and barrier fusion welding, a through crack is generated in the weld region to cause direct fracture of the joint. During the separation melting-brazing, Ag and Cu are added as intermediate layers to optimize the structure of a welding seam, so that a good separation effect is achieved in the welding process, the formation of brittle intermetallic compounds between Ti and Fe is reduced, and the welding quality of the titanium alloy and the stainless steel is improved. Meanwhile, by carrying out X-ray flaw detection test, no obvious crack, no pore defect and the like are found. However, the properties of the welded joint still need to be further improved.

Disclosure of Invention

The invention aims to provide a vacuum electron beam welding method for dissimilar metals of titanium alloy and stainless steel, so as to solve the problem of poor welding quality of the dissimilar metals of C4 titanium alloy and 316L stainless steel.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a dissimilar metal vacuum electron beam welding method for titanium alloy and stainless steel comprises the following specific steps:

(1) cleaning the surface of a welding sample: cleaning surfaces to be welded of titanium alloy and stainless steel, copper foil and niobium foil to obtain a welding sample with a clean surface; the thickness of the copper foil is 450-550 mu m, and the thickness of the niobium foil is 500-600 mu m;

(2) placing a welding sample: sequentially butting and placing the titanium alloy, the stainless steel, the copper foil and the niobium foil after surface cleaning; the sequence is as follows: titanium alloy-niobium foil-copper foil-stainless steel, or stainless steel-copper foil-niobium foil-titanium alloy;

(3) welding: fixing the placed sample by using a clamp, and then placing the sample into a vacuum chamber of a vacuum electron beam welding machine for vacuum electron beam welding; in the step (3), when the sample is fixed, ensuring that the gap of the butt joint surface between the materials is less than 0.1 mm; and then placing the mounted sample in a vacuum chamber of a vacuum electron beam welding machine, vacuumizing, and starting to perform electron beam welding on the sample to be welded when the vacuum degree reaches 0.05Pa, wherein the welding is two welding steps, which are respectively as follows:

first welding: welding the interface of the copper foil and 316L stainless steel, taking the clearance position of the stainless steel and the copper foil as an origin, and enabling the electron beam to deviate 0.2-0.5mm to the copper foil side, thereby realizing fusion welding between the copper foil and the stainless steel;

and (3) second welding: and placing the electron beam in the middle of the niobium foil for welding to realize the fusion welding of the titanium alloy and one side of the niobium foil.

The inventor of the application starts with the thickness optimization of the copper foil and the niobium foil of the intermediate interlayer through a large number of tests, simultaneously adopts two welding steps and optimizes the positions of electron beams of the first welding step and the second welding step respectively, obtains unexpected technical effects through the mutual cooperation of the improvement factors, obviously improves the quality of a welded joint of the titanium alloy and the stainless steel, and particularly can enable the tensile strength of the welded joint of the titanium alloy and the stainless steel to reach more than 350MPa by adopting an electron beam welding method through the consideration of the positions of the electron beams of the two welding steps.

Electron beam welding is an advanced welding technique that uses the energy generated to heat the metal being welded by bombarding the metal surface with focused high velocity electrons to achieve good fusion. The method has the characteristics of small heat affected zone, high beam current density, accurate control of welding positions and the like, and is suitable for welding of dissimilar metals. In the research, the performance of the welding seam can be adjusted by changing parameters such as electron beam flow, acceleration voltage, welding speed, beam offset distance and the like, and the welding seam with lower hardness, higher tensile strength, no obvious defects such as air holes, cracks and the like is obtained.

According to the welding method of the titanium alloy and the stainless steel, the copper-niobium composite intermediate layer is added, so that element transition in a joint welding line is realized, and the generation of brittle intermetallic compounds in the welding line is avoided. Meanwhile, a vacuum electron beam welding machine is adopted for vacuum welding, so that the combination of welding interfaces is facilitated, the deformation of a welding sample is prevented, the grain refinement is promoted and the range of a heat affected zone is reduced by means of rapid heating and cooling; the added metal composite interlayer can realize the formation of solid solution phases between the titanium alloy and the niobium foil and between the copper foil and the stainless steel, thereby inhibiting the generation of brittle intermetallic compounds and being beneficial to the improvement of the quality of a welding joint.

The optimal copper foil thickness and niobium foil thickness are designed in the welding method, so that solid solution phases with sufficient content can be formed at the copper-stainless steel interface, the copper-niobium interface and the niobium-titanium alloy interface, and the reaction of iron element and niobium element and the reaction of titanium element and copper element can be avoided by the residual metal interlayer; in the welding process, two welding steps are adopted, so that the welding between the copper foil and the stainless steel and the welding between the niobium foil and the titanium alloy are realized, and the niobium foil and the copper foil are combined together by means of heat transfer. This facilitates accurate control of the thickness of the interlayer, facilitating further optimisation of the tissue.

Compared with other welding methods, the method has the advantages of simple and efficient welding process, low requirements on the shape and the size of a welding sample, and capability of successfully realizing the welding between the titanium alloy and the stainless steel.

Further, in the step (1), the purity of the copper foil and the niobium foil is more than 98 wt%,

more preferably, the purity of the copper foil and niobium foil is greater than 99.9 wt%. The higher the purity, the less impurities, and the more favorable the quality of the welding joint.

Further, in the step (1), cleaning the to-be-welded surface of the welding sample comprises grinding, polishing and pickling.

Preferably, the sanding and polishing process is as follows: and grinding and polishing the surfaces to be welded of the titanium alloy and the stainless steel. More preferably, the roughness Ra is made 1.0 μm or less, so as to facilitate the contact between the surfaces to be welded.

Preferably, the surfaces of the titanium alloy and the copper foil are subjected to acid pickling treatment. Since the surfaces of titanium alloys and copper foils are sensitive to oxygen, oxide films are easily formed on the surfaces, which adversely affects the diffusion of atoms during the soldering process. Further, the presence of oxygen atoms impairs the welding quality, so that it is necessary to remove the oxide film on the surface. More preferably, a mixed solution of hydrofluoric acid and nitric acid is used for removing the oxide film on the surface of the titanium alloy; with simultaneous use of dilute H₂SO₄The solution removes the oxide film on the surface of the copper foil.

Further, in the step (1), the cleaning of the surface of the welding sample mainly comprises: and (3) putting the polished welding sample, copper foil and niobium foil into acetone for ultrasonic cleaning for 10-15min, and then drying by cold air to obtain clean titanium alloy, stainless steel, copper foil and niobium foil. Preferably, after ultrasonic cleaning, the surface to be welded of the sample is wiped with alcohol and then air-dried.

Further, in the step (2), the welding sample is rigidly fixed in a jig with a forming groove.

Further, in the step (3), the gap between the samples in the clamp is less than or equal to 0.2 mm. Preferably, the gap between the respective materials is ensured to be less than 0.1 mm.

Further, when electron beam welding is carried out, the first welding: the accelerating voltage is 45-65Kv, the electron beam current is 5-10mA, and the welding speed is 5-10 mm/s; and (3) second welding: the accelerating voltage is 45-65Kv, the electron beam current is 4-8mA, and the welding speed is 5-10 mm/s.

Preferably, the first welding: the accelerating voltage is 50-60Kv, the electron beam current is 5-7mA, and the welding speed is 5-9 mm/s; and (3) second welding: the accelerating voltage is 50-60Kv, the electron beam current is 4-6mA, and the welding speed is 5-9 mm/s.

Due to the fact that materials at different welding positions are different, appropriate and preferable technological parameters need to be selected according to the characteristics of the materials, and therefore the welding effect can be controlled favorably, and the welding joint can achieve the best effect.

As the optimal technical scheme, a copper foil and a niobium foil are used as intermediate layers, the thickness of the copper foil is 510 mu m, and the thickness of the niobium foil is 560 mu m; in the first welding, the position of the electron beam preferably deviates 0.3mm towards the copper foil side; the electron beam is preferably positioned in the middle of the niobium foil during the second pass, and under such process conditions the joint may have a surprisingly high tensile strength of 416 MPa.

The method is particularly suitable for welding the TC4 titanium alloy and the 316L stainless steel.

Compared with the prior art, the invention has the advantages that:

(1) the welding method of the titanium alloy and the stainless steel is implemented by adopting vacuum electron beam welding, and the welding quality is improved by depending on the advantages of the electron beam welding.

(2) The method adopts the copper-niobium composite intermediate layer, realizes the formation of solid solution phases between the titanium alloy and the niobium foil and between the copper foil and the stainless steel, and avoids the formation of brittle intermetallic compounds in welding seams, thereby being beneficial to the improvement of the quality of welding joints.

(3) The method of the invention depends on the characteristics of rapid heating and cooling of the electron beam welding technology, promotes the refinement of crystal grains and reduces the range of a weld seam heat affected zone, thereby improving the welding quality of the crystal grains and the weld seam heat affected zone.

(4) Compared with other welding methods, the method has the advantages of simple and efficient welding process, low requirements on the shape and the size of a welding sample, and capability of successfully realizing the welding between the titanium alloy and the stainless steel.

Drawings

FIG. 1 is a schematic view of a copper-niobium composite interlayer added in the present invention;

FIG. 2 is a schematic view of the electron beam position of the present invention;

FIG. 3 is a microstructure map in the weld zone in example 3;

the labels in the figure are: 1 is stainless steel, 2 is copper foil, 3 is niobium foil, 4 is titanium alloy, 5 is a first electron beam current, and 6 is a second electron beam current.

Detailed Description

The present invention will be described in further detail with reference to test examples and specific embodiments. It should be understood that the scope of the above-described subject matter is not limited to the following examples, and any techniques implemented based on the disclosure of the present invention are within the scope of the present invention.

The titanium alloy and the stainless steel adopted in the embodiment of the invention are provided by Shanghai technical physics of Chinese academy of sciences, and the used copper foil and niobium foil are purchased from the Mitsui research New Material science and technology Co., Ltd in Beijing.

The 316L stainless steel of the following examples is illustrated by AISI316L stainless steel, and the titanium alloy is illustrated by TC4 titanium alloy, and those skilled in the art will understand that the method of the present invention is equally applicable to other types of titanium alloys and stainless steels; the purities of the copper foil and the niobium foil are both more than 98 wt%.

Example 1

Grinding and polishing the surfaces to be welded of the TC4 titanium alloy and the AISI316L stainless steel to ensure that the surface roughness Ra is less than or equal to 1.0 mu m; then, carrying out acid cleaning on the polished sample, and removing an oxide film on the surface of the titanium alloy by using a mixed solution of hydrofluoric acid and nitric acid; for the oxide film on the surface of the copper foil, dilute H is adopted₂SO₄Removing the solution; then, putting the processed titanium alloy, stainless steel, copper foil and niobium foil into acetone for ultrasonic cleaning for 15min, wiping the surface to be welded of the sample with alcohol, and drying the sample by cold air to obtain the processed titanium alloy, stainless steel, copper foil and niobium foil; the above cleaning methods are all known in the art;

the processed titanium alloy, stainless steel, 500-micron copper foil and 550-micron niobium foil are butted and placed according to a certain sequence, and the sequence is stainless steel-copper foil-niobium foil-titanium alloy. Specifically, as shown in fig. 1, stainless steel 1, copper foil 2, niobium foil 3, and titanium alloy 4 are sequentially arranged and rigidly fixed in a fixture with a forming groove to ensure that the gap between the materials is less than 0.1 mm;

then, the assembled clamp is placed in a vacuum chamber of a vacuum electron beam welding machine, operation and welding process parameter setting are carried out according to a standard flow, and welding is started when the vacuum degree reaches 0.05 Pa; first welding: the accelerating voltage is 55Kv, the electron beam current is 7mA, and the welding speed is 7 mm/s; and (3) second welding: the accelerating voltage is 55Kv, the electron beam current is 5.5mA, the welding speed is 7mm/s, the thickness of the copper foil selected in the experiment is 500 μm, and the thickness of the niobium foil is 550 μm. The welding sequence is as follows: welding the interface of the copper foil and the stainless steel by the first welding, wherein the electron beam deviates 0.1mm to the copper foil side; and then the electron beam is placed in the middle of the niobium foil for second welding.

Specifically, as shown in fig. 2, the first electron beam 5 is directed to the right side of the gap between the stainless steel 1 and the copper foil 2 and is close to the copper foil 2; the second electron beam current 6 is directed at the middle position of the niobium foil 3. And after welding, waiting for the cooling of the welding sample, opening a vacuum chamber of the welding machine, taking out the sample, and finally obtaining the welding sample of the TC4 titanium alloy and the AIS316L stainless steel.

Example 2

The same welding process as in example 1 was used to weld the titanium alloy and stainless steel. The procedure of example 1 was repeated except that the first welding was performed to weld the interface between the copper foil and the stainless steel, and the electron beam was shifted by 0.2mm toward the copper foil side.

Example 3

The same welding process as in example 1 was used to weld the titanium alloy and stainless steel. The procedure of example 1 was repeated except that the first welding was performed to weld the interface between the copper foil and the stainless steel, and the electron beam was shifted by 0.3mm toward the copper foil side.

The microstructure topography in the weld zone of this example is shown in FIG. 3, where it can be seen that the copper foil side consists essentially of a solid solution of copper and iron and the niobium foil side consists essentially of a solid solution of titanium and niobium.

Example 4

The same welding process as in example 1 was used to weld the titanium alloy and stainless steel. The procedure of example 1 was repeated except that the first welding was performed to weld the interface between the copper foil and the stainless steel, and the electron beam was shifted by 0.4mm toward the copper foil side.

Example 5

The same welding process as in example 1 was used to weld the titanium alloy and stainless steel. The procedure of example 1 was repeated except that the first welding was performed to weld the interface between the copper foil and the stainless steel, and the electron beam was shifted by 0.5mm toward the copper foil side.

Test 1

The effect of different beam deflection distances (first pass) on electron beam welding of titanium alloys and stainless steel was compared and the results are as follows.

The invention is regulated according to the national standard GB/T228-2002, and the tensile test is carried out on the welding sample at room temperature, and the loading rate is 0.5 mm/min. And observing the tensile fracture by using a scanning electron microscope, and judging the fracture property according to the existence of the characteristics of the tough pits, the river flower shape and the like.

TABLE 1 mechanical Properties of titanium alloy/stainless Steel Metal welded parts

From the test results of table 1, it can be found that when the welding test is performed by using the welding method of stainless steel and titanium alloy of the present invention, the selection of the beam offset distance in the first pass has a significant influence on the tensile strength of the welded part. When the beam deflection is small, the welding heat cannot be effectively transferred to one side of the niobium foil, which is not favorable for the connection of the copper foil and the niobium foil, and the welding strength is weakened. When the beam deflection is large, the welding heat transmitted to the stainless steel side is insufficient, which is disadvantageous to the connection between the copper foil and the stainless steel, and becomes a weak portion in the weld, and is liable to break. Thus, in the first pass, the preferred beam offset is: shifted 0.3mm to the copper foil side.

Example 6

Grinding and polishing the surfaces to be welded of the TC4 titanium alloy and the AISI316L stainless steel to ensure that the surface roughness Ra is less than or equal to 1.0 mu m; then, carrying out acid cleaning on the polished sample, and removing an oxide film on the surface of the titanium alloy by using a mixed solution of hydrofluoric acid and nitric acid; for the oxide film on the surface of the copper foil, dilute H is adopted₂SO₄The solution is removed. Then, putting the processed titanium alloy, stainless steel, copper foil and niobium foil into acetone for ultrasonic cleaning for 15min, wiping the surface to be welded of the sample with alcohol, and drying the sample by cold air to obtain the processed titanium alloy, stainless steel, copper foil and niobium;

the processed titanium alloy, stainless steel, 510 mu m copper foil and 560 mu m niobium foil are butted and placed according to a certain sequence, the sequence is stainless steel-copper foil-niobium foil-titanium alloy, and the stainless steel-copper foil-niobium foil-titanium alloy is rigidly fixed in a clamp with a forming groove, so that the gap among the materials is ensured to be less than 0.1 mm.

Then, the assembled clamp is placed in a vacuum chamber of a vacuum electron beam welding machine, operation and welding process parameter setting are carried out according to a standard flow, and welding is started when the vacuum degree reaches 0.05 Pa. First welding: the accelerating voltage is 55Kv, the electron beam current is 7mA, and the welding speed is 7 mm/s; and (3) second welding: the accelerating voltage is 55Kv, the electron beam current is 5.5mA, and the welding speed is 7 mm/s. The welding sequence is as follows: welding the interface of the copper foil and the stainless steel by the first welding, wherein the electron beam deviates 0.3mm to the copper foil side; and then the electron beam is placed in the middle of the niobium foil for welding.

And after welding, waiting for the cooling of the welding sample, opening a vacuum chamber of the welding machine, taking out the sample, and finally obtaining the welding sample of the TC4 titanium alloy and the AIS316L stainless steel.

Comparative example 1

Effect of copper foil and niobium foil thickness

The same material and preparation method as in example 6 was used, and the material was clamped with a jig. And welding after placing the material in a vacuum chamber of a vacuum electron beam welding machine. Wherein the welding parameters of the first welding and the second welding are the same as those of the embodiment 6. Except that the selected copper foil has a thickness of 440 μm and the selected niobium foil has a thickness of 490 μm. And after welding, waiting for the welding sample to be cooled, opening a vacuum chamber of a welding machine to take out the sample, and finally obtaining the welding sample of the TC4 titanium alloy and the AISI316L stainless steel.

Comparative example 2

Effect of copper foil and niobium foil thickness

The same material and preparation method as in example 6 was used, and the material was clamped with a jig. And welding after placing the material in a vacuum chamber of a vacuum electron beam welding machine. Wherein the welding parameters of the first welding and the second welding are the same as those of the embodiment 6. Except that the selected copper foil was 560 μm thick and the selected niobium foil was 620 μm thick. And after welding, waiting for the welding sample to be cooled, opening a vacuum chamber of a welding machine to take out the sample, and finally obtaining the welding sample of the TC4 titanium alloy and the AISI316L stainless steel.

Comparative example 3

Single electron beam bombardment welding

The same material and preparation method as in example 6 was used, and the material was clamped with a jig. And welding after placing the material in a vacuum chamber of a vacuum electron beam welding machine. Setting primary electron beam welding, wherein the technological parameters are as follows: the voltage is 65KV, the electron beam current is 9mA, the welding speed is 5mm/s, and the position of the electron beam is opposite to the interface of the copper foil and the niobium foil. When the device is used for primary electron beam welding, the required electron beam energy is higher, and the welding speed is slower. And after welding, waiting for the welding sample to be cooled, opening a vacuum chamber of a welding machine to take out the sample, and finally obtaining the welding sample of the TC4 titanium alloy and the AISI316L stainless steel.

Example 7

Titanium alloy, stainless steel, copper foil and niobium foil were treated in the same manner as in example 6. And then, the cleaned samples are butted and placed according to a certain sequence, namely titanium alloy-niobium foil-copper foil-stainless steel.

The treated samples were rigidly fixed in a jig with a forming groove while ensuring that the gap between the materials was as small as possible. Then placing the workpiece in a vacuum chamber of a vacuum electron beam welding machine, then operating according to a standard flow, selecting reasonable welding process parameters, and starting welding when the vacuum degree reaches 0.05 Pa. The welding sequence is as follows: firstly, welding an interface of a copper foil and stainless steel, and inclining to the copper foil side by 0.3 mm; and then the electron beam is placed in the middle of the niobium foil for welding. The welding parameters were as follows: first welding: the accelerating voltage is 60KV, the electron beam current is 7mA, and the welding speed is 7 mm/s; and (3) second welding: the accelerating voltage is 60KV, the electron beam current is 5.5mA, and the welding speed is 7 mm/s. And (4) performing point-fixing welding by adopting an electron beam welding machine. And after welding, waiting for the cooling of the welding sample, opening a vacuum chamber of the welding machine, taking out the sample, and finally obtaining the welding sample of the TC4 titanium alloy and the AISI316L stainless steel.

Comparative example 4

The transition layer is made of niobium foil only

Titanium alloy, stainless steel and niobium foil were treated in the same manner as in example 7. A560 μm niobium foil was placed between the titanium alloy and the stainless steel, and the treated sample was rigidly fixed in a jig with a forming groove while ensuring that the gap between the materials was as small as possible and not more than 0.05 mm. Then, the assembled clamp is placed in a vacuum chamber of a vacuum electron beam welding machine, operation and welding process parameter setting are carried out according to a standard flow, and welding is started when the vacuum degree reaches 0.05 Pa. In the welding process, the electron beam welds the middle position of the niobium foil, and the welding parameters are as follows: the voltage is 65KV, the electron beam current is 8mA, and the welding speed is 4.5 mm/s. And after welding, waiting for the cooling of the welding sample, opening a vacuum chamber of the welding machine, taking out the sample, and finally obtaining the welding sample of the TC4 titanium alloy and the AIS316L stainless steel.

Comparative example 5

Only copper foil is used as the transition layer

Titanium alloy, stainless steel and copper foil were treated in the same manner as in example 7. A510 μm copper foil was placed between the titanium alloy and stainless steel, and the treated sample was rigidly fixed in a jig with a molding groove while ensuring that the gap between the materials was as small as possible and not more than 0.05 mm. Then, the assembled clamp is placed in a vacuum chamber of a vacuum electron beam welding machine, operation and welding process parameter setting are carried out according to a standard flow, and welding is started when the vacuum degree reaches 0.05 Pa. In the welding process, the electron beam welds the middle position of the copper foil, and the welding parameters are as follows: the voltage is 60KV, the electron beam current is 8mA, and the welding speed is 4.5 mm/s. And after welding, waiting for the cooling of the welding sample, opening a vacuum chamber of the welding machine, taking out the sample, and finally obtaining the welding sample of the TC4 titanium alloy and the AIS316L stainless steel.

Comparative example 6

This comparative example compares to example 7 only in that the metallic interlayer material uses 560 μm chromium foil instead of niobium foil. The treated samples were rigidly fixed in a jig with a shaped groove and then welded in a vacuum chamber, and the welding process and welding parameters were selected as in example 7. And after welding, waiting for the cooling of the welding sample, opening a vacuum chamber of the welding machine, taking out the sample, and finally obtaining the welding sample of the TC4 titanium alloy and the AIS316L stainless steel.

Test 2

The welding samples welded in the above examples 6 to 7 and comparative examples 1 to 5 were tested to compare the effects of different welding processes, interlayers and other parameters on the electron beam welding of titanium alloy and stainless steel.

TABLE 2 mechanical Properties of titanium alloy/stainless Steel welded joints

Test specimen	Tensile strength (MPa)	Fracture properties
			Example 6	416.6	Toughness of
Comparative example 1	243.3	Toughness of
			Comparative example 2	261.5	Toughness of
Comparative example 3	120.3	Brittleness
			Example 7	276.2	Toughness of
Comparative example 4	130.5	Brittleness
			Comparative example 5	189.5	Toughness of
Comparative example 6	89.6	Brittleness

According to the test results, when the welding scheme of the stainless steel and the titanium alloy is adopted, the electron beam position of the first welding can effectively reduce the melting of the stainless steel in the middle of the copper foil, so that the diffusion of excessive iron elements and chromium elements is inhibited, and the tensile strength of a welding joint is effectively improved. When single electron beam welding is adopted, the energy is blocked from being transmitted in the welding seam, so that the melting quantity of each part of the welding seam is uneven, and the quality of the joint cannot be effectively improved. When only copper foil is adopted for welding, some brittle iron-titanium intermetallic compounds can still be generated in the welding seam; when only niobium foil is adopted for welding, niobium-iron brittle compounds can be generated in welding seams, and the quality of joints can still be damaged; when the welding is performed by using chromium foil instead of niobium foil, titanium chromium compounds are generated in the weld, and a joint with better quality is still difficult to obtain. In addition, when the thickness of the copper foil and the niobium foil is reduced, a small amount of intermetallic compounds are generated in the weld due to incomplete blocking of the diffusion of the iron element and the titanium element. Therefore, in the first pass, the position of the electron beam is preferably shifted to the copper foil side by 0.3 mm; in the second pass, the electron beam is preferably positioned in the middle of the niobium foil, preferably with the copper foil having a thickness of 510 μm and the niobium foil having a thickness of 560 μm.

The invention is not limited to the foregoing embodiments. The invention extends to any novel feature or any novel combination of features disclosed in this specification and any novel method or process steps or any novel combination of features disclosed.

Claims

1. A dissimilar metal vacuum electron beam welding method of titanium alloy and stainless steel is characterized by comprising the following steps:

2. The dissimilar metal vacuum electron beam welding method for titanium alloy and stainless steel according to claim 1, wherein in the step (1), the method for cleaning the surfaces to be welded of the titanium alloy and the stainless steel comprises the following steps: sanding by using sand paper and polishing to ensure that the surface roughness Ra of the sand paper is less than or equal to 1.0 mu m; removing an oxide film on the surface of the titanium alloy by adopting a mixed solution of hydrofluoric acid and nitric acid; by dilute H₂SO₄Removing the oxide film on the surface of the copper foil by using the solution; and then, putting the processed welding sample, copper foil and niobium foil into an acetone solution for ultrasonic cleaning for 10-15min, wiping the surface with alcohol, drying by cold air to avoid introducing impurities, and finally obtaining clean titanium alloy, stainless steel, copper foil and niobium foil to be welded.

3. The dissimilar metal vacuum electron beam welding method of titanium alloy and stainless steel according to claim 1,

the first welding process comprises the following steps: the accelerating voltage is 45-65Kv, the electron beam current is 5-10mA, and the welding speed is 5-10 mm/s;

the second welding process comprises the following steps: the accelerating voltage is 45-65Kv, the electron beam current is 4-8mA, and the welding speed is 5-10 mm/s.

4. The dissimilar metal vacuum electron beam welding method of titanium alloy and stainless steel according to claim 3,

the first welding process comprises the following steps: the accelerating voltage is 50-60Kv, the electron beam current is 5-7mA, and the welding speed is 5-9 mm/s;

the second welding process comprises the following steps: the accelerating voltage is 50-60Kv, the electron beam current is 4-6mA, and the welding speed is 5-9 mm/s.

5. The dissimilar metal vacuum electron beam welding method according to claim 1, wherein the titanium alloy is a TC4 titanium alloy, and the stainless steel is316L stainless steel.