Ultrathin-wall niobium-tungsten alloy and titanium alloy dissimilar metal electron beam welding method

Abstract

The invention provides an ultrathin-wall niobium-tungsten alloy and titanium alloy dissimilar metal electron beam welding method which comprises the following steps: step 1, cleaning the to-be-welded parts of niobium-tungsten alloy and titanium alloy by using absolute ethyl alcohol, and then drying; step 2, assembling; the niobium-tungsten alloy and the titanium alloy part are in butt joint and fixed; 3, vacuum electron beam welding is used for positioned welding; and 4, formal welding is conducted. After welding, the surface of a welding seam is formed well, good metallurgical fusion is achieved, and the welding seam welded through a vacuum electron beam meets the QJ 20622-2016 I-level standard; under the room temperature condition, the tensile strength of the welding seam reaches 80% of that of titanium alloy base metal; a hydraulic strength test is carried out on a welding seam, and the welding seam is free of leakage and deformation when the pressure is maintained for 5 minutes under 4.1 MPa. An airtight test is carried out on a welding seam, the requirement that air leakage is avoided under the pressure of 3 MPa for 5 min is met, and the design structure size is promoted to continuously break through in the miniaturization and precision direction.

Description

Technical Field

[0001] This invention belongs to the field of dissimilar metal welding technology, and specifically relates to an electron beam welding method for ultra-thin-walled niobium-tungsten alloy and titanium alloy with a thickness of less than 1 mm. Background Technology

[0002] Niobium-tungsten alloys possess inherent material properties such as high melting point, high specific strength, and excellent high-temperature mechanical properties, while also exhibiting good machinability and weldability. Currently, my country's independently developed NbW5-1 niobium-tungsten alloy is widely used in high-temperature structural components and thermal protection materials in the aerospace field. With the increasing development of the aerospace industry both domestically and internationally, the requirements for high-temperature resistance and lightweighting of structural materials are becoming increasingly stringent. Therefore, dissimilar metal welding of niobium-tungsten alloys and titanium alloys has significant practical implications. Achieving the welding of ultra-thin-walled structural components made of niobium-tungsten alloys and titanium alloys will help drive continuous breakthroughs in the miniaturization and precision of structural designs.

[0003] TC4 titanium alloy, widely used in the aerospace field, is characterized by its low density, high specific strength, and good weldability, making it a mature solution for lightweighting aircraft. TC4 titanium alloy is an α+β dual-phase titanium alloy, with vanadium (V) introduced as a β-phase stabilizing element. During high-energy beam welding such as electron beam welding, the rapid cooling rate easily leads to the β→α phase transformation, resulting in cracks in the weld metal. Furthermore, the introduced β-phase stabilizing element V tends to segregate in the molten pool, causing uneven element distribution. This is particularly problematic for ultra-thin-walled structures with a thickness of less than 1 mm, where welding process parameters are highly sensitive, easily causing defects such as weld leaks and weld collapse, representing a current welding challenge. Summary of the Invention

[0004] The technical problem solved by this invention is to provide a method for electron beam welding of dissimilar metals, namely, ultrathin-walled niobium-tungsten alloy and titanium alloy, which solves the welding defects such as burn-through, weld pits, and surface cracks that are prone to occur during the electron beam welding of annular ultrathin-walled niobium-tungsten alloy and titanium alloy.

[0005] The technical solution adopted in this invention is: a method for electron beam welding of dissimilar metals, namely ultrathin-walled niobium-tungsten alloy and titanium alloy, comprising the following steps: Step 1: Clean the areas of the niobium-tungsten alloy and titanium alloy to be welded with anhydrous ethanol, and then dry them; Step 2, Assembly; The niobium-tungsten alloy and titanium alloy parts are butt-jointed and fixed. The butt joint uses a mechanically interlocked bottom-locking structure. The base material thickness is no more than 1.0 mm. The niobium-tungsten alloy butt joint end is a smaller diameter convex ring, and the titanium alloy butt joint end is a larger diameter concave ring. The convex ring is inserted into the inner wall of the concave ring to limit the butt joint of the niobium-tungsten alloy and titanium alloy, forming the parts to be welded. The bottom-locking structure is designed to improve the welding qualification rate and facilitate welding from a process perspective. Because the thickness of the ultra-thin wall structure is less than 1 mm, and the welding method used is vacuum electron beam welding, high precision is required for the assembly of parts before welding. The bottom-locking structure limits the parts through mechanical interlocking, achieving precise fit and improving positioning accuracy. Strict mechanical dimensional tolerances in the structural design reduce misalignment caused by human error during assembly and positioning; it also reduces misalignment deformation caused by the difference in thermal expansion coefficients of dissimilar metals during welding.

[0006] Step 3: Use vacuum electron beam welding for tack welding; perform in a vacuum chamber with a vacuum degree of no more than 5×10-2 Pa, use vacuum electron beam welding for tack welding, with the weld center as the 0mm position, and the electron beam bombardment position offset 0.1-0.2mm to the niobium-tungsten alloy side, and use lower surface focusing welding. Step 4: Perform formal welding; with the weld center as 0mm, shift the electron beam bombardment position 0.2mm to the niobium-tungsten side and use lower surface focusing welding; Step 5: Perform a hydraulic strength test on the weld, which should meet the requirements of 4.1 MPa, and hold the pressure for 5 minutes without leakage or deformation; Step 6: Conduct an airtightness test on the weld, ensuring no air leakage for 3MPa and 5 minutes.

[0007] Preferably, in step 2, when the workpiece to be welded is in the clamping state, the position runout of the weld is controlled to be less than 0.15mm.

[0008] Preferably, the assembly gap of the workpiece to be welded in step 2 is less than 0.03 mm.

[0009] Preferably, the welding parameters for the tack welding in step 3 are: accelerating voltage of 60KV; electron beam current of 4mA; focusing amount J-J0 of 10mA, where J is the actual focusing current used for welding and J0 is the focusing current on the workpiece surface, in mA.

[0010] Preferably, the welding parameters for step 4 are: accelerating voltage 50-60KV; electron beam current preferably 8-9mA; focusing amount J-J0 is -10 to -15mA; and welding speed is 10mm / s.

[0011] Preferably, the welding parameters for step 4 are: accelerating voltage 60KV; electron beam current 8.5-9mA; focusing amount -10mA; and welding speed 10mm / s.

[0012] Preferably, the titanium alloy is a duplex titanium alloy.

[0013] The beneficial effects of this invention are: by adopting the electron beam welding method of this invention, the welding capability of annular ultrathin-walled niobium-tungsten alloy and titanium alloy butt joints is realized. It is safe, reliable, and highly precise, forming a good metallurgical bond, ensuring good surface formation of the weld after electron beam welding, having good mechanical properties, and meeting the airtightness requirements; and promoting continuous breakthroughs in the miniaturization and precision of design structure dimensions. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure for the butt welding of dissimilar metals, ultrathin-walled niobium-tungsten alloy and titanium alloy.

[0015] Figure 2 This is a macroscopic image of the weld formation in Example 2.

[0016] Figure 3 The image shows a low-magnification image of the weld seam in Example 2 under a backscattered scanning electron microscope, along with the corresponding EDS elemental line scan distribution map.

[0017] Reference numerals: 1-Niobium-tungsten alloy, 2-Weld, 3-Titanium alloy. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0019] like Figure 1 As shown, the present invention involves welding a niobium-tungsten alloy thin-walled ring structure and a titanium alloy thin-walled ring structure. The base material thickness is no more than 1.0 mm. The butt joint adopts a mechanical interlocking bottom locking butt joint structure. The niobium-tungsten alloy butt joint end is a convex ring with a smaller diameter, and the titanium alloy butt joint end is a concave ring with a larger diameter. The convex ring is inserted into the inner wall of the concave ring to limit the butt joint of the niobium-tungsten alloy and the titanium alloy to form the workpiece to be welded.

[0020] Example 1: An electron beam welding method for ultrathin-walled niobium-tungsten alloy and titanium alloy dissimilar metals includes the following steps: Step 1: Clean the areas of the niobium-tungsten alloy and titanium alloy to be welded with anhydrous ethanol, and then dry them.

[0021] Step 2, Assembly; Connect and secure the niobium-tungsten alloy parts to the titanium alloy parts.

[0022] Step 3: Perform tack welding using vacuum electron beam welding. This is done in a vacuum chamber with a vacuum level not exceeding 5×10⁻² Pa. Position the weld using vacuum electron beam welding, with the weld center at 0 mm. Offset the electron beam bombardment position 0.1-0.2 mm towards the niobium-tungsten alloy side. Use lower surface focusing welding. Welding parameters are: accelerating voltage 60 kV; electron beam current 4 mA; focusing amount J-J0 10 mA, where J is the actual focusing current used in welding, and J0 is the focusing current on the workpiece surface, in mA.

[0023] Step 4: Perform formal welding; with the weld center as 0mm, the electron beam bombardment position is offset by 0.2mm to the niobium-tungsten side, and lower surface focusing welding is used; the welding parameters are: accelerating voltage of 60KV; electron beam current of 8.5mA; focusing amount J-J0 of -15mA; and welding speed of 10mm / s.

[0024] The weld surface exhibits good formation after welding, with a weld penetration depth of 1 mm. The weld, produced by vacuum electron beam welding, meets the Class I standard of QJ20622-2016. At room temperature, the tensile strength of the weld reaches 80% of that of the titanium alloy base material. A hydraulic strength test was conducted on the weld, which met the requirements of 4.1 MPa, maintaining pressure for 5 minutes without leakage or deformation. An airtightness test was also conducted, which met the requirements of 3 MPa, maintaining airtightness for 5 minutes.

[0025] Example 2: An electron beam welding method for ultrathin-walled niobium-tungsten alloy and titanium alloy dissimilar metals includes the following steps: Step 1: Clean the areas of the niobium-tungsten alloy and titanium alloy to be welded with anhydrous ethanol, and then dry them.

[0026] Step 2, Assembly; Connect and secure the niobium-tungsten alloy parts to the titanium alloy parts.

[0027] Step 3: Perform tack welding using vacuum electron beam welding. This is done in a vacuum chamber with a vacuum level not exceeding 5×10⁻² Pa. Position the weld using vacuum electron beam welding, with the weld center as the 0mm position. Offset the electron beam bombardment position 0.1-0.2mm towards the niobium-tungsten alloy side, using lower surface focusing welding. Welding parameters are: accelerating voltage 60KV; electron beam current 4mA; focusing quantity J-J0 = -10mA, where J is the actual focusing current used in welding, and J0 is the focusing current on the workpiece surface, in mA.

[0028] Step 4: Perform formal welding; with the weld center as 0mm, the electron beam bombardment position is offset by 0.2mm to the niobium-tungsten side, and the lower surface focusing welding is used; the welding parameters are: accelerating voltage of 60KV; electron beam current of 9mA; focusing amount J-J0 of -10mA; and welding speed of 10mm / s.

[0029] like Figure 2 As shown, the weld surface has good formation after welding, the weld penetration is 1.1 mm, and the weld welded by vacuum electron beam welding meets the Class I standard of QJ 20622-2016. Figure 3 As shown under an electron microscope, the dissimilar metal weld between the niobium-tungsten alloy and the titanium alloy forms a relatively obvious Ti-Nb transition zone. The metal contrast within the weld is seamless, and the elements are dispersed throughout the weld region, with Nb generally slightly higher than Ti and distributed stably. The weld metal exhibits good metallurgical fusion. At room temperature, the tensile strength of the weld reaches over 80% of that of the titanium alloy base material. A hydraulic strength test was conducted on the weld, meeting the requirements of 4.1 MPa for 5 minutes without leakage or deformation. An airtightness test was also performed, meeting the requirements of 3 MPa for 5 minutes without leakage.

[0030] Comparative Example 1: The positioning parameters are the same as in Example 2. In step 4, the electron beam current is adjusted to 10mA, while the rest remain the same. After welding, the weld penetrates the lock bottom structure.

[0031] Comparative Example 2: Compared with the parameters in Example 1, the electron beam current in the welding parameters of step 4 was adjusted to 8mA, while the rest remained the same, and the weld was not fully penetrated.

[0032] The above describes specific embodiments of the present invention and the technical principles employed. Any modifications or equivalent transformations based on the technical solutions of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for electron beam welding of dissimilar metals, namely ultrathin-walled niobium-tungsten alloy and titanium alloy, characterized in that, Includes the following steps: Step 1: Clean the areas of the niobium-tungsten alloy and titanium alloy to be welded with anhydrous ethanol, and then dry them; Step 2, Assembly; Connect and fix the niobium-tungsten alloy and titanium alloy parts. The connection adopts a mechanical interlocking bottom connection structure. The thickness of the base material is not greater than 1.0mm. The niobium-tungsten alloy connection end is a convex ring with a smaller diameter, and the titanium alloy connection end is a concave ring with a larger diameter. The convex ring is inserted into the inner wall of the concave ring to limit the connection between the niobium-tungsten alloy and the titanium alloy to form the part to be welded. Step 3: Use vacuum electron beam welding for tack welding; perform in a vacuum chamber with a vacuum degree of no more than 5×10-2 Pa, use vacuum electron beam welding for tack welding, with the weld center as the 0mm position, and the electron beam bombardment position offset 0.1-0.2mm to the niobium-tungsten alloy side, and use lower surface focusing welding. Step 4: Perform formal welding; with the weld center as 0mm, shift the electron beam bombardment position 0.2mm to the niobium-tungsten side and use lower surface focusing welding; Step 5: Perform a hydraulic strength test on the weld, which should meet the requirements of 4.1 MPa, and hold the pressure for 5 minutes without leakage or deformation; Step 6: Conduct an airtightness test on the weld, ensuring no air leakage for 3MPa and 5 minutes.

2. The electron beam welding method for ultra-thin-walled niobium-tungsten alloy and titanium alloy dissimilar metals according to claim 1, characterized in that: In step 2, when the workpiece is clamped, the positional runout of the weld is controlled to be less than 0.15 mm.

3. The electron beam welding method for ultra-thin-walled niobium-tungsten alloy and titanium alloy dissimilar metals according to claim 1, characterized in that: In step 2, the assembly gap of the parts to be welded is controlled to be less than 0.03 mm.

4. The electron beam welding method for ultra-thin-walled niobium-tungsten alloy and titanium alloy dissimilar metals according to claim 1, characterized in that: The welding parameters for the tack welding in step 3 are: accelerating voltage of 60KV; electron beam current of 4mA; and focusing amount J-J0 of 10mA.

5. The electron beam welding method for ultra-thin-walled niobium-tungsten alloy and titanium alloy dissimilar metals according to claim 1, characterized in that: The welding parameters for step 4 are: accelerating voltage 50-60KV; electron beam current preferably 8-9mA; focusing amount J-J0 is -10 to -15mA; welding speed is 10mm / s.

6. The electron beam welding method for ultra-thin-walled niobium-tungsten alloy and titanium alloy dissimilar metals according to claim 1, characterized in that: The welding parameters for step 4 are: accelerating voltage 60KV; electron beam current 8.5-9mA; focusing amount -10mA; welding speed 10mm / s.

7. The electron beam welding method for ultrathin-walled niobium-tungsten alloy and titanium alloy dissimilar metals according to claim 1, characterized in that: The titanium alloy is a duplex titanium alloy.

Images