Method and device for optimizing brazing of dissimilar metals

Abstract

A kind of heterogeneous metal material fusion brazing optimization method and device, Ti2AlNb plate and titanium alloy plate are sequentially arranged between electrode and controllable magnetic field, welding current is applied on Ti2AlNb plate by electrode to generate Joule heat, the barrier effect of high resistivity oxide film between plate is used, the upper surface of titanium alloy plate is uniformly heated to melt to form molten material, the high-speed flow and stirring of molten material under the controllable magnetic field and Lorentz force generated by welding current below titanium alloy plate, the aggregation of oxide film defects near the interface is inhibited, and the interface on both sides of heterogeneous material forms thin and uniform intermetallic compound.The present application adopts high melting point metal heating, and the phased matching of controllable magnetic field and welding current is set, and the local melting of low melting point metal is realized by the uniform heating and heat transfer of high melting point metal, the precise regulation of fusion nucleus growth process and low melting point metal oxide film breaking process is realized, and finally brazing interface is formed.

Description

Technical Field

[0001] This invention relates to a technology in the field of fusion brazing, specifically an optimized method and apparatus for fusion brazing of dissimilar metal materials. Background Technology

[0002] Titanium alloys (such as TC4) and titanium-aluminum intermetallic compounds (such as Ti2AlNb) are the core materials of the heat insulation structure. They are usually connected by fusion brazing. The process involves direct resistance heating of low-melting-point metals, which causes the molten low-melting-point metals to be squeezed out, forming pits and causing severe local thinning of the joint. Summary of the Invention

[0003] This invention addresses the shortcomings of existing technologies, such as severe thinning of the low-melting-point side plate, thick and uneven intermetallic compounds at the interface, short electrode wear life on the low-melting-point side plate, and the accumulation of oxide film on the surface of the low-melting-point side plate at the interface of highly different plates, leading to easy defect formation. It proposes an optimized method and apparatus for fusion brazing of dissimilar metal materials. By heating the high-melting-point side material, the heat input to the low-melting-point side material is reduced, thus decreasing the thinning rate of the low-melting-point material, eliminating surface indentations, and controlling the thickness of the intermetallic compound layer. The interaction of an external magnetic field and current generates a Lorentz force, driving the molten low-melting-point material to flow at high speed, improving the weld nugget structure and defect distribution on the low-melting-point side material, and enhancing the mechanical properties of the weld joint. By avoiding direct contact between the copper electrode and the low-melting-point side material, electrode wear is reduced, improving the performance, appearance quality, and weld quality stability of fusion brazed joints of highly different metal materials.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to an optimized method for brazing dissimilar metal materials. A titanium-aluminum intermetallic compound plate and a titanium alloy plate are sequentially positioned between an electrode and a controllable magnetic field. A multi-stage pulsed current is applied to the titanium-aluminum intermetallic compound plate via the electrode to generate Joule heating. Utilizing the barrier effect of the high-resistivity oxide film between the plates, the upper surface of the titanium alloy plate is uniformly heated to melt and form a molten material. Under the influence of the controllable magnetic field and the Lorentz force generated by the multi-stage pulsed current below the titanium alloy plate, the molten material flows and stirs at high speed to reduce the temperature gradient during the lateral growth stage of the weld nugget, increase the weld nugget diameter, and suppress the accumulation of oxide film defects near the interface. A thin and uniform intermetallic compound is formed on both sides of the interface.

[0006] The multi-stage pulsed current includes: a preheating stage, a transverse growth stage of the weld nugget, a longitudinal growth stage of the weld nugget, and a stirring stage. Specifically: the preheating stage uses a current of 4-6 kA for 200-400 ms; the transverse growth stage of the weld nugget uses a current of 7-9 kA for 40-80 ms; the longitudinal growth stage of the weld nugget uses a current of 7-9 kA for 40-80 ms; and the stirring stage uses 8-10 pulsed currents with a welding time of 40 ms and a cooling time of 5 ms. The welding current is increased from 10 kA to 12 kA.

[0007] The controllable magnetic field is set to match the intensity of the multi-stage pulse current, specifically: a preheating stage and a longitudinal growth stage of the melt nucleus with a magnetic field strength of zero, and a transverse growth stage and a stirring stage of the melt nucleus with a magnetic field strength of 0.5-2.5T.

[0008] Technical effect

[0009] Compared to existing technologies that directly heat low-melting-point metals during welding, this invention utilizes the barrier effect of a high-resistivity oxide film between high-melting-point and low-melting-point plates to ensure uniform heating of the low-melting-point plate. This reduces heat input to the low-melting-point plate side during welding, creating a shallow but large melting zone. This reduces severe thinning caused by excessive melting of the low-melting-point plate, inhibits excessive growth of the intermetallic compound layer, reduces surface indentation of the low-melting-point plate, and improves the surface quality of the weld joint. Furthermore, this invention uses an external magnetic field to generate a Lorentz force that stirs the molten low-melting-point plate, causing the oxide film on the plate surface to disperse and suppressing the aggregation of oxide film defects at the interface of highly different materials, thus improving the mechanical properties of the weld joint. During welding, neither the first nor the second electrode of this invention comes into contact with the low-melting-point plate, effectively solving the problem of severe electrode wear in traditional brazing processes of highly different materials, and improving welding stability and consistency. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the structure of the present invention;

[0011] Figure 2 This is a schematic diagram of the structure supporting the base;

[0012] In the diagram: a is a 3D view; b is a cross-sectional view;

[0013] Figure 3 This is a schematic diagram of the current density distribution during the welding process;

[0014] In the figure: First electrode 1, Second electrode 2, High melting point plate to be connected 3, Low melting point plate to be connected 4, Support base 5, Current density distribution 6, First electrode rod 101, First electrode cap 102, Second electrode rod 201, Second electrode cap 202, Insulating shell 501, Magnetic field source 502, Height adjustment mechanism 503. Detailed Implementation

[0015] like Figure 1 As shown, this embodiment relates to an optimized device for fusion brazing of dissimilar metal materials, comprising: Ti2AlNb intermetallic compound plate 3 and TC4 titanium alloy plate 4 stacked on top of each other, two first electrodes 1 and 2 disposed on the Ti2AlNb intermetallic compound plate 3, and a support base 5 disposed below the TC4 titanium alloy plate 4.

[0016] The thickness of the Ti2AlNb intermetallic compound plate is 1.0 mm, and the thickness of the TC4 titanium alloy plate is 0.5 mm.

[0017] The two first electrodes 1 and 2 have the same structure, each including an electrode rod and an electrode cap arranged in sequence, wherein the electrode cap is located at the free end of the electrode rod.

[0018] The electrode caps of both electrodes are spherical and made of chromium-zirconium copper.

[0019] The inner diameter of all the electrode rods is 10 mm.

[0020] The support base 5 includes a support platform 501, a magnetic field source 502 and a height adjustment mechanism 503 disposed therein, wherein the support platform 501 is located below the TC4 titanium alloy plate 4, and the height adjustment mechanism 503 is located at the bottom of the magnetic field source 502 and connected to the magnetic field source 502.

[0021] The upper surface of the support platform 501 is flat and is preferably made of ceramic.

[0022] The magnetic field source 502 is a permanent magnet with a diameter of 30 mm and a thickness of 10 mm. The height H of the upper surface of the magnetic field source 502 from the inner wall surface of the support platform 501 is 1.2 mm.

[0023] This embodiment relates to a fiber optic welding method using the aforementioned device. A high-melting-point Ti2AlNb plate and a low-melting-point TC4 titanium alloy plate are positioned between an electrode and a controllable magnetic field. By applying a welding current, Joule heating is generated within the high-melting-point plate. Utilizing the barrier effect of the high-resistivity oxide film between the high-melting-point and low-melting-point plates, the side of the low-melting-point plate closest to the high-melting-point plate heats up uniformly. A thin, large-area molten region forms on the side of the low-melting-point plate closest to the high-melting-point plate. The molten low-melting-point plate flows and stirs at high speed under the Lorentz force generated by the magnetic field and current, suppressing the accumulation of oxide film defects near the interface. Thin, uniform intermetallic compounds are formed between the heterogeneous materials on both sides of the interface. This process specifically includes:

[0024] ① Fix the support base 5, the first electrode 1 and the second electrode 2 move downwards, and apply an electrode pressure of 2.0 kN respectively. The high melting point plate 3 and the low melting point plate 4 to be connected are fastened between the first electrode 1, the second electrode 2 and the support base 5.

[0025] ② The welding current application includes four stages: preheating, transverse growth of the weld nugget, longitudinal growth of the weld nugget, and stirring. The preheating stage uses a current of 6kA for 200ms, the transverse growth stage uses a current of 8kA for 40ms, the longitudinal growth stage uses a current of 8kA for 80ms, and the stirring stage uses a pulse current of 10 welding times of 40ms and a cooling time of 5ms. The welding current is increased from 10kA to 12kA.

[0026] ③ Apply a controllable magnetic field corresponding to the welding current. Apply the magnetic field in the two stages of transverse growth and stirring of the weld nugget. The magnetic field strength is 1.2T, and the magnetic field strength is zero in other stages.

[0027] ④ Due to the barrier effect of the high resistivity oxide film between the high-melting-point plate 3 and the low-melting-point plate 4 to be connected, the current density is mainly concentrated in the high-melting-point plate 3, while the current density in the low-melting-point plate 4 is relatively small. The high-melting-point plate 3 is heated by thermal conduction, causing the low-melting-point plate 4 to melt within a certain depth near the high-melting-point plate, forming molten metal 6. The heterogeneous materials on both sides of the interface diffuse into each other, forming an intermetallic compound. Under the action of the Lorentz force generated by the magnetic field source 502, the molten metal 6 undergoes three-dimensional flow, achieving a diffuse distribution of the oxide film near the interface.

[0028] Through specific practical experiments, under the specific environmental settings of the embodiments, welding TC4 titanium alloy and Ti2AlNb using the magnetron-assisted brazing parameters described in the embodiments can significantly reduce the severe thinning problem caused by excessive heat input of TC4 titanium alloy. The surface indentation on the TC4 titanium alloy side of the joint can be controlled within the range of 0-0.02mm. Compared with the approximately 0.2-0.5mm indentation on the TC4 titanium alloy side obtained by existing TC4 titanium alloy and brazing equipment, the surface quality of the joint is improved; the thickness of the intermetallic compound layer at the TC4 titanium alloy / Ti2AlNb interface is less than 5 mm. µm, which is 20%~30% smaller than existing fusion brazing; the Lorentz force generated by the external magnetic field stirs the molten TC4 titanium alloy, making the oxide film distribution more dispersed and inhibiting the accumulation of oxide film defects at the interface of highly different materials. The tensile shear strength of the joint increases from 8.1kN in traditional double-sided resistance fusion brazing to 10.5kN, an improvement of 29.6%; during the welding process, neither the first nor the second electrode comes into contact with the TC4 titanium alloy plate, effectively solving the problem of severe electrode wear in traditional fusion brazing process and improving welding stability and consistency.

[0029] Compared with existing technologies, this invention can significantly reduce the problem of severe thinning of low-melting-point metals caused by excessive heat input during brazing. In the embodiment, the surface indentation on the TC4 titanium alloy side of the joint can be controlled within the range of 0-0.02mm, which is significantly better than the approximately 0.2-0.5mm indentation on the TC4 titanium alloy side obtained by existing TC4 titanium alloy and fusion brazing devices, thus improving the surface quality of the joint. The thickness of the intermetallic compound layer at the TC4 titanium alloy / Ti2AlNb interface is less than 5 µm, which is 20%~30% less than that of existing fusion brazing. The Lorentz force generated by the external magnetic field stirs the molten TC4 titanium alloy, making the oxide film distribution more dispersed and inhibiting the aggregation of oxide film defects at the interface of highly different materials. The tensile shear strength of the joint increases from 8.1kN in traditional bilateral resistance fusion brazing to 10.5kN, an increase of 29.6%. During the welding process, neither the first nor the second electrode contacts the TC4 titanium alloy plate, effectively solving the problem of severe electrode wear in traditional fusion brazing processes and improving welding stability and consistency.

[0030] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A method for optimizing brazing of dissimilar metals, characterized by, Titanium-aluminum intermetallic compound plates and titanium alloy plates are sequentially placed between an electrode and a controllable magnetic field. A multi-stage pulsed current is applied to the titanium-aluminum intermetallic compound plate through the electrode to generate Joule heating. Utilizing the barrier effect of the high resistivity oxide film between the plates, the upper surface of the titanium alloy plate is uniformly heated to melt and form a molten material. The molten material flows and stirs at high speed under the action of the controllable magnetic field and the Lorentz force generated by the multi-stage pulsed current below the titanium alloy plate, thereby reducing the temperature gradient during the lateral growth stage of the melt nugget, increasing the diameter of the melt nugget, and suppressing the aggregation of oxide film defects near the interface. The heterogeneous materials on both sides of the interface form a thin and uniform intermetallic compound. The multi-stage pulsed current includes: a preheating stage, a lateral growth stage of the melt nucleus, a longitudinal growth stage of the melt nucleus, and a stirring stage; the controllable magnetic field is set to match the intensity of the multi-stage pulsed current. The preheating stage uses a current of 4-6kA for 200-400ms, the transverse growth stage of the weld nugget uses a current of 7-9kA for 40-80ms, the longitudinal growth stage of the weld nugget uses a current of 7-9kA for 40-80ms, and the stirring stage uses 8-10 pulse currents with a welding time of 40ms and a cooling time of 5ms. The welding current is increased from 10kA to 12kA.

2. The optimized method for brazing dissimilar metal materials according to claim 1, characterized in that, The controllable magnetic field is set to match the intensity of the multi-stage pulse current, specifically: a preheating stage and a longitudinal growth stage of the melt nucleus with a magnetic field strength of zero, and a transverse growth stage and a stirring stage of the melt nucleus with a magnetic field strength of 0.5-2.5T.

3. A dissimilar metal brazing apparatus for implementing the method of claim 1 or 2, characterized in that, include: The titanium-aluminum intermetallic compound and titanium alloy plate are stacked on top of each other, two electrodes are set on the titanium-aluminum intermetallic compound, and a support base is set below the titanium alloy plate. The two electrodes have the same structure, both including an electrode rod and an electrode cap arranged in sequence, wherein the electrode cap is located at the free end of the electrode rod; The support base includes a support platform and a magnetic field source and a height adjustment mechanism disposed therein, wherein the support platform is located below the titanium alloy plate, and the height adjustment mechanism is located at the bottom of the magnetic field source and connected to the magnetic field source.

4. The dissimilar metal brazing apparatus according to claim 3, characterized in that, The ends of the electrode caps are all spherical and made of chromium-zirconium copper.

5. The dissimilar metal brazing apparatus according to claim 3, characterized in that, The upper surface of the support platform is a flat surface made of ceramic.

6. The dissimilar metal brazing apparatus according to any one of claims 3-5, characterized in that, The thickness of the titanium-aluminum intermetallic compound plate is 1.0 mm, and the thickness of the titanium alloy plate is 0.5 mm.

7. The dissimilar metal brazing apparatus according to claim 3, characterized in that, The magnetic field source is a permanent magnet with a diameter of 30 mm and a thickness of 10 mm. The height H of the upper surface of the magnetic field source from the inner wall surface of the support platform is 1.2 mm.

8. An optimized method for dissimilar metal brazing of the device according to any one of claims 3-7, characterized in that, Specifically, it includes: ①After fixing the support base, drive the first electrode and the second electrode to move downwards, and apply an electrode pressure of 2.0 kN respectively. The high melting point plate and the low melting point plate to be connected are fastened between the first electrode, the second electrode and the support base. ② The welding current application includes four stages: preheating, transverse growth of the weld nugget, longitudinal growth of the weld nugget, and stirring. The preheating stage uses a current of 6kA for 200ms, the transverse growth stage uses a current of 8kA for 40ms, the longitudinal growth stage uses a current of 8kA for 80ms, and the stirring stage uses a pulse current of 10 welding times of 40ms and a cooling time of 5ms. The welding current is increased from 10kA to 12kA. ③ Apply a controllable magnetic field, corresponding to the welding current, and apply the magnetic field in the two stages of transverse growth and stirring of the weld nugget. The magnetic field strength is 1.2T, and the magnetic field strength is zero in other stages. ④ Due to the barrier effect of the high resistivity oxide film between the high-melting-point plate to be connected and the low-melting-point plate to be connected, the current density is mainly concentrated in the high-melting-point plate to be connected, while the current density in the low-melting-point plate to be connected is relatively small. The high-melting-point plate to be connected is heated by heat conduction, causing the low-melting-point plate to be connected to melt within a certain depth range near the high-melting-point plate to be connected, forming molten metal. The heterogeneous materials on both sides of the interface diffuse into each other, forming intermetallic compounds. Under the action of the Lorentz force generated by the magnetic field source, the molten metal undergoes three-dimensional flow, realizing the diffuse distribution of the oxide film near the interface.

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