Kovar alloy and oxygen-free copper composite material and welding method thereof

Abstract

The invention provides a Kovar alloy and oxygen-free copper composite material and a welding method thereof. The welding method comprises the steps that S1, 4J29 Kovar alloy and TU1 oxygen-free copper plates are machined to serve as base materials; s2, an Ag-based amorphous foil strip is adopted as brazing filler metal; s3, polishing to-be-welded surfaces of the 4J29 kovar alloy and the TU1 oxygen-free copper, and performing acid pickling and blow-drying; s4, the welding face of the 4J29 kovar alloy base metal to be welded is placed upwards, the Ag-based amorphous foil strip is placed on the middle layer, the welding face of the TU1 oxygen-free copper base metal is placed downwards on the upper portion of the middle layer, and a composite workpiece to be welded is formed; s5, the composite to-be-welded workpiece is placed in a double-heat-source vacuum brazing furnace, an electrode pressure head makes contact with the TU1 oxygen-free copper base metal on the upper layer, current is conducted in the welding process, and the current passes through the assembled composite to-be-welded workpiece to form a loop; and S6, double-heat-source vacuum brazing is conducted, and the kovar alloy and oxygen-free copper composite material workpiece is obtained. According to the method, reliable dissimilar metal connection is formed in a double-heat-source vacuum brazing mode, and the composite material with excellent performance is prepared.

Description

Technical Field

[0001] The invention belongs to the technical field of composite materials, and in particular relates to a composite material of Kovar alloy and oxygen-free copper and a welding method thereof. Background Art

[0002] Kovar alloy (4J29) is a special alloy composed of iron, nickel, cobalt and other elements. It is called "constant expansion alloy" because it can maintain a low and stable thermal expansion coefficient below the Curie point. This alloy can still maintain good mechanical properties and corrosion resistance at high temperatures, and has been widely used in high-end industrial fields such as aerospace, semiconductors, and automobiles. However, the poor thermal conductivity of Kovar alloy limits its application. Oxygen-free copper (TU1) has excellent electrical conductivity, thermal conductivity and ductility, and is an ideal choice for electronic packaging materials. Kovar alloy is combined with oxygen-free copper to prepare a Kovar alloy / copper composite material with high electrical conductivity, high thermal conductivity and low expansion coefficient, thereby meeting the needs of high-performance electronic packaging materials. The existing technology mostly uses a traditional vacuum brazing furnace to complete the entire welding process through a single heat source heating method of radiation heating, which is time-consuming and energy-intensive. For large-sized brazing specimens, there are problems such as uneven heating, which are prone to welding defects, resulting in low bonding strength between the two metals, and the composite material is prone to separation during welding. Summary of the invention

[0003] In view of the above technical problems, the purpose of the present invention is to provide a Kovar alloy and oxygen-free copper composite material and a welding method thereof. The self-resistance heating in the preparation method effectively enhances the fluidity of the solder, thickens the diffusion layer at the weld, improves the bonding strength of the two metals, solves the problem that the composite material is prone to separation during welding, and prepares a Kovar alloy and oxygen-free copper composite material with excellent performance.

[0004] The present invention adopts dual heat source vacuum brazing as a connection method of Kovar alloy and oxygen-free copper, which can significantly reduce the defects of welding joints, form a good metallurgical bond at the brazing seam, and easily obtain high-quality joints with stable performance, which well solves the problem of insufficient mechanical properties after welding of dissimilar alloys.

[0005] The dual heat source vacuum brazing adopted in the present invention means that the welding process is completed by two heating methods: radiation heating and self-resistance heating. Compared with the traditional brazing technology, the addition of current-assisted self-resistance heat generation mainly solves the problem of uneven temperature distribution in the welding system, and can provide additional driving force for interface reaction gap closure and atomic diffusion, thereby forming a reliable connection at a relatively low temperature and in a short time, which is of great significance for brazing connection of composite materials.

[0006] Note that the description of these objectives does not prevent the existence of other objectives. One embodiment of the present invention does not need to achieve all of the above objectives. Objectives other than the above objectives can be extracted from the description of the specification, drawings, and claims.

[0007] The present invention achieves the above technical objectives through the following technical means.

[0008] A method for welding a kovar alloy and an oxygen-free copper composite material comprises the following steps:

[0009] Step S1: Processing 4J29 Kovar alloy and TU1 oxygen-free copper plates with a thickness of A as base materials;

[0010] Step S2: using Ag-based amorphous foil as solder with a melting point of T0;

[0011] Step S3: polish the 4J29 Kovar alloy and TU1 oxygen-free copper surfaces to be welded in step S1, pickle and blow dry to make the surfaces clean, free of oil stains and oxide layer;

[0012] Step S4: assembling the workpiece to be welded, placing the welding surface of the 4J29 Kovar alloy base material to be welded upward, placing the Ag-based amorphous foil strip as the solder in the middle layer, and placing the welding surface of the TU1 oxygen-free copper base material downward on the middle layer to form a composite workpiece to be welded with a "sandwich" structure;

[0013] Step S5: placing the composite workpiece to be welded assembled in step S4 in a dual-heat source vacuum brazing furnace, with the electrode pressure head in contact with the upper layer of TU1 oxygen-free copper base material, and passing current during the welding process so that the current passes through the assembled composite workpiece to be welded to form a loop;

[0014] Step S6: starting the dual-heat source vacuum brazing furnace, setting brazing parameters, and performing dual-heat source vacuum brazing to obtain a Kovar alloy and oxygen-free copper composite material workpiece.

[0015] In the above scheme, the thickness A of the 4J29 Kovar alloy and the TU1 oxygen-free copper in step S1 is 5 mm, with an error of ±0.1 mm.

[0016] In the above scheme, the Ag-based amorphous foil solder composition in step S2 is BAg30CuZnSn, BAg45CuZn or BAg72Cu.

[0017] In the above scheme, in step S2, the melting point T0 of the alloy is 745-779°C.

[0018] In the above scheme, in step S3, the surfaces to be welded of the 4J29 Kovar alloy and the TU1 oxygen-free copper base material are polished with 400-grit sandpaper, and then pickled in a 35% HCl solution for 1 hour.

[0019] In the above scheme, the vacuum degree of the dual heat source vacuum brazing furnace is 0.002Pa, the heating rate is 10℃ / min, the current is set to 1000A, the brazing temperature T1 is 850℃, the insulation time S is 40min, and the dual heat sources are heated simultaneously, so that the inside of the workpiece is heated quickly and evenly.

[0020] A composite material of Kovar alloy and oxygen-free copper is prepared according to the welding method of the composite material of Kovar alloy and oxygen-free copper.

[0021] In the above scheme, the interface width of the Kovar alloy and oxygen-free copper composite material is 274.22-402.12 μm, and the shear strength is 128-157.01 MPa.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The dual heat source vacuum brazing of the present invention generates heat through two methods: radiation heating and self-resistance heating. The addition of electric current can reduce the surface tension of the liquid solder, improve its wettability on the base material, and reduce unfused defects. At the same time, the electric current drives the migration of metal ions (electromigration effect), promotes the atomic diffusion between the solder and the base material, enhances the metallurgical bonding at the interface, inhibits the excessive growth of brittle intermetallic compounds (such as Cu-Fe and Cu-Ni phases) at the interface, and improves the toughness of the joint. The composite material of Kovar alloy 4J29 and oxygen-free copper TU1 prepared under the dual heat source vacuum brazing method and condition parameters of the present invention has an interface width of 274.22 to 402.12 μm and a shear strength of 128 to 157.01 MPa. It can be seen that the prepared composite material has high interface bonding strength, high stability and reliability, and significantly improved mechanical properties.

[0024] 2. The present invention adopts the process of dual heat source vacuum brazing. The Joule heat generated when the current passes through the joint can achieve local rapid heating, reduce the overall heat input, and thus reduce the residual stress caused by the difference in thermal expansion coefficients of dissimilar parent materials. The addition of current-assisted self-resistance heat generation makes the temperature distribution in the welding system uniform, effectively shortens the brazing heating time, improves welding production efficiency, reduces welding energy consumption, and reduces welding costs.

[0025] Note that the description of these effects does not prevent the existence of other effects. One embodiment of the present invention does not necessarily have all of the above effects. Effects other than the above can be clearly seen and extracted from the description of the specification, drawings, claims, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of the lap welding structure of the 4J29 Kovar alloy and TU1 oxygen-free copper composite material prepared in the present invention;

[0027] Figure 2It is a temperature setting curve diagram of the dual heat source vacuum brazing of 4J29 Kovar alloy and TU1 oxygen-free copper composite material of the present invention;

[0028] Figure 3 This is a metallographic image of the interface of the 4J29 Kovar alloy and TU1 oxygen-free copper composite material prepared in Example 1;

[0029] Figure 4 This is a metallographic image of the interface of the 4J29 Kovar alloy and TU1 oxygen-free copper composite material prepared in Example 2;

[0030] Figure 5 This is a metallographic image of the interface of the 4J29 Kovar alloy and TU1 oxygen-free copper composite material prepared in Example 3;

[0031] Figure 6 Metallographic image of the interface of 4J29 Kovar alloy and TU1 oxygen-free copper composite material prepared by vacuum brazing of BAg30CuZnSn single heat source in comparative example 1;

[0032] Figure 7 Metallographic image of the interface of 4J29 Kovar alloy and TU1 oxygen-free copper composite material prepared by vacuum brazing of 2BAg45CuZn single heat source in comparative example;

[0033] Figure 8 This is the metallographic diagram of the interface of 4J29 Kovar alloy and TU1 oxygen-free copper composite material prepared by vacuum brazing of 3BAg72Cu single heat source in comparative example. DETAILED DESCRIPTION

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. The features in the embodiments of the present invention can be combined with each other without conflict. In addition, unless otherwise specified, the preparation processes in the following embodiments are conventional means in the prior art of the art, and therefore, they are not described in detail; the raw materials used in the following embodiments are all commercially available products.

[0035] Example 1

[0036] A method for welding a kovar alloy and an oxygen-free copper composite material comprises the following steps:

[0037] Step S1: Processing pre-treated plates: Using machining, 4J29 Kovar alloy and TU1 oxygen-free copper plates are obtained, with the length, width and thickness dimensions of 30mm*30mm*5mm and a thickness error of ±0.1mm;

[0038] Step S2: using BAg30CuZnSn amorphous foil as the intermediate layer solder, the alloy melting point T0 is 755°C;

[0039] Step S3: Use 400-grit sandpaper to polish the 4J29 and TU1 surfaces to be welded in step S1, and soak them in 35% HCl solution for pickling for 1 hour to remove the oxide layer on the surface of the material and produce acid etching on the material matrix to roughen the surface, which is helpful for the wetting of the solder on the material surface. After pickling, blow dry for standby use.

[0040] Step S4: Assemble the parts to be welded, such as Figure 1 As shown, the welding surface of the 4J29 Kovar alloy base material to be welded is placed upward, the BAg30CuZnSn amorphous foil is placed as the solder in the middle layer, and the welding surface of the TU1 oxygen-free copper base material is placed downward on the middle layer to form a "sandwich" structure of the workpiece to be welded.

[0041] Step S5: placing the workpiece to be welded assembled in step S4 in a dual-heat source vacuum brazing furnace, with the electrode pressure head in contact with the upper layer of TU1 oxygen-free copper base material, and passing current during the welding process so that the current passes through the assembled composite workpiece to be welded to form a loop;

[0042] Step S6: Start the dual heat source vacuum brazing furnace, and the vacuum degree in the furnace is 0.002 Pa. Set the brazing parameters, such as Figure 2 As shown, the welding temperature is 850℃ and the holding time is 40min. Figure 2 As shown, the heating rate is 10°C / min, the current is set to 1000A, and dual heat source vacuum brazing is performed to obtain a Kovar alloy and oxygen-free copper composite material workpiece.

[0043] After step S6, a metallographic sample is cut from the vertical weld using a wire cutting device. After grinding, polishing and etching, it is quickly washed with clean water, dehydrated with alcohol, dried with a hair dryer and its metallographic structure is observed under a metallographic microscope.

[0044] Figure 3 The metallographic image of the weld of the Kovar alloy and oxygen-free copper composite material prepared in Example 1; Figure 3 It can be seen that due to the heat generated by the current, the interface is uneven on the copper and solder bonding side, and a large number of local melting areas are found on the surface of the copper base material, which are wavy pits. This increases the contact area between copper and solder to a certain extent, which helps to improve the bonding strength of the interface; on the Kovar alloy and solder bonding side, significant capillary condensation is observed at the interface. Under the action of the current, the current effect promotes the diffusion of interface elements, and the solder spreads in the Kovar alloy matrix like a tree root. A large number of solder elements penetrate and diffuse along the Kovar alloy grain boundaries.

[0045] Example 2

[0046] The specific preparation steps are the same as those in Example 1. The difference between this example and Example 1 is that:

[0047] The Ag-based solder composition in step S2 is BAg45CuZn, the solder melting point T0 is 755°C, the brazing temperature T1 is set to 850°C, the holding time is 40min, the current is set to 1000A, and the other parameters are the same as in Example 1.

[0048] Figure 4 The metallographic image of the weld of the Kovar alloy and oxygen-free copper composite material prepared in Example 2; Figure 4 It can be seen that due to the heat generated by the current, a local melting area was also found on the copper base metal side, but the melting depth was relatively shallow. Since the current effect promotes the diffusion of interface elements, the brazing filler metal elements produce a small amount of grain boundary diffusion on the Kovar alloy side, but the diffusion depth is shallow.

[0049] Example 3

[0050] The specific preparation steps are the same as those in Example 1. The difference between this example and Example 1 is that:

[0051] The Ag-based solder composition in step S2 is BAg72Cu, the solder melting point T0 is 779°C, the brazing temperature T1 is set to 850°C, the holding time is 40min, the current is set to 1000A, and the other parameters are the same as in Example 1.

[0052] Figure 5 The metallographic image of the weld of the Kovar alloy and oxygen-free copper composite material prepared in Example 3; Figure 5 It can be seen that a small amount of local melting area is still found on the copper base metal side due to the heat generated by the current. Since the current effect promotes the diffusion of interface elements, the brazing filler metal elements produce a small amount of grain boundary diffusion on the Kovar alloy side, but the diffusion depth is shallow.

[0053] The test method adopted by the present invention is as follows:

[0054] In the present invention, the performance results of the prepared Kovar alloy and oxygen-free copper composite material are shown in Table 1:

[0055] Table 1 Properties of 4J29 / TU1 composite materials prepared in Examples 1-3

[0056] Example Interface width (μm) Shear strength(MPa) Example 1 293.89-402.12 157.01 Example 2 274.22-356.58 135.44 Example 3 276.39-337.54 128

[0057] The main detection methods are as follows:

[0058] (1) Interface thickness: The metallographic structure was taken with a Zeiss scope to analyze the interface bonding characteristics of the Kovar alloy and oxygen-free copper (4J29 / TU1) composite material. Multiple fields of view were selected to obtain the interface width, and the maximum and minimum values ​​were taken to form a range of interface width values.

[0059] (2) Shear strength: The joint shear test is carried out in accordance with GB / T11363-2008 "Brazed joint strength test method". The shear speed is 0.5 mm / min and the entrance force is 10 N.

[0060] The interface widths of Examples 1, 2, and 3 are significantly reduced. The solder in Example 1 has the lowest Ag content, but the interface layer width is significantly higher than that of Examples 2 and 3. The electron migration effect is obvious. On the side where the Kovar alloy and the solder are combined, a significant capillary condensation phenomenon is observed at the interface. The solder spreads in the Kovar alloy matrix in the shape of a tree root, and a large amount of solder elements penetrate and diffuse along the Kovar alloy grain boundary. Figure 3 It can be seen that a small amount of Cu element penetrates into the grain boundary of Kovar alloy. By comparing the shear strength of the composite material, it can be seen that the bonding strength of the low Ag solder in Example 1 is greater, indicating that the bonding is more solid, the mechanical properties are the best, and the diffusion layer on the Kovar alloy side is the thickest, while the shear strength of Examples 2 and 3 is slightly lower.

[0061] Comparative Examples 1, 2, and 3 adopt the traditional brazing method - single heat source vacuum brazing, to prepare 4J29 Kovar alloy and TU1 oxygen-free copper (4J29 / TU1) composite materials. Compared with the dual heat source vacuum brazing of the present invention, Comparative Examples 1, 2, and 3 lack current heat generation and current effect. Comparative Examples 1, 2, and 3 all use a single heat source vacuum brazing furnace to set the following parameters: vacuum degree 0.002Pa, heating rate 10°C / min, brazing temperature 850°C, and insulation time 60min. The difference is that Comparative Examples 1, 2, and 3 use brazing materials of different compositions to conduct welding experiments. The brazing material composition used in Comparative Example 1 is BAg30CuZnSn, the brazing material composition used in Comparative Example 2 is BAg45CuZn, and the brazing material composition used in Comparative Example 3 is BAg72Cu. The metallographic images of the welds obtained in Comparative Examples 1, 2, and 3 are shown in the figure below. Figure 6 , Figure 7 , Figure 8Under the same welding temperature, the welded joint obtained by single heat source vacuum brazing obviously has multiple hole welding defects, the diffusion layer is narrow, the interface on the Cu side is relatively flat, and the intergranular diffusion phenomenon on the Kovar alloy side is not obvious. The properties of the composite materials of 4J29 Kovar alloy and TU1 oxygen-free copper (4J29 / TU1) prepared by single heat source vacuum brazing in Comparative Examples 1, 2, and 3 are shown in Table 2. The interface width of the composite materials of 4J29 Kovar alloy and TU1 oxygen-free copper (4J29 / TU1) obtained by single heat source vacuum brazing is slightly lower than the interface width of the weld obtained in the present invention. The above interface characteristics make the shear strength of the composite materials obtained by single heat source vacuum brazing much lower than the shear strength obtained in the present invention.

[0062] Table 2 Properties of 4J29 / TU1 composites prepared by single heat source vacuum brazing

[0063] Comparative Example Interface width (μm) Shear strength(MPa) Comparative Example 1 300.75-356.14 79 Comparative Example 2 342.63-352.17 72 Comparative Example 3 303.75-350.68 69

[0064] The invention discloses a process method for preparing high-performance 4J29 / TU1 composite materials by dual heat source vacuum brazing. Under the conditions of dual heat source vacuum brazing process parameters of: brazing temperature of 850°C, holding time of 40min, and current setting of 1000A, a composite material of Kovar alloy 4J29 and oxygen-free copper TU1 is prepared. The electromigration effect promotes atomic diffusion between the brazing material and the parent material, enhances interface metallurgical bonding, inhibits excessive growth of brittle intermetallic compounds at the interface, improves joint toughness, and prepares a composite material with a high bonding strength interface. The interface width is 274.22-402.12μm, and the shear strength is 128-157.01MPa. It can be seen that the prepared composite material has high interface bonding strength, high stability and reliability, and significantly improved mechanical properties.

[0065] The present invention prepares high-performance 4J29 Kovar alloy and TU1 oxygen-free copper (4J29 / TU1) composite materials by dual-heat source vacuum brazing, fully utilizing the advantages of adding current in brazing technology, and realizing local rapid heating through Joule heating effect, which not only reduces overall heat input and residual stress, but also significantly improves the quality and production efficiency of 4J29 / TU1 brazed joints through uniform temperature distribution, shortening heating time and reducing energy consumption, and provides an efficient, energy-saving and reliable solution for welding dissimilar materials. Therefore, the present invention can fully meet the industry's demand for such materials.

[0066] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0067] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. All equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for welding a composite material of Kovar alloy and oxygen-free copper, characterized in that: The following steps are involved: Step S1: Processing 4J29 Kovar alloy and TU1 oxygen-free copper plates with a thickness of A as base materials; Step S2: using Ag-based amorphous foil as solder with a melting point of T0; Step S3: polishing the 4J29 Kovar alloy and TU1 oxygen-free copper surfaces to be welded in step S1, pickling and drying; Step S4: assembling the workpiece to be welded, placing the welding surface of the 4J29 Kovar alloy base material to be welded upward, placing the Ag-based amorphous foil strip as the solder in the middle layer, and placing the welding surface of the TU1 oxygen-free copper base material downward on the middle layer to form a composite workpiece to be welded with a "sandwich" structure; Step S5: placing the composite workpiece to be welded assembled in step S4 in a dual-heat source vacuum brazing furnace, with the electrode pressure head in contact with the upper layer of TU1 oxygen-free copper base material, and passing current during the welding process so that the current passes through the assembled composite workpiece to be welded to form a loop; Step S6: starting the dual-heat source vacuum brazing furnace, setting brazing parameters, and performing dual-heat source vacuum brazing to obtain a Kovar alloy and oxygen-free copper composite material workpiece.

2. The process for preparing high-performance 4J29 / TU1 composite materials by dual heat source vacuum brazing according to claim 1, characterized in that: In the step S1, the thickness A of the 4J29 Kovar alloy and the TU1 oxygen-free copper is 5 mm.

3. The process for preparing high-performance 4J29 / TU1 composite materials by dual heat source vacuum brazing according to claim 1, characterized in that: In the step S2, the solder composition of the Ag-based amorphous foil strip is BAg30CuZnSn, BAg45CuZn or BAg72Cu.

4. The process for preparing high-performance 4J29 / TU1 composite materials by dual heat source vacuum brazing according to claim 1 is characterized in that: In the step S2, the alloy melting point T0 is 745-779°C.

5. The process for preparing high-performance 4J29 / TU1 composite materials by dual heat source vacuum brazing according to claim 1, characterized in that: In step S3, the surfaces to be welded of the 4J29 Kovar alloy and the TU1 oxygen-free copper base material are polished with 400-grit sandpaper, and then pickled in a 35% HCl solution for 1 hour.

6. The titanium alloy current-assisted vacuum brazing process according to claim 1, characterized in that: In step S6, the vacuum degree of the dual heat source vacuum brazing furnace is 0.002Pa.

7. The titanium alloy current-assisted vacuum brazing process according to claim 1, characterized in that: In step S6, the heating rate is 10°C / min and the current is set to 1000A.

8. The titanium alloy current-assisted vacuum brazing process according to claim 1, characterized in that: In step S6, the brazing temperature T1 is 850° C. and the holding time S is 40 min.

9. A composite material of Kovar alloy and oxygen-free copper, characterized in that: Prepared by the welding method of Kovar alloy and oxygen-free copper composite material according to any one of claims 1-8.

10. The composite material of Kovar alloy and oxygen-free copper according to claim 9, characterized in that: The interface width of the Kovar alloy and oxygen-free copper composite material is 274.22-402.12 μm, and the shear strength is 128-157.01 MPa.

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