A brazing material for copper-aluminum flame brazing, its preparation method and application

Abstract

The present invention belongs to the technical field of brazing materials for dissimilar copper-aluminum metals, and particularly relates to a brazing material for flame brazing of copper-aluminum, a preparation method thereof, and an application. The brazing material for flame brazing of copper-aluminum according to the present invention is composed of the following components by mass percentage: 15-20% of Al, 1-3% of Mn, 0.5-1.5% of Sr, and the balance is Zn. The brazing material for flame brazing of copper-aluminum according to the present invention can improve the oxidation resistance of the filler metal and refine the structure of the filler metal. When used for flame brazing of dissimilar copper-aluminum metal joints, it can effectively improve the mechanical strength of the copper-aluminum joints. The shear strength of the brazed lap copper-aluminum joints reaches 95.2-105.3 MPa, and it has a good application prospect in the field of brazing of copper-aluminum joints.

Description

Technical Field

[0001] The present invention belongs to the technical field of brazing materials for dissimilar copper-aluminum metals, and particularly relates to a brazing material for copper-aluminum flame brazing, a preparation method thereof, and an application thereof. Background Art

[0002] Connecting copper and aluminum to form a dissimilar copper-aluminum metal joint can not only reduce the consumption of scarce metal copper and reduce the weight of components, but also give full play to the respective performance advantages of copper and aluminum, and has been widely used in the fields of electric power and refrigeration equipment.

[0003] At present, in the manufacturing process of Cu / Al joints in electric power and refrigeration equipment, flame brazing is often used to realize the welding of copper and aluminum. In the process of flame brazing of copper-aluminum composites, the filler metals used mainly include Sn-Pb series, Sn-Zn series, Al-Si series, and Zn-Al series filler metals. Soft filler metals such as Sn-Pb and Sn-Zn need to be combined with corrosive solutions with relatively low melting points such as ZnCl2 and NH4Cl as brazing fluxes, and the process is complex and the cost is high, which limits their application. Compared with Al-Si filler metals, the brazing temperature of Zn-Al series filler metals is generally 100°C or even more lower, which can provide a wider process window for the brazing process of aluminum and copper, and can reduce the thermal stress of the joint and the generation amount of intermetallic compounds. Moreover, since the melting point of Zn-Al filler metal is between that of soft filler metal and hard filler metal, its melting point can be conveniently adjusted, and it has excellent processing performance and mechanical properties. Therefore, the application of flame brazing with Zn-Al filler metal to dissimilar copper-aluminum metals has gradually begun in industry, and currently, Zn-2Al, Zn-10Al, Zn-15Al, and Zn-22Al are commonly used. Since the melting points of Zn-2Al, Zn-10Al, and Zn-15Al filler metals are relatively low and their compatibility with the currently most commonly used CsF-AlF3 non-corrosive brazing flux is poor, Zn-22Al has become the most commonly used choice.

[0004] Although Zn-22Al filler metal has achieved certain effects in Cu / Al flame brazing, there are still some problems that are difficult to solve: Firstly, the oxide on the surface of Zn-22Al filler metal is basically composed of ZnO, and the ZnO film structure is loose and cannot play a protective role for the filler metal; at the same time, the large amount of this oxide during the brazing process will also deteriorate the brazing performance of the filler metal. Secondly, due to the relatively high Al content in Zn-22Al, it is still inevitable to react with the Cu base metal to form brittle compound phases, resulting in a significant reduction in the mechanical strength of the brazed joint and affecting the mechanical properties of the brazed component.

[0005] Therefore, how to optimize the composition of Zn-22Al filler metal to further improve the mechanical properties of the copper-aluminum joint obtained by brazing with Zn-22Al filler metal has become an urgent technical problem to be solved. Summary of the Invention

[0006] To solve the above problems, the object of the present invention is to provide a brazing material for copper-aluminum flame brazing, and the obtained copper-aluminum joint has excellent mechanical strength, belonging to the brazing application of copper-aluminum joints.

[0007] The present invention also provides a preparation method of the above brazing material for copper-aluminum flame brazing, and its process is simple and suitable for industrial production.

[0008] The present invention also provides the application of the above brazing material for copper-aluminum flame brazing, specifically the application in the preparation of copper-aluminum composite joints by flame brazing.

[0009] In order to achieve the above object, the brazing material for copper-aluminum flame brazing of the present invention adopts the following technical solution:

[0010] A brazing material for copper-aluminum flame brazing is composed of the following components in mass percentage: 15-20% of Al, 1-3% of Mn, 0.5-1.5% of Sr, and the balance is Zn.

[0011] For the brazing material for copper-aluminum flame brazing of the present invention, by controlling the addition amounts of Zn and Al elements, and introducing Mn and Sr elements into the Zn-Al filler metal at the same time, a new Zn-Al-Mn-Sr filler metal is prepared to optimize the filler metal microstructure and improve the brazing performance. Among them, the alkaline earth metal Sr is introduced in the present invention. During the melting process of the filler metal, Sr is easy to form SrO and SrO2 films with oxygen atoms in the air. The films are not only dense but also extremely easy to adhere to the surface of the filler metal. When the melting of the filler metal is completed and enters the heat preservation process, the dense film layer will hinder the interfacial reaction process, thereby reducing the generation rate of ZnO and improving the oxidation resistance of the filler metal. The improvement of the oxidation resistance can significantly reduce the viscosity of the filler metal, which is beneficial to the improvement of the wetting and spreading performance of the filler metal and the brazing performance. Further, the present invention also adds Mn element while adding Sr element. The two cooperate to achieve the purpose of refining the filler metal structure. As a result, after the Zn-Al-Mn-Sr filler metal of the present invention is used for copper-aluminum brazing, the brittle phases at the interface are also refined, and the smaller-sized interfacial compounds help to inhibit the growth and expansion of cracks, thereby effectively improving the mechanical properties of the joint.

[0012] In order to further optimize the brazing performance of the brazing material, preferably, the brazing material for copper-aluminum flame brazing is composed of the following components in mass percentage: 16.5% of Al, 1.8% of Mn, 0.9% of Sr, and the balance is Zn.

[0013] The preparation method of the brazing material for copper-aluminum flame brazing of the present invention adopts the following technical solution:

[0014] The preparation method of the brazing material for copper-aluminum flame brazing includes the following steps:

[0015] Take Zn, Al, Al-Mn master alloy, and Al-Sr master alloy according to the elements and proportions of the brazing material for copper-aluminum flame brazing. After melting Zn and Al, raise the temperature to 740 - 760 °C, add the Al-Mn master alloy for melting, cover with a covering agent after heat preservation, continue to raise the temperature to 950 - 1050 °C, add the Al-Sr master alloy and continue melting, and then carry out pouring, extrusion, and reducing diameter processing after heat preservation to obtain the brazing material for copper-aluminum flame brazing.

[0016] The preparation method of the brazing material for copper-aluminum flame brazing of the present invention has a simple process and is suitable for industrial production. In the method of the present invention, the way of adding master alloy for melting is adopted. The master alloy can reduce the melting temperature of the metal and reduce the energy consumption in the step-by-step melting process. Moreover, the master alloy can reduce the segregation during metal melting and avoid the occurrence of segregation phenomena in the step-by-step melting process, which helps to improve the strength of the brazed joint.

[0017] Preferably, when adding the Al-Mn master alloy for melting, the heat preservation time is 25 - 35 min.

[0018] Furthermore, when adding the Al-Sr master alloy and continuing melting, the heat preservation time is 15 - 25 min.

[0019] Preferably, the covering agent is composed of KCl and NaCl; the mass ratio of KCl to NaCl is 1:1.

[0020] Furthermore, before pouring, it also includes the step of refining the melt by blowing argon gas.

[0021] The application of the brazing material for copper-aluminum flame brazing of the present invention is specifically the application in the preparation of copper-aluminum composite joints by flame brazing.

[0022] Preferably, in the copper-aluminum composite joint, the copper used is oxygen-free copper and the aluminum used is pure aluminum.

[0023] Furthermore, the brazing flux used in the flame brazing is the CsF-AlF3 non-corrosive brazing flux; the mass percentage composition of the brazing flux is: 71.4% CsF, 28.6% AlF3; the temperature of the flame brazing is 450 - 500 °C, and the heat preservation time is 10 - 20 min. The present invention uses the non-corrosive brazing flux with the above composition, which has a low cost. And the brazing material of the present invention can be effectively adapted to the CsF-AlF3 non-corrosive brazing flux and exhibit good brazing performance.

[0024] The brazing material for copper-aluminum flame brazing of the present invention can improve the oxidation resistance of the filler metal and effectively enhance the mechanical strength of the copper-aluminum joint. When brazing a copper-aluminum joint using the flame brazing process, the shear strength of the brazed lap joint of copper and aluminum reaches 95.2 - 105.3 MPa, showing good application prospects in the field of brazing copper-aluminum joints. Brief Description of the Drawings

[0025] Figure 1 It is a thermogravimetric analysis result diagram of the brazing material for copper-aluminum flame brazing in Example 1 of the present invention and the Zn-22Al filler metal in Comparative Example 1 under different oxidation times. Detailed Description of the Invention

[0026] The technical solutions of the present invention will be further described below in conjunction with specific embodiments. However, those skilled in the art should understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. In the following examples, the raw materials involved are all conventional commercially available products unless otherwise specified.

[0027] Among them, in the Al-Mn master alloy, the mass ratio of Al to Mn is 70:30; in the Al-Sr master alloy, the mass ratio of Al to Sr is 60:40.

[0028] Example 1

[0029] The brazing material for copper-aluminum flame brazing in this example is composed of the following components by mass percentage: 16.5% of Al, 1.8% of Mn, 0.9% of Sr, and the balance is Zn.

[0030] The preparation method of the above brazing material for copper-aluminum flame brazing includes the following steps:

[0031] Take Zn, Al, Al-Mn master alloy, and Al-Sr master alloy according to the elements and ratios of the brazing material for copper-aluminum flame brazing; put the metals Zn and Al into an intermediate frequency furnace for melting. When the temperature of the molten metal in the furnace reaches 750 °C, add the Al-Mn master alloy for melting, cover with a covering agent after holding for 30 minutes. The covering agent is a mixture of KCl and NaCl with a mass ratio of 1:1. Continue to heat up to 1000 °C, add the Al-Sr master alloy and continue melting. After holding for 20 minutes, cool down, and blow argon for refining. When the temperature cools to 700 °C, the melting is completed. Pour the solution into a casting mold to form an ingot. During the pouring process, turn on the cooling system to rapidly cool the ingot, obtaining a rod-shaped ingot with a diameter of 32 mm. The rod-shaped ingot is processed into a filamentous filler metal through extrusion and wire drawing with diameter reduction, that is, the brazing material for copper-aluminum flame brazing is obtained.

[0032] Example 2

[0033] The brazing material for copper-aluminum flame brazing in this embodiment is composed of the following components by mass percentage: 15% Al, 1% Mn, 0.5% Sr, and the balance is Zn.

[0034] The preparation method of the above-mentioned brazing material for copper-aluminum flame brazing includes the following steps:

[0035] Take Zn, Al, Al-Mn master alloy, and Al-Sr master alloy according to the elements and ratio of the brazing material for copper-aluminum flame brazing; put the metals Zn and Al into an intermediate frequency furnace for melting. When the temperature of the molten liquid in the furnace reaches 740 °C, add the Al-Mn master alloy for smelting. After holding for 30 min, cover it with a covering agent, which is a mixture of KCl and NaCl with a mass ratio of 1:1. Continue to heat up to 950 °C, add the Al-Sr master alloy and continue smelting. After holding for 20 min, cool it, and blow argon for refining. When the temperature cools to 700 °C, the smelting is completed. Pour the solution into a mold to form an ingot. During the pouring process, turn on the cooling system to quickly cool the ingot, and obtain a rod-shaped ingot with a diameter of 32 mm. The rod-shaped ingot is processed into a filamentous filler metal through extrusion and wire drawing with diameter reduction, and thus the brazing material for copper-aluminum flame brazing is obtained.

[0036] Example 3

[0037] The brazing material for copper-aluminum flame brazing in this embodiment is composed of the following components by mass percentage: 20% Al, 3% Mn, 1.5% Sr, and the balance is Zn.

[0038] The preparation method of the above-mentioned brazing material for copper-aluminum flame brazing includes the following steps:

[0039] Take Zn, Al, Al-Mn master alloy, and Al-Sr master alloy according to the elements and ratio of the brazing material for copper-aluminum flame brazing; put the metals Zn and Al into an intermediate frequency furnace for melting. When the temperature of the molten liquid in the furnace reaches 760 °C, add the Al-Mn master alloy for smelting. After holding for 30 min, cover it with a covering agent, which is a mixture of KCl and NaCl with a mass ratio of 1:1. Continue to heat up to 1050 °C, add the Al-Sr master alloy and continue smelting. After holding for 20 min, cool it, and blow argon for refining. When the temperature cools to 700 °C, the smelting is completed. Pour the solution into a mold to form an ingot. During the pouring process, turn on the cooling system to quickly cool the ingot, and obtain a rod-shaped ingot with a diameter of 32 mm. The rod-shaped ingot is processed into a filamentous filler metal through extrusion and wire drawing with diameter reduction, and thus the brazing material for copper-aluminum flame brazing is obtained.

[0040] Comparative Example 1

[0041] The brazing material in this comparative example is a Zn-22Al filler metal, which is composed of the following components by mass percentage: 22% Al, and the balance is Zn.

[0042] Comparative Example 2

[0043] The brazing material of this comparative example is a Zn-Al brazing filler metal, which is composed of the following components by mass percentage: 16.5% of Al, and the balance is Zn.

[0044] Comparative Example 3

[0045] The brazing material of this comparative example is a Zn-Al-Mn brazing filler metal, which is composed of the following components by mass percentage: 16.5% of Al, 1.8% of Mn, and the balance is Zn.

[0046] Comparative Example 4

[0047] The brazing material of this comparative example is a Zn-Al-Sr brazing filler metal, which is composed of the following components by mass percentage: 16.5% of Al, 0.9% of Sr, and the balance is Zn.

[0048] Test Example

[0049] I. Thermogravimetric analysis test

[0050] The test was carried out using a Pyris Diamond thermogravimetric / differential thermal comprehensive thermal analyzer from Perin-Elmer. During the test, the heating rate was 20 °C / min, the initial weight of the brazing filler metal was 20 mg, the final heating temperature was 530 °C, and the holding time was 30 min. The test atmosphere was air. The change curves of the mass of the brazing filler metal with temperature and time during the heating process were recorded respectively. The thermogravimetric loss mass of the Zn-Al-Mn-Sr brazing filler metal of Example 1 and the traditional Zn-22Al brazing filler metal of Comparative Example 1 under different oxidation times was analyzed. The results are as Figure 1 shown.

[0051] It can be Figure 1 seen that during the holding process, the weight of the Zn-22Al brazing filler metal continued to increase with the increase of the heating time, indicating that the oxidation process of the Zn-22Al brazing filler metal continued during the heating process. While the weight of the Zn-Al-Mn-Sr brazing filler metal of the present invention added with Sr and Mn elements showed a trend of first increasing and then gradually stabilizing. This is presumably because the Sr element in the Zn-Al-Mn-Sr brazing filler metal reacts with oxygen atoms in the air to form SrO and SrO2 films. This dense film layer will hinder the interfacial reaction process and reduce the diffusion rate of oxygen atoms, thereby reducing the ZnO generation rate and effectively improving the oxidation resistance of the brazing filler metal.

[0052] II. Brazing performance test

[0053] The brazing performance test was carried out using pure aluminum and copper as base materials, with dimensions of 60 mm × 25 mm × 3 mm. The lap length of the lap joint was 3 mm, and the joint was placed with a normal gap (about 0.15 mm). The brazing flux was CsF-AlF3 non-corrosive brazing flux, and the brazing flux composition was 71.4% CsF and 28.6% AlF3. The flame brazing temperature was 475 °C, and the holding time was 15 min. The shear performance test of the brazed joint was carried out with reference to the national standard GB / T 11363-2008 "Test Method for Strength of Brazed Joints". The equipment was a SANS-CMT5105 universal tensile testing machine, and the loading rate during the tensile process was 3 mm / min. The shear strength of the copper-aluminum joints of the same specification obtained by flame brazing of the brazing materials in Examples 1 to 3 and Comparative Examples 1 to 4 was measured respectively. The results are shown in Table 1.

[0054] Table 1 Composition of brazing materials in Examples 1 to 3 and Comparative Examples 1 to 4 and strength of copper-aluminum joints obtained by brazing

[0055]

[0056] As can be seen from Table 1, the Al / Cu alloy brazed joints obtained by brazing with the Zn-Al-Mn-Sr filler metal of the present invention exhibit excellent mechanical properties, and the shear strength of the joints is as high as 95.2 - 105.3 MPa. The strength of the brazed joints in Comparative Examples 1 to 4 is significantly lower than that of the present invention. It can be seen that by adding Mn and Sr elements in the present invention, the microstructure and properties of the filler metal and the brazed joint are improved, and the strength of the brazed joint can be greatly increased.

[0057] In summary, the brazing material for copper-aluminum flame brazing of the present invention can improve the oxidation resistance of the filler metal and effectively improve the mechanical strength of the copper-aluminum joint. When brazing the copper-aluminum joint by the flame brazing process, the shear strength of the brazed lap copper-aluminum joint reaches 95.2 - 105.3 MPa, and it has good application prospects in the field of brazing of copper-aluminum joints.

Claims

1. A brazing material for copper-aluminum flame brazing, characterized in that, It consists of components with the following mass percentages: 15-20% of Al, 1-3% of Mn, 0.5-1.5% of Sr, and the balance is Zn.

2. The brazing material for copper-aluminum flame brazing according to claim 1, characterized in that, It consists of components with the following mass percentages: 16.5% of Al, 1.8% of Mn, 0.9% of Sr, and the balance is Zn.

3. The preparation method of the brazing material for copper-aluminum flame brazing according to claim 1, characterized in that, It includes the following steps: Take Zn, Al, Al-Mn master alloy, and Al-Sr master alloy according to the elements and ratios of the brazing material for copper-aluminum flame brazing; after melting Zn and Al, heat up to 740-760 °C, add the Al-Mn master alloy for melting, cover with a covering agent after heat preservation, continue to heat up to 950-1050 °C, add the Al-Sr master alloy and continue melting, and after heat preservation, carry out casting, extrusion, and reducing processing to obtain the brazing material for copper-aluminum flame brazing.

4. The preparation method of the brazing material for copper-aluminum flame brazing according to claim 3, characterized in that, When adding the Al-Mn master alloy for melting, the heat preservation time is 25-35 min.

5. The preparation method of the brazing material for copper-aluminum flame brazing according to claim 3, characterized in that, When adding the Al-Sr master alloy and continuing melting, the heat preservation time is 15-25 min.

6. The preparation method of the brazing material for copper-aluminum flame brazing according to any one of claims 3 to 5, characterized in that, The covering agent consists of KCl and NaCl; the mass ratio of KCl to NaCl is 1:

1.

7. The preparation method of the brazing material for copper-aluminum flame brazing according to any one of claims 3 to 5, characterized in that, Before casting, it also includes the step of refining the melt by blowing argon gas.

8. The application of the brazing material for copper-aluminum flame brazing according to claim 1 or 2, characterized in that, Application in the preparation of copper-aluminum composite joints by flame brazing.

9. The application of the brazing material for copper-aluminum flame brazing according to claim 8, characterized in that, In the copper-aluminum composite joint, the copper used is oxygen-free copper and the aluminum is pure aluminum.

10. The application of the brazing material for copper-aluminum flame brazing according to claim 8, characterized in that, The brazing flux used in the flame brazing is CsF-AlF3 non-corrosive brazing flux; the mass percentage composition of the brazing flux is: 71.4% CsF, 28.6% AlF3; the temperature of the flame brazing is 450-500 °C, and the heat preservation time is 10-20 min.

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