CN116021188A - A kind of brazing material for copper-aluminum flame brazing and its preparation method and application - Google Patents

Abstract

The invention belongs to the technical field of copper-aluminum dissimilar metal brazing materials, and particularly relates to a brazing material for copper-aluminum flame brazing as well as a preparation method and application thereof. The brazing material for copper-aluminum flame brazing consists of the following components in percentage by mass: 15-20% of Al, 1-3% of Mn, 0.5-1.5% of Sr and the balance of Zn. The brazing material for copper-aluminum flame brazing can improve the oxidation resistance of the brazing filler metal and refine the brazing filler metal structure, can effectively improve the mechanical strength of copper-aluminum joints when being used for flame brazing copper-aluminum dissimilar metal joints, has the shearing strength of braze lap joint copper-aluminum joints reaching 95.2-105.3 MPa, and has good application prospects in the field of brazing copper-aluminum joints.

Description

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

technical field

The invention belongs to the technical field of copper-aluminum dissimilar metal brazing materials, and in particular relates to a brazing material for copper-aluminum flame brazing and its preparation method and application.

Background technique

Connecting copper and aluminum to form copper-aluminum dissimilar metal joints can not only reduce the amount of scarce metal copper and reduce the weight of components, but also give full play to the respective performance advantages of copper and aluminum. It has been widely used in electric power, refrigeration equipment and other fields.

At present, flame brazing is often used to realize copper-aluminum welding of Cu/Al joints in the manufacturing process of electric power and refrigeration equipment. In the flame brazing process of copper-aluminum composite, the solders used mainly include Sn-Pb, Sn-Zn, Al-Si and Zn-Al solders. Solder materials such as Sn-Pb and Sn-Zn need to be combined with corrosive solutions with low melting points such as ZnCl ₂ and NH ₄ Cl as fluxes. The process is complicated and the cost is high, which limits their application. Compared with Al-Si solder, the brazing temperature of Zn-Al solder is generally 100 ° C or more lower, which can provide a wider process window for the brazing process of aluminum and copper, and can reduce the heat of the joint. Stress and the amount of intermetallic compound formation. Moreover, since the melting point of the Zn-Al solder is between the solder and the hard solder, its melting point can be adjusted conveniently, and it has excellent processability and mechanical properties. Therefore, the use of flame brazing with Zn-Al solder to braze copper-aluminum dissimilar metals has been gradually applied in the industry. At present, Zn-2Al, Zn-10Al, Zn-15Al, and Zn-22Al are commonly used. Due to the relatively low melting point of Zn-2Al, Zn-10Al, and Zn-15Al solders, their compatibility with the most commonly used CsF-AlF ₃ non-corrosive flux is poor, so Zn-22Al has become the most commonly used choice.

Although the Zn-22Al solder has achieved certain effects in Cu/Al flame brazing, there are still some problems that are difficult to solve: First, the oxide on the surface of the Zn-22Al solder is basically composed of ZnO, and the ZnO film layer The structure is loose and cannot protect the solder; at the same time, the existence of a large number of oxides in the brazing process will also deteriorate the brazing performance of the solder. Second, due to the high Al content in Zn-22Al, it is inevitable that it will react with the Cu base material to form a brittle compound phase, resulting in a significant decrease in the mechanical strength of the brazed joint and affecting the mechanical properties of the brazed component.

Therefore, how to optimize the composition of Zn-22Al solder to further improve the mechanical properties of the copper-aluminum joint brazed with Zn-22Al solder has become an urgent technical problem to be solved.

Contents of the invention

In order to solve the above problems, the object of the present invention is to provide a brazing material for copper-aluminum flame brazing, the mechanical strength of the copper-aluminum joint obtained by brazing is excellent, and it belongs to the brazing application of copper-aluminum joints.

The invention also provides a preparation method of the brazing material for copper-aluminum flame brazing, which has a simple process and is suitable for industrial production.

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

In order to achieve the above object, the brazing material for copper-aluminum flame brazing of the present invention adopts the technical scheme as follows:

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 of Zn.

In the brazing material for copper-aluminum flame brazing of the present invention, by controlling the addition of Zn and Al elements, and simultaneously introducing Mn and Sr elements into Zn-Al brazing filler metal, a new type of Zn-Al-Mn-Sr brazing filler metal is prepared , in order to optimize the structure of the solder and improve the brazing performance. Wherein, the present invention introduces alkaline earth metal Sr, and Sr easily forms SrO and _SrO2 film with oxygen atoms in the air during the solder melting process, which is not only dense but also very easy to attach to the solder surface, when the solder melts and enters the heat preservation process , the dense film layer will hinder the interfacial reaction process to reduce the ZnO formation rate and improve the oxidation resistance of solder. The improvement of anti-oxidation ability can significantly reduce the viscosity of solder, which is beneficial to the improvement of solder wetting and spreading performance and brazing performance. Further, the present invention also adds the Mn element while adding the Sr element, and the synergy between the two can achieve the purpose of refining the solder structure, so that the Zn-Al-Mn-Sr solder of the present invention is used for copper-aluminum brazing Finally, the brittle phase at the interface is also refined, and the smaller interface compound helps to inhibit the growth and expansion of cracks, thereby effectively improving the mechanical properties of the joint.

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 by mass percentage: 16.5% of Al, 1.8% of Mn, 0.9% of Sr, and The amount is Zn.

The preparation method of brazing material for copper-aluminum flame brazing of the present invention adopts the technical scheme as follows:

The preparation method of brazing material for copper-aluminum flame brazing comprises the following steps:

Take Zn, Al, Al-Mn master alloy and Al-Sr master alloy according to the elements and proportions of the brazing materials for copper-aluminum flame brazing; melt Zn and Al and raise the temperature to 740-760°C, and add Al-Mn intermediate Alloy smelting, covering with covering agent after heat preservation, continue to heat up to 950~1050℃, add Al-Sr intermediate alloy to continue smelting, pour, extrude, and reduce diameter after heat preservation to obtain brazing materials for copper-aluminum flame brazing .

The preparation method of the brazing material for copper-aluminum flame brazing of the invention has a simple process and is suitable for industrialized production. In the method of the present invention, the method of adding an intermediate alloy for smelting is adopted, and the intermediate alloy can lower the melting temperature of the metal and reduce the energy consumption in the step-by-step smelting process; moreover, the intermediate alloy can reduce segregation during metal smelting and avoid the step-by-step smelting process The appearance of medium segregation helps to improve the strength of brazed joints.

Preferably, when the Al-Mn master alloy is added for smelting, the holding time is 25-35 minutes.

Further, when the Al-Sr master alloy is added to continue the smelting, the heat preservation time is 15-25 minutes.

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

Furthermore, the step of refining the melt by argon blowing is also included before pouring.

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

Preferably, in the copper-aluminum composite joint, the copper used is red copper, and the aluminum is pure aluminum.

Further, the flux used in the flame brazing is CsF-AlF ₃ non-corrosive flux; the mass percentage composition of the flux is: 71.4% CsF, 28.6% AlF ₃ ; the temperature of the flame brazing is 450-500°C, The holding time is 10-20 minutes. The invention adopts the non-corrosion brazing flux of the above composition, and the cost is low. Moreover, the brazing material of the present invention can be effectively adapted to CsF-AlF ₃ non-corrosive flux, and can exert good brazing performance.

The brazing material for copper-aluminum flame brazing of the present invention can improve the oxidation resistance of the brazing filler metal, and effectively improve the mechanical strength of the copper-aluminum joint. When the flame brazing process is used to braze copper-aluminum joints, the shear strength of brazed lap joints can reach 95.2-105.3MPa, which has a good application prospect in the brazing field of copper-aluminum joints.

Description of drawings

Fig. 1 is a graph showing the thermogravimetric analysis results of the brazing material for copper-aluminum flame brazing in Example 1 of the present invention and the Zn-22Al brazing material in Comparative Example 1 under different oxidation times.

Detailed ways

The technical solutions of the present invention will be further described below in combination with specific embodiments. However, those skilled in the art should understand that the following examples are only for illustrating the present invention, and should not be considered as limiting the scope of the present invention. In the following examples, the raw materials involved are conventional commercially available products unless otherwise specified.

Wherein, in the Al-Mn master alloy, the mass ratio of Al and Mn is 70:30; in the Al-Sr master alloy, the mass ratio of Al and Sr is 60:40.

Example 1

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

The preparation method of above-mentioned brazing material for copper-aluminum flame brazing comprises the following steps:

Take Zn, Al, Al-Mn master alloy and Al-Sr master alloy according to the elements and proportions of the brazing materials for copper-aluminum flame brazing; put the metal Zn and Al into the intermediate frequency furnace to melt, and the temperature of the melt in the furnace reaches At 750°C, add Al-Mn master alloy for smelting, keep warm for 30 minutes and cover with covering agent, 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 Al-Sr master alloy to continue smelting , keep warm for 20 minutes, cool down, blow argon for refining, and when the temperature cools to 700°C, the smelting ends, and the solution is poured into the mold to form an ingot. Ingot casting and rod-shaped ingot are extruded, drawn and reduced in diameter and processed into filament-like brazing filler metal, which is the brazing material for copper-aluminum flame brazing.

Example 2

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

The preparation method of above-mentioned brazing material for copper-aluminum flame brazing comprises the following steps:

Take Zn, Al, Al-Mn master alloy and Al-Sr master alloy according to the elements and proportions of the brazing materials for copper-aluminum flame brazing; put the metal Zn and Al into the intermediate frequency furnace to melt, and the temperature of the melt in the furnace reaches At 740°C, add Al-Mn master alloy for smelting, keep it warm for 30 minutes and cover it with a covering agent, the covering agent is a mixture of KCl and NaCl with a mass ratio of 1:1, continue to heat up to 950°C, add Al-Sr master alloy to continue smelting , keep warm for 20 minutes, cool down, blow argon for refining, and when the temperature cools to 700°C, the smelting ends, and the solution is poured into the mold to form an ingot. Ingot casting and rod-shaped ingot are extruded, drawn and reduced in diameter and processed into filament-like brazing filler metal, which is the brazing material for copper-aluminum flame brazing.

Example 3

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

The preparation method of above-mentioned brazing material for copper-aluminum flame brazing comprises the following steps:

Take Zn, Al, Al-Mn master alloy and Al-Sr master alloy according to the elements and proportions of the brazing materials for copper-aluminum flame brazing; put the metal Zn and Al into the intermediate frequency furnace to melt, and the temperature of the melt in the furnace reaches At 760°C, add Al-Mn master alloy for smelting, keep warm for 30 minutes and cover with covering agent, the covering agent is a mixture of KCl and NaCl with a mass ratio of 1:1, continue to heat up to 1050°C, add Al-Sr master alloy to continue smelting , keep warm for 20 minutes, cool down, blow argon for refining, and when the temperature cools to 700°C, the smelting ends, and the solution is poured into the mold to form an ingot. Ingot casting and rod-shaped ingot are extruded, drawn and reduced in diameter and processed into filament-like brazing filler metal, which is the brazing material for copper-aluminum flame brazing.

Comparative example 1

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

Comparative example 2

The brazing material of this comparative example is Zn-Al brazing filler metal, which consists of the following components in mass percentage: 16.5% Al, and the balance is Zn.

Comparative example 3

The brazing material of this comparative example is Zn-Al-Mn solder, which consists of the following components in mass percentage: 16.5% Al, 1.8% Mn, and the balance is Zn.

Comparative example 4

The brazing material of this comparative example is Zn-Al-Sr solder, which is composed of the following components in mass percentage: 16.5% Al, 0.9% Sr, and the balance is Zn.

Test case

1. Thermogravimetric analysis test

The experiment was carried out using a Pyris Diamond thermogravimetric/differential thermal analyzer from Perin-Elmer. During the test, the heating rate is 20°C/min, the initial weight of the solder is 20mg, the termination heating temperature is 530°C, the holding time is 30min, the test atmosphere is air, and the change curves of the solder mass with temperature and time during the heating process are recorded respectively. The thermogravimetric mass loss of the Zn-Al-Mn-Sr solder in Example 1 and the traditional Zn-22Al solder in Comparative Example 1 was analyzed under different oxidation times. The result is shown in Figure 1.

It can be seen from Figure 1 that the weight of Zn-22Al solder continues to rise with the increase of heating time during the heat preservation process, indicating that the oxidation process of Zn-22Al solder continues during the heating process. And the weight of Zn-Al-Mn-Sr brazing filler metal of the present invention that has added Sr, Mn element presents the trend that rises first and then stabilizes gradually, and this speculation is because Sr element in Zn-Al-Mn-Sr brazing filler metal and air SrO and SrO ₂ films are formed by the oxygen atoms, and the dense film layer will hinder the interfacial reaction process and reduce the diffusion rate of oxygen atoms, thereby reducing the rate of ZnO formation and effectively improving the oxidation resistance of the solder.

2. Brazing performance test

The brazing performance test uses pure aluminum and copper as the base material, the size is 60mm×25mm×3mm, the lap length of the lap joint is 3mm, the joint is placed with a normal gap (about 0.15mm), and the flux is CsF-AlF ₃ without Corrosion brazing flux, the composition of the flux is 71.4% CsF, 28.6% AlF ₃ , the flame brazing temperature is 475°C, and the holding time is 15 minutes. The shear performance test of brazed joints is carried out in accordance with the national standard GB/T11363-2008 "Test Method for Strength of Brazed Joints". The equipment is a SANS-CMT5105 universal tensile testing machine, and the loading rate during the tensile process is 3mm/min. The shear strength of copper-aluminum joints of the same specification obtained by flame brazing the brazing materials of Examples 1-3 and Comparative Examples 1-4 respectively. The results are shown in Table 1.

Table 1 The brazing material composition of Examples 1 to 3 and Comparative Examples 1 to 4 and the strength of the copper-aluminum joint obtained by brazing

It can be seen from Table 1 that the Al/Cu alloy brazed joints obtained by brazing with Zn-Al-Mn-Sr solder in the present invention exhibit excellent mechanical properties, and the shear strength of the joints is as high as 95.2-105.3 MPa. However, the brazed joint strengths of Comparative Examples 1-4 are significantly lower than those of the present invention. It can be seen that the addition of Mn and Sr elements in the present invention improves the structure and performance of the solder and the brazed joint, and can greatly increase the strength of the brazed joint.

It can be seen from the above that the brazing material for copper-aluminum flame brazing of the present invention can improve the oxidation resistance of the brazing filler metal, and effectively improve the mechanical strength of the copper-aluminum joint. When the flame brazing process is used to braze copper-aluminum joints, the shear strength of brazed lap joints can reach 95.2-105.3MPa, which has a good application prospect in the brazing field of copper-aluminum joints.

Claims (10)

1. A brazing material for copper-aluminum flame brazing, characterized in that it is made up of the following components in mass percent: 15-20% Al, 1-3% Mn, 0.5-1.5% Sr, balance for Zn. 2. the brazing material for copper-aluminum flame brazing according to claim 1, is characterized in that, is made up of the component of following mass percentage: the Al of 16.5%, the Mn of 1.8%, the Sr of 0.9%, surplus is Zn. 3. the preparation method of brazing material for copper-aluminum flame brazing as claimed in claim 1, is characterized in that, comprises the following steps: Take Zn, Al, Al-Mn master alloy and Al-Sr master alloy according to the elements and proportions of the brazing materials for copper-aluminum flame brazing; melt Zn and Al and raise the temperature to 740-760°C, and add Al-Mn intermediate Alloy smelting, covering with covering agent after heat preservation, continue to heat up to 950~1050℃, add Al-Sr intermediate alloy to continue smelting, pour, extrude, and reduce diameter after heat preservation to obtain brazing materials 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 the Al-Mn master alloy is added for smelting, the heat preservation time is 25 to 35 minutes. 5. The preparation method of brazing material for copper-aluminum flame brazing according to claim 3, characterized in that, when the Al-Sr master alloy is added and the smelting is continued, the heat preservation time is 15-25 minutes. 6. according to the preparation method of the copper-aluminum flame brazing described in any one of claim 3～5, it is characterized in that, described covering agent is made up of KCl and NaCl; The mass ratio of KCl and NaCl is 1: 1. 7 . The method for preparing the brazing material for copper-aluminum flame brazing according to any one of claims 3 to 5 , characterized in that the step of refining the melt by argon blowing is also included before pouring. 8. The application of the brazing material for copper-aluminum flame brazing as claimed in claim 1 or 2, characterized in that it is used 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 red copper, and the aluminum is pure aluminum. 10. the application of brazing material for copper-aluminum flame brazing according to claim 8, is characterized in that, the flux that described flame brazing adopts is CsF-AlF ₃ corrosion-free flux; The mass percentage composition of flux It is: 71.4% CsF, 28.6% AlF ₃ ; the temperature of flame brazing is 450-500°C, and the holding time is 10-20min.

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