WO2013134974A1 - Method for brazing copper tube and aluminum tube without brazing flux - Google Patents

Description

 Copper-aluminum tube fluxless brazing method

Technical field

 The invention relates to a brazing method between metal materials, in particular to a method of brazing between copper and aluminum tubes without flux brazing.

Background technique

 The connection technology of copper and aluminum tubes is widely used in the refrigeration industry. The use of aluminum tubes instead of copper tubes as the main material for the internal pipes, connecting pipes and circulation system pipes of the heat exchanger not only reduces the weight of the equipment, but also greatly reduces the product cost. Because of this, the development of thin-walled copper-aluminum pipe joining technology has always been a hot spot in the refrigeration industry.

 The technical specifications of copper and aluminum pipe joints include: joint strength, corrosion resistance and air tightness. The main factors affecting these technical indicators are: joint weld line length, joint internal stress, joint impurity and pore content, and joint structure. Composition and distribution. There are a series of difficulties in the connection of copper-aluminum heterogeneous metals, such as: the physical properties of copper and aluminum (melting point, thermal conductivity, coefficient of linear expansion, heat of fusion, etc.) are large, and it is easy to remain in the weld during direct welding. Large internal stress; In addition, a layered brittle metal is easily formed between copper and aluminum. This compound will have an important influence on the joint strength, fatigue resistance, and plasticity of the copper-aluminum pipe joint. Furthermore, the surface of the aluminum The presence of a dense alumina film greatly hinders the wetting of the surface of the parent metal. Therefore, it is the key to obtain high-quality copper-aluminum welded joints to alleviate the difference in physical properties between heterogeneous base metals and reduce the formation of layered brittle intermetallic compounds in order to promote the wetting of the base metal surface and increase the length of the weld line.

 At present, the copper-aluminum tube connection methods commonly used in production are mainly solid phase welding and brazing. Among them, the solid phase connection method of copper and aluminum tubes mainly includes three kinds of friction butt welding, electric resistance welding and energy storage welding. Because of the direct combination of copper and aluminum, the copper and aluminum joints prepared by these methods all have brittleness of a certain thickness. The intermetallic compound (ICC) still has a large internal stress; these methods require a large upset pressure on the base material during the implementation, and vigorous mutual friction or discharge to locally melt the base material, so The method is not suitable for the connection of ultra-thin copper and aluminum tubes (such as the wall thickness less than 0.5mm); in addition, it is difficult to obtain copper-aluminum pipe joints with long fusion lines by solid phase welding (generally less than 5mm) .

Brazing is more common in the joining of dissimilar materials than solid phase welding. Compared with fusion welding and solid phase welding, the use of brazing filler metal in brazing relieves the difference in physical properties between heterogeneous base metals and enhances the fatigue load resistance of joints. In addition, brazing also has adaptability to complex workpieces. Strong, good joint sealing, weak ability to dissolve base metal, strong online production and many other advantages. However, brazing also has a prominent disadvantage, that is, flux must be used. When a copper-aluminum pipe joint is prepared by brazing, the use of the flux is easy to generate pores and inclusions in the weld, thereby greatly reducing the corrosion resistance of the joint; It is also easy to cause the solder which overflows from the weld to adhere to the pipe wall, making it difficult to remove the slag after welding. In addition, in flux brazing, once the temperature reaches the activation temperature of the flux during the heating process, the surface of the base material is wetted by the brazing material, thereby increasing the reaction time of the brazing material and the base material. The longer reaction time between the material and the base metal will cause excessive corrosion of the base metal on the one hand, which is not conducive to the preparation of the thin-walled copper-aluminum pipe joint; on the other hand, it is easy to breed thick brittle intermetallic compounds, resulting in Poor joint reliability.

 Chinese patent application CN102151930A brazing method between heterogeneous metal materials, discloses a fluxless brazing method for dissimilar metal pipes or bars by ultrasonic vibration assistance, the patent application has no flux brazing for ultrasonic assisted copper and aluminum tubes The principle of welding, joint shape, fixtures and related technical indicators are described in detail. However, further research has found that the copper-aluminum pipe welded joint prepared by the method of the invention has shortcomings such as short welding line and low welding success rate, and the method is not suitable for welding of ultra-long tubes and non-straight joints.

Summary of the invention

 In order to overcome the above deficiencies of the prior art, the present invention provides a copper-aluminum tube fluxless brazing method, which can obtain a long fusion wire copper-aluminum pipe welded joint by the method of the present invention.

 The technical solution adopted by the invention is: a copper-aluminum tube fluxless brazing method, the copper and aluminum tubes each comprise a straight pipe section to be welded, the brazing method comprises a preparation step of brazing a preset joint and an ultrasonic method The vibration assisted brazing step, the step of preparing the brazed preset joint includes the following substeps:

A1, the straight pipe section of any one of the copper and aluminum pipes is used as the first welded pipe, one end of which is expanded into a socket by a thermal expansion method, and the other straight pipe section is used as a second welded pipe; the socket includes The straight pipe portion and the socket transition portion are inserted, the inner diameter of the socket straight pipe portion is 50-800 μm larger than the outer diameter of the second welded pipe, and the depth of the straight pipe portion is 5-20 mm;

 A2, using a stamping forming method, the solder alloy sheet is made into a thin thin tube of solder, the inner diameter of the thin thin tube of the solder is smaller than the outer diameter of the second welded tube by 0-50 μΓΠ, and the thickness of the thin wall of the thin thin tube of the solder is higher than the first a welded pipe socket straight pipe portion inner diameter and a second welded pipe outer diameter difference half of 0-50μΓΠ, the length of the solder thin pipe is greater than the depth of the socket straight pipe portion 1 -10mm;

 A3. The solder thin tube is placed in the socket straight tube portion of the first welded tube, and then one end of the second welded tube is inserted into the solder thin tube so that the port is tightly pressed against the socket transition portion of the first welded tube. Forming a tight fit between the straight pipe portion of the first welded pipe and the brazing material thin tube, the brazing material thin tube and the second welding tube to obtain a brazed preset joint;

 The ultrasonic assisted brazing step includes the following substeps:

B1. Mounting the brazing preset joint on the welding fixture: one of the first welded pipe and the second welded pipe Clamping with a fixture, and another welded tube is fitted over the defining fixture so that the tube can only slide along its axial direction (weld tube that can slide axially);

 B2. Locally heating the socket portion of the welding preset joint by induction heating to make the temperature of the thin tube of the solder reach the welding temperature, and applying a welding pressure along the axial direction of the tube to the axially sliding welded tube, the pressure is 0.5-10MPa;

 B3, applying ultrasonic vibration to the axially slidable welded pipe, the ultrasonic action time is 0.5-20 seconds;

 B4. Turn off the induction heating after the ultrasonic vibration stops or before the ultrasonic vibration stops, and continue to maintain the pressure of the pressure device until the welded joint is cooled to 20-300 °C.

 The solder alloy described therein is an aluminum-based solder, a tin-based solder, a base-based solder, a copper-based solder or a silver-based solder alloy.

 As a further improvement, in the step B2, the welding pressure is directly applied from the top of the axially slidable welded pipe by the ultrasonic horn, and the direction of the ultrasonic vibration in the step B3 is parallel to the axial direction of the welded pipe.

 As a further improvement, the ultrasonic vibration in the step B3 is applied from the side of the axially slidable welded pipe by single-point or multi-point point ultrasonic vibration, and the direction of the ultrasonic vibration is perpendicular to the cut surface of the contact pipe wall. The contact pressure between the ultrasonic horn and the tube wall is 0.1 -5 MPa.

 As a further improvement, the defining fixture in the step B1 is an ultrasonic horn, the head of the ultrasonic horn includes a fastening device, and the ultrasonic horn has a degree of freedom parallel to the axial direction of the welded tube. The fastening device is for fixing the other welded pipe to make the pipe slide only in the axial direction thereof; the welding pressure in the step B2 and the ultrasonic vibration in the step B3 are passed through the ultrasonic vibration The fastening means of the arranging is applied, the direction of the welding pressure being parallel to the axial direction of the welded pipe, the direction of the ultrasonic vibration being perpendicular or parallel to the axial direction of the welded pipe.

 Preferably, in the above technical solution, the welding temperature in the step B2 is 1 - 150 ° C higher than the melting point of the solder alloy.

 Preferably, in the above technical solution, the frequency of the ultrasonic vibration in the step B3 is 10-70 kHz, and the amplitude is 8-60 μηη.

 The copper-aluminum tube fluxless brazing method of the invention has the following beneficial technical effects:

 1. In the method of the invention, the welded joint adopts a cup-shaped nozzle and a tightly matched integral solder sheet method, and the uniform hooking effect of the ultrasonic in the weld promotes the formation of the fusion line, and realizes the preparation of the long fusion line weld. Moreover, the joint is dense, the porosity is low, and the weld structure is fine and uniform, thereby greatly improving the joint tightness and the joint strength;

2. The formation of layered IMC is reduced, and the IMC layer can be effectively controlled below 3μηη, which is much lower than In the copper-aluminum welded joint, the critical thickness value (about 10μηη) of the IMC layer when the joint is aged due to brittle IMC improves the reliability of the joint;

 3. The wetting reaction will not occur between the base metal and the brazing material before the ultrasonic vibration is applied, thereby shortening the reaction time between the brazing material and the base metal, and weakening the dissolution of the brazing material on the base metal, which is suitable for the thin-walled copper-aluminum tube. Connection

 4. In the area outside the wall of the joint pipe, even if there is solder overflow, it will be removed from the pipe wall due to the vibration of the pipe wall; the copper-aluminum pipe insertion pipe is tightly coupled with the bottom of the cup-shaped flare and is added in the axial direction of the copper-aluminum pipe. A constant pressure is applied, so that the molten solder will be difficult to overflow in the tube, so that there is substantially no stubborn residue after welding by this method;

 5. The method of the invention has short welding time and high production efficiency, and can realize automatic welding;

 6. By changing the position of the ultrasonic vibration application, the connection of the elbow and the long copper-aluminum tube can be realized. DRAWINGS

 Figure 1 is a schematic view showing the welding of ultrasonic vibration on the top of an aluminum tube;

 Figure 2 is a schematic view of the welding of ultrasonic vibration on the bottom of the copper tube;

 Figure 3 is a schematic view showing the welding of ultrasonic vibration on the side wall of the aluminum tube;

 Figure 4 is a schematic view showing the welding of the ultrasonic vibration perpendicularly acting on the side wall of the aluminum tube in the manner of the contact of the ring wall; Figure 5 is a schematic view showing the welding of the ultrasonic vibration in the axial direction of the aluminum tube in parallel with the axial direction of the aluminum tube;

 Fig. 6 is a schematic view showing the ultrasonic horn of the ring wall contact mode shown in Fig. 4 and Fig. 5.

detailed description

 The invention is further clarified by the following examples, and the invention is not limited by the invention.

Example 1

 Referring to Fig. 1, take Τ2 copper tube 1 and 1060 aluminum tube 2 each, copper and aluminum tube sizes are: tube wall thickness 0.5mm, tube length 80mm, eve diameter 8mm. After the copper and aluminum pipe nozzles are flattened, the one end pipe of the copper pipe 1 is expanded into a socket by a thermal expansion method, and the socket includes a socket straight pipe portion 11 and a socket transition portion 12, wherein the socket pipe portion 11 has a depth of 10 mm and an inner diameter of 8.2 mm. A Zn-4AI solder alloy sheet (melting point: 380 ° C) was used, and a thin tube of solder having a thickness of 0.1 mm, an inner diameter of 8 mm, and a length of 12 mm was punched out by a press machine. The aluminum tube 2 to be welded at one end of the tube, the copper tube 1 socket and the solder thin tube 3 are cleaned and dried by an ultrasonic cleaner, and then the solder thin tube 3 is inserted into the socket straight tube portion 11 of the copper tube 1 socket. Then, the end of the aluminum tube 2 to be welded is inserted into the thin tube 3 of the solder and the port is pressed against the socket transition portion 12, so that the straight tube portion 11 of the copper tube 1 and the thin tube 3 of the solder are thin. A tight fit is formed between the tube 3 and the end to be welded of the aluminum tube 1.

Mount the assembled copper and aluminum tube bracing fittings on the welding fixture, and place the aluminum tube 2 In the defining jig 5, the jig 5 is defined such that the aluminum tube 2 can only slide in the axial direction thereof (i.e., axially slides), and the copper tube 1 is clamped by the fixing jig 4. The fixed copper and aluminum tube brazing preset joints are moved into the induction wire 圏6, and the wire 圏6 covers the socket portion of the copper pipe 1 to enable local heating of the brazing preset joint; adjusting the infrared temperature measurement The instrument, and the welding temperature is monitored in real time during the welding process.

 Turn on the induction heating device to locally heat the copper and aluminum tube brazing preset joints. When the temperature reaches 420 °C, start the pressure device of the ultrasonic vibration machine to make the ultrasonic horn 7 from the other end of the aluminum tube 2. A constant welding pressure of 5 MPa was applied along the axial direction of the tube. After 1 second, the ultrasonic vibration was automatically turned on and the high-frequency vibration along the axial direction of the tube was applied to the aluminum tube 2, the ultrasonic vibration frequency was 20 kHz, the amplitude was 30 μηη, and the vibration time was 4 seconds. After the vibration is over, the induction heating is stopped. When the temperature of the copper and aluminum tubes is lowered to 60 °C, the pressure is stopped and the welded copper and aluminum tubes are taken out.

 The longitudinal section of the welded copper and aluminum pipe joints was analyzed by microscopic analysis. The results show that the average length of the welded fusion line is 10 mm, that is, the copper and aluminum tube coincident parts in the socket are welded; the weld structure is dense, and the structure is tight. The distribution is uniform, no obvious pores and inclusions exist; the average thickness of the weld IMC layer is about 2.3μηη. Tensile tests were carried out on copper and aluminum tubes, and joint failure failure occurred in the aluminum base metal.

Example 2

 Referring to FIG. 2, the present embodiment is different from the first embodiment in that when the soldering pre-joint is mounted on the jig, the copper tube 1 is placed in the defining jig 5, and the jig 5 is defined so that the copper tube 1 can only follow it. Sliding in the axial direction (ie, axial sliding), the aluminum tube 2 is clamped by the fixing fixture 4; the welding pressure and the ultrasonic vibration are applied from the other end of the copper tube 1 along the tube axial direction through the ultrasonic horn 7, and other steps The same as in the first embodiment.

 The longitudinal section of the welded copper and aluminum pipe joints was analyzed by microscopic analysis. The results showed that the average length of the welded fusion line reached 10 mm, that is, the copper and aluminum tube coincidence parts were welded in the socket; the weld structure was dense and the microstructure was distributed. Uniform, no obvious porosity and inclusions; the average thickness of the weld IMC layer is about 2.2μηη. Tensile tests were carried out on copper and aluminum tubes, and joint failure failure occurred in the aluminum base metal.

Example 3

 Referring to Fig. 3, the present embodiment is different from the first embodiment in that the welding pressure is applied axially at the end of the aluminum tube 2 through the pressure device 8, and the ultrasonic vibration is transmitted from the side wall of the aluminum tube 2 by the ultrasonic horn 7. The other steps were the same as in Example 1.

The specific implementation process is as follows: After the temperature of the joint reaches 420 ° C, a constant welding pressure is applied to the end of the aluminum tube 2 through the pressure device 8, and the pressure is 3 MPa; after the pressure is stabilized, the ultrasonic pressure device is activated to make the ultrasonic amplitude change. The rod 7 applies a contact pressure of 0.5 MPa to the wall of the aluminum tube 2, and then ultrasonic vibration is started, the vibration direction is perpendicular to the axial direction of the aluminum tube, the ultrasonic vibration frequency is 30 kHz, and the amplitude is 20 μηη, when vibrating The interval is 5 seconds; after the end of the vibration, the induction heating is stopped, the ultrasonic horn 7 is removed, and the pressure device 8 is continuously maintained. The longitudinal section of the welded copper and aluminum pipe joints is microscopically analyzed, and the results show the average length of the welded fusion line. Up to 10mm, that is, the copper and aluminum tube coincident parts in the socket are welded; the weld structure is dense, the microstructure is evenly distributed, and no obvious pores and inclusions exist; the average thickness of the weld IMC layer is about 2.5μηη. Tensile tests were carried out on copper and aluminum tubes, and joint failure failure occurred in the aluminum base metal.

Example 4

 Referring to FIG. 4, the present embodiment is different from the first embodiment in that: the fixing jig is a fastening device for the head of the ultrasonic horn 7 , as shown in FIG. 6 , the fastening device includes two and the aluminum tube 2 The end of the snap ring 71 and the movable snap ring 72, the two ends of the two snap rings can be fastened by bolts or the ends of the two ends of the hinge can be fastened by bolts to the aluminum tube 2, ultrasonic horn 7 has a degree of freedom parallel to the axial direction of the aluminum tube 2, so that the aluminum tube 2 can only slide along its axial direction; the welding pressure and ultrasonic vibration are applied by the ultrasonic horn 7 through the fastening device, and the direction of the ultrasonic vibration is perpendicular to the aluminum The axial direction of the tube 2. The other steps are the same as in the first embodiment.

 The specific implementation process is as follows: The copper tube 1 in the assembled copper and aluminum tube brazing preset joint is clamped by the fixing fixture 4, and then the aluminum tube 2 is fixed on the fastening device of the ultrasonic horn 7. The induction wire is moved to the welded joint of the copper and aluminum tubes, and then the induction heating device is turned on to locally heat the copper and aluminum tube welded joints. When the temperature reaches 420 °C, the pressure on the ultrasonic horn 7 is started. The device is such that the ultrasonic horn 7 applies a welding pressure along the axial direction of the aluminum tube 2 to the aluminum tube 2, and the pressure is 2 MPa. After 1 second, the ultrasonic vibration is automatically opened and the aluminum tube 2 is applied perpendicularly to the axis of the aluminum tube 2. High frequency vibration. The ultrasonic vibration frequency is 60 kHz, the amplitude is 20 μηη, and the vibration time is 4 seconds. Stop 0.5 seconds before the end of the vibration Induction heating and continue to hold the pressure. When the temperature of the copper and aluminum tubes drops below 300 °C, stop applying pressure and take out the welded copper and aluminum tubes.

 The longitudinal section of the welded copper and aluminum pipe joints was analyzed by microscopic analysis. The results showed that the average length of the welded fusion line reached 10 mm, that is, the copper and aluminum tube coincidence parts were welded in the socket; the weld structure was dense and the microstructure was distributed. Uniform, no obvious porosity and inclusions; the average thickness of the weld IMC layer is about 2.7 μηη. Tensile tests were carried out on copper and aluminum tubes, and joint failure failure occurred in the aluminum base metal.

Example 5

 Referring to Fig. 5, the only difference between this embodiment and the embodiment 4 is that the direction in which the ultrasonic vibration is applied is parallel to the axial direction of the aluminum tube 2, and the other steps are the same as in the fourth embodiment.

Microscopic analysis of the longitudinal section of the welded copper and aluminum pipe joints shows that the average length of the welded fusion line reaches 10 mm, that is, the copper and aluminum tube coincident parts in the socket are welded; the weld structure is dense. The microstructure is evenly distributed without significant pores and inclusions; the average thickness of the weld IMC layer is about 3.0 μηη. Tensile tests were carried out on copper and aluminum tubes, and joint failure failure occurred in the aluminum base metal.

 The above is a further description of the present invention in connection with the specific embodiments, and the scope of the present invention is not limited to the description. In the above embodiment, one end of the aluminum tube may be expanded into a socket, and the copper tube may be inserted into the welding, or ultrasonic vibration may be applied to the copper tube, etc., for those skilled in the art without departing from the invention. Under the premise of the conception, some deductions or substitutions should be considered as belonging to the scope of protection of the present invention.

Claims

Claim  A brazing method for a copper-aluminum tube without flux, wherein the copper and aluminum tubes each comprise a straight pipe section to be welded, characterized in that: the brazing method comprises a preparation step of brazing a preset joint and ultrasonic vibration assisting The brazing step, the step of preparing the brazed pre-joint includes the following sub-steps:  A1, the straight pipe section of any one of the copper and aluminum pipes is used as the first welded pipe, one end of which is expanded into a socket by a thermal expansion method, and the other straight pipe section is used as a second welded pipe; the socket includes The straight pipe portion and the socket transition portion are inserted, the inner diameter of the socket straight pipe portion is 50-800 μm larger than the outer diameter of the second welded pipe, and the depth of the straight pipe portion is 5-20 mm;  A2, using a stamping forming method, the solder alloy sheet is made into a thin thin tube of solder, the inner diameter of the thin thin tube of the solder is smaller than the outer diameter of the second welded tube by 0-50 μΓΠ, and the thickness of the thin wall of the thin thin tube of the solder is higher than the first a welded pipe socket straight pipe portion inner diameter and a second welded pipe outer diameter difference half of 0-50μΓΠ, the length of the solder thin pipe is greater than the depth of the socket straight pipe portion 1 -10mm;  A3. The solder thin tube is placed in the socket straight tube portion of the first welded tube, and then one end of the second welded tube is inserted into the solder thin tube so that the port is tightly pressed against the socket transition portion of the first welded tube. Forming a tight fit between the straight pipe portion of the first welded pipe and the brazing material thin tube, the brazing material thin tube and the second welding tube to obtain a brazed preset joint;  The ultrasonic assisted brazing step includes the following substeps: B1. Mounting the brazing preset joint on the welding fixture: one of the first welded pipe and the second welded pipe is clamped by a fixing device, and the other welded pipe is assembled on the fixing fixture so that the pipe is only Can slide along its axis;  B2. Locally heating the socket portion of the welding preset joint by induction heating to make the temperature of the thin tube of the solder reach the welding temperature, and applying a welding pressure along the axial direction of the tube to the axially sliding welded tube, the pressure is 0.5-10MPa;  B3, applying ultrasonic vibration to the axially slidable welded pipe, the ultrasonic action time is 0.5-20 seconds;  B4. Turn off the induction heating after the ultrasonic vibration stops or before the ultrasonic vibration stops, and continue to maintain the pressure of the pressure device until the welded joint is cooled to 20-300 °C.  2. The copper-aluminum tube fluxless brazing method according to claim 1, wherein: the soldering temperature in the step B2 is 1 to 150 ° C higher than the melting point of the solder alloy.  The copper-aluminum tube fluxless brazing method according to claim 1 or 2, wherein the ultrasonic vibration frequency in the step B3 is 10-70 kHz and the amplitude is 8-60 μηη. The copper-aluminum tube fluxless brazing method according to claim 1 or 2, wherein: the step In B2, the welding pressure is directly applied from the top of the axially slidable welded pipe by the ultrasonic horn, and the direction of the ultrasonic vibration in step B3 is parallel to the axial direction of the welded pipe. The copper-aluminum tube fluxless brazing method according to claim 1 or 2, wherein: the ultrasonic vibration in the step B3 is in single-point or multi-point contact from the side of the axially slidable welded pipe The ultrasonic vibration is applied in a manner that the direction of the ultrasonic vibration is perpendicular to the cut surface of the pipe wall to be contacted, and the contact pressure between the ultrasonic horn and the pipe wall is 0.1 -5 MPa. The copper-aluminum tube fluxless brazing method according to claim 1 or 2, wherein: the defining fixture in the step B1 is an ultrasonic horn, and the head of the ultrasonic horn includes a fastening The ultrasonic horn has a degree of freedom parallel to the axial direction of the welded pipe, and the fastening device is for fastening the other welded pipe to slide the pipe only in the axial direction thereof; The welding pressure in B2 and the ultrasonic vibration in the step B3 are applied by the fastening means of the ultrasonic horn, the direction of the welding pressure being parallel to the axial direction of the welded pipe, the direction of the ultrasonic vibration being vertical Or parallel to the axial direction of the welded pipe.