Aluminum alloy low-temperature and low-pressure connecting method based on liquid phase and solid phase combined diffusion

Abstract

The application discloses a low-temperature and low-pressure connecting method for aluminum alloy based on liquid-phase and solid-phase combined diffusion, and relates to the field of welding. The method specifically comprises the following steps: one, pretreating an intermediate layer and aluminum alloy base material; two, assembling the aluminum alloy and the intermediate layer alloy and heating to a welding temperature, and removing the gas film and the material surface oxide film at the interface by mechanical methods such as mutual friction or ultrasonic wave; and three, applying pressure and conducting heat preservation to obtain a high-strength Zn-Al eutectoid structure joint. The application realizes the low-temperature and low-pressure diffusion welding of the aluminum alloy under the atmospheric condition by realizing the low-temperature and low-pressure diffusion welding of the aluminum alloy in the semi-solid temperature interval of the intermediate layer, removes the oxide film by the mechanical film breaking method, and promotes the sufficient interdiffusion between the semi-solid intermediate layer and the base material by heat preservation to obtain the high-strength joint with the strength equivalent to that of the base material. The application is applied to the field of aluminum alloy welding.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of aluminum alloy welding, and particularly relates to a method for low-temperature and low-pressure diffusion welding of aluminum alloy by using a semi-solid intermediate layer in an atmospheric environment. BACKGROUND

[0002] Aluminum alloy micro-channel heat sinks have shown irrefutable potential in military radar heat dissipation systems due to their small size, good heat transfer performance, and significant weight reduction. Diffusion welding, as a method to obtain joints with strength close to the base material, has been widely used in the manufacture of micro-channel heat sinks for high-power electronic devices. High temperature and high pressure are necessary conditions for effective interdiffusion of aluminum alloy and removal of oxide film. However, such harsh conditions bring many difficulties to diffusion welding, including the softening of the base material at temperatures usually above 500℃, and the deformation of the joint at welding pressures above 5MPa. In addition, diffusion welding must be carried out in a vacuum or Ar gas environment to avoid the influence of secondary oxidation on the connected joint, which increases the complexity of the process. Therefore, it is necessary to develop a low-temperature and low-pressure diffusion welding technology for aluminum alloy under atmospheric conditions.

[0003] The low-temperature diffusion welding method for aluminum alloy is mainly below 450℃, using Ag foil, Zn foil as an intermediate layer for solid-phase diffusion welding and Ar ion bombardment for diffusion welding. Chips can be bonded to Al substrates at 400-450℃ with Ag foil as an intermediate layer. During bonding, Ag and Al atoms diffuse through the thin Al2O3 phase, reacting to form Ag2Al and Ag3Al compounds. In addition, solid-phase bonding of aluminum alloy can be achieved at 360℃ through a Zn intermediate layer. During bonding, Zn atoms can diffuse through the cracks in the oxide film to achieve diffusion of Zn into aluminum alloy. Another study has shown that Ar ion bombardment can remove the oxide film on the surface of Al, change the microstructure of the bombarded surface, and then obtain a good bonded joint under lower diffusion welding parameters. Vacuum diffusion welding of Al / Al can be achieved at 350℃ and 450℃, respectively, by using an Ar ion beam to treat the surface of pure Al. It is worth noting that 350℃ is the lowest bonding temperature in all Al or Al alloy diffusion welding processes. However, the pressure needs to be increased to more than 5MPa, which will cause joint deformation.

[0004] Compared with solid state diffusion bonding, TLP usually requires a pressure lower than 1 MPa to achieve the diffusion bonding of aluminum alloys. The commonly used interlayers for TLP bonding of aluminum alloys are Cu, Ag, Ag-28Cu and Zn. The bonding temperature depends on the eutectic reaction temperature between the interlayer and the base metal, which is generally required to be 546℃ (Al-Cu binary eutectic), 567℃ (Al-Ag binary eutectic), 490℃ (Al-Ag-Cu ternary eutectic) and 389℃ (Al-Zn binary eutectic). Obviously, Zn and Al have a large mutual solubility, and have the potential of low temperature and low pressure bonding, so Zn interlayer has a great attraction in TLP bonding of aluminum alloys. In previous studies, Zn foil was used as the interlayer, and the 7034 fine-grained alloy was successfully bonded in air at 400℃ and 0.2 MPa by ultrasonic-assisted rapid TLP bonding, and a full α-Al solid solution joint was obtained, and the joint shear strength reached 223 MPa. The same method was also used to bond Al-50Si alloy at 390℃. Unfortunately, the current Zn interlayer TLP bonding is faced with the problem that the bonding temperature can only be reduced to 390℃, and it is difficult to break through the temperature below the Zn-Al eutectic point; secondly, the removal of the oxide film needs to rely on the ultrasonic-assisted interface friction.

[0005] At present, there are still many technical problems in the low temperature and low pressure diffusion bonding of aluminum alloys under atmospheric conditions: first, the removal of the oxide film of aluminum alloy under atmospheric conditions requires special film removal process; second, the diffusion bonding process is difficult to meet the process conditions of low temperature and low pressure at the same time.

[0006] From the summary of the existing research, low temperature diffusion bonding requires a suitable low temperature interlayer, and the oxide film is difficult to be removed directly during the bonding process, and the residual oxide film in the joint will affect the mechanical properties of the joint. Although Ar ion bombardment assisted diffusion bonding of aluminum alloy can reduce the welding temperature to 350℃, it increases the process complexity, and the bonding process usually requires a pressure higher than 5 MPa.

[0007] Low pressure diffusion bonding is limited to TLP bonding, but it usually requires a bonding temperature higher than 500℃, in addition, the liquid phase tends to be squeezed out during the diffusion bonding process. Although Zn interlayer can reduce the bonding temperature to 390℃, the removal of the oxide film during the bonding process needs to rely on the mechanical friction of ultrasonic waves, and it is difficult to continue to reduce the bonding temperature.

[0008] The above results prove that low temperature diffusion bonding requires a low temperature interlayer, low pressure diffusion bonding requires the presence of liquid phase in the joint, and the removal of the oxide film of the base metal under atmospheric conditions needs to rely on mechanical friction. In summary, the most suitable way for low temperature and low pressure diffusion bonding of aluminum alloys under atmospheric conditions is to use a low melting point semi-solid interlayer that combines the advantages of liquid and solid interlayers, and to remove the oxide film by mechanical action. SUMMARY

[0009] The problems to be solved by the present application include: (1) the process limitation of aluminum alloy solid phase diffusion welding, which can only be carried out in vacuum or protective gas cavity; (2) the welding temperature is too high, which is easy to cause the softening of aluminum alloy material; the welding pressure is too large, which is easy to cause the deformation of the joint; (3) the oxide film is difficult to break during the diffusion connection process of aluminum alloy under atmospheric conditions. In view of the above shortcomings in the prior art, a simple and easy-to-use diffusion welding aluminum alloy method based on liquid phase and solid phase combined diffusion is provided.

[0010] Further, the aluminum alloy is 1 series aluminum alloy, 2 series aluminum alloy, 3 series aluminum alloy, 5 series aluminum alloy, 6 series aluminum alloy, 7 series aluminum alloy or fine-grain strengthened ultra-fine-grain aluminum alloy.

[0011] Further, the intermediate layer is Zn-Sn, Zn-Bi, Zn-Ga or Zn-In based Zn alloy.

[0012] Further, the intermediate layer is in the form of metal foil, mixed solder paste, alloy block or metal powder.

[0013] Further, the assembly form of the intermediate layer and the aluminum alloy is direct prefabrication, electroplating, chemical plating, atomization spraying, solder coating, ultrasonic coating or magnetron sputtering.

[0014] Further, the heating method is resistance heating table, high-frequency induction coil heating, infrared heating or hot gas heating.

[0015] Further, the thickness of the intermediate layer is 10-300 μm.

[0016] Further, the heating temperature range is between the solid-liquid phase line temperature of the selected intermediate layer alloy, i.e. T s -T L .

[0017] In the above technical solution, the friction film removal method is to remove the oxide film by moving the upper aluminum alloy to generate relative friction between the aluminum alloys.

[0018] Further, the ultrasonic film removal method is to remove the oxide film by applying ultrasonic waves to the upper side of the sample by the sonotrode through the cavitation effect of liquid metal. The ultrasonic application time is 0.1-10 s, and the sonotrode output amplitude is 1-20 μm.

[0019] Further, the pressure holding in step three is divided into direct pressure holding and diffusion and sonotrode pressure holding and ultrasonic wave assisted diffusion.

[0020] Further, the pressure diffusion stage is applied to the upper side of the sample with a pressure of 1-3 MPa.

[0021] Further, the pressurized diffusion holding time is 10-120 min.

[0022] Further, the ultrasonic-assisted diffusion process applies ultrasonic waves for 10-60 min.

[0023] The principle of the present application is as follows: firstly, the interface gas film and the oxide film are removed and the aluminum alloy is wetted by the physical action and mechanical behavior of the solid-phase particles in the semi-solid intermediate layer and the liquid metal during the mechanical action process (friction or ultrasonic); the principle of the friction film removal is that the transverse shear force generated by the friction between the solid-phase particles in the semi-solid state and the surface of the base material causes the oxide film to break, and then the liquid metal underflow to the lower side of the oxide film lifts the oxide film, and the broken oxide film is broken under the transverse shear action of the solid-phase particles. The principle of ultrasonic film removal is that ultrasonic waves as an external energy field can generate cavitation bubbles in the liquid metal, and when the cavitation bubbles collapse at the liquid-solid interface, they can generate shock waves and micro-jet actions, promoting the removal of the oxide film on the surface of the aluminum alloy. Under the action of ultrasonic waves, the oxide film is removed very quickly. Secondly, the low-melting-point liquid metal in the weld is depleted by liquid-phase diffusion; finally, the joint organization composition is adjusted by solid-phase diffusion to obtain a high-strength joint. The present application uses a low-melting-point Zn-based alloy as an intermediate layer to diffusion weld aluminum alloys, and through holding, the intermediate layer and the aluminum alloy are diffusion welded to obtain a high-strength Zn-Al eutectoid structure joint.

[0024] The present application has the following advantages:

[0025] I. The mechanical action in the first stage destroys the original oxide film of the aluminum alloy, and the low-melting-point liquid metal prevents the formation of a new stable oxide film on the surface of the aluminum alloy after wetting under the action of the mechanical action, so that the oxide film on the aluminum alloy does not need to be removed again during the diffusion welding process;

[0026] II. Compared with traditional diffusion welding, the present application realizes aluminum alloy diffusion welding in an atmospheric environment, reduces the welding temperature and welding pressure, and simplifies the process. The low-melting-point alloy is used as a semi-solid intermediate layer to prevent the softening of the aluminum alloy due to heating and thus reduce the mechanical properties;

[0027] III. The semi-solid intermediate layer reduces the liquid phase content, solving the problem of large overflow of liquid phase during TLP welding; the low-melting-point elements in the semi-solid intermediate layer are used to reduce the welding temperature, and after combining the low-melting-point elements with Zn, Zn plays a role in assisting the rapid diffusion of the low-melting-point elements to the Al alloy.

[0028] Fourthly, the diffusion process of the second stage firstly makes the liquid metal completely diffuse into the base material, and after the liquid phase is exhausted, part of the η-Zn solid phase remains, then the η-Zn and Al undergo solid-phase diffusion, the η-Zn gradually transforms into the homogenized Zn-Al eutectoid structure, and finally the full Zn-Al eutectoid structure joint is obtained. The welded joint has the advantages of small thermal damage, small deformation and higher strength than the base material.

[0029] Compared with CN114871560A "A method for improving joint service temperature and corrosion resistance of ultrasonic-assisted low-temperature diffusion welding of aluminum alloy", the joint performance obtained by the method of the present application is different: the joint strength of CN114871560A can only reach 89% of the base material. The strength of the Zn-Al eutectoid joint obtained by the present application is higher than that of the base material itself, and the strength coefficient is 100% ( Figure 3 ), which means that the failure position during the tensile test is on the base material far away from the welding interface, such as Figure 4 . BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a schematic diagram of diffusion welding of aluminum alloy in Example 1: wherein 1 is an aluminum alloy base material, 2 is a Zn-Sn interlayer, and 3 is a clamp;

[0031] Figure 2 is the microstructure of the joint of the diffusion welded aluminum alloy in Example 1 at different holding times;

[0032] Figure 3 is the tensile strength of the joint of the diffusion welded aluminum alloy in Example 1 at different holding times;

[0033] Figure 4 is a tensile failure sample photo of the joint of the diffusion welded aluminum alloy in Example 1 with a holding time of 60 min;

[0034] Figure 5 is an interface diagram of the interdiffusion sample of Zn-30Sn and Al alloy; (a) SEM diagram and (b) interface element line scan test results;

[0035] Figure 6 is an enlarged SEM diagram of the aluminum alloy joint obtained in Example 1, wherein a diagram is an enlarged SEM diagram of the joint with a diffusion time of 45 min, and b is an enlarged SEM diagram of the joint with a diffusion time of 60 min. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear and explicit, the spirit of the present application will be described in detail below, and any person skilled in the art can make changes and modifications to the technology taught by the present application content without departing from the spirit and scope of the present application content.

[0037] The schematic embodiments of the present application and the descriptions thereof are used to explain the present application, but not as a limitation of the present application.

[0038] Embodiment one:

[0039] The aluminum alloy low-temperature and low-pressure connecting method based on liquid phase and solid phase combined diffusion in the embodiment is performed according to the following steps:

[0040] Firstly, 180-mesh sandpaper is used to mechanically polish the surfaces of 6063 aluminum alloy and Zn-30Sn interlayer, and then the surfaces are cleaned with acetone and dried;

[0041] Secondly, 150-μm-thick Zn-30Sn interlayer is placed between two aluminum alloys to be welded (see Figure 1 a), and after assembly, the sample is placed on a heating table and heated to 360℃, and the initial pressure applied to the upper side of the sample is 0.03 MPa. The upper aluminum alloy is moved horizontally to generate relative friction to remove the oxide film (see Figure 1 b).

[0042] Thirdly, the pressure applied to the upper side is increased to 1 MPa, and the temperature is kept constant; the Zn-30Sn interlayer and the Al alloy are diffused with each other (see Figure 1 c), and the holding time is 15, 30, 45, and 60 min, respectively; and then the sample is cooled to room temperature, and the low-temperature diffusion welding of the aluminum alloy is completed (see Figure 1 d).

[0043] The microstructure of the Zn-30Sn alloy ultrasonic-assisted semi-solid diffusion welded 6063 aluminum alloy joint with different holding times is shown in Figure 2 It can be seen from Figure 2 that when the holding time is 60 min, the interlayer and the base material are fully diffused, and the joint with full Zn-Al eutectoid structure is finally obtained. The tensile strength of the joint is 127.1 MPa, which reaches 100% of the tensile strength of the same heat-treated base material (see Figure 3 ). It is proved that the present application can obtain high-strength aluminum alloy diffusion welded joints under low-temperature and low-pressure conditions.

[0044] It can be seen from the interface element line scan test results of the Zn-30Sn and Al alloy interdiffusion sample that Figure 5 the Zn in the embodiment plays a role in assisting the rapid diffusion of low-melting-point elements to the Al alloy. Through the holding diffusion experiment of Zn-Sn on the surface of the aluminum alloy, it can be shown that the diffused elements at the grain boundaries of the aluminum alloy include Zn and Sn, and the diffusion distance of the Zn element is farther, and the Sn element follows the Zn element, so it is proved that the low-melting-point Sn element diffuses into the Al alloy under the assistance of the Zn element. Through Figure 6It can be seen that when the diffusion time is 45 min, the composition of the joint is Zn-Al eutectoid + η-Zn, but when the diffusion time increases to 60 min, the residual η-Zn and Al interdiffuse to obtain a full Zn-Al eutectoid joint, thereby obtaining a high-strength joint by adjusting the joint structure.

[0045] Example two:

[0046] The aluminum alloy low-temperature and low-pressure connection method based on liquid phase and solid phase combined diffusion in this embodiment is performed in the following steps:

[0047] Firstly, 180-mesh sandpaper is used to mechanically polish the surfaces of the 6063 aluminum alloy and the Zn-20Sn interlayer, and then the surfaces are cleaned with acetone and dried.

[0048] Secondly, the 150-μm-thick Zn-20Sn interlayer is placed between the two aluminum alloys to be welded, and after assembly, the sample is placed on a heating table and heated to 360℃, and the initial pressure applied to the upper side of the sample is 0.03 MPa. The upper aluminum alloy is moved horizontally to generate relative friction to remove the oxide film.

[0049] Thirdly, the pressure applied to the upper side is increased to 1 MPa, and the Zn-20Sn interlayer and the Al alloy are allowed to interdiffuse, and the holding time is 15, 30, 45, and 60 min, respectively. Then, the sample is cooled to room temperature, and the low-temperature diffusion welding of the aluminum alloy is completed.

[0050] Compared with example one, the interlayer in this embodiment is changed to Zn-20Sn alloy, and the Zn-Sn liquid phase content in the molten interlayer at the same temperature is reduced, and the interdiffusion between the base material and the interlayer is completed in a shorter time.

[0051] Example three:

[0052] The aluminum alloy low-temperature and low-pressure connection method based on liquid phase and solid phase combined diffusion in this embodiment is performed in the following steps:

[0053] Firstly, 180-mesh sandpaper is used to mechanically polish the surfaces of the 6063 aluminum alloy and the Zn-30Ga interlayer, and then the surfaces are cleaned with acetone and dried.

[0054] Secondly, the 150-μm-thick Zn-30Ga interlayer is placed between the two aluminum alloys to be welded, and after assembly, the sample is placed on a heating table and heated to 360℃, and the initial pressure applied to the upper side of the sample is 0.03 MPa. The upper aluminum alloy is moved horizontally to generate relative friction to remove the oxide film.

[0055] III. The upper side pressure is increased to 1 MPa, and heat preservation is carried out; the Zn-30Ga intermediate layer and the Al alloy are diffused with each other, and the heat preservation time is 15, 30, 45 and 60 minutes respectively; then, cooling to room temperature is carried out, and the low-temperature diffusion welding of the aluminum alloy is completed.

[0056] Compared with example one, the intermediate layer is changed to Zn-30Ga alloy in this implementation, and the Ga element in the molten intermediate layer is more easily diffused into the Al alloy at the same temperature, and the interdiffusion between the base material and the intermediate layer is completed in a shorter time.

[0057] Example four:

[0058] The aluminum alloy low-temperature low-pressure connection method based on liquid-phase and solid-phase combined diffusion in this example is carried out according to the following steps:

[0059] I. First, the surface of the 6063 aluminum alloy and the Zn-30Sn intermediate layer is mechanically polished using 180-mesh sandpaper, and then the surface is cleaned with acetone and dried;

[0060] II. The 150-μm-thick Zn-30Sn intermediate layer is placed between the two aluminum alloys to be welded, and after assembly, it is placed on a heating table and heated to 360℃. The sonotrode is applied to the upper side of the base material, the amplitude is 3.5 μm, the time is 1 s, and the air film between the semi-solid Zn-30Sn and the base material and the oxide film on the surface of the Zn-30Sn and the aluminum alloy are removed;

[0061] III. After the ultrasonic wave in the previous step is completed, the upper side pressure is increased to 1 MPa, and heat preservation is carried out; the Zn-30Sn intermediate layer and the Al alloy are diffused with each other, and the heat preservation time is 15, 30, 45 and 60 minutes respectively; then, cooling to room temperature is carried out, and the low-temperature diffusion welding of the aluminum alloy is completed.

[0062] Compared with example one, the film removal method is changed from friction film removal to ultrasonic film removal in this implementation, and the oxide film can be removed more quickly.

[0063] Example five:

[0064] The aluminum alloy low-temperature low-pressure connection method based on liquid-phase and solid-phase combined diffusion in this example is carried out according to the following steps:

[0065] I. First, the surface of the 6063 aluminum alloy and the Zn-30Sn intermediate layer is mechanically polished using 180-mesh sandpaper, and then the surface is cleaned with acetone and dried;

[0066] II. A 150 μm thick Zn-30Sn interlayer was placed between two aluminum alloys to be welded, and assembled on a heating table to heat to 360 °C. The sonotrode was applied to the top of the base material with an amplitude of 3.5 μm and a time of 1 s to remove the air film between the semi-solid Zn-30Sn and the base material and the oxide film on the surface of the Zn-30Sn and the aluminum alloy;

[0067] III. After the ultrasonic treatment in the previous step, the heating temperature was maintained, and continuous ultrasonic treatment was applied again to diffuse the Zn-30Sn interlayer and the Al alloy with each other for 15, 30, 45, and 60 min, respectively. Subsequently, the temperature was cooled to room temperature to complete the low-temperature diffusion welding of the aluminum alloy.

[0068] Compared with Example 4, the diffusion process in this example was changed from pressure diffusion to ultrasonic-assisted diffusion, which accelerated the diffusion process and completed the interdiffusion between the base material and the interlayer in a shorter time.

Claims

1. A method for joining aluminum alloys at low temperature and low pressure based on the combined diffusion of liquid and solid phases, characterized in that The method is performed according to the following steps: I. The surfaces to be welded of the aluminum alloy and the intermediate layer are mechanically polished, polished and placed in an acetone solution to remove and dry, to obtain the pretreated material to be welded; II. The semi-solid interlayer is placed between two aluminum alloys to be welded, assembled and placed on a heating table to heat to the welding temperature, and the interface gas film and oxide film are removed by mechanical means; the heating temperature range is between the solid-liquid phase line temperature of the selected interlayer alloy, i.e. T s —T L ; III. The upper side of the welded part is pressed and heat treated, and then cooled to room temperature, to complete the low-temperature diffusion bonding of the aluminum alloy; The pressing and heat treatment is divided into direct pressing and heat treatment diffusion and sonotrode pressing and ultrasonic assisted diffusion; the ultrasonic assisted diffusion is applied for 10-60 min; the pressure applied on the upper side of the sample during the heat treatment diffusion is 1-3 Mpa, and the heat treatment diffusion is heat treated for 15 min, 30 min, 45 min or 60 min; The semi-solid intermediate layer is Zn-30Sn, Zn-20Sn or Zn-30Ga.

2. The aluminum alloy low-temperature and low-pressure joining method based on the combined diffusion of liquid and solid phases according to claim 1, characterized in that The mechanical method is friction or ultrasonic treatment.

3. The aluminum alloy low-temperature and low-pressure joining method based on the combined diffusion of liquid and solid phases according to claim 2, characterized in that The ultrasonic removal of the interface gas film and the oxide film is achieved by applying ultrasonic waves to the upper side of the sample through a sonotrode to remove the oxide film, and the ultrasonic application time is 0.1-10 s, and the sonotrode output amplitude is 1-20 μm; the friction removal of the interface gas film and the oxide film is achieved by moving the upper aluminum alloy to generate relative friction between the aluminum alloys to remove the oxide film.

4. The aluminum alloy low-temperature and low-pressure joining method based on the combined diffusion of liquid and solid phases according to claim 1, characterized in that The aluminum alloy is a 1-series aluminum alloy, a 2-series aluminum alloy, a 3-series aluminum alloy, a 5-series aluminum alloy, a 6-series aluminum alloy, a 7-series aluminum alloy or a fine-grain strengthened ultra-fine-grain aluminum alloy.

5. The aluminum alloy low-temperature and low-pressure joining method based on the combined diffusion of liquid and solid phases according to claim 1, characterized in that The intermediate layer is in the form of a metal foil, a mixed solder paste, an alloy block or a metal powder.

6. The aluminum alloy low-temperature and low-pressure joining method based on the combined diffusion of liquid and solid phases according to claim 1, characterized in that The thickness of the intermediate layer is 10-300 μm.

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