CN114871560A

CN114871560A - Method for improving service temperature and corrosion resistance of joint by ultrasonic-assisted low-temperature diffusion welding of aluminum alloy

Info

Publication number: CN114871560A
Application number: CN202210478778.8A
Authority: CN
Inventors: 赵普; 闫久春; 许志武; 修子扬
Original assignee: Harbin Institute of Technology
Current assignee: Harbin Institute of Technology
Priority date: 2022-04-29
Filing date: 2022-04-29
Publication date: 2022-08-09

Abstract

A method for improving the service temperature and corrosion resistance of a joint by ultrasonic-assisted low-temperature diffusion welding of aluminum alloy relates to the field of alloy welding. The invention aims to solve the problems of the existing aluminum alloy brazing and diffusion welding at the same time, and the joint which can be used for high-temperature service and corrosion resistance is obtained under the condition of low-temperature welding. The method of the invention comprises the following steps: firstly, preprocessing an intermediate layer and an aluminum alloy base material; assembling and heating the aluminum alloy and the intermediate layer alloy to the welding temperature, and applying ultrasonic waves to remove the air film between the materials and the oxide film on the surface of the materials; and thirdly, applying pressure and applying ultrasonic again to obtain the aluminum alloy direct connection joint without the welding seam. The ultrasonic-assisted diffusion welding method can realize aluminum alloy diffusion welding under atmospheric conditions without high temperature of traditional diffusion welding, and can ensure that low-melting-point liquid metal is completely diffused into the base metal under the ultrasonic action. The high-temperature resistant and corrosion resistant joint with the strength close to that of the base material can be obtained while the base material is protected from excessive welding heat. The invention is applied to the field of aluminum alloy welding.

Description

Method for improving service temperature and corrosion resistance of joint by ultrasonic-assisted low-temperature diffusion welding of aluminum alloy

Technical Field

The invention belongs to the field of aluminum alloy welding, and particularly relates to a method for improving service temperature and corrosion resistance of a joint by ultrasonic-assisted low-temperature diffusion welding of aluminum alloy.

Background

With the rapid development of electronic technology and the integration of electronic products, the power of aerospace, military and civil electronic equipment is continuously increased, the working temperature of the electronic equipment is continuously increased due to the increase of the power, and the failure rate of electronic components is rapidly increased along with the increase of the temperature. Therefore, the heat dissipation problem inevitably becomes one of the key factors that restrict the application of the high power device in various fields.

The aluminum alloy micro-channel heat dissipation plate has high heat dissipation coefficient, can be used for efficiently cooling high-power devices, is one of main devices for improving the utilization rate of equipment, and is widely applied to the fields of automobiles, radars, central heating, machinery and the like. The structure of the micro-channel radiator is that a channel is directly processed on an aluminum alloy plate and a cover plate is added on the channel. Based on the functionality of the aluminum alloy micro-flow channel structure, each flow channel and the cover plate are required to realize compact connection and small deformation, and the conventional connection methods are brazing and diffusion welding.

Currently, the solders commonly used for brazing aluminum alloys include Al-Si, Zn-Al and Sn-Zn solders. The soldered joint of Al-Si-based solder can meet the reliability and high temperature resistance of the aluminum alloy radiator, but the higher soldering temperature can not avoid overburning and softening of the base metal. The Zn-Al brazing filler metal as the intermediate temperature brazing filler metal reduces the welding temperature to a certain extent, but the extremely high intersolubility between Zn and Al causes serious corrosion of aluminum alloy in the brazing process, and the phenomenon of dissolution and penetration easily occurs to the thin-wall aluminum alloy heat sink. The inevitable low melting point Zn-Al eutectic phase in the joint makes the joint heat resistant up to 382 deg.C. The Sn-Zn solder realizes the low-temperature brazing of the aluminum alloy by virtue of the low welding temperature, but the existence of the low-melting-point element mainly comprising Sn in the welding seam makes the joint not meet the use requirements of different high-temperature environments.

The diffusion welding can obtain the joint with the microstructure close to the base material, so the joint has high strength, strong corrosion resistance and stable quality. In the diffusion welding process of aluminum alloy, harsh welding conditions are required for the purposes of removing an oxide film on the surface to be welded, eliminating interface pores, realizing full diffusion of base metal and the like. The welding temperature is usually above 500 ℃, the growth of the base material crystal grains is easily caused, and the welding process is usually completed in equipment in vacuum or protective atmosphere. In order to remove the aluminum alloy oxide film and realize the full diffusion of aluminum atoms under the low temperature condition, methods of surface activation assisted diffusion welding and low-melting point intermediate layer Transient Liquid Phase (TLP) bonding by ion bombardment and the like are provided. The surface activation auxiliary diffusion welding method combines the ion bombardment technology and the diffusion welding technology, effectively removes the oxide film on the surface of the aluminum alloy and realizes surface activation, eliminates the adverse effect of the oxide film on the diffusion welding of the aluminum alloy, and fresh aluminum alloy can realize mutual diffusion at lower welding temperature (350 ℃) (Chinese patent: CN 201810184006.7). But surface activation adds process difficulty and does not allow for the removal of vacuum or protective atmosphere welding equipment.

In the low-temperature TLP bonding, a low-melting-point intermediate layer material is placed between to-be-welded parent metals, eutectic reaction occurs in the intermediate layer material parent metals after the welding temperature is reached, a layer of extremely thin liquid film is formed on the interface of to-be-welded workpieces, liquid metal wets and fills joint gaps, mutual diffusion between the liquid metal and the parent metals is promoted, and welding is realized by completing isothermal solidification and joint component homogenization. The common intermediate layer for low-temperature TLP bonding of aluminum alloy is Zn foil, the bonding temperature can be reduced to 400 ℃ or below, and the TLP aluminum alloy is ultrasonically assisted by Zn as the intermediate layer, so that the welding process can be directly realized under atmospheric conditions, and a nearly full solid solution joint is obtained (Chinese patent: CN 201811535520.7; CN 201811537062.0; CN 201811537063.5). However, the solubility of Zn to Al is too high, the corrosion of the welding process to aluminum is serious, and the phenomenon of dissolution penetration may occur to a thin-wall aluminum plate or an aluminum pipe. Furthermore, the temperature resistance of the bond joint does not exceed the eutectic temperature of Zn-Al (381 ℃). The Sn-based intermediate layer has low melting point and low solubility to Al, and solves the problems of overhigh temperature, corrosion and the like in the aluminum alloy welding process (Chinese patent: CN 201010289606.3). Thus, the use of a Sn-based interlayer for low temperature liquid phase diffusion welding of aluminum alloys appears to solve the problems present in current diffusion welding processes. However, the aluminum alloy joint mainly comprising the Sn-based intermediate layer has lower strength and temperature resistance. The large potential difference between Sn and Al leads to poor corrosion resistance of the joint, and particularly for an aluminum alloy micro-channel heat dissipation plate taking liquid as a heat dissipation medium, the reliability of the aluminum alloy micro-channel heat dissipation plate cannot be guaranteed.

In summary, the existing aluminum alloy brazing and diffusion welding still have more technical problems. The solid phase diffusion welding has the problems of high temperature, large pressure, long time, harsh welding conditions and the like. Surface activation assisted diffusion although the problem of parent metal softening and overburning is solved by lowering the temperature, surface activation increases the process difficulty. The ultrasonic-assisted low-temperature TLP solves the problems of deterioration, large deformation, harsh welding conditions and the like of the traditional diffusion welding base material by reducing the temperature and the pressure, but the Zn intermediate layer has serious corrosion to aluminum. The Sn-based intermediate layer has low solubility to aluminum alloy, but the joint obtained by the Sn-based intermediate layer has the problems of low strength and temperature resistance and poor corrosion resistance, and cannot be directly used for connecting the aluminum alloy micro-channel heat dissipation plate.

Disclosure of Invention

The problems to be solved by the present invention include: (1) the traditional diffusion welding is limited in environment and can only be carried out in a vacuum or protective gas cavity; (2) the softening of the aluminum alloy material is easily caused by overhigh welding temperature; (3) the problem that the joint with high temperature service performance and strong corrosion resistance can not be obtained by welding under the low temperature condition. Aiming at the technical defects in the prior art, the method for ultrasonic-assisted low-temperature diffusion welding of the aluminum alloy is simple, convenient and feasible and has strong applicability. The method utilizes low-melting-point Sn-based metal as an intermediate layer to perform diffusion welding on aluminum alloy, and completely diffuses the Sn-based intermediate layer into a base material by virtue of an ultrasonic effect to obtain the approximate weldless diffusion connection joint with the Al directly bonded.

The invention discloses a method for improving the service temperature and corrosion resistance of a joint by ultrasonic-assisted low-temperature diffusion welding of an aluminum alloy, which comprises the following steps:

firstly, mechanically grinding and polishing the surfaces to be welded of the intermediate layer and the aluminum alloy, placing the surfaces in an acetone solution for cleaning and drying to obtain the intermediate layer and the aluminum alloy after pretreatment;

secondly, placing the intermediate layer alloy with the melting point lower than 300 ℃ between two aluminum alloys to be welded to obtain a sample piece to be welded; heating the alloy to a temperature above the melting point of the intermediate alloy; applying ultrasonic vibration on the upper side of the parent metal, removing a gas film between the molten interlayer alloy and the aluminum alloy, and removing an oxide film of the aluminum alloy and the molten interlayer alloy;

and thirdly, continuously keeping the heating to the temperature above the melting point of the intermediate layer alloy after the last step of ultrasonic processing is finished, applying pressure on the aluminum alloy base material, applying ultrasonic processing again, and then cooling to the room temperature to finish the low-temperature diffusion welding of the aluminum alloy.

Further, the intermediate layer is pure Sn, a Sn-Zn based alloy, a Sn-Pb based alloy, a Sn-In based alloy, a Sn-Bi based alloy, a Sn-Ga based alloy, or a Sn-Sb based alloy.

Further, the heating to the temperature above the melting point of the interlayer alloy means that: heating to the liquidus temperature of the interlayer alloy to the liquidus temperature +100 ℃.

The liquidus temperature ensures that the intermediate layer is completely melted; the liquidus temperature plus 100 ℃ in the range ensures that the intermediate layer can be fully diffused into the parent metal in the later period to obtain the weldless joint.

Further, the ultrasonic time in the step two is 0.1-10 s; the ultrasonic time in the third step is 1-60 min; and in the second step and the third step, the output amplitude of the sonotrode of the ultrasound is 1-20 mu m.

Further, the ultrasound in the third step is continuous ultrasound during the incubation period or intermittent ultrasound during the incubation period.

Further, the intermittent ultrasonic mode during the heat preservation period is three, and the first ultrasonic mode is as follows: keeping the temperature for 30min, and performing ultrasonic treatment for 1 time/5 min and 3 s/time; the second ultrasonic mode is as follows: keeping the temperature for 60min, and performing ultrasonic treatment for 1 time/5 min and 1 s/time; the third ultrasonic mode is as follows: keeping the temperature for 60min, and performing ultrasonic treatment for 1 time/10 min and 5 s/time.

Further, the pressure in the third step is 0.1-2 Mpa.

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 or 7 series aluminum alloy; or the aluminum alloy is fine-grain reinforced ultra-fine-grain aluminum alloy.

Further, the assembly form of the intermediate layer alloy and the aluminum alloy is direct prefabrication, electroplating, chemical plating, atomized spraying, iron coating, ultrasonic coating or magnetron sputtering.

Further, the thickness of the interlayer alloy is 1-100 μm.

The intermediate layer forms include but are not limited to metal foils, mixed solder paste, alloy blocks and metal powder.

The position of the ultrasonic position applying in the third step of the present invention includes, but is not limited to, the lower parent material or the upper parent material.

The heating modes of the invention include but are not limited to: resistance heating, high frequency induction coil heating, infrared heating, hot gas heating, and the like.

The invention has the beneficial effects that:

firstly, the ultrasonic action in the first stage of the invention destroys the original oxide film of the aluminum alloy, and ensures that the oxide film can not obstruct the mutual diffusion of metals in the atmospheric environment; the Sn-based liquid metal wets the aluminum alloy under the ultrasonic action to prevent the surface of the aluminum alloy from generating a new stable oxide film again, and the oxide film of the aluminum alloy does not need to be removed again in the diffusion welding process; and (3) the liquid metal in the middle layer is forced to diffuse towards the base metal by the second ultrasonic wave until the middle layer is completely diffused into the base metal, so that the base metals on the two sides are contacted, and a diffusion welding joint close to a weldless joint is obtained (see figure 2). The welded joint has the advantages of strength close to that of a base material, good corrosion resistance, good temperature resistance, small interface thermal resistance and the like.

Secondly, the traditional process cannot realize the diffusion welding in the atmospheric environment because of the obstruction of the oxide film; compared with the traditional diffusion welding, the diffusion welding method disclosed by the invention has the advantages that the diffusion welding of the aluminum alloy is realized in the atmospheric environment, and the technological process is simplified. The low-melting-point alloy is used as the intermediate layer to protect the aluminum alloy from softening by heating; the invention selects the low-melting-point metal to ensure low welding temperature, and for the aluminum alloy, high-temperature welding usually causes softening of the aluminum alloy and reduction of mechanical properties, which is a great problem faced by high-temperature welding of the aluminum alloy. Therefore, the selection of the low-melting intermediate layer is one of the essential means for solving the problem.

The aluminum alloy and the main component Sn element of the middle layer have smaller intersolubility, so that the problem of transition corrosion of liquid metal to the base metal in the welding process is solved;

the invention has wider application range and can be used for low-temperature, medium-temperature and high-temperature diffusion welding of various aluminum alloys. The intermediate layer may be selected from Sn and Sn-based alloys, In and In-based alloys, Bi and Bi-based alloys and Ga-based alloys or Zn and Zn-based alloys, Al-Si and Al-Si-based alloys according to the soldering temperature. The Sn-Zn alloy selected by the invention also has the following functions:

sn has a low melting point and thus a low soldering temperature, but Sn does not easily diffuse into Al, and a relatively long time is required even when ultrasound is applied;

zn is easy to diffuse into Al, but the melting point of Zn is high, and the corrosion to Al is large. After Sn and Zn are combined, Sn plays a role in reducing the welding temperature, and Zn plays a role in assisting Sn to diffuse to Al quickly.

The invention is applied to the field of aluminum alloy welding, and is suitable for connection and batch production of aluminum alloy micro-channel heat dissipation plates of large electronic power devices.

Drawings

FIG. 1 is a schematic view of an aluminum alloy in the first embodiment by ultrasonic-assisted diffusion welding: wherein 1 is an upper parent metal, 2 is an intermediate layer, and 3 is a lower parent metal;

FIG. 2 is a microstructure of an ultrasonic assisted diffusion welding 6063 aluminum alloy joint using a Sn-9Zn interlayer in a first example;

FIG. 3 is a graph of the normal and high temperature tensile strength of an 6063 aluminum alloy joint ultrasonically assisted by diffusion welding with an Sn-9Zn interlayer in example one;

FIG. 4 is a view of the microstructure of (a) an ultrasonically assisted diffusion bonded joint with Sn-9Zn as an intermediate layer and (b) a soldered joint using Sn-9Zn as a solder after being corroded in a 0.6mol/L NaCl solution for 72 hours in example one.

Detailed Description

For the purpose of promoting a clear understanding of the objects, aspects and advantages of the embodiments of the invention, reference will now be made in detail to the embodiments of the present disclosure, and it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the disclosure.

The first embodiment is as follows:

the method for improving the service temperature and the corrosion resistance of the joint by ultrasonic-assisted low-temperature diffusion welding of the aluminum alloy comprises the following steps:

firstly, sequentially mechanically grinding and polishing the surfaces to be welded of the middle layer and the 6063 aluminum alloy by using 400-mesh, 800-mesh and 1500-mesh sand paper and a 0.5-micron polishing agent, cleaning the surfaces by using acetone, and drying;

secondly, placing a Sn-9Zn foil with the thickness of 5 microns between two aluminum alloys to be welded (shown in figure 1a), placing the assembled aluminum alloys on a heating table, heating the assembled aluminum alloys to 300 ℃, applying ultrasonic waves to the upper side of the base metal by a sonotrode, wherein the amplitude is 3.5 microns, the time is 5 seconds, and removing a gas film between liquid Sn-9Zn and the base metal and an oxide film on the surfaces of the Sn-9Zn and the aluminum alloys, shown in figure 1 b;

thirdly, applying 1.5MPa pressure on the parent metal at the upper end after the ultrasonic treatment is finished, and applying the ultrasonic treatment again for 30min to promote the residual liquid Sn-9Zn to be completely diffused to the parent metal; subsequent cooling to room temperature completes the low temperature diffusion welding of the aluminum alloy, see fig. 1 c.

The microstructure of the Sn-9Zn alloy 6063 aluminum alloy joint by ultrasonic-assisted diffusion welding is shown in figure 2. It can be seen from fig. 2 that the solder is fully diffused to the base material to finally obtain a joint close to a weldless joint, and after Sn is fully diffused, Al on both sides are in contact with each other, so that the thermal resistance of the joint is reduced and the thermal conductivity is improved. The normal temperature tensile strength of the joint is 143MPa, and reaches 89.9 percent of the tensile strength of the parent metal subjected to the same heat treatment. The joint reached 93.5%, 91.4% and 77.8% of the parent material in tensile strength at high temperatures of 200 ℃, 300 ℃ and 400 ℃, respectively (see fig. 3). The invention proves that the connector in service under high temperature can be obtained by low temperature welding.

And respectively carrying out electrochemical corrosion experiments on the 6063 aluminum alloy ultrasonic brazing joint with the brazing filler metal being Sn-9Zn and the welding seam thickness being 50 mu m and the 6063 aluminum alloy ultrasonic auxiliary diffusion welding joint with the middle layer being Sn-9Zn by using 0.6mol/L NaCl solution, and comparing the micro-morphologies of the experiments. As can be seen from fig. 4, the ultrasonic diffusion weld after 72h of corrosion had only a few corrosion pits (fig. 4a), whereas the braze weld had completely cracked (fig. 4 b). The ultrasonic-assisted diffusion welding aluminum alloy joint is proved to have extremely strong corrosion resistance and be suitable for connecting a micro-channel heat dissipation plate.

Example two:

placing a 5-micron thick Sn-9Zn foil between two aluminum alloys to be welded, placing the assembled aluminum alloys on a heating table, heating the assembled aluminum alloys to 300 ℃, applying ultrasonic waves to the upper side of the base metal by a sonotrode, wherein the amplitude is 3.5 microns, the time is 5 seconds, and removing an air film between liquid Sn-9Zn and the base metal and an oxidation film on the surfaces of the Sn-9Zn and the aluminum alloys;

thirdly, after the ultrasonic treatment is finished, applying 1.5MPa pressure on the parent metal at the upper end, carrying out heat preservation on the sample, applying intermittent ultrasonic treatment, carrying out heat preservation for 30min, and carrying out ultrasonic treatment for 1 time/5 min and 3 s/time during the heat preservation period to promote the residual liquid Sn-9Zn to be completely diffused to the parent metal; and then cooling to room temperature to complete the low-temperature diffusion welding of the aluminum alloy.

Compared with the first embodiment, the first embodiment changes continuous ultrasound into intermittent ultrasound, shortens the ultrasound time, avoids long-time heating of the ultrasound sonotrode, and provides a new ultrasound applying mode.

Example three:

secondly, placing a 5-micron thick Sn-9Zn foil between two aluminum alloys to be welded, placing the assembled aluminum alloys on a heating table, heating the assembled aluminum alloys to 250 ℃, applying ultrasonic waves to the upper side of the base metal by a sonotrode, wherein the amplitude is 3.5 microns, the time is 5 seconds, and removing an air film between liquid Sn-9Zn and the base metal and an oxidation film on the surfaces of the Sn-9Zn and the aluminum alloys;

thirdly, applying 1.5MPa pressure on the parent metal at the upper end after the ultrasonic treatment is finished, and applying the ultrasonic treatment again for 60min to promote the residual liquid Sn-9Zn to be completely diffused to the parent metal; and then cooling to room temperature to complete the low-temperature diffusion welding of the aluminum alloy.

Compared with the first embodiment, the welding temperature is reduced, and the second ultrasonic time is prolonged to ensure that the intermediate layer is completely diffused to the aluminum alloy.

Example four:

placing a 5-micron thick Sn foil between two aluminum alloys to be welded, placing the assembled Sn foil on a heating table, heating the assembled Sn foil to 300 ℃, applying ultrasonic waves to the upper side of the base metal by a sonotrode, wherein the amplitude is 3.5 microns, the time is 5 seconds, and removing a gas film between liquid Sn and the base metal and an oxide film on the surfaces of the Sn and the aluminum alloys;

thirdly, applying 1.5MPa pressure to the parent metal at the upper end after the ultrasonic treatment is finished, and applying the ultrasonic treatment again for 60min to promote the residual liquid Sn to be completely diffused to the parent metal; and then cooling to room temperature to complete the low-temperature diffusion welding of the aluminum alloy.

Compared with the first embodiment, the intermediate layer is changed into the pure Sn foil, so that the smelting of the alloy is avoided, but the complete diffusion of the liquid Sn to the aluminum alloy is ensured by prolonging the ultrasonic time.

Example five:

firstly, mechanically grinding and polishing the to-be-welded surface of 6063 aluminum alloy by using 400-mesh, 800-mesh and 1500-mesh sand paper and 0.5-micron polishing agent, cleaning the surface by using acetone, and drying;

secondly, chemically plating pure Sn layers with the thickness of 8 microns on the surfaces of two aluminum alloy to be welded, placing the aluminum alloy on a heating table after assembling, heating the aluminum alloy to 300 ℃, applying ultrasonic waves to the upper side of the base metal by a sonotrode, wherein the amplitude is 3.5 microns, the time is 1s, and removing gas films and oxidation films between liquid Sn;

Compared with the first embodiment, the embodiment changes the prefabricated middle layer into the surface chemical plating of the base material, and can randomly chemically plate metal layers with different thicknesses.

Example six:

placing a 5-micron thick Sn-9Zn foil between two aluminum alloys to be welded, placing the assembled aluminum alloys on a high-frequency induction coil heater to be heated to 300 ℃, applying ultrasonic waves to the upper side of the base metal by a sonotrode, wherein the amplitude is 3.5 microns, the time is 5 seconds, and removing a gas film between liquid Sn-9Zn and the base metal and an oxidation film on the surfaces of the Sn-9Zn and the aluminum alloys;

thirdly, applying 1.5MPa pressure on the parent metal at the upper end after the ultrasonic treatment is finished, and applying the ultrasonic treatment again for 30min to promote the residual liquid Sn-9Zn to be completely diffused to the parent metal; and then cooling to room temperature to complete the low-temperature diffusion welding of the aluminum alloy.

Compared with the first embodiment, the first embodiment changes the heating mode into high-frequency induction coil heating, and improves the temperature rise rate.

Claims

1. A method for improving the service temperature and the corrosion resistance of a joint by ultrasonic-assisted low-temperature diffusion welding of aluminum alloy is characterized by comprising the following steps:

2. The method of claim 1, wherein the intermediate layer is pure Sn, a Sn-Zn based alloy, a Sn-Pb based alloy, a Sn-In based alloy, a Sn-Bi based alloy, a Sn-Ga based alloy, or a Sn-Sb based alloy.

3. The method for improving the service temperature and the corrosion resistance of the joint by ultrasonically assisting the low-temperature diffusion welding of the aluminum alloy according to claim 1, wherein the heating to the temperature higher than the melting point of the intermediate layer alloy is as follows: heating to the liquidus temperature of the interlayer alloy to the liquidus temperature +100 ℃.

4. The method for improving the service temperature and the corrosion resistance of the joint by ultrasonically assisting the low-temperature diffusion welding of the aluminum alloy according to claim 1, wherein the ultrasonic time in the second step is 0.1-10 s; the ultrasonic time in the third step is 1-60 min; and in the second step and the third step, the output amplitude of the sonotrode of the ultrasound is 1-20 mu m.

5. The method for improving the service temperature and the corrosion resistance of the joint by ultrasonically assisting the low-temperature diffusion welding of the aluminum alloy according to the claim 1 or 4, characterized in that the ultrasound in the third step is continuous ultrasound during the heat preservation period or intermittent ultrasound during the heat preservation period.

6. The method for improving the service temperature and the corrosion resistance of the joint by ultrasonically assisting the low-temperature diffusion welding of the aluminum alloy according to claim 5, wherein the intermittent ultrasonic modes during the heat preservation period are three, and the first ultrasonic mode is as follows: keeping the temperature for 30min, and performing ultrasonic treatment for 1 time/5 min and 3 s/time; the second ultrasonic mode is as follows: preserving heat for 60min, and performing ultrasonic treatment for 1 time/5 min and 1 s/time; the third ultrasonic mode is as follows: keeping the temperature for 60min, and performing ultrasonic treatment for 1 time/10 min and 5 s/time.

7. The method for improving the service temperature and the corrosion resistance of the joint by ultrasonically assisting the low-temperature diffusion welding of the aluminum alloy according to claim 1, wherein the pressure in the third step is 0.1-2 Mpa.

8. The method for improving the service temperature and the corrosion resistance of the joint by ultrasonically assisting the low-temperature diffusion welding of the aluminum alloy according to claim 1, wherein 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 or a 7-series aluminum alloy; or the aluminum alloy is fine-grain reinforced ultra-fine-grain aluminum alloy.

9. The method of claim 1, wherein the intermediate layer alloy and the aluminum alloy are assembled in the form of direct prefabrication, electroplating, chemical plating, spray coating, iron coating, ultrasonic coating or magnetron sputtering.

10. The method for improving the service temperature and the corrosion resistance of the joint by ultrasonically-assisted low-temperature diffusion welding of the aluminum alloy according to claim 1, wherein the thickness of the interlayer alloy is 1-100 μm.