Vacuum brazing method for pure aluminum part

Abstract

The invention relates to a vacuum brazing method for a pure aluminum part, which comprises the following steps: a first pure aluminum plate and a second pure aluminum plate are assembled after being subjected to surface pretreatment, and an obtained combined part is subjected to vacuum treatment and brazing treatment to obtain the pure aluminum part, the brazing treatment comprises first heat treatment, second heat treatment, third heat treatment and fourth heat treatment of which the temperatures are increased in sequence. According to the method, specific brazing process parameters are selected, the assembly is subjected to vacuum brazing treatment, the welding binding rate and the welding strength of the pure aluminum part can be remarkably improved, the obtained welding seam components are kept consistent with a base body, and therefore the use requirements of semiconductor components can be met.

Description

Technical Field

[0001] The invention relates to the technical field of metal welding, and in particular to a vacuum brazing method for pure aluminum parts. Background Art

[0002] Pure aluminum is a common metal material, widely used in construction, aerospace, vehicle manufacturing, electronic products and other fields. In the field of electronic products, pure aluminum is mainly used in containers, heat sinks, terminals and metal electrodes. Pure aluminum is widely used in electronic devices because of its good electrical and thermal conductivity.

[0003] In order to ensure the stable working performance of electronic devices, the welding of pure aluminum parts is usually required to have a high welding bonding rate and strength, and a uniform microstructure without defects. However, the welding rate of pure aluminum brazing in the current existing technology is low, and the weld composition is very different from the matrix, which cannot meet the requirements of the high-end electronics industry for electronic devices, and the application of aluminum parts is subject to certain limitations.

[0004] CN 107457496A discloses a welding process for pure aluminum materials, which includes the following steps: 1) processing welding grooves; 2) grinding and removing the aluminum oxide film metal layer on the surface of the pure aluminum material; 3) preheating the welding part with a manual baking gun; 4) welding the pure aluminum material, and heating the welding part during welding; 5) continuing to post-heat treat the pure aluminum material with a manual baking gun after welding; 6) using a pneumatic or electric scraper to perform root cleaning on the back of the weld of the pure aluminum material; 7) preheating the back of the weld of the pure aluminum material; 8) welding the back of the weld of the pure aluminum material, and heating the welding part during welding; 9) continuing to post-heat treat the pure aluminum material with a manual baking gun after welding. However, the welding rate and strength of the obtained pure aluminum material still need to be improved, and the welding process is not suitable for preparing aluminum electronic devices in the high-end electronics industry.

[0005] CN 109807452A discloses a welding method for a high-purity aluminum rotating target, wherein the welding method is divided into three steps to weld the end welding port or the tail cover welding port, wherein the first step is spot welding, the second step is arc segment welding, and the third step is circumferential welding. The inventive method can prevent the high-purity aluminum rotating target material from deforming, the aluminum alloy end and the high-purity rotating target material have high coaxiality, and the interface welding effect of the aluminum alloy end and the high-purity rotating target material is good, but it cannot provide guidance for the welding of the plate, and cannot solve the problem of low welding rate and strength between pure aluminum parts.

[0006] In view of the shortcomings of the prior art, it is necessary to provide a pure aluminum welding method in which the composition of the weld is consistent with that of the substrate and the welding rate and strength are high. Summary of the invention

[0007] The purpose of the present invention is to provide a vacuum brazing method for pure aluminum parts, which can weld pure aluminum parts by adjusting the vacuum brazing process to obtain pure aluminum parts with a weld composition consistent with that of a substrate, a high welding rate and strength, and meet the use requirements of semiconductor components.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] The present invention provides a vacuum brazing method for pure aluminum parts, and the vacuum brazing method comprises the following steps:

[0010] The first pure aluminum plate and the second pure aluminum plate are assembled after surface pretreatment, and the obtained assembly is subjected to vacuum treatment and brazing treatment to obtain the pure aluminum part;

[0011] The brazing process includes a first heat treatment, a second heat treatment, a third heat treatment and a fourth heat treatment with temperatures increasing in sequence.

[0012] The vacuum brazing method for pure aluminum parts provided by the present invention can significantly improve the welding bonding rate of pure aluminum parts, and the welding strength is also improved by setting the first heat treatment, the second heat treatment, the third heat treatment and the fourth heat treatment with successively increasing temperatures, thereby performing vacuum brazing treatment on the assembly parts. The composition of the obtained weld is consistent with that of the substrate, thereby being able to meet the use requirements of semiconductor components.

[0013] Preferably, the models of the first pure aluminum plate and the second pure aluminum plate include A1050.

[0014] Preferably, the first pure aluminum plate and the second pure aluminum plate have a thickness of 18-22 mm and a width of 295-305 mm respectively.

[0015] The thickness of the first pure aluminum plate and the second pure aluminum plate are respectively 18-22 mm, for example, 18 mm, 19 mm, 20 mm, 21 mm or 22 mm, but are not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0016] The widths of the first pure aluminum plate and the second pure aluminum plate are 295-305 mm respectively, for example, 295 mm, 298 mm, 300 mm, 302 mm or 305 mm, but are not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0017] Preferably, the flatness and parallelism of the first pure aluminum plate and the second pure aluminum plate are both less than 5 wires, for example, 4 wires, 3 wires, 2 wires or 1 wire, but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] Preferably, the surface pretreatment comprises acetone degreasing, alkali immersion, acid immersion, water washing and vacuum drying performed in sequence.

[0019] Preferably, the reagent used for alkali leaching includes a sodium hydroxide solution with a mass fraction of 9-11%, for example, it can be 9%, 9.5%, 10%, 10.5% or 11%, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] Preferably, the alkali leaching temperature is 50-70°C, for example, 50°C, 55°C, 60°C, 65°C or 70°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0021] Preferably, the alkali leaching time is 2-4 min, for example, 2 min, 2.5 min, 3 min, 3.5 min or 4 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] Preferably, the reagent used for acid leaching includes a nitric acid solution with a volume fraction of 9-11%, for example, it can be 9%, 9.5%, 10%, 10.5% or 11%, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] Preferably, the acid leaching time is 2-4 min, for example, 2 min, 2.5 min, 3 min, 3.5 min or 4 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0024] Preferably, a welding intermediate layer is provided in the assembly, and the welding intermediate layer comprises a welding sheet and a brazing flux.

[0025] Preferably, the model of the welding piece includes 4004 and / or 4043.

[0026] Preferably, the flux includes KF-AlF 3 -10K 2 SiF 6 .

[0027] Preferably, the assembly is placed in a vacuum brazing furnace before the vacuum treatment.

[0028] After the assembly is placed in the vacuum brazing furnace, it is necessary to ensure that the assembly is level and that the fixture and the assembly are assembled stably.

[0029] Preferably, the end point of the vacuum treatment is to make the vacuum degree of the vacuum brazing furnace less than 1×10 -3 Pa, for example, can be 0.8×10 -3Pa, 0.5×10 -3 Pa, 1×10 -4 Pa, 0.8×10 -4 Pa or 0.5×10 -4 Pa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] Preferably, the heating rate of the first heat treatment is 10-15°C / min, for example, it can be 10°C / min, 11°C / min, 12°C / min, 13°C / min or 15°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] Preferably, the temperature rising end point of the first heat treatment is 195-205°C, for example, it can be 195°C, 198°C, 200°C, 202°C or 205°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] Preferably, the holding time of the first heat treatment is 30-60 min, for example, 30 min, 35 min, 40 min, 50 min or 60 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] Preferably, the heating rate of the second heat treatment is 10-15°C / min, for example, it can be 10°C / min, 11°C / min, 12°C / min, 13°C / min or 15°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] Preferably, the temperature rising end point of the second heat treatment is 395-405°C, for example, it can be 395°C, 398°C, 400°C, 402°C or 405°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] Preferably, the holding time of the second heat treatment is 60-90 min, for example, 60 min, 65 min, 70 min, 80 min or 90 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] Preferably, the heating rate of the third heat treatment is 5-10°C / min, for example, 5°C / min, 6°C / min, 8°C / min, 9°C / min or 10°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] Preferably, the temperature rising end point of the third heat treatment is 500-560°C, for example, 500°C, 510°C, 520°C, 540°C or 560°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] Preferably, the holding time of the third heat treatment is 55-65 min, for example, it can be 55 min, 58 min, 60 min, 62 min or 65 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] Preferably, the heating rate of the fourth heat treatment is 2-3°C / min, for example, it can be 2°C / min, 2.2°C / min, 2.5°C / min, 2.8°C / min or 3°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] Preferably, the temperature rise end point of the fourth heat treatment is 570-610°C, for example, 570°C, 580°C, 590°C, 600°C or 610°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] Preferably, the holding time of the fourth heat treatment is 5-30 min, for example, 5 min, 10 min, 15 min, 20 min or 30 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] Preferably, after the fourth heat treatment, the product is furnace cooled to ≤100°C, for example, 100°C, 90°C, 80°C, 70°C or 60°C, but not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable, and then taken out.

[0043] After the furnace is cooled, take it out and let it air to room temperature.

[0044] As a preferred technical solution of the vacuum brazing method of the present invention, the vacuum brazing method comprises the following steps:

[0045] The first pure aluminum plate and the second pure aluminum plate are assembled after being degreased with acetone, alkaline-soaked with a sodium hydroxide solution with a mass fraction of 9-11% at 50-70°C for 2-4 minutes, acid-soaked with a nitric acid solution with a volume fraction of 9-11% for 2-4 minutes, washed with water, and vacuum-dried. A welding intermediate layer is provided in the assembly, and the welding intermediate layer includes a welding sheet and a brazing flux. The obtained assembly is placed in a vacuum brazing furnace and vacuum-treated until the vacuum degree of the vacuum brazing furnace is less than 1×10 -3Pa and brazing treatment to obtain the pure aluminum part; the thickness of the first pure aluminum plate and the second pure aluminum plate are 18-22 mm, the width are 295-305 mm, and the flatness and parallelism are both less than 5 wires;

[0046] The brazing treatment includes a first heat treatment, a second heat treatment, a third heat treatment and a fourth heat treatment with temperatures rising in sequence; the heating rate of the first heat treatment is 10-15°C / min, the heating end point is 195-205°C, and the insulation time is 30-60min; the heating rate of the second heat treatment is 10-15°C / min, the heating end point is 395-405°C, and the insulation time is 60-90min; the heating rate of the third heat treatment is 5-10°C / min, the heating end point is 500-560°C, and the insulation time is 55-65min; the heating rate of the fourth heat treatment is 2-3°C / min, the heating end point is 570-610°C, and the insulation time is 5-30min.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] The vacuum brazing method for pure aluminum parts provided by the present invention performs vacuum brazing treatment on the assembly by setting a first heat treatment, a second heat treatment, a third heat treatment and a fourth heat treatment with successively increasing temperatures. Combined with specific brazing process parameters, the welding bonding rate of the pure aluminum parts can reach 99%, the welding strength can reach 87MPa, and the obtained weld composition is consistent with the substrate, thereby being able to meet the use requirements of semiconductor components. DETAILED DESCRIPTION

[0049] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0050] Example 1

[0051] This embodiment provides a vacuum brazing method for pure aluminum parts, and the vacuum brazing method comprises the following steps:

[0052] The first pure aluminum plate and the second pure aluminum plate, both of which are A1050, are successively degreased with acetone, alkaline-soaked with a sodium hydroxide solution with a mass fraction of 10% at 60°C for 3 minutes, acid-soaked with a nitric acid solution with a volume fraction of 10% for 3 minutes, washed with water, and vacuum-dried before being assembled. A welding intermediate layer is provided in the assembly, and the welding intermediate layer is a 4004 welding sheet and a KF-AlF 3 -10K 2 SiF 6 The obtained assembly is placed in a vacuum brazing furnace and vacuum treated until the vacuum degree of the vacuum brazing furnace is 1×10-4 Pa and brazing treatment to obtain the pure aluminum part; the thickness of the first pure aluminum plate and the second pure aluminum plate are 20 mm and 300 mm respectively, and the flatness and parallelism are both 1 wire;

[0053] The brazing treatment includes a first heat treatment, a second heat treatment, a third heat treatment and a fourth heat treatment in which the temperatures are raised successively; the heating rate of the first heat treatment is 12°C / min, the heating end point is 200°C, and the holding time is 40min; the heating rate of the second heat treatment is 12°C / min, the heating end point is 400°C, and the holding time is 70min; the heating rate of the third heat treatment is 8°C / min, the heating end point is 540°C, and the holding time is 60min; the heating rate of the fourth heat treatment is 2.5°C / min, the heating end point is 590°C, and the holding time is 15min.

[0054] Example 2

[0055] This embodiment provides a vacuum brazing method for pure aluminum parts, and the vacuum brazing method comprises the following steps:

[0056] The first pure aluminum plate and the second pure aluminum plate, both of which are A1050, are assembled after being degreased with acetone, alkaline-soaked in a sodium hydroxide solution with a mass fraction of 9% at 50°C for 4 minutes, acid-soaked in a nitric acid solution with a volume fraction of 9% for 4 minutes, washed with water, and vacuum-dried. A welding intermediate layer is provided in the assembly, and the welding intermediate layer is a 4004 welding sheet and a KF-AlF 3 -10K 2 SiF 6 The obtained assembly is placed in a vacuum brazing furnace and vacuum treated until the vacuum degree of the vacuum brazing furnace is 0.5×10 -3 Pa and brazing treatment to obtain the pure aluminum part; the thickness of the first pure aluminum plate and the second pure aluminum plate are 18 mm, the width are 295 mm, and the flatness and parallelism are both 3 wires;

[0057] The brazing treatment includes a first heat treatment, a second heat treatment, a third heat treatment and a fourth heat treatment with temperatures rising in sequence; the heating rate of the first heat treatment is 10°C / min, the heating end point is 195°C, and the holding time is 60min; the heating rate of the second heat treatment is 10°C / min, the heating end point is 395°C, and the holding time is 90min; the heating rate of the third heat treatment is 5°C / min, the heating end point is 500°C, and the holding time is 65min; the heating rate of the fourth heat treatment is 2°C / min, the heating end point is 570°C, and the holding time is 30min.

[0058] Example 3

[0059] This embodiment provides a vacuum brazing method for pure aluminum parts, and the vacuum brazing method comprises the following steps:

[0060] The first pure aluminum plate and the second pure aluminum plate, both of which are A1050, are successively degreased with acetone, alkaline-soaked with a sodium hydroxide solution with a mass fraction of 11% at 70°C for 2 minutes, acid-soaked with a nitric acid solution with a volume fraction of 11% for 2 minutes, washed with water, and vacuum-dried before being assembled. A welding intermediate layer is provided in the assembly, and the welding intermediate layer is a 4043 welding sheet and a KF-AlF 3 -10K 2 SiF 6 The obtained assembly is placed in a vacuum brazing furnace and vacuum treated until the vacuum degree of the vacuum brazing furnace is 0.8×10 -3 Pa and brazing treatment to obtain the pure aluminum part; the thickness of the first pure aluminum plate and the second pure aluminum plate are 22 mm, the width are 305 mm, and the flatness and parallelism are both 4 wires;

[0061] The brazing treatment includes a first heat treatment, a second heat treatment, a third heat treatment and a fourth heat treatment with successively increasing temperatures; the heating rate of the first heat treatment is 15°C / min, the heating end point is 205°C, and the holding time is 30min; the heating rate of the second heat treatment is 15°C / min, the heating end point is 405°C, and the holding time is 60min; the heating rate of the third heat treatment is 10°C / min, the heating end point is 560°C, and the holding time is 55min; the heating rate of the fourth heat treatment is 3°C / min, the heating end point is 610°C, and the holding time is 5min.

[0062] Example 4

[0063] This embodiment provides a vacuum brazing method for pure aluminum parts, which is different from Embodiment 1 in that, except for adjusting the flatness and parallelism of the first pure aluminum plate and the second pure aluminum plate to 5 wires, the rest is the same as Embodiment 1.

[0064] Example 5

[0065] This embodiment provides a vacuum brazing method for pure aluminum parts, which is different from Embodiment 1 in that, except that the reagent used for the alkali leaching is adjusted to a 4% pure alkali aqueous solution, the rest is the same as Embodiment 1.

[0066] Example 6

[0067] This embodiment provides a vacuum brazing method for pure aluminum parts, which is different from Embodiment 1 in that, except for adjusting the type of the brazing flux to FB201S-3, the rest is the same as Embodiment 1.

[0068] Example 7

[0069] This embodiment provides a vacuum brazing method for pure aluminum parts. The difference from Embodiment 1 is that, in addition to adjusting the vacuum degree of the vacuum brazing furnace to 5×10 -3 Except for Pa, the rest are the same as those in Example 1.

[0070] Example 8

[0071] This embodiment provides a vacuum brazing method for pure aluminum parts, which is different from Embodiment 1 in that, except for adjusting the temperature rise end point of the first heat treatment to 300° C., the rest is the same as Embodiment 1.

[0072] Example 9

[0073] This embodiment provides a vacuum brazing method for pure aluminum parts, which is different from Embodiment 1 in that, except for adjusting the temperature rise end point of the third heat treatment to 500° C., the rest is the same as Embodiment 1.

[0074] Comparative Example 1

[0075] This comparative example provides a vacuum brazing method for pure aluminum parts, which differs from Example 1 in that the steps of acetone degreasing, alkali immersion, acid immersion, water washing and vacuum drying are omitted, and the rest are the same as Example 1.

[0076] Comparative Example 2

[0077] This comparative example provides a vacuum brazing method for pure aluminum parts, which differs from Example 1 in that the fourth heat treatment step is omitted, and the rest is the same as Example 1.

[0078] Pure aluminum parts were obtained by the vacuum brazing method provided in Examples 1-9 and Comparative Examples 1 and 2. A scanning electron microscope was used to perform microscopic inspection of the welds. An ultrasonic flaw detector was used to test the welding bonding rate of the pure aluminum parts. A tensile testing machine was used to test the welding strength of the pure aluminum parts. The results are shown in Table 1.

[0079] Table 1

[0080]

[0081]

[0082] It can be seen from Table 1 that the vacuum brazing method provided by the present invention has a high welding bonding rate and welding strength for pure aluminum parts, and the obtained weld composition is consistent with the matrix;

[0083] By comparing Example 1 with Example 4, it can be seen that the flatness and parallelism of the first pure aluminum plate and the second pure aluminum plate are too large, which will lead to a decrease in the subsequent welding effect; by comparing Example 1 with Example 5, it can be seen that the surface decontamination effect is reduced by using other alkaline agents for alkali leaching, thereby affecting the welding effect; by comparing Example 1 with Example 6, it can be seen that the use of other fluxes for brazing will reduce the welding rate and strength; by comparing Example 1 with Example 7, it can be seen that the vacuum degree in the vacuum treatment is too large, which will affect the subsequent welding effect; by comparing Example 1 with Examples 8 and 9, it can be seen that the temperature of the first heat treatment and the third heat treatment exceeds the limited range, which will reduce the welding strength of the pure aluminum parts;

[0084] By comparing Example 1 with Comparative Example 1, it can be seen that without surface pretreatment, the subsequent welding effect will be significantly reduced; by comparing Example 1 with Comparative Example 2, it can be seen that without the fourth heat treatment, the welding bonding rate and strength of the pure aluminum parts are significantly reduced.

[0085] In summary, the vacuum brazing method for pure aluminum parts provided by the present invention performs vacuum brazing treatment on the assembly by setting the first heat treatment, the second heat treatment, the third heat treatment and the fourth heat treatment with successively increasing temperatures, and combines specific brazing process parameters to achieve a welding bonding rate of the pure aluminum parts of 99% and a welding strength of 87 MPa. The composition of the obtained weld is consistent with that of the substrate, thereby being able to meet the use requirements of semiconductor components.

[0086] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A vacuum brazing method for pure aluminum parts, characterized in that: The vacuum brazing method comprises the following steps: The first pure aluminum plate and the second pure aluminum plate are assembled after surface pretreatment, and the obtained assembly is subjected to vacuum treatment and brazing treatment to obtain the pure aluminum part; The brazing process includes a first heat treatment, a second heat treatment, a third heat treatment and a fourth heat treatment with temperatures increasing in sequence.

2. The vacuum brazing method according to claim 1, characterized in that: The models of the first pure aluminum plate and the second pure aluminum plate include A1050; Preferably, the thickness of the first pure aluminum plate and the second pure aluminum plate are 18-22 mm, and the width are 295-305 mm, respectively; Preferably, the flatness and parallelism of the first pure aluminum plate and the second pure aluminum plate are both less than 5 wires.

3. The vacuum brazing method according to claim 1 or 2, characterized in that: The surface pretreatment includes acetone degreasing, alkali leaching, acid leaching, water washing and vacuum drying in sequence; Preferably, the reagent used for the alkaline leaching includes a sodium hydroxide solution with a mass fraction of 9-11%; Preferably, the temperature of the alkali leaching is 50-70°C; Preferably, the alkali leaching time is 2-4 minutes; Preferably, the reagent used for the acid leaching includes a nitric acid solution with a volume fraction of 9-11%; Preferably, the acid leaching time is 2-4 minutes.

4. The vacuum brazing method according to any one of claims 1 to 3, characterized in that: A welding intermediate layer is provided in the assembly, and the welding intermediate layer includes a welding sheet and a brazing flux; Preferably, the model of the welding sheet includes 4004 and / or 4043; Preferably, the type of flux includes KF-AlF3-10K2SiF6.

5. The vacuum brazing method according to any one of claims 1 to 4, characterized in that: Placing the assembly in a vacuum brazing furnace before the vacuum treatment; Preferably, the end point of the vacuum treatment is to make the vacuum degree of the vacuum brazing furnace less than 1×10 -3 Pa.

6. The vacuum brazing method according to any one of claims 1 to 5, characterized in that: The heating rate of the first heat treatment is 10-15°C / min; Preferably, the temperature rise endpoint of the first heat treatment is 195-205°C; Preferably, the holding time of the first heat treatment is 30-60 minutes.

7. The vacuum brazing method according to claim 6, characterized in that: The heating rate of the second heat treatment is 10-15°C / min; Preferably, the temperature rise endpoint of the second heat treatment is 395-405°C; Preferably, the holding time of the second heat treatment is 60-90 min.

8. The vacuum brazing method according to claim 7, characterized in that: The heating rate of the third heat treatment is 5-10°C / min; Preferably, the temperature rise end point of the third heat treatment is 500-560°C; Preferably, the holding time of the third heat treatment is 55-65 minutes.

9. The vacuum brazing method according to claim 8, characterized in that: The heating rate of the fourth heat treatment is 2-3°C / min; Preferably, the temperature rise end point of the fourth heat treatment is 570-610°C; Preferably, the holding time of the fourth heat treatment is 5-30 min; Preferably, after the fourth heat treatment, the product is cooled in the furnace to ≤100° C. and then taken out.

10. The vacuum brazing method according to any one of claims 1 to 9, characterized in that: The vacuum brazing method comprises the following steps: The first pure aluminum plate and the second pure aluminum plate are assembled after being degreased with acetone, alkaline-soaked with a sodium hydroxide solution with a mass fraction of 9-11% at 50-70°C for 2-4 minutes, acid-soaked with a nitric acid solution with a volume fraction of 9-11% for 2-4 minutes, washed with water, and vacuum-dried. A welding intermediate layer is provided in the assembly, and the welding intermediate layer includes a welding sheet and a brazing flux. The obtained assembly is placed in a vacuum brazing furnace and vacuum-treated until the vacuum degree of the vacuum brazing furnace is less than 1×10 -3 Pa and brazing treatment to obtain the pure aluminum part; the thickness of the first pure aluminum plate and the second pure aluminum plate are 18-22 mm, the width are 295-305 mm, and the flatness and parallelism are both less than 5 wires; The brazing treatment includes a first heat treatment, a second heat treatment, a third heat treatment and a fourth heat treatment with temperatures rising in sequence; the heating rate of the first heat treatment is 10-15°C / min, the heating end point is 195-205°C, and the insulation time is 30-60min; the heating rate of the second heat treatment is 10-15°C / min, the heating end point is 395-405°C, and the insulation time is 60-90min; the heating rate of the third heat treatment is 5-10°C / min, the heating end point is 500-560°C, and the insulation time is 55-65min; the heating rate of the fourth heat treatment is 2-3°C / min, the heating end point is 570-610°C, and the insulation time is 5-30min.

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