JPH0853731A - Aluminum alloy material for noncorrosive flux brazing and its production - Google Patents

Abstract

(57) [Summary] [Objective] For example, when applying a mixture of non-corrosive flux and metallic silicon to the surface of an aluminum material for advantageous brazing, even after the mixture is in a non-uniform state, The present invention provides a low-priced aluminum alloy material which is a brazed product excellent in strength and corrosion resistance by uniformizing the remaining thickness of the aluminum material and its manufacturing method. [Composition] 10% of the plate thickness near the surface in the plate cross section perpendicular to the rolling forming direction of the brazing member under the temperature condition immediately before brazing
Is composed of a fine crystal grain region having an average grain size of less than 50 μm, and an inner region thereof has a metal structure of a coarse grain region having an average grain size of 50 μm or more in a single layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy material for brazing non-corrosive flux and a method for manufacturing the same, and for example, applying a mixture of non-corrosive flux and metallic silicon to the surface of an aluminum material for advantageous brazing. In doing so, a low-cost aluminum alloy that can even out the residual thickness of the aluminum material after brazing even if the applied mixture is in a non-uniform state and obtain a brazed product with excellent strength and corrosion resistance. It is intended to provide a material and obtain a preferable manufacturing method thereof.

[0002]

2. Description of the Related Art Forming a device by brazing aluminum or an aluminum alloy material has been widely adopted since it has advantages such as light weight and heat conductivity that cannot be obtained from other metal materials. In particular, in a heat exchanger for a vehicle, a tube material brazed with a fin material is generally used.

However, in the brazing using the aluminum or aluminum alloy material as described above, the conventional method in which the brazing material and the flux are added and supplied to the joint to heat the brazing material is complicated and costly. Moreover, because of disadvantages such as poor brazing and uneven brazing quality, it has been widely adopted to use a brazing sheet in which a brazing material and a skin material layer are clad as a core material.
That is, the brazing is achieved all at once by charging the brazing material layer into the furnace in a combined state so as to be joined to the mating member and heating.

However, in recent years, some proposals have been made for brazing without using the above-mentioned clad material, and one of such methods is a non-corrosive fluoride flux of potassium aluminum fluoride system. Brazing with a mixture of metallic silicon powders is US Pat. No. 51.
Published in No. 00048. That is, in this method, the silicon applied to the surface of the aluminum material rapidly diffuses into the aluminum material at the brazing temperature, and the surface layer of the aluminum material is
Melting occurs near the Al-Si eutectic composition (eutectic temperature: 577
C.), and the components are joined together by soldering.

Specifically, a mixture of a fluoride-based flux and metallic silicon powder is supplied as a dry powder or is suspended and applied in a volatile liquid such as water or alcohol, and the mixture is mixed in a weight ratio of 1 :. About 1 to 3: 1, the coating amount of the mixture is 5 to 30 g / m ² , the brazing temperature is 577 ° C. or higher, and the time is 2 to 5 minutes, but the optimum condition is a mixture of about 30% silicon. It is applied at ²⁰ to 30 g / m ^{2, and as a} brazing material, pure Al material or Al-1% Mn material is shown.

[0006]

The method according to US Pat. No. 5100048 as described above has a great advantage in terms of process and cost since it is not necessary to use it as a clad material, and also in terms of material utilization such as scrap reuse. However, it is difficult to evenly apply the mixture of non-corrosive flux and metallic silicon to the surface of the aluminum material, and in the case where it is partially unevenly applied, The aluminum material locally largely dissolves in a portion where a large amount of silicon powder adheres. For this reason, the remaining thickness of the aluminum material after brazing becomes non-uniform, resulting in a decrease in strength and corrosion resistance, and in some cases, a through hole is generated.

[0007]

SUMMARY OF THE INVENTION The present invention solves the problems in the prior art as described above, and the local dissolution in the aluminum material is small even under the condition that the mixture is unevenly applied. After studying how to obtain an aluminum material that has a relatively uniform residual thickness after brazing and obtaining an advantageous heat exchange device, etc., control the crystal structure near the surface at the temperature immediately before brazing and in the central part of the plate thickness. This has succeeded in obtaining favorable results simply and at low cost, and is as follows.

(1) Under the temperature condition immediately before brazing, 10% of the plate thickness in the vicinity of the surface in the plate cross section of the brazing member at right angles to the rolling direction consists of fine crystal grain regions with an average grain size of less than 50 μm. The inner region has an average crystal grain size of 50μ
An aluminum alloy material for non-corrosive flux brazing, characterized in that a metal structure consisting of a coarse grain region of m or more is formed in a single layer.

(2) The aluminum alloy sheet is cold-rolled, and an intermediate annealing is performed until it is cold-rolled to the final sheet thickness, and the cold rolling rate after the intermediate annealing is not more than 30%, and the final A method for producing an aluminum alloy material for non-corrosive flux brazing, characterized in that cold rolling is carried out by a rolling roll having a surface roughness of Rz 5 μm or more.

[0010]

[Function] The non-corrosive flux used in the present invention is LiF, Na
F, KF, CaF, AlF ₃ , powder mixture of fluorides such as SiF ₄ , or powders obtained by melting these, or complex compounds of the above fluorides, for example, KAlF ₄ , K ₂ AlF ₅ , K ₃ AlF ₆ , K ₂
A single or a mixture of SiF ₆ or the like, or a powder obtained by melting these, or the like, and none of such fluoride-based fluxes has corrosiveness to aluminum as chlorides do. The powder size of this product is 0 on average.
1 to 30 μm, preferably 1 to 10 on average
μm.

Metals that form a braze by alloying with the surface texture portion and melting, include zinc in addition to silicon, and a silicon-zinc alloy containing Zn, preferably 10 to 30% Zn. is there. Such a metal may be formed as a brazed member, for example, may be sprayed on the tube surface of a heat exchanger, or may be powdered, and the powder is applied to the brazed member or mixed with the flux powder. It may be applied as a slurry. In this case, in addition to silicon powder, 10 to
You may add and mix 30% zinc powder and 2-20% copper powder, and apply. Particularly, alloying metallic silicon to be supplied to a brazed member in advance has a disadvantage that the cost is high, and thermal spraying is a thermal spray material, and also has a disadvantage due to thermal spraying. It is preferably applied to a member for use. Of these, silicon is preferable because it easily forms an Al-Si eutectic alloy at the brazing temperature.

The reaction mechanism of the brazing method as described above can be analyzed in the following process when it is specifically shown by using metallic silicon powder and potassium aluminum fluoride eutectic non-corrosive flux. Melting of potassium aluminum fluoride-based non-corrosive flux around 562 ° C Destruction of oxide film on aluminum material surface Diffusion of Si into aluminum material surface texture area Surface texture area with high Si concentration melts at Al-Si eutectic temperature Start (577 ° C) An Al-Si eutectic melt is generated while melting the aluminum material until the metallic silicon powder is completely extinguished. The eutectic melt becomes a brazing filler metal and flows to the joint to form a fillet (up to about 600 ° C). During the subsequent cooling process, the fillet solidifies and brazing is completed.

In the above reaction mechanisms of
Since the reaction of ~, that is, the diffusion of Si into the aluminum brazing member occurs in a short time, if the metallic silicon powder is non-uniformly adhered, the aluminum material is remarkably locally melted in a large amount thereof. . Since the diffusion rate of Si is much larger than the so-called intragranular diffusion that occurs inside the crystal grains, where the so-called grain boundary diffusion, which is routed through the subgrain boundaries and crystal grain boundaries of the aluminum alloy, is the surface that contacts the flux and the metal silicon powder mixture. Even if a large amount of silicon powder locally adheres by forming a fine recrystallized structure with an average grain size of less than 50 μm in the vicinity,
After the vicinity of the surface is alloyed with metallic silicon and melts and becomes brazed, the residual surface texture part where the crystal grains are large and the diffusion speed is faster than the central part of the plate thickness where diffusion is slow will be laterally diffused to form a braze. The melting at the central portion of the plate thickness where the diffusion is slow is significantly reduced, and the nonuniformity of the remaining plate thickness is eliminated.

That is, the average number of recrystallized grains in the surface texture portion is 50 μm.
If it is more than m, the lateral spread in the surface texture portion will not be sufficient, and if the average grain size of the central portion of the plate thickness is less than 50 μm, the diffusion of Si through the grain boundaries of the surface texture portion will be large, and in both cases, It is difficult to obtain the above-mentioned effects.

The surface texture portion is formed to have a required thickness on one or both sides of the central portion of the plate thickness. Such an aluminum alloy material, for example, is cut into a predetermined size and is formed into a fin material, or is formed and welded into a pipe material, and is used as a brazing member to obtain the following advantages. . (A) The complexity of rolling and clad a brazing material containing Si is reduced. (B) By using an aluminum alloy material that does not contain a brazing material, it is possible to prevent die wear during molding of an aluminum member. (C) Si from brazing material in scrap during rolling and forming
Can be reused because it does not mix.

The aluminum alloy material as described above is used as at least one of the members to be brazed, a mixture of flux and silicon powder is applied to the member, and brazing is performed to make the erosion depth of the aluminum alloy material uniform. In addition, it is possible to obtain a preferable brazing by improving the formation state of the joint fillet. This situation applies not only to metallic silicon powder but also to silicon alloy powder or thermal spraying.

In the present invention, a microstructure portion having a plate thickness of 10% from the surface has a microstructure having an average crystal grain size of less than 50 μm in a cross section perpendicular to the rolling forming direction under the temperature condition immediately before brazing, and the center portion of the plate thickness is an average. In order to obtain a coarse grain structure of 50 μm or more, an aluminum alloy sheet is cold-rolled, intermediate annealing is performed until cold rolling to the final sheet thickness, and the cold rolling rate after the intermediate annealing is 30%. Below. If the cold rolling ratio after this intermediate annealing exceeds 30%, the crystal grains become fine inside the plate under the temperature conditions immediately before brazing, and it is not possible to control the diffusion of Si through the grain boundaries of the surface texture portion as described above. .

By defining the surface roughness of the roll used for the final cold rolling to be Rz 5 μm or more, a large cold strain is given to the vicinity of the surface, so that the average recrystallized grains of the surface layer structure part under the temperature condition immediately before brazing can be obtained. The diameter can be less than 50 μm, generally less than 40 μm. Such roll roughness adjustment can be performed not only by ordinary roll grinding but also by shot dull, discharge dull, or the like. Rz roughness generally depends on the arithmetic mean of 10-point average roughness, but the upper limit of this Rz roughness is 20 μm,
It is preferably 15 μm.

For the aluminum alloy plate, for example, molten metal is DC
It may be produced by casting (semi-continuous casting), homogenization treatment, hot rolling, cold rolling, or casting of the molten metal using a twin roll casting machine, a casting machine such as a belt caster, and so on. It can also be rolled and manufactured.

[0020]

EXAMPLES Specific examples of the present invention will be described below. Example 1 An aluminum alloy having the composition shown in Table 1 below was melted by a usual method, and DC cast into an ingot having a thickness of 550 mm.
Homogenization treatment at 0 ℃ for 18 hours, hot rolling to 5mm thickness, then 1.30mm, 0.87mm, 0.76mm respectively
Cold rolled to 400 ° C for 1 hour and then annealed for 1 hour,
Finally, it was cold rolled to a thickness of 0.65 mm. The cold rolling rates after the intermediate annealing are 50%, 25%, 15% and 35%, respectively. The surface roughness of the roll used for the final cold rolling is Rz 8.0 μm and Ra 1.0 μm.

[0021]

[Table 1]

In order to observe the metal structure immediately before brazing,
The temperature was raised to 550 ° C. at a temperature rising rate of 50 ° C./min, immediately cooled with water, and the crystal grain size of the plate cross section perpendicular to the rolling direction was measured. For brazing, a test piece having a width of 30 mm and a length of 50 mm was sampled from the plate, and a potassium aluminum fluoride eutectic flux having an average particle size of less than 20 μm and a particle size of 10 to 80 were used.
Metallic silicon powder of μm was mixed at a weight ratio of 2: 1, 100 g of this mixture was suspended in 400 g of pure water, spray-coated on a test piece, and dried by heating at 150 ° C. for 5 minutes. The average coating weight of the mixture is 26 g / m ² . Furthermore, the brazing test was carried out on the above-mentioned test piece with a thickness of 0.5 mm and a width of 25 mm.
An inverted T-shaped test piece in which a 3003-H14 material having a length of 40 mm is vertically erected is assembled, and a temperature rising rate is 50 in a nitrogen gas atmosphere.
C./min and 600.degree. C. were held for 3 min, and the bondability was judged by observing the crystal grain size of the plate and the state of fillet formation in the joint part of the test piece after brazing and the erosion state of the braze. The results are shown in Table 2 below.

[0023]

[Table 2]

That is, in the example of the present invention, the plate thickness is 1 from the surface.
0% (65 μm) average grain size is less than 50 μm,
On the other hand, the central part of the plate thickness has a considerably different grain size difference of 80 μm or 120 μm, whereas the comparative example has all the layers of 35 to 45 μm and has a particle size between the surface and the central part of the plate thickness. Almost no difference was obtained, and the difference between the maximum erosion part and the minimum erosion part after brazing reached 80 μm, which was 20 to 4 of the present invention.
Corrosion that is considerably deeper than 0 μm occurs, and that of the present invention does not reach the comparatively rough crystal structure part in the central part of the plate thickness, whereas in the comparative example, the erosion exceeds the surface structure part range of 65 μm from the surface. It was confirmed that

Example 2 An aluminum alloy having the alloy composition shown in Table 3 below was melted by a conventional method, hot-rolled by continuous casting to a thickness of 5 mm, and then cold-rolled to a thickness of 0.87 mm.

[0026]

[Table 3]

The 0.87 mm thick aluminum alloy plate obtained as described above was then subjected to intermediate annealing at 400 ° C. for 1 hour, and the surface roughness Rz, Ra was measured by using the rolls shown in Table 4 below. And finally cold rolled to a thickness of 0.65 mm. The cold-rolled sheet thus obtained was subjected to intermediate annealing at 400 ° C. for 1 hour, and the surface roughness Rz and Ra were finally rolled up to a thickness of 0.65 mm by using rolls as shown in Table 4 below. Cold rolled. In order to observe the metal structure of this material immediately before brazing, the temperature was raised to 550 ° C. at a temperature rising rate of 50 ° C./min, immediately water-cooled, and the crystal grain size of the plate cross section perpendicular to the rolling direction was measured. For brazing, a test piece having a width of 30 mm and a length of 50 mm was sampled from the above plate, and a potassium aluminum fluoride eutectic flux having an average particle size of less than 10 μm and a particle size of 10 to 80.
Metallic silicon powder of μm was mixed at a weight ratio of 2: 1, 100 g of this mixture was suspended in 400 g of pure water, spray-coated on a test piece, and dried by heating at 150 ° C. for 5 minutes. The average coating amount of the mixture was 26 g / m ² , and the brazing test was carried out on the above-mentioned test piece with a thickness of 0.5 mm, a width of 25 mm and a length of 4
Assemble an inverted T-shaped test piece in which a 0 mm 3003-H14 material is erected vertically, and heat up at 50 ° C / mi in a nitrogen gas atmosphere.
n, held at 600 ° C. for 3 minutes.

Regarding the results as described above, the roll surface roughness, the average crystal grain size in the plate cross section, the fillet formation state in the joint portion of the test piece after brazing, and the erosion state of the braze were observed to confirm the jointability. The judged test results are shown in Table 4 below.

[0029]

[Table 4]

That is, according to the present invention, the crystal grain size in the plate cross section is considerably different between the surface portion and the center portion of the plate thickness, and the erosion depth of the braze after brazing is 20 to 40 μm. It was confirmed that the particle size was significantly smaller than that of the example of 60 to 100 μm, and that it remained within the crystal structure near the surface where the average crystal grain size was 40 μm or less.

[0031]

As described above, according to the present invention, when a non-corrosive flux is used on the surface of an aluminum material and a metal forming a brazing alloy is melted by alloying with a surface texture portion is applied nonuniformly. Even in the case of aluminum, it is possible to appropriately prevent the aluminum material from being locally melted to cause significant non-uniformity in the residual thickness of the aluminum material after brazing, and brazing with favorable durability and strength in a uniform residual thickness state. In addition, it is possible to provide the aluminum alloy material for brazing described above easily and at low cost because the corrosion depth at the time of brazing is small and the clad process is not required. It is an invention that has a great effect.

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[Procedure amendment]

[Submission date] August 26, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

[0020]

EXAMPLES Specific examples of the present invention will be described below. Example 1 An aluminum alloy having the composition shown in Table 1 below was melted by a usual method, and DC cast into an ingot having a thickness of 550 mm.
Homogenization treatment at 00 ° C for 18 hours, hot rolling to a thickness of 5 mm, and then thicknesses of 1.30 mm and 0.87 m, respectively.
m, 0.76mm , cold rolled to 1.0mm , 400
After an intermediate annealing at ℃ for 1 hour, the final thickness is 0.65mm
Cold rolled until. The cold rolling rate after intermediate annealing is 50 each.
%, 25%, 15% and 35%. The surface roughness of the roll used for the final cold rolling was Rz 8.0 μm, R
a is 1.0 μm.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0024

[Correction method] Change

[Correction content]

That is, in the example of the present invention, the plate thickness is 1 from the surface.
0% (65 μm) average grain size is less than 50 μm,
On the other hand, the center part of the plate thickness has a considerably different grain size difference of 70 μm or 90 μm , whereas the comparative example has all 3 layers.
It is 5 to 47 μm , and almost no difference is required between the surface vicinity and the plate thickness center part, and the difference between the maximum erosion part and the minimum erosion part after brazing reaches 65 μm, which is 15 μm of the present invention example. Since a considerably deep erosion occurred, the present invention did not reach the comparatively coarse crystallographic texture portion in the central portion of the plate thickness, whereas the comparative example eroded beyond the surface texture portion area of 65 μm from the surface. Was confirmed.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0030

[Correction method] Change

[Correction content]

That is, using a roll having a rough roll surface,
Those of the present invention produced under a reduction ratio is considerably say between the crystal grain size of the surface portion and the plate thickness center part in the plate cross-section, the difference between the wax corrosion depth after brazing < It was found that the average particle size of 15 to 20 μm , which is significantly smaller than that of the comparative example of 80 to 90 μm , remained within the crystal structure having a crystal average grain size of 40 μm or less near the surface , And confirmed.

Claims (2)

[Claims] 1. A plate thickness near the surface in a plate cross section perpendicular to the rolling forming direction of the brazing member under a temperature condition immediately before brazing is 1
0% consists of fine crystal grain regions with an average crystal grain size of less than 50 μm, and the inner region has a metallographic structure consisting of a coarse crystal grain region with an average crystal grain size of 50 μm or more in a single layer. Aluminum alloy material for corrosive flux brazing. 2. An aluminum alloy sheet is cold-rolled and intermediate-annealed until it is cold-rolled to a final sheet thickness, and the cold-rolling rate after the intermediate-annealing is set to 30% or less, and the final cold-rolling is performed. A method for producing an aluminum alloy material for non-corrosive flux brazing, characterized in that hot rolling is performed by a rolling roll having a surface roughness of Rz 5 μm or more.