JPH07113146B2 - Surface treatment method for aluminum or its alloys - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface treatment method for aluminum or an aluminum alloy, and particularly to a plate, a tube or the like made of aluminum or its alloy in a flux solution at a predetermined temperature. The present invention relates to a surface treatment method capable of imparting excellent corrosion resistance to these structures by having a step of immersing the structures.

[Background of the Invention]

Conventionally, aluminum (hereinafter referred to as Al and elemental symbols)
Or, as a prior art for improving the corrosion resistance of Al alloy, there is an electrochemical treatment. This electrochemical treatment is to form a zinc (hereinafter referred to as Zn) plating layer on the surface of Al or Al alloy. However, this electrochemical treatment is not sufficient for the corrosion resistance of Al or Al alloys because the Zn plating layer is peeled off and Zn is eliminated early by corrosion due to the thin plating layer. In addition, this Zn-plated Al or
When brazing an Al alloy, a chemically stable Zn coating is formed on the surface of the member to be brazed, which makes brazing difficult.

Therefore, for the purpose of improving the corrosion resistance of Al or Al alloy,
There is a conventional example in which a Zn film is formed on the surface and heat-treated to diffuse Zn into Al or an Al alloy (Sumitomo Light Metal Co., Ltd., April 1980, pages 12 to 19). This conventional example is A
The purpose is to improve the corrosion resistance of Al or Al alloy by cathodic protection with a sacrificial anode. However, there is a concern that Zn cannot be sufficiently diffused into Al or Al alloy by the anticorrosion method according to this conventional example.

[Object of the Invention]

An object of the present invention is to provide a surface treatment method for aluminum or its alloy, which is more excellent in corrosion resistance, by sufficiently diffusing Zn into the aluminum or aluminum alloy.

[Outline of Invention]

The present invention is, by weight _{ratio, ZnF 2: 3~35%, AlF} 3: 38~54%, K
F: Fluorine-based flux powder containing 25-40% or ZnCl
₂ : 6-10%, KCl: 30-55%, NaCl: 20-30%, LiCl: 13-4
Chlorine-based flux powder containing 0% is immersed in an aqueous solution containing 60% to 80 ° C in a weight ratio of 85% or more, and a member to be treated made of aluminum or its alloy is dipped into the surface of the member to be treated with zinc. A coating film and an adhesion layer of the flux powder are formed at the same time, and then heated to a temperature above the melting temperature of zinc and below the melting temperature of the member to be treated to diffuse zinc into the member to be treated and to braze at the same time. And a surface treatment method for aluminum or its alloy.

The flux powder used in the present invention includes fluorine-based powder and chlorine-based powder. These fluxes contain a Zn compound as an essential component for forming the Zn layer on the surface of the member to be treated.

In the case of fluorine-based flux, the main component is 38-
It contains 54% AlF ₃ , 25-40% KF, and 3-35% ZnF ₂ .

The main components of chlorine-based flux are 30-55% KCl, 20-30% N
aCl, 13~40% LiCl, is 6~10% ZnCl _2.

It is desirable that the main component of these fluxes is 85% or more based on the total weight of the flux. If it is less than 85%, the melting point of the flux rises, which causes inconvenience in diffusing the Zn layer formed on the surface of the member to be processed into the member to be processed.

In the above flux, LIF, NaF, MgF, Ca consisting of alkali metal and fluorine are added as a component in addition to the main component.
It is effective to add 0.5 to 9% by weight of at least one selected from F. A particularly preferable range for the composition of the flux is 44-50 by weight in the case of a fluorine-based flux.
% AlF ₃ , 32-36% KF, 7-15% ZnF ₂ and 3-6% LiF
Is.

As the flux used in the present invention, a fluorine-based flux is more effective than a chlorine-based flux. This is to cool the member to be processed after diffusing Zn into the member to be processed, but in the case of chlorine-based flux, since the residual flux remaining on the surface of the member to be processed has hygroscopicity,
Chloride ions are generated according to this moisture absorption, and corrode the surface of the member to be treated. Therefore, when a chlorine-based flux is used, it is necessary to thoroughly wash the surface of the member to be processed after diffusing Zn. On the other hand, the fluorine-based flux does not have hygroscopicity, and thus there is no need to perform such corrosion and cleaning on the surface of the member to be treated.

The above-mentioned flux powder is effective because the fine powder is more easily suspended in water. For example, Al contained in fluorine flux
For F _3, AlF generated before the AlF ₃ is manufactured ₃ · 3H ₂ O
It is more preferable to use the fine powder of. In the case of ZnF ₂ , it is also effective to use ZnF ₂ · 4H ₂ O which is a hydrate.

If the flux concentration of the hot aqueous solution in which the flux is suspended is lower than 3%, it is difficult to form a uniform Zn film, and the wettability of Zn on the surface of the member to be treated also decreases. Further, if the concentration is higher than 50, it becomes difficult to remove the residue of the flux after Zn is diffused in the member to be treated. A particularly preferred range of flux concentration is 10-20%.

For the aqueous solution in which the flux powder used in the present invention is suspended, a solution of alcohol or the like can be used instead of water. The solution in which the flux is suspended is preferably a hot solution of 60 to 80 ° C in the case of water. This is because if the temperature is 50 ° C or lower, it takes too long to form the Zn layer and the flux layer, and if the temperature is 80 ° C or higher, the adhesion and uniformity of the Zn layer are poor.

In order to increase the Zn concentration on the surface of the member to be treated, it is necessary to increase the amount of Zn compound in the flux, for example ZnF _2, or increase the concentration of the aqueous flux solution to increase the amount of flux attached to the surface of the member to be treated. . However, the latter method of increasing the amount of adhered flux has problems such as an increase in the melting point of the flux, an increase in residues, and a decrease in the brazing performance of the surface-treated member to be treated. Therefore, in order to accelerate the reaction between Al of the member to be treated and Zn in the flux, the aqueous flux solution is heated and the member to be pretreated in advance is immersed therein. As a result, a Zn layer is formed on the surface of the member to be treated, and a flux layer is further formed on this Zn layer. Then, by heating above the melting temperature of Zn and below the melting temperature of the member to be treated, a member to be treated having excellent corrosion resistance can be obtained. The Zn layer formed on the surface of the member to be processed is uniformly formed over the entire immersed portion of the member to be processed.

After a member to be treated is dipped in a hot aqueous solution in which flux powder is suspended to form a Zn layer and a flux layer, it is necessary to dry the member to be treated before diffusing Zn.
Since the aqueous flux solution is also heated during drying, the higher the drying temperature is, the more effective it is. However, heating the aqueous flux solution is more effective in diffusing Zn.

The thickness of the Zn layer can be increased by increasing the immersion time of the member to be treated in the aqueous flux solution. However, if the layer is too thick, peeling easily occurs. For example, if a member to be treated is immersed in a suspension solution at 90 ° C. for 10 minutes, a Zn layer having a thickness of about 5 μm can be obtained, but the Zn layer may peel off during drying, so the immersion time is 5 minutes. It is preferable to stay within minutes. Usually the desired Zn layer thickness is 1-5 μm as measured by a fluorescent X-ray thickness gauge.
It is a degree.

When the member to be treated is immersed in a hot aqueous solution in which the flux powder is suspended, Zn in the flux decreases, and if the Zn film forming ability decreases, Zn compound, for example, in the case of fluorine-based flux, ZnF ₂ is used. The Zn film forming ability is restored only by adding.

The member to be treated is immersed in a hot aqueous solution in which flux powder is suspended to form a Zn layer and a flux on the surface, and then this treated portion is dried. Then, Zn is diffused into the member to be treated at a temperature not lower than the melting temperature of Zn and not higher than the melting temperature of the member to be treated. The melting temperature (melting point) is about 600 ° C. because Zn is 420 ° C. and Al of the member to be processed is 660 ° C.

When the member to be treated is heated to 600 ° C., the flux layer is activated and combines with the oxides on the Al surface and the Zn surface to make the surface pure.

When the member to be processed is heated near 600 ° C., the Zn layer formed on the member to be processed diffuses in the member to be processed. This diffusion is caused by a Zn concentration of 1-2% relative to Al on the surface of the member to be treated.
And the depth of the diffusion layer is about 100 μm. Then, after the diffusion is completed, it is cooled, and the residue present on the member to be treated is washed and removed. Zn diffused in the member to be treated is
For sacrificial anodic corrosion against the surrounding corrosive environment,
It is possible to prevent corrosion of Al or its alloy that is the member to be treated.

Such a Zn diffusion layer is uniformly formed in the member to be processed.

AlF ₃ used for a fluoride-based flux has a wet method and a dry method as a manufacturing method. Today, most of its production is the dry method, and the wet method currently accounts for less than 10% of the total production of Japan.

For AlF ₃ by the wet method, an equivalent amount of aluminum hydroxide is added to a hot aqueous solution of hydrofluoric acid to form a metastable AlF ₃ and silica gel precipitate, and the silica gel is rapidly separated, and the filtrate is crystallized by a crystallizer. And adding seed crystals and stirring at 100 ° C. for 3 to 4 hours, β-AlF ₃ .3H ₂ O crystals are precipitated. AlF ₃ is
This crystal is obtained by drying and then heating and baking at 600 ° C. AlF ₃ · 3H ₂ O obtained in the course of manufacturing of the AlF ₃ is fine powder, the flux is preferred. In addition, AlF ₃ crystals obtained by the wet method are β-
Since the water of crystallization of AlF ₃ 3H ₂ O is removed, it becomes porous and its surface area increases. Therefore, it reacts with KF and ZnF ₂ in the heated flux aqueous solution, and is effective in forming a Zn film.

On the other hand, the production of AlF ₃ by the dry method is a continuous production method using a fluidized bed by a fluid reaction of hydrogen fluoride and aluminum hydroxide. This dry method is a method in which aluminum hydroxide, aluminum and a gas of hydrogen fluoride are produced by a solid-gas phase reaction, and dehydration and fluorination of aluminum hydroxide are performed by reaction heat. The AlF ₃ crystal produced by the dry method is a dense crystal.

No difference in AlF ₃ between the wet method and the dry method is recognized by the analysis by the X-ray diffraction method. However, when used as a flux raw material and used as a flux, when the Zn coating film is formed on the surface of Al or Al alloy with the flux aqueous solution, the difference becomes obvious. That is, the Zn coating is formed by the flux using AlF ₃ by the wet method, but the Zn coating is not formed by the flux using AlF ₃ by the dry method.

1 g each of AlF ₃ by the wet method and AlF ₃ by the dry method
Each was dissolved in 100 ml of deionized water of pH 5.7 and the pH was measured. As a result, it was found that the wet method AlF ₃ was 54.5 and the dry method AlF ₃ was 6.00. Also, the pH of the 15% aqueous flux solution is
F ₃ used flux is 7.15, wet AlF ₃ used flux is
At 5.61, the flux using wet AlF ₃ was more acidic. From this, it is understood that the acidic pH of the aqueous flux solution is preferable for the Zn film formation. The pH of the aqueous flux solution is generally 6.70 or less, which is effective for uniform formation of the Zn layer, and particularly 6.00 or less, a preferable result is obtained. In particular, when using AlF ₃ produced by a dry method for AlF ₃ which is a raw material of flux powder, it is necessary to add an organic acid to this flux aqueous solution so that the pH of the flux aqueous solution is 5.6 or less, preferably 5.30 or less. Is.

As the organic acid that makes the aqueous flux solution acidic, acids such as salicylic acid, oxalic acid, acetic acid, phthalic acid, tartaric acid, and ascorbic acid are preferably used, and acetic acid is particularly preferable.

〔Example〕

Hereinafter, Examples 1 to 4 will be described up to the stage before brazing, and Examples 5 to 7 will be described including a brazing step.

Example 1 Fluoride-based flux (1) consisting of 49% AlF ₃ , 37% KF and 14% ZnF _{2 by} weight, 46% AlF ₃ , 34% KF, 14% ZnF ₂ and 6%
Fluoride flux composed of LiF (2) and 25% N
Chloride flux consisting of aCl, 45% KCl, 14% LiCl, 8% ZnCl ₂ and 8% LiF (3) Suspended powder in water, 15% by weight
An aqueous solution of (remaining water content) was prepared. AlF ₃ was manufactured by a wet method.

In the method for producing the flux, the powder of the compound that is the raw material of the flux is mixed and water is added to form a paste. In this case, the weight ratio of water 0.6 to 0.8 to the raw material 1 of the flux was good, and the raw materials were added little by little into water and kneaded in a mortar until a paste was formed. After that, in a 120 ° C constant temperature bath, 2
It was dried for 5 hours, cooled, and then ground. The powder used as the raw material has a particle size of 40 μm or less (-400 mesh) with a vibrating mill.
I had crushed it. This powder flux was suspended in water to obtain a flux aqueous solution.

This flux aqueous solution is heated and stirred, and a 50 mm x 50 mm x 1 mm Al plate (A1050), which has been subjected to degreasing and cleaning treatment in advance, is immersed,
Hold at the specified temperature for 30 seconds and then pull up. Then
The flux adhering to the surface was removed by washing with water, and after drying, the Zn analysis on the surface of the Al plate was performed by a fluorescent X-ray analyzer. The measurement conditions are: secondary target: Ge, primary X-ray tube voltage: 25 kV, primary X-ray tube current: 10 mA, measurement time: 500 seconds, Z
Line irradiation area: φ24 mm.

Fig. 1 shows the relationship between the X-ray intensity of the Al surface and the temperature of various flux aqueous solutions. With the fluoride-based fluxes (1) and (2), it can be seen that the X-ray intensity of Zn sharply increases when the flux melting temperature is 50 ° C or higher.

The Zn coating formed on the Al surface can be visually confirmed,
Its color is blackish gray. With the chloride flux (3), the X-ray intensity becomes strong at 60 ° C and above, but it is not colored enough to be visually confirmed, and even at 90 ° C it is 1/10 of that of the fluoride flux (1) and (2). It was about. However, when treated at 90 ° C for 30 minutes, the Al surface exhibited the gloss of metallic Zn and the adhesion was good.

Moreover, the Zn coating formed by the fluoride flux (2) was observed by a scanning electron microscope, and it was found that the flux temperature of 60 to 70 ° C was the best in terms of coating uniformity and adhesion. It was

The thickness of the Zn coating can be increased by prolonging the immersion time in the aqueous flux solution, but if it is too thick, peeling easily occurs. For example, holding at 90 ℃ for 10 minutes, about 5μm
However, there is a risk of peeling at the time of drying, so it is preferable to stay within 5 minutes. One method is to prevent this peeling.

Example 2 An Al plate (01050) of 50 mm × 25 mm × 1 mm was immersed for 60 seconds in the flux aqueous solution produced in Example 1 while being heated to 60 ° C., then pulled up, dried at 120 ° C. for 5 minutes, and degassed with N ₂ gas. Was heated to 600 ° C. in an atmosphere of −30 ° C. or lower to diffuse Zn into the Al plate. The Zn surface concentration and the diffusion depth of the Al plate in which Zn was diffused were measured by EPMA. Zn concentration is 0 by weight.
A calibration curve was created from the standard samples of 1%, 0.5%, 1.0%, 5.0% and the remaining Al, and estimated. The results are shown in FIG. As is clear from the figure, Al is treated with any of the fluoride fluxes (1) and (2) and the chloride flux (3).
The Zn concentration is almost the same, 1.5% on the surface, and the diffusion depth is 0.1.
It is 2 to 0.13 mm. However, chloride flux (3)
Therefore, the flux residue removing step after the diffusion treatment is unavoidable, and the flux residue removing step is indispensable especially for complex structures.

Example 3 FIG. 3 shows the Zn film forming ability. 7.5g of fluoride flux (2) against 42.5g of deionized water
Make the added aqueous solution and apply the flux aqueous solution at 60 ℃
Then, the Al plate (A1050) having a predetermined area was immersed for 150 seconds. After withdrawing after immersion, the amount of ZnF _{2 in} the flux was measured by chemical analysis. ZnF ₂ in the flux is Zn
The film formation area decreases almost linearly up to 1000 cm ² ((1) in the figure). Thereafter, the decrease rate decreases and the Zn film forming ability decreases, but the forming ability is restored by adding ZnF ₂ ((2) in the figure).

Example 4 Using AlF ₃ produced by the dry method, 46% Al by weight
Fluoride flux powder (4) consisting of F ₃ , 34% KF, 14% ZnF ₂ and 6% LiF was suspended in water, and 15% by weight (residual water content)
Of water. The manufacturing method of the flux is the same as that of the first embodiment.

Acetic acid was added dropwise to this aqueous flux solution, the pH of the aqueous flux solution was changed to 60 ° C., and a 50 mm × 50 mm × 1 mm Al plate (A1050) that had been degreased and washed was immersed for 60 seconds.
It was pulled up and the flux adhering to the surface was removed by washing with water. After the removal, the Al plate was dried, and then the Zn on the surface of the Al plate was analyzed by a fluorescent X-ray analyzer. The measurement conditions are the same as in Example 1. For comparison, the fluoride-based flux (2) was also measured under the same conditions.

Fig. 4 shows the relationship between the X-ray intensity on the Al surface and the pH of the aqueous flux solution. It can be seen that when the pH value becomes smaller than 6.7, the X-ray intensity of Zn is rapidly increased.

Salicylic acid other than acetic acid, oxalic acid, phthalic acid, tartaric acid,
Similar effects were obtained with organic acids such as ascorbic acid,
Almost no effect was obtained with hydrofluoric acid and nitric acid.

Example 5 In this example, Zn is Al or Al in the final purpose diffusion treatment.
This is a surface treatment method in which it is sufficiently diffused into the alloy and at the same time brazing is performed.

FIG. 5 is a perspective view of a corrugated heat exchanger composed of fins and tubes. In FIG. 5 (A), fins 6 are arranged between the flat tubes 5 and the respective contact portions are brazed. Flat tube 5
JIS standard A1050 Al material, the cross-sectional dimension of which is hollow with 20 mm x 5 mm (6 holes), and the fins 6 are Al-Si series on the surface of the core material (JIS standard A3003) 7 made of Al plate. The brazing material (BA4343) 8 is clad with a brazing sheet, and its cross-sectional dimension is 22 mm × 0.1 mm. The gap between the flat tubes 5 and the flat tubes 5 was 16 mm, and the fins 6 formed in this gap were inserted and combined in three stages. Flux concentration of this brazed material heated to 60 ° C 3,5,1
It was immersed in an aqueous solution of 5,30,50% by weight (residual water content) for 90 seconds and then dried at 120 ° C. to evaporate the water content. Subsequently, the N ₂ gas was heated to 615 ° C. in an atmosphere with a dew point of −30 ° C. or lower, and brazing was performed while Zn was diffused in Al. The flux used here is the flux produced by the method of Example 1, and is 46% AlF ₃ , 34% KF, 14% ZnF ₂ , 6% by weight.
The fluoride-based flux (2) made of LiF ₂ and the fluoride-based flux (4) described in Example 4. The fluoride type flux (4) was used after adjusting the pH to 5.6 with acetic acid. For comparison, the fluoride type flux (2) was immersed in a flux aqueous solution at room temperature for 90 seconds, and brazing was performed under the same conditions except for the above.

When brazing is completed, as shown in FIG. 5 (B), a brazing material coating layer is formed on the surface of the core material 7, and a fillet 9 is formed between the core material 7 and the flat tube 5.

The surface treatment effect of Zn diffusion on the fins 6 and tubes 5 was performed for 200 hours by the Cass test method (corrosion resistance test method for anodic oxide coatings of Al and Al alloys) specified in JIS H8681, and evaluated by pitting depth. did. Again tube 5
The Zn concentration and the diffusion depth of the surface were measured by EPMA. A test piece for measurement was applied by cutting out a part of the heat exchanger. The results are shown in Table 1. Regarding the brazability of the tube 5 and the fin 6, the fillet 9 formed at the contact portion
The shape was determined.

The Zn concentration on the tube surface, the Zn diffusion depth into the tube, and the pitting corrosion depth after 200 hours of the cass test all show the effect of heating the aqueous flux solution to treat the member to be treated. Originally, the diffusion depth was determined by the heating temperature and the heating time, but it tended to become shallow when the flux concentration was low.

In addition, the maximum pitting depth of the tube in the Cass test for 200 hours was 15% at a flux concentration of 3% of 0.85 mm, 5% of 0.50 mm at a solution temperature of 20 ° C.
30% and 50% show the form of general corrosion. On the other hand, all the samples treated by the treatment method of the present invention showed the form of general corrosion, and at the flux concentration of 5%, the maximum pitting corrosion depth was 0.12 mm and 0.15 mm, which was 20 of (2). ℃ 50
It is shallower than%. From this result, it was revealed that the pitting corrosion resistance was excellent when the flux concentration was 5% or more and the flux aqueous solution concentration was 60 ° C.

Almost no decrease in brazing property was observed due to the formation of the Zn coating, and the fillet formation was slightly poor at the flux concentration of 3%, but the joining was sufficiently performed.
As for the appearance, as the flux concentration increases, the amount of flux residue increases, resulting in poor finish. When used in a heat exchanger, the flux concentration is preferably 30% or less because it causes clogging of fins and increases ventilation resistance.

Example 6 Surface treatment and brazing of the same heat exchanger as used in Example 5 were performed with a fluoride flux (1) and a chloride flux (3), and the maximum pitting depth after 200 hours of the cass test was determined. It was measured. The flux production method and the surface treatment method were all the same as in Example 5, and the flux concentration was 15%. The results are shown in Table 2.

While all the comparative examples have pitting corrosion, the examples of the present invention show a mode of general corrosion, and it is clear that they are excellent in pitting corrosion resistance.

When brazing the tubes and fins of the heat exchanger, the flux is applied by immersing the tubes and fins in an aqueous solution of flux to attach the flux.

Example 7 In this example, a comparative test with a conventional surface treatment method of electrochemical treatment by plating was performed.

50mm × 50mm × 1mm Al plate (A1050) with 15% concentration of fluoride flux (1) solution, chloride flux (3)
Each was immersed in the aqueous solution. Immersion conditions are 60 ° C. and 90 seconds. Then pull up, dry at 120 ° C, and 600 in N ₂ atmosphere.
It was heated to ℃ and Zn was diffused into Al to obtain a corrosion test piece.
Further, an Al plate (A1050) having the same shape was used as a corrosion test piece while being electroplated with 5 μm. As the corrosion test, a cast test was performed. The result is shown in FIG. In the figure, (1) in the figure is the result for the fluoride flux, (2) is the result for the liquefaction flux, and (3) in the figure.
Indicates the result of the plating method.

The maximum pitting depth was about 300 μm in 720 hours of the surface test using flux, whereas it was 5 μm.
In electroplating, total corrosion was exhibited in 200 hours, 210μ
It was a depth of m. The Zn-plated film on the surface of the test piece is considered to have been eluted during the test or the plating surface was peeled off. In any case, since the Zn coating has disappeared, it seems that the corrosion proceeds rapidly.

〔The invention's effect〕

As explained above, according to the present invention, the temperature is 60 to 80
By having a step of immersing a plate, tube, or other structure made of aluminum or its alloy in a flux aqueous solution at a temperature of ℃, Zn is sufficiently diffused into the member to be treated, and those structures are It is possible to obtain excellent corrosion resistance. Also, the pH of the above flux aqueous solution for dipping the structure
By setting the range to 6.7 or more, more evenly,
Moreover, the Zn film can be formed on the structure with high adhesion, which also leads to the structure having excellent corrosion resistance.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the flux aqueous solution temperature and the X-ray intensity of Zn on the surface of the member to be treated, FIG. 2 is a graph showing the relationship between the Zn concentration on the surface of the member to be treated and the diffusion depth, and FIG. 3 is Zn
A graph showing the relationship between the film forming area and the amount of ZnF ₂ in the flux, FIG. 4 is a graph showing the relationship between the pH of the flux and the X-ray intensity of Zn on the surface of the member to be treated, and FIG. 5 (A) is the present invention. FIG. 5B is a perspective view of a heat exchanger showing an example of an application of the surface treatment method according to FIG. 5, FIG. 5B is an enlarged view of the brazing part of FIG. 5A, and FIG. It is a graph which shows the test time with the surface treatment concerning invention, and the relationship of pitting depth. 1 ... Fluoride flux (1), 2 ... Fluoride flux (2), 3 ... Chloride flux (3),
4 ... Fluoride flux (4), 75 ... Flat tube, 6 ... Fin, 7 ... Core material, 8 ... Brazing material, 9 ...
Fillet.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazushige Nakata 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitate Manufacturing Co., Ltd. (56) References JP-A-59-205467 (JP, A) JP-A-SHO 59-47088 (JP, A) JP-B-55-36433 (JP, B2)

Claims (3)

[Claims] 1. A weight ratio of ZnF ₂ : _{3 to} 35% and AlF ₃ : 38 to 54
%, KF: fluorine-based containing 25% to 40% flux powder _{or, ZnCl 2: 6~10%, KCl} : 30~55%, NaCl: 20~30%, Li
Chlorine flux powder containing 13: 40% Cl: 8 by weight
A member to be treated made of aluminum or its alloy is dipped in an aqueous solution of 60 to 80 ° C. containing 5% or more to simultaneously form a zinc coating and an adhesion layer of the flux powder on the surface of the member to be treated, and thereafter. A surface treatment method for aluminum or an alloy thereof, which comprises heating to a temperature not lower than a melting temperature of zinc and not higher than a melting temperature of the member to be treated to diffuse zinc into the member to be treated and at the same time brazing. 2. The pH of the solution according to claim 1 is
A surface treatment method for aluminum or its alloy, which is 6.7 or less. 3. The pH of the solution according to claim 1.
Acetic acid, salicylic acid, oxalic acid, phthalic acid, tartaric acid,
A surface treatment method for aluminum or its alloy, wherein the pH is adjusted to 6.7 or less by adding at least one acid selected from ascorbic acid.