JPS6083771A - Brazing method of aluminum material - Google Patents

Abstract

PURPOSE:To form a defect-free joint part brazed by a small amt. of brazing material by bringing a part of an Al material desired to be brazed into contact with a treating liquid contg. K and F to form a chemical conversion-treated layer and heating said material to braze the Al material to the mating material. CONSTITUTION:At least a part of an Al material desired to be brazed is brought into contact with an aq. soln. of KHF2, etc. contg. K and F. The chemical conversion-treated layer consisting of potassium pentafluoroaluminate (K2AlF5) as a flux for brazing is thus formed. The chemical conversion-treated material is tentatively assembled with the mating material and the assembly is put into a heating furnace, etc. by which the assembly is brazed and the molten metal is penetrated to the part desired to be brazed. The wettability between the brazing material and the Al material is improved by the above-mentioned method, by which the normal brazed joint part is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of forming a chemical conversion layer as a flask on the surface of an aluminum-based material and then brazing desired parts by heating.

Recently, heat exchangers such as radiators for automobiles have been manufactured from aluminum or aluminum alloy materials (in the present invention, aluminum-based materials) due to the need to reduce weight. In order to finish products such as these, at least a method is needed to bond the materials together.Brazing is the most suitable bonding method in terms of work efficiency and the form of bonding that can be obtained.

Conventionally, AI, which has a slightly lower melting point than aluminum-based materials, has been used as a brazing material for brazing aluminum-based materials! -8
Four-eutectic alloys are mainly used.

Furthermore, in order for the brazing filler metal to bond well with an aluminum-based material, it is necessary to remove dirt such as an oxide film present on the surface of the aluminum-based material. To remove this dirt, flux is applied to the braze joint along with the brazing material.

Commonly used fluxes include zncg2, N
There are mixed substances of metal chlorides such as aCe. However, when a chloride-based flux is used, the flux remaining in the brazing area after the brazing process may corrode the aluminum-based material or the brazing material. However, after brazing, it was necessary to thoroughly wash the product to remove flux.

On the other hand, it is known that potassium tetrafluoroaluminate (KAeF4) is useful as a flux used for 1° brazing of aluminum-based materials. K
AeF4 is a complex salt obtained by mixing and melting equimolar amounts of potassium fluoride (KF) and aluminum fluoride (AgF2). When using this as a flux, it is powdered and applied to the parts for brazing. This flux melts at a temperature of approximately 570°C and removes or dissolves oxides present on the surface of aluminum-based materials, but is essentially inert to metal aluminum and is used for brazing. It has excellent properties as Even if the flux remains in the brazing area after brazing, it is extremely insoluble in water and will not corrode aluminum-based materials.

Therefore, there is no need for cleaning after brazing, which is required when using chloride-based fluxes, and it is also possible to perform painting work without applying any special treatment to the product. has.

However, this flux has the disadvantage that the method of supplying the flux to the brazing part is complicated. That is, as mentioned above, this flux is mainly a powder of potassium tetrafluoroaluminate. To apply this powder to a brazing part, first suspend this powder and powdered brazing material in water,
Into this, the assembly made of aluminum-based material is immersed prior to brazing. It has been proposed to collect flux and brazing material in the brazing area by thoroughly immersing the assembly, then removing it from the suspension and drying it.

Next, when the assembly is heated to a predetermined temperature to melt the flux and the brazing material, the brazing material penetrates into the brazing parts, and after cooling, the brazing parts are joined by the brazing material. In this method, in order to supply the necessary amount of flux and brazing material to the brazing part, the amount of flux and brazing material in the suspension water, the lifting speed after the assembly is immersed, the lifting posture, etc. must be carefully adjusted. It has the disadvantage that it cannot be used.

In view of the drawbacks of the above-mentioned conventional brazing methods used for brazing aluminum-based materials, the inventors of the present invention conducted extensive research, and as a result, they came up with the invention of the present application.

The purpose of the present invention is to form a flux layer that firmly adheres to the surface of the aluminum material that is used for brazing.
It is an object of the present invention to provide a brazing method that allows brazing at desired locations to be easily performed and that does not cause corrosion due to flux residue after brazing.

In the present invention, brazing is performed on the surface of the aluminum material by contacting at least a desired portion of the aluminum material with a treatment solution containing potassium and fluorine. Brazing of aluminum-based materials consists of a chemical conversion treatment step to form a chemical conversion treatment layer, and a brazing step of heating the forming part of the chemical conversion treatment layer and brazing the aluminum-based material to a mating material with a brazing filler metal. is a method.

According to the present invention, the flow of the aluminum-based brazing material into the processing solution is smooth, and the brazing material evenly spreads over the brazing area.

As a result, a defect-free brazing joint can be formed with a small amount of brazing metal, and the brazing joint will not corrode even if the brazing part does not have to be cleaned after brazing. .

Further, since the chemical conversion treatment layer as a flux is firmly attached to the aluminum-based material, the flux does not fall off even when parts are manufactured from the aluminum-based material by sheet metal processing or the like. Therefore, the brazing material flows easily during brazing after processing, and a sound brazing joint can be obtained. Such excellent effects can be obtained because the treatment solution for forming the chemical conversion treatment layer contains potassium and fluorine.

The present invention will be explained in more detail below.

The chemical conversion treatment step in the present invention is a step of bringing an aluminum-based material into contact with a treatment solution containing potassium and fluorine to form a chemical conversion layer made of potassium pentafluoroaluminate (K2AeFs) on the surface of the aluminum-based material. .

In the present invention, the aluminum-based material refers to an aluminum material or an aluminum alloy material. Aluminum alloy materials include aluminum, silicon (SL),
Copper (Cu), manganese (Mn), zinc (Zn), titanium (Ti), rim (Cr), zirconium (Z
There are alloys to which at least one element, such as magnesium (Mj+), or magnesium (Mj+), is added. Specifically, JIS BooB,
There are aluminum alloy materials such as 1050.7072.

Furthermore, as the aluminum alloy material, 7 to 12 wt.
% M-8i eutectic alloy may be coated.

Specifically, a JI88008 surface clad with 4348 material (such as nA12pc) may be used. If it is plate-shaped, it is called a praising sheet.

The treatment solution used in this chemical conversion treatment step is a solution containing potassium and fluorine. When the aluminum-based material is brought into contact with this solution by a method such as immersion, potassium and fluorine in the treatment solution are mixed with the aluminum-based material AI! A layer of F6 is generated. K,
A/F5 effectively acts as a soldering flux in the next heating step.

What is important in the present invention is that the 2AeF5 layer is formed by the reaction described above.

There are several methods for preparing the treatment solution used in this step.

First, one of them is the potassium hydrogen fluoride (KHF2) mentioned above.
) in water. The dissolved amount of KHF2 is 1 to 809 parts per 11 parts of water, which is suitable for producing 2AeF5. When the amount of KHF2 is less than 19/1, the formation rate of the K2AtF chemical conversion layer is low and it takes a long time to generate the desired amount of 2AeF.

On the other hand, in the case of 8(H1/J or more), the solution concentration is high, so K and AgF are likely to be produced, and K2AeF cannot be obtained efficiently.

Another method for preparing the treatment solution is potassium fluoride (
KF) and hydrogen fluoride (HF) may be dissolved in water to form a mixed aqueous solution. Alternatively, potassium hydroxide (KOH) and hydrogen fluoride dissolved in water may be used.

These aqueous solutions preferably have a molar ratio of fluorine to potassium of 1 to 10, and a potassium content of 0.5 to 409/l. When the above molar ratio is 10 or more, the aluminum-based material is strong;
Corrosion is not preferable because the surface condition becomes rough. Furthermore, if the molar ratio is less than 1, it becomes difficult to generate K2AlF3.

The reason why these treatment solutions are low-potassium fluoride or mixed aqueous solutions of potassium hydroxide and hydrogen fluoride is to increase the molar ratio of fluorine by adding fluorine, as well as to make the treatment solution acidic. This is also to promote the reaction with aluminum.

In addition to the above method of immersing the aluminum material in contact with the treatment solution, there is also a method of coating or spraying the aluminum material onto a desired portion at least for brazing. At this time, it is necessary to supply a relatively large amount of potassium and fluorine in the processing solution so that they do not become insufficient.

The contact time between the aluminum-based material and the treatment solution is not necessarily determined depending on the concentration of potassium and fluorine in the treatment solution and the temperature of the treatment solution, but is, for example, 0.5 seconds to 20 seconds.
A range of about minutes is good.

Because the treatment solution is a mixture of KF and HF, the contact destroys the oxide film present on the surface of the aluminum-based material, chemically reacts aluminum, potassium, and fluorine, and forms 2AeF5. generate. In particular, the production of 2A/F5 also changes depending on the temperature of the processing solution. Naturally, the chemical reaction proceeds satisfactorily even at room temperature. but,
Increasing the temperature of the treatment solution to 40 DEG -70 DEG C. results in particularly complete and rapid removal of the oxide layer. As a result, K2AlF3 is formed as a strong chemical conversion treatment layer on the surface of the aluminum-based material.

These materials may be subjected to the chemical conversion treatment process as they are as raw materials, or may be processed into a predetermined shape, or may be assembled and then subjected to the chemical conversion treatment process. Before subjecting the aluminum-based material to the chemical conversion treatment step, the surface of the material may be degreased with an organic solvent such as trichlorethylene. Alternatively, the oxide film may be removed in advance using hydrogen fluoride or the like. In this way, the chemical conversion treatment step may be performed after the surface of the aluminum-based material is cleaned.

Further, in this chemical conversion treatment step, 2A/F may be generated on the surface of the aluminum-based material by using the aluminum-based material as an anode and applying electricity in the treatment solution. In this case, the cathode material is preferably a material that does not elute into the processing solution as ions, such as carbon, which has a surface area equivalent to that of the anode.

Furthermore, chemical conversion treatment may be performed without passing an alternating current. In this case, prepare two sets of aluminum-based materials,
Full voltage is applied to both aluminum materials. Then,
2A/F for the aluminum material with higher voltage
2AIFs is not eluted when 5 is generated and becomes low. Therefore, both aluminum-based materials have 2AeF only when the voltage is high.

will be generated.

In both cases, when a DC voltage is applied or when an AC voltage is applied, the generation rate of 2 AI Fs is faster than when no voltage is applied, so the desired amount of 2A Fs can be produced in a short time. A chemical conversion treatment layer made of -eFs can be obtained.

As described above, K2AIFg is 0.0% per unit surface area.
It is preferable to cut off the contact between the aluminum-based material and the treatment solution when the aluminum-based material reaches 1 to 109/-.

After this, unreacted potassium and fluorine remain on the surface of the aluminum-based material subjected to the above chemical conversion treatment step. The remaining potassium and fluorine may be washed with water, but there is no problem in the subsequent steps even if the water is not washed.

Furthermore, the treated aluminum-based material may be subjected to a drying process. The drying step is a step of dissipating water adhering to the surface of the aluminum-based material. If washing with water is not performed after the chemical conversion treatment, potassium and fluorine remaining on the surface of the aluminum-based material can be reacted with aluminum through this step to further produce -2Al Fs. However, when the residual potassium and fluorine are in excess, the potassium and fluorine
2, and the residual moisture is dissipated. As a result, KHF2 containing no moisture remains on the surface of the aluminum-based material.

KIIF2, which does not contain water, does not deliquesce and naturally absorbs moisture from the air and does not become sticky, making the material easy to handle and causing no harm during subsequent brazing. Never.

A specific method for drying may be to leave it in the air, but this requires a relatively long time. Also, from room temperature to 100
This may be done by blowing warm air at ℃. Also 100-2
You may also blow hot air at 00°C. In particular, when hot air is blown, the moisture in the chemical conversion treatment layer disappears, the chemical conversion treatment layer is baked onto the surface of the aluminum-based material, and the layer becomes stronger.

Furthermore, since the subsequent brazing process does not generate water vapor, there is an advantage that the dew point in the heating furnace does not increase and harmful hydrogen fluoride vapor is not generated.

The aluminum-based material having the chemical conversion treatment layer obtained as described above has 2AI on the surface of the aluminum-based material.
F5 or 0.1-10 f/rr? It is preferable that K2AeFs acts as a flux in the next brazing process when the material is somewhat fixed.

As mentioned earlier, the aluminum-based material can be used as is, for example, in the form of a plate block, or as a part molded into a desired shape, such as the cooling water distribution core and fins of an automobile radiator, or by assembling these into a mating material. The brazing in combination with the brazing may be a temporary assembly having the desired parts.

When a chemical conversion treatment process is performed on the raw material, the raw material is processed into a desired shape and combined with a mating material to form a temporary assembly.

The mating material may be an aluminum-based material subjected to the chemical conversion treatment described above, or may be an aluminum-based material that is not subjected to the chemical conversion treatment process. Alternatively, it may be coated with flux by a conventional method. During processing of the material, the chemical conversion treatment layer is strongly bonded to the aluminum-based material, so it is unlikely to peel off. In particular, when the amount of 2MF5 deposited is between O11 and 8η, it will not peel off even when subjected to quite severe processing.

If the amount of adhesion exceeds 10 V/-, it may peel off when the curvature is increased and bent, so care must be taken when processing.

In the above temporary assembly, the desired part for brazing is the part where two or more members are combined.

For the brazing step B, it is necessary to supply brazing material to the desired part before performing the next step of brazing. As a method for supplying the brazing material, it is simple and preferable to use a material clad with a brazing material for at least one of the members to be assembled. As another method, brazing filler metal in the form of a bar or wire powder may be supplied along the desired portion.

The above-mentioned brazing filler metal may also be subjected to the above-mentioned chemical conversion treatment step to adhere 2A-eF5 in advance.

The temperature is preferably below the melting point of the aluminum-based material and above the melting point of the brazing material.

The heated ambient atmosphere is most preferably a non-oxidizing atmosphere, but may also be an atmosphere in which a small amount of oxygen is present.

In the crystallization process, 2A is present as the chemical conversion treatment layer.
Since eF5 acts as a flux, the "wettability" between the brazing material and the aluminum-based material is good, and a normal brazing joint can be obtained.

Although the details of the phenomenon in the brazed portion when the 3-441-cho-o-fu process is applied are not clear, it is thought to be as follows.

First, the temperature rises and the flux begins to melt. The melted flux reacts on the surface of the aluminum-based material, and the oxide film that was generated during heating or remained from the beginning is removed. Originally, there is little oxide film on the surface of an aluminum-based material that has been subjected to a chemical conversion treatment process, so even a raw flux as in the present invention is sufficient to remove the oxide film.

Thereafter, the brazing material melts and comes into contact with the surface of the aluminum-based material. Since the oxide film has been removed from aluminum-based materials, they have good "wettability" with the brazing filler metal.
The brazing filler metal penetrates into the gaps between the brazing parts. After the brazing filler metal has sufficiently penetrated into the brazing area, if it is cooled, the brazing filler metal will solidify and bond the aluminum-based materials together to form a joint.

As described above, the penetration power of the brazing filler metal is very strong, so defects such as pinholes are less likely to occur in the brazing filler metal that forms the joint. Additionally, although flux residues are present at or near braze joints, they do not corrode aluminum-based materials because they are substantially insoluble in water.

Conversely, these residues have a greater affinity for water than aluminum-based materials. Therefore, for example, water that has condensed on the fins of a heat exchanger for an air conditioner can easily move toward the water tray. As a result, the flow of air in the narrow air passages of the heat exchanger is not obstructed by the condensed water, so that heat exchange is performed smoothly, resulting in advantages such as improved efficiency of the heat exchanger.

The present invention will be explained in detail below.

Example 1 As an aluminum-based material, size 3 (x x 13 cm,
A pure aluminum plate and an aluminum alloy plate with a thickness of 2 mm are prepared, and these plates are immersed in a treatment solution containing potassium and 1 nitric oxide, subjected to the chemical conversion treatment process in the invention, and flux-coated aluminum-based material 15 I got the seeds. The names of these materials, processing conditions, etc.
Shown in the table.

Tetsu:Furthermore, on the surface of each material, the X-ray cycle! When the pattern was observed, K2 A/' B s·H2O was generated, as shown in FIG. After that, glue the surface of each material, A/F5・H,
0 adhesion amount was investigated. The amount of adhesion is 0.0 mm per 1♂ material surface.
2 to 1 Oy, and the amount of adhesion for each material with each implementation number is shown in Table 1.

Next, a brazing experiment was conducted using the above materials. First, as shown in Fig. 2, the materials 1 with work numbers 1 to 16 are placed horizontally, and the plating sheet 2 with work number 17 is fixed on top of these so that its surface is vertical. A test piece was prepared for brazing.

Table 1 For each brazing test piece, place it in a heating furnace under nitrogen gas atmosphere.
After heat treatment was performed at 610° C. for 2 minutes, it was taken out from the furnace, left to stand, and cooled. Thus, each specimen was brazed in part 1.
1 was joined by brazing. The joint status of the joint is indicated by A or B in the joint evaluation column of Table 1. The joint evaluation is A,
It was classified into two levels: B. The appearance of each joint is shown in the 8th section.
It is shown in Fig. 4. FIG. 8 shows case A, in which the brazing filler metal has penetrated uniformly. FIG. 4 shows case B, in which there is some non-uniformity in the penetration of the brazing filler metal. However, no areas where the filler metal is missing are visible.

From these results, the brazing material (484B material) clad on the surface of the plating sheet 20 melts, and the brazing is performed in part 1.
1, it was found that the brazing was almost uniformly distributed over the parts, and that the aluminum-based materials were well joined by the brazing filler metal.

Example 2 The aluminum material 1 of Example No. 11 coated with the brazing flux shown in Table 1 and the plating sheet material 2 of Example No. 17 were combined as shown in FIG. A brazing experiment was conducted using a stainless steel rod 8 having a diameter of 1.6 mm held between the materials, and the spreading ability of the brazing material was investigated.

On the other hand, as a comparative example, the same type as above without chemical conversion treatment,
A test piece for brazing was prepared by combining aluminum-based materials of the same size. The brazing flux used for this comparative test piece was KAeF4, which was obtained by mixing equal moles of potassium fluoride (KF) and aluminum fluoride (AlF2) and melting them by heating. The powder was pulverized to a powder with a particle size of about 200 mesh, and the powder was dispersed in 10 parts of water and 11 parts of water, and while stirring well, the comparative test piece was immersed, taken out, and dried. The flux was attached to the brazing parts.

Next, the side brazing test piece was placed in the heating furnace used in Example 1 and heated at 610° C. for 2 minutes to perform brazing.

In the test piece using the aluminum material subjected to the chemical conversion treatment in the present invention, brazing was performed from the edge of the part at 1-24±
The brazing filler metal flowed up to a position of 11 m (5 test pieces), but in the comparison test piece, 1=28+2xx'Qa-
)is.

From these results, it can be seen that in the brazing method of the present invention, the flow of the brazing material becomes easy, and good joining can be achieved even in the brazed portions that are in poor condition when assembling materials.

Example 3 Two pieces of the flux-coated aluminum material of Example No. 2 shown in Table 1 were assembled in the same manner as the brazing test piece of Example 1, and a brazing material was added along section 11 for brazing. A 98% AJ-7% St wire with a diameter of one head was placed. After that, it was placed in the heating furnace used in Example 1 and heated to 610°C.
A heat treatment was performed for 2 minutes to cause the brazing material to flow into the braze joint and form the braze joint. As a result, a brazed joint in which the brazing material was evenly distributed was obtained as shown in FIG.

[Brief explanation of drawings]

Figure 1 shows the surface of the chemical conversion treatment layer obtained in the example, Figure 5 shows the example, and Figure 2 shows the wax produced by combining aluminum-based materials that have been subjected to the chemical conversion treatment process. Figures 3 and 4 are perspective views showing the brazing condition of the test piece, and Figure 5 is a perspective view showing the brazing condition of the test piece.
This is a test piece for brazing having a gap in the brazing part, and is a perspective view showing the state of brazing. 1.2... Aluminum-based material 1 subjected to chemical conversion treatment
1...Brazing is part 3......Stainless steel rod applicant Toyota Central Research Institute Co., Ltd.

Claims (7)

[Claims] (1) For brazing, at least the desired portion of the aluminum-based material is brought into contact with a treatment solution containing potassium and fluorine, and the surface of the aluminum-based material is brazed with a chemical compound consisting of potassium pentafluoroaluminate as a flux. A method for brazing aluminum-based materials, which comprises a chemical conversion treatment step to form a treated layer, and a brazing step to braze the aluminum-based material to a mating material using a brazing filler metal by heating the area where the chemical conversion treatment layer is formed. . (2) The above aluminum-based material is one in which at least a portion of the surface of the aluminum-based material is coated with a eutectic alloy of A/-S having a melting point lower than the melting point of the aluminum-based material. Brazing of aluminum-based materials as described in item (1) is a method. (3) The above treatment solution contains 1 to 80% potassium hydrogen fluoride.
A method for brazing aluminum-based materials according to claim (1), which is an aqueous solution containing 9/l. (4) The processing solution is an aqueous solution in which the molar ratio of fluorine to potassium is 1 to 10, and the potassium content is 0.5 to 41/J. Brazing of aluminum-based materials as described in item (1) is a method. (5) Claim (1) or (4), wherein the treatment solution is a mixed aqueous solution of potassium fluoride and hydrogen fluoride.
The method for brazing aluminum-based materials described in Section 1. (6) Claim (1) or (4) wherein the treatment solution is a mixed aqueous solution of potassium hydroxide and hydrogen fluoride.
) Brazing method for aluminum-based materials. (7) The chemical conversion treatment layer has a chemical conversion treatment layer of 0.1 to 1
Claims (1), (3) to (6) consisting of potassium pentafluoroaluminate No. 01
The method for brazing aluminum-based materials described in Section 1.