JPS61103673A - Production of aluminum brazing article excellent in corrosion resistance - Google Patents

Abstract

PURPOSE:To improve a productivity with reducing a production man-hour by using the solution containing ZnO, NaOH as the suspension for a flux. CONSTITUTION:A fluoride flux is suspended in the form of a slurry into the solution containing ZnO, NaOH. The flux consisting of the mixture mixing 80-99.8wt% KalF4, 20-0.2wt% KF is used for the fluoride flux. This suspension is then coated uniformly on at least either one part of the joining member made of Al. After coating the zinc containing in the suspension is uniformly precipitated on the surface of the joining member by a plating action. The precipitation amount is in the range of 0.1-4g/m<2>. The brazing is thereafter performed with melting the brazing filler metal with heating to the temp. lower than the melting point of the joining member and higher than the melting point of the flux with using the Al alloy brazing filler metal having lower melting point than the joining member in the nonoxidizing atmosphere of an inert gas atmosphere, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for producing aluminum brazed products with corrosion resistance, and particularly to a method for producing aluminum brazed products that are suitable for producing aluminum heat exchangers due to their brazability properties. Regarding the manufacturing method.

In this specification, the term aluminum is used to include its alloys.

Conventional Technology and Problems Conventionally, when manufacturing aluminum heat exchangers such as automobile radiators, car cooler evaporators, or condensers by flux brazing, chloride-based 7lux containing zinc chloride, etc. is used. A method of brazing and joining components for a heat exchanger using a method is known.

At the same time as each member is joined by brazing, zinc is precipitated on the surface of the component member by heat added to the brazing and diffused into the member, and the sacrificial anode effect of the zinc diffusion layer improves the corrosion resistance of the heat exchanger. This is because we hope that this will also improve the results.

However, in this method, the flux used is essentially water-soluble and has strong hygroscopic properties, so it is necessary to wash away any remaining flux immediately after brazing. The drawbacks were that the installation costs were high, the process was complicated, and a heavy workload was required.

Moreover, since the diffusion layer is formed using a small amount of zinc contained in the flux, it is not possible to form a sufficient diffusion layer, and therefore, it is not able to exhibit sufficient corrosion prevention effects. Ta.

Therefore, in order to eliminate the need for flux cleaning after brazing and improve the corrosion resistance of brazed products, non-corrosive fluoride flux is used as the flux, while chemical plating, electroplating, etc. are used to improve brazing properties. A predetermined amount of zinc is precipitated on the surface of the parts to be joined using the zinc precipitation method described above, and then a suspension of the above flux is applied and brazed, thereby depositing a uniform and sufficient amount of zinc on the surface of the parts to be brazed. A method of forming a zinc diffusion layer has been proposed (for example, JP-A-57-160595).

However, in the above method, zinc must be deposited on the surface of the joining parts in a separate process from the brazing process, which increases the number of manufacturing steps, making it difficult to improve the productivity of brazed products and reduce manufacturing costs. This was problematic.

This invention has been made in view of the above-mentioned problems, and it is possible to improve the productivity of brazed products and reduce manufacturing costs while maintaining corrosion resistance equivalent to that achieved by the conventional method. The purpose is to provide a method for manufacturing brazed products.

Means for Solving the Problems To achieve this object, the present invention improves the process of applying the flux suspension and the zinc precipitation treatment by using an aqueous solution containing ZnO1NaOH as the liquid in which the flux is to be suspended. It is characterized in that the steps are performed simultaneously.

That is, this invention suspends a fluoride flux in an aqueous solution containing Zn 01 Na OH, applies the suspension to a bonding member made of aluminum, and then heats it to a predetermined temperature in a non-oxidizing atmosphere. The present invention provides a method for manufacturing aluminum brazed products with excellent corrosion resistance, which is characterized in that brazing is performed by melting a joining brazing filler metal.

The above-mentioned aqueous solution containing znO, NaOH is generally used as a treatment solution in so-called zincate treatment as a pretreatment when plating aluminum. The fluoride flux shall be suspended in the form of a slurry.

As a fluoride-based flux, one having a composition of fluoroaluminum complex salts (K3 AQ Fs and KAj2F+) is well known, and it goes without saying that these 7 fluxes can be applied, but preferably KAlF4: 80-99.8wt% and KF: 20
It is preferable to use a flux consisting of a mixture of -0.2 wt%. The reason for this is that while the flux has properties equivalent to those of the flux containing the fluoroaluminum complex salt in terms of non-corrosion when left in the water and melting temperature range, both KAλF4 and KF are easily available as commercial products. Therefore, it can be easily prepared by simply mixing them. That is, the method for producing a flux whose composition is a fluoroaluminum complex salt is as follows:
In the case of actual industrial production and use, AgF2 and KF are generally used as starting materials, and the starting materials are mixed with KAlF4, which is a eutectic mixture thereof, to form 3 AgF
2 is mixed in a dry state at an appropriate ratio close to the eutectic point, this mixture is once melted, and the molten mixture is further cooled and solidified. There are problems such as a large number of man-hours and troublesome preparation. Therefore, KA is easy to prepare without such problems.
It is advantageous to use fluxes based on 1F4-KF. The mixing ratio of this KAλF4-KF flux was selected as above because its melting point was low so that 7 lux could be effectively applied during brazing heating.
If KF is less than the allowable lower limit, the effect will be poor, and conversely, if too much KF is mixed beyond the allowable upper limit, the complete melting temperature (liquidus temperature) will rise, resulting in good brazing. - There is a risk that the reaction temperature of the flux will become higher than the melting point of aluminum as a joining member, making brazing itself impossible. Further, during suspension, the powder particle size of the flux component is preferably approximately 2.0 .mu.m or less in order to facilitate suspension and application and to improve brazing properties.

Next, the above suspension is uniformly applied to at least one of the joining members made of aluminum. The means of application is
Although it is possible to apply spraying or brushing, it is recommended to use a dipping method as a uniform application method suitable for mass production.

After the suspension is applied, the zinc contained in the suspension is uniformly deposited on the surface of the joining member due to the plating action. The amount of zinc deposited is preferably in the range of 0.1 to 4 g/g. If the precipitation amount is less than 0.1 g/m2, there is a risk that the sacrificial anode effect required after brazing may not be sufficiently obtained, and conversely,
If the corrosion resistance exceeds 50%, the surface zinc a content of the brazed product will increase, and initial corrosion will be rapid and severe, and there is a risk that the desired sacrificial corrosion protection effect will not be achieved.

Thereafter, the joining member is brazed.

Brazing is performed using an aluminum alloy brazing filler metal whose melting point is lower than that of the joining member, in a non-oxidizing atmosphere such as an inert gas atmosphere, at approximately 580 to 620°C, which is lower than the melting point of the joining member and higher than the melting point of the flux. This is done by melting the brazing filler metal by heating it to . The above-mentioned brazing filler metal is usually an Aρ-3i alloy with a content of about 4.5 to 13.5 it% of 3. It is preferable to clad at least one of the aluminum structural members. Along with the heating in this brazing step, the zinc deposited on the surface of the aluminum material is diffused toward the center of the aluminum material, and a uniform and sufficient zinc diffusion layer is formed on the surface of the aluminum material. The thickness of this diffusion layer is desirably 50 μm or more from the viewpoint of anticorrosion effect.

After brazing, it is preferable to wash the brazed product with water or hot water. This is because NaOH in the flux suspension, which deteriorates corrosion resistance, can be removed to further improve corrosion resistance.

Effects of the Invention According to the implementation of the present invention as described above, by using an aqueous solution containing Zn 01 Na OH as the flux suspension, the flux suspension application process and the zinc precipitation process are performed simultaneously. Since there is no need to precipitate zinc in a separate process before applying the suspension as in the past, aluminum brazing improves product productivity and reduces manufacturing costs by reducing manufacturing man-hours. It will be useful to contribute effectively. Since brazing is performed by precipitating zinc on the surface of the aluminum material, a uniform and sufficient zinc diffusion layer is formed on the surface of the aluminum material by heating during brazing, and the sacrificial anode effect of this diffusion layer causes the solder to be soldered. can significantly improve the corrosion resistance of Of course, since a fluoride-based flux that does not leave any corrosive residue is used as the flux, it goes without saying that defluxing treatment after brazing is not necessary.

EXAMPLES Next, examples of the present invention will be shown in comparison with comparative examples.

A hollow flat extruded tube material made of A1050 alloy with a wall thickness of 0.7 mm is bent into a serpentine shape having a straight pipe part, and the tube material is held with scissors/v with a thickness of 1.0 mm made of A1100 alloy on both sides. Place the side plate of B△12
A corrugated fin material made of a double-sided plating sheet (A4343 alloy skin material is clad on both sides of a Δ3003 alloy core material at a cladding ratio of 12% on one side) with a thickness of 0.145 mm is attached to the side plate and the extruded tube material. It was assembled into a corrugated fin type heat exchanger by interposing it between the straight pipe parts of the tube material and between the straight pipe parts of the tube material.

Then, a flux consisting of a mixture of KAlF4 and KF and a flux consisting of a mixture of KAΩF4 and 3AgF2 were suspended in an aqueous solution containing ZnO1NaOH to prepare a suspension having the composition ratio shown in samples Nos. 011 to 6 in the table below. did. In addition, the powder particle size of the flux component during suspension is 5
It was set to 0 μm or less. The heat exchanger assembly was immersed in this suspension to deposit zinc of the numbers shown in the table on the surface of the aluminum material.

After that, each of the above assemblies was heated at 610°C for 5 minutes using N2 gas in a furnace adjusted to a dew point of -35°C, brazed, washed with hot water, dried, and then heated with A7N gas using a torch.
A heat exchanger was obtained by brazing the O1 union in place.

Then, the brazing condition of each heat exchanger obtained above was examined, and in order to examine its corrosion resistance, J15-H
A Cath test based on -8681 was conducted. The results are shown in the same table.

According to the above results, the heat exchanger manufactured by the present invention (
It was confirmed that samples Nα1 to Nα6) indicate good brazing condition and corrosion resistance. Therefore, it can be seen that the present invention, which requires fewer manufacturing steps, is advantageous in terms of improving productivity, reducing manufacturing costs, etc.

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Claims (3)

[Claims] (1) Fluoride flux is suspended in an aqueous solution containing ZnO and NaOH, the suspension is applied to a bonding member made of aluminum, and then heated to a predetermined temperature in a non-oxidizing atmosphere. A method for manufacturing aluminum brazed products with excellent corrosion resistance, which involves melting and brazing brazing filler metal. (2) Fluoride flux is KAlF_4:80~
99.8 wt%, KF: 20 to 0.2 wt% mixture according to claim 1. (3) Aluminum brazing with excellent corrosion resistance according to claim 1 or 2, wherein the amount of zinc precipitation on the surface of the joining member after applying the suspension is 0.1 to 4 g/m^2 method of manufacturing the product.