JP2680763B2 - Aluminum shaped article coated with brazing material - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated aluminum shaped article, and more particularly during the fabrication of a heat exchanger during assembly of the shaped article into heat exchange fins. When heating
Aluminum hollow shaped article coated with a fluxless metal layer that acts as a soldering material or a low temperature brazing material,
For example, aluminum tubes and methods for coating aluminum shaped articles as described above. The term aluminum as used herein is intended to mean aluminum and aluminum-based alloys. The joining of heat exchange fins with tubes in heat exchangers / radiators installed in motor vehicles is currently secured mainly by two methods: mechanical expansion of the tubes or brazing of the tubes to the heat exchange fins. ing. The secure joining provided by the mechanical expansion of the tubes is only achieved when using substantially circular tubes, which implies a limited thermal performance of the heat exchanger. A large amount of brazed copper flat tubes or brass flat tubes are used in automobile radiators,
It provides good performance when using the inexpensive known brazing techniques. In the automotive industry, steel and copper are increasingly being replaced by lighter materials such as aluminum or magnesium. However, the soldering or brazing of aluminum to aluminum or other metals is a difficult task due to the presence of the aluminum oxide layer which forms as soon as the surface of the aluminum member is exposed to the atmosphere. Is. This oxide layer has less wetting properties and thus prevents the formation of strong metallic bonds between the brazed components. Therefore, it is practically necessary to pre-treat the aluminum surface to remove the aluminum oxide prior to soldering / brazing. Various methods are used to remove the oxide layer depending on the subsequent use of the aluminum component. Called flux brazing, which consists of immersing the aluminum part in a bath of molten salt and brazing flux or exposing it to a brazing flux which removes the oxide layer from the preheated part. The method is widely used. Although the method is very effective at removing oxides, it is virtually impossible to avoid that the flux remains in the brazed seams and presents a significant corrosion problem. Further, commonly used brazing materials are:
It is an Al-Si alloy which is an alloy for high temperature brazing. When actually assembling a device to be brazed by placing parts at predetermined positions on the cladding tube, the assembly is then loaded into a vacuum furnace and heated. However, the melting temperature of this brazing alloy is not much lower than that of aluminum, 565 ° C to 5 ° C.
It is in the range of 95 ° C and consequently the temperature has to be controlled very precisely. However, there is a tendency for silicon from the braze alloy to vaporize and deposit on surfaces within the heating device containing the temperature sensor, which at best results in uncertain control. Therefore, this method is less reliable and less effective. The fluxless brazing process can be conveniently carried out under reduced pressure or in an inert atmosphere and is described in US Pat. Nos. 3,373,482 and 3,979,042. The general drawbacks of the above method are that it does not eliminate the need for cleaning / pretreatment operations, and that it requires higher temperatures to destroy the oxide layer or create cracks in the oxide layer. To do so. Therefore, the method described above is expensive and limited to special applications. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide coated aluminum shaped articles, particularly soldering materials suitable for carrying out fluxless solder / fluxless brazing at low temperatures. Or to provide a hollow shaped article, such as a tube, with a fluxless coating of brazing material. Another object of the present invention is to provide an aluminum shaped article which is primed with a soldering or brazing material which has improved corrosion resistance of the aluminum shaped article, i.e. an aluminum shaped article which is particularly suitable for a brazed aluminum heat exchanger. It is in. The shaped article is an angled piece, an I-shaped beam, an H-shaped beam or many other shaped articles forming elongated aluminum members or elongated aluminum elements with a cross-section such as a flange, in particular hollow shaped articles, such as internal partition walls as appropriate. It also means a tube having various cross-sectional shapes such as a circle or a flat oval which can have a large number of spaces. An aluminum shaped article according to the present invention provided by extruding aluminum into a desired shape and size, or by another method of forming a shaped article from aluminum, has the shaped article formed into another structural member in the next step. And a fluxless solder or a fluxless low temperature braze, eg a fluxless soldering substance or flux for soldering or brazing tubes with heat exchange fins in the production of heat exchangers It is covered with a metallic layer which constitutes the brazing substance. The soldering or brazing substance applied as a coating layer consists of a zinc-based alloy. The composite aluminum shaped article of the present invention has a surface to prevent oxidation of the surface of the shaped article before performing the step of forming aluminum in a desired shape, the next step of coating the outer surface of the aluminum shaped article with a metal layer. And a subsequent step of coating the outer surface of the shaped article with a metallic layer. The present invention will now be described in more detail with reference to the accompanying FIG. 1 which schematically illustrates an example and method and apparatus for providing the composite aluminum shaped article of the present invention. . Soldering applied to an aluminum shaped article according to the present invention /
The brazing coating is a zinc-based alloy, Al 1.0-1
A ZnAl alloy containing 0.0% by weight and, if necessary, 3.5% by weight or less of Cu and the balance being zinc is preferable. The alloy composition can be low temperature coated at about 385-420 ° C, resulting in low temperature and low cost brazing of the coated tubes and heat exchange fins during assembly of the heat exchanger. By selectively adding 3.0 to 6.0% by weight of Al, the wettability of aluminum by molten zinc is improved, and the combined use of Cu has sufficient ductility for a molded article with high tensile strength in the cold state. Form a film. Example 1 An aluminum drawn tube is mechanically cleaned of oxides on the surface of the tube in a protective atmosphere of nitrogen, and then the tube is directly, ie in a nitrogen protective atmosphere, with 5.8% by weight of Al and Cu 1.0
It was sent to a molten bath of a zinc alloy containing 5% by weight and the balance being mainly zinc. The temperature of the zinc bath was maintained at 450 ° C in order to prevent excessive zinc condensation on cold aluminum. After a contact time of 3 seconds, the tube was removed from the zinc bath and then cooled by sprinkling it with water. A zinc coated adherent layer could be achieved by bathing an aluminum draw tube as described above. An apparatus for producing a composite aluminum shaped article of the present invention as shown in FIG. 1 is a molding apparatus for molding an aluminum member (2) having a desired shape, such as an extruder (1), particularly an extruder ( Extruder for forming tubes from aluminum (3) fed to 1)
Including (1). The portion around the exit from the extrusion die (4) of the extruder and the end of the extruder on the extrusion die side where the gas is substantially sealed is the antioxidant chamber (5), and the inlet (6) An antioxidant gas, for example an inert gas such as nitrogen, is supplied through. The antioxidant chamber is sufficiently short so that the extruded shaped article does not cool below the desired coating temperature before passing through the chamber. An aluminum shaped article extruded from an antioxidation chamber is a device for coating the shaped article without exposing it to the atmosphere, i.e. to prevent oxidation of the aluminum shaped article, such as a soldering or brazing material. Sent to the bath (7). In a special embodiment of the device according to the invention, this is done by attaching the bath (7) directly to the outlet of the antioxidant chamber (5). In this particular embodiment, the aluminum shaped article coated as described above is then passed through a conventional wiper (8) to wipe excess coated metal from the shaped article and then cooled in ambient atmosphere, or Alternatively, the coated aluminum shaped article can be cooled by passing it through a cooling device such as a water quench device (not shown). The device described above for applying the coating is a bath through which the aluminum shaped article (2) passes directly.
This is shown as (7) in this specification. However, various known coating operations such as dipping, spray coating and vapor deposition can be used within the scope of the present invention. Between the time when the extruded shaped article leaves the extruder and the time when it is coated,
Care must be taken not to expose the shaped article to the ambient air or other oxidizing atmosphere. After exiting the extrusion die, the shaped article has a nascent fresh surface, is free of oxides on all surfaces, and holds a temperature of about 400 ° C to about 425 ° C. As a result, there is no need to heat the shaped article further. The resulting coated aluminum profile provides a corrosion resistant, leaktight tube that is particularly suitable for heat exchangers. Another advantageous feature imparted to the extruded shaped articles by the method of the present invention, as compared to conventional coating methods, is improved workability. In the conventional method, extruded aluminum shaped articles were extruded to remove the oxide film before applying the brazing flux to the extruded aluminum shaped article or before impregnating the molten salt and brazing flux baths. The shaped article is sufficiently preheated, but in that case, in the aluminum shaped article, crystal grains grow on aluminum, thereby reducing workability. In the method of the present invention, since the coating is performed immediately after the extrusion without the intermediate heating step, the time is insufficient for the crystal grains to grow completely. Example 2 A hollow aluminum tube having a flat oval cross section was extruded from a conventional extruder at a temperature of about 510 ° C., the tube being substantially gas-exposed to the extruder around the extruder extrusion die. Are sealed and communicated directly to the anti-oxidation chamber, that is, without exposure to the ambient atmosphere. The antioxidant chamber is filled with nitrogen and is about 70 cm to about 100 cm long. At the end of the oxidation chamber, the hollow aluminum tube is cooled to about 400 ° C., which is a good temperature for applying soldering or brazing material to the tube. The tube thus cooled is then filled with about 3.5-4.5% by weight of Al, C
Zn having a temperature of 380 to 382 ° C., in which u is about 2.5 to 3.5% by weight, Mg is about 0.05% by weight and the balance is Zn.
-Directly to a bath of Al fluxless soldering alloy, i.e. without exposure to ambient air. The tube coated as described above was then passed through a conventional wiper to wipe excess coating metal from the tube and then cooled in air. As described above, the pipe can be easily assembled by soldering parts to the thus completed pipe. For example, if the tube forms a radiator core tube, fins may be placed over the tube to provide about 400
The fins can be soldered to the tube by simply passing through a heating chamber at a temperature of ° C. There is no need to use a soldering flux and the soldering temperature is very low unlike the prior art, which means that the radiator can be assembled at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an example of an apparatus for producing the composite aluminum shaped article of the present invention. [Explanation of Codes] 1 Extruder 2 Aluminum member 5 Antioxidant chamber 7 Bath of brazing substance

   ────────────────────────────────────────────────── ─── Continuation of front page    (73) Patent holder 591237869               0240 OSLO, NORWAY (56) References JP-A-58-204169 (JP, A)                 JP 57-98798 (JP, A)                 JP-A-58-41692 (JP, A)                 JP-A-57-207141 (JP, A)                 JP-A-55-30349 (JP, A)

Claims (1)

(57) [Claims] Among the substantially aluminum molded while maintaining the absence of oxides or aluminum alloy surface
A composite aluminum shaped article suitable for manufacturing a heat exchanger, comprising an empty core and an outer coating layer of a non- fluxing agent soldering or brazing substance deposited on the surface of the core. Al is used as a soldering or brazing material.
1.0 to 6.0 wt% and Cu if required 3.
A zinc-based alloy containing 5% by weight, in the molten state, and in a molten state, to a thickness sufficient to serve as a soldering or brazing substance when the core is bonded to other members in the next step. Alternatively, while maintaining the surface of the core of the aluminum alloy on the new surface substantially in the absence of oxide, for soldering or brazing in an inert gas atmosphere.
A composite aluminum shaped article that is deposited after cooling to a temperature near the melting point of the edible substance . 2. The composite aluminum shaped article of claim 1, wherein Al is present in the 3.0-6.0 wt% zinc-based alloy. 3. Al is 3.5-4.5% by weight and Cu is 2.5-3.
The composite aluminum shaped article according to claim 1 or 2, which is present in a 5 wt% zinc-based alloy.