Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2001-03-09
2002-05-21
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C205S183000, C205S185000, C228S219000, C228S221000, C228S262510, C428S648000, C428S650000, C428S658000, C428S680000, C428S935000, C428S936000
Reexamination Certificate
active
06391476
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a brazing sheet product in which a layer comprising nickel is plated onto a surface of a clad layer made of an Al—Si alloy containing Si in the range of 2 to 18 weight %. The invention also relates to a brazed assembly comprising at least one component made of the brazing sheet product and to a method of manufacturing an assembly of brazed components.
BACKGROUND OF THE INVENTION
For the purpose of this invention brazing sheet is to be understood as a core sheet, for example of aluminium or aluminium alloy, having on at least one side a brazeable aluminium alloy. Typical brazeable aluminium alloys useful as such a clad layer are the Aluminium Association (AA) 4xxx-series alloys, typically having Si in the range of 2 to 18 weight %. The brazeable aluminium alloys may be coupled to the core alloy in various ways known in the art, for example by means of roll bonding, cladding, or semi-continuous or continuous casting.
Controlled Atmosphere Brazing (CAB) and Vacuum Brazing (VB) are the two main processes used for industrial scale aluminium brazing. Industrial vacuum brazing has been used since the 1950's, while CAB became popular in the early 1980's after the introduction of the NOCOLOK (trade mark) brazing flux. Vacuum brazing is an essentially discontinuous process and puts high demands on material cleanliness. The disruption of the oxide layer present is mainly caused by the evaporation of magnesium from the clad alloy. There is always more magnesium present in the clad alloy then necessary. The excess magnesium condenses on the cold spots in the furnace and has to be removed frequently. The capital investment for suitable equipment is relatively high.
CAB requires an additional process step prior to brazing as compared to VB, since a brazing flux has to be applied prior to brazing. CAB is essentially a continuous process in which, if the proper brazing flux is being used, high volumes of brazed assemblies can be manufactured. The brazing flux dissolves the oxide layer at brazing temperature allowing the clad alloy to flow properly. When the NOCOLOK flux is used the surface needs to be cleaned thoroughly prior to flux application. To obtain good brazing results the brazing flux has to be applied on the total surface of the brazed assembly. This can cause difficulties with certain types of assemblies because of their design. For example, because evaporator type heat exchangers have a large internal surface, problems can arise because of poor access to the interior. For good brazing results the flux has to adhere to the aluminium surface before brazing. Unfortunately the brazing flux after drying can easily fall off due to small mechanical vibrations. During the brazing cycle, corrosive fumes such as HF are generated. This puts a high demand on the corrosion resistance of the materials applied for the furnace.
Ideally, a material should be available that can be used for CAB but does not have the requirements and defects of the brazing flux application. Such a material can be supplied to a manufacturer of brazed assemblies and is ready to use directly after shaping of the assembly parts. No additional brazing fluxing operations have to be carried out. Presently, only one process for flux-less brazing is used on an industrial scale. The material for this process can be for example standard brazing sheet made from an AA3xxx-series core alloy and clad on both sides with a cladding of an AA4xxx-series alloy. Before the brazing sheet can be used the surface has to be modified in such a way that the naturally occurring oxide layer does not interfere during the brazing cycle. The method of achieving good brazing is to deposit a specific amount of nickel on the surface of the clad alloy. If properly applied, the nickel reacts with the underlying aluminium. The nickel can be applied by using a shim of nickel between two parts to be joined or can be deposited by electroplating. When electroplating is used the adherence of the nickel should be sufficient to withstand typical shaping operations being used in for example heat exchanger manufacture.
The processes for nickel-plating of aluminium brazing sheet are known from each of U.S. Pat. Nos. 3,970,237, 4,028,200, 4,164,454, and SAE-paper No. 880446 by B. E. Cheadle and K. F. Dockus. According to each of these documents, nickel is preferably deposited in combination with lead. Alternatively, cobalt is deposited in combination with lead. It is known in the art that instead of nickel, cobalt or combinations thereof, also iron may be used. The lead addition is used to improve the wettability of the clad alloy during the brazing cycle. An important characteristic of these plating processes is that the nickel is preferentially deposited on the silicon particles of the clad alloy. To obtain sufficient nickel for brazing on the surface, the clad alloy should contain a relatively large number of silicon particles to act as nuclei for the nickel deposition. It is believed that to obtain sufficient nucleation sites before plating a part of the aluminium in which the silicon particles are embedded should be removed by chemical and/or mechanical pre-treatment. This is believed a necessary condition to obtain a sufficient nickel coverage to serve as nuclei for the wetting action of the brazing or clad alloy. On a microscopic scale the surface of the Si-containing cladding of the brazing sheet is covered with nickel globules.
Some other disclosures of Ni-plating found in the prior art literature will be mentioned below.
General textbook by Wernick and Pinner, “The Surface Treatment and Finishing of Aluminium and its Alloys”, 5th edition, Volume 2, pp.1023-1071. This textbook describes in general immersion processes for plating on aluminium.
Paper by the Bureau of Mines Technology, “Aluminium Soft-Soldering”, 2301 N.T.I.S. Tech Notes (manufacturing), 1985, January No.1G, Springfield, Va., USA, pp.12-13. This paper describes a method of manufacturing aluminium for soft-soldering wherein the aluminium surfaces are joined by conventional tin-lead solder. The method includes firstly cleaning the aluminium surface carefully prior to the zinc application. Secondly a thin zinc coat is deposited and subsequently electroplated with an alloy of nickel-copper. After the nickel-copper plating has been accomplished, soldering using normal procedures can be accomplished.
FR-A-2,617,868 describes a method of manufacturing aluminium product with a brazeable surface coating of tin or a tin-bismuth alloy, wherein the product is provided with an intermediate layer. This intermediate layer is composed of a first layer of zinc and a second layer of nickel, which nickel has been deposited by electrolysis from a neutral electrolyte. Here, the underlying aluminium or aluminium alloy is not melted in the brazing process.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a brazing sheet product having a core sheet and filler material, to be melted during brazing, said filler material comprising a clad layer of an Al—Si alloy and a nickel layer on the clad layer, in which there is good adhesion of the nickel layer to the clad layer.
It is an object of the invention to provide a brazing sheet product which can be used in a vacuum brazing process as well as in an controlled atmosphere brazing process in the absence of a brazing-flux, but ideally suitable for CAB process in the absence of a brazing-flux.
It is another object of the invention to provide a method of manufacturing an assembly of brazed components using the brazing sheet product of this invention.
In accordance with the invention in one aspect there is provided a brazing sheet product having a core sheet (
1
) made of an aluminium alloy, having at least one of the surfaces of said core sheet clad with an aluminium clad layer (
2
), and a layer (
3
) comprising nickel on the outersurface of at least one of said aluminium clad layer or layers (
2
), and wherein there is a layer (
4
) comprising zinc or tin as a bonding layer between said outersurfa
Wijenberg Jacques Hubert Olga Joseph
Wittebrood Adrianus Jacobus
Corus Aluminium Walzprodukte GmbH
Koehler Robert R.
Stevens Davis Miller & Mosher LLP
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