Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2001-11-06
2003-01-07
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C205S176000, C205S177000, C205S181000, C205S185000, C205S255000, C205S271000, C205S305000, C228S219000, C228S221000, C228S262100, C228S262510, C428S646000, C428S650000, C428S652000, C428S655000, C428S656000, C428S658000, C428S680000, C428S926000, C428S935000
Reexamination Certificate
active
06503640
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of manufacturing an assembly of components joined by brazing, comprising the steps of forming the components of which at least two components are dissimilar to each other, assembling the components into an assembly, brazing the assembly, and cooling the brazed assembly. The invention further relates to an assembly manufactured using the method of this invention.
DESCRIPTION OF THE RELATED ART
For the purpose of this invention multi-layered brazing sheet product is to be understood as a core alloy on at least one side coupled to a clad aluminium alloy. Typical clad aluminium alloys are those of the Aluminium Association (AA)4000-series alloys and having a Si content in the range of 2 to 18% by weight, and more preferably 5 to 14% by weight. The clad 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.
Electrochemical fuel cells convert a fuel and an oxidant into electricity, water and heat. Proton Exchange Membrane Fuel Cells (“PEMFC”) generally employ a membrane electrode assembly (“MEA”) which comprises an ion exchange membrane or solid electrolyte disposed between two electrodes formed of porous, electrically conductive sheet material. These types of fuel cell are showing great promise for use in automotive applications as well as so-called stationary applications. There are various requirements for the metals used in a fuel cell, such as good resistance to corrosion, high strength and low manufacturing costs. Furthermore, there is a requirement of good formability. For example by means of bending, to allow for the design and manufacturing of complex shaped components. Similar requirements apply for heat-exchanger devices. As a result of these requirements various dissimilar metals may be employed in manufacturing electrochemical fuel cells. These dissimilar metals or metal alloys need to be bonded to each other in such a manner that a strong and reliable bond is obtained. A suitable method of bonding metals to each other may be brazing processes.
Brazing, by definition, employs filler metal having a liquidus temperature above 450° C. and below the solidus temperature of the base metal. Brazing is distinguished from soldering by the melting point of the filler metal: solders melt below 450° C.
Controlled Atmosphere Brazing (“CAB”) and Vacuum Brazing (“VB”) are the two main processes used for industrial scale brazing. VB is essentially a discontinuous process and puts high demands on material cleanliness. Traditional CAB requires an additional process step prior to brazing as compared to VB, namely a brazing flux has to be applied prior to brazing. CAB is essentially a continuous process where if the proper brazing flux is being used high volumes of brazed assemblies can be produced. To obtain good brazing results the brazing flux has to be applied on the total surface of the assembly. This can cause difficulties with traditional powder or wet fluxes, like NOCOLOK (trade mark) brazing flux, and certain type of assemblies because of their design. 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 forming of the assembly parts. No additional brazing fluxing operations have to be carried out. Presently, only one process for fluxless brazing is used on an industrial scale. The material for this process can be for example standard brazing sheet made from an AA3000-series core alloy clad on both sides with a cladding of an AA4000-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, presumably exothermically, with the underlying aluminium. The nickel can be applied by using a shim of nickel between the 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 in an alkaline solution of aluminium brazing sheet are known from each of U.S. Pat. No. 3,970,237, U.S. Pat. No. 4,028,200, U.S. Pat. No. 4,164,454, and SAE-paper no. 880446 by B. E. Cheadle and K. F. Dockus. According to these documents, nickel or cobalt, or combinations thereof, are most preferably deposited in combination with lead. 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 pickling 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 sufficient nickel coverage to serve as nuclei for the plating 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.
However, the use of lead for manufacturing brazed assemblies and used in various market areas is undesirable, and it is envisaged that in the near future there might possibly even be a ban on lead comprising products or products manufactured via one or more intermediate processing steps comprising lead or lead-based components.
SUMMARY OF THE INVENTION
An object of the invention is to provide a method of manufacturing an assembly of dissimilar metal components joined by brazing, and comprising the steps of forming the components of which at least two components are dissimilar to each other and at least one of which is a multi-layered brazing sheet product, assembling the components into an assembly, brazing the assembly, and cooling the brazed assembly.
A further object of the invention is to provide a method of manufacturing an assembly of dissimilar components joined by brazing, and comprising the steps of forming the components of which at least two components are dissimilar to each and cooling the brazed assembly, and wherein one of the components is multi-layered brazing sheet which has improved formability characteristics.
A further object of the present invention is to provide a method of manufacturing an assembly of dissimilar metal components joined by brazing, where the components of at least the multi-layered brazing sheet product are lead-free.
In accordance with the invention in one aspect there is provided a method of manufacturing an assembly of components joined by brazing, comprising the steps of:
(i) forming said components of which at least one is made from a multi-layered brazing sheet product, said multi-layered brazing sheet product comprising a core sheet (a) having on at least one surface of said core sheet an aluminium clad layer (b), the aluminium clad layer being made of an aluminium alloy comprising silicon in an amount in the range of 2 to 18% by weight, preferably in the range of 5 to 14% by weight, a layer (c) comprising nickel on the outer surface of said aluminium clad layer, and a layer (d) comprising zinc or tin as a bonding layer between said outer surface of said aluminium clad layer and said layer comprising nickel;
(ii) forming at least one other component of a metal dissim
Wijenberg Jacques Hubert Olga Joseph
Wittebrood Adrianus Jacobus
Corus Aluminium Walzeprodukte GmbH
Koehler Robert R.
Stevens Davis Miller & Mosher LLP
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