Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2001-05-07
2002-05-07
Zimmerman, John J. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S652000, C428S654000, C428S935000, C205S255000, C228S262510
Reexamination Certificate
active
06383661
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of manufacturing an Al or Al alloy workpiece, such as a brazing sheet product, comprising the steps of providing an Al or Al alloy workpiece, pre-treating of the outersurface of the Al or Al alloy workpiece, and plating a metal layer comprising nickel onto the outersurface of the pre-treated workpiece. The invention also relates to a brazed assembly comprising at least one component made of the workpiece obtained by the method of this invention. The invention further relates to an aqueous plating bath for use in the method of this invention.
DESCRIPTION OF THE RELATED ART
For the purpose of this invention brazing sheet is to be understood as a core sheet, for example of aluminum or aluminum alloy, having on at least one side a brazeable aluminum alloy. Typical brazeable aluminum alloys useful as a clad layer are the Aluminum Association (AA) 4xxx-series alloys, typically having Si in the range of 2 to 18 weight %, and preferably in the range of 7 to 14%. The brazeable aluminum alloys may be coupled to the core alloy in various ways known in the art, for example by means of roll bonding, cladding, spray-forming or semi-continuous or continuous casting.
Controlled Atmosphere Brazing (“CAB”) and Vacuum Brazing (“VB”) are the two main processes used for industrial scale aluminum 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 furnace 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 result,, 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 aluminum 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 forming 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 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 aluminum clad alloy. If properly applied, the nickel reacts with the underlying aluminum. 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 aluminum 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 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 aluminum 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 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 the production of a suitable nickel and/or cobalt layer on brazing sheet has several disadvantages. The plating baths for electroplating are rather complex and due to the presence of lead comprising components such as salts thereof, these baths are much more environmentally unfriendly than plating baths comprising nickel- or cobalt-components alone. The use of lead for manufacturing products, such as automotive products, is undesirable and it is envisaged that in the very 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. A further disadvantage of the plating bath described in U.S. Pat. No. 4,028,200 is the considerable generation of ammonia fumes on the workshop floor due to the use of significant amounts of ammonia in the plating bath used.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of manufacturing an Al or Al alloy workpiece, comprising the steps of providing an Al or Al alloy workpiece, pretreating of the outersurface of the Al or Al alloy workpiece, and plating a metal layer comprising nickel onto the outersurface of the pre-treated Al or Al alloy workpiece, by which method a product is obtained having good brazeability and/or weldability without the mandatory addition of lead to the nickel-layer.
It is another object of the present invention to provide a method of manufacturing a brazing sheet product comprising the steps of (a) providing a sheet comprising a core sheet coupled on at least one surface of said core sheet to an aluminum clad layer, the aluminum clad layer being made of an aluminum alloy comprising silicon in an amount in the range of 2 to 18% by weight, (b) pre-treating of the outersurface of the aluminum clad layer, and (c) plating a metal layer comprising nickel onto the outersurface of the pre-treated aluminum clad layer, by which method a brazing sheet product is obtained having good brazeability without the mandatory addition of lead to the nickel-layer.
It is a further object of the present invention to provide a method of manufacturing an Al or Al alloy workpiece, ideally a brazing sheet product, the method comprising the steps of (a) providing an Al or Al alloy workpiece, in particular a brazing sheet comprising a core sheet coupled on at least one surface of said core sheet to an aluminum cl
Mooij Joop Nicolaas
Wijenberg Jacques Hubert Olga Joseph
Wittebrood Adrianus Jacobus
Corus Aluminium Walzprodukte GmbH
Stevens Davis Miller & Mosher LLP
Zimmerman John J.
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