Stock material or miscellaneous articles – All metal or with adjacent metals – Having composition – density – or hardness gradient
Reexamination Certificate
1999-08-20
2002-12-17
Zimmerman, John J. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having composition, density, or hardness gradient
C428S615000, C428S654000, C164S096000, C228S235200
Reexamination Certificate
active
06495269
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a metallurgical product comprising a core, on at least one side of the core an interlayer bonded to the core and a cladding bonded to the interlayer, and to a method of producing such a metallurgical product. Particularly but not exclusively, the invention relates to such a metallurgical product in the form of a brazing sheet or a brazing plate, and also to a brazed assembly including the metallurgical product as at least one component.
DESCRIPTION OF THE PRIOR ART
A metallurgical product comprising a core alloy with on at least one side an interlayer and at least one cladding layer, which is bonded to the interlayer has been obtained by roll cladding the different layers together. U.S. Pat. No. 2,821,014 typically describes this method and product. A disadvantage of roll cladding is the handling and processing, e.g. rolling and surface treatment, of all the different types of layers. Consequently roll cladding is time consuming and is expensive.
Direct adhesion of clad layers to a core layer to make brazing sheet by rolling is also known, e.g. from EP-A-326337.
U.S. Pat. No. 5,476,725 describes a method of manufacture of a composite brazing product having an aluminium core and at least one clad layer. The clad layer or layers in band form are fed to opposed cooled rolls simultaneously with molten core material, which is solidified in contact with the clad layer or layers. It is stated that, despite the fact that the clad layer melts at a lower temperature than the core, it does not melt when it contacts the molten core material in the roll bite. Subsequently the composite is cold-rolled. In one variant of the method, interlayers of zinc are thermally sprayed onto the clad bands as they are unwound from coils prior to the contact of the bands with the molten core material. A similar process is described in JP-A-56-091970.
JP-A-61-111745 describes a method of making a material intended for brazing to another member to provide a corrosion and wear resistant layer. Brazing metal is solidified as a band on one roll of a pair of rolls, and a second molten metal in the form of a Co alloy containing ceramic fibres is solidified onto the band at the nip of the two rolls.
Some further prior art relating generally to casting processes is discussed below.
SUMMARY OF THE INVENTION
An object of the invention is to provide a metallurgical product of the type described above which can be produced at lower costs compared to the existing products.
According to the invention in a first aspect there is provided a metallurgical product comprising a core, on at least one side of the core an interlayer bonded to the core and a cladding bonded to the interlayer, characterized in that said core and interlayer are a compositely cast material having at their mutual interface a bond formed by their simultaneous solidification from contacting melts of their respective materials in a casting process.
According to the invention in a second aspect there is provided a metallurgical product comprising a core, on at least one side of the core an interlayer bonded to the core and a cladding bonded to the interlayer, characterized in that said core and interlayer are a compositely cast material having at their mutual interface a bonding zone formed by mutual mixing of their respective compositions in the molten state prior to their solidification in a casting process.
The metallurgical product in accordance with this invention is therefore characterized in that the core and the interlayer are bonded in a casting process in which the core and the interlayer are solidified simultaneously from the molten state as to form a composite material. Subsequently, the clad layer is applied. The core alloy and the interlayer alloy are simultaneously solidified from the molten state during a continuous or semicontinuous casting process in such a manner that the obtained solidified core is covered at least on one side, and preferably on the whole outer surface, with the interlayer alloy so as to form a compositely cast material. Such a compositely cast material is obtained at significant lower costs than a conventional roll clad composite material, because scalping of the core alloy and the steps of casting, rolling and surface treatment of the interlayer prior to bonding onto the core are no longer required.
A further advantage of the invention is the excellent strong bonding of the interlayer and the core, due to their simultaneous solidification in contact with each other. This contact of the two molten materials with consequent mixing at their interface produces in the solidified product a narrow interface bonding zone which has a metallurgical nature characteristic of the product and method of this invention. Such an interface bonding zone is readily recognizable by the expert in the product, and is different from and distinguishable from the prior art products described above in which one or both of two layers is solid prior to the bonding.
In the metallurgical product in accordance with the invention, when in plate or sheet form, at least on one side of the core the interlayer thickness is preferably 1-30% of the thickness of the compositely cast material. In the case of a product of the invention in the form of a bar, rod or wire, the interlayer is likewise preferably 1-30% of the radius (half width) of the compositely cast material. This allows for a great flexibility in thickness of the interlayer, this flexibility being significantly larger compared to roll cladding.
It is an advantage obtainable with the invention that the core and the interlayer are essentially free from oxides at their interface. An important advantage of such a compositely cast material compared to roll bonded material is the improved bonding between the core and the interlayer due to the absence of oxides or oxide-compounds at their interface. Such compounds can be present in roll bonded material even after proper surface treatment prior to roll bonding.
In the metallurgical product in accordance with the invention the cladding may have a solidus temperature different from that of the core and more preferably the cladding has a solidus temperature lower than that of the core. The metallurgical product in these cases embodiments is very suitable for brazing sheet applications.
While the invention is in principle applicable to a wide range of metals, preferably the core is an aluminium alloy, which makes the product suitable for a wide range of applications, e.g. brazing sheet. Depending on the required final properties for the application or use of the metallurgical product, one may select a heat treatable aluminium alloy as the core alloy, e.g. AA2xxx, AA6xxx or AA7xxx-series alloys, or a non-heat treatable aluminium alloy, e.g. AA3xxx or AA5xxx-series alloys.
When the cladding is a brazing alloy, preferably it is an aluminium brazing alloy. Depending on the final use or application of the metallurgical product of the invention, also another cladding can be applied, e.g. AA1xxx-series alloys to obtain a mirror like surface finish, or the application of zinc or a zinc alloy or a zinc containing aluminium alloy to improve corrosion resistance.
Preferably the interlayer has a corrosion potential different from that of the core, and more preferably lower than that of the core. In this case the interlayer acts as an anodic interlayer and improves the corrosion resistance of the metallurgical product. Depending on the type of core alloy and the application or use of the metallurgical product one may prefer an interlayer comprising a heat treatable aluminium alloy, e.g. AA2xxx, AA6xxx or AA7xxx-series alloys, or an interlayer comprising non-heat treatable aluminium alloys, e.g. AA1xxx, AA3xxx or AA5xxx-series alloys. Alternatively the use of zinc or a zinc alloy or a zinc-containing aluminium alloy is possible.
Preferably the interlayer constitutes, in known manner, a diffusion barrier between the cladding and the core. In this case the interlayer shields the core material from elements coming from the
Brandner Dietmar Franz
Haszler Alfred Johann Peter
Corus Aluminium Walzprodukte GmbH
Stevens Davis Miller & Mosher LLP
Zimmerman John J.
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