Metal fusion bonding – Process – With pretreating other than heating or cooling of work part...
Reexamination Certificate
2001-12-03
2003-11-18
Elve, M. Alexandra (Department: 1725)
Metal fusion bonding
Process
With pretreating other than heating or cooling of work part...
C228S214000, C228S217000, C228S223000, C228S224000, C228S207000, C148S023000, C148S024000, C148S025000, C148S026000
Reexamination Certificate
active
06648212
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation of international application Ser. No. PCT/EP00/04777, filed May 25, 2000, designating the United States of America, the entire disclosure of which is incorporated herein by reference. Priority is claimed based on Federal Republic of Germany patent application No. DE 199 25 301.3, filed Jun. 2, 1999.
BACKGROUND OF THE INVENTION
The invention relates to a process for depositing an aluminum-silicon alloy on aluminum or aluminum alloys, the resulting components which are obtained, and a brazing process.
Techniques for brazing components made of aluminum or aluminum alloys are known. The components are joined with the aid of a brazing metal and a flux while being heated. The brazing metal can either be added separately or components plated with brazing metal can be used. The preferred fluxes are potassium fluoroaluminate and/or cesium fluoroaluminate.
U.S. Pat. No. 4,906,307 discloses a process for brazing components made of an aluminum alloy. Brazing metal plated components are used with a flux comprising 70 to 90 wt % potassium hexafluorosilicate and 30 to 10 wt % aluminum trifluoride, with the addition of lithium fluoride and sodium fluoride.
U.S. Pat. No. 5,785,770 (=EP 810,057) discloses fluxes for brazing aluminum, which can contain up to 20 wt % of a metal fluorosilicate (in addition to a fluoroaluminate complex, e.g., potassium tetrafluoro-aluminate). Solderless brazing is also possible with certain alkali metal fluorosilicates within certain weight ranges.
U.S. Pat. No. 6,019,856 (=DE 196 36 897) discloses that solderless brazing of aluminum components is possible using a flux containing 6 to 50 wt % potassium hexafluorosilicate and, in addition, potassium fluoroaluminate.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a process that can be used to deposit an aluminum-silicon alloy on aluminum or aluminum alloys (or corresponding components) without a brazing metal having to be applied by roller plating.
A further object of the invention is to provide a process for brazing aluminum or aluminum alloy components where a separate addition of a brazing metal is not necessary.
An additional object of the invention is to provide aluminum or aluminum alloy components which can be brazed without a separate addition of brazing metal.
These and other objects are attained in accordance with the present invention by providing a process for producing a component of aluminum or an aluminum alloy with a coating comprising alkali metal hexafluorosilicate, comprising applying alkali metal hexafluorosilicate or a mixture of alkali metal hexafluorosilicate and up to 5 wt % of a fluoroaluminate, relative to the alkali metal hexafluorosilicate, to the component by a dry or a wet fluxing process.
In accordance with a further aspect of the invention, the objects are achieved by providing a process for producing a component of aluminum or an aluminum alloy with a coating that comprises an aluminum-silicon alloy, comprising applying alkali metal hexafluorosilicate or a mixture of alkali metal hexafluorosilicate and up to 5 wt % of a fluoroaluminate, relative to the alkali metal hexafluorosilicate, to the component, and heating the component until the aluminum-silicon alloy is formed.
The objects are achieved in yet another aspect of the invention by providing a process for joining components of aluminum or aluminum alloys, comprising coating the components with a coating comprising alkali metal hexafluorosilicate, placing the components in contact, and brazing the components together.
In accordance with a still further aspect of the invention by providing a process for joining components of aluminum or aluminum alloys, comprising coating the components with a coating comprising an aluminum-silicon alloy, placing the components in contact, and brazing the components together.
Another aspect of the invention fulfills the objects thereof by providing components of aluminum or an aluminum alloy coated with a coating comprising at least one alkali metal hexafluorosilicate.
The objects of yet another aspect of the invention are achieved by providing components of aluminum or an aluminum alloy coated with a coating comprising an aluminum-silicon alloy.
The process according to the invention for producing aluminum or an aluminum alloy with a coating that comprises an aluminum silicon alloy includes coating the aluminum or an aluminum alloy with alkali metal hexafluorosilicate and heating the coated aluminum or aluminum alloy until the aluminum silicon alloy forms.
Preferred alkali metal hexafluorosilicates include potassium hexafluorosilicate, cesium hexafluorosilicate or mixtures thereof. Potassium hexafluorosilicate is especially preferred.
It is particularly preferred to deposit the alkali metal fluorosilicate with a weight per unit area of 30 to 60 g/m
2
. This can be accomplished, for example, by electrostatically depositing the dry hexafluorosilicate powder, or the deposition can be effected from an aqueous phase (i.e., from a solution or suspension of the silicate). If the weights per unit area are lower, a thinner alloy coating results, if they are higher the alloy coating is thicker. Alloy formation for joining components occurs even at weights per unit area starting from 5 g/m
2
. For most applications, a weight per unit area of at least 20 g/m
2
to 60 g/m
2
is more advantageous because correspondingly more alloy metal will then be available for a stable brazing joint (brazing seam) of the assembly.
The alkali metal hexafluorosilicate may be applied to the material to be joined in the form of a slurry in water or in organic solvents or also in the form of a paste. These slurries advantageously contain 15 to 75 wt % of hexafluorosilicate. In addition to water, organic liquids may also be used, particularly alcohols, such as methanol, ethanol, propanol or isopropanol, or polyols. Other suitable organic liquids include ether, e.g., diethylene glycol monobutyl ether, ketones such as acetone, esters of monobasic alcohols, diols or polyols. An example of a suitable binder for use in paste form is ethyl cellulose. Film formers, which typically are polymers that are soluble in organic solvents such as acetone, can be used to apply the hexafluorosilicate to the component. After evaporation of the solvent they form a firmly adhering film. Suitable polymers include, for example, acrylates and/or methacrylates.
A material with a fine grain spectrum is particularly suitable for wet fluxing. A material with a coarser grain spectrum is particularly well suited for dry fluxing. A material with a desired fine or coarser grain spectrum can be produced by means of known methods. Typically, an alkali lye is used with hexafluorosilicic acid (precursors are also suitable, e.g., alkali carbonate). The way to influence the grain size is generally known. Smaller crystals are created at a low reaction temperature, faster reaction rate, faster drying and stronger movement of the reaction mixture. Larger crystals are produced at a higher temperature, through standing over the mother liquor, little movement of the reaction mixture and slower mixing of the reactants.
Hexafluorosilicate, or mixtures containing it, which essentially have particles of a grain size of 8 to less than 20 &mgr;m, e.g., up to 18 &mgr;m, are very suitable for dry fluxing. For instance, K
2
SiF
6
was produced with X
D10
=2.04 &mgr;m, X
D50
=6.94 m and X
D50
=12.35 &mgr;m and an average grain diameter of 6.94 &mgr;m. Another product was finer still, with an X
D50
of 4.6 &mgr;m. This grain size data relates to the average grain size diameter for 50% of the particles (X
D50
) as determined by laser diffraction. Fluxes essentially having particles with a grain size ranging from 1 to 12.5 &mgr;m can be particularly well applied as a slurry in water or organic liquids using the wet fluxing method.
The aluminum or aluminum alloy is preferably heated to a temperature ranging from 400 to 610° C., preferably 540 to 610° C
Becker Andreas
Frehse Joachim
Seseke-Koyro Ulrich
Crowell & Moring LLP
Edmondson L.
Elve M. Alexandra
Solvay Pharmaceuticals GmbH
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