This application claims priority to European application No. 14164856.8
filed April 16, 2014, the whole content of this application being incorporated
herein by reference for all purposes.
The present invention concerns a process for brazing of aluminum alloys
containing magnesium, and a suitable flux.
It is well known in the art that brazing of aluminum parts can be performed
utilizing fluxes based on alkali metal fluoroaluminates. Fluxes of this type are
generally considered to be noncorrosive. For example, a flux is described in US
patent 4,579,605 which comprises 5 % to 95 % by weight of K2AIF 5 or its
hydrate; the remainder is KAIF 4 . The flux may be prepared by dissolving
aluminum hydroxide in hydrofluoric acid having a concentration of 5 % to 40 %
by weight to give an A1:F ratio of 1:4 to 1:4.5 and neutralizing this mixture with
potassium carbonate or hydroxide to give a A1:K ratio of 1:1-1.5.
The addition of magnesium to aluminum to form aluminum magnesium
alloys improves the formability, corrosion resistance and tensile strength of parts
made therefrom. On the other hand, brazing of such alloys with potassium
fluoroaluminate based fluxes becomes more and more difficult with increased
Mg content of the alloy. It was already known to add cesium fluoroaluminate to
fluoroaluminate based fluxes to improve the brazing properties of the flux in
view of aluminum magnesium alloys. See, for example, CA 1,239,525.
Japanese patent application JP-S6 199569 discloses a method for brazing of
aluminum using a flux which contains, on one hand, 73.6 % by weight of KAIF 4
and 0.2 to 18.4 % by weight of KF, and, on the other hand, 0.1 to 8.0 % by
weight, of one or more additives of the group consisting of LiF, NaF and CaF2.
According to the examples, the content of KF in the flux used is from 9.8 to 11
% by weight.
Nevertheless, the process and the fluxes for brazing of parts made from
aluminum magnesium alloys are still open for improvements.
According to one aspect, the invention relates to a process for brazing of
parts of aluminum alloy comprising equal to or more than 0.5 % by weight of
magnesium in the interface, comprising a step of applying a brazing flux to at
least one of parts to be joined, a step of assembling the parts to be joined and a
step of heating the parts to be joined to a temperature of equal to or higher
than 450°C to provide brazed joint parts, wherein the brazing flux comprises
equal to or more than 65 % by weight, preferably equal to or more than 80 % by
weight, relative to the total weight of the brazing flux, of a first component and
equal to or more than 3 % by weight of a second component, relative to the total
weight of the brazing flux, with the proviso that the first component and the
second component are not identical, and wherein the first component is selected
from monoalkali tetrafluoroaluminates selected from KA1F4, CsAlF and
mixtures thereof, and the second component is at least one alkaline or alkaline
earth metal compound selected from the group consisting of KA1F , CsAlF ,
Li3AlF6, CaF2, CaC0 3, MgF2, MgC0 3, SrF2, SrC0 3, BaF2, BaC0 3, and
mixtures of two or more thereof; preferably with the proviso that, if at least one
compound selected from the group consisting of LiF, NaF and CaF2 are
comprised, the content of free KF is lower than 0.1 % by weight, relative to the
total weight of the brazing flux.
The proviso that, if at least one compound selected from the group
consisting of LiF, NaF and CaF2 are comprised, the content of free KF is lower
than 0.1 % by weight, relative to the total weight of the brazing flux, relates to
the presence of effective amounts; preferably, the proviso relates to the presence
of at least one compound selected from the group consisting of LiF, NaF and
CaF2 if the sum of all compounds of this group is equal to or greater than 0.1 %
by weight, more preferably, lower than 0.05 % by weight. " The term "free", e.g.
in connection with free KF, denotes the binary salt, e.g. KF which is present as
such, thus is not complexed, e.g. in the form of potassium fluoroaluminates.
Likewise, the term "free" also denotes binary LiF, CaF2 or NaF, which is not
complexed. In a preferred embodiment, the content of free KF is lower than 0.1
% by weight, and more preferably, lower than 0.05 % by weight, relative to the
total weight of the flux, in all embodiments. In a still more preferred
embodiment, the sum of the content of free KF and of free or complexed NaF is
lower than 0.1 % by weight, more preferably, lower than 0.5 % by weight, in all
embodiments. In another preferred embodiment, the content of free KF is lower
than 0.1 % by weight, relative to the total weight of the brazing flux if at least
one compound selected from the group consisting of LiF, NaF and CaF 2 are
comprised in the flux. Generally, in this embodiment, the at least one compound
selected from the group consisting of LiF, NaF and CaF2 is not complexed, also
denoted as free LiF, NaF or CaF2.
In certain other embodiments, the sum of the content of free KF, free or
complexed NaF and free LiF is lower than 0.1 % by weight, more preferably,
lower than 0.05 % by weight, relative to the total content of the flux. In another
embodiment, the flux is essentially free, and preferably, free, of LiF, NaF and
CaF2.
Preferably, the brazing flux comprises equal to or more than 80 % by
weight, relative to the total weight of the brazing flux, of CsAlF4, or, equal to or
more than 80 % by weight of KA1F4, relative to the total weight of the brazing
flux, or both KA1F4 and CsAlF , the sum of which is equal to or more than 80 %
by weight.
The term "at the interface" is now explained. If two parts of Al or Al-Mg
alloy are assembled to be brazed, the areas forming a joint are called "interface".
The Mg percentage of both parts is added,and the result of the addition provides
the percentage of Mg at the interface. For example, if two parts with 0.5 % by
weight of Mg are assembled, the content of Mg at the interface is 1 % by weight.
If a part comprising 1 % by weight of Mg is assembled with a part containing
no Mg, the Mg content at the interface is also 1% by weight.
The upper limit of the Mg content at the interface depends from the brazing
conditions. For example, if flame brazing (i.e. providing heat with an open
flame) is used to braze the parts, the Mg content may be up to 2 % by weight at
the interface, and even higher. If brazing is performed according to the
Controlled Atmosphere Brazing, i.e. heat is provided by electrical installations
and the rise of temperature of the parts is slower than when a flame is used,
the Mg content at the interface is preferably equal to or lower than 1.5 % by
weight, more preferably, equal to or lower than 1.4 % by weight.
The brazing temperature is dependent on the nature of the flux. If the first
component is predominantly or completely constituted by CsAlF , the brazing
temperature may be as low as 450°C. If the first component is predominantly or
completely constituted by KA1F , the brazing temperature preferably is equal to
or greater than 560°C. Here, the upper limit is often 610 to 625°C.
In a preferred embodiment, the first component consists essentially
of KA1F4 .
Preferably, the second component is selected from the group consisting
of CsAlF , Li3AlF6, CaF2, MgF2, SrF2, BaF2, and mixtures of two or more
thereof.
If a Mg containing compound is present, the flux preferably contains less
than 1%by weight of the sum of Mg containing compounds such as MgF2 or
MgC0 3.
More preferably, the second component is selected from the group
consisting of CsAlF4, Li3AlF6, BaF2, and mixtures of two or more thereof.
Especially preferably, the second component comprises CsAlF and Li3A1F6,
and optionally also BaF2.
In certain embodiments, the sum of the content of free KF, free or
complexed NaF, free LiF and CaF2 is lower than 0.1 %by weight, more
preferably, lower than 0.05 %by weight, relative to the total content of the flux.
Preferably, the second component is present in an amount of equal to or
greater than 2 %by weight, more preferably, in an amount of equal to or greater
than 3 %by weight, and often, in an amount of equal to or greater than 5 %by
weight.
Preferably, the second component is present in an amount of equal to or
less than 30 %by weight, more preferably, in an amount of equal to or less than
20 %by weight. If two or more of said components mentioned above belonging
to the group of second components is present, their total amount is equal to or
less than 30 %by weight.
If present, CaF2 or CaC0 3 is preferably contained in an amount of equal to
or more than 5 %by weight. If present, MgF2 or MgC0 3 is preferably contained
in an amount of equal to or more than 5 %by weight. If present, SrF2 or SrC0 3
is preferably contained in an amount of equal to or more than 5 %by weight. If
present, BaF2 or BaC0 3 is preferably contained in an amount of equal to or more
than 5 %by weight. If mixtures of fluorides and/or carbonates are present, then
their total content is preferably equal to or more than 5 % by weight.
If present, CsAlF is preferably present in an amount of equal to or more
than 1%by weight.
If present, Li3AlF6 is preferably present in an amount of equal to or greater
than 1%by weight.
If present, CaF2 or CaC0 3 is preferably contained in an amount of equal to
or less than 20 % by weight. If present, MgF2 or MgC0 3 is preferably contained
in an amount of equal to or less than 30 % by weight. If present, SrF2 or SrC0 3
is preferably contained in an amount of equal to or more than 30 %by weight. If
present, BaF2 or BaC0 3 is preferably contained in an amount of equal to or less
than 30 % by weight. If mixtures of fluorides and/or carbonates are present, then
the sum of their content is preferably equal to or less than 30 % by weight.
If present, CsAlF 4 is preferably present in an amount of equal to or less
than 10 % by weight, more preferably, equal to or less than 5 % by weight.
If present, Li3AlF6 is preferably present in an amount of equal to or less
than 8 % by weight.
Especially preferred ranges are : CaF2 or MgF2 in an amount of from 5
to 20 % by weight, SrF2 or BaF2 in an amount of from 10 to 20 % by weight; a
combination of SrF2 or BaF2 in a total amount of from 10 to 20 % by weight;
CsAlF in an amount of from 1 to 5 % by weight; Li3AlF6 in an amount of from
1 to 8 %by weight; CsAlF in an amount of from 1 to 5 % by weight
and Li3AlF6 in an amount of from 1 to 8 % by weight.
More preferably, the second component is selected from the group
consisting of CsAlF , Li3AlF6, BaF2, and mixtures of two or more thereof; and
still more preferably, the second component is a composition consisting
of CsAlF and Li3AlF6; and optionally additionally BaF 2.
Highly preferred brazing fluxes are used which comprise, or consist of,
KA1F in a range of from equal to or greater than 80 to equal to or lower
than 98 % by weight, CsAlF in a range of from equal to or more than 1 % by
weight to equal to or less than 10 % by weight, Li3AlF6 in a range of from equal
to or more than 1% by weight to equal to or less than 10 % by weight, and BaF2
in a range of from 0 to equal to or less than 15 % by weight.
Preferred brazing fluxes are given in tables 1 to 4.
Table 1 : Preferred brazingfluxes for use in Al-Mg alloy brazing
"AEF 2" denotes alkaline earth metal fluoride.
If desired, KA1F4 can be introduced in the form of commercially available
mixtures with K2AlFs or its hydrates. Such a mixture which comprises
approximately 80 % by weight of KA1F4 and approximately 20 % by weight
of K2A1F5 or its hydrates, is available from Solvay Fluor GmbH under the
tradename Nocolok ®. Preferred mixtures of this kind are given in table 2.
Table 2 : Preferred brazingfluxes for use in Al-Mg alloy brazing with a mixture
of KA1F4 and K2A1F5 (4:1 w/w).
KA1F4 / K2A1F5 mixture AEF2 CsAlF 4 Li3AlF6
[ weight] [ weight] [ weight] [ weight]
85 CaF2 15 — —
85 MgF2 15 — —
85 SrF2 15 — —
85 BaF2 15 — —
90 CaF2 10 — —
90 SrF2 10 — —
90 BaF2 10 — —
84 BaF2 10 2 4
93 — 4 3
94 — 2 4
83 BaF2 10 4 3
60 KA1F4 30 - —
BaF2 10
If desired, KA1F4 and Li3AlF6 can be introduced in the form of
commercially available mixtures with K2AlFs or its hydrates. Such a mixture
which comprises approximately 77 % by weight of KA1F4 , approximately 19 %
by weight of K2AlFs or its hydrates, and approximately 4 % by weight
of L 13AIF 6 is available from Solvay Fluor GmbH under the tradename
Nocolok ® Li. Preferred mixtures of this kind are given in table 3.
Table 3 : Preferred brazingfluxes for use in Al-Mg alloy brazing with a mixture
ofKAlF 4, K2AIF5 andLi AlF6 (77:19:4 w/w/w)
If desired, KA1F4 and CsAlF 4 can be introduced in the form of
commercially available mixtures with K2AlFs or its hydrates. Such a mixture
which comprises approximately 79 % by weight of KA1F4 , approximately 19 %
by weight of K2AlFs or its hydrates, and approximately 2 % by weight of
CsAlF 4 is available from Solvay Fluor GmbH under the tradename Nocolok ®-
Cs. Preferred mixtures of this kind are given in table 4.
Table 4 : Preferred brazingfluxes for use in Al-Mg alloy brazing with a mixture
ofKAlF 4, K2AIF5 and CsAlF4 (79:19:2 w/w/w)
According to one preferred embodiment, the first component is KAIF 4 in
an amount of equal to or greater than 80 % by weight relative to the total weight
of the brazing flux, and the second component is present in an amount of equal to
or greater than 5 % by weight, relative to the total weight of the brazing flux, and
is selected from the group consisting of CsAlF, Li3AlF6 anda mixture of both;
additionally, CaF2, MgF2, SrF2, BaF2, and mixtures of two or more thereof may
be present.
If the flux does not consist of said first and second components, the
balance to 100 % by weight are constituted from other fluxes known in the art,
preferably, K2AlFs or K2AlFs-H 20 . Preferably, the content of K3A1F6 is lower
than 1 % by weight, including 0 % by weight.
It is preferred that KA1F4 is essentially the only potassium fluoroaluminate
in the brazing flux. The total content of K2AlFs, its hydrate and of K3A1F6, if
present, is preferably equal to or lower than 5 % by weight, relative to the total
weight of the brazing flux.
According to one embodiment, the brazing flux consists of said first and
second components.
The brazing process can be performed applying the brazing flux according
to the dry fluxing method. The flux may, for example, be provided to the surface
of the items to be brazed by pneumatic transport and adheres mechanically to the
surface of the items to be brazed.
If the brazing flux is not applied according to the dry fluxing method, it is
applied according to the wet fluxing method. In the wet fluxing method, a
brazing flux composition is applied which contains the flux and additives; liquid
carriers like water or alcohols are considered as additives in the present
invention.
The brazing flux composition can, for example, be sprayed onto at least
one of the parts to be joined, it can be painted on their surface with brushes, or it
can be applied by immersing parts into liquid composition.
According to one embodiment, the brazing flux composition of the present
invention is applied according to the wet fluxing method and contains the
brazing flux suspended in water, water-free organic liquids or aqueous organic
liquids. Preferred liquids are those that have a boiling point at ambient pressure
( 1 bar abs) of equal to or lower than 350°C. The term "suspended in water" does
not exclude that a part of the flux composition is dissolved in the liquid; this may
be the case especially when water or aqueous organic liquids are contained.
Liquids that are preferred are deionized water, mono-, di- or tribasic aliphatic
alcohols, especially those with 1 to 4 carbon atoms, e.g. methanol, ethanol,
isopropanol, or ethylene glycol, or glycol alkyl ethers, wherein alkyl preferably
denotes linear aliphatic CI to C4 alkyl or branched C3 to C4 alkyl. Non-limiting
examples are glycol monoalkyl ethers, e.g. 2-methoxyethanol or diethylene
glycol, or glycol dialkyl ethers, for example, dimethyl glycol (dimethoxyethane).
Mixtures comprising two or more of the liquids are also suited very well.
Isopropanol or mixtures containing isopropanol are especially suitable.
In a preferred embodiment, the composition comprising the brazing flux
and a liquid also contains further additives which improve the brazing flux
composition properties.
In an especially preferred embodiment the brazing flux is present in the
form of a flux composition wherein the flux is suspended in a liquid which also
contains a binder. Binders improve, for example, the adhesion of the brazing
flux after its application on the parts to be brazed. Thus, the wet flux method
using a brazing flux composition comprising the brazing flux, binder and water,
organic liquid or aqueous organic liquid is a preferred embodiment of the brazing
process of the present invention. The liquid serves as solvent for some additives
or as a carrier to disperse the flux or other insoluble components of the
composition.
Suitable binders can be selected for example from the group consisting of
organic polymers. These binders form a coating on aluminum parts or aluminum
alloy parts when they are physically dried (i.e., they form a solid coating after the
liquid is removed by evaporation), or when they are chemically dried (they form
a solid coating e.g. under the influence of chemicals, e.g. oxygen or light which
causes a cross linking of the molecules, or by a thermal treatment which
provokes cross linking). Both mechanisms may occur simultaneously. Suitable
polymers include polymers which are present in the composition in the form of a
dispersion of solid particles dispersed in the liquid, and polymers which are
present in the form of a solution dissolved in the liquid. Highly suitable binders
are polyolefines, e.g. butyl rubbers, polyurethanes, resins, phthalates,
polyacrylates, polymethacrylates, vinyl resins, epoxy resins, nitrocellulose,
polyvinyl acetates or polyvinyl alcohols. Brazing flux compositions containing
water as a liquid and water-soluble polymer or a polymer dispersed in water, for
example, polyvinyl alcohol or polyurethane, are especially suitable because they
have the advantage that, during the brazing process, water is evaporated instead
of possibly flammable organic liquids.
The compositions may include other additives which improve the
properties of the composition, for example, suspension stabilizers, surfactants,
especially nonionic surfactants, e.g. Antarox BL 225, a mixture of linear C8
to CIO ethoxylated and propoxylated alcohols, thickeners, e.g. methyl butyl
ether, thixotropic agents, e.g. gelatine or pectines, or a wax as described
in EP-A 1808264.
The content of the brazing flux in the total brazing flux composition
(including, for example, liquid or liquids, thixotropic agents, surfactants and
binders, if present) generally is equal to or greater than 0.75 % by weight.
Preferably, the content of the brazing flux in the flux composition is equal to or
greater than 1%by weight. More preferably, the brazing flux content in the
brazing flux composition is equal to or greater than 5 % by weight, very
preferably, equal to or greater than 10 %by weight of the total flux composition.
Generally, the brazing flux content in the brazing flux composition is equal
to or lower than 70 % by weight. Preferably, it is equal to or lower than 50 %by
weight.
The binder, if present, is generally contained in an amount of equal to or
greater than 0.1% by weight, preferably equal to or greater than 1 %by weight
of the total brazing flux composition. The binder, if present, is generally
contained in an amount equal to or lower than 30 %by weight, preferably equal
to or lower than 25 % by weight of the total brazing flux composition.
The thixotropic agent, if present, is generally contained in an amount of
equal to or greater than 1 %by weight of the total brazing flux composition.
Generally, if present, it is contained in an amount equal to or lower than 20 %by
weight, preferably in an amount equal to or lower than 10 %by weight.
The thickener, if present, is generally contained in an amount of equal to or
greater than 1%by weight, preferably equal to or greater than 5 %by weight of
the total brazing flux composition. Generally, the thickener, if present, is
contained in an amount equal to or lower than 15 %by weight, preferably equal
to or lower than 10 % by weight, of the total brazing flux composition.
Highly suitable brazing flux compositions for wet applications contain 10
to 70 %by weight of the brazing flux, 1 to 25 % by weight binder, 0 to 15 % by
weight of a thickener, 0 to 10 %by weight of a thixotropic agent, and 0 to 5 %
by weight of other additives, e.g. a surfactant or a suspension stabilizer.
Preferably, the remainder to 100 %by weight is water, an organic solvent or an
aqueous organic solvent; water is especially preferred.
In another embodiment, the flux composition is free of any water or waterfree
or aqueous organic liquid, but contains the flux (and, if desired, additives,
e.g. surfactants, thickener or thixotropic agents) as described above, and a watersoluble
organic polymer as a binder which is present in the form of a water
soluble package for the flux. For example, polyvinyl alcohol is very suitable as
water-soluble package for the flux as described in US patent application
publication 2006/023 1162. Such packages can be handled without dust
formation, and after addition of water or aqueous organic solvents, they form a
suspension of the flux in water while the water soluble polymer dissolves and
provides the binder function.
The suspension can be applied in a known manner, e.g. by spraying,
painting, or by dipping the parts to be joined into the suspension.
If desired, parts coated with the flux composition can be dried before
brazing and then later be brazed, or drying and brazing can be performed
immediately after one another.
The components can be applied separately to the parts or in the form of a
premixed brazing flux.
The weight per area of the brazing flux applied on the parts to be brazed is
preferably equal to or higher than 4 g/m2 . More preferably, it is equal to or
higher than 5 g/m2 . Preferably, it is equal to or lower than 50 g/m2 , especially
preferably equal to or lower than 20 g/m2 . If a brazing flux composition is
applied, the flux load is correspondingly higher to achieve the brazing flux load
as mentioned above. If, to give an example for calculation, a brazing flux
composition comprising 50 % by weight of the brazing flux is applied, then the
load of the brazing flux composition is preferably equal to or higher than 8 g/m
to achieve a brazing flux load of equal to or higher than 4 g/m .
The heat needed for brazing the parts may be provided by an open flame,
but inductive heating or heating by means of a laser is also possible. It is
preferred to braze according to the Controlled Atmosphere Brazing ("CAB")
process in the presence of N2 or Ar gas.
Generally, a solder metal is applied. Often, solders consisting of Al and Si
are applied. It is preferred to braze parts which are clad with a solder.
The process is generally performed to braze parts of Al-Mg alloys
(which may contain further metals) with parts of Al-Mg alloys (which may
contain further metals) or with Al parts (which may contain other metals
than Mg). The content of Mg in the parts depends on the desired flux loading
and of the sum of the magnesium content of the alloys at the interface of the
parts to be joined. For example, if a flux loading in the upper range, e.g. from 10
to 20 g/m is technically acceptable, an interface comprising equal to or more
than 0 % by weight to equal to or less then 1.8 % by weight of Mg, preferably
equal to or more than 0.8 % by weight to equal to or less then 1.5 % by weight of
Mg can preferably be brazed.
If a flux loading in the lower range, e.g. from 4 to 10 g/m is desired, an
interface comprising equal to or more than 0 % by weight to equal to or less
then 1.0 % by weight of Mg, preferably equal to or more than 0.6 % by weight to
equal to or less then 1.0 % by weight of Mg can preferably be brazed.
The Mg content at the interface is calculated by adding the sum of Mg
percentages in both parts to be joined. If, for example, two parts each
with 0.68 % by weight of Mg are to be joined, the Mg content at the interface
is (0.68 + 0.68 =) 1.36 % by weight. If a part with 0.68 % by weight of Mg and
a part with 0 % by weight of Mg are brazed, the Mg content at the interface
is (0.68 + 0 =) 0.68 % by weight.
Brazing of parts with a Mg content in the interface in a range of from 0.6 to
1 % by weight and a brazing flux load in a range of from 4 to 10 g/m is
preferred.
For example, the following kind of parts can be brazed : Heat exchangers
(heater cores for oil coolers/water coolers, radiators, air conditioners and parts
thereof, e.g. condensers, evaporators ), sheets, thin sheets, fin to tube, endplates
(used as core reinforcement) brazed to fin, headers to tube, fin to headers, tube to
tube, folded tubes, extruded tubes, and fittings (e.g. nuts and bolts). Another
aspect of the present invention concerns a brazing flux which may be used in the
above described process for brazing of Al-Mg alloys.
The invention also relates to a brazing flux which is suitable to be used in
the process of the invention mentioned above. The claimed brazing flux is a
selection of the flux explained above in the description of the process of the
invention.
Preferably, the brazing flux has a content of KA1F4 which is equal to or
greater than 80 % by weight, relative to the total weight of the flux.
The brazing flux of the invention comprises, relative to the total weight of
the brazing flux, equal to or more than 80 % by weight of a first component
selected from the group consisting of KA1F and CsAlF , and a second
component selected from the group consisting of Li3AlF6, CaF2, CaC0 3, MgF2,
MgC0 3, SrF2, SrC0 3, BaF2, BaC0 3, and mixtures of two or more of said
second components; or it consists of said first and second components.
Preferably, the brazing flux of the invention also is a selection in that the
claimed flux mandatorily contains equal to or more than 1% by weight of
CsAlF 4 . Preferably, the flux comprises , relative to the total weight of the
brazing flux, equal to or more than 80 % by weight of KA1F , equal to or more
than 1 % by weight of CsAlF , and equal to or more than 2 % by weight of at
least one component selected from the group consisting of Li3AlF6, CaF2,
CaC0 3, MgF2, MgC0 3, SrF2, SrC0 3, BaF2, BaC0 3, and mixtures of two or
more of said second components; or it consists of said components.
More preferably, the brazing flux of the invention comprises, or consists
of, relative to the total weight of the brazing flux, equal to or more than 80 % by
weight of KA1F , euqal to or more than 1% by weight of CsAlF , and equal to or
more than 3 % by weight of at least one component selected from the group
consisting of Li3AlF6, CaF2, CaC0 3, MgF2, MgC0 3, SrF2, SrC0 3, BaF2,
BaC0 3, and mixtures of two or more of these latter components.
Preferably, the brazing flux of the invention comprises, relative to the total
weight of the brazing flux, equal to or more than 80 % by weight of KA1F , and
equal to or more than 1 % by weight of CsAlF , and equal to or more than 2 %
by weight of a second component selected from the group consisting of Li3A1F6,
CaF2, CaC0 3, SrF2, SrC0 3, BaF2, BaC0 3, and mixtures of two or more of said
second components; or it consists of KA1F , CsAlF and one or more of said
second components.
If the flux does not consist of said components, the balance to 100 % by
weight are other flux components known in the art, preferably, K2AlFs or
K2A1F5 -H20 . Preferably, the content of K3A1F6 is lower than 1 % by weight,
including 0 % by weight.
In certain embodiments, the sum of the content of free KF, free or
complexed NaF and free LiF is lower than 0.1 % by weight, more preferably,
lower than 0.05 % by weight, relative to the total content of the flux of the
invention. In another embodiment, the flux of the invention is essentially free,
and preferably, free, of LiF, NaF and CaF2 .
Preferably, the second component is selected from the group consisting
of Li3AlF6, CaF2, MgF2, SrF2, BaF2, and mixtures of two or more of said
second components.
A preferred embodiment of the brazing flux comprises or consists of,
relative to the total weight of the brazing flux, equal to or more than 80 % by
weight of KA1F , equal to or more than 1% by weight of CsAlF ; and equal to
or more than 3 % by weight of a second component selected from the group
consisting of Li3AlF6, CaF2, MgF2, SrF2, BaF2, and mixtures of two or more of
said second components.
According to one embodiment, the brazing flux consists essentially
of KA1F4 , CsAlF 4, and at least one second component selected from Li3A1F6,
SrF2, BaF2, and mixtures of 2 or more thereof. The term "essentially " in the
present invention preferably denotes a content of equal to or less than 5 %
by weight of other salts like K2AlFs, its hydrates, and K3A1F6 .
A very preferred brazing flux consists essentially of KA1F , CsAlF ,
Li3AlF6 and optionally includes one or more of CaF 2, MgF2, SrF2, and BaF2 .
A still more preferred brazing flux consists essentially of KA1F , CsAlF ,
and Li3AlF6 and optionally includes BaF2.
Highly preferred brazing fluxes comprise, or consist of, KA1F in a range
of from equal to or greater than 80 to equal to or lower than 98 % by weight,
CsAlF in a range of from equal to or more than 1 % by weight to equal to or
less than 10 % by weight, Li3A1F6 in a range of from equal to or more than 1 %
by weight to equal to or less than 10 % by weight, and BaF2 in a range of from 0
to equal to or less than 15 % by weight.
Still more preferred brazing fluxes comprise, or consist of, KA1F in a
range of from equal to or greater than 80 to equal to or lower than 98 % by
weight, CsAlF in a range of from equal to or more than 1 % by weight to equal
to or less than 5 % by weight, Li3A1F6 in a range of from equal to or more
than 1 % by weight to equal to or less than 8 % by weight, and BaF2 in a range
of from 0 to equal to or less than 12 % by weight.
The total content of K2AlFs and its hydrates and of K3A1F6 in the brazing
flux is preferably equal to or lower than 4 % by weight, more preferably, equal to
or lower than 3 % by weight.
The brazing fluxes described above can be manufactured by mixing the
separate components, for example, by mixing KA1F , Li3AlF6, CsAlF
and BaF2, or by co-precipitation. For example, HalF is reacted with KOH,
CsOH and Ba(OH) 2 to provide a brazing flux comprising potassium cesium
tetrafluoroaluminate and BaF2 . Here, the content of K+ and Cs+ is such that a
neutral complex with A1F is formed.
Still another embodiment of the present invention concerns a brazing flux
composition which comprises the brazing flux as described above and at least
one brazing additive. Preferred brazing additives are described above, for
example, liquids, binders, suspension stabilizers, surfactants, thickeners, and
thixotropic agents.
Preferred features of the brazing flux and of the brazing flux composition
correspond to those features described above as being preferred embodiments of
the fluxes and compositions.
Still another aspect of the present invention are coated parts of aluminum
(which may contain other metals except Mg) or aluminum-magnesium alloys
(which may contain other metals), coated with a flux as described above, or
coated with a brazing flux composition as described above. The brazing flux
load preferably is equal to or greater than 4 g/m ; preferably, the flux load is
equal to or lower than 15 g/m . Parts with a flux load in the range of from 5
to 10 g/m are especially preferred. If the brazing flux is contained in a brazing
flux composition, the load of the brazing flux composition is repectively higher
as explained above. Preferred coated parts are : Heat exchangers (and parts
thereof, e.g. heater cores for oil coolers/water coolers, radiators, air conditioners
and parts thereof, e.g. condensers, evaporators), sheets, thin sheets, fins and
tubes, endplates (used as core reinforcement) to be brazed to fins, headers to be
brazed to a tube, fins to be brazed to headers, tubes to be brazed to a tube, folded
tubes, extruded tubes, and fittings (e.g. nuts and bolts). For example, thin Al-Mg
alloy sheets (fins) with a thickness of equal to or lower than 0.1mm down to
0.06 mm can be brazed, as well as tubes with a thickness of equal to or lower
than 0.5 mm down to 0.25 mm.
Another aspect of the present invention concerns brazed parts, obtained by
brazing respective parts using the inventive brazing flux, obtained by brazing
coated parts according to the invention, or by brazing parts according to the
process of the present invention.
The advantage of the brazing process, the brazing flux and the brazing flux
composition described above is especially that they allow brazing of Al-Mg
alloys with a high amount of Mg, especially with equal to or more than 0.5 %by
weight of Mg at the interface, and up to 2 % by weight and even more.
Additionally, many of the brazing fluxes have a lower corrosion potential than
known fluxes.
Should the disclosure of any patents, patent applications, and publications
which are incorporated herein by reference conflict with the description of the
present application to the extent that it may render a term unclear, the present
description shall take precedence.
The examples which follow are intended to illustrate the present invention
without, however, limiting the scope thereof.
Examples
GENERAL REMARKS :
Used aluminum parts :
a) Commercially available AMAG 6951 brazing sheet (0.68 % Mg, 4343 clad)
and clad-less AMAG angle material (0.68 % Mg) from Austria Metal AG
were used. The Mg content in the metal-to-metal interface adds up to 1.36 %
by weight Mg (2 x 0.68 ) in total.
b) Commercially available AMAG 6951 brazing sheet (0.68 % Mg, 4343 clad)
and clad-less AMAG AA1050 (Al 99.5 %) angle from Austria Metal AG
were used. The Mg content in the metal-to-metal interface adds up to 0.68 %
by weight Mg (0.68 + 0 ) in total.
Brazing process :
Brazing was performed according to a standard CAB brazing profile
and 25 by 25 mm clad sheet coupons (single side) with angle on top. Fluxing
was done manually (flux load weight on precision scale, drops of isopropanol
and homogenous spreading). Each test was performed 3 times.
Evaluation of joints :
After brazing, the angle was removed by pulling, and the interface section
was analyzed by Scanning Electron Microscopy coupled with Energy Dispersive
X-ray (SEM/EDX) Spectroscopy.
Example 1 :AMAG 6951 brazing sheet (0.68 %Mg, 4343 clad) and clad-less
AMAG angle material (0.68 %Mg)
The flux load in examples l.X was always 10 g/m .
Example 1.1 (comparison) : Brazing with Nocolok®Cs
Nocolok ®Cs was used as flux. SEM/EDX showed a very thin seam with a
low and in part no meniscus.
Example 1.2. : Brazing with KAIF4 and BaF2
A mixture of KA1F4 (90 % by weight) and BaF2 (10 % by weight) was
used as flux. SEM/EDX showed a very thin seam with a small meniscus.
Accordingly, the joint was slightly better with this flux.
Example 1.3 : Brazing with KAlF4/CsAlF4/Li3AlF6
A mixture of KA1F4 (94 % by weight), CsAlF 4 (2 % by weight)
and Li3AlF6 (4 % by weight) was used as a flux. The brazing was performed 3
times. Two times, a good brazing result was achieved.
Example 1.4 : Brazing with KAlF4/CsAlF4/Li3AlF6
A mixture of KA1F4 (93 % by weight), CsAlF 4 (4 % by weight)
and Li3AlF6 (3 % by weight) was used as a flux. The brazing was performed 3
times. The seam was thin, the meniscus was small.
Examples 2.X : The flux load in examples l.X was always 15 g/m2.
Examples 1.1 to 1.4 were repeated, but with said 15 g/m flux load.
All specimens showed a small meniscus. Examples 2.2 to 2.4 (according
to the invention) always showed a better brazing result than comparison
example 2.1.
Example 3 : Brazing with AMAG 6951 brazing sheet (0.68 %Mg, 4343 clad)
and clad-less AMAG AA1050 (Al 99.5 ) angle
The flux load always was 5 g/m .
Example 3.1 (comparison) : Brazing with Nocolok®Cs
Brazing was performed using Nocolok ®Cs. After brazing, a partial thin
meniscus was observed.
Example 3.2 : Brazing with KAIF4, CsAlF4 and L13AIF6 (4 % by weight)
A mixture of KA1F4 (94 % by weight), CsAlF 4 (2 % by weight)
and L 13AIF 6 (4 % by weight) was used as a flux. The brazing was performed 3
times. All three times, a well-developed meniscus was observed.
The examples above demonstrate that the fluxes according to the invention
are superior to Nocolok ®Cs, a flux recommended for brazing of Al-Mg alloys,
and which comprises approximately 79 % by weight of KA1F , approximately
19 % by weight of K2AIF 5 or its hydrates, and approximately 2 % by weight
of CsAlF 4 .
Example 4 : Flame brazing
A brazing sheet and an angle, both from Al-Mg alloy with 0.75 % by
weight of Mg, clad with Al-Sil2 alloy, are assembled and heated with a torch
flame until flux and then the cladding melts to provide a brazed assembly.

claims
1 A process for brazing of parts of aluminum alloy comprising equal to
or more than 0.5 by weight of magnesium in the interface, comprising a step of
applying a brazing flux to at least one of parts to be joined, a step of assembling
the parts to be joined and and a step of heating the parts to be joined to a
temperature of equal to or higher than 450°C to provide brazed joint parts,
wherein the brazing flux comprises equal to or more than 65 % by weight,
preferably equal to or more than 80 % by weight, relative to the total weight of
the brazing flux, of a first component and equal to or more than 3 % by weight of
a second component, relative to the total weight of the brazing flux, with the
proviso that the first component and the second component are not identical, and
wherein the first component is selected from monoalkali tetrafluoroaluminates
selected from KA1F4 , CsAlF 4 and mixtures thereof, and the second component is
at least one alkaline or alkaline earth metal compound selected from the group
consisting of KA1F4, CsAlF 4 , Li3AlF6, CaF2, CaC0 3, MgF2, MgC0 3, SrF2,
SrC0 3, BaF2, BaC0 3, and mixtures of two or more thereof.
2. The process of claim 1 wherein the first component is KA1F .
3. The process of claim 1 or 2 wherein the second component is selected
from the group consisting of Li3A1F6, CsAlF , CaF2, MgF2, SrF2, BaF2, and
mixtures of two or more thereof.
4. The process of anyone of claims 1 to 3 wherein the content of free KF is
lower than 0.1 % by weight, relative to the total weight of the brazing flux if at
least one compound selected from the group consisting of LiF, NaF and CaF2 is
comprised in the flux.
5. The process of anyone of claims 1 to 4 wherein the second component
is selected from the group consisting of Li3A1F6, CsAlF , BaF2, and mixtures
of 2 thereof, or mixtures of Li3AlF6, CsAlF and BaF2.
6. The process of anyone of claims 1 to 5 wherein the first component
is KA1F in an amount of equal to or greater than 80 % by weight relative to the
total weight of the brazing flux, and the second component is present in an
amount of equal to or greater than 5 % by weight, relative to the total weight of
the brazing flux, and is selected from the group consisting of Li3AlF6, CsAlF 4,
BaF2, and mixtures of two or more thereof.
7. The process of anyone of claims 1 to 6 wherein the flux consists of
said first and second components.
8. The process of anyone of claims 1 to 7 wherein additionally a brazing
additive is applied.
9. The process of anyone of claims 1 to 8 wherein parts with a
magnesium content of at least 0.6 % by weight at the interface are brazed.
10. The process of anyone of claims 1 to 9 wherein parts of heat
exchangers are brazed.
11. A brazing flux comprising or consisting of, relative to the total weight
of the brazing flux, equal to or more than 80 % by weight of KA1F4 and equal to
or more thanl % by weight of CsAlF , and equal to or more than 2 % by weight
of a second component selected from the group consisting of Li3AlF6, CaF2,
CaC0 3, MgF2, MgC0 3, SrF2, SrC0 3, BaF2, BaC0 3, and mixtures of two or
more of said second components.
12. The brazing flux of claim 11 comprising or consisting of, relative to
the total weight of the brazing flux, equal to or more than 80 % by weight
of KA1F , equal to or more than 1 % by weight of CsAlF , and equal to or more
than 3 % by weight of a second component selected from the group consisting
of Li3AlF6, CaF2, MgF2, SrF2, BaF2, and mixtures of two or more of said
second components.
13. The brazing flux of claim 11 or 12 comprising or consisting of,
relative to the total weight of the brazing flux, equal to or more than 80 % by
weight of KA1F , equal to or more than 1 % by weight of CsAlF , and wherein
the second component is selected from the group consisting of Li3A1F6, BaF2,
and mixtures thereof.
14. The brazing flux of anyone of claims 1 1 to 13 consisting essentially
of KA1F , CsAlF and Li3A1F6 and optionally additionally further contains
BaF2.
15. A brazing flux composition comprising a brazing flux according to
anyone of claims 1 1 to 14 and at least one brazing additive.
16. Coated parts of aluminum or aluminum-magnesium alloys, coated
with a flux according to anyone of claims 11 to 14 or a brazing flux composition
according to claim 15.