U.S. patent application number 09/801840 was filed with the patent office on 2001-11-15 for brazing sheet product and method of manufacturing an assembly using the brazing sheet product.
Invention is credited to Wijenberg, Jacques Hubert Olga Joseph, Wittebrood, Adrianus Jacobus.
Application Number | 20010040180 09/801840 |
Document ID | / |
Family ID | 27439996 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010040180 |
Kind Code |
A1 |
Wittebrood, Adrianus Jacobus ;
et al. |
November 15, 2001 |
Brazing sheet product and method of manufacturing an assembly using
the brazing sheet product
Abstract
A brazing sheet product having a core sheet (1) made of an
aluminium alloy, having one or both of the surfaces of the core
sheet clad with an aluminium clad layer (2), and a layer (3)
comprising nickel on the outersurface of one or both the aluminium
clad layer or layers (2). There is a layer (4) comprising zinc or
tin as a bonding layer between the outersurface of the aluminium
clad layer or layers (2) and the layer (3) comprising nickel. The
aluminium clad alloy layer comprises, in weight percent: Si 2 to
18, Mg up to 8.0, Zn up to 5.0, Cu up to 5.0, Mn up to 0.30, In up
to 0.30, Fe up to 0.80, Sr up to 0.20, at least one element
selected from the group consisting of: Bi 0.01 to 1.0, Pb 0.01 to
1.0, Li 0.01 to 1.0, Sb 0.01 to 1.0, impurities each up to 0.05,
total up to 0.20; and balance aluminium.
Inventors: |
Wittebrood, Adrianus Jacobus;
(Velserbroek, NL) ; Wijenberg, Jacques Hubert Olga
Joseph; (Amsterdam, NL) |
Correspondence
Address: |
STEVENS, DAVIS
MILLER & MOSHER, LLP
1615 L Street N.W., Suite 850
Washington
DC
20036
US
|
Family ID: |
27439996 |
Appl. No.: |
09/801840 |
Filed: |
March 9, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60209973 |
Jun 8, 2000 |
|
|
|
Current U.S.
Class: |
228/219 ;
228/262.51; 428/648; 428/650; 428/654; 428/658 |
Current CPC
Class: |
Y10S 428/936 20130101;
Y10T 428/12764 20150115; B23K 35/002 20130101; C25D 5/44 20130101;
E04C 2002/3433 20130101; E04C 2002/3472 20130101; Y10T 428/12944
20150115; E04C 2002/3455 20130101; E04C 2002/3466 20130101; Y10T
428/12792 20150115; B23K 35/0238 20130101; Y10T 428/12722 20150115;
B23K 35/286 20130101; Y10T 428/12736 20150115; C25D 5/611 20200801;
C25D 5/12 20130101; Y10S 428/935 20130101 |
Class at
Publication: |
228/219 ;
428/654; 428/658; 428/648; 428/650; 228/262.51 |
International
Class: |
B32B 015/20; B23K
035/38; C25D 005/10; B23K 035/24 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 10, 2000 |
EP |
00200868.8 |
May 18, 2000 |
IB |
PCT/EP00/04608 |
May 31, 2000 |
EP |
00201936.2 |
Jul 27, 2000 |
EP |
00202673 |
Claims
1. Brazing sheet product comprising: a core sheet (1) made of an
aluminium alloy; an aluminium clad layer (2) cladding at least one
of the surfaces of said core sheet; a layer (3) comprising nickel
on the outersurface of one or both said aluminium clad layer or
layers (2); and a layer (4) comprising zinc or tin as a bonding
layer between said outersurface of said aluminium clad layer or
layers and said layer (3) comprising nickel; wherein said aluminium
clad layer (2) is made of an alloy which comprises, in weight
percent:
6 Si 2 to 18 Mg up to 8.0 Zn up to 5.0 Cu up to 5.0 Mn up to 0.30
In up to 0.30 Fe up to 0.80 Sr up to 0.20
at least one element selected from the group consisting of:
7 Bi 0.01 to 1.0 Pb 0.01 to 1.0 Li 0.01 to 1.0 Sb 0.01 to 1.0
impurities each up to 0.05, total impurities up to 0.20, balance
aluminium.
2. Brazing sheet product according to claim 1, wherein said bonding
layer (4) is an electroplated layer.
3. Brazing sheet product according to claim 1, wherein said bonding
layer (4) has a thickness of not more than 0.5 .mu.m.
4. Brazing sheet product according to claim 3, wherein said bonding
layer (4) has a thickness in the range 20 to 150 nm.
5. Brazing sheet product according to claim 1, wherein said layer
(3) comprising nickel has a thickness of not more than 2.0
.mu.m.
6. Brazing sheet product according to claim 1, wherein said
aluminium clad layer (2) contains by weight Mg in an amount in the
range of 0.5 to 5.0%.
7. Brazing sheet product according to claim 1, wherein said
aluminium clad layer (2) contains by weight Zn in an amount in the
range of 0.5 to 3.0%.
8. Brazing sheet product according to claim 1, wherein said
aluminium clad layer (2) contains by weight Bi in an amount in the
range of 0.01 to 0.5%.
9. Brazing sheet product according to claim 1, wherein said core
sheet (1) is coupled to said aluminium clad layer (2) via an
intermediate layer (5).
10. Brazing sheet product according to claim 1, wherein said core
sheet (1) is an aluminium alloy comprising magnesium in an amount
in the range of up to 8.0%.
11. An assembly of components joined by brazing, at least one said
components being a brazing sheet product according to claim 1.
12. A method of manufacturing an assembly of brazed components,
comprising the sequential process steps of: (a) forming said
components of which at least one is made from brazing sheet product
according to claim 1; (b) assembling the components into an
assembly; (c) brazing the assembly under a vacuum or in an inert
atmosphere in the absence of a brazing-flux at elevated temperature
for a period long enough for melting and spreading of the clad
layer; and (d) cooling the brazed assembly.
13. A method of use of an aluminium clad alloy in a brazing sheet
according to claim 1 comprising brazing an assembly comprising said
aluminium clad alloy.
14. A method of use of an aluminium clad alloy according to claim 1
comprising brazing an assembly comprising said aluminium clad alloy
in an inert atmosphere brazing process in the absence of a
brazing-flux material.
15. The method of use according to claim 14, wherein the aluminium
clad alloy comprises, in weight %, Si 2 to 18 Bi 0.01 to 1.0
elements other than aluminium, Si and Bi, each up to 0.05%, total
up to 0.20% balance aluminium.
16. The method of use according to claim 14, wherein the aluminium
clad alloy comprises, in weight %,
8 Si 2 to 18 Mg 0.5 to 8.0 Bi 0.01 to 1.0
elements other than aluminium, Si, Mg, and Bi each up to 0.05%,
total up to 0.20% balance aluminium.
17. The method of use according to claim 14, wherein the aluminium
clad alloy comprises, in weight %,
9 Si 2 to 18, Zn up to 5.0, Bi 0.01 to 1.0,
elements other than aluminium, Si, Zn, and Bi each up to 0.05%,
total up to 0.20% balance aluminium.
18. The method of use according to claim 14, wherein the aluminium
clad alloy comprises, in weight %,
10 Si 7 to 18 Bi 0.01 to 0.5
elements other than aluminium, Si and Bi each up to 0.05%, total up
to 0.20% balance aluminium.
19. The method of use according the claim 14, wherein the aluminium
clad alloy comprises, in weight %,
11 Si 7 to 18 Mg 0.5 to 2.5 Bi 0.01 to 0.5
elements other than aluminium, Si, Mg, and Bi each up to 0.05%,
total up to 0.20% balance aluminium.
20. The method of use according the claim 14, wherein the aluminium
clad alloy comprises, in weight %,
12 Si 7 to 18 Zn 0.5 to 3.0 Bi 0.01 to 0.5
elements other than aluminium, Si, Zn, and Bi each up to 0.05%,
total up to 0.20% balance aluminium.
21. Brazing sheet product according to claim 1, wherein said
aluminium clad layer (2) contains by weight Mg in an amount in the
range of 0.2 to 2.0%.
22. Brazing sheet product according to claim 1, wherein the total
of Bi, Pb, Li and Sb contained by said aluminium clad layer (2) is
by weight an amount in the range of .ltoreq.1.0%.
23. Brazing sheet product according to claim 1, wherein said
bonding layer (4) has a thickness of not more than 0.3 .mu.m.
24. Brazing sheet product according to claim 1, wherein said layer
(3) comprising nickel has a thickness of not more than 1.0
.mu.m.
25. Brazing sheet product according to claim 1, wherein the
aluminium clad layer (2) alloy consists of, in weight percent:
13 Si 2 to 18 Mg up to 8.0 Zn up to 5.0 Cu up to 5.0 Mn up to 0.30
In up to 0.30 Fe up to 0.80 Sr up to 0.20
at least one element selected from the group consisting of:
14 Bi 0.01 to 1.0 Pb 0.01 to 1.0 Li 0.01 to 1.0 Sb 0.01 to 1.0
impurities each up to 0.05, total impurities up to 0.20, balance
aluminium.
26. Brazing sheet product according to claim 25, wherein said
aluminium clad layer (2) contains by weight Mg in an amount in the
range of 0.2 to 2.0%.
Description
[0001] This claims priority under 35 USC 119 from U.S. provisional
patent application Ser. No. 60/209,973, filed Jun. 8, 2000,
incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The invention relates to a brazing sheet product in which a
layer comprising nickel is plated onto a surface of a clad layer
made of an Al--Si alloy containing Si in the range of 2 to 18
weight %. The invention also relates to a brazed assembly
comprising at least one component made of the brazing sheet product
and to a method of manufacturing an assembly of brazed
components.
BACKGROUND OF THE INVENTION
[0003] For the purpose of this invention brazing sheet is to be
understood as a core sheet, for example of aluminium or aluminium
alloy, having on at least one side a brazeable aluminium alloy.
Typical brazeable aluminium alloys useful as such a clad layer are
the Aluminium Association (AA) 4xxx-series alloys, typically having
Si in the range of 2 to 18 weight %. The brazeable 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.
[0004] Controlled Atmosphere Brazing (CAB) and Vacuum Brazing (VB)
are the two main processes used for industrial scale aluminium
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 clad alloy 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.
[0005] 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 results 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 aluminium
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.
[0006] 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 shaping 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 and 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 clad alloy. If properly
applied, the nickel reacts with the underlying aluminium. The
nickel can be applied by using a shim of nickel between 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.
[0007] The processes for nickel-plating 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 each of these documents,
nickel is preferably deposited in combination with lead.
Alternatively, cobalt is deposited in combination with lead. It is
known in the art that instead of nickel, cobalt or combinations
thereof, also iron may be used. 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 plating
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 a sufficient nickel
coverage to serve as nuclei for the wetting 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.
[0008] Some other disclosures of Ni-plating found in the prior art
literature will be mentioned below.
[0009] General textbook by Wernick and Pinner, "The Surface
Treatment and Finishing of Aluminium and its Alloys", 5th edition,
Volume 2, pp.1023-1071. This textbook describes in general
immersion processes for plating on aluminium.
[0010] Paper by the Bureau of Mines Technology, "Aluminium
Soft-Soldering", 2301 N.T.I.S. Tech Notes (manufacturing), 1985,
January, No.1G, Springfield, Va., USA, pp.12-13. This paper
describes a method of manufacturing aluminium for soft-soldering
wherein the aluminium surfaces are joined by conventional tin-lead
solder. The method includes firstly cleaning the aluminium surface
carefully prior to the zinc application. Secondly a thin zinc coat
is deposited and subsequently electroplated with an alloy of
nickel-copper. After the nickel-copper plating has been
accomplished, soldering using normal procedures can be
accomplished.
[0011] FR-A-2,617,868 describes a method of manufacturing aluminium
product with a brazeable surface coating of tin or a tin-bismuth
alloy, wherein the product is provided with an intermediate layer.
This intermediate layer is composed of a first layer of zinc and a
second layer of nickel, which nickel has been deposited by
electrolysis from a neutral electrolyte. Here, the underlying
aluminium or aluminium alloy is not melted in the brazing
process.
SUMMARY OF THE INVENTION
[0012] It is an object of the invention to provide a brazing sheet
product having a core sheet and filler material, to be melted
during brazing, said filler material comprising a clad layer of an
Al--Si alloy and a nickel layer on the clad layer, in which there
is good adhesion of the nickel layer to the clad layer.
[0013] It is an object of the invention to provide a brazing sheet
product which can be used in a vacuum brazing process as well as in
an controlled atmosphere brazing process in the absence of a
brazing-flux, but ideally suitable for CAB process in the absence
of a brazing-flux.
[0014] It is another object of the invention to provide a method of
manufacturing an assembly of brazed components using the brazing
sheet product of this invention.
[0015] In accordance with the invention in one aspect there is
provided a brazing sheet product having a core sheet (1) made of an
aluminium alloy, having at least one of the surfaces of said core
sheet clad with an aluminium clad layer (2), and a layer (3)
comprising nickel on the outersurface of at least one of said
aluminium clad layer or layers (2), and wherein there is a layer
(4) comprising zinc or tin as a bonding layer between said
outersurface of said aluminium clad layer or layers and said layer
(3) comprising nickel and further wherein the aluminium clad alloy
comprising, in weight percent:
1 Si 2 to 18 Mg up to 8.0 Zn up to 5.0 Cu up to 5.0 Mn up to 0.30
In up to 0.30 Fe up to 0.8 Sr up to 0.20
[0016] at least one element selected from the group consisting
of:
2 Bi 0.01 to 1.0 Pb 0.01 to 1.0 Li 0.01 to 1.0 Sb 0.01 to 1.0
[0017] (preferably the magnesium level in the clad layer does not
exceed 2.0%, i.e., Mg is 0.2 to 2.0, when it is present essentially
only to promote the wetting action of the brazing alloy)
[0018] other elements/impurities each up to 0.05, total up to 0.20
balance aluminium.
[0019] In the present specification, the term "up to" means
".ltoreq.", for example "up to 0.20" means ".ltoreq.0.20".
[0020] By the zinc or tin comprising bonding layer a very effective
bond between the aluminium alloy clad layer and the layer
comprising nickel is formed, the bond remaining effective during
subsequent deformation of the brazing sheet, for example by
bending. The coverage of the nickel layer is no longer dependent on
the surface characteristics of the bare clad layer. The brazing
sheet product obtained is suitable for flux-less brazing under
controlled atmosphere conditions.
[0021] The invention is based in part on the insight that to obtain
a well-bonded nickel layer on the Si-containing aluminium clad
layer of the brazing sheet product so that the bond remains
effective under large deformation, pretreatment of the clad layer
is extremely important. The prior art processes apparently aimed at
applying the nickel in a distributed form, principally to the
silicon particles at the surface of the clad layer, rather than
trying to achieve a uniform nickel layer. In the present invention
the surface of the Si-containing clad alloy is altered in such a
way that the nickel coverage is independent of the silicon
particles at its surface. The nickel plating does not take place on
the silicon particles but on the applied bonding layer comprising
zinc or tin. Since the nickel thus is deposited on the total
surface of the aluminium clad layer the necessary reaction before
brazing can take place much more easily as compared to the process
of the prior art. The zinc or tin applied does not interfere at all
during the brazing process, and may contain a component to assist
the brazing, as described below. Since the nickel is deposited
smoothly and uniformly on the surface, the use of lead to promote
wetting during brazing can be reduced or avoided, or other elements
such as bismuth may be used for this purpose. A further important
advantage of the nickel or nickel-lead deposited smoothly and
uniformly on the surface is that the total amount of nickel to be
applied in order to achieve good flux-less brazing can be reduced.
Another advantage is that the complete surface coverage avoids any
difficulty caused by aluminium oxide at the surface of the clad
layer.
[0022] Furthermore, the invention is based in part on the insight
that the aluminium clad layer comprise at least one or more
elements selected from the group consisting of bismuth, lead,
lithium and antimony, each in a range of 0.01 to 1.0%, and the
combination of two or more elements does preferably not exceed
1.0%, and that magnesium may be present in a range of 0.2 to 2.0%.
The combination of magnesium with one or more other elements from
this group does preferably not exceed 2.5%. Hence, magnesium may be
present in the aluminium clad layer up to 8.0%, preferred ranges
have been set out below, to enhance amongst others the mechanical
properties of the aluminium clad layer, whereas it has also been
found that magnesium in a range of 0.2 to 2.0% may also act in a
similar way as elements selected from the group bismuth, lead,
lithium and antimony. Preferably the magnesium level in the clad
layer does not exceed 2.0% when it is present essentially only to
promote the wetting action of the brazing alloy in combination with
the lead-free nickel layer. Further alloying elements may be added
to improve specific properties of the clad layer. In U.S. Pat. No.
3,970,237 it is mentioned that the aluminium clad layer is
preferably coated with a layer of nickel, nickel-lead, cobalt,
cobalt-lead or combinations thereof. The additions of lead is
believed to improve the wettability during brazing. However, in
accordance with the invention it has been found that the nickel
and/or cobalt layer itself does not need to comprise the lead as an
alloying addition. Surprisingly it has been found that an equal or
even better results can be obtained if one or more elements of the
group Bi, Pb, Li and Sb and Mg is being added in the given ranges
to the aluminium clad layer itself. Adding one or more of these
alloying elements to the aluminium clad layer has the advantage
that the composition of the plating bath becomes less complex,
which is a major achievement in itself, whereas the alloying
addition to the cladding is very simple when manufacturing the clad
layer. As a result the electroplated nickel layer applied may
essentially consist of nickel and unavoidable impurities. From an
operational point of view bismuth is the most preferred alloying
element to the aluminium clad layer. Furthermore it has been found
that the element bismuth is the most preferred alloying element to
promote wetting, and consequently less of this element is required
to achieve a similar effect as with lead addition in the nickel
layer. Although, lead as alloying element in the clad layer in the
given range results in the desired effect, the addition of this
element is preferably avoided since it is from an environmentally
point of view a highly undesirable element.
[0023] While it is in known to apply a zinc layer prior to
nickel-plating of articles, it is believed that this has not been
done in a nickel-plated aluminium alloy clad brazing sheet product,
in which as discussed above it has been thought necessary to plate
the nickel directly on the Si-containing clad layer.
[0024] Very good results of the brazing sheet according to the
invention may be obtained where the bonding layer is applied with
an immersion zincate treatment or immersion stannate treatment,
often also referred to as displacement plating.
[0025] In an embodiment of the brazing sheet product according to
the invention the applied layer comprising zinc or tin has a
thickness only up to 0.5 .mu.m, more preferably up to 0.3 .mu.m
(300 nm), and most preferably in the range of 0.01 to 0.15 .mu.m
(10-150 nm). In the best results obtained so far a thickness of
about 30 nm has been used. A coating thickness of greater than 0.5
.mu.m requires a prolonged treatment time, e.g. for displacement
plating, and is thought to have no further advantages for improving
the adhesion.
[0026] The zinc or tin layer applied in the brazing sheet product
of the invention may be essentially a pure zinc or tin layer or may
be primarily zinc or tin (e.g. at least 50 weight %). Minor amounts
of impurity elements or deliberately added elements may be present,
as discussed in more detail below. Typically impurity elements are
present at less than 10%, more usually less than 5% by weight in
the zinc or tin layer.
[0027] The layer comprising nickel is preferably an electroplated
layer. The adhesion of the layer comprising nickel applied on the
layer comprising zinc or tin is excellent and can withstand
relatively severe shaping operations without the occurrence of
delamination.
[0028] Preferably in this brazing sheet product the layer
comprising nickel has a thickness up to 2.0 .mu.m, preferably up to
1.0 .mu.m, and more preferably up to 0.5 .mu.m. A coating thickness
of greater than 2.0 .mu.m requires a prolonged treatment time for
plating, may result in wrinkling of the molten filler material
during brazing. A preferred minimum thickness for this
Ni-containing layer is 0.3 .mu.m. However, other techniques such as
roll bonding, thermal spraying, Chemical Vapour Deposition and
Physical Vapour Deposition may be used.
[0029] Preferably in this brazing sheet product each aluminium clad
layer has a thickness ranging from about 2 to 20% of the total
thickness of the total brazing sheet product thickness.
[0030] Preferably in the brazing sheet product the material which
on brazing becomes molten, commonly known as the filler material,
in particular the nickel layer and/or the zinc or tin layer
comprise one or more elements to reduce the surface tension of the
molten brazing alloy during brazing. In the invention it has been
found surprisingly that contrary to the teaching of the prior art,
it is not necessary to add lead as an alloying element to the
Ni-layer in order to promote the wetting action of the brazing
alloy. Nevertheless, lead and other suitable elements, for which
bismuth is preferred to most, may be added to the nickel layer or
the zinc or tin layer or to both. This has various advantages from
the manufacturing point of view of the brazing sheet.
[0031] In the filler material as a whole therefore, there may be
present, in weight %, at least one of
3 Bi 0.01 to 0.5, preferably 0.05 to 0.5 Mg 0.2 to 2.0 Li 0.01 to
0.5, preferably 0.05 to 0.5 Sb 0.01 to 0.5, preferably 0.05 to
0.5
[0032] The zinc or tin layer itself may thus comprise one or more
additional elements selected from the group consisting of bismuth,
lead, lithium and antimony. The amount of the additional element or
elements in total may be up to 50%, but preferably is less than
25%, e.g. in the range 1 to 25%.
[0033] In a preferred embodiment of the brazing sheet product
according to the invention the bismuth addition in the aluminium
clad layer has an upper limit of 0.5%. A suitable lower limit for
the bismuth addition is 0.01% and more preferably 0.05%.
[0034] In a preferred embodiment of the brazing sheet product
according to the invention the lithium addition in the aluminium
clad layer has an upper limit of 0.5%. A suitable range for the
lithium addition is 0.01-0.3%.
[0035] In a preferred embodiment of the brazing sheet product
according to the invention the antimony addition in the aluminium
clad layer has an upper limit of 0.5%. A suitable range for the
antimony addition is 0.01-0.3%.
[0036] In an embodiment the aluminium clad layer comprises, in
weight %, Si in the range of 2 to 18%, and preferably 7 to 18%, as
alloying element and further magnesium in the range of up to 8.0%,
and preferably up to 5.0%. Preferably the magnesium is in the range
of 0.5 to 5%, and more preferably 0.5 to 2.5%. Further alloying
elements may be added such as, but not limited to, Cu, Zn, and Sr
in suitable ranges. It has been found that in use of the brazing
sheet product the presence of magnesium in the clad layer has no
detrimental effects during brazing. This is a major improvement
over known brazing sheet products. It allows for the design of
aluminium clad layers which may contribute to the strength of the
total brazing sheet product or alternatively the brazing sheet
products having thinner clad layers. Furthermore, it allows that
Mg-containing brazing sheet may be applied in both Vacuum Brazing
and flux-less Controlled Atmosphere Brazing. The latter possibility
has many economical and technical advantages. In addition it has
been found that the addition of both bismuth and magnesium as
alloying elements overcomes the mandatory need for the addition of
wetting or bonding promoting alloying elements to the sequentially
electroplated nickel layer. The brazing sheet product according to
the invention may readily be used in the existing industrial
brazing lines.
[0037] In another embodiment the aluminium clad layer comprises, in
weight %, Si in the range of 2 to 18%, and preferably 7 to 18%, as
alloying element and further zinc in the range of up to 5%.
Preferably the zinc is in the range of 0.5 to 3%. Further alloying
elements may be added such as, but not limited to, Mg and Cu in
suitable ranges. In accordance with the invention it has been found
that when this brazing sheet product is used the presence of zinc
in the cladding has no detrimental effects during brazing. This is
a major improvement over known brazing sheet products. It allows
for the design of a cladding which may contribute to the strength
of the total brazing sheet product. Further, the brazing sheet
product wherein the cladding contains zinc as a deliberate alloying
element may be applied in both Vacuum Brazing and flux-less
Controlled Atmosphere Brazing, both processes being used on an
industrial scale.
[0038] In another embodiment the aluminium clad layer comprises, in
weight %, Si in the range of 2 to 18%, and preferably 7 to 18%, as
alloying element and further copper in the range of up to 5%.
Preferably the copper is in the range of 3.2 to 4.5%. Further
alloying elements may be added such as, but not limited to, Mg, and
Zn in suitable ranges. In accordance with the invention it has been
found that when this brazing sheet product is used the presence of
copper in the cladding has no detrimental effects during brazing.
This is a major improvement over known brazing sheet products. It
allows for the design of a cladding which may contribute to the
strength of the total brazing sheet product. Further, the brazing
sheet product wherein the cladding contains copper as a deliberate
alloying element may be applied in both Vacuum Brazing and
flux-less Controlled Atmosphere Brazing, both processing being used
on an industrial scale.
[0039] In all embodiments of the aluminium clad layer indium ("In")
in a range of up to 0.30% may be present as an alloying element to
reach a more electronegative corrosion potential of the aluminium
clad alloy as compared to the aluminium core alloy. Indium has been
found to be much more effective in reducing the corrosion potential
of the alloy as compared to zinc additions. Typically 0.1% In is as
effective as 2.5% Zn.
[0040] In all embodiments of the aluminium clad layer each of
manganese and zirconium may be present in the aluminium clad layer
as an impurity element in a range of up to 0.30%, and is preferably
present only up to 0.10% and more preferably up to 0.05%.
[0041] In all embodiments of the aluminium clad layer iron may be
present in the clad layer as a typical impurity element in
aluminium alloys in a range of up to 0.8%, and preferably in a
range of up to 0.4%.
[0042] In all embodiments of the aluminium clad layer strontium in
a range of up to 0.20% may be added to modify the silicon present
in the clad layer during the solidification when casting the clad
alloy. A more preferred maximum for the strontium addition is up to
0.05%.
[0043] In an embodiment of the brazing sheet product according to
the invention, the core sheet is an aluminium alloy comprising
magnesium in a range of up to 8.0%. In a preferred embodiment
magnesium is in a range of 0.5 to 5.0%. Further alloying elements
may be added such as, but not limited to, Cu, Zn, Bi, V, Fe, Zr,
Ag, Si, Ni, Co and Mn in suitable ranges. It has been found that
when the brazing sheet product of the invention is used, the
presence of magnesium in the aluminium clad layer has no
detrimental effects during brazing. This is a major improvement
over the known brazing sheets. The diffusion of Mg from the core to
the cladding during the manufacturing of the brazing sheet product
itself and its application in a subsequent brazing process, appears
to have no detrimental effects on the brazeability of the brazing
sheet product in accordance with the invention. This allows for the
design of high strength brazing sheet products having an aluminium
core sheet having magnesium in the given range as a strengthening
element. The product may be applied in both Vacuum Brazing (VB) and
flux-less Controlled Atmosphere Brazing (CAB), both processes being
used extensively on an industrial scale.
[0044] In the brazing sheet product according to the invention the
core sheet may be coupled to the aluminium clad layer via an
intermediate layer. The benefits of having such an intermediate
layer or interlayer are described in for example U.S. Pat. No.
2,821,014, the contents of which are incorporated here by
reference.
[0045] The invention further provides a brazed assembly comprising
at least one component made of the brazing sheet product produced
in accordance with the invention described above and elsewhere in
the present specification.
[0046] In a further aspect of the invention there is provided in a
method of manufacturing a brazed assembly using the brazing sheet
product in accordance with the invention, comprising the sequential
process steps of:
[0047] (a) shaping parts of which at least one is made from the
brazing sheet product of the invention as set out above;
[0048] (b) assembling the parts into an assembly;
[0049] (c) brazing the assembly under a vacuum or in an inert
atmosphere in the absence of a brazing-flux at elevated temperature
for a period long enough for melting and spreading of the filler
alloy, whereby the filler alloy is formed by at least the clad
alloy (2), the bonding layer (4) and the Ni layer (3);
[0050] (d) cooling the brazed assembly. The cooling rate may be in
the range of typical brazing furnace cooling rates. Typical cooling
rates are cooling rates of at least 10.degree. C./min or more,
typically 40.degree. C./min or more.
[0051] In dependence on the aluminium alloy of the core sheet the
process may include the further processing step (e) of ageing of
the brazed and cooled assembly in order to optimise the mechanical
and/or corrosion properties of the resultant assembly. The use of
the brazing sheet product in accordance with the invention has been
found to result in a lower brazing temperature by about 10.degree.
C. This reduced brazing temperature allows for a significant
reduction of the industrial scale processing time for a whole
brazing cycle, typically a time reduction of 20% or more has been
found.
[0052] In a further aspect of the invention there is provided in a
method of use of the aluminium clad alloy, set out above and set
forth elsewhere in the present specification, in a brazing sheet
product.
[0053] In a further aspect of the invention there is provided in a
method of use of the aluminium clad alloy, set out above and set
forth elsewhere in the present specification, in a brazing sheet
product in a method of manufacturing a brazed assembly in an inert
atmosphere brazing (CAB) process in the absence of a
brazing-flux.
[0054] Patent Cooperation Treaty application number PCT/EP00/04608,
filed May 18, 2000, is incorporated herein by reference in its
entirety.
BRIEF DESCRIPTION OF THE DRAWINGS
[0055] The invention will now be illustrated by several
non-limitative examples, and with reference to the drawings,
wherein:
[0056] FIG. 1 is a schematic longitudinal section showing the
structure of brazing sheet product according to the state of the
art;
[0057] FIG. 2 is a schematic longitudinal section showing the
structure of brazing sheet product according to the invention;
[0058] FIG. 3 is a schematic longitudinal section showing the
structure of brazing sheet product according to the invention;
DESCRIPTION OF PREFERRED EMBODIMENTS
[0059] FIG. 1 shows schematically brazing sheet in accordance with
the prior art as would be obtained by the process in accordance
with for example U.S. Pat. No. 3,970,237. The brazing sheet product
consists of a core sheet 1 on one or both sides clad with a
aluminium clad layer 6 comprising an Al--Si-alloy. On top of the
clad layer 6 a thin nickel layer 3, preferably a nickel-lead layer,
is applied by means of electroplating.
[0060] FIG. 2 shows schematically brazing sheet in accordance with
the present invention in which between the clad layer 2 comprising
an Al--Si--Bi alloy and the Ni-layer 3 a further layer 4 of zinc or
tin is applied, the advantages of which are set out above. In FIG.
2 the layers 4 and 3 have been shown on only one side of the
brazing sheet, but it will be immediately apparent to the skilled
person that they may also be applied on both sides of the brazing
sheet product. The composition of the various layers and their
advantages have been set out above.
[0061] FIG. 3 shows schematically a further brazing sheet in
accordance with the present invention which has the layers of FIG.
2 and a further intermediate layer 5 between the core sheet 1 and
the clad layer 2 on both sides. In FIG. 3 the layers 4 and 3 have
been shown on only one side of the brazing sheet, but it will be
immediately apparent to the skilled person that they may also be
applied on both sides of the brazing sheet product. In addition the
intermediate layer 5 may also be applied on one side of the brazing
sheet, preferably on the side comprising also the layers 4 and 3.
The possible compositions of the various layers and their
advantages have been set out above.
EXAMPLE
[0062] On a laboratory scale of testing aluminium brazing sheets
manufactured from an Aluminium Association (AA)3003 core alloy clad
on one side with AA4000 -series aluminium clad alloys of four
different compositions (see Table 1), and having a total thickness
of 0.5 mm, and a clad layer thickness of about 50 .mu.m, were
treated as set out in Table 2.
[0063] The treatment consisted of the following sequential process
steps:
[0064] cleaning by immersion for 180 sec. in ChemTec 30014 (a
commercial available degreaser and alkaline etch cleaner), followed
by rinsing;
[0065] alkaline etching for 20 sec. in ChemTec 30203 (a commercial
available alkaline etch cleaner) at ambient temperature, followed
by rinsing;
[0066] optionally desmutting for 4 sec. in an acidic oxidizing
bath, typically 25-50 vol % nitric acid, comprising ChemTec 11093
(a commercial available pickle activator) at ambient temperature,
followed by rinsing;
[0067] zincate immersion using ChemTec 024202 for 12 sec. at room
temperature followed by rinsing;
[0068] nickel electroplating, and rinsing.
[0069] For the nickel electroplating a basic bath without lead has
been used, indicated as "L-" in Table 2. The lead-free basic bath
comprised 50 g/l nickel sulphate, 50 g/l nickel chloride, 30 g/l
sodium citrate, and 75 ml/l ammonium hydroxide (30%). The plating
conditions at 26.degree. C. were such that a plating time of 50
sec. resulted in a nickel plated layer of 0.5 .mu.m thickness using
a current density of 3 A/dm.sup.2.
[0070] The nickel plated specimens have been tested for adhesion
using the Erichsen dome test (5 mm), and the T-bend test. A value
assessment is then given to the adhesion where: (-)=poor,
(.+-.)=fair, and (+)=good. The brazeability has been assessed as
follows. On a laboratory scale of testing the brazing tests were
carried out in a small quartz furnace. Small coupons of 25
mm.times.25 mm were cut from the nickel-plated sheets. A small
strip of an AA3003 alloy measuring 30 mm.times.7 mm.times.1 mm was
bent in the center to an angle of 45.degree. and laid on the
coupons. The strip on the coupon samples were heated under flowing
nitrogen, with heating in about 10 minutes from room temperature to
580.degree. C., dwell time at 580.degree. C. for 1 minute, cooling
from 580.degree. C. to room temperature. The brazing process was
judged on possible formation of wrinkles, capillary depression and
fillet formation. An overall assessment was given where: (-)=poor
brazeability, (-/.+-.)=fair brazeability, (.+-.)=good brazeability,
and (+)=excellent brazeability. The results obtained are summarised
in Table 2.
[0071] From the results from Table 2 it can be seen that applying a
zincate treatment is essential to have a good adhesion of the
Ni-plated layer. From the results of clad alloy no. 1 it can be
seen that omitting the desmutting step still results in a good
adhesion of the Ni-plated layer. The results of clad layer no. 2
demonstrate that adding Bi to the cladding results in an excellent
brazeability. Consequently, the addition of lead to the nickel
layer can be omitted in accordance with the invention. The results
of clad layer no. 3 demonstrate that adding Bi to the cladding in
combination with magnesium still results in an excellent
brazeability. The results of clad layer no. 4 demonstrate that
adding Bi to the cladding in combination with zinc still results in
an excellent brazeability. Whereas having neither bismuth nor lead
present in the clad layer nor lead present in the nickel layer
results in a poor brazeability (see clad alloy no. 1).
4TABLE 1 Composition of the aluminium clad alloy, in weight %.
Balance Al and inevitable impurities (each < 0.05%, total <
0.20%). Alloy Si Fe Cu Mn Mg Zn Ti Bi 1 10.0 0.3 <0.01 <0.02
<0.02 <0.02 0.003 -- 2 8.5 0.2 <0.01 <0.02 <0.02
<0.02 0.003 0.09 3 9.6 0.25 <0.01 <0.02 1.35 <0.02
0.003 0.13 4 7.6 0.35 <0.01 <0.02 <0.02 1.02 0.003
0.11
[0072]
5TABLE 2 Pretreatment applied and testing results. Clad Ni- Braze-
alloy no. Clean. Etching Desmut. Zincate plating Adhesion ability 1
yes yes yes yes L- + - 1 yes yes no yes L- + - 2/3/4 yes yes yes
yes L- + +
[0073] Having now fully described the invention, it will be
apparent to one of ordinary skill in the art that many changes and
modifications can be made without departing from the spirit or
scope of the invention as herein described.
* * * * *