U.S. patent application number 09/849238 was filed with the patent office on 2002-01-31 for method of manufacturing an aluminum product.
Invention is credited to Mooij, Joop Nicolaas, Wijenberg, Jacques Hubert Olga Joseph, Wittebrood, Adrianus Jacobus.
Application Number | 20020012811 09/849238 |
Document ID | / |
Family ID | 27222595 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020012811 |
Kind Code |
A1 |
Wittebrood, Adrianus Jacobus ;
et al. |
January 31, 2002 |
Method of manufacturing an aluminum product
Abstract
The invention relates to a method of manufacturing an Al or Al
alloy workpiece, including the steps of (a) providing an Al or Al
alloy workpiece, (b) pre-treating of the outersurface of the Al or
Al alloy workpiece, and (c) plating a metal layer including nickel
onto the outersurface of the pre-treated Al or Al alloy workpiece.
During step (c) the metal layer including nickel is deposited by
electroplating both nickel and bismuth using an aqueous bath
comprising a nickel-ion concentration in a range of 10 to 100 g/l
and a bismuth-ion concentration in the range of 0.01 to 10 g/l. The
invention further relates to an aqueous plating bath for use in the
method of this invention.
Inventors: |
Wittebrood, Adrianus Jacobus;
(Velserbroek, NL) ; Wijenberg, Jacques Hubert Olga
Joseph; (Amsterdam, NL) ; Mooij, Joop Nicolaas;
(Castricum, NL) |
Correspondence
Address: |
STEVENS, DAVIS, MILLER & MOSHER, LLP
1615 L Street N.W., Suite 850
Washington
DC
20036
US
|
Family ID: |
27222595 |
Appl. No.: |
09/849238 |
Filed: |
May 7, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09849238 |
May 7, 2001 |
|
|
|
09573980 |
May 19, 2000 |
|
|
|
Current U.S.
Class: |
428/652 ;
106/1.22; 427/434.6; 427/436; 428/654; 428/658; 428/936 |
Current CPC
Class: |
B32B 15/017 20130101;
B23K 35/0238 20130101; E04C 2002/3433 20130101; E04C 2002/3466
20130101; Y10T 428/12736 20150115; B23K 35/286 20130101; Y10T
428/12764 20150115; E04C 2002/3472 20130101; Y10S 428/935 20130101;
Y10T 428/12792 20150115; C25D 3/562 20130101; Y10T 428/1275
20150115; C25D 5/44 20130101; E04C 2002/3455 20130101 |
Class at
Publication: |
428/652 ;
428/654; 428/936; 428/658; 427/436; 427/434.6; 106/1.22 |
International
Class: |
B32B 015/20; B05D
001/18 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 21, 2001 |
EP |
01200628.4 |
Sep 25, 2000 |
EP |
00203304.1 |
May 18, 2000 |
EP |
PCT/EP00/04608 |
Claims
1. A method of manufacturing an Al or Al alloy workpiece, which
method comprises the steps of (a) providing an Al or Al alloy
workpiece, (b) pre-treating of the outersurface of the Al or Al
alloy workpiece, and (c) plating a metal layer comprising nickel
onto said outersurface of the Al or Al alloy workpiece, wherein
during step (c) said metal layer comprising nickel is deposited by
plating both nickel and bismuth using an aqueous bath having a pH
in the range of 2.5 to 10, and comprising a nickel-ion
concentration in a range of 10 to 100 g/l, a bismuth-ion
concentration in the range of 0.01 to 10 g/l, a citrate-ion
concentration in the range of 40 to 150 g/l, a gluconate-ion
concentration in the range of 2 to 80 g/l, a chloride- or
fluoride-ion concentration in the range of 1 to 50 g/l.
2. A method according to claim 1, wherein the nickel-ion
concentration is in the range of 20 to 70 g/l.
3. A method according to claim 1, wherein the bismuth-ion
concentration is in the range of 0.02 to 5 g/l.
4. A method according to claim 1, wherein the aqueous bath and the
resultant metal layer comprising nickel are essentially
lead-free.
5. A method according to claim 1, wherein the gluconate-ion
concentration is in the range of 4 to 50 g/l.
6. A method according to any of claims 1, wherein said layer
comprising nickel has a thickness of not more than 2.0 microns.
7. A method according to any of claims 1, wherein said layer
comprising nickel has a thickness in the range of 0.03 to 1.0
micron.
8. A method according to any of claims 1, wherein said layer
comprising nickel has a thickness in the range of 0.05 to 0.5
micron.
9. A method according to any one of claims 1, wherein the Bi-ion
concentration results from the dissolution of one or more from the
group consisting of bismuth carbonate, bismuth oxide, bismuth
citrate and bismuth chloride.
10. A method according to any one of claims 1, wherein the
temperature of the aqueous bath during plating is in the range of
30 to 70.degree. C.
11. A method according to any one of claims 1, wherein the
workpiece is aluminum alloy sheet or aluminum alloy wire or
rod.
12. A method according to claim 1, wherein the aluminum alloy
comprises silicon as an alloying element in the range of 2 to 18%
by weight.
13. A method according to claim 1, wherein the workpiece is a
brazing sheet product comprising a core sheet coupled on at least
one surface of said core sheet to an aluminum clad layer, the
aluminum clad layer being made of an aluminum alloy comprising
silicon in an amount in the range of 2 to 18% by weight, and
wherein during step (b) at least the outersurface of the aluminum
clad alloy is being pre-treated.
14. A method according to claim 1, wherein the workpiece is a
brazing sheet product comprising a core sheet being made of an
AA3xxx, AA5xxx, or AA6xxx-series alloy coupled on at least one
surface of said core sheet to an aluminum clad layer, the aluminum
clad layer being made of an aluminum alloy comprising silicon in an
amount in the range of 2 to 18% by weight, and wherein during step
(b) at least the outersurface of the aluminum clad alloy is being
pre-treated.
15. A method according to claim 1, wherein the workpiece is a
brazing sheet product comprising a core sheet being made of an
AA3xxx, AA5xxx, or AA6xxx-series alloy coupled on at least one
surface of said core sheet to an aluminum clad layer, the aluminum
clad layer being made of an aluminum alloy comprising silicon in an
amount in the range of 2 to 18% by weight, and wherein during step
(b) at least the outersurface of the aluminum clad alloy is being
pre-treated by applying a thin zinc layer having a thickness of not
more than 0.3 micron.
16. A method according to claim 1, wherein the workpiece is a
brazing sheet product comprising a core sheet being made of an
AA3xxx, AA5xxx, or AA6xxx-series alloy coupled on at least one
surface of said core sheet to an aluminum clad layer, the aluminum
clad layer being made of an aluminum alloy comprising silicon in an
amount in the range of 2 to 18% by weight, and wherein during step
(b) at least the outersurface of the aluminum clad alloy is being
pre-treated by applying a thin zinc layer having a thickness in the
range of 10 to 150 nm.
17. An aqueous bath for the electrodeposition of a layer of nickel
and bismuth on an Al or Al alloy workpiece, having a pH in the
range of 2.5 to 10, and comprising a nickel-ion concentration in a
range of 10 to 100 g/l, a bismuth-ion concentration in the range of
0.01 to 10 g/l, a citrate-ion concentration in the range of 50 to
150 g/l, a gluconate-ion concentration in the range of 2 to 80 g/l,
a chloride- or fluoride-ion concentration in the range of 1 to 50
g/l.
18. An aqueous bath according to claim 17, wherein the nickel-ion
concentration is in the range of 20 to 70 g/l.
19. An aqueous bath according to claim 17, wherein the bismuth-ion
concentration is in the range of 0.02 to 5 g/l.
20. An aqueous bath according to claim 17, wherein the
gluconate-ion concentration is in the range of 4 to 50 g/l.
21. An aqueous bath according to claim 17, wherein the following
salts have been used, in grams per liter: nickel sulphate in a
range of 45 to 450 g/l, chloride-ion concentration in a range of 1
to 50 g/l, sodium citrate in a range of 55 to 180 g/l, sodium
gluconate in range of 2 to 90 g/l, ammonium sulphate in a range up
to 270 g/l, bismuth oxide in a range of 0.02 to 22 g/l, or bismuth
carbonate in a range of 0.03 to 29 g/l.
22. A method of use of the aqueous bath of claim 17 for the
manufacturing of Ni-plated products for use in a brazing operation,
comprising plating a metal layer comprising nickel onto an
outersurface of an Al or Al alloy workpiece, wherein during said
plating said metal layer comprising nickel is deposited by plating
both nickel and bismuth using the aqueous bath.
23. A method of use of the aqueous bath of claim 17 for the
manufacturing of Ni-plated brazing sheet products, comprising
plating a metal layer comprising nickel onto an outersurface of an
Al or Al alloy workpiece, wherein during said plating said metal
layer comprising nickel is deposited by plating both nickel and
bismuth using the aqueous bath.
24. An assembly of components joined by brazing, at least one said
components being an Al or Al alloy workpiece produced by the method
in accordance with claim 1.
25. Method of manufacturing an assembly of brazed components,
comprising the steps of: (a) shaping parts of which at least one is
made from an Al or Al alloy workpiece obtained by the method
according to claim 1; (b) assembling the parts into the assembly;
(c) brazing the assembly 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 molten filler; (d) cooling the brazed
assembly to below 100.degree. C.
26. Method according to claim 25, wherein at least one other
component is selected from the group comprising steel, aluminized
steel, stainless steel, plated or coated stainless steel, bronze,
brass, nickel, nickel alloy, titanium, or plated or coated
titanium.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This is a continuation-in-part of U.S. patent application
Ser. No. 09/573,980, filed May 19, 2000, now pending, incorporated
herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The invention relates to a method of manufacturing an Al or
Al alloy workpiece, such as a brazing sheet product, comprising the
steps of providing an Al or Al alloy workpiece, pre-treating of the
outersurface of the Al or Al alloy workpiece, and plating a metal
layer comprising nickel onto the outersurface of the pre-treated
workpiece. The invention also relates to a brazed assembly
comprising at least one component made of the workpiece obtained by
the method of this invention. The invention further relates to an
aqueous plating bath for use in the method of this invention.
DESCRIPTION OF THE RELATED ART
[0003] For the purpose of this invention brazing sheet is to be
understood as a core sheet, for example of aluminum or aluminum
alloy, having on at least one side a brazeable aluminum alloy.
Typical brazeable aluminum alloys useful as a clad layer are the
Aluminum Association (AA) 4xxx-series alloys, typically having Si
in the range of 2 to 18 weight %, and preferably in the range of 7
to 14%. The brazeable aluminum alloys may be coupled to the core
alloy in various ways known in the art, for example by means of
roll bonding, cladding, spray-forming or semi-continuous or
continuous casting.
[0004] Controlled Atmosphere Brazing ("CAB") and Vacuum Brazing
("VB") are the two main processes used for industrial scale
aluminum brazing. Industrial vacuum brazing has been used since the
1950's, while CAB became popular in the early 1980's after the
introduction of the Nocolok (trade mark) brazing flux. Vacuum
brazing is an essentially discontinuous process and puts high
demands on material cleanliness. The disruption of the oxide layer
present is mainly caused by the evaporation of magnesium from the
clad alloy. There is always more magnesium present in the furnace
then necessary. The excess magnesium condenses on the cold spots in
the furnace and has to be removed frequently. The capital
investment for suitable equipment is relatively high.
[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 aluminum
surface before brazing. Unfortunately the brazing flux after drying
can easily fall off due to small mechanical vibrations. During the
brazing cycle, corrosive fumes such as HF are generated. This puts
a high demand on the corrosion resistance of the materials applied
for the furnace.
[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 forming of
the assembly parts. No additional brazing fluxing operations have
to be carried out. Presently, only one process for flux-less
brazing is used on an industrial scale. The material for this
process can be for example standard brazing sheet made from an
AA3xxx-series core alloy clad on both sides with a cladding of an
AA4xxx-series alloy. Before the brazing sheet can be used the
surface has to be modified in such a way that the naturally
occurring oxide layer does not interfere during the brazing cycle.
The method of achieving good brazing is to deposit a specific
amount of nickel on the surface of the aluminum clad alloy. If
properly applied, the nickel reacts with the underlying aluminum.
The nickel can be applied by using a shim of nickel between the two
parts to be joined or can be deposited by electroplating. When
electroplating is used the adherence of the nickel should be
sufficient to withstand typical shaping operations being used in
for example heat exchanger manufacture.
[0007] The processes for nickel-plating in an alkaline solution of
aluminum 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 these documents, nickel or cobalt, or combinations thereof, are
most preferably deposited in combination with lead. The lead
addition is used to improve the wettability of the clad alloy
during the brazing cycle. An important characteristic of these
plating processes is that the nickel is preferentially deposited on
the silicon particles of the clad alloy. To obtain sufficient
nickel for brazing on the surface, the clad alloy should contain a
relatively large number of silicon particles to act as nuclei for
the nickel deposition. It is believed that to obtain sufficient
nucleation sites before pickling a part of the aluminum in which
the silicon particles are embedded should be removed by chemical
and/or mechanical pre-treatment. This is believed a necessary
condition to obtain a sufficient nickel coverage to serve as nuclei
for the plating action of the brazing or clad alloy. On a
microscopic scale the surface of the Si-containing cladding of the
brazing sheet is covered with nickel globules.
[0008] However, the use of lead for the production of a suitable
nickel and/or cobalt layer on brazing sheet has several
disadvantages. The plating baths for electroplating are rather
complex and due to the presence of lead comprising components such
as salts thereof, these baths are much more environmentally
unfriendly than plating baths comprising nickel- or
cobalt-components alone. The use of lead for manufacturing
products, such as automotive products, is undesirable and it is
envisaged that in the very near future there might possibly even be
a ban on lead comprising products or products manufactured via one
or more intermediate processing steps comprising lead or lead-based
components. A further disadvantage of the plating bath described in
U.S. Pat. No. 4,028,200 is the considerable generation of ammonia
fumes on the workshop floor due to the use of significant amounts
of ammonia in the plating bath used.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide a method
of manufacturing an Al or Al alloy workpiece, comprising the steps
of providing an Al or Al alloy workpiece, pretreating of the
outersurface of the Al or Al alloy workpiece, and plating a metal
layer comprising nickel onto the outersurface of the pre-treated Al
or Al alloy workpiece, by which method a product is obtained having
good brazeability and/or weldability without the mandatory addition
of lead to the nickel-layer.
[0010] It is another object of the present invention to provide a
method of manufacturing a brazing sheet product comprising the
steps of (a) providing a sheet comprising a core sheet coupled on
at least one surface of said core sheet to an aluminum clad layer,
the aluminum clad layer being made of an aluminum alloy comprising
silicon in an amount in the range of 2 to 18% by weight, (b)
pre-treating of the outersurface of the aluminum clad layer, and
(c) plating a metal layer comprising nickel onto the outersurface
of the pre-treated aluminum clad layer, by which method a brazing
sheet product is obtained having good brazeability without the
mandatory addition of lead to the nickel-layer.
[0011] It is a further object of the present invention to provide a
method of manufacturing an Al or Al alloy workpiece, ideally a
brazing sheet product, the method comprising the steps of (a)
providing an Al or Al alloy workpiece, in particular a brazing
sheet comprising a core sheet coupled on at least one surface of
said core sheet to an aluminum clad layer, the aluminum clad layer
being made of an aluminum alloy containing silicon in an amount in
the range of 2 to 18% by weight, (b) pre-treating of the
outersurface of the Al workpiece, in particular the aluminum clad
layer, and (c) plating a metal layer comprising nickel onto the
outersurface of the pre-treated workpiece, in particular of the
pre-treated aluminum clad layer, by which method there is no
generation of ammonia fumes originating from the plating bath when
operated on an industrial scale.
[0012] It is also an object of the invention to provide an aqueous
plating bath for use in the method according to the invention and
which can be employed in an industrial environment.
[0013] In accordance with the invention in one aspect there is
provided a method of manufacturing an aluminum or aluminum alloy
workpiece, the method comprising the sequential steps of (a)
providing an Al or Al alloy workpiece, (b) pre-treating of the
outersurface of the aluminum workpiece, and (c) plating a metal
layer comprising nickel onto said outersurface of the pre-treated
aluminum or aluminum alloy workpiece. This method is characterized
in that during step (c) said layer comprising nickel being
deposited by plating both nickel and bismuth using an aqueous bath
having:
[0014] a pH in the range of 2.5 to 10, and
[0015] comprising a nickel-ion concentration in a range of 10 to
100 g/l, and preferably in a range of 20 to 70 g/l,
[0016] a bismuth-ion concentration in the range of 0.01 to 10 g/l,
and preferably in the range of 0.02 to 5 g/l,
[0017] a citrate-ion concentration in the range of 40 to 150 g/l,
and preferably in the range of 80 to 110 g/l,
[0018] a gluconate-ion concentration in the range of 2 to 80 g/l,
and preferably in the range of 4 to 50 g/l,
[0019] a chloride- or fluoride-ion concentration in the range of 1
to 50 g/l, and preferably in the range of 1 to 30 g/l.
[0020] In accordance with the invention it has been found
surprisingly that the nickel layer does not need to comprise any
lead as a mandatory alloying addition in order to achieve good
brazeability when using the aluminum workpiece in a brazing
operation. Surprisingly it has been found that equal or even better
results can be obtained if bismuth is added to the nickel layer,
such that said nickel layer can be kept essentially lead-free and
simultaneously also in the plating bath used for the deposition of
this Ni--Bi layer. By using this aqueous plating bath the need for
the addition of lead has been overcome, which is a significant
achievement from an enviromental point of view.
[0021] This aqueous plating bath demonstrated to be operational in
a very wide pH range, and can be used on industrial scale coil
plating lines using a high current density, which in turn allows
for fairly high line speeds. Further advantages of this plating
bath are that it does not generate any ammonia fumes, it can be
composed using standard and readily available chemicals, and
bismuth can easily be replenished to the plating bath from a
bismuth concentrate or otherwise.
[0022] Preferably said layer comprising nickel being deposited by
plating both nickel and bismuth using an aqueous bath comprising a
nickel-ion concentration in a range of 20 to 70 g/l and a
bismuth-ion concentration in the range of 0.02 to 5 g/l.
[0023] The nickel-ion concentration to the aqueous bath can be
added via the addition of nickel chloride, nickel fluoborate,
nickel sulfamate, nickel acetate or nickel suplhate. However, there
is a preference to use the addition of nickel sulfate
(NiSO.sub.4.6H.sub.2O). At a too high level of nickel salt in the
aqueous bath there is the risk of the crystallization of the salt
in the solution, which might damage a continuous process. At too
low levels the resultant bath becomes uneconomical due to too long
plating times and low current density.
[0024] Bi-ion in the concentration set out above can be added in
various ways to the aqueous bath. In theory many bismuth compounds
could be used for this purpose. However, many bismuth compounds
have been tried out but only a very few appear to provide reliable
and reproducible results. For example the addition of bismuth
acetate has been tried, but it has been found that this compound
did not dissolve in the plating bath used, whereas the addition of
lead acetate did not result in any problems with respect to having
this compound dissolved. For example also the combination of a bath
of nickel-ions and bismuth-ions and a tartrate at a pH in the range
of more than 8 resulted in the formation of an undesirable Ni
containing sludge. This Ni containing sludge did not re-dissolve
upon heating, indicating amongst others that Ni is unstable in the
presence of a tartrate in the mentioned pH range. In accordance
with the invention very good results have been obtained when
Bi-ions are being added via the addition of one or more of the
group consisting of bismuth carbonate ( Bi.sub.2(CO.sub.3).sub.3 ),
bismuth oxide ( Bi.sub.2O.sub.3 ), bismuth citrate
(BiC.sub.6H.sub.5O.sub.7) and bismuth chloride (BiCl.sub.3 ).
Optionally some sodium hydroxide may be added also to regulate the
pH of the aqueous bath. By using bismuth carbonate or bismuth oxide
in the presence of nickel a suitable plating bath has been obtained
which is stable at a very wide pH range. At too high levels of
Bi-ion concentration in the aqueous bath the resultant deposit has
a undesired high Bi-concentration. Preferably the Bi-concentration
in the resultant Ni--Bi layer on the brazing sheet product is not
more than 5 percent by weight, and preferably not more than 3
percent by weight. At too low levels the resultant bath becomes
uneconomical due to too long plating times and low current
density.
[0025] Preferably in the workpiece, in particular a brazing sheet
product, the layer comprising nickel and bismuth has a thickness up
to 2.0 .mu.m, preferably in the range of 0.03 to 1.0 .mu.m, and
more preferably in the range of 0.05 to 0.5 .mu.m. A coating
thickness of greater than 2.0 .mu.m requires a prolonged treatment
time for plating, and may result in wrinkling of the molten filler
material during subsequent brazing operations. A preferred
thickness for this Ni--Bi containing layer is 0.3 .mu.m. Also other
techniques such as roll bonding, thermal spraying, Chemical Vapor
Deposition and Physical Vapor Deposition or other techniques for
depositing of metal or metal alloys from a gas or vapor phase may
be used.
[0026] Baths using the following salts have proved particularly
effective, in grams per liter:
[0027] Nickel sulphate in a range of 45 to 450 g/l, and preferably
90 to 315 g/l,
[0028] Chloride-ion concentration in a range of 1 to 50 g/l, and
preferably 1 to 30 g/l,
[0029] Sodium citrate in a range of 55 to 180 g/l, and preferably
110 to 150 g/l,
[0030] Sodium gluconate in range of 2 to 90 g/l, and preferably 5
to 55 g/l,
[0031] Ammonium sulphate in a range up to 270 g/l,
[0032] Bismuth oxide in a range of 0.02 to 22 g/l, and preferably
0.05 to 11 g/l, or Bismuth carbonate in a range of 0.03 to 29 g/l,
and preferably 0.06 to 14 g/l.
[0033] The addition of an ion from the group consisting of chloride
and fluoride is required for inducing anode corrosion. A suitable
source of chloride-ion concentration can be done by the addition of
nickel chloride (NiCl.sub.2.6H.sub.2O) in a range of up to 415 g/l,
and preferably in a range up to 250 g/l.
[0034] (H+) or (OH--) can be added to regulate the pH in a range of
2.5 to 10. The use of ammonium hydroxide should preferably be
avoided in view of the generation of ammonia fumes.
[0035] Optionally for reducing stress in the deposit layer
comprising the Ni and Bi an ammonium-ion concentration in a range
up to 40 g/l, and preferably in range of 1 to 25 g/l, or a
triethenalamine-ion concentration in a range of up to 40 g/l, or
combinations thereof, or other equivalent components may be added
to the aqueous bath. Any soluble ammonium salt can be used as a
source of NH.sub.4.sup.+.
[0036] The plating bath used in the method according to the
invention can operate in a wide pH range of 2.5 to 10, and
preferably in the range of 4 to 8, without affecting the properties
of the bath and without dissolving the aluminum clad layer or any
other metal layer thereon. If the aluminum workpiece, such as a
brazing sheet product having an aluminum clad layer, is provided
with a thin intermediate zinc layer, e.g. by means of a zincate
treatment via direct or immersion plating, prior to the plating of
the Ni--Bi layer, the pH is preferably in the range of 5 to 8, and
more preferably in the range of 5.4 to 7.5. In the embodiment of an
applied intermediate layer comprising zinc, the layer has a
thickness 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 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.
Instead of zinc also tin may be used.
[0037] The method according to the invention is preferably employed
using a plating bath having a temperature in the rang of 30 to
70.degree. C., and more preferably in the range of 40 to 65.degree.
C. In this temperature range the ion-mobility increases and there
is no need to cool the plating bath to compensate for the heat
generation during plating.
[0038] The invention further relates to an aqueous bath for the
electro-deposition of a layer comprising both nickel and bismuth on
a brazing sheet product having:
[0039] a pH in the range of 2.5 to 10, and
[0040] comprising a nickel-ion concentration in the range of 10 to
100 g/l, and preferably in a range of 20 to 70 g/l,
[0041] a bismuth-ion concentration in the range of 0.01 to 10 g/l,
and preferably in a range of 0.02 to 5 g/l,
[0042] a citrate-ion concentration in the range of 50 to 150 g/l,
and preferably in a range of 80 to 110 g/l,
[0043] a gluconate-ion concentration in the range of 2 to 80 g/l,
and preferably in a range of 4 to 50 g/l,
[0044] a chloride- or fluoride-ion concentration in the range of 1
to 50 g/l, and preferably in a range of 1 to 30 g/l. This aqueous
plating bath demonstrated to be operational in a very wide pH
range, and at a wide temperature range, and further can be used on
industrial scale coil plating lines using a high current density,
which in turn allows for fairly high line speeds. Further
advantages of this plating bath are that it does not generate any
ammonia fumes, it can be composed used standard and readily
available chemicals, and the bismuth concentration can easily be
replenished to the plating bath from a bismuth concentrate or
otherwise.
[0045] The adhesion of the layer comprising both nickel and bismuth
to the aluminum workpiece, such as the cladding of a brazing sheet
product, is fairly good, but may be further improved by a proper
pre-treatment of the outersurface of the aluminum workpiece on
which the Ni--Bi layer is being deposited, such as the clad layer
of a brazing sheet product. The pre-treatment comprises a
preliminary cleaning step during which the surface is made free
from grease, oil, or buffing compounds. This can be accomplished in
many ways, and can be accomplished amongst others by vapor
degreasing, solvent washing, or solvent emulsion cleaning. Also a
mild etching may be employed. Following the preliminary cleaning,
the surface should preferably be conditioned. Several methods can
be applied successfully, such as, but not limited thereto:
[0046] (a) acid desmutting in an solution comprising nitric acid
(typically 25-50%), optionally in combination with a fluoride
and/or chromic acid and/or sulphuric acid. Suitable sources for the
fluoride can be, for example, hydrofluoric acid or ammonium
bifluoride, see also e.g. "The surface treatment and finishing of
aluminum and its alloys", by S. Wernick et al., ASM international,
5th edition, 1987, Vol.1, pp.181-182.
[0047] (b) mechanical preparation such as polishing, abrasion or
brushing. These may also be applied while the surface is in contact
with a lower alcohol, such as for example isopropanol, see e.g.
also U.S. Pat. No. 4,388,159.
[0048] (c) alkaline etching, see e.g. "The surface treatment and
finishing of aluminum and its alloys", by S. Wernick et al., ASM
international, 5th edition, 1987, Vol.1, pp.191-203.
[0049] (d) aqueous detergent cleaning;
[0050] (e) anodic oxidation, see e.g. "The surface treatment and
finishing of aluminum and its alloys", by S. Wernick et al., ASM
International, 5th edition, 1987, Vol.2, pp.1006 ff.
[0051] (f) electrograining.
[0052] (g) pre-treatments described in for example U.S. Pat. No.
4,741,811, U.S. Pat. No. 5,245,847, U.S. Pat. No. 5,643,434.
[0053] (h) immersion processes such as zincate and stannate, see
"The surface treatment and finishing of aluminum and its alloys",
by S. Wernick et al., ASM international, 5th edition, 1987, Vol.2,
Chapter 14 and 15.
[0054] Also combinations of one or more conditioning steps set out
above can be applied successfully.
[0055] In an embodiment the Al or Al alloy workpiece is an aluminum
alloy sheet or aluminum alloy wire or aluminum alloy rod. Although
various aluminum alloys may be applied, e.g. those within the
Aluminum Association (AA)3xxx- and AA6xxx-series aluminum alloys.
Particular suitable aluminum alloys are those within the
AA4xxx-series alloys, typically having Si as the most important
alloying element in the range of 2 to 18% by weight, more
preferably 7 to 14% by weight. Other alloying elements may be
present to improve specific properties, the balance is made by iron
up to 0.8%, and impurities each up to 0.05 wt. %, total up to 0.20
wt. %, and aluminum. An AA4xxx-series aluminum alloy sheet can be
plated with Ni--Bi alloy in accordance with the method of the
invention, and may be employed in subsequent brazing operations, in
particular in an inert atmosphere brazing (CAB) operation in the
absence of a brazing-flux material. Also aluminum alloy wire or
rods being made of an AA4xxx-series alloy may be plated with a
Ni--Bi layer, and subsequently employed in brazing operations in
particular in an inert atmosphere brazing (CAB) operations in the
absence of a brazing-flux material, and may also be employed as
weld filler wire or weld filler rod in a welding operation.
[0056] In a preferred embodiment the aluminum alloy workpiece is a
brazing sheet product comprising a core sheet coupled at least one
surface of said core sheet to n aluminum clad layer, the aluminum
clad layer being made of an aluminum AA4xxx-series alloy comprising
silicon in the range of 2 to 18% by weight, preferably in the range
of 7 to 14%. In an embodiment of the aluminum brazing sheet
product, the core sheet is made of an aluminum alloy, in particular
those within the AA3xxx, AA5xxx, or AA6xxx-series alloys.
[0057] The invention further provides a brazed assembly comprising
at least one component made of the aluminum alloy workpiece, in
particular a brazing sheet product, obtained by the method in
accordance with the invention described above. Preferably the
resultant brazing sheet product has a Ni--Bi layer comprising Bi,
by weight percent, in a range of up to 5%, preferably not more than
3%, and more preferably up to 1.0%, and most preferably in a range
of 0.01 to 0.05%.
[0058] In an embodiment there is provided a brazed assembly wherein
at least one of the parts to be joined by brazing is made of the
aluminum alloy workpiece, in particular a brazing sheet product,
produced by the method in accordance with the invention described
above, and at least one other part is made of steel, aluminized
steel, stainless steel, plated or coated stainless steel, bronze,
brass, nickel, nickel alloy, titanium, or plated or coated
titanium.
[0059] In a further aspect of the invention there is provided in a
method of manufacturing a brazed assembly using the aluminum alloy
workpiece, in particular a brazing sheet product, produced by the
method in accordance with this invention, comprising the steps
of:
[0060] (a) shaping or forming parts of which at least one is made
from the aluminum alloy workpiece, ideally a brazing sheet product,
obtained by the method in accordance with this invention as set out
above;
[0061] (b) assembling the parts into the assembly;
[0062] (c) brazing the assembly under a vacuum or in an inert
atmosphere (CAB) in the absence of a brazing-flux at elevated
temperature for a period long enough for melting and spreading of
the molten filler alloy;
[0063] (d) cooling the brazed assembly to below 100.degree. C. 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.
[0064] In dependence on the material, particularly aluminum alloy,
of the cores sheet the process may include the further processing
step (e) of aging of the brazed and cooled assembly in order to
optimize the mechanical and/or corrosion properties of the
resultant assembly. The use of the brazing sheet product obtained
from the method according to the invention set out above has been
found to result in a lower brazing temperature by at least
10.degree. C. This reduced brazing temperature allows a significant
reduction of the industrial scale processing time of a complete
brazing cycle, typically a time reduction of 15% or more has been
found.
[0065] In an embodiment of the method of manufacturing a brazed
assembly in step (a) at least one of the parts to be joined by
brazing is made of the brazing sheet product produced by the method
in accordance with the invention described above, and at least one
other part is made of steel, aluminized steel, stainless steel,
plated or coated stainless steel, bronze, brass, nickel, nickel
alloy, titanium, or plated or coated titanium.
EXAMPLE.
[0066] On a laboratory scale of testing aluminum brazing sheets
manufactured from an AA3003 core alloy clad on both sides with an
AA4045 clad alloy, and having a total thickness of 0.5 mm and a
clad layer thickness of 50 microns each, was treated using the
following sequential process steps:
[0067] cleaning by immersion for 180 sec. in ChemTec 30014 (a
commercial available alkaline (etch) degreaser), followed by
rinsing;
[0068] alkaline etching for 20 sec. in ChemTec 30203 (a commercial
available alkaline etch cleaner) at ambient temperature, followed
by rinsing;
[0069] 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;
[0070] nickel electroplating, and rinsing.
[0071] The nickel plating bath used has the composition of Table 1
and having a pH of 5.5. The Bi-ion concentration has been added to
the plating bath using a Bi-ion concentrate of 160 g/l sodium
hydroxide, 300 g/l sodium gluconate and 110 g/l bismuth oxide. The
bismuth oxide could have been replaced also by bismuth carbonate.
The electroplating of a Ni--Bi layer was performed at 57.degree. C.
using three different current densities and plating times. The
composition of the resultant layer was measured using ICP and is
given in Table 2. ICP stands for Induced Coupled Plasma. The
results given are for the sum of both plated sides. For comparison
similar brazing sheet material has been Ni-plated with Ni--Pb. The
plating bath comprised 50 g/l nickel sulphate, 50 g/l nickel
chloride, 100 g/l/sodium citrate, 1 g/l lead acetate, and 75 ml/l
ammonium hydroxide (30%). The plating conditions at 26.degree. C.
were such that a plating time of 200s resulted in a nickel-lead
plated layer of 2.0 microns using a current density of 3
A/dm.sup.2. Due to the presence of ammonium-hydroxide ammonia fumes
are being generated.
[0072] 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 results are given in Table 2.
Further the brazeability has been assessed. 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 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 summarized in Table 2.
[0073] This example shows how an electroplated nickel layer
containing Bi, but comprising no Pb, may be applied and resulting
in a product having at least a fair adhesion of the nickel layer
and excellent brazeability. Normally bismuth is not easily
maintained in a stable nickel-plating solution without sludge
formation.
[0074] It will be apparent to the skilled person that the Ni--Bi
plating operations according to the invention may be applied also
on one or both sides of an aluminum alloy sheet or strip made of an
AA4xxx-series aluminum alloys, which aluminum alloy sheet is not
being provided with a core sheet to form a brazing sheet product.
Such a Ni--Bi plated sheet or strip, typically having a gauge in
the range of up to 3 mm, preferably in the range of 0.05 to 2 mm,
may be employed also in a brazing operation as set out in this
example. A similar approach can be used for plating aluminum alloy
wires or rods. Such Ni--Bi plated wires or rods may be employed in
a brazing operation as set out in this example or used as filler
material in a welding operation, such as for laser welding
operations.
[0075] The current efficiency of Ni deposition appears to be
100%.
[0076] The samples plated with Ni--Bi at 3 A/dm.sup.-2 showed some
black spots, but the samples plated at the higher current densities
have excellent appearance. About 0.5 g.m.sup.-2 bismuth was
deposited. The bismuth content of the deposited alloy layer can
easily be varied, e.g. by lowering the bismuth concentration in the
plating bath, to give a lower Bi content.
[0077] This plating bath has many advantages compared to the
standard known Pb-containing baths:
[0078] no ammonia fumes
[0079] more practical operating temperatures, typically 40 to
70.degree. C.
[0080] high current density
[0081] bismuth can easily be replenished to the plating bath.
[0082] Further, standard chemicals were employed.
1 TABLE 1 Compound Concentration [g/l] Nickel sulphate 142 Ammonium
sulphate 34 Nickel chloride 30 Sodium citrate 140 Sodium gluconate
30 Bismuth ions 1
[0083]
2TABLE 2 Current Density Time Ni Bi Invention [A/dm.sup.2] [sec.]
[g/m.sup.2] [g/m.sup.2] Adhesion Brazeability yes 3 50 9.1 0.66
.+-. + yes 6 25 10.4 0.50 .+-. + yes 10 15 9.5 0.46 .+-. + no 3 50
9.4 -- .+-. +
[0084] 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.
* * * * *