U.S. patent application number 12/244156 was filed with the patent office on 2010-04-08 for novel cyanide-free electroplating process for zinc and zinc alloy die-cast components.
Invention is credited to Roderick D. Herdman, Craig Robinson, Anthony J. Rowan.
Application Number | 20100084278 12/244156 |
Document ID | / |
Family ID | 42073800 |
Filed Date | 2010-04-08 |
United States Patent
Application |
20100084278 |
Kind Code |
A1 |
Rowan; Anthony J. ; et
al. |
April 8, 2010 |
Novel Cyanide-Free Electroplating Process for Zinc and Zinc Alloy
Die-Cast Components
Abstract
The proposed invention comprises a process for plating upon zinc
die cast articles without the use of cyanide in the plating
solution The process proposes the plating of the zinc die cast
articles with a zinc alloy layer first, followed by plating with
copper, nickel, chromium, tin or brass. The preferred zinc alloy
initial coating is zinc-nickel.
Inventors: |
Rowan; Anthony J.;
(Leicestershire, GB) ; Herdman; Roderick D.;
(Staffordshire, GB) ; Robinson; Craig; (Coventry,
GB) |
Correspondence
Address: |
ARTHUR G. SCHAIER;CARMODY & TORRANCE LLP
50 LEAVENWORTH STREET, P.O. BOX 1110
WATERBURY
CT
06721
US
|
Family ID: |
42073800 |
Appl. No.: |
12/244156 |
Filed: |
October 2, 2008 |
Current U.S.
Class: |
205/239 |
Current CPC
Class: |
C25D 5/12 20130101; C25D
3/22 20130101; C25D 3/12 20130101; C25D 3/38 20130101 |
Class at
Publication: |
205/239 |
International
Class: |
C25D 3/56 20060101
C25D003/56 |
Claims
1. A process for plating upon a zinc die-cast article, said process
comprising: (a) cleaning said article; (b) electroplating said
article in an aqueous solution comprising (i) zinc ions, (ii)
nickel ions, and (iii) counter ions, by making said article a
negative cathode in said solution to produce a zinc-nickel alloy
coating thereon; and (c) electroplating said article with a metal
selected from the group consisting of copper, nickel, chromium,
tin, and alloys of the foregoing.
2. (canceled)
3. (canceled)
4. A process according to claim 1 wherein the article is made
cathodic prior to contacting it with the aqueous solution of step
(b).
5. A process according to claim 18 wherein the article is made
cathodic prior to contacting it with the aqueous solution of step
(b).
6. A process according to claim 1, wherein the source of the nickel
ions in step (b) is selected from the group consisting of nickel
chloride, nickel sulfate and nickel acetate.
7. A process according to claim 6, wherein the nickel ions are
present in the aqueous solution of step (b) at a concentration of
between about 10 g/l and about 100 g/l.
8. A process according to claim 7, wherein the nickel ions are
present in the aqueous solution of step (b) at a concentration of
between about 50 g/l and about 55 g/l in the aqueous solution in
step (b).
9. A process according to claim 1 wherein the source of the zinc
ions in step (b) is a water soluble zinc salt.
10. A process according to claim 9 wherein the water soluble zinc
salt is selected from the group consisting of zinc chloride, zinc
sulfate, zinc acetate and alkali metal zincates.
11. A process according to claim 9 wherein the aqueous solution of
step (b) comprises a buffering compound selected from the group
consisting of ammonium ions and borate ions.
12. A process according to claim 9 wherein the water soluble zinc
salt is present in the aqueous solution of step (b) at a
concentration of between about 10 g/l and about 100 g/l.
13. A process according to claim 12 wherein the water soluble zinc
salt is present in the aqueous solution of step (b) at a
concentration of between about 45 g/l and about 50 g/l.
14. A process according to claim 1 wherein the source of the zinc
ions of step (b) is an alkali metal zinc ate; and wherein the
aqueous solution of step (b) additionally comprises an amine
compound.
15. A process according to claim 14, wherein the alkali metal
zincate is selected from the group consisting of sodium zincate and
potassium zincate.
16. A process according to claim 14, wherein the alkali metal
zincate is present in the aqueous solution of step (b) at a
concentration of between about 2 and about 30 g/l.
17. A process according to claim 16, wherein the alkali metal
zincate is present in the aqueous solution of step (b) at a
concentration of between about 8 and about 12 g/l.
18. A process for plating upon a zinc die-cast article, said
process comprising: (a) cleaning said article; (b) electroplating
said article in an aqueous alkaline solution comprising (i) zinc
ions, (ii) alloy metal ions, and (iii) counter ions, by making said
article a negative cathode in said solution to produce a
zinc-nickel alloy coating thereon; and (c) electroplating said
article with a metal selected from the group consisting of copper,
nickel, chromium, tin, and alloys of the foregoing, wherein said
aqueous alkaline solution has a pH in the range of about 4.5 to
about 7.0.
19. A process according to claim 18, wherein the pH of the aqueous
solution in step (b) is between about 5.0 to about 5.5.
20. A process according to claim 18 wherein the concentration of
zinc ions in the aqueous solution of step (b) is from about 10 to
about 100 g/l.
21. A process according to claim 1 wherein the concentration of
alloy ions in the aqueous solution of step (b) is from about 10 to
about 100 g/l.
Description
FIELD OF THE INVENTION
[0001] The present invention is directed to a method for covering
an article manufactured from zinc or zinc alloy with an adherent
metallic coating, said method being substantially free from cyanide
ions. The coating of the invention renders the article suitable for
subsequent electroplating in other metals such as copper, nickel
and chromium.
BACKGROUND OF THE INVENTION
[0002] Zinc and zinc alloy products are generally produced as die
castings and are commonly used in applications such as automotive
parts or fittings. To enhance the decorative appearance of such
articles and to provide them with protection against corrosion,
said articles are commonly coated with other metals by the process
of electrolytic or electroless plating. The most common metals for
this application are copper, nickel, chromium and brass. Further
enhancements in appearance or corrosion protection may be obtained
by the use of organic coatings.
[0003] Zinc and zinc alloy articles are traditionally electroplated
with a first coating of copper, which is applied from a process
that contains cyanide ions. The copper solution is alkaline in
order to minimize chemical attack on the substrate and the cyanide
ions are necessary to provide a stable complex of copper (I) ions.
Efforts have been made to replace copper cyanide electroplating
solutions in order to eliminate the use of cyanide ions due to
their high toxicity.
[0004] Suitable stable aqueous complexes of copper (I) ions to
replace cyanide ions in alkaline copper electroplating baths have
proved elusive. U.S. Pat. No. 5,750,018 describes an alkaline
copper (l) solution using imides such as succinimide or a hydantoin
such as dimethylhydantoin, but these solutions require the
permanent presence of a reducing agent such as an alkali sulphite
or bisulphite, or an amine such as hydroxylamine or hydrazine.
However the copper (I) ion remains inherently unstable, oxidation
to copper (II) occurs readily, and such baths are not robust,
requiring close monitoring and maintenance. They have not found
favour in industrial applications.
[0005] Alkaline copper (II) baths containing complexants have been
suggested, with pyrophosphate being a well know example. However
the pyrophosphate complex is not stable enough to prevent the
chemical deposition of copper from copper(II) onto the zinc-based
substrate, with the corresponding chemical dissolution of zinc from
the surface, even with a cathodic potential applied prior to
immersion in the bath. Such immersion deposits produce poorly
adherent coatings that either flake off or exhibit blistering.
[0006] U.S. Pat. No. 3,928,147 claims a method of immersing the
zinc articles in a solution of an organophosphorus chelating agent
prior to immersion in the cyanide-free copper(II) electroplating
bath in order to inhibit the immersion deposition of copper.
[0007] More recently U.S. Pat. No. 4,469,569 and U.S. Pat. No.
4,521,282 have described the use of organophosphonate complexing
agents in a copper plating bath, and U.S. Pat. No. 6,054,037
describes an organophosphonate bath modified by the addition of
halogen ions to stabilise copper(I) ions in the cathode film. These
types of bath are found to be suitable to electroplate onto steel
and in some instances are found to work on zinc substrates with a
cathodic potential applied prior to immersion in the bath. However,
in general, immersion deposits still occur in the aforementioned
baths even with the application of cathodic potential prior to
immersion, and in this respect the foregoing types of copper(II)
baths have not found general use for the application of
electroplating on zinc die-cast articles.
[0008] Most recently U.S. Patent Application 2008/0156652 describes
an alkaline electroplating bath of copper (II) salts with a
tartrate complexant and an additive selected from phosphate or
hypophosphite, wherein the article is electroplated at 0.002 to
0.02 A/dm2. However the inventors of the present invention have
found this system to also give immersion deposits with inherently
poorer adhesion than electroplated deposits.
[0009] Alternative approaches to replacing cyanide have been
directed to replacing copper with a different metal coating.
GB2272001 describes an electrolyte containing zinc and tin for use
on zinc die-casts prior to electroplating with alkaline
cyanide-free copper, which would be believed to be of the
copper(II) pyrophosphate type.
[0010] U.S. Pat. No. 6,827,834 proposes the use of an alkaline
pyrophosphate nickel bath to deposit an immersion nickel coating
prior to a pyrophosphate copper electroplating stage. However,
immersion deposits are inherently less adherent than electroplated
deposits and in addition, any deposit of a different metal needs to
be thick enough to provide a non-porous film in order to prevent
further immersion deposition of copper from the subsequent
copper(II) solution. Immersion deposits are not thick enough to
give non-porous layers. Thus this method still suffers from poor
adhesion and a general lack of robustness when compared to the
current cyanide-based electroplating technique.
[0011] Accordingly, U.S. Patent Application 2006/0096868 describes
a mildly acidic near-neutral nickel electroplating bath used to
deposit a thick nickel layer on the zinc die-cast article. Although
the deposits from this type of bath are thick enough to protect the
substrate from attack in subsequent process stages, the electrolyte
has poor throw into recesses and therefore some zinc substrate can
remain exposed on complex-shaped parts. Additionally the deposits
from this electrolyte exhibit very high internal stress and poor
ductility.
[0012] Although the above prior art describes the production of
adherent deposits, a typical electroplater will be required to test
the adhesion of the coatings on zinc die-cast articles by heating
the articles, for example for 1 hour. After the heating stage the
articles are immediately plunged into water at ambient temperature.
A common heating temperature for such a test is 180.degree. C. This
heat and quench test can reveal a lack of adhesion of all the
coatings of the prior art, demonstrated by the appearance of large
blisters on the articles. The current method of using
cyanide-containing copper(I) baths for electroplating the first
layer onto the article provides blister-free results from this
test.
[0013] Thus there remains a requirement to provide a process for
electroplating zinc die-cast articles without the use of baths
containing copper cyanide, and which is capable of demonstrating
excellent adhesion when subjected to the aforementioned heat and
quench test. Such a process must also be robust enough to withstand
continuous use under typical industrial production conditions with
a minimum of technical control and maintenance.
[0014] The present invention is directed to a method for producing
an adherent metallic coating on a zinc or zinc alloy article
without the use of cyanide ions in the process. The zinc or zinc
alloy article is first cleaned in the normal manner and then
electroplated with a zinc alloy coating, said zinc alloy coating
being preferably a zinc-nickel alloy. The said zinc alloy coating
has good adhesion to the substrate and provides a metallic layer
suitable for subsequent electroplating stages.
SUMMARY OF THE INVENTION
[0015] The present invention describes an electroplating bath and
method which provide for producing a zinc alloy coating on a zinc
die-cast substrate, said coating providing a suitable base for
subsequent electroplating, without the use of cyanide ions.
Preferably the zinc alloy coating is a zinc-nickel alloy. The
method comprises the following steps; [0016] (a) cleaning and
activation of the zinc die-cast article; [0017] (b) electroplating
of the article in a bath comprising zinc ions, alloying metal ions
(which are preferably nickel ions), and counter ions; [0018] (c)
subsequently coating the article by electrolytic or electroless
means with one or more of the following; copper, nickel, chromium,
tin, brass, or other metal as desired and optionally a final
organic coating to achieve an attractive and corrosion resistant
finish on the article.
DETAILED DESCRIPTION OF THE INVENTION
[0019] This invention describes a method of treating zinc die-cast
articles to produce an adherent coating suitable for the
application of subsequent electroplated metallic coatings without
the use of solutions containing cyanide ions. The method of the
invention generally includes the steps of: [0020] (a) optionally,
but preferably, cleaning and activating the zinc die-cast article;
[0021] (b) electroplating the article in a bath comprising zinc
ions, alloying metal ions (which are preferably nickel ions), and
counter ions; [0022] (c) subsequently coating the article by
electrolytic or electroless means with further metallic layers and
optionally a final organic coating.
[0023] The cleaning and activating step is preferred to provide a
surface that is suitable for electroplating. Defects such as lack
of adhesion, porosity, roughness, dark spots and non-uniform
coating are likely to occur on poorly prepared parts. The surface
preparation process also serves to activate the surface of the part
so that it is optimally receptive to the deposition of the metal
coating.
[0024] The zinc die-cast articles are first cleaned in a neutral or
alkaline degreasing cleaner to remove oils from the surface of the
articles and also any residual buffing compound that may be present
from post-casting buffing operations. The articles are thoroughly
rinsed and then activated to remove surface oxides by a short
immersion in a weakly acid solution such as 5-10% sulphuric acid.
Thorough rinsing is preferred between all cleaning stages and also
prior to electroplating to remove all traces of acid and alkali
from any porous areas on the article. After cleaning and
activating, the zinc die-cast article is electroplated by making it
the cathode in an aqueous solution containing zinc ions, alloying
metal ions, which are preferably nickel ions, and counter ions.
[0025] The source of zinc and alloying ions in the invention are
any water soluble zinc or alloying metal salts. Of particular
preference for zinc are zinc chloride, zinc sulphate, zinc acetate
and alkali metal zincates. The preferred source of the alloying
ions is the chloride, sulphate or acetate salt of the chosen
alloying metal, preferably nickel. The concentration of zinc ions
in the electrolyte is generally between 2 and 100 g/l, and the
concentration of alloying metal is generally between 0.2 and 100
g/l. The counter ions merely refers to the anions (eg. chloride,
sulfate, acetate, etc.) that are associated with the metal ions in
the salt chosen. Other useful alloying metals include cobalt,
copper and iron.
[0026] In addition to the zinc and alloying metal salts the
solution may contain other salts and additives, for example (i)
sources of hydrogen ion or hydroxide ion to adjust the pH of the
electrolyte, (ii) buffering compounds such as ammonium ions, borate
ions or organic acid species, (iii) complexing agents such as an
amine to prevent precipitation of metal hydroxides, (iv) additional
inorganic salts to improve the conductivity of the electrolyte, and
(v) wetting agents and brightening agents.
[0027] In a first embodiment of the invention, the electrolyte is
composed of a water soluble zinc salt providing zinc ions
preferably in the concentration range of 10-100 g/l, a water
soluble alloying metal salt providing alloying metal ions
preferably in the concentration range of 10-100 g/l, a buffering
compound and optionally further inorganic salts, wetting agents and
brighteners. Preferably the zinc salt is zinc chloride, the
alloying metal salt is most preferably nickel chloride or nickel
sulphate, and ammonium chloride or boric acid are the preferred
buffering agent. The electrolyte is operated at a mildly acidic pH
in the range 4.5-7.0, preferably about 5.0-5.5, and can be operated
in the temperature range of 10-90.degree. C. but preferably at
20-30.degree. C.
[0028] In a second embodiment of the invention, the electrolyte is
composed of an alkali metal zincate providing zinc ions preferably
in the concentration range of 2-30 g/l, a water soluble alloying
metal salt providing alloying metal ions preferably in the
concentration range of 0.2-5 g/l, an amine compound to act as a
chelating agent for the alloying metal ions, an alkali metal
hydroxide, optionally an alkali metal carbonate and optionally
wetting and brightening agents. Preferably the alkali metal zincate
is sodium or potassium zincate, the alloy metal salt is nickel
sulphate, the chelating agent is a polymeric amine or a substituted
ethylenediamine compound and the alkali metal hydroxide is sodium
or potassium hydroxide. The electroplating solution is operated at
a pH of between 10 and 14 and can be operated in the temperature
range of 10-90.degree. C. but preferably at 20-30.degree. C.
[0029] Both embodiments of the invention provide a zinc alloy
deposit which normally consists of 70-90% zinc and 10-30% of
alloying metal, preferably nickel.
[0030] The anode in the electroplating baths may be either metallic
zinc, the alloying metal which is preferably nickel, or insoluble
anodes for example titanium coated with mixed metal oxides. For the
first embodiment of the invention a zinc anode is preferred, and
for the second embodiment of the invention an anode of the alloying
metal, which is most preferably nickel, or a coated titanium anode
is preferred.
[0031] The articles are electroplated in the solutions of the
invention at current densities of between 0.1 and 5.0 A/dm2,
preferably between 1 and 4 A/dm2, and the plating time is normally
2-10 minutes, preferably 4-8 minutes. Under these conditions an
adherent zinc alloy, preferably a zinc-nickel alloy, is deposited.
Typically the deposit contains 10-30% of alloying metal with the
remainder being zinc. Both embodiments of the invention have
minimal or no attack on the zinc die-cast articles and provide for
deposits with excellent coverage into the recesses of
complex-shaped parts, thereby providing optimum protection during
subsequent processing stages.
[0032] Although both embodiments of the invention can produce the
desired coating, the preferred embodiment is the mildly acidic bath
described in the first embodiment.
[0033] After electroplating in the bath of the invention the
articles are subsequently electroplated with any suitable
electroplating bath, however due to the coating of the invention
being 70-90% zinc, processing in alkaline baths is preferred with
pyrophosphate copper being most preferred. For optimum adhesion of
the pyrophosphate copper deposit to the coating of the invention,
it is preferred to apply a voltage to the article before immersion
in the copper pyrophosphate bath.
[0034] The following non-limiting examples demonstrate the
application of the invention.
EXAMPLES
[0035] In the following examples, unless specified differently, all
zinc die-cast parts have been treated according to the following
procedure;
[0036] Neutral soak cleaner to degrease (65.degree. C., 5
minutes)
[0037] Alkaline electrolytic (anodic) cleaner (2 volts, 30
seconds)
[0038] Rinse
[0039] Activator (25 g/l sodium bisulphate and 2 g/l sodium
fluoride, room temperature, 30 seconds)
[0040] Rinse
[0041] Electroplate as described in the example
[0042] Rinse
[0043] Electroplate in alkaline copper (II) pyrophosphate bath (3
A/dm2, 20 minutes)
[0044] Electroplate in conventional Watts bright nickel bath (4
A/dm2, 13 minutes)
[0045] Electroplate in chromium (conventional hexavalent chromium
bath, 10 A/dm2, 5 mins)
[0046] Rinse and dry the part.
[0047] Heat the part to 180.degree. C. for 1 hour
[0048] Dip the part in cold water
[0049] Assess the deposit for blistering and other indicators of
poor adhesion
Examples of the Prior Art
Example 1
[0050] A zinc die-cast part was pretreated and then electroplated
in a conventional alkaline cyanide copper(I) electroplating bath at
1 A/dm2 for 5 minutes at a temperature of 55.degree. C. This
example is representative of the conventional established process
of the prior art.
Example 2
[0051] An alkaline copper(II) pyrophosphate electrolyte was
prepared as follows;
TABLE-US-00001 copper (II) ions (added as copper pyrophosphate) 25
g/l potassium pyrophosphate 250 g/l ammonium hydroxide 35% 3 ml/l
potassium hydroxide or sulphuric acid to adjust to pH 8.7
[0052] A zinc die-cast part was pretreated and then electroplated
in the solution at 3.5 A/dm2 for 20 minutes at a temperature of
55CC followed by conventional nickel and chromium plating.
Example 3
[0053] An electrolyte was prepared as follows;
TABLE-US-00002 copper (II) ions (added as copper sulphate) 15 g/l
1-hydroxyethylidene-1,1-diphosphonic acid 100 g/l potassium
hydroxide to achieve a pH of 9.5 potassium carbonate 15 g/l
[0054] A zinc die-cast part was pretreated and then electroplated
in the solution for 15 minutes at 0.5 A/dm2 and a temperature of
55.degree. C. A cathodic potential was applied to the part prior to
immersion. This electroplating stage was followed by conventional
nickel and chromium plating. This example is believed to be
representative of the prior art of U.S. Pat. No. 4,469,569 and U.S.
Pat. No. 4,521,282.
Example 4
[0055] An electrolyte was prepared as follows;
TABLE-US-00003 copper (II) ions (added as copper sulphate) 10 g/l
1-hydroxyethylidene-1,1-diphosphonic acid 80 g/l potassium
hydroxide to achieve a pH of 9.5 potassium carbonate 20 g/l
potassium chloride 15 g/l
[0056] A zinc die-cast part was pretreated and electroplated in the
solution for 15 minutes at 0.5 A/dm2 and a temperature of
55.degree. C. A cathodic potential was applied to the part prior to
immersion. This electroplating stage was followed by conventional
nickel and chromium plating. This example is believed to be
representative of the prior art of U.S. Pat. No. 6,054,037.
Example 5
[0057] A solution was prepared as follows;
TABLE-US-00004 1-hydroxyethylidene-1,1-diphosphonic acid 60 g/l pH
1.7
[0058] A zinc die-cast part was pretreated and then immersed in the
above solution for 1 minute prior to being electroplated in the
solution of Example 3 for 15 minutes at 0.5 A/dm2 and a temperature
of 55.degree. C., followed by conventional nickel and chromium
plating. This example is believed to be representative of the prior
art of U.S. Pat. No. 3,928,147.
Example 6
[0059] An electrolyte was prepared as follows;
TABLE-US-00005 copper (II) ions (added as copper sulphate) 8 g/l
sodium potassium tartrate 100 g/l sodium hydroxide 25 g/l sodium
hypophosphite 25 g/l
[0060] A zinc die-cast part was pretreated and immersed in the
solution. A displacement copper deposit formed immediately upon
immersion into the solution. The part was electroplated in the
solution for 10 minutes at 0.01 A/dm2 and a temperature of
30.degree. C. and subsequently electroplated by conventional
pyrophosphate copper, nickel and chromium plating. This example is
believed to be representative of the prior art of U.S. Patent
Application 2008/0156652.
Example 7
[0061] An electrolyte was prepared as follows;
TABLE-US-00006 Zinc chloride 4.5 g/l Potassium hydroxide 100 g/l
Sodium stannate trihydrate 75 g/l
[0062] A zinc die-cast part was pretreated and electroplated in the
solution for 2 minutes at 2.0 A/dm2 and a temperature of 55.degree.
C. This electroplating stage was followed by conventional
pyrophosphate copper, nickel and chromium plating. This example is
believed to be representative of the prior art of GB2272001.
Example 8
[0063] A solution was prepared as follows;
TABLE-US-00007 Nickel (II) ions (added as nickel 20 g/l sulphate)
Potassium pyrophosphate 100 g/l Ammonium hydroxide to achieve a pH
of 9.0
[0064] A zinc die-cast part was pretreated and immersed in the
solution for 3 at a temperature of 50.degree. C. An immersion
nickel deposit formed. This stage was followed by conventional
pyrophosphate copper, nickel and chromium plating. This example is
believed to be representative of the prior art of U.S. Pat. No.
6,827,834.
Example 9
[0065] A zinc die-cast part was pretreated and electroplated in the
solution of example 8 for 10 minutes at 1.0 A/dm2 and a temperature
of 50.degree. C. This electroplating stage was followed by
conventional pyrophosphate copper, nickel and chromium plating.
Example 10
[0066] A solution was prepared as follows;
TABLE-US-00008 Nickel (II) ions (added as nickel sulphate) 55 g/l
Sodium chloride 18 g/l Boric acid 25 g/l Salicylic acid 4 g/l
4-acetamido-5-hydroxy-2,7-naphthalene- 1 g/l disulphonic acid,
disodium salt Sulfonated alcohol alkoxylate 1.0 g/l
[0067] A zinc die-cast part was pretreated and electroplated in the
solution for 5 minutes at 4.0 A/dm2 and a temperature of 55.degree.
C. and subsequently electroplated in conventional pyrophosphate
copper, nickel and chromium plating. This example is believed to be
representative of the prior art of U.S. Patent Appl.
2006/0096868.
TABLE-US-00009 TABLE I Adhesion Results Adhesion after heat
treatment at Adhesion 180.degree. C. for 1 hour followed by cold
Example directly after plating water quench 1 Complete adhesion
Complete adhesion 2 Blistering Not tested 3 Complete adhesion
Severe blistering 4 Complete adhesion Severe blistering 5 Complete
adhesion Severe blistering 6 Blistering Not tested 7 Complete
adhesion Severe blistering after heat only 8 Complete adhesion
Severe blistering after heat only 9 Complete adhesion Severe
blistering after heat only 10 Complete adhesion Blistering after
heat only
Examples of the Invention
Example 11
[0068] An electrolyte was prepared as follows;
TABLE-US-00010 zinc ions (added as zinc chloride) 45 g/l nickel
ions (added as nickel chloride) 55 g/l ammonium chloride 30 g/l
[0069] A zinc die-cast part was pretreated and electroplated in the
solution for 10 minutes at 2.0 A/dm2 and a temperature of
30.degree. C. A cathodic potential was applied to the part prior to
immersion. This electroplating stage was followed by conventional
pyrophosphate copper (with a cathodic potential applied prior to
immersion), nickel and chromium plating.
Example 12
[0070] An electrolyte was prepared as follows;
TABLE-US-00011 zinc ions (added as zinc chloride) 50 g/l nickel
ions (added as nickel sulphate) 50 g/l boric acid 30 g/l
[0071] A zinc die-cast part was pretreated and electroplated in the
solution for 10 minutes at 1.0 A/dm2 and a temperature of
30.degree. C. A cathodic potential was applied to the part prior to
immersion. This electroplating stage was followed by conventional
pyrophosphate copper (with a cathodic potential applied prior to
immersion), nickel and chromium plating.
Example 13
[0072] An electrolyte was prepared as follows;
TABLE-US-00012 zinc ions (added as zinc chloride) 50 g/l nickel
ions (added as nickel chloride) 50 g/l ammonium chloride 30 g/l
[0073] A zinc die-cast part was pretreated and electroplated in the
solution for 5 minutes at 2.0 A/dm2 and a temperature of 20.degree.
C. A cathodic potential was applied to the part prior to immersion.
This electroplating stage was followed by conventional
pyrophosphate copper (with a cathodic potential applied prior to
immersion), nickel and chromium plating.
Example 14
[0074] An electrolyte was prepared as follows;
TABLE-US-00013 zinc ions (added as zinc sulphate) 50 g/l nickel
ions (added as nickel chloride) 50 g/l potassium chloride 30 g/l
boric acid 30 g/l sodium acetate 20 g/l
[0075] A zinc die-cast part was pretreated and electroplated in the
solution for 5 minutes at 4.0 A/dm2 and a temperature of 25.degree.
C. A cathodic potential was applied to the part prior to immersion.
This electroplating stage was followed by conventional
pyrophosphate copper (with a cathodic potential applied prior to
immersion), nickel and chromium plating.
Example 15
[0076] An electrolyte was prepared as follows;
TABLE-US-00014 zinc ions (added as sodium zincate) 8.0 g/l nickel
ions (added as nickel sulphate) 0.8 g/l sodium hydroxide 110 g/l
tetraethylenepentamine 10 g/l triethanolamine 2 g/l
N,N,N',N'-tetra(3-hydroxypropyl)- 15 g/l ethylenediamine
[0077] A zinc die-cast part was pretreated and electroplated in the
solution for 10 minutes at 1.0 A/dm2 and a temperature of
25.degree. C. A cathodic potential was applied to the part prior to
immersion. This electroplating stage was followed by conventional
pyrophosphate copper (with a cathodic potential applied prior to
immersion), nickel and chromium plating.
Example 16
[0078] An electrolyte was prepared as follows;
TABLE-US-00015 zinc ions (added as sodium zincate) 12.0 g/l nickel
ions (added as nickel sulphate) 1.3 g/l sodium hydroxide 100 g/l
tetraethylenepentamine 15 g/l N,N,N',N'-tetra(3-hydroxypropyl)- 20
g/l ethylenediamine
[0079] A zinc die-cast part was pretreated and electroplated in the
solution for 5 minutes at 2.0 A/dm2 and a temperature of 25.degree.
C. A cathodic potential was applied to the part prior to immersion.
This electroplating stage was followed by conventional
pyrophosphate copper (with a cathodic potential applied prior to
immersion), nickel and chromium plating.
TABLE-US-00016 TABLE II Adhesion Results Adhesion after heat
treatment at Adhesion 180.degree. C. for 1 hour followed by cold
Example directly after plating water quench 11 Complete adhesion
Complete adhesion 12 Complete adhesion Complete adhesion 13
Complete adhesion Complete adhesion 14 Complete adhesion Complete
adhesion 15 Complete adhesion Complete adhesion 16 Complete
adhesion Complete adhesion
[0080] The foregoing description and examples are provided by way
of illustration only. Although the invention has been described
with reference to particular and preferred features and embodiments
it will be understood to those skilled in the art that these are
not intended as limitations of the scope of the invention.
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