Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Depositing predominantly single metal coating
Reexamination Certificate
1999-10-28
2001-09-04
Wong, Edna (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Depositing predominantly single metal coating
C205S213000, C205S099000, C205S101000, C205S148000, C106S001110, C106S001270
Reexamination Certificate
active
06284123
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the plating of aluminum and aluminum alloy substrates, and more particularly to the plating of aluminum and aluminum alloy substrates with iron.
BACKGROUND OF THE INVENTION
It is generally known to use aluminum or aluminum alloy substrates as structural members for many applications. The use of aluminum in many applications provides numerous advantages, because it is lightweight, easily handled, and generally inexpensive.
In various applications, however, it is desirable to coat the aluminum or aluminum alloy substrate with a dissimilar metal that is harder than aluminum. For example, it is known to use an aluminum or aluminum alloy substrate to make internal combustion engines with aluminum pistons wherein the aluminum piston or the cylinder bore is coated with another metal that is harder than aluminum to prevent piston skirt scuffing, galling and subsequent engine seizure.
One method for depositing iron coatings onto aluminum or aluminum alloy substrates is by electroplating. One such method for electroplating iron onto substrates containing aluminum is disclosed by U.S. Pat. No. 5,516,419 issued to Phan et al. (hereinafter “Phan”). In the process disclosed by Phan, a bath separate from the electroplating bath is required to activate the aluminum or aluminum alloy substrate. See Phan, Column 2, Lines 48-58. Additionally, after the substrate is activated, another separate bath is required to place a transitory protective layer, such as a zinc layer, onto the activated substrate to prevent aluminum oxides from reforming after the substrate has been activated. See Phan, Column 2, Lines 59-67, and Column 3, Lines 1-2. Finally, in Phan, an undercoating or intermediate layer, such as a nickel layer, is plated onto the substrate prior to plating iron onto the intermediate layer in another separate plating bath. See Phan, Column 3, Lines 3-25. The undercoating layer is required to provide a layer to which the subsequently-plated iron layer will adhere. See Phan, Column 3, Lines 16-22. In essence, the iron is not directly plated to the aluminum or aluminum alloy substrate, but is instead plated to an undercoating layer of a different metal which has in turn been plated onto the aluminum or aluminum alloy substrate.
The use of a method for electroplating as described in Phan has significant shortcomings for high volume commercial production. The use of a separate activation bath, a transitory layer, and a undercoating layer all add to the expense, complexity, and time involved with plating an iron layer onto an aluminum or aluminum alloy substrate. Additionally, the use of these separate steps and separate baths adds the difficulty and expense of disposing of the waste produced in each of these steps and baths.
Another problem that has existed with iron plating baths is that after use, impurities, such as copper or aluminum, remain in the bath solution and adversely affect further plating processes. When impurity concentration becomes too high, the iron plating process must be stopped so that the bath solution can be cleaned or changed.
An electroplating bath and electroplating method which permitted higher throughput before requiring bath cleaning would be highly desirable. In addition, the electroplated product should have good hardness or wear resistance properties.
It is desirable to provide a formulation and method for electroplating iron directly onto an aluminum or aluminum alloy substrate without the need of a separate activation bath, a transitory layer, or an undercoating layer.
It is also desirable to provide for a method and apparatus for purifying an iron plating bath solution to remove impurities from the bath without stopping the plating process to clean or change the bath solution.
SUMMARY OF THE INVENTION
The present invention is directed to an electroplating bath and a method of electroplating which provides high throughput for high volume commercial production. The resulting electroplated layer also has good hardness properties. Thus, larger volumes of product having greater hardness may be produced using the present invention.
One aspect of the present invention is a method for electroplating an iron layer onto an aluminum or aluminum alloy surface of a cathode from an iron-containing anode, the method comprising immersing the iron-containing anode and the cathode in an electroplating bath, which includes boric acid in a concentration of at least about 50 grams per liter (g/L), and applying electrical current to the cathode to electroplate an iron layer onto the cathode.
Another aspect of the invention includes a method for electroplating an iron layer onto an aluminum or aluminum alloy surface of an aluminum or aluminum alloy substrate cathode. The method includes providing an activation/electroplating bath solution including the following: (1) Fe
+2
having a concentration ranging from about 0.65 to about 2.5 moles per liter of solution; (2) at least one anion associated with the Fe
+2
ion; (3) a reducing agent in an amount sufficient to prevent oxidation of Fe
+2
to Fe
+3
; (4) Cl
−
in an amount sufficient to promote dissolution of the anode and increase the conductivity of the solution; (5) a wetting agent in an amount sufficient to prevent pitting of the aluminum electroplated surface; and (6) boric acid in a concentration of about 50 to about 90 grams per liter of solution. The surface of the cathode is activated by immersing the cathode in the solution. The anode is also immersed in the solution. The iron layer is electroplated onto the activated aluminum or aluminum alloy surface of the cathode in the solution.
Another aspect of the invention includes the electroplating bath solution as disclosed above. In addition to the high throughput mentioned above, one feature and advantage of the current invention is to provide an iron coating on an aluminum substrate with the thickness of about 0.25 to about 0.6 mils and a micro-hardness up to about 60 Rockwell C that has exceptional adhesion and wear resistance characteristics.
Another feature and advantage of the current invention is to provide an iron plating formulation and method wherein the iron plating solution acts as both the chemical activation solution for the aluminum or aluminum alloy substrate and acts as the electroplating bath for depositing a hard iron layer directly onto the aluminum or aluminum alloy substrate.
Another feature and advantage of the current invention is to provide for plating iron directly onto an aluminum or aluminum alloy substrate without the need of a transitory layer to prevent oxidation of the activated surface of the substrate after activation.
Another feature and advantage of the current invention is to plate iron directly onto an aluminum or aluminum alloy substrate without the need of an undercoating.
Another feature and advantage of the current invention is to provide an iron coating on an aluminum substrate with the thickness of about 0.25 to about 0.6 mils and a micro-hardness up to about 60 Rockwell C that has exceptional adhesion and wear resistance characteristics.
Another feature and advantage of the present invention includes providing for removal of impurities that are dissolved in the electroplating bath on a continuous basis without the need to interrupt the electroplating process.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description and claims.
Before embodiments in the invention are explained in detail, it is to be understood that the invention is not limited in its application for the details of the composition or concentrations of components set forth in the following description. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The pr
Cimermancic John A.
Dallman Jerold J.
Briggs & Stratton Corporation
Michael & Best & Friedrich LLP
Wong Edna
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