Iron-plated aluminum alloy parts and method for planting same

Coating processes – Immersion or partial immersion – Metal base

Reexamination Certificate

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Details

C427S438000, C427S405000, C205S185000, C205S187000, C205S270000, C205S301000

Reexamination Certificate

active

06258415

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the plating of aluminum and aluminum alloys, and, more particularly, to the plating of 390 aluminum alloys with iron.
2. Description of Related Art
In the use of aluminum internal combustion engines with aluminum pistons for vehicles, it is essential that either the piston or the cylinder bore be coated with another metal harder than aluminum to prevent piston skirt scuffing during cold starts. Commonly, an iron coating is plated onto the surface of the aluminum pistons, generally employing a copper undercoat.
In one process, copper cyanide and iron chloride baths are used in the plating. Copper cyanide is a highly toxic and tightly regulated material. The iron chloride bath is also a highly toxic and extremely corrosive bath that is very destructive to the equipment around it.
An alternative approach is to insert an iron sleeve into the cylinder bore. Still another approach is to coat the inside of the bore with a suitable metal alloy by thermal spray coating processes and then re-machining the bore. These approaches are estimated to be 8 to 14 times as expensive as piston plating.
It is desired to provide a method, preferably inexpensive, for plating aluminum pistons with an acceptable iron coating that will pass all the required adhesion, hardness, and abrasion tests without using highly toxic or hazardous substances.
SUMMARY OF THE INVENTION
In accordance with the invention, a substitute for cyanide is provided, namely, electroless nickel. The process for plating 390 aluminum alloy substrates with iron comprises:
(a) plating on the aluminum substrate a layer of zincate from a zincate bath;
(b) plating on the zincate layer a layer of nickel from an electroless nickel bath;
(c) plating on the nickel layer a layer of iron from an iron sulfate bath; and
(d) plating on the iron layer a layer of tin from an alkaline tin bath.
All of these baths are environmentally much safer than copper cyanide and ferric chloride. They are also cost effective and can be utilized in a totally closed loop plating system.
The resulting iron-plated aluminum alloy parts comprise a first layer of nickel on a surface of the part, a second layer of iron on the first layer of nickel and a third layer of tin on the second layer of iron. The coating evidences good adhesion and wear properties.


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