Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
1998-10-09
2001-10-16
Sheehan, John (Department: 1742)
Stock material or miscellaneous articles
Composite
Of metal
C148S273000, C148S275000, C148S279000, C148S283000
Reexamination Certificate
active
06303232
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART STATEMENT
This invention relates to a surface treatment method for aluminum or an aluminum alloy, and pistons surface-treated thereby, as well as a surface-treating film for aluminum or an aluminum alloy, and sliding members having a sliding surface coated therewith.
More particularly, this invention relates to a surface treatment method which requires simple equipment, can reduce treating costs, and can yield aluminum or an aluminum alloy having excellent abrasion resistance, corrosion resistance and other properties, as well as pistons having undergone a surface treatment according to this method. It also relates to a surface-treating film suitable for use on the sliding surfaces (or sleeve surfaces) of internal combustion engines and having excellent abrasion resistance, initial fitness, oil retention and other properties, and sliding members coated with such a slide film.
The Alumite treatment which has conventionally been employed is a method for anodizing aluminum in an acid bath to form a hard aluminum oxide film on the aluminum surface.
However, this method has the disadvantage that it requires equipment for electric power supply and that it involves a considerable cost because of a slow rate of film formation.
On the other hand, the skirt of an aluminum piston as an E/G component is plated with tin. Although the deposited tin film is soft and hence effective in bring about good initial fitness, it cannot be expected to have the effect of improving abrasion resistance.
OBJECT AND SUMMARY OF THE INVENTION
In view of the above-described problems of conventional surface treatment techniques, the present inventors made intensive investigations for the purpose of develop a surface treatment method which requires simple equipment, can reduce treating costs, and can form a uniform film having excellent corrosion resistance, abrasion resistance and other properties, as well as sliding members surface-treated by such a method.
As a result, the present inventors have found that the above-described problems can be solved by a surface treatment method comprising the steps of soaking aluminum or an aluminum alloy in a treating solution containing a fluorine compound and ammonium silicofluoride, and treating the aluminum or aluminum alloy in the treating solution at a temperature in the range of 70 to 100° C. Moreover, it has been found that the above-described problems can also be solved by coating the whole surface of a sliding member or the sliding surface thereof with a specific film consisting, for example, of a compound of aluminum, fluorine and the hydroxyl group, or by using a specific film formed on a surface of aluminum or an aluminum alloy and consisting of an aluminum fluoride hydroxide compound and silicon particles dispersed therein.
The present invention has been completed from this point of view.
That is, according to a first aspect of the present invention, there is provided a surface treatment method comprising the steps of soaking aluminum or an aluminum alloy in a treating solution (or a heated aqueous solution) containing a fluorine compound and ammonium silicofluoride, and treating the aluminum or aluminum alloy in the treating solution at a temperature in the range of 70 to 100° C. In this surface treatment method, the aforesaid treating solution (or heated aqueous solution) preferably contains 0.1 to 20 parts by weight of the fluorine compound and 0.05 to 15 parts by weight of ammonium silicofluoride, per 100 parts by weight of water. As used herein, the term “fluorine compound” comprehends fluorine compounds other than ammonium silicofluoride [(NH
4
)
2
SiF6]. Among these compounds, silicofluorides are preferred and magnesium silicofluoride (MgSiF
6
·6H
2
O) is especially preferred.
The present invention also provides a piston having undergone a surface treatment according to the above-described surface treatment method.
According to a second aspect of the present invention, there is provided a piston wherein a surface thereof is coated with a film consisting of an Al-OH-F compound or an NH
4
MgAlF
6
compound, or both, and preferably its whole surface including the piston ring grooves, piston pin boss, skirt, piston head and internal piston surface is coated with the aforesaid film. In this piston, the thickness of the film consisting of an Al-OH-F compound or the like is preferably in the range of 1 to 10 &mgr;m.
According to a third aspect of the present invention, there is provided a sliding member made of a base metal comprising aluminum or an aluminum alloy, wherein the whole surface of the sliding member or the sliding surface thereof is coated with a slide film which comprises a film consisting of a compound of aluminum, fluorine and the hydroxyl group, a film consisting of a hydrate of the compound, a film consisting of an NH
4
MgAlF
6
compound, or a film consisting of a mixture of these compounds, has a cubic crystal structure, and shows no crystalline orientation. Moreover, there is also provided a sliding member wherein the whole surface of the sliding member or the sliding surface thereof is coated with a slide film which has a thickness of 1 to 100 &mgr;m and consists of a plurality of aggregates having a size of 1 to 100 &mgr;m, each aggregate being formed of microcrystals having a size of 1 &mgr;m or less.
According to a fourth aspect of the present invention, there is provided a surface-treating film for an aluminum alloy wherein the surface-treating film is a film formed on a surface of aluminum or an aluminum alloy and consisting of an aluminum fluoride hydroxide compound or an NH
4
MgAlF
6
compound, or both, and silicon particles dispersed therein, the content of silicon particles dispersed in the film is in the range of 1 to 24% by weight and preferably 6 to 24% by weight, and the content of silicon in the aluminum alloy is in the range of 4 to 24% by weight and preferably 7 to 24% by weight.
REFERENCES:
patent: 4566960 (1986-01-01), Mohr
patent: 4650525 (1987-03-01), Yoshida et al.
patent: 5125989 (1992-06-01), Hallman
patent: 5584946 (1996-12-01), Karmaschek et al.
patent: 695182 (1940-07-01), None
patent: 2445622A1 (1976-04-01), None
patent: 3512442A1 (1985-10-01), None
patent: 0020163386AA (1990-06-01), None
patent: WO 85/05131 (1985-11-01), None
Mihoya Makoto
Mitsuoka Shigehi
Nomura Masaya
Myers Bigel Sibley & Sajovec P.A.
Oltmans Andrew L.
Sheehan John
Suzuki Motor Corporation
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