Metal treatment – Process of modifying or maintaining internal physical... – Carburizing or nitriding using externally supplied carbon or...
Patent
1997-06-02
2000-06-13
Sheehan, John
Metal treatment
Process of modifying or maintaining internal physical...
Carburizing or nitriding using externally supplied carbon or...
148 27, 148441, 148440, 148439, 420533, 420542, 420513, 420521, 420407, 420411, C23C 824
Patent
active
060744944
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a nitriding method of forming a nitride layer on a surface portion of an aluminum material, and a nitriding auxiliary agent used for nitriding.
BACKGROUND ART
As is commonly known, an aluminum material has a lower hardness than steel and the like, and very easily seizes and wears away when it slides against steel and the like. Therefore, various surface treatments of aluminum materials using metal plating, spray forming, and anodizing have been studied and practiced. These surface treatments are mainly to form an aluminum oxide layer on the surface of an aluminum material. Although nitriding has been attempted, nitride layers formed on the surface are thin, and satisfactory surface nitrided aluminum base materials have not been obtained. This is supposed to be because an aluminum material is a metal which is very active and easily oxidized, and always has some oxide layer on the surface.
The present inventors proposed a nitriding method comprising contacting at least part of the surface of an aluminum material with a nitriding auxiliary agent including aluminum powder, and with keeping this state, nitriding the surface of the aluminum material by an atmospheric gas substantially comprising nitrogen gas at a nitriding temperature which is equal to or lower than a melting point of the aluminum material in the publication of Japanese Unexamined Patent Publication (KOKAI) No.H7-166321. In this method, when aluminum powder used as a nitriding auxiliary agent is contacted with nitrogen gas at a predetermined temperature, the aluminum powder is nitrided in itself, and at this time, nascent nitrogen (N*) generates and diffuses into the interior of the aluminum material, thereby forming a nitride layer.
It is desirable that an aluminum material to be nitrided or an aluminum material constituting a nitriding auxiliary agent contains magnesium, because nitriding is promoted, nitriding speed is increased, and a thicker nitride layer is formed. This is supposed to be because magnesium serves as an oxygen getter.
In regard to aluminum, although pure aluminum is used alone, aluminum alloys containing copper, zinc, silicon, magnesium or the like in addition to aluminum are used industrially. In particular, as aluminum alloys used as castings, aluminum-silicon alloys are often used because of excellent castability (fluidity).
On the other hand, in the aforementioned surface nitriding method of an aluminum material, in the case where aluminum alloy powder containing magnesium, which has a strong nitriding power, is used as a nitriding auxiliary agent, and nitriding treatment is applied to an aluminum alloy material by using pure nitrogen gas at a nitriding temperature of 500 to 550.degree.C. for five to ten hours, a nitride layer of 50 to 300 .mu.m is obtained. In the case where an aluminum alloy material to be nitrided contains silicon, however, even if nitriding treatment is applied under the same nitriding conditions, the thickness of an obtained nitride layer is about one fifth to one tenth of that in the case where an aluminum alloy material containing no silicon is used.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of nitriding an aluminum material in which a thick nitride layer can be relatively easily formed on such an aluminum alloy material containing silicon, and a nitriding auxiliary agent used in nitriding.
It is another object of the present invention to provide a method of nitriding an aluminum material in which nitriding can be done at a lower temperature than conventional nitriding temperatures (500 to 550.degree. C.), and in which a nitride layer of the same depth can be obtained in a shorter nitriding time, and a nitriding auxiliary agent used in nitriding.
The present inventors have researched from various viewpoints on the cause why aluminum alloy materials containing silicon are hardly nitrided, and have concluded that the cause lies in the following two points. containing silicon is observed, aluminum port
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Katoh Haruzo
Miura Hirohisa
Yamada Yasuhiro
Sheehan John
Toyo Aluminium Kabushiki Kaisha
Toyota Jidosha & Kabushiki Kaisha
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