Metal treatment – Stock – Aluminum base
Reexamination Certificate
2001-04-25
2004-03-16
Wyszomierski, George (Department: 1742)
Metal treatment
Stock
Aluminum base
C420S530000, C420S554000, C428S614000
Reexamination Certificate
active
06706126
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to an Al—Sn based aluminum-alloy for sliding bearing. More particularly, the present invention relates to an Al—Sn based aluminum-alloy exhibiting improved fatigue resistance at high-temperature region due to dispersion of fine particles, while maintaining the compatibility at a room-temperature region, when used as a sliding bearing. The present invention also relates to a production method of the Al—Sn based sliding bearing, in which fine particles are dispersed.
2. Description of Related Art
Aluminum alloy and copper alloy are two major materials of the sliding-bearing materials. Representative additive components of the aluminum alloy are Sn, Pb and the like, which impart the lubricating property and compatibility, as well as Si and the like which impart the wear resistance.
One means for enhancing the fatigue resistance of the aluminum alloy is to add such elements as Si, Cr, Cu and Mg in some extent as to utilize the precipitation hardening of these elements. The heat treatment for precipitation hardening is usually the solution heat-treatment followed by aging at room temperature (T
4
) or artificial aging at approximately 150° C. (T
6
) Another means for enhancing the fatigue resistance is to add such elements as Cu and Mg within the solubility limit and hence to utilize the solution strengthening. The heat treatment usually employed is the solution heat-treatment followed by aging at room temperature. (T
4
)
The effects of solution strengthening method mentioned above are lost at elevated temperature. Both strength and hardness increase with the temperature increase from room temperature to somewhat high temperature in each case of solution strengthening and precipitation hardening. However, the compatibility, which is important for sliding bearing, deteriorates as strength and handness increase. Along with deterioration of compatibility, there arises danger of seizure and fatigue.
Various proposals have been made to improve the compositions of aluminum alloys described above. A proposal made by one of the present applicants and employed in actual machines is disclosed in German Patent DE 32 49 133 C2. The aluminum-alloy used for sliding bearing proposed in this patent is characterized in that hard particles of Si, Fe and the like having average particle diameter of from 4 to 5 &mgr;m are coarsely precipitated. The nodular cast iron of the opposed shaft is shaved by the coarse hard particles, thereby forming compatible bearing-surface and enhancing the bearing performance.
Similar proposal has been made by one of the present applicants and is disclosed in U.S. Pat. No. 4,153,756. The Al—Sn based sliding bearing proposed in the patent contains a small amount of Cr, and prevents the coarsening of the Sn particles due to the effects of Cr and hence the fatigue from occurring.
Meanwhile, it is known to apply the ceramic-particle dispersion strengthening to the aluminum-alloy (for example, Japanese Patent No. 2709097). The aluminum alloy, which is strengthened by the ceramic fine particles, is usually produced by the powder metallurgy method. This alloy is appropriate for the wear resistant parts. But can not meet sever compatibility which may be required for the sliding bearing.
It is also known to add the ceramic particles to molten aluminum-alloy. For example, the ceramic particles are added during the die casting (Japanese Patent No. 2739580). In Japanese Unexamined Patent Publication No. 6-17165, the ceramic particles fed into the melt from mother alloy. A green compact consisting of Ti powder, graphite powder and Al (alloy) powder is prepared and is then impregnated with the Al (alloy) melt, followed by heating to form TiC particles. The so treated green compact is used as the mother alloy of TiC.
When the ordinary aluminum alloy is compared with the composite ceramic-aluminum alloy, hardness at room temperature and compatibility of the former are lower and higher, respectively, than these of the latter. However, the hardness of the former abruptly drops at high temperature so that the fatigue resistance becomes unsatisfactory. On the other hand, since the latter is harder at high temperature than the former, the fatigue resistance of the latter is superior to that of the former. The compatibility of latter is poor due to high hardness at room temperature.
SUMMARY OF INVENTION
It is therefore an object of the present invention to provide an aluminum alloy which exhibits improved fatigue resistance at a high temperature region, while maintaining compatibility at low temperature not with standing improved fatigue resistance.
It is also an object of the present invention to provide a method for producing an aluminum alloy, which exhibits improved fatigue resistance at a high temperature region, while maintaining compatibility at low temperature not with standing improved fatigue resistance.
In accordance with the objects of the present invention, there is provided a fine-particle dispersion type Al—Sn based aluminum alloy, which consists of from 2 to 20% by weight of Sn, 3% by weight or less of Cu, and from 0.3 to 5% by volume of TiC particles, the balance being Al and unavoidable impurities.
There is also provided a sliding bearing comprising the fine-particle dispersion type Al—Sn based aluminum alloy mentioned above in the form of a lining.
There is also provided a method for producing a fine TiC particle-dispersing type Al—Sn based aluminum alloy comprising the steps of:
preparing either Al mother-alloy or metallic raw materials of the Al alloy and a green compact, in which TiC is dispersed;
melting the Al mother-alloy or the metallic raw materials of the Al alloy to form an Al alloy melt;
bringing the Al alloy melt and the green compact, in which TiC is dispersed, into contact with one another, thereby dispersing the TiC in the Al-alloy melt;
casting the Al-alloy melt, in which TiC is dispersed, into an aluminum-alloy ingot, in which TiC is dispersed; and,
rolling the ingot. The present invention is described hereinafter in detail.
DESCRIPTION OF PREFERRED EMBODIMENTS
In the composition mentioned above, Sn is dispersed in the form of soft minority phase and realizes the compatibility. When the Sn amount is less than 2% by weight, the compatibility is unsatisfactory. On the other hand, when the Sn amount is more than 20% by weight, the strength of Al alloy is lowered. The Sn amount should, therefore, be from 2 to 20% by weight. The Sn amount is preferably from 2 to 12% by weight, more preferably form 2 to 8% by weight.
Cu strengthens the Al matrix due to solution-strengthening and makes the fatigue difficult to occur. When the Cu amount is more than 3% by weight, hardness becomes so high in a temperature range of from room temperature to the operating temperature of bearing that the compatibility is not maintained. The Cu amount is preferably 0.1% by weight or more, and more preferably from 0.1 to 2% by weight.
TiC particles enhance the high-temperature strength and fatigue strength due to dispersion-strengthening. Features of TiC particles from the viewpoint of compatibility are that: they have no compatibility for their self because of hard particles; since TiC particles are not precipitated from the Al matrix, no precipitation hardening occurs. Deterioration of compatibility due to the precipitation does not occur due to the TiC particles; and, the compatibility of TiC is relatively good among the hard particles because of lower hardness than the other hard particles.
Smaller average diameter of TiC particles is more preferable from the viewpoints of fatigue resistance and compatibility. Drawbacks become prominent when the average particle diameter is greater than 5 &mgr;m. When the TiC particles are less than 0.3% by volume, they are not very effective for enhancing the high-temperature strength. On the other hand, when the TiC particles are much more than 5% by volume, the compatibility is seriously lowered. Preferably, TiC particles have 2 &mgr;m or less of average particle diameter a
Desaki Toru
Kamiya Soji
Nukami Tetsuya
Okouchi Yukio
Sato Kazuaki
Armstrong Westerman & Hattori, LLP
Combs-Morillo Janelle
Taiho Kogyo Co. Ltd.
Wyszomierski George
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