Metal treatment – Process of modifying or maintaining internal physical... – With casting or solidifying from melt
Reexamination Certificate
2001-03-02
2003-12-30
Ip, Sikyin (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
With casting or solidifying from melt
C148S700000, C148S701000
Reexamination Certificate
active
06669792
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to aluminum alloys, and specifically to high tensile strength aluminum-silicon (Al—Si) hypereutectic alloy suitable for high temperature applications such as heavy-duty pistons and other internal combustion applications. It relates particularly to a process for producing cast articles from this high tensile strength and high wear resistance Al—Si hypereutectic alloy.
2. Discussion of the Related Art
Al—Si casting alloys are the most versatile of all common foundry cast alloys in the production of pistons for automotive engines. Depending on the Si concentration in weight percent, the Al—Si alloy systems fall into three major categories: hypoeutectic (<12 wt. % Si), eutectic (12-13 wt. % Si) and hypereutectic (14-25 wt. % Si). In hypereutectic alloys, Si plays an important role by enhancing the cast article's surface hardness and wear resistance properties more than hypoeutectic and eutectic alloys. High silicon content in hypereutectic alloys also results in higher elastic modulus and lower thermal expansion. Currently, hypereutectic Al—Si alloys are crucial for high wear resistance applications such as pistons and reciprocate connecting rods. However, conventional hypereutectic alloys, such as 390, are not suitable for high temperature applications, such as in the automotive field, because their mechanical properties, such as tensile strength, are not as high as desired in the temperature range of 500° F.-700° F. Above an elevated service temperature of about 450° F., the major alloy strengthening phases such as the &thgr;′ (Al
2
Cu) and S′ (Al
2
CuMg) will precipitate rapidly, coarsen, or dissolve, and transform themselves into the more stable &thgr; (Al
2
Cu) and S (Al
2
CuMg) phases. The undesirable microstructure and phase transformation results in drastically reduced mechanical properties, more particularly the ultimate tensile strength and high cycle fatigue strengths, for hypereutectic Al—Si alloys.
One approach taken by the art is to use ceramic fibers or particulates to increase the strength and improve wear resistance of Al—Si alloys as a substitute for conventional hypereutectic alloys.
This approach is known as the aluminum Metal Matrix Composites (MMC) technology. For example, R. Bowles has used ceramic fibers to improve tensile strength of 332.0 alloy, in a paper entitled, “Metal Matrix Composites Aid Piston Manufacture,”
Manufacturing Engineering
, May 1987. Moreover, A. Shakesheff has used ceramic particulates for reinforcing another type of A359 alloy, as described in “Elevated Temperature Performance of Particulate Reinforced Aluminum Alloys,”
Materials Science Forum
, Vol. 217-222, pp. 1133-1138 (1996). In a similar approach, cast aluminum MMC for pistons using a eutectic alloy such as the 413.0 type, has been described by P. Rohatgi in a paper entitled, “Cast Aluminum Matrix Composites for Automotive Applications,”
Journal of Metals
, April 1991.
Another approach taken by the art is the use of the Ceramic Matrix Composites (CMC) technology in the place of Al—Si alloys. For example, W. Kowbel has described the use of non-metallic carbon—carbon composites for making pistons to operate at high temperatures in a paper entitled, “Application of Net-Shape Molded Carbon—Carbon Composites in IC Engines,”
Journal of Advanced Materials
, July 1996. Unfortunately, the material and processing costs of these MMC and CMC technologies are substantially higher than those for conventional casting, and they therefore cannot be considered for large usage in mass production, such as engine pistons.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide a process for making a cast article from an aluminum alloy, which cast article has improved mechanical properties at elevated temperatures.
According to the present invention, an aluminum alloy having the following composition, by weight percent, is first provided:
Silicon (Si)
14.0-25.0
Copper (Cu)
5.5-8.0
Iron (Fe)
0-0.8
Magnesium (Mg)
0.5-1.5
Nickel (Ni)
0.05-1.2
Manganese (Mn)
0-1.0
Titanium (Ti)
0.05-1.2
Zirconium (Zr)
0.12-1.2
Vanadium (V)
0.05-1.2
Zinc (Zn)
0-0.9
Phosphorus (P)
0.001-0.1
Aluminum (Al)
balance
In this aluminum alloy the ratio of Si:Mg is 15-35, preferably 18-28, and the ratio of Cu:Mg is 4-15.
An article is then cast from this composition, and the cast article is aged at a temperature within the range of 400° F. to 500° F. for a time period within the range of four to 16 hours.
In a particularly preferred embodiment, after the article is cast from the alloy, the cast article is first heat treated in a specifically-defined solutionizing step which dissolves unwanted precipitates and reduces any segregation present in the alloy. After this solutionizing step, the cast article is quenched, and is subsequently aged at an elevated temperature for maximum strength.
REFERENCES:
patent: 3716355 (1973-02-01), Wikle et al.
patent: 4147074 (1979-04-01), Noguchi et al.
patent: 61259829 (1986-11-01), None
patent: 5230692 (1993-09-01), None
patent: 7216487 (1995-08-01), None
patent: 8104937 (1996-04-01), None
Mielke, Steffens, Beer, Henning; New Aluminum Piston Alloy with Increased Fatigue Strength at High Temperatures; SAE International The Engineering Society for Advancign Mobility Land Sea Air and Space; Feb. 23-26, 1998; pp. 41-45; 980687; Society of Automotive Engineers, Inc.; Warrendale, Pa, USA.
J.A. Taylor, G.B. Schaffer, D.H. Stjohn; The Effect of Iron Content on the Formation of Porosityand Shrinkage Defects in Al-Si-Cu-Mg Alloy Casting; Solidification Processing 1997 Proceedings of the 4th Decennial International Conference on Solidification Processing; Jul. 7-10, 1997; Ranmoor House, University of Scheffield, UK.
Hatch, John E.; Constitution of Alloys; Aluminum Properties and Physical Metallurgy; 1984 pp. 25-27; Chapter 2; American Society for Metals; Metals Park, Oh; USA.
Hatch, John E.; Properties and Physical Metallurgy, Specific Alloying Elements and Impurities; Aluminum Properties and Physical Metallurgy; 1984; pp. 224-229; American Society for Metals; Metals Park, Oh; USA.
W. Kowbel, V. Chellappa, J.C. Withers; Applications of Net-Shape Molded Carbon-Carbon Compositeis in IC Engines; Journal of Advanced Materials; Jul. 1996; pp. 2-7; vol. 27 No. 4; USA.
A.J. Shakesheff, P.D. Pitcher; Elevated Temperature Performance of Particulate Reinforced Aluminium Alloys; Materials Science Forum, Proceedings of the 5th International Conf. ICAA5, Jul. 1-5, 1996; pp. 1133-1138; vol. 217-222; 1996 Transtec Publications Switzerland Rohatgi, Pradeep; Cast Aluminum-Matrix Composites for Automotive Applications; JOM the Journal of the Minerals, Metals & Materials Society; Apr. 1991; pp. 10-15.
R.R. Bowles; D.L. Mancini, M.W. Toaz; Metal Matrix Composites Aid Piston Manufacture; CIM Technology, Manufacturing Engineering; May 1987; pp. 61-62.
Chen Po-Shou
Lee Jonathan A.
Helfrich George F.
Ip Sikyin
McGroary James J.
The United States of America as represented by the Administrator
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