Metal treatment – Stock – Magnesium base
Reexamination Certificate
1999-12-15
2001-11-27
Ip, Sikyin (Department: 1742)
Metal treatment
Stock
Magnesium base
C420S407000, C420S408000, C420S409000, C420S410000
Reexamination Certificate
active
06322644
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to magnesium based casting alloys having improved elevated temperature performance and more particularly relates to magnesium-aluminum-strontium alloys having good salt-spray corrosion resistance and good creep resistance, tensile yield strength and bolt-load retention, particularly at elevated temperatures of at least 150° C.
BACKGROUND OF THE INVENTION
Magnesium-based alloys have been widely used as cast parts in the aerospace and automotive industries and are mainly based on the following four systems:
Mg—Al system (i.e., AM20, AM50, AM60);
Mg—Al—Zn system (i.e., AZ91D);
Mg—Al—Si system (i.e., AS21, AS41); and
Mg—Al—Rare Earth system (i.e., AE41, AE42).
Magnesium-based alloy cast parts can be produced by conventional casting methods which include diecasting, sand casting, permanent and semi-permanent mold casting, plaster-mold casting and investment casting.
These materials demonstrate a number of particularly advantageous properties that have prompted an increased demand for magnesium-based alloy cast parts in the automotive industry. These properties include low density, high strength-to-weight ratio, good castability, easy machineability and good damping characteristics.
AM and AZ alloys, however, are limited to low-temperature applications where they are known to lose their creep resistance at temperatures above 140° C. AS and AE alloys, while developed for higher temperature applications, offer only a small improvement in creep resistance and/or are expensive.
It is therefore an object of the present invention to provide relatively low cost magnesium-based alloys with improved elevated-temperature performance.
It is a more particular object to provide relatively low cost magnesium-aluminum-strontium alloys with good creep resistance, tensile yield strength and bolt-load retention, particularly at elevated temperatures of at least 150° C., and good salt-spray corrosion resistance.
SUMMARY OF THE INVENTION
The present invention therefore provides a magnesium-based casting alloy comprising, in weight percent, 2 to 9% aluminum and 0.5 to 7% strontium with the balance being magnesium except for impurities commonly found in magnesium alloys.
The foregoing and other features and advantages of the present invention will become more apparent from the following description and accompanying drawings.
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Mihriban O. Pekguleryuz, PhD; “Magnesium Automotive Alloy Development at Noranda”; Dec. 1995; Magnesium Industry; p. 37 and 38.*
Makhmudov, et al., “Study of the Liquidus Surface of the Strontium/Strontium-Magnesium (SRMG2) Strontium-Aluminum (SRA14) System”, Zavod. Lab. (1982), 48(10), 61-2.
Makhmudov, et al., “Thermodynamic Activity of Strontium in Alloys with Aluminum and Magnesium”, DOKL. AKAD. NAUK TADZH. SSR (1981) 24(4), 242-5.
Mihriban O. Pekguleryuz, Ph.D., “Magnesium Automotive Alloy Development at Noranda”, By M.O. Pekguleryuz, PhD, Magnesium Industry, No. 10, Jun. 1999, at 36-38.
Mihriban O. Pekguleryuz, Ph.D., Development of Creep Resistant Magnesium Diecasting Alloys—An Overview, Presented in Aalen, Germany, on Sep. 30, 1999.
Nussbaum, G., et al., “New magnesium-aluminum based alloys with improved casting and corrosion properties”, Chemical Abstracts (Nov. 1, 1993), vol. 119, Abstract No. 18. “Magnesium Alloys Their Appl.”, [Pap. DGM Conf.] 1992, 351-8; Edited by Mordike, Barry L., et al., DGM Informationsges, Oberursel, Germany. Abstract and full-text article copy enclosed.
Labelle Pierre
Pekguleryuz Mihriban Ozden
Bonzagni, Esq. Mary R.
Holland & Bonzagni, P.C.
Ip Sikyin
Norands, Inc.
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