Magnesium-based casting alloys having improved elevated...

Alloys or metallic compositions – Magnesium base – Aluminum containing

Reexamination Certificate

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C420S408000, C420S409000, C420S410000, C148S420000

Reexamination Certificate

active

06342180

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to magnesium-based casting alloys having improved elevated temperature properties and more particularlyrelates to magnesium-aluminum-strontium-calcium alloys having improved creep resistance and tensile yield strength, particularly at elevated temperatures of at least 150° C., and good salt-spray corrosion resistance.
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, permanentand 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 because they are known to lose their creep resistance at temperatures above 150° 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 properties.
It is a more particular object to provide relatively low cost magnesium-aluminum-strontium-calcium alloys with good creep resistance and tensile yield strength, 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 that comprises: 1 to 12% by weight (wt.) aluminum; 0.1 to 0.6% by wt. strontium; and 0.1 to 0.5% by wt. calcium, with the balance being magnesium except for impurities commonly found in magnesium alloys.


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