High performance creep resistant magnesium alloys

Abstract

The invention provides a magnesium based alloy consisting of at least 94.8% magnesium, 2.5-4.6% neodymium, 0.05-0.40% yttrium, and 0.03-0.65% zirconium, exhibiting good castability, high strength, high corrosion resistance and high creep resistance even at high temperatures. The alloy is suitable for high pressure die casting, sand casting, investment casting, permanent mold casting, twin roll casting, or direct chill casting.

Description

FIELD OF THE INVENTION[0001]The present invention relates to creep-resistant magnesium-based alloys for applications at high temperatures which exhibit good castability, particularly suitable for high-pressure die casting, but advantageously used also in a processes comprising sand casting, investment casting, permanent mold casting, as well as direct chill casting or twin-roll casting.BACKGROUND OF THE INVENTION[0002]The magnesium industry is experiencing dramatic growth, in part due to the demands of the transportation industry to improve fuel economy and emissions. In addition, a great progress in weight reduction has been made in consumer applications of magnesium alloys such as power hand tools, lawn and garden equipment, electronic and optical equipment, etc. In order to significantly expand the above applications, new advanced alloys are required.[0003]High pressure die casting (HPDC) is the dominant form of casting due to its productivity and suitability for mass production....

AI Technical Summary

Benefits of technology

[0020]The invention provides a lightweight alloy for high-pressure die casting (HPDC) process, consisting of at least 94.8 wt % magnesium, 2.5 to 4.6 wt % neodymium, 0.05 to 0.40 wt % yttrium, 0.03 to 0.65 wt. % zirconium, and incidental impurities. In one embodiment, the alloy according to the invention further contains up to 0.02 wt % calcium. The alloy according to the invention comprises essentially no heavy rare earth (HRE) elements with the atomic number from 61 to 70. The alloy according to the invention comprises essentially no cerium, lanthanum, and praseodymium. The alloy according to the invention comprising essentially no zinc. In one embodiment, the alloy according to the invention contains Nd and Y in an amount higher than 4.3 wt. %. Said incidental impurities usually comprise Si, Fe, Cu, and Ni in an amount of up to 0.02 wt %. The lightweight alloy according to the invention is suitable for prolonged operations at high temperatures of up to 200° C. The alloys for HPDC and other applications according to the invention exhibit superior casting properties, high strength, high creep resistance, high corrosion resistance, and the articles manufactured from the alloys show superior performance at high temperatures. The alloy according to the invention is usable for high pressure dies casting (HPDC), but it may be also used for a process selected from the group consisting of sand casting, investment casting, and permanent mold casting. The alloy according to the invention are also usable for a process comprising either twin roll casting with subsequent rolling, or direct chill casting with subsequent forging, extrusion or rolling.

Problems solved by technology

However, these alloys cannot serve at temperatures higher than 150-170° C. under high stresses of 60-100 MPa.

High-pressure die casting of the alloys results in low strength (TYS=120 MPa, UTS=165 MPa) and elongation (E=2%).

However, the HPDC is not addressed.

The complexity of the technology significantly increases the cost of the final alloy product.

The alloys are mainly designated for sand casting and, in addition, they are expensive due to the use of heavy rare earth elements, such as Gd in amounts of 1.0-1.6%.

The high Ca content results in increased porosity, embrittlement and hot cracking in HPDC processes.

The alloy is unsuitable for HPDC process.

Furthermore, the high content of heavy rare earth elements leads to high cost of these alloys.

The alloys are not suitable for HPDC process and are expensive.

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