MAGNESIUM ALLOY

Abstract

The present invention relates to creep resistant magnesium alloys. The magnesium alloy includes aluminum in an amount by mass of 5 to 20 percent, nanoparticles in an amount by mass of 0.1 to 10 percent, and the remainder being magnesium and unavoidable impurities. The nanoparticles contain Y2O3 in an amount by mass of 5 to 15 percent, ZrO2 in an amount by mass of 85 to 95 percent. The sizes of nanoparticles are in the range from 5 nm to 200 nm. The present magnesium alloys have higher creep resistance compared with conventional magnesium alloys, such as AE42 alloy.

Description

FIELD OF THE INVENTION

The invention relates generally to magnesium alloys, more particularly, to a magnesium alloy having a high creep resistance property.

DESCRIPTION OF RELATED ART

Magnesium alloys have the lowest specific gravity among practical metal materials, and therefore in recent years, they have increasingly been used in casings of portable equipment and as raw materials for automobiles, equipments and electronic consumer products requiring lightweight components. Magnesium alloys are usually 5 to 20 percent aluminum by mass with the majority being magnesium. The use of magnesium alloys to reduce weight in automobiles has grown approximately 20% annually since the early 1990s.

If the advantages of magnesium alloys are to be extended to current uses, for example automobiles and electronic consumer products, several existing problems will have to be overcome. Four issues for the use of magnesium alloys are: (1) creep (i.e., continued strain under stress), (2) cost, (3) castability and (4) corrosion. Creep means a strain that is a function of time and temperature under load. For example, the commercial die casting magnesium alloys (AZ91D, containing aluminum, zinc and manganese; AM60 and AM50, both containing aluminum and manganese) currently used in automobiles are limited to near-room-temperature applications because their mechanical properties decrease at higher temperatures and they are susceptible to creep at high operating temperatures.

AE42 is a rare earth element-containing magnesium die casting alloy (E designates mischmetal) that has creep resistance sufficient for automatic transmission operating temperatures (up to 150.degree. C.), but not engine temperatures (above 150.degree. C.). Another conventional creep resistant magnesium alloy is one that contains aluminum in an amount by mass of 1.5 to 4 percent, silicon in an amount by mass of 0.5 to 1.8 percent, rhenium in an amount by mass of 0.05 to 0.6 percent, strontium in an amount by mass of 0.005 to 1.5 percent, and the balance magnesium and unavoidable impurities.

Some magnesium alloys do provide good high-temperature properties and are used in aerospace and nuclear reactors. However, the high costs of exotic elements (Ag, Y, Zr and rare earths) used in these alloys make their use in automobiles and electronic consumer products prohibitively expensive. Besides, these conventional alloys contain smaller amount of aluminum, it results in lower hardness and strength of the alloys.

What is needed, therefore, is magnesium alloys which have high creep resistance, appropriate strength and cost effectiveness.

SUMMARY OF INVENTION

In one embodiment, a magnesium alloy contains aluminum in an amount by mass of 5 to 20 percent, 0.1 to 10 percent by mass of nanoparticles in an amount by mass of 0.1 to 10 percent, with the remainder being magnesium and unavoidable impurities. The nanoparticles contain Y2O3 in an amount by mass of 5 to 15 percent, ZrO2 in an amount by mass of 85 to 95 percent. The remainder further contains strontium in an amount by mass of 0.3 to 1.5 percent. The sizes of nanoparticles are in the range from 5 nm to 200 nm.

Advantages and novel features of the present invention will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

Many aspects of the present magnesium alloy can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, the emphasis instead being placed upon clearly illustrating the principles of the present magnesium alloy.

FIG. 1 is a schematic view of a creep resistant magnesium alloy in accordance with a preferred embodiment; and

FIG. 2 is a graph showing a relationship between creep strain and time for the magnesium alloy of FIG. 1.

Corresponding reference characters indicate corresponding parts throughout the views. The exemplifications set out herein illustrate at least one preferred embodiment of the present invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION

Reference will now be made to the drawing to describe embodiments of the present invention, in detail.

In one embodiment, a magnesium alloy contains aluminum in an amount by mass of 5 to 20 percent, nanoparticles in an amount by mass of 0.1 to 10 percent, with the remainder being magnesium and unavoidable impurities. The nanoparticles contain Y2O3 in an amount by mass of 5 to 15 percent, Al2O3 in an amount by mass of 3 to 8 percent, AlN in an amount by mass of 1 to 3 percent, with the remainder being ZrO2. The remainder can further contain strontium in an amount by mass of 0.3 to 1.5 percent. The sizes of nanoparticles are in the range from 5 nm to 200 nm. Preferably, the nanoparticles are in an amount by mass of 0.5 to 2 percent and the sizes of nanoparticles are in the range of 10 nm to 100 nm.

In another embodiment, a magnesium alloy contains aluminum in an amount by mass of 5 to 20 percent, nanoparticles in an amount by mass of 0.1 to 10 percent, with the remainder being magnesium and unavoidable impurities. The nanoparticles contains Y2O3 in an amount by mass of 5 to 15 percent, Al2O3 in an amount by mass of 3 to 8 percent, and ZrO2 in an amount by mass of 77 to 92 percent. Furthermore, the remainder contains strontium in an amount by mass of 0.3 to 1.5 percent. The sizes of nanoparticles are in the range from 5 nm to 200 nm. Preferably, the nanoparticles are in an amount by mass of 0.5 to 2 percent and the sizes of nanoparticles are in the range from 10 nm to 100 nm.

In third embodiment, a magnesium alloy contains aluminum in an amount by mass of 5 to 20 percent, nanoparticles in an amount by mass of 0.1 to 10 percent, with the remainder being magnesium and unavoidable impurities. The nanoparticles contains Y2O3 in an amount by mass of 5 to 15 percent, and ZrO2 in an amount by mass of 85 to 95 percent. Furthermore the remainder contains strontium in an amount by mass of 0.3 to 1.5 percent. The sizes of nanoparticles are in the range from 5 nm to 200 nm. Preferably, the nanoparticles are in an amount by mass of 0.5 to 2 percent and the sizes of nanoparticles are in the range from 10 nm to 100 nm.

Referring to FIG. 1, the magnesium alloy 10 contains a small percentage of nanoparticles 12 that is incorporated into the magnesium-aluminum alloy 11 so as to improve the mechanical properties and reduce the creep problems associated therewith. Also referring to FIG. 2, creep is strain under load as a function of time. Before receiving an external load, a structure of the nanoparticles 12 is monoclinic. The structure transforms into tetragonal phase after receiving the external load with time. The tetragonal phases forms blocks in front of crack 13 and have higher strength to stop crack 13 propagation in the magnesium alloy 10 as shown in FIG. 1.

A key mechanical parameter of metal alloys is fracture toughness K1C. The higher value of K1c, the better mechanical performance is for alloys. K1C is proportional to σ(nc/d)0.5, where σ is yield strength; c is crack length and d is material grain size. The fracture toughness, K1C is inversely proportional to a square root of a grain size. The smaller the grain size, the higher the value of fracture toughness K1C is. The nanocomposite particles of the present magnesium alloys have small grain sizes, so that they have high fracture toughness K1C for resisting creep.

Compared with conventional magnesium alloys, such as AE42 alloy, the present magnesium alloys have high creep resistance. Besides, by adding nanocomposite particles AlN, a good thermal conductor, the present magnesium alloys have good heat dissipation. This is an advantage when used in electronic consumer product casting, such as notebook or laptop computers.

Finally, it is to be understood that the above-described embodiments are intended to illustrate rather than limit the invention. Variations may be made to the embodiments without departing from the spirit of the invention as claimed. The above-described embodiments illustrate the scope of the invention but do not restrict the scope of the invention.

Claims

1. A magnesium alloy comprising:

aluminum in an amount by mass of 5 to 20 percent;

nanoparticles in an amount by mass of 0.1 to 10 percent;

remainder being magnesium; and

unavoidable impurities; wherein

the nanoparticles contains Y2O3 in an amount by mass of 5 to 15 percent, Al2O3 in an amount by mass of 3 to 8 percent, AlN in an amount by mass of 1 to 3 percent, with the remainder being ZrO2.

2. The magnesium alloy as claimed in claim 1, wherein the nanoparticles are in an amount by mass of 0.5 to 2 percent.

3. The magnesium alloy as claimed in claim 1, wherein the remainder further containing strontium in an amount by mass of 0.3 to 1.5 percent.

4. The magnesium alloy as claimed in claim 1, wherein the sizes of nanoparticles are in the range from 5 nm to 200 nm.

5. The magnesium alloy as claimed in claim 4, wherein the preferred sizes of nanoparticles are in the range from 10 nm to 100 nm.

6. A magnesium alloy comprising:

aluminum in an amount by mass of 5 to 20 percent;

nanoparticles in an amount by mass of 0.1 to 10 percent;

remainder being magnesium, and

unavoidable impurities; wherein

the nanoparticles contains Y2O3 in an amount by mass of 5 to 15 percent, Al2O3 in an amount by mass of 3 to 8 percent, and ZrO2 in an amount by mass of 77 to 92 percent.

7. The magnesium alloy as claimed in claim 6, wherein the nanoparticles are in an amount by mass of 0.5 to 2 percent.

8. The magnesium alloy as claimed in claim 6, wherein the remainder further comprises strontium in an amount by mass of 0.3 to 1.5 percent.

9. The magnesium alloy as claimed in claim 6, wherein the sizes of nanoparticles are in the range from 5 nm to 200 nm.

10. The magnesium alloy as claimed in claim 9, wherein the preferred sizes of nanoparticles are in the range from 10 nm to 100 nm.

11. A magnesium alloy comprising:

aluminum in an amount by mass of 5 to 20 percent;

nanoparticles in an amount by mass of 0.1 to 10 percent;

reminder being magnesium and

unavoidable impurities; wherein

the nanoparticles contains Y2O3 in an amount by mass of 5 to 15 percent, and ZrO2 in an amount by mass of 85 to 95 percent.

12. The magnesium alloy as claimed in claim 11, wherein the nanoparticles are in an amount by mass of 0.5 to 2 percent.

13. The magnesium alloy as claimed in claim 11, wherein the reminder further comprises strontium in an amount by mass of 0.3 to 1.5 percent.

14. The magnesium alloy as claimed in claim 11, wherein the sizes of nanoparticles are in the range from 5 nm to 200 nm.

15. The magnesium alloy as claimed in claim 14, wherein the preferred sizes of nanoparticles are in the range from 10 nm to 100 nm.