US20090074603A1

US20090074603A1 - Method for making magnesium-based composite material and equipment for making the same

Info

Publication number: US20090074603A1
Application number: US12/100,277
Authority: US
Inventors: Kam-Shau Chan; Cheng-Shi Chen; Qing-Chun Du; Wen-Zhen Li
Original assignee: Tsinghua University; Hon Hai Precision Industry Co Ltd
Current assignee: Tsinghua University; Hon Hai Precision Industry Co Ltd
Priority date: 2007-09-14
Filing date: 2008-04-09
Publication date: 2009-03-19
Also published as: CN101386926B; CN101386926A

Abstract

A method for fabricating a magnesium-based composite material, the method includes the steps of: (a) providing a large amount of magnesium-based powder and a large amount of nanoscale reinforcements; (b) uniformly mixing the magnesium-based powder and the nanoscale reinforcements to form a mixture; and (c) compacting the mixture at a high velocity in a protective gas to achieve the magnesium-based composite material. High velocity compaction equipment for fabricating the magnesium-based composite material includes a sealing chamber, a gas pumping device, a mold, and a hammer. The gas pumping device is connected to the sealing chamber. The mold is disposed in the sealing chamber with an aperture formed on the top thereof. The hammer is disposed in the sealing chamber and above the mold, and moving along longitudinal thereof at a controllable ramming speed.

Description

BACKGROUND

1. Field of the Invention
The present invention relates to methods for fabricating composite materials and equipments for fabricating the same, and, particularly, to a method for fabricating a magnesium-based composite material and equipment for fabricating the same.
2. Discussion of Related Art
Nowadays, various alloys have been developed for special applications. Among these alloys, magnesium-based alloys have relatively superior mechanical properties, such as good wear resistance, and high elastic modulus. Generally, two kinds of magnesium-based alloys have been developed: casting magnesium-based alloy and wrought magnesium-based alloy. However, the toughness and the strength of the magnesium-based alloys are not able to meet the increasing needs of the automotive and aerospace industries for tougher and stronger alloys.
To address the above-described problems, magnesium-based composite materials have been developed. In the magnesium-based composite material, nanoscale reinforcements are mixed with the magnesium metal or alloy. The most common methods for making the metallic composite material are through powder metallurgy and stir casting. However, in stir casting, the nanoscale reinforcements are added to metal or alloy melt and are prone to aggregation. As such, the nanoscale reinforcements are not well dispersed. In powder metallurgy, the density of the composite material is relatively low. Density influences material properties considerably, and particularly, fatigue properties. As such, in prior art, the composite material formed by powder metallurgy requires an additional hot-extrusion step to improve the density thereof. Recently, a new method of powder metallurgy called high velocity compaction (HVC) has been developed. The density of composite material can be improved by the HVC method. However, the conventional HVC can't be used in the production of the magnesium-based composite materials as the magnesium is easily oxidized in powder form. In particular, the magnesium powder may spontaneously combust due to oxidization.
What is needed, therefore, is to provide a method for fabricating a magnesium-based composite material and equipment for fabricating the same, in which the above problems are eliminated or at least alleviated.

SUMMARY

In one embodiment, a method for fabricating a magnesium-based composite material includes the steps of: (a) providing a large amount of magnesium-based powder and a large amount of nanoscale reinforcements; (b) uniformly mixing the magnesium-based powder and the nanoscale reinforcements to form a mixture; and (c) compacting the mixture at a high velocity in a protective gas to achieve the magnesium-based composite material.
Other advantages and novel features of the present method for fabricating the magnesium-based composite material and the equipment for fabricating the same will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present method for fabricating the magnesium-based composite material and the equipment for fabricating the same 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 method for fabricating the magnesium-based composite material and the equipment for fabricating the same.

FIG. 1 is a flow chart of a method for fabricating a magnesium-based composite material, in accordance with a present embodiment.

FIG. 2 is a schematic view of high velocity compaction equipment, in accordance with the present embodiment.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one preferred embodiment of the present method for fabricating the magnesium-based composite material and the equipment for fabricating the same, in at least one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made to the drawings to describe, in detail, embodiments of the present method for fabricating the magnesium-based composite material and the equipment for fabricating the same.
Referring to FIG. 1, a method for fabricating a magnesium-based composite material includes the steps of: (a) providing a large amount of magnesium-based powder and a large amount of nanoscale reinforcements; (b) uniformly mixing the magnesium-based powder and the nanoscale reinforcements to form a mixture; and (c) compacting the mixture at a high velocity in a protective gas to achieve the magnesium-based composite material.
In step (a), the material of the magnesium-based powder can, beneficially, be pure magnesium or magnesium-based alloys. Components of the magnesium-based alloys include magnesium and other elements selected from a group consisting of zinc (Zn), manganese (Mn), aluminum (Al), thorium (Th), lithium (Li), silver, calcium (Ca), and any combination thereof. A weight ratio of the magnesium to the other elements can advantageously, be more than 4:1. A diameter of the particles of the magnesium-based powder can, suitably, be less than about 74 microns. A weight percentage of the nanoscale reinforcements in the total amount of the nanoscale reinforcements and the magnesium-based powder can, opportunely, be in the approximate range from 0.01% to 30%. The nanoscale reinforcements can, beneficially, be made up of carbon nanotubes, carbon nanofibers, silicon carbide nano-particles, alumina (Al₂O₃) nano-particles, titanium carbide (TiC) nano-particles, and any combination thereof. The diameter of the nanoscale reinforcements can, advantageously, be in the approximate range from 1 nanometer to 10 microns.
In the present embodiment, the material of the magnesium-based powder includes magnesium, aluminum, zinc, and manganese, and the weight percentage are, respectively, in the approximate ranges from 88.5% to 97.89%, 2% to 10%, 0.1% to 1%, 0.01% to 0.5%. The nanoscale reinforcements are carbon nanotubes in a diameter of about 1 nanometer to 150 nanometers, and in a length of about 1 nanometer to 10 microns.
In step (b), the magnesium-based powder and the nanoscale reinforcements are mixed in a ball mill with a protective gas filled therein. Depending on the amount of the magnesium-based powder and the nanoscale reinforcements, milling time can, suitably, be in the approximate range from 0.5 to 24 hours, and milling speed can, usefully, be in the approximate range from 100 to 300 rotations per minute. The protective gas can, opportunely, be nitrogen (N₂) and/or a noble gas.
In step (c), referring to FIG. 2, high velocity compaction equipment 100 includes a sealing chamber 110, a gas pumping device 120, a mold 140 with an aperture 150 formed on the top thereof, and a hammer 130 disposed above the mold 140. The gas pumping device 120 is disposed outside the sealing chamber 110 and connected thereto. The hammer 130 and the mold 140 are disposed in the sealing chamber 110. The hammer 130 is operated by a hydraulic impact unit (not shown) and can press along an axis direction (i.e., a direction along the longitudinal thereof) at a controllable ramming speed. A cross section of the hammer 130 has the same size as the aperture 150 of the mold 140. The ramming speed of the hammer 130 can, beneficially, be in the approximate range from 2 to 30 meters per second. A weight of the hammer 130 can, beneficially, be in the approximate range from 5 to 1200 kilograms.
The gas pumping device 120 can, suitably, further include a vacuum pump for evacuating the air in the sealing chamber 110, and a gas source (e.g. a gas cylinder) for providing protective gas in the sealing chamber 110. The protective gas can, opportunely, be nitrogen (N₂) and/or a noble gas.
In step (c), the compacting process further includes substeps of: (c1) disposing the mixture in the mold 140 of the high velocity compaction equipment 100 in a protective gas; (c2) lightly pressing the mixture in the mold 140 through the aperture 150 by the hammer 130; and (c3) repeatedly compacting the mixture in the mold 140 through the aperture 150 by the hammer 130 at a high speed to achieve the magnesium-based composite material.
In step (c2), the gas in interspaces in the mixture is exhausted by the pressing of the hammer 130. In step (c3), the ramming speed of the hammer 130 can, suitably, be in the approximate range from 2 to 30 meters per second. In the present embodiment, the speed is about 7 meters per second. The density of the magnesium-based composite material is about 1.77 grams per cubic centimeter.
In high velocity compaction, density can increase as compacting. The compaction energy is transferred through the hydraulically operated hammer 130 to the mixture. As such, densification is achieved by intensive shock waves created by the hydraulically operated hammer 130. The mass of the hammer 130 and the velocity at the moment of impact thereof determine the compaction energy and the amount of densification. In the compacting processes, the temperature of the mixture can increase to about 200° C. The protective gas in the sealing chamber 110 can prevent the oxidization of the mixture.
In one useful embodiment, an additional step (d) of sintering the magnesium-based composite material in protective gas can, advantageously, be further provided after the step (c).
In step (d), the magnesium-based composite material can, suitably, be sintered in a furnace. The protective gas can, opportunely, be nitrogen (N₂) and/or a noble gas. The sintering temperature can, usefully, be in the approximate range from 400° C. to 680° C. The sintering time can, advantageously, be in the approximate range from 0.5 to 1 hour. With sintering the magnesium-based powder and the nanoscale reinforcements can be compactly combined.
The high velocity compaction equipment 100 provided in the present embodiment can be used for fabricating the magnesium-based composite material. The density of the magnesium-based composite material fabricated in the present embodiment can be improved by the high velocity compaction process. Therefore, the toughness and the strength of the magnesium-based composite material can be enhanced. Further, the achieved magnesium-based composite material after the high velocity compaction process can be used directly without the additional hot-extrusion step. As such, the method can be easily used in mass production.
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 method for fabricating a magnesium-based composite material, the method comprising the steps of:

(a) providing a large amount of magnesium-based powder and a large amount of nanoscale reinforcements;

(b) uniformly mixing the magnesium-based powder and the nanoscale reinforcements to form a mixture; and

(c) compacting the mixture at a high velocity in a protective gas to achieve the magnesium-based composite material.

2. The method as claimed in claim 1, wherein the material of the magnesium-based powder is one of pure magnesium and magnesium-based alloys.

3. The method as claimed in claim 2, wherein components of the magnesium-based alloy comprises magnesium and other elements selected from a group consisting of zinc, manganese, aluminum, thorium, lithium, silver, calcium, and any combination thereof.

4. The method as claimed in claim 3, wherein a weight ratio of the magnesium to the other elements in the magnesium-based alloy is more than 4:1.

5. The method as claimed in claim 2, wherein the diameter of particles of the magnesium-based powder is less than about 74 microns.

6. The method as claimed in claim 1, wherein the nanoscale reinforcements are made up of carbon nanotubes, carbon nanofibers, silicon carbide nano-particles, alumina (Al₂O₃) nano-particles, titanium carbide (TiC) nano-particles, and any combination thereof.

7. The method as claimed in claim 6, wherein the diameter of the nanoscale reinforcements is in the approximate range from 1 nanometer to 10 microns.

8. The method as claimed in claim 1, wherein a weight percentage of the nanoscale reinforcements in the mixture is in the approximate range from 0.01% to 30%.

9. The method as claimed in claim 1, wherein step (c) is performed in a high velocity compaction equipment and comprises substeps of:

(c1) disposing the mixture in a mold of the high velocity compaction equipment in a protective gas;

(c2) lightly pressing the mixture in the mold through an aperture thereon by a hammer; and

(c3) repeatedly compacting the mixture in the mold through the aperture thereon by the hammer at a high speed to achieve the magnesium-based composite material.

10. The method as claimed in claim 1, wherein step (b) is executed in a ball mill with a protective gas filled therein.

11. The method as claimed in claim 10, wherein a milling time is in the approximate range from 0.5 to 24 hours, and a milling speed is in the approximate range from 100 to 300 rotations per minute.

12. The method as claimed in claim 1, wherein an additional step (d) of sintering the magnesium-based composite material in protective gas is further provided after the step (c).

13. The method as claimed in claim 12, wherein the magnesium-based composite material is sintered in a furnace, and the sintering temperature is in the approximate range from 400° C. to 680° C., and the sintering time is in the approximate range from 0.5 to 1 hour.

14. The method as claimed in claim 1, wherein the protective gas in step (c) is nitrogen (N₂) and/or a noble gas.

15. A high velocity compaction equipment for fabricating the magnesium-based composite material comprising:

a sealing chamber,

a gas pumping device disposed outside the sealing chamber and connected thereto,

a mold disposed in the sealing chamber with an aperture formed on a top thereof, and

a hammer disposed in the sealing chamber and above the mold, and the hammer moving along longitudinal thereof at a controllable ramming speed.

16. The high velocity compaction equipment as claimed in claim 15, wherein a cross section of the hammer has the same size as the aperture of the mold.

17. The high velocity compaction equipment as claimed in claim 15, wherein the ramming speed of the hammer is in the approximate range from 2 to 30 meters per second.

18. The high velocity compaction equipment as claimed in claim 15, wherein a weight of the hammer is in the approximate range from 5 to 1200 kilograms.