U.S. patent application number 11/308400 was filed with the patent office on 2007-01-04 for creep resistant magnesium alloy.
Invention is credited to Ga-Lane Chen.
Application Number | 20070000577 11/308400 |
Document ID | / |
Family ID | 37132523 |
Filed Date | 2007-01-04 |
United States Patent
Application |
20070000577 |
Kind Code |
A1 |
Chen; Ga-Lane |
January 4, 2007 |
CREEP RESISTANT MAGNESIUM ALLOY
Abstract
The present invention relates to a creep resistant magnesium
alloy, which includes aluminium (Al) in an amount of 5 to 20
percent by weight, carbon nanotubes (CNT) in an amount of 0.1 to 10
percent by weight, strontium (Sr) in an amount of 0 to 2 percent by
weight, remainder being magnesium (Mg) and impurities commonly
found in magnesium alloys.
Inventors: |
Chen; Ga-Lane; (Shenzhen,
CN) |
Correspondence
Address: |
NORTH AMERICA INTELLECTUAL PROPERTY CORPORATION
P.O. BOX 506
MERRIFIELD
VA
22116
US
|
Family ID: |
37132523 |
Appl. No.: |
11/308400 |
Filed: |
March 21, 2006 |
Current U.S.
Class: |
148/420 |
Current CPC
Class: |
C22C 23/02 20130101;
C22C 49/04 20130101 |
Class at
Publication: |
148/420 |
International
Class: |
C22C 23/00 20060101
C22C023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 22, 2005 |
CN |
200510034367.6 |
Claims
1. A magnesium alloy comprising, by weight, aluminum in an amount
of 5 to 20 percent, carbon nanotubes in an amount of 0.1 to 10
percent, strontium in an amount of 0 to 2 percent, remainder being
magnesium and impurities commonly found in magnesium alloys.
2. The magnesium alloy as claimed in claim 1, wherein the aluminum
is in an amount of 8 to 10 percent by weight.
3. The magnesium alloy as claimed in claim 1, wherein the carbon
nanotube is in an amount of 0.5 to 2 percent by weight.
4. The magnesium alloy as claimed in claim 1, wherein an average
length of the carbon nanotubes is in the range from 5 to 500
nanometers.
5. The magnesium alloy as claimed in claim 4, wherein the average
length of the carbon nanotubes is in the range from 20 to 200
nanometers.
6. The magnesium alloy as claimed in claim 1, wherein strontium is
in an amount by weight of 1 to 2 percent.
7. The magnesium alloy as claimed in claim 1, wherein the average
size of the strontium is in the range from 20 to 500
nanometers.
8. The magnesium alloy as claimed in claim 7, wherein the average
size of the strontium is in the range from 100 to 300 nanometers.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to magnesium alloys,
particularly to a magnesium alloy having good creep resistance and
high strength.
DESCRIPTION OF RELATED ART
[0002] Magnesium alloys have been widely utilized in the automotive
industry to reduce component weight while providing a high
structural rigidity. Magnesium alloys are the lightest structural
material among metals, with a specific gravity being merely 1.8,
which is one-fourth of that of copper, two-thirds of that of
aluminum, and is similar to that of plastic materials. In addition,
magnesium alloys have good mechanical properties, such as good
castability. Due to the above advantages, magnesium alloys are
widely used in many fields, for example, electronic products, car
industry, aerospace industry, etc.
[0003] However, conventional magnesium alloys exhibiting good
castability also have poor creep resistance. Creep is a phenomenon
that occurs when a material continues to deform under constant
stress at a certain temperature. Generally, creep of magnesium
alloys seldom occurs at room temperature, under stress below
elasticity limitation. However, the creep phenomenon occurs when
the temperature increases to a high degree, under stress below
elasticity limitation. Therefore, creep resistant magnesium alloys
are desired.
[0004] Generally, magnesium alloys capable of undergoing a
temperature above 150 degrees centigrade without significant creep
can be called creep resistant magnesium alloys. Creep resistance is
a desirable characteristic for alloys under compressive load and
high temperature. This characteristic is also important in
maintaining bolt torque and dimensional stability of cast bodies
during operation. However, compared with aluminum alloys,
conventional magnesium alloys are disadvantageous in mechanical
strength, toughness, and creep resistance.
[0005] Many efforts have been paid to solve the above problems. It
has been suggested that grain refinement is a useful technology to
improve the mechanical properties of magnesium alloys, such as
creep resistance and toughness.
[0006] It is known to all that with the presence of aluminum
component, magnesium-aluminum alloy exhibits improved strength,
toughness and castability. However, an interphase of bulky Mg17Al12
grains is formed between magnesium phase and aluminum phase. With
the presence of Mg17Al12 grains, the toughness and creep resistance
of magnesium-aluminum alloys are reduced. Accordingly, optimizing
the configuration and distribution of the interphase is considered
another possible approach to improve the mechanical properties of
magnesium alloys or magnesium-aluminum alloys.
[0007] For example, a magnesium-zinc-copper alloy has been
provided. The magnesium-zinc-copper alloy contains a large amount
of copper (about 5 percent by weight) for improvement of mechanical
properties including toughness and creep resistance thereof.
However, those mechanical properties can only be realized after
aging treatment during fusing process. Furthermore, a large amount
of copper can lead to a high melting point for the alloy, which
leads to difficulties in casting, poor anti-corrosion properties
and high cost. Moreover, the grain refinement of copper can only be
realized in the absence of aluminum, this further restricts
magnesium alloy's application.
[0008] Therefore, a heretofore-unaddressed need exists in the
industry to address the aforementioned deficiencies and
inadequacies.
SUMMARY OF THE INVENTION
[0009] In a preferred embodiment, a magnesium alloy is provided,
which includes aluminum in an amount of 5 to 20 percent by weight,
carbon nanotubes in an amount of 0.1 to 10 percent by weight,
nano-sized strontium in an amount of 0 to 2 percent by weight,
remainder being magnesium and impurities commonly found in
magnesium alloys.
[0010] Compared with the conventional magnesium matrix materials,
the magnesium alloy of the preferred embodiment has the following
advantages. Firstly, the presence of aluminum leads to good
intensity, toughness and castability for the alloy. Secondly,
nanotube and nano-sized strontium can refine grain, thus leading to
high fracture toughness of the alloy, and finally leads to good
creep resistance.
DETAILED DESCRIPTION OF THE INVENTION
[0011] The following description of the preferred embodiments is
merely exemplary in nature and is in no way intended to limit the
invention, its application, or uses.
[0012] A magnesium alloy of a preferred embodiment contains, by
weight, 5 to 20 percent aluminum, preferably 8 to 10 percent; 0.1
to 10 percent carbon nanotube, preferably 0.5 to 2 percent; 0 to 2
percent strontium, preferably 1 to 2 percent; with remainder being
magnesium and impurities commonly found in magnesium alloys.
[0013] An average particle size (i.e. length) of the carbon
nanotubes ranges from 5 to 500 nanometers, preferably 20 to 200
nanometers. Carbon nanotubes have a high Young's modulus, and a
mechanical strength similar to that of diamond. Thus, carbon
nanotubes have a good creep resistance and can prevent any micro
cracks. In addition, carbon nanotubes have good electrical
conductivity, therefore, when use in electronic customer products,
carbon nanotubes can effectively prevent electro-magnetic
interference (abbreviated as EMI). Furthermore, carbon nanotubes
are good thermal conductors with a heat conductivity (k) of 6,000
W/mK, which is 30 times to that of aluminum, 20 times to that of
copper, and 2 times to that of diamond.
[0014] Strontium is widely used in many technical fields, such as
metallurgy, chemical industry, photoelectric cell. When a little
strontium particle is added into a magnesium alloy, refined
structure will be produced. Accordingly, it can effectively prevent
the occurrence of a micro crack caused by outer effect, and can
further improve the creep resistant property of magnesium
alloy.
[0015] For metal alloys or plastics, particle size is an important
factor which can affect fracture toughness of the materials.
Fracture toughness (K.sub.1c) is one of main mechanical parameters
for metal alloys and plastics. Fracture toughness indicates an
ability of the material for preventing micro crack extension.
Generally, when the fracture toughness is high, the material
exhibits good mechanical properties. The fracture toughness
satisfies the following formula: K 1 .times. .times. c ~ .sigma. y
( 3.14159 .times. c d ) 0.5 ##EQU1##
[0016] wherein K.sub.1c represents fracture toughness; ay
represents yield strength, also known as yield limit; c represents
crack length; and d represents particle size. It can be deduced
from the above formula that the smaller the particle size, the
larger the fracture toughness. Due to the small size of carbon
nanotubes and strontium particles, the fracture toughness of the
magnesium alloy of the preferred embodiment is improved. Thus, the
magnesium alloy has the advantages of preventing micro crack
extension, high resistance to creep and improved mechanical
properties.
[0017] A magnesium alloy of the first preferred example includes,
by weight, 10 percent aluminum, 0.1 percent carbon nanotubes, 1
percent strontium, with the remainder being magnesium with an
acceptable amount of impurities.
[0018] A magnesium alloy of the second preferred example includes,
by weight, 8 percent aluminum, 10 percent carbon nanotubes, 2
percent strontium, with the remainder being magnesium with an
acceptable amount of impurities commonly found in magnesium
alloys.
[0019] A magnesium alloy of the third preferred example includes,
by weight, 10 percent aluminum, 0.5 percent carbon nanotubes, 1
percent strontium, with the remainder being magnesium with an
acceptable amount of impurities commonly found in magnesium
alloys.
[0020] A magnesium alloy of the fourth preferred example includes,
by weight, 9 percent aluminum, 2 percent carbon nanotubes, 1
percent strontium, with the remainder being magnesium with an
acceptable amount of impurities commonly found in magnesium
alloys.
[0021] A magnesium alloy of the fifth preferred example includes,
by weight, 5 percent aluminum, 5 percent carbon nanotubes, 2
percent strontium, with the remainder being magnesium with an
acceptable amount of impurities commonly found in magnesium
alloys.
[0022] A magnesium alloy of the sixth preferred example includes,
by weight, 20 percent aluminum, 5 percent carbon nanotubes, 2
percent strontium, with the remainder being magnesium with an
acceptable amount of impurities commonly found in magnesium
alloys.
[0023] A magnesium alloy of the seventh preferred example includes,
by weight, 20 percent aluminum, 10 percent carbon nanotubes, with
the remainder being magnesium with an acceptable amount of
impurities commonly found in magnesium alloys.
[0024] A magnesium alloy of the eighth preferred example includes,
by weight, 5 percent aluminum, 0.1 percent carbon nanotubes, with
the remainder being magnesium with an acceptable amount of
impurities commonly found in magnesium alloys.
[0025] The magnesium alloy provided hereinabove can be used as
outer shells and nameplates for mobile phones, computer cases,
personal digital assistants, DVDs, digital cameras, and the
like.
[0026] It is believed that the present embodiments and their
advantages will be understood from the foregoing description, and
it will be apparent that various changes may be made thereto
without departing from the spirit and scope of the invention or
sacrificing all of its material advantages, the examples
hereinbefore described merely being preferred or exemplary
embodiments of the invention.
* * * * *