Magnesium alloy and thin workpiece made of the same

An exemplary magnesium alloy includes: by weight, magnesium as a main ingredient, aluminum in an amount from 7.5% to 7.8%, zinc in an amount from 0.35% to 1.0%, manganese in an amount from 0.15% to 0.5%, silicon less than 0.1%, copper less than 0.03%, iron less than 0.005%, and nickel less than 0.002%. The present invention also provides a thin workpiece made of the magnesium alloy.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a magnesium alloy and, particularly, to a thin workpiece made of magnesium alloy.

2. Discussion of the Related Art

Magnesium is a metal that is the lightest in weight among metal materials. Magnesium alloys are composed of the magnesium and other metals, such as aluminum and zinc. In recent years, there has been an increase in demand for magnesium alloys used as structural materials for computers, mobile phones, and other electronic products.

For example, AZ91D magnesium alloy is widely used in electronic products. The AZ91D magnesium alloy includes magnesium as a main ingredient, in addition, the AZ91D magnesium alloy also includes, aluminum in an amount by weight from 8.3% to 9.7%, zinc in an amount by weight from 0.45% to 0.9%, manganese in an amount by weight from 0.17% to 0.4%, and some silicon, copper, iron, and impurities. In the AZ91D magnesium alloy, aluminum is use to modify the mechanical strength, the corrosion resistance, and the castability of the AZ91D magnesium alloy. A strengthening phase of the AZ91D magnesium alloy is generally obtained from Mg12Al17eutectic phase. However if the AZ91D magnesium alloy is heated, a lot of Mg12Al17eutectic phases may separate out to grain boundaries, thereby increasing brittleness of the AZ91D magnesium alloy. Thus, if thin workpieces used in electronic products, such as frames, that require excellent toughness, the AZ91D magnesium alloy would not meet the requirements.

Therefore, a new magnesium alloy and thin workpiece made of the magnesium alloy are desired in order to overcome the above-described shortcomings.

SUMMARY

A magnesium alloy includes: by weight, magnesium as a main ingredient, aluminum in an amount from 7.5% to 7.8%, zinc in an amount from 0.35% to 1.0%, manganese in an amount from 0.15% to 0.5%, silicon less than 0.1%, copper less than 0.03%, iron less than 0.005%, and nickel less than 0.002%.

A thin workpiece made of magnesium alloy. The magnesium alloy includes: by weight, magnesium as a main ingredient, aluminum in an amount from 7.5% to 7.8%, zinc in an amount from 0.35% to 1.0%, manganese in an amount from 0.15% to 0.5%, silicon less than 0.1%, copper less than 0.03%, iron less than 0.005%, and nickel less than 0.002%.

Other novel features will become more apparent from the following detailed description, when taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made to the drawings to describe preferred embodiments of the present magnesium alloy and a thin workpiece made of the magnesium alloy in detail.

A magnesium alloy according to a preferred embodiment includes magnesium as a main ingredient, preferably, in an amount by weight from 90.543% to 92%. The magnesium alloy also includes, by weight, aluminum in an amount from 7.5% to 7.8%, zinc in an amount from 0.35% to 1.0%, manganese in an amount from 0.15% to 0.5%, silicon less than 0.1%, copper less than 0.03%, iron less than 0.005%, and nickel less than 0.002%. In an alternative embodiment, the magnesium alloy can further include impurities in an amount by weight less than 0.02%.

In this embodiment, since the amount of aluminum in the magnesium alloy is relatively low, an amount of the Mg12Al17eutectic phases in the magnesium alloy is reduced. That way, while heating the magnesium alloy, occurrences of separation of the Mg12Al17eutectic phases to grain boundaries is reduced, and also inhibiting any increase in brittleness and ensuring the magnesium alloy having excellent toughness. Furthermore, a magnesium alloy with greater than 7.5% aluminum in an amount by weight would have good castability properties, so the magnesium alloy of this embodiment having 7.5%-7.8% of aluminum in an amount by weight would have excellent castability properties.

A toughness test is performed on two AZ91D magnesium alloy samples and three AZ91D magnesium alloy samples. The test result of the toughness test is listed in Table 1 below. Sample a0, a1 are the two AZ91D magnesium alloys, and samples a2, a3, a4 are the three magnesium alloys according to the embodiment of the present invention prepared by modifying the amount of aluminum in the AZ91D magnesium alloy. A shape of each of the samples a0, a1, a2, a3, a4, a5 is a cuboid, and the length, width, and height of each of the five samples are 55 millimeters, 10 millimeters, and 10 millimeters respectively. Generally, how much energy a material absorbs reflects the impact strength of the material and further reflects the toughness, i.e. the more energy the material absorbs the higher the impact strength and better toughness of the material.

TABLE 1SampleAbsorbedno.Sample descriptionenergy(J)a0AZ91D magnesium alloy having aluminum in16.64the amount by weight 8.25%a1AZ91D magnesium alloy having aluminum in13.80the amount by weight 8.96%a2the magnesium alloy according to the23.38embodiment of the present invention havingaluminum in the amount by weight 7.51%a3the magnesium alloy according to the23.99embodiment of the present invention havingaluminum in the amount by weight 7.64%a4the magnesium alloy according to the23.15embodiment of the present invention havingaluminum in the amount by weight 7.74%

As seen from the test results, the magnesium alloys according to the embodiment of the present invention absorbs more energy than the AZ91D magnesium alloys. Therefore the magnesium alloys according to the embodiment of the present invention have excellent toughness.

Furthermore, in order to determine when the magnesium alloy according to the embodiment of the present invention is used as a thin workpiece also has excellent toughness, some thin workpieces made of the magnesium alloy according to the embodiment of the present invention having special structures and some thin workpieces made of the AZ91D magnesium alloy having special structures are tested correspondingly.

An example of the thin workpiece10made of the magnesium alloy according to the embodiment of the present invention or made of the AZ91D magnesium alloy is shown inFIGS. 1 and 2. The thin workpiece10can be used as a frame of the portable electronic product, such as mobile phone. The thin workpiece10is substantially a rectangular frame in shape. A thickness of the thin workpiece10can be in a range from about 0.5 millimeters to about 1 millimeter. The thin workpiece10includes a first side rim101, a second side rim103, a third side rim105, and a fourth side rim107. The first side rim101and the third side rim105are on opposite sides of the thin workpiece. The second side rim103or the fourth side rim107is connected to the first side rim101and the third side rim105. The four side rims101,103,105, and107cooperatively define an opening109. An outer end of the first side rim110has a bent portion1011extending outwards. The bent portion101is curved. The thin workpiece10is molded by die-casting, then heated for 20 minutes at 120 degrees centigrade, and then the surfaces of the thin workpiece10are treated for 30 minutes at 150 degrees centigrade.

A drop test is performed on the thin workpiece10to determine the toughness of the thin workpieces10. While testing, the thin workpieces10made of the magnesium alloy according to the embodiment of the present invention or made of the AZ91D magnesium alloy is dropped such that the bent portion1011of the first side rim101hits the ground first. A toughness of the thin workpiece10made of magnesium alloy according to the embodiment of the present invention or the AZ91D magnesium alloy is defined by the average drop count before the bent portion1011becomes fractured. From the test, an average drop count of the thin workpieces10made of the AZ91D magnesium alloy is 2.5, and the average drop count of the thin workpieces10made of the magnesium alloy according to the embodiment of the present invention is 4.5. Thus, the thin workpieces10made of the magnesium alloy according to the embodiment of the present invention have better toughness than that made of the AZ91D magnesium alloy.

It is noted that the scope of the present magnesium alloy and thin workpiece made of the magnesium alloy are not limited to the embodiments described above. For example, the structure of the thin workpiece10can be a cover having no opening thereon.