MAGNESIUM ALLOY

Abstract

A magnesium alloy is disclosed. The magnesium alloy includes magnesium (Mg), 6-12 wt % of lithium (Li) and 1-10 wt % of aluminum (Al). A temperature range between a solidus and a liquidus of the magnesium alloy is equal to or larger than 50° C.

Description

This application claims the benefit of Taiwan application Serial No. 103141813, filed on Dec. 2, 2014, the subject matter of which is incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates in general to an alloy, and more particularly to a magnesium alloy.

BACKGROUND

Semi-solid metal casting is one of the casting technologies. In comparison to the conventional casting technology, the semi-solid metal casting process provides smaller grains and superior mechanical properties. One of the prerequisites of the semi-solid metal casting process is that the temperature range between the solidus and the liquidus of the metal/alloy used in the semi-solid metal casting process must be large enough. That is, a temperature range from the temperature at which the alloy starts to melt to the temperature at which the alloy completely melts, i.e., the solid-liquid co-existence region, must large enough for the control easiness of the casting temperature. As such, casting pieces with complicated shapes and excellent mechanical properties can be produced.

Magnesium alloys have been widely used due to the feature of lightweight. Magnesium lithium alloy (Mg—Li alloy) is the lightest among the commonly used magnesium alloys. For example, LZ91 (Mg-9% Li-1% Zn) has a specific gravity only about 1.5, which is much lower than 1.81, the specific gravity of the magnesium alloy AZ91 (Mg-9% Al-1% Zn) currently used for commercial purpose. However, the temperature range between the solidus and the liquidus of M—Li alloy is small. For example, the temperature range between the solidus and the liquidus of the Mg-6 wt % Li alloy is only 4° C. Such alloy is not suitable to be used in the semi-solid metal casting process.

SUMMARY

The disclosure is directed to a magnesium alloy. The temperature range between a solidus and a liquidus of the magnesium alloy is expanded through the addition of several kinds of elements. As such, the magnesium alloy is suitable to be used in a semi-solid metal casting process. Further, the magnesium alloy has a feature of lightweight.

According to some embodiments of the disclosure, the magnesium alloy includes magnesium (Mg), 6-12 wt % of lithium (Li) and 1-10 wt % of aluminum (Al). A temperature range between a solidus and a liquidus of the magnesium alloy is equal to or larger than 50° C.

According to some embodiments of the disclosure, the magnesium alloy includes magnesium (Mg), 6-12 wt % of lithium (Li), 1-10 wt % of aluminum (Al), 0.2-3 wt % of zinc (Zn), 0.3 wt % of manganese (Mn), 0.2 wt % of silicon (Si), 1.0 wt % of calcium (Ca) and 1.0 wt % of tin (Sn).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a differential scanning calorimetry (DSC, SDT Q600 V20.9 Build 20) curve of one example of the disclosure.

FIG. 2 shows a DSC curve of one example of the disclosure.

FIG. 3 shows a characteristic collection of examples and comparative examples of the present invention.

In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.

DETAILED DESCRIPTION

The disclosure is directed to a magnesium alloy. The temperature range between a solidus and a liquidus of the magnesium alloy can be adjusted through the addition of several kinds of elements. The magnesium alloy includes magnesium (Mg), 6 to 12 wt % of lithium (Li) and 1 to 10 wt % of aluminum (Al). A temperature range between the solidus and the liquidus of the magnesium alloy is equal to or larger than 50° C. Since the magnesium alloy has a larger temperature range between the solidus and the liquidus, the magnesium alloy is suitable to be used in a semi-solid metal casting process. In a preferred embodiment, the temperature range between the solidus and the liquidus of the magnesium alloy is equal to or larger than 95° C. In some embodiments, the magnesium alloy has a specific gravity smaller than 1.65. In general, a metal casting piece with a smaller density will have a larger strength-to-weight ratio (the ratio of strength to density), and is suitable to be used in a mobile device.

Magnesium is the main ingredient of said magnesium alloy. That is, the magnesium alloy is mainly formed of magnesium apart from other disclosed ingredients. Since magnesium is the main ingredient, the magnesium alloy has the feature of lightweight. The addition of lithium reduces the density of the magnesium alloy to be smaller than 1.65 g/cm³ but at the same time reduces the temperature range between the solidus and the liquidus of the magnesium alloy. In general, when 1 wt % of lithium is added to the magnesium alloy, the liquidus will drop by about 10° C. but the solidus will drop by only about 5° C., therefore the temperature range between the solidus and the liquidus will become smaller. When aluminum is added to the magnesium alloy, the temperature range between the solidus and the liquidus of the magnesium alloy will expand, but the density of the magnesium will slightly increase. In general, when 1 wt % of aluminum is added to the magnesium alloy, the liquidus will drop by about 2° C., but the solidus will drop be about 10° C., therefore the temperature range between the solidus and the liquidus of the magnesium alloy will expand. By adjusting the ratio between lithium and aluminum, a larger temperature range between the solidus and the liquidus and a smaller specific gravity can be achieved.

The magnesium alloy can include other ingredients. For example, zinc (Zn) can be added to the magnesium alloy to enhance its corrosion resistance and reduce its melting point. A small amount of manganese (Mn) can be added to the magnesium alloy to enhance its strength and corrosion resistance. A small amount of silicon (Si) can be added to the magnesium alloy to enhance its strength. Moreover, during the solidification process, the heat released by the Mg—Si compound improves the casting property of the magnesium alloy. A small amount of calcium (Ca) can be added to the magnesium alloy to prevent combustion during the semi-solid metal casting process. A small amount of tin (Sn) can be added to the magnesium alloy to enhance the strength of the alloy at a high temperature. Specifically, the magnesium alloy can further include 0.2 to 3 wt % of zinc, ≦3 wt % of manganese, ≦2 wt % of silicon, ≦1.0 wt % of calcium and ≦1.0 wt % of tin.

Now, the effects of the disclosure are presented with several examples and comparative examples. All of the examples and comparative examples are alloys of Mg-(X wt %)Li-(Y wt %)Al-(1 wt %)Zn, and the values of X and Y of the examples and comparative examples are listed in Table 1.

	TABLE 1
	X (wt %)	Y (wt %)
	Comparative example 1	6	0
	(CE1)
	Comparative example 2	7	0
	(CE2)
	Comparative example 3	8	0
	(CE3)
	Comparative example 4	9	0
	(CE4)
	Comparative example 5	10	0
	(CE5)
	Comparative example 6	12	0
	(CE6)
	Example 1 (E1)	8	1
	Example 2 (E2)	9	1
	Example 3 (E3)	6	6
	Example 4 (E4)	7	6
	Example 5 (E5)	6	7
	Example 6 (E6)	7	7
	Example 7 (E7)	6	8
	Example 8 (E8)	8	8

FIG. 1 shows a DSC curve of Example 4. FIG. 2 shows a DSC curve of Example 5. As shown in FIGS. 1 and 2, the temperature range between the solidus and the liquidus is equal to or larger than 50° C. in both cases. The temperature range between the solidus and the liquidus in Example 5 is even equal to or larger than 95° C. The specific gravity (SG) and the temperature range between the solidus and the liquidus (S-L range) of the examples and the comparative examples are shown in blocks 061 to 0101, 0121, 181, 191, 661, 671, 761, 771, 861 and 881 of FIG. 3. In comparison to the comparative examples, each of the example according to this disclosure provides a larger temperature range between the solidus and the liquidus. Also, each of the examples according to this disclosure provides a specific gravity 1.65, which is lower than 1.8, the specific gravity of a typical magnesium alloy.

To summarize, by adjusting the varieties and amounts of the elements added to the magnesium alloy, the magnesium alloy having a larger temperature range between the solidus and the liquidus and suitable to be used in a semi-solid metal casting process can be obtained. Moreover, the magnesium alloy has the feature of lightweight, and is suitable to be used in a mobile device.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.

Claims

1. A magnesium alloy, comprising:

magnesium (Mg);

6-12 wt % of lithium (Li); and

1-10 wt % of aluminum (Al);

wherein a temperature range between a solidus and a liquidus of the magnesium alloy is equal to or larger than 50° C.

2. The magnesium alloy according to claim 1, wherein the temperature range is equal to or larger than 95° C.

3. The magnesium alloy according to claim 1, further comprising:

0.2-3 wt % of zinc (Zn);

≦0.3 wt % of manganese (Mn);

≦0.2 wt % of silicon (Si);

≦1.0 wt % of calcium (Ca); and

≦1.0 wt % of tin (Sn).

4. The magnesium alloy according to claim 1, having a specific gravity smaller than 1.65.

5. A magnesium alloy, comprising:

magnesium (Mg);

6-12 wt % of lithium (Li);

1-10 wt % of aluminum (Al);

0.2-3 wt % of zinc (Zn);

≦0.3 wt % of manganese (Mn);

≦0.2 wt % of silicon (Si);

≦1.0 wt % of calcium (Ca); and

≦1.0 wt % of tin (Sn).

6. The magnesium alloy according to claim 5, wherein a temperature range between a solidus and a liquidus of the magnesium alloy is equal to or larger than 95° C.

7. The magnesium alloy according to claim 1, having a specific gravity smaller than 1.65.