US20130209311A1

US20130209311A1 - Aluminum alloy, and aluminum alloy casting

Info

Publication number: US20130209311A1
Application number: US13/700,550
Authority: US
Inventors: Seoung-Jin Lee; Hyung-Chul Lee
Original assignee: Interplex Quantum Co Ltd
Current assignee: Interplex Quantum Co Ltd
Priority date: 2010-05-29
Filing date: 2011-05-12
Publication date: 2013-08-15
Also published as: KR101124235B1; KR20110131327A; CN103069029A; DE112011101836T5; WO2011152617A3; JP2013529255A; WO2011152617A2

Abstract

Provided are a metal alloy and more particularly, to an aluminum alloy used for electrical, electronic, and mechanical components, and an aluminum alloy casting manufactured using the aluminum alloy. The aluminum alloy according to an embodiment includes 4 to 13 wt % of silicon (Si), 1 to 5 wt % of copper (Cu), 26 wt % or more and less than 40 wt % of zinc (Zn), and a balance being aluminum (Al) and unavoidable impurities.

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2010-0050693, filed on May 29, 2010, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a metal alloy, and more particularly, to an aluminum alloy used for electrical, electronic, and mechanical components, and an aluminum alloy casting manufactured using the aluminum alloy.
2. Description of the Related Art
Recently, the needs for high-strength materials that are more resistant to deformation are increasing as electronic products such as a notebook and a mobile phone become more complicated in aspects of appearances and functions. Particularly, components, such as a bracket supporting a portion of a liquid crystal display (LCD) panel and a hinge having thin and complicated shapes, require a lightweight material for a portability as well as a high strength similar to stainless steels (e.g., stainless steel 304). However, although stainless steels can be shaped by pressing or forging, the stainless steels have limitations in mass production and achievement of a precise product shape, and the stainless steels having a specific gravity of about 8.00 g/cm³are heavy. Therefore, the need for developing a high-strength and lightweight alloy is increasing.

SUMMARY OF THE INVENTION

The present invention provides an aluminum alloy lighter than about a half of a weight of a typical stainless steel as well as having a strength similar to the typical stainless steel (e.g., stainless steel 304) and better than a typical commercial aluminum alloy even through a general die casting method, and an aluminum alloy casting manufactured using the foregoing aluminum alloy. Objects of the present invention are exemplarily provided, and the scope of the present invention is not limited by these objects.
According to an aspect of the present invention, there is provided an aluminum alloy including: 4 wt % to 13 wt % of silicon (Si); 1 wt % to 5 wt % of copper (Cu); 26 wt % or more and less than 40 wt % of zinc (Zn); and a balance being aluminum (Al) and unavoidable impurities.
According to another aspect of the aluminum alloy, a content of the silicon (Si) may be 5 wt % to 10 wt %.
According to another aspect of the aluminum alloy, the content of the silicon (Si) may be 5 wt % to 8 wt %. In this case, a content of the copper (Cu) may be 2 wt % to 5 wt %, and further, a content of the zinc (Zn) may be 26 wt % to 35 wt %.
According to another aspect of the present invention, there is provided an aluminum alloy including: 4 wt % to 13 wt % of silicon (Si); 1 wt % to 5 wt % of copper (Cu); 26 wt % or more and less than 40 wt % of zinc (Zn); 0.1 wt % or less of strontium (Sr); and 43 wt % to 69 wt % of aluminum (Al).
According to another aspect of the aluminum alloy, a content of the silicon (Si) may be 5 wt % to 10 wt %.
According to another aspect of the aluminum alloy, the content of the silicon (Si) may be 5 wt % to 8 wt %. At this time, a content of the copper (Cu) may be 2 wt % to 5 wt %, and further, a content of the zinc (Zn) may be 26 wt % to 35 wt %.
According to another aspect of the aluminum alloy, a content of the strontium (Sr) may be greater than 0 wt % and 0.04 wt % or less.
According to another aspect of the aluminum alloy, the content of the strontium (Sr) may be greater than 0 wt % and 0.02 wt % or less.
According to another aspect of the aluminum alloy, the aluminum alloy may further include a total of 3 wt % or less (more than 0) of any one or more elements selected from the group consisting of titanium (Ti), magnesium (Mg), nickel (Ni), vanadium (V), tin (Sn), iron (Fe), chromium (Cr), zirconium (Zr), scandium (Sc), and manganese (Mn).
According to another aspect of the present invention, there is provided an aluminum alloy casting which is manufactured by using the foregoing aluminum alloy

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:

FIG. 1 show tensile test results of a commercial ADC12 aluminum alloy and an aluminum alloy according to an embodiment of the present invention;

FIG. 2 shows a comparison result between microstructures of a commercial aluminum alloy and an aluminum alloy according to an embodiment of the present invention; and

FIGS. 3 and 4 show observation results on microstructures of an aluminum alloy according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art.
In embodiments of the present invention, a weight % (wt %) denotes a weight occupied by one component among a total weight of an alloy as a percentage. It can be understood that a boundary value is not included when a range of weight % is more than or less than; and the boundary value is included when simply designated as a range, or designated as equal to or greater than or equal to or smaller than.
In embodiments of the present invention, unavoidable impurities may denote impurities which may be introduced unintentionally during manufacturing of an aluminum alloy or an aluminum casting.
An aluminum alloy according to an embodiment of the present invention may be formed by adding silicon (Si), copper (Cu) and zinc (Zn) to a main element, aluminum (Al). A content of aluminum, the main element of the aluminum alloy, may occupy the balance other than additional elements. Therefore, the content of aluminum may be changed according to the contents of the additional elements. The aluminum alloy may include unavoidable impurities which are contained in each element itself or contained unintentionally during an alloying operation.
For example, the aluminum alloy may contain 4 to 13 wt % of silicon, 1 to 5 wt % of copper, and 26 wt % or more and less than 40 wt % of zinc, and a balance being aluminum and unavoidable impurities.
Silicon may be added to increase fluidity of a molten aluminum and improve feeding ability during solidification. Also, in the case of an aluminum-silicon alloy (Al—Si alloy), a hybrid structure having a primary α-aluminum phase and a eutectic silicon phase may be formed during casting. Mechanical strength may be considerably improved when the structure of the eutectic silicon phase is refined from a needle shape to a particulate shape or a fibrous shape by performing a modification treatment.
However, since mechanical properties are deteriorated in some cases due to an increase in the brittleness of an alloy, products may be damaged when the products are separated from a mold during a die casting process. Therefore, when considering all the foregoing effects, silicon content according to the present embodiment may be limited to a range of 4 to 13 wt %, specifically a range of 5 to 10 wt %, and more specifically, a range of 5 to 8 wt % or less.
Copper has the maximum solubility of 5.6 wt % with respect to aluminum at a eutectic temperature of 548° C., and may exhibit a solid solution strengthening effect when dissolved in aluminum. Also, copper forms an Al—Zn—Cu compound by reacting with zinc and aluminum when copper together with zinc is added to aluminum. Since the Al—Zn—Cu compound acts as obstacles preventing dislocation movements during the deformation of an alloy or prevents grain growth, the compound may contribute to improving the strength of the alloy.
However, when a copper content is too high, mechanical properties are deteriorated due to an increase in brittleness. Also, since copper is heavier than aluminum, it is not effective to reduce the specific gravity of the alloy. Moreover, the excessive copper content may cause castability of aluminum to be deteriorated. Therefore, when considering all the foregoing effects, the copper content in the present embodiment may be limited to a range of 1 to 5 wt %, specifically, a range of 2 to 5 wt %.
80 wt % of zinc is dissolved at 382° C. when added into aluminum, but the solubility of zinc is rapidly decreased as temperature decreases. Therefore, in the case of the aluminum alloy according to the present invention, 18 wt % of zinc is dissolved in the matrix of the cast aluminum alloy. At this time, undissolved surplus zinc may react with aluminum and copper to form the Al—Cu—Zn compound as described above. Therefore, it is necessary to add 26 wt % or more of zinc into aluminum in order to obtain both of the solid solution strengthening effect and compound forming effect by means of zinc.
However, since zinc is an element heavier than aluminum, it is unfavorable to achieve a lightweight alloy. When a zinc content is more than 38 wt %, strength may be decreased because a content of an eutectoid structure having low strength and high elongation may be increased as the eutectoid transformation of a β-phase to a two-phase hybrid structure of β′-phase and α-phase is progressed. Also, since the eutectic Si-phase exists in the primary α-phase of the aluminum alloy when the zinc content is 40 wt %, strength may be decreased due to an increase in the grain size of the aluminum alloy. Therefore, the added amount of zinc may be limited to less than 40 wt % in consideration of the foregoing effects.
An aluminum alloy according to another embodiment of the present invention may include 4 to 13 wt % of silicon (Si), 1 to 5 wt % of copper (Cu), 26 wt % or more and less than 40 wt % of zinc (Zn), 0.1 wt % or less of strontium (Sr) and 43 to 69 wt % of aluminum (Al).
For example, since strontium refines the crystal structure of an aluminum alloy when strontium is additionally added, the strength of the aluminum alloy may be improved. That is, in the case of the aluminum alloy including silicon, the hybrid structure of the primary α-phase and eutectic Si-phase may be obtained during casting, and strontium may contribute to improving strength by refining the structure of the eutectic Si-phase.
However, when strontium content is high, mechanical properties may be poorer due to the crystallization of a compound including strontium. Therefore, when considering all these effects, the strontium content according to the present embodiment may be limited to 0.1 wt % or less, specifically a range of greater than 0 wt % and 0.04 wt % or less, and more specifically, a range of greater than 0 wt % and 0.02 wt % or less.
Also, a trace amount of additive elements in addition to silicon, copper, zinc and strontium may be added to aluminum, in order to improve the strength of the aluminum alloy. The additive elements may include titanium (Ti), magnesium (Mg), nickel (Ni), vanadium (V), tin (Sn), iron (Fe), chromium (Cr), zirconium (Zr), scandium (Sc), and manganese (Mn). The total amount of one or more elements selected from the above additive elements may not exceed 3 wt %.
An aluminum alloy casting according to an embodiment of the present invention may be manufactured by using the above-described aluminum alloy. Herein, casting may include pure casting products manufactured through casting and products obtained by molding a preformed casting into predetermined shapes, e.g., a billet for extrusion, a plate for rolling, etc. Examples of the pure casting may include sand casting, die casting, gravity casting, low-pressure casting, squeeze casting, lost wax casting, thixo casting, and the like.
Gravity casting may denote a method of pouring a molten alloy into a mold by using gravity, and low-pressure casting may denote a method of pouring a melt into a mold by applying a pressure to the surface of the molten alloy using a gas. Thixo casting, which is a casting process performed in a semi-solid state, is a combination method of adopting the advantages of typical casting and forging processes.
The aluminum alloy casting according to this embodiment may be manufactured through any process including the foregoing processes, and may have appropriate strength and machinability without performing a heat treatment. Alternatively, the aluminum alloy casting may be subjected to a heat treatment process after manufacturing according to the applications and shapes thereof.
Hereinafter, Experimental Examples are provided to more clearly understand the present invention. However, Experimental Examples below are merely provided to more clearly understand the present invention, not to limit the scope of the present invention.
Table 1 shows alloy compositions of Experimental Examples according to the present invention and Comparative Example, and results of tensile strength as a mechanical property according to the alloy compositions.

TABLE 1

					Tensile Strength
Si	Cu	Zn	Al	Sr	(MPa)

Example 1	5.0	2.0	26.0	66.7	0.0	433.4
Example 2	6.0	2.0	26.0	65.7	0.0	441.6
Example 3	6.0	3.5	30.0	60.2	0.0	451.8
Example 4	6.0	5.0	30.0	58.7	0.0	439.4
Example 5	7.0	2.0	26.0	64.7	0.0	444.6
Example 6	7.0	2.0	30.0	60.7	0.0	440.9
Example 7	6.0	5.0	30.0	58.7	0.0	436.2
Example 8	6.0	3.5	31.0	59.2	0.0	443.1
Example 9	6.0	2.0	32.0	59.7	0.0	419.7
Example 10	6.0	2.0	32.0	59.7	0.0	416.8
Example 11	6.0	2.0	35.0	56.7	0.0	443.2
Example 12	6.0	3.5	35.0	55.2	0.0	444.0
Example 13	6.0	5.0	35.0	53.7	0.0	440.6
Example 14	8.0	2.0	26.0	63.7	0.0	441.7
Example 15	8.0	2.0	27.0	62.4	0.0	441.9
Example 16	8.0	3.5	28.0	60.2	0.0	436.7
Example 17	8.0	2.0	30.0	59.7	0.0	430.2
Example 18	6.0	2.0	30.0	61.5	0.0	420.2
Example 19	6.0	2.0	30.0	61.7	0.02	488.8
Example 20	6.0	2.0	28.0	63.6	0.02	465.1
Example 21	6.0	2.0	30.0	61.6	0.1	438.0
Comparative	0.0	2.1	30.1	67.4	0.0	321.1
Example 1

High purity aluminum (99.8%) and zinc (99.9%) were used in order to manufacture the aluminum alloys according to the present invention, and aluminum master alloys, in which silicon, copper and strontium are added, were used in order to add silicon, copper and strontium, respectively.
Each alloying element was melted by using an electric resistance furnace, and degassing and ash removing were performed prior to pouring by blowing an argon (Ar) gas for 5 minutes with a degassing device.
In the case of strontium, an aluminum master alloy including strontium was added and specimens were manufactured by tapping after maintaining for a predetermined time.
Specimens used for mechanical property measurement in each Experimental Example were manufactured by using die casting. Specifically, rod-shaped tensile test specimens were cast by using a TOYO die casting machine having a mold clamping force of 1300 KN, and tensile tests were then performed two days later after the specimens were cast in order to reduce deviations in mechanical properties. Seven or more specimens were used for measuring mechanical property and an average value thereof was presented as a result.
Die casting used in the present test was performed under conditions that a casting temperature ranges from 963 to 987 K and a die temperature ranges 463 to 473 K. The specimens used in the tests were prepared as No. 14 rod-shaped proportional specimens according to the KSB0802 standard.
Also, samples were collected from a center portion of the tensile test specimens for microstructural observations by using an optical microscope. The collected samples were polished by using polishing papers and clothes, then cleaned with alcohol for 20 minutes, and thereafter etched. Also, analyses using a scanning electron microscope (SEM) and an energy dispersive spectrometer (EDS) were performed in order to analyze the solubility of zinc in the α-aluminum phase matrix and the types and shapes of the eutectic phase formed.
Meanwhile, a commercial aluminum ADC12 alloy was used as a subject for comparing tensile strengths of the aluminum alloys according to Experimental Examples, and FIG. 1 shows tensile test results of alloys prepared by Experimental Example 19 and the ADC12 alloy.
Referring to Table 1, when comparing Example 21 and Comparative Example 1 having the same copper and zinc compositions, the tensile strength of Example 21 with silicon added was increased 110 MPa in comparison with Comparative Example 1 with no silicon added. Therefore, it can be understood that values of tensile strength are considerably improved according to the addition of silicon in the case of the aluminum alloy according to an embodiment of the present invention.
Also, referring to FIG. 1, it can also be understood that excellent results are obtained, in which the tensile strengths of the alloys according to the present Experimental Examples 19 is 120 MPa or more higher than the tensile strength of the ADC12 alloy which is a commercial aluminum alloy having zinc and copper as major alloying elements.
Therefore, it can be understood that the aluminum alloys according to an embodiment of the present invention exhibit very good mechanical strength characteristics in comparison with a typical commercial aluminum alloy.
The reason why the aluminum alloys according to the present Experimental Examples exhibit better properties than the ADC12 alloy is considered that alloy structures are refined by adding silicon together with zinc and copper to aluminum.
Hereinafter, for the simplicity of the description, Al-xZn-ySi-zCu denotes an aluminum alloy, where x, y, and z are weight percents of zinc, silicon, and copper added to aluminum, respectively.
FIGS. 2( a), 2(b) and 2(c) show SEM observation results obtained from the alloy structures of Al-30Zn, Al-30Zn-6Si-2Cu and Al-40Zn-6Si-2Cu alloys, respectively.
Referring to FIG. 2( a), in the case of the Al-30Zn alloy, it can be understood that an Al—Zn eutectic phase is uniformly distributed in grain boundaries due to the surplus zinc which is not dissolved in the primary α-phase.
In contrast, referring to FIG. 2( b), it can be understood that the grain size in the Al-30Zn-6Si-2Cu alloy is considerably decreased to a range of about few μm to 20 μm because the growth of the primary α-phase is prevented.
FIG. 3 shows EDS analysis results of zinc contents (wt %) in each regions of the Al-30Zn-6Si-2Cu alloy shown in FIG. 2( b) together with a table.
As shown in FIG. 3, it can be understood that zinc is dissolved up to 18 wt % in a α-Al phase (Region 1) and zinc also stably exists up to 18 wt % around a eutectic Si-phase (Region 2). At this time, it is considered that the surplus zinc undissolved reacts with aluminum and copper to form Al—Zn—Cu compounds (Regions 3 and 4). It is estimated that the Al—Zn—Cu compounds contribute to the refinement of grains by preventing the movement of the grains. Therefore, it is considered that the crystallization of the Al—Cu—Zn compounds as well as the eutectic Si-phase may contribute to improving the strength of the aluminum alloy.
However, as shown in FIG. 2( c), the eutectic Si-phase is not distributed at grain boundaries but exists in the primary α-phase. As a result, the size of the grains increases so that a decrease in the strength is expected. Therefore, in terms of strength improvement, it is estimated that the zinc content may be adjusted to less than 40 wt %.
Experimental results according to the alloy compositions presented in Table 1 will be described in more detail below.
Referring to Table 1, Experimental Examples 5, 6, 14, 15, 16 and 17, in which the silicon content is in a range of more than 6 wt % to 8 wt % or less and the copper content is in a range of 2 to 3.5 wt %, showed relatively excellent tensile strengths in a range of 430 to 445 MPa for all zinc contents.
Therefore, it is considered that the aluminum alloys according to an embodiment of the present invention show relatively excellent and stable strength characteristics when the silicon content is more than 6 wt % in comparison with when the silicon content is 6 wt % or less. All of Experimental Examples 19 to 21 correspond to aluminum alloys in which strontium is further added to 0.02 to 0.1 wt % as an additive element of the aluminum alloy in addition to silicon, copper, and zinc. When Experimental Examples 19 and 20 are compared with Experimental Examples 18 and 2, tensile strengths are increased in a range of 20 to 60 MPa or more. It is considered that the considerable increases in the tensile strengths are due to the refinement of the eutectic Si-phase according to the addition of strontium.
FIGS. 4( a) and 4(b) show SEM observation results obtained from the alloy structures of Experimental Example 18 with no strontium added and an aluminum alloy which has the same silicon, copper and zinc compositions as Experimental Example 18 with 0.04 wt % of strontium further added.
When comparing between the microstructures (see arrows) of the eutectic Si-phases in FIGS. 4( a) and 4(b), it can be confirmed that the finer eutectic Si-phase is obtained when strontium is added.
Meanwhile, when comparing Experimental Examples 19 and 21, a relatively better tensile strength was obtained when the strontium content is 0.02 wt % in comparison with when the strontium content is 0.1 wt %. Therefore, it can be understood that the strontium content needs to be maintained less than 0.1 wt %.
Aluminum alloys and aluminum alloy castings according to the embodiments of the present invention have excellent strengths in comparison with typical commercial aluminum alloys, and also exhibit extremely lightweight characteristics in comparison with stainless steels. Therefore, the aluminum alloys and aluminum alloy castings according to the embodiments of the present invention can be stably applied to compact and lightweight products as well as large products.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

Claims

What is claimed is:

1. An aluminum alloy comprising:

4 wt % to 13 wt % of silicon (Si);

1 wt % to 5 wt % of copper (Cu);

26 wt % or more and less than about 40 wt % of zinc (Zn); and

a balance being aluminum (Al) and unavoidable impurities.

2. The aluminum alloy of claim 1, wherein a content of the silicon (Si) is 5 wt % to 10 wt %.

3. The aluminum alloy of claim 2, wherein the content of the silicon (Si) is 5 wt % to 8 wt % or less.

4. The aluminum alloy of claim 3, wherein a content of the copper (Cu) is 2 wt % to 5 wt %.

5. The aluminum alloy of claim 4, wherein a content of the zinc (Zn) is 26 wt % to 35 wt %.

6. An aluminum alloy comprising:

4 wt % to 13 wt % of silicon (Si);

1 wt % to 5 wt % of copper (Cu);

26 wt % or more and less than 40 wt % of zinc (Zn);

0.1 wt % or less of strontium (Sr); and

43 wt % to t 69 wt % of aluminum (Al).

7. The aluminum alloy of claim 6, wherein a content of the silicon (Si) is 5 wt % to 10 wt %.

8. The aluminum alloy of claim 7, wherein the content of the silicon (Si) is 5 wt % to 8 wt % or less.

9. The aluminum alloy of claim 8, wherein a content of the copper (Cu) is 2 wt % to 5 wt %.

10. The aluminum alloy of claim 9, wherein a content of the zinc (Zn) is 26 wt % to 35 wt %.

11. The aluminum alloy of claim 6, wherein a content of the strontium (Sr) is 0.04 wt % or less (excluding 0).

12. The aluminum alloy of claim 11, wherein the content of the strontium (Sr) is 0.02 wt % or less (excluding 0).

13. The aluminum alloy of claim 6, further comprising a total of about 3 wt % or less (more than 0) of any one or more elements selected from the group consisting of titanium (Ti), magnesium (Mg), nickel (Ni), vanadium (V), tin (Sn), iron (Fe), chromium (Cr), zirconium (Zr), scandium (Sc), and manganese (Mn).

14. An aluminum alloy casting manufactured by using the aluminum alloy according to any one of claims 1 to 13.