US20140234159A1 - HIGH THERMAL CONDUCTIVITY Al-Si-Fe-Zn ALLOY FOR DIE CASTING

Info

Abstract

Description

Claims

US20140234159A1

Publication number: US20140234159A1
Application number: US14/350,080
Authority: US
Inventors: Ki Tae Kim; Je Sik Shin; Se Hyun Ko
Original assignee: Korea Institute of Industrial Technology KITECH
Current assignee: Korea Institute of Industrial Technology KITECH
Priority date: 2011-10-10
Filing date: 2012-10-09
Publication date: 2014-08-21
Also published as: WO2013055075A3; KR101375671B1; WO2013055075A2; KR20130038639A

Disclosed is high thermal conductivity Al—Si—Fe—Zn alloy for die casting which comprises 1.0 weight % to 2.0 weight % of silicon (Si), 0.5 weight % to 1.6 weight % of iron (Fe), 0.6 weight % to 1.6 weight % of zinc (Zn), with the remainder being aluminum (Al) and inevitable impurities.

TECHNICAL FIELD

The present invention relates to a high thermal conductivity aluminum alloy for die casting, and more particularly, to an aluminum alloy having excellent thermal conductivity as well as excellent castability.

BACKGROUND ART

Die-casting is also referred to as a metal casting process. The die casting is a precision casting method in which molten metal is injected into a steel mold cavity which is precisely machined so as to be completely matched with a required casting shape, thereby obtaining a casting having the same shape as the mold cavity.
Since the die castings have accurate dimensions, they have advantages, such as excellent mechanical properties, possibility of mass production as well as little or no finishing operations. Meanwhile, metals used in die casting are generally alloys of zinc, aluminum, tin, copper, magnesium, and the like, and after melted to molten metals, these alloys are injected into a mold cavity by a pressing apparatus, such as an air pressure device, a hydraulic pressure device and an oil pressure device, etc., to be quenched and then solidified.
The die castings manufactured through these processes are used in a variety of fields, and specially, employed in vehicle components, and also widely used in manufacturing of components, such as components of electronic instruments, optical instruments, vehicles, weaving machines, construction equipments and measuring instruments.
Meanwhile, Al—Si based alloys and Al—Mg based alloys with excellent castability are mainly used as aluminum alloys for die casting. Since Al—Si based alloys or Al—Mg based alloys have excellent castability, but a low thermal conductivity of 90-140 W/mK, the use thereof in heat dissipation components for electric devices, electronic devices, and vehicles requiring a high thermal conductivity of 160 W/mK or more is limited.
In heat dissipation devices requiring such a high thermal conductivity, while products cast with pure aluminum having a very high thermal conductivity of 220 W/mK or higher are partly used in rotors for electrical and electronic products, since pure aluminum has an excellent thermal conductivity, but a low tensile strength and low castability, its application in structural components requiring excellent mechanical properties as well as the excellent thermal conductivity is limited.
Therefore, for use in heat dissipation components for electric devices, electronic devices and vehicles, the development of aluminum alloys for die casting having a high thermal conductivity of 160 W/mK or more as well as excellent castability is acutely needed, but aluminum alloys having a thermal conductivity of 160 W/mK or more as well as excellent castability have not yet been developed. Therefore, Al—Si based alloys, Al—Mg based alloys, and the like with the thermal conductivity of 90-140 W/mK are currently used as aluminum alloys for die casting.

DISCLOSURE OF THE INVENTION

Technical Problem

The present invention is devised to solve the above-described problems of existing arts, and an object of the present invention provides an aluminum alloy for die casting, which has a higher strength than pure aluminum together with excellent castability, and a thermal conductivity of 160 W/mK or more so as to be capable of being applied to a variety of structural components requiring excellent thermal conductivity.

Technical Solution

In order to accomplish the above-described objects, the present invention provides an aluminum alloy for die casting including 1.0 weight % to 2.0 weight % of silicon (Si), 0.5 weight % to 1.6 weight % of iron (Fe), 0.6 weight % to 1.6 weight % of zinc (Zn), with the remainder being aluminum (Al) and inevitable impurities.
Also, in the aluminum alloy according to the present invention, a thermal conductivity may be 160 W/mK or more, and preferably 170 W/mK or more.
Also, in the aluminum alloy according to the present invention, a difference (ΔT) between the solidus temperature and the liquidus temperature in a two-phase Mushy zone is 70° C. or less.
Also, in the aluminum alloy according to the present invention, a tensile strength may be 110 MPa or more, and preferably 120 MPa or more.
Also, in the aluminum alloy according to the present invention, the aluminum alloy may include Fe compounds dispersed in the microstructure thereof.

Advantageous Effects

An aluminum alloy according to the present invention, may secure castability required for obtaining healthy castings in a die casting process, and also have a good mechanical strength and an excellent thermal conductivity through controlling components of silicon (Si), iron (Fe) and zinc (Zn), so that the aluminum alloy may be suitably used in manufacturing of heat dissipation components for electrical devices, electronic devices and vehicles requiring a high thermal conductivity of 160 W/mK or more.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph of a flow length measurement device for evaluating castability of an aluminum alloy according to the present invention.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an aluminum alloy according to preferred embodiments of the present invention will be described in detail but the present invention is not limited to the following embodiments. Therefore, it will be apparent to those skilled in the art that many modifications and variations may be made without departing from the spirit thereof.
Also, the terms of a single form used for explaining exemplary embodiments may include plural forms unless otherwise specified.
An aluminum alloy according to the present invention is a high thermal conductivity aluminum alloy for die casting obtained by alloying Silicon (Si), iron (Fe) and zinc (Zn), and includes 1.0 weight % to 2.0 weight % of silicon (Si), 0.5 weight % to 1.6 weight % of iron (Fe), 0.6 weight % to 1.6 weight % of zinc (Zn), with the remainder being aluminum (Al) and inevitable impurities.
By complexly adding alloy elements capable of improving the castability of aluminum depending on the respective compositions, alloy elements solid-solutioned in an aluminum matrix metal to be capable of obtaining effects of solid solution strengthening, and alloy elements capable of minimizing the deterioration of thermal conductivity due to the very low solid solubility in the aluminum matrix metal, the aluminum alloy for die casting according to the present invention may represent a thermal conductivity of 160 W/mK or more as well as excellent castability and good mechanical properties.
The reason why the respective alloy elements are added and limited in content is as follows.
Silicon (Si) is an element which may be added in aluminum as an alloy element to improve castability and improve a tensile strength according to the effects of solid solution strengthening. 1.0 weight % to 2.0 weight % of silicon is added in the aluminum alloy for die casting according to the present invention. This is because if the content of silicon is less than 0.5 weight %, the castability is lowered, so that a non-molded part partly occurs to considerably damage healthiness of products when products are molded by die casting, and if the content of silicon exceeds 0.9 weight %, a thermal conductivity is lowered, so that a thermal conductivity of 160 W/mK or more targeted by the present invention may not be obtained.
Since iron (Fe) has a very low solubility of 0.052 weight % in aluminum at room temperature, and after casting, is mostly crystallized as intermetallic compounds, such as Al₃Fe, and the like, iron is an element which may be added in aluminum to minimize the degradation of thermal conductivity of aluminum, improve the strength of aluminum, and reduce die soldering when aluminum alloy products are molded by die-casting. 0.5 weight % to 1.6 weight % of iron is added in the aluminum alloy for die casting according to the present invention. this is because if the content of iron is less than 0.5 weight %, the effects of preventing die soldering is lowered, so that soldering phenomena of products occur on a part of the mold cavity and a mechanical strength is not sufficient, and if the content of iron exceeds 1.6 weight %, a Fe-rich phase is excessively crystallized to reduce the castability of the alloy. More preferable content of iron is from 0.8 weight % to 1.2 weight %.
Zinc (Zn) is an element which may be added in aluminum as an alloy element to improve the castability and a tensile strength according to the effects of solid solution strengthening. 0.6 weight % to 1.6 weight % of zinc is added in the aluminum alloy for die casting according to the present invention. this is because if the content of magnesium is less than 0.6 weight %, the castability of the alloy is lowered, so that a non-molded part partially occurs when products are molded by die casting, and if the content of magnesium exceeds 1.6 weight %, a thermal conductivity of the alloy is lowered, so that a thermal conductivity of 160 W/mK or more targeted by the present invention may not be obtained. More preferable content of zinc (Zn) is from 0.8 weight % to 1.2 weight %.

EXAMPLES

A high thermal conductivity Al—Si—Fe—Zn alloy for die casting according to exemplary embodiments of the present invention will be described in detail with reference to Tables 1 and 2 below.
The inventors of the present invention manufactured specimens of alloys having compositions shown in Table 1 below in order to manufacture a high conductivity Al—Si—Fe—Zn alloy for die casting by using a melt stirring method which is typically used in die casting.

Example	1	1.03	0.89	1.00	bal.
	2	1.21	1.08	0.97	bal.
	3	1.67	0.84	1.00	bal.
	4	1.21	0.59	1.42	bal.
	5	1.51	0.57	1.44	bal.
comparative	1	10.20	1.17	0.92	bal.
example	2	0.56	0.79	1.02	bal.
	3	4.5	0.8	0.60	bal.
	4	1.12	1.83	0.75	bal.
	5	1.33	1.14	0.46	bal.
	6	1.58	0.97	1.45	bal.

In detail, raw materials of aluminum alloy were prepared so as to have compositions shown in Table 1, the raw materials were charged into an electric resistance melting furnace and melted to form molten metals in atmosphere, and then flow test specimens for evaluating castability were manufactured by using a flow length measurement device as shown in FIG. 1 and also specimens for evaluating properties used for measurement of a thermal conductivity, the liquidus temperature, and the solidus temperature, and the like were manufactured.
With respect to the thermal conductivity that is one among main objects of the alloy according to the present invention, firstly, the electrical conductivity of manufactured specimens was measured by using a electrical conductivity meter at room temperature, and then the thermal conductivity was obtained by the conversion formula of [formula 1].
K=5.02σT×10⁻⁹+0.03 [Formula 1]
(where K is a thermal conductivity, σ is a electrical conductivity and T is an absolute temperature)
Also, in order to evaluate the castability that is essential in die cast casting, the molten alloy was injected into a mold cavity maintained at a temperature of 200° C. and having a width of 12 mm, a thickness of 5 mm and a maximum length of 780 mm as shown in FIG. 1, and a flow length was measured through a method of measuring a solidified length, and also the size (ΔT) of a two-phase Mushy zone was measured through a method of measuring a difference between the liquidus temperature and the solidus temperature by using a thermal analyzer.
Table 2 shows results in which the flow length, the thermal conductivity, the liquidus temperature, the solidus temperature, and the difference there between (
)→between the liquidus temperature and the solidus temperature were evaluated.

TABLE 2

	flow	Thermal	Liquidus	Solidus
	length	conductivity	temperature	temperature
Alloy	(mm)	(W/mK )	(° C.)	(° C.)	ΔT (° C.)

Example	1	780	175	654	620	34
	2	780	171	652	616	36
	3	780	163	650	606	44
	4	780	182	652	602	50
	5	780	179	650	588	62
Comparative	1	780	95	575	501	74
example	2	720	186	656	620	36
	3	—	142	630	575	55
	4	560	165	—	—	—
	5	750	168	—	—	—
	6	780	155	—	—	—

As identified in Table 2 above, all of aluminum alloys according to exemplary embodiments 1 to 5 of the present invention have a thermal conductivity of 160 W/mK or more (furthermore, 170 W/mK or more), which is a level or more required in heat dissipation devices. It may be understood that the thermal conductivities of the alloys of Example 1 having a low silicon content in a range in which the castability is not deteriorated, Example 2 having a relatively high iron (Fe) content, and Examples 4 and 5 among these alloys are very high, that is, are all 170 W/mK or more.
Also, the flow length and the difference (ΔT) between the liquidus temperature and the solidus temperature shown in Table 2 are primary indices capable of evaluating the castability of alloys, in which as the more the flow length, the more the fluidity of the alloy is excellent and the less the difference ΔT, the more the castability is excellent.
As identified in Table 2 above, all of aluminum alloys according to Examples of the present invention have the flow length of 780 mm, which is a level comparable to that of an Al—Si alloy (ADC 12, Comparative example 1) widely used as an aluminum alloy for die casting.
Furthermore, the difference (ΔT) between the liquidus temperature and the solidus temperature in the aluminum alloys according to Examples 1 to 5 of the present invention is less than 70° C., and is lower than 74° C. that is the difference (ΔT) of Comparative example 1 that is an Al—Si alloy (ADC 12) widely used as an aluminum alloy for die casting.
Meanwhile, since the alloys according to Examples 1 to 5 of the present invention, in two indices that represent the castability, that is, the flow length and ΔT, have equal to or more excellent level than that of Comparative example 1 widely used as an aluminum alloy for die casting, the alloys may be treated to have the castability required in die casting.
Meanwhile, Comparative example 2 is an Al—Si—Fe—Zn alloy having a silicon content of 0.56 weight %, which is lower than those of Examples of the present invention, and as a result, the flow length of 720 mm, which is lower than those of the alloys according to Examples of the present invention, and thus the castability is low.
Furthermore, Comparative example 3 is an Al—Si—Fe—Zn alloy having a silicon content of 4.5 weight %, which is remarkably higher than those of Examples of the present, and as a result, the thermal conductivity is 142 W/mK, and thus it is hard to satisfy the level required in the dissipation products.
Furthermore, Comparative example 4 is an Al—Si—Fe—Zn alloy having an iron (Fe) content of 1.83 weight %, which is higher than those of Examples of the present invention, and as a result, the flow length of 560 mm, and thus the castability is remarkably lower than those of the alloys according to Examples of the present invention.
Furthermore, Comparative example 5 is an Al—Si—Fe—Zn alloy having a zinc (Zn) content of 0.46 weight %, which is lower than those of Examples of the present invention, is added, and as a result, the flow length of 720 mm, and thus the castability is remarkably lower than those of the alloys according to Examples of the present invention.
Furthermore, Comparative example 6 is an Al—Si—Fe—Zn alloy having a zinc (Zn) content of 1.45 weight %, which is higher than those of Examples of the present invention, and as a result, the castability is a level comparable to those of Examples of the present, but the thermal conductivity is 155 W/mK, which is lower than that required in the dissipation products.

Alloy (weight %)

1. An aluminum alloy for die casting, comprising 1.0 weight % to 1.6 weight % of silicon (Si), 0.5 weight % to 1.6 weight % of iron (Fe), 0.6 weight % to 1.6 weight % of zinc (Zn), with the remainder being aluminum (Al) and inevitable impurities.

2. The aluminum alloy for die casting of claim 1, wherein the content of iron (Fe) is from 0.8 weight % to 1.2 weight %.

3. The aluminum alloy for die casting of claim 1, wherein the content of zinc (Zn) is from 0.8 weight % to 1.2 weight %.

4. The aluminum alloy for die casting of claim 1, wherein thermal conductivity of the aluminum alloy is 160 W/mK or more.

5. The aluminum alloy for die casting of claim 1, wherein thermal conductivity of the aluminum alloy is 170 W/mK or more.

6. The aluminum alloy for die casting of claim 1, wherein a difference (ΔT) between the solidus temperature and the liquidus temperature of the aluminum alloy is not more than 70° C.