KR20140025043A - Al-zn alloy having high tensile strength and high thermal conductivity for die casting - Google Patents

Abstract

The present invention relates to an aluminum alloy for die casting which can obtain excellent thermal conductivity while simultaneously having a remarkable casting property and satisfactory tensile characteristics, and thus can be applied to a product for various structures requiring radiation characteristics. According to the present invention, the aluminum alloy for die casting comprises 5.5-8.5 wt% of zinc (Zn), 0.5-3.0 wt% of magnesium (Mg), 0.4-1.5 wt% of iron (Fe), and the rest including aluminum (Al) and inevitable impurities.

Description

Al-Zn ALLOY HAVING HIGH TENSILE STRENGTH AND HIGH THERMAL CONDUCTIVITY FOR DIE CASTING}

The present invention relates to a high-strength, high thermal conductivity die-casting aluminum alloy, and more particularly, to an aluminum alloy capable of obtaining excellent castability and at the same time excellent tensile strength and thermal conductivity.

Die casting, also known as die casting, is a precision casting method in which molten metal is injected into steel molds that are precisely machined to perfectly match the required casting shape to obtain the same casting as the mold. Products manufactured by casting are called diecast castings.

Die casting castings are characterized by their excellent mechanical properties and mass production in addition to the advantage that their dimensions are accurate and require no finishing. On the other hand, the metal used for die casting casting is generally an alloy of zinc, aluminum, tin, copper, magnesium, and the like, and these alloys are melted and made of molten metal, and then pressurized through a pressurization device such as air pressure, hydraulic pressure, hydraulic pressure, etc. It is injected into the mold and solidified rapidly.

Die casting castings produced through this process are used in various fields, particularly in automobile parts, and are widely used in the production of parts for electric devices, optical instruments, vehicles, textile machines, architectural instruments, and the like.

On the other hand, as the aluminum alloy for die casting, an Al-Si alloy and an Al-Mg alloy which are excellent in casting are mainly used. However, in the case of Al-Si-based alloys or Al-Mg-based alloys, the tensile strength is 230MPa or more but the thermal conductivity is low as 90 ~ 130W / mK. Because of this, the tensile strength is 230MPa or more, and at the same time, the use of heat dissipation parts for electric, electronic, and automotive applications requiring high tensile strength and thermal conductivity of 130W / mK or more has been limited.

In addition, in the case of heat dissipation parts that require high thermal conductivity, products which have been die-cast pure aluminum having a very high thermal conductivity of 220 W / mK or more are used in electric and electronic rotors, but pure aluminum has excellent thermal conductivity but is tensile. Since the strength is as low as 100 MPa, there is a limit to apply to structural parts that require excellent tensile strength together with thermal conductivity.

Accordingly, there is an urgent need for the development of die casting aluminum alloys having excellent castability and high thermal conductivity of 130 W / mK and tensile strength of 230 MPa or more for use in heat dissipating parts for electric, electronic and automotive applications. Al-Si alloys with tensile strength of 230 MPa or more and thermal conductivity of 90-130 W / mK have not been developed because die casting aluminum alloys having excellent castability and high thermal conductivity of 130 W / mK and tensile strength of 230 MPa or more have not been developed. And Al-Mg alloys are used as die casting aluminum alloys for electric, electronic and automotive heat dissipation parts.

The present invention has been made to solve the above problems, by adding zinc (Zn) as the main alloying element and controlling the content of magnesium (Mg) and iron (Fe), while having excellent castability and at the same time more than 130W / mK An object of the present invention is to provide an aluminum alloy for die casting having a thermal conductivity and a tensile strength of 230 MPa or more.

In order to solve the above problems, the present invention comprises 5.5 to 8.5% by weight of zinc (Zn), 0.5 to 3.0% by weight of magnesium (Mg) and 0.5 to 1.5% by weight of iron (Fe), with the remainder being aluminum (Al). It provides an aluminum alloy for die casting consisting of and inevitable impurities.

In addition, the aluminum alloy according to the present invention has a thermal conductivity of 130 W / mK or more and a tensile strength of 230 MPa or more.

The aluminum alloy according to the present invention has a flow field of 720 mm or more, which is an index indicating castability.

Further, in the aluminum alloy according to the present invention, ΔT (T _L -T _S ), which is a difference between the liquidus temperature T _L and the solid phase temperature T _S , which is another index indicating castability, is 70 ° C. or less.

The aluminum alloy according to the present invention, by controlling the composition of magnesium (Mg) and iron (Fe) while using zinc (Zn) as a main alloying element, to ensure sufficient castability required to obtain a sound casting in the die casting casting method and At the same time, it has a thermal conductivity in the range of 130 to 165 W / mK and a tensile strength in the range of 230 MPa to 300 MPa, which can be used for the manufacture of heat dissipating parts for electric, electronic and automotive which require high thermal conductivity and require a considerable level of mechanical strength. have.

1 is a photograph of equipment for evaluating the castability of an aluminum alloy.

Hereinafter, an aluminum alloy according to a preferred embodiment of the present invention will be described in detail, but the present invention is not limited to the following examples. Accordingly, it is obvious that those skilled in the art can variously change the present invention without departing from the technical idea of the present invention.

Furthermore, the singular forms used to describe the embodiments of the present invention are meant to include plural forms unless the phrases expressly have the opposite meaning.

The aluminum alloy according to the present invention is a high thermal conductivity aluminum alloy for die casting in which zinc (Zn), magnesium (Mg) and iron (Fe) are alloyed, and includes 5.5 to 8.5% by weight of zinc (Zn) and 0.5 to magnesium (Mg). 3.0% by weight and 0.5-1.5% by weight of iron (Fe), the remainder is composed of aluminum (Al) and unavoidable impurities.

The present invention provides an alloy element capable of improving the castability of aluminum, an alloy element which can be dissolved in an aluminum base metal to obtain a solid solution strengthening and precipitation strengthening effect, and a solid solubility in an aluminum base metal according to the respective composition amounts. It is low, which minimizes the thermal conductivity and increases the tensile strength by precipitating the intermetallic compound, and simultaneously adds the alloying element that can reduce the mold adhesion when forming the aluminum alloy product by die casting. It is a high strength, high thermal conductivity aluminum alloy for die casting that exhibits thermal conductivity of mK or higher and tensile strength of 230 MPa or higher.

The reasons for the addition and content of each alloy element are as follows.

Zinc (Zn) can be added as an alloying element to aluminum to increase the tensile strength according to the solid-solution strengthening effect. Also, zinc (Zn) is precipitated as an intermetallic compound such as MgZn ₂ , thereby increasing the tensile strength while minimizing the decrease in thermal conductivity of aluminum. Alloy element. In the alloy according to the present invention, it is preferable that zinc is added in an amount of 5.5 to 8.5% by weight. If the zinc content is less than 5.5% by weight, tensile strength of 230 MPa or more cannot be obtained. This is because the thermal conductivity is lowered, and thermal conductivity of 130 W / mK or more cannot be obtained.

Magnesium (Mg) is an alloying element that can be added as an alloying element to aluminum to improve the castability of the aluminum alloy and also to increase the tensile strength while minimizing a decrease in thermal conductivity of aluminum because it is precipitated as an intermetallic compound such as MgZn ₂ . In the die-casting aluminum alloy according to the present invention, it is preferable that 0.5 to 3.0% by weight of magnesium be added. If the magnesium content is less than 0.5% by weight, tensile strength of 230 MPa or more cannot be obtained, and the content of magnesium is 3.0% by weight. If it exceeds, the thermal conductivity of an alloy will fall and it will be impossible to obtain thermal conductivity of 130 W / mK or more.

Iron (Fe) has a very low solubility in aluminum at normal temperature of 0.052% by weight, and after casting it is mainly crystallized as an intermetallic compound such as Al ₃ Fe. Therefore, it is added to aluminum to increase the strength while minimizing deterioration of thermal conductivity of aluminum And at the same time, it is an alloying element which can reduce mold seizure when molding an aluminum alloy product by die casting. In the die casting alloy according to the present invention, iron is preferably added in an amount of 0.5 to 1.5% by weight. When the iron content is less than 0.5% by weight, the effect of preventing the metal from adhering to the die is reduced, so that a part of the mold part is formed when forming a product by die casting. The sintering phenomenon of the product occurs and the tensile strength is not sufficient, and when the iron content exceeds 1.5% by weight, the Fe-rich phase (Fe-rich phase) is excessively crystallized in the alloy, thereby decreasing the castability of the alloy. Because it is.

The unavoidable impurity means an impurity unintentionally incorporated by a raw material or a manufacturing apparatus in the process of producing an alloy according to the present invention, and examples thereof include Ti, Cr, V, Mn, Li, and Zr. Impurity components are kept at 0.1% by weight or less, preferably 0.01% or less, so as not to affect the alloy properties.

[Example]

A high strength, high thermal conductivity die casting aluminum alloy according to an embodiment of the present invention will be described in detail with reference to Tables 1 and 2 below.

The inventors of the present invention prepared a test piece by a method of producing a molten stirred aluminum alloy commonly used in the die casting production of an alloy having a composition shown in Table 1 to produce a high strength, high thermal conductivity die casting aluminum alloy.

alloy Composition (% by weight) Zn Mg Fe Si Al Example One 6.06 0.64 1.02 - honey. 2 6.10 1.25 1.04 - honey. 3 6.05 1.59 0.53 - honey. 4 5.92 2.08 0.60 - honey. 5 7.93 0.73 0.93 - honey. 6 8.14 1.62 0.97 - honey. 7 7.90 2.07 0.49 - honey. 8 8.10 2.71 0.56 - honey. Comparative Example 9 0.92 0.21 0.97 10.20 honey. 10 1.95 1.11 0.52 - honey. 11 2.30 1.11 0.53 - honey. 12 9.16 2.22 0.29 - honey. 13 3.97 0.39 0.96 - honey.

Specifically, a raw material for an aluminum alloy was prepared so as to have the composition shown in Table 1, and then charged in an electric resistance type melting furnace to dissolve the raw materials in the atmosphere to prepare a molten metal. Then, a fluidity test piece And the test specimens for the evaluation of properties such as thermal conductivity, liquidus temperature and solid phase temperature were prepared.

With respect to the thermal conductivity, which is one of the main objects of the alloy according to the embodiment of the present invention, the conductivity of the specimen manufactured first is measured at room temperature by using a conductivity meter and then converted into a conversion formula of the following formula Thermal conductivity was obtained.

[Formula 1]

K = 5.02? T x 10 ^-9 + 0.03

(Where K is thermal conductivity, σ is conductivity, and T is absolute temperature)

In addition, for the evaluation of castability necessary for die casting casting, flow field evaluation generally performed in a manner well known in the art (flow field evaluation method is performed by injecting alloy molten metal into a fluidity test mold such as FIG. 1 maintained at a temperature of 200 ° C. After measuring the solidified length after the molten alloy flows a certain distance, the flow field specimen size is 12mm in width, 5mm in thickness, the maximum length is 780mm), and liquid phase temperature (T _L ) using a thermal analyzer ) And the solidus temperature (T _S ) was measured.

Table 2 shows the results of evaluating the flow field, the thermal conductivity, the liquidus temperature (T _L ), the solidus temperature (T _S ) and the difference (ΔT = T _L -T _S ) and the tensile properties of each alloy.

alloy Flow field
(Mm) Thermal conductivity
(W / mK) Liquid temperature
(℃) Solid-state temperature
(℃) ΔT
(℃) The tensile strength
(MPa) Yield strength
(MPa) Elongation
(%) Example One 780 163 649 616 33 254 210 12 2 720 152 646 600 46 307 250 8 3 780 152 640 587 53 280 242 4 4 780 148 640 577 63 256 190 8 5 720 156 638 600 38 293 231 6 6 770 144 643 589 54 285 216 4 7 780 144 639 572 67 242 202 2 8 780 133 637 567 70 290 185 2 Comparative Example 9 780 95 575 501 74 134 120 3 10 - 175 - - - 141 103 30 11 - 171 - - - 151 110 22 12 - 116 - - - 299 230 2 13 - 175 - - - 171 122 20

As confirmed in Table 2, the aluminum alloys according to the embodiments of the present invention (No. 1 to 8) are all thermal conductivity of 130W / mK or more, excellent thermal conductivity of the level or more required in various heat dissipation parts Have

In addition, T, which is the difference between the flow field and the liquidus temperature and the solidus temperature shown in Table 2, is a major index for evaluating the castability of the alloy. The larger the flowfield, the better the fluidity of the alloy. Smaller T means better castability.

As confirmed in Table 2, the aluminum alloys according to the embodiment of the present invention has a flow field of 720 ~ 780mm, and the flow field of 780mm and Al-Si alloy (ADC 12, Comparative Example 9) that is widely used as a die casting aluminum alloy It can be seen that compared to 90% flow field.

In addition, as confirmed in Table 2, ΔT (T _L -T _S ), which is a difference between the liquidus temperature (T _L ) and the solid state temperature (T _S ) of the aluminum alloys according to an embodiment of the present invention is 33 ~ 70 ΔT (T _L -T _S ), which is the difference between the liquidus temperature (T _L ) and the solidus temperature (T _S ) of Comparative Example Alloy 9, which is an Al-Si alloy (ADC 12) widely used as an aluminum alloy for die casting. Lower level compared to 74 ° C.

In other words, the aluminum alloy according to the embodiment of the present invention has a casting level equivalent to that of Al-Si alloy widely used in conventional die casting.

In addition, as confirmed in Table 2, the tensile strength of the alloys according to Examples 1 to 8 of the present invention is 240MPa or more, a conventional Al-Si alloy (ADC 12, Comparative Example) widely used as an aluminum alloy for die casting It has better tensile strength than alloy 9).

Comparative Alloy 10 and Comparative Alloy 11 had a zinc content of 1.95% by weight and 2.30% by weight, respectively, compared to the embodiments of the present invention. As a result, the thermal conductivity was 170 W / mK or higher but the tensile strength was 141 MPa and 151 MPa, respectively. As a result, the tensile strength is relatively low compared to the embodiments of the present invention.

In addition, Comparative Example Alloy 12 has a higher zinc content of 9.16% by weight compared to the embodiments of the present invention. As a result, the thermal conductivity is 116 W / mK. It is unreasonable to apply to parts requiring heat dissipation.

In addition, Comparative Example 13 has a low zinc content of 3.97% by weight and a magnesium content of 0.39% by weight compared to the embodiments of the present invention. As a result, the thermal conductivity is relatively high at 175 W / mK, but the tensile strength is 171 MPa, respectively. The tensile strength is relatively low compared to the embodiments of the present invention.

As described above, the aluminum alloy according to an embodiment of the present invention is a die-casting aluminum material for heat dissipation parts that requires a certain level of tensile strength and excellent thermal conductivity properties required for parts with a castability capable of die casting. May be suitably used.

Claims (3)

Die-casting aluminum alloy containing 5.5 to 8.5% by weight of zinc (Zn), 0.5 to 3.0% by weight of magnesium (Mg) and 0.5 to 1.5% by weight of iron (Fe), with the remainder being aluminum (Al) and unavoidable impurities. The method of claim 1,
The aluminum alloy has a thermal conductivity of 130 W / mK or more and a tensile strength of 230 MPa or more. The method of claim 1,
The difference between the liquidus temperature (T _L ) and the solidus temperature (T _S ) of the aluminum alloy is 70 ℃ or less die casting aluminum alloy.

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