Patent Application
20210180159
This application claims the priority benefit of Korean Patent Application No. 10-2019-0167378, filed on Dec. 16, 2019, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
The present invention relates to an aluminum alloy for die casting and a method of producing a cast aluminum alloy using the same. The aluminum alloy for die casting may have excellent thermal conductivity and corrosion resistance, and may thus be used for parts requiring heat dissipation and high corrosion resistance.
In general, aluminum (Al) has been widely used throughout various industries because it is easy to cast, alloys well with other metals, has excellent corrosion resistance in an ambient atmosphere, and exhibits superior electrical and thermal conductivity.
In particular, in recent years, aluminum has been actively used to reduce the weight of vehicles and improve fuel efficiency, and aluminum alloys, obtained by mixing aluminum with other metals, have been commonly used because aluminum itself is not as strong as other metals.
Die casting has been widely used as a method of manufacturing a product using such an aluminum alloy. Die casting is a precision casting method that involves injecting a molten metal into a mold having a cavity precisely machined to have a desired shape to obtain a cast product having the same shape as the cavity.
For the die casting to produce the molded alloy product, aluminum alloys may need properties that meet the requirements of methods including filling the cavity in the die with a molten metal at a high rate and under high pressure, followed by solidification. For example, aluminum alloys for die casting should have a fluidity suitable for high-pressure casting and compensate for shrinkage defects that may occur during solidification by providing appropriate levels of high-temperature viscosity and latent heat.
Currently widely used aluminum alloys for die casting include Al—Si-based alloys such as ADC 3, ADC 10 and ADC 12 and Al—Mg-based alloys such as ADC 5 and ADC 6. However, these aluminum alloys for die casting have a limitation on widening the application range due to the low heat dissipation and corrosion resistance thereof.
In the related field, aluminum alloys for die casting capable of improving thermal conductivity and corrosion resistance have been reported.
However, although thermal conductivity and corrosion resistance may be improved to some extent, there has been limitation in effectiveness in improving the thermal conductivity and corrosion resistance due to the low ratio of Mg content to Si content in conventional aluminum alloys.
The above information disclosed in this Background section is provided only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.
In preferred aspects, provided are an aluminum alloy for die casting which has excellent thermal conductivity and corrosion resistance, a molded product, such as parts or vehicle parts requiring heat dissipation and high corrosion resistance and a method of producing a cast aluminum alloy using the same. Particularly, the aluminum alloy may be obtained by controlling the contents of Si, Mg, Fe and Mn, contained along with Al,
In an aspect, provided is an aluminum alloy for die casting which can maintain superior castability and formability while maintaining excellent thermal conductivity and corrosion resistance, by controlling the contents of Si and Mg and the ratio therebetween. In another aspect, provided is a method of producing a cast aluminum alloy using the same.
An aluminum alloy for die casting may include an amount of about 7.8 to 10.5 wt % of silicon (Si); an amount of about 3.6 to 5.5 wt % of magnesium (Mg); an amount of about 0.3 to 1.0 wt % of iron (Fe); an amount of about 0.1 to 1.0 wt % of manganese (Mn); and a balance of aluminum (Al) and other inevitable impurities. All the wt % are based on the total weight of the aluminum alloy.
The aluminum alloy may further include an amount of about 0.002 to 0.02 wt % of beryllium (Be).
Preferably, the aluminum alloy may include the silicon (Si) in an amount of about 8.0 to 10.5 wt %.
A ratio of Si/Mg may be not less than about 1.5 and less than about 3.0.
A total content of copper (Cu), zinc (Zn) and nickel (Ni) contained as impurities in the aluminum alloy may be in an amount of about 0.2 wt % or less.
The aluminum alloy may have a yield strength of about 260 MPa or greater.
The aluminum alloy may have a tensile strength of about 320 MPa or greater.
The aluminum alloy may have an elongation of about 2.0 to 3.0%.
The aluminum alloy may have a thermal conductivity of about 135 w/m·K or greater.
The aluminum alloy may have an electrical conductivity of about 30% IACS or greater.
Further provided is a method of producing a cast aluminum alloy. The method may include: preparing a molten aluminum (Al) batch by melting aluminum (Al) or an Al scrap; preparing heating the prepared molten Al batch; preparing a primary molten alloy by adjusting a content of silicon (Si) in the heated molten Al to about 7.8 to 10.5 wt % thereby conducting a primary alloying; secondary heating the primary molten alloy; preparing a secondary molten alloy by adjusting a content of iron (Fe) in the heated primary molten alloy to about 0.3 to 1.0 wt % and adjusting a content of manganese (Mn) to about 0.1 to 1.0 wt % thereby conducting a secondary alloying; cooling the secondary molten alloy; and preparing a tertiary molten alloy by adjusting a content of magnesium (Mg) in the cooled secondary molten alloy to about 3.6 to 5.5 wt % thereby conducing a tertiary alloying. All wt % are based on the total weight of the cast aluminum alloy.
The primary alloying may include adjusting the content of Si to about 8.0 to 10.5 wt % to prepare a primary molten alloy.
The secondary alloying may include further adding an amount of about 0.002 to 0.02 wt % of beryllium (Be) to the heated primary molten alloy.
The primary heating may include heating the molten Al batch to a first temperature of about 800 to 850° C.
The secondary heating may include heating the primary molten alloy to a second temperature of about 900 to 950° C.
The cooling may include cooling the secondary molten alloy to a third temperature of about 700 to 750° C.
The method may further include casting of injecting the tertiary molten alloy into a mold to produce a cast aluminum alloy.
The casting may include injecting the tertiary molten alloy at a casting temperature of about 680 to 750° C. into a mold for die casting.
Also provided is a molded product, for example, vehicle part, that includes the aluminum alloy as described herein. For example, the molded part may be manufactured by the methods described herein, using the aluminum alloy.
Other aspect of the invention are disclosed infra.
The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. However, the present invention is not limited to the embodiments, and may be implemented in various forms. The embodiments are provided only to fully illustrate the present invention and to completely inform those having ordinary knowledge in the art of the scope of the present invention.
The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.”
In as aspect, an aluminum alloy for die casting may include an amount of about 7.8 to 10.5 wt % of silicon (Si); an amount of about 3.6 to 5.5 wt % of magnesium (Mg); an amount of about 0.3 to 1.0 wt % of iron (Fe); an amount of about 0.1 to 1.0 wt % of manganese (Mn); and the balance of aluminum (Al) and inevitable impurities. All the wt % are based on the total weigh of the aluminum alloy. In addition, the aluminum alloy may further include an amount of about 0.002 to 0.02 wt % of beryllium (Be).
In addition, the aluminum alloy for die casting may, optionally, not contain copper (Cu), zinc (Zn) and nickel (Ni). However, the aluminum alloy may contain copper (Cu), zinc (Zn) and nickel (Ni) as inevitable impurities. However, even when copper (Cu), zinc (Zn) and nickel (Ni) are contained as impurities, it is preferable to adjust the total content thereof to about 0.2 wt % or less.
Next, the reason for limiting alloy ingredients and the composition ranges thereof will be described. All the wt % are based on the total weight of the aluminum alloy (or its composition).
Silicon (Si) in an Amount of about 7.8 to 10.5 wt %
Silicon (Si) is a main element that may improve castability and abrasion resistance and affect thermal conductivity and strength.
When silicon (Si) is added in an amount less than about 7.8 wt %, the effects of improving castability, abrasion resistance and strength are unsatisfactory, and when silicon (Si) is added in an amount greater than about 10.5 wt %, processability such as machinability of the obtained cast product may be deteriorated and heat treatment may be ineffective. Thus, the content of silicon (Si) is limited to this range.
In particular, silicon (Si) is an essential element for securing the fluidity and formability of the molten metal during the die-casting process. Corrosion resistance may be improved as the content of magnesium (Mg) increases, whereas formability and fluidity are remarkably deteriorated as the content of magnesium (Mg) increases. In order to compensate for these problems, the temperature of the molten metal may be increased during die casting so as to obtain products. However, when the temperature of the molten metal increases, productivity may be lowered and the defect rate is increased. For example, hot cracking of products may occur and the lifetime of the mold for die casting may be reduced.
In order to regulate this problem in the alloy, the Si content may be increased. The Si content may be adjusted to about 7.8 to 10.5 wt % to ensure corrosion resistance, castability and productivity. Preferably, the Si content may range from about 8.0 to about 10.5 wt %, or particularly from about 8.5 to about 10.5 wt %.
Magnesium (Mg) in an Amount of about 3.6 to 5.5 wt %
Magnesium (Mg) is a main element which may improve not only corrosion resistance, but also strength and elongation, and processability of castings, when it becomes a sacrificial corrosion site due to the Mg2Si crystallized phase formed by reaction with silicon (Si).
When the magnesium (Mg) is present in an amount of less than about 3.6 wt %, the effects of improving corrosion resistance, strength and elongation may be insignificant. When the magnesium (Mg) is present in an amount greater than about 5.5 wt %, the castability may be decreased due to reduced flowability of the molten metal during casting and the dross may be increased due to increased oxidation tendency of the molten metal. Thus, the content of magnesium (Mg) is limited to this range.
Iron (Fe) in an Amount of about 0.3 to 1.0 wt %
Iron (Fe) is an element that contributes to preventing mold burn-on and product scratching.
In this case, when iron (Fe) is present in an amount less than 0.3%, the effect of improving strength is insignificant, and when iron (Fe) is present in an amount exceeding 1%, abrasion resistance and thermal conductivity are deteriorated. Thus, the content of iron (Fe) is limited to this range.
Manganese (Mn) in an Amount of about 0.1 to 1.0 wt %
Manganese (Mn) is an element that may contribute to the reinforcement of the solid solution along with iron (Fe), thus improving the high-temperature strength of the casting, preventing mold burn-on and improving solubility.
When the manganese (Mn) is present in an amount of less than about 0.1 wt %, the effect of improving strength may be insignificant, and when the manganese (Mn) is present in an amount greater than about 1.0 wt %, castability and machinability may be decreased and thermal conductivity may be reduced. Thus, the content of manganese (Mn) is limited to this range.
Beryllium (be) in an Amount of about 0.002 to 0.02 wt %
Beryllium (Be) is an element which may prevent the oxidation of magnesium (Mg), inhibit the formation of dross during casting, and improve corrosion resistance.
When the beryllium (Be) is present in an amount of less than about 0.002 wt %, the effect of improving corrosion resistance may be insignificant, and when the beryllium (Be) is present in an amount greater than about 0.02 wt %, the corrosion resistance may be decreased. Thus, the content of beryllium (Be) is limited to this range.
Meanwhile, other than the aforementioned ingredients, the balance is composed of aluminum (Al) and other inevitable impurities.
For example, in order to ensure corrosion resistance of the aluminum alloy to a desired level, the aluminum alloy preferably does not optionally contain copper (Cu), zinc (Zn), or nickel (Ni), which are elements causing corrosion. However, even when copper (Cu), zinc (Zn) and/or nickel (Ni) are inevitably contained, it is preferable to adjust the total content thereof to about 0.2 wt % or less.
In addition, the ratio of Si/Mg may be limited to not less than about 1.5 and less than about 3.0, for properly generating Mg2Si, which is a factor enhancing corrosion resistance. In addition, the Si content may be adjusted in order to prevent a decrease in castability compared to the improvement in abrasion resistance and strength, a decrease in productivity due to the increased incidence of hot cracking, and an increase in the defect rate, all of which are caused by the increased Mg content. The increase in thermal conductivity can be expected through optimization of the two ingredients.
When the ratio of Si/Mg is less than about 1.5, the Si content may be relatively less than the Mg content, which cause problems in that castability is lowered and hot cracking occurs during casting. In addition, when the ratio of Si/Mg is greater than about 3.0, the relative Si content may be increased and the Mg content is decreased, which causes problems in that the improvements in corrosion resistance and strength do not reach desired levels. In an aspect, provided is a method for producing a cast aluminum alloy. The case aluminum alloy may include the composition of the aluminum alloy described herein.
First, aluminum (Al) or an Al scrap may be melted at a temperature of about 750° C. to prepare molten Al (preparing molten Al). High-quality Al scrap may be preferably used n order to minimize the content of impurities contained in the Al scrap. For example, in order to reduce the content of Cu, which is an element lowering corrosion resistance, to about 0.15 wt %, it is preferable to use only a wrought aluminum high-quality aluminum scrap as the Al scrap. Therefore, preferably, 1000-, 6000-, and 7000-based Al scraps should not be used.
When molten Al is prepared by sufficiently melting Al or Al scrap, the prepared molten Al may be heated to a first temperature of about 800 to 850° C. (primary heating).
When the molten Al is heated to the first temperature of 800 to 850° C., the content of Si in the molten Al may be adjusted to about 8.5 to 10.5 wt % to prepare a primary molten alloy in which Si is sufficiently melted (primary alloying).
When the primary molten alloy having a controlled Si content in Al is prepared as described above, the primary molten alloy may be heated to a second temperature of about 900 to 950° C. (secondary heating).
Then, the content of Fe in the heated primary molten alloy may be adjusted to about 0.3 to 1.0 wt % and the content of Mn may be adjusted to about 0.1 to 1.0 wt % to prepare a secondary molten alloy (secondary alloying).
The content of Be in the heated primary molten alloy may be adjusted to about 0.002 to 0.02 wt %.
In order to sufficiently melt Fe, Mn and Be in the primary molten alloy, the elevated temperature may sufficiently be maintained for about 5 hours.
Thus, when the secondary molten alloy is prepared, the secondary molten alloy may be cooled to a third temperature of about 700 to 750° C. (cooling).
Then, the content of Mg in the cooled secondary molten alloy may be adjusted to about 3.6 to 5.5 wt % to prepare a tertiary molten alloy (tertiary alloying).
Meanwhile, the temperature ranges presented in the primary heating, the secondary heating and the cooling may be designed to control aluminum (Al) oxide and magnesium (Mg) oxide, and unnecessary aluminum (Al) oxide and magnesium (Mg) oxide may be produced out of the temperature range suggested in each step, which impedes homogeneous alloying, so the desired physical properties cannot be achieved in the present invention.
For example, when the temperature maintained during the cooling is less than the suggested third temperature, magnesium carbonate may be generated during the tertiary alloying, causing the aluminum alloy to have an undesirable yellow color. In addition, when the temperature maintained in the cooling is greater than the suggested third temperature, magnesium oxide may be generated during the tertiary alloying, causing the aluminum alloy to have an unwanted blue color.
At this time, cooling may be slowly conducted while maintaining the temperature of the tertiary molten alloy at the temperature of about 700 to 750° C. for about 1 hour. Thus, dross and oxides produced in the tertiary molten alloy may be removed.
The adjusting the content of each alloyed element during the primary to tertiary alloying described above may include adjusting the content of each alloyed element contained in the molten alloy to the desired range. Accordingly, in the case of preparing the molten Al using pure Al in the preparation of molten Al, the content of each alloyed element during each alloying step may be adjusted by adding the element in the content to be adjusted. On the other hand, in the case of preparing molten Al using an Al scrap in the preparation of molten Al, the other alloyed elements may already be contained in the molten Al as impurities, before the addition of each alloyed element during each alloying. As such, the content of each alloyed element can be adjusted by measuring the content of the corresponding element and then adding the corresponding element in an amount corresponding to the difference from the content to be adjusted.
When the tertiary molten alloy is prepared, the tertiary molten alloy may be injected into a mold to produce a cast aluminum alloy product (casting).
The casting may be carried out by injecting the tertiary molten alloy into a mold for die casting while maintaining the tertiary molten alloy at a casting temperature of about 680 to 750° C. in order to ensure smooth casting.
The casting may be a step of casting a final product by injection into the mold for die casting, but the casting is not limited to the step of casting the final product, and may be a step of casting an ingot or intermediate product prepared to produce the final product.
According to the present invention, oxidation of the Mg component may be prevented as much as possible by adjusting the timing of addition of Mg, adjusting the temperature and retention time during the alloying, and adjusting the addition of Be and the timing of addition thereof.
Hereinafter, the present invention is described with reference to Examples and Comparative Examples.
Various compositions of Examples according exemplary embodiments of the present invention and Comparative Examples are shown in Table 1 below, and the specimens according to Examples and Comparative Examples are produced as ASTM sub-size specimens by heating the tertiary molten alloy prepared according to the method for producing a cast aluminum alloy as described above to a temperature of 680 to 750° C. and by injecting the same into an ASTM sub-size plate mold at 75 MPa.
Comparative Example 1 is an alloy composition in the related art, and Comparative Example 2 is ALDC12, which is a conventional general aluminum alloy for die casting and is a commercially available Al—Si-based alloy.
In addition, the produced specimens were tested to measure thermal conductivity, electrical conductivity, tensile strength, yield strength and elongation, and the results are shown in Table 2 below.
Thermal conductivity and electrical conductivity were measured after processing the prepared specimens into specimens 10 mm*10 mm*2t in size. At this time, the thermal conductivity was measured according to the thermal conductivity measurement test (ASTM E 1461).
In addition, the tensile strength and yield strength were measured according to the tensile test (KS B 0802).
In addition, the saline spray test was carried out, and the results are shown in
The saline spray test was carried out according to the saline spray test (KS D 9502) using 5% NaCl as saline after preparing the prepared ASTM subsize die-casting tensile test specimen.
As shown in Table 2, exemplary cast aluminum alloys had excellent physical properties, for example, the thermal conductivity thereof was 135 W/m·K or greater, the electrical conductivity thereof was 30% IACS or greater, the tensile strength thereof was 320 MPa or greater, the yield strength thereof was 260 MPa or greater and elongation thereof was 2.0 to 3.0% or greater.
In particular, when compared with Comparative Example 2, which is a conventional general aluminum alloy for die casting, the yield strength of the exemplary aluminum alloy was improved by about 70% or greater, the thermal conductivity was improved by 40% or greater, and the elongation can be secured at an equivalent level or higher. Thus, the cast products in exemplary embodiments of the present invention having substantially improved properties compared to those of conventional cast products were produced. Thus, the aluminum alloy for die casting according to exemplary embodiment of the present invention can be used for electronic parts for vehicles and portable electronic devices.
In addition,
As shown in
In addition, as shown in
An experiment was also performed in order to determine whether or not Mg2Si microstructures were formed according to the variation in Mg content.
In order to determine the formation of Mg2Si microstructures depending on the variation in the content of Mg, an aluminum alloy containing an amount of 8.5 wt % of Si, an amount of 0.5 wt % of Fe, an amount of 0.1 wt % of Mn, and the balance of Al and other inevitable impurities was prepared as the wt % was based on the total weight of the aluminum alloy. The aluminum alloy was prepared by changing the contents of Mg to 1.5 wt %, 3.0 wt % and 4.5 wt %, respectively, and then the microstructure of the specimen prepared according to an exemplary method of producing an aluminum alloy using the aluminum alloy was observed.
As shown in
Additional experiment was conducted to determine the effect of improving the corrosion resistance depending on the variation in the content of Mg.
In order to determine the effect of improving the corrosion resistance according to the variation in Mg content, an aluminum alloy containing an amount of 8.5 wt % of Si, an amount of 0.5 wt % of Fe, an amount of 0.1 wt % of Mn, and the balance of Al and inevitable impurities was prepared as the Mg content was changed to 3.0 wt % and 4.5 wt %, respectively, a saline spray test was performed on the specimen prepared according to an exemplary method of producing an aluminum alloy using the aluminum alloy, and the results are shown in
The saline spray test was carried out according to the saline spray test (KS D 9502) using 5% NaCl as saline after obtaining a prepared ASTM sub-size die casting tensile test specimen. At this time, the observation was separately conducted at 0 hour, 48 hours and 96 hours.
As shown in
On the other hand, the specimen having a Mg content of 4.5 wt % had very excellent corrosion resistance. In particular, when compared with the 0-hr specimen, the 48-hr and 96-hr specimens had no corrosion on the surface of the specimen even after the passage of time.
These results demonstrate a significant difference in corrosion resistance depending on the amount of the Mg2Si microstructure.
The exemplary embodiments of the present invention have effects of ensuring excellent thermal conductivity and corrosion resistance compared to conventional aluminum alloys for die casting, thereby enabling the production of a variety of cast products used in the manufacture of electronic parts for vehicles and portable electronic devices, which require heat dissipation and high corrosion resistance.
In addition, the exemplary embodiments of the present invention have an effect of producing cast products having excellent strength and elongation compared to conventional aluminum alloys for die casting.
Although the various exemplary embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2019-0167378 | Dec 2019 | KR | national |
