Patent Application
20190161834
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The present invention relates to an aluminum alloy for die casting, a method for producing the same, and a method for producing a casting using the same, and more particularly to a high-strength aluminum alloy for die-casting having excellent corrosion resistance and thermal conductivity, which exhibits excellent corrosion resistance and heat dissipation properties and high thermal conductivity, tensile strength and yield strength, and thus can be easily formed into a thin sheet and manufactured into an electronic device or automotive part having a complex shape or structure, and to a method for producing the same, and a method for producing an aluminum alloy casting using the same.
Generally, methods for producing aluminum products include: a plastic working method of forming an aluminum sheet into a desired shape by plastic working; and a die casting method of pouring an aluminum melt into a mold machined into a product shape, thereby producing a casting having the same shape as the mold.
Products produced by the die casting method have the advantage of having precise dimensions. Due to this advantage, these products are widely used for automotive or aircraft parts, electronic devices, optical devices and the like, which require a relatively complex design. However, as products are required to have high functionality, aluminum alloys are required to have, in addition to lightweight properties, corrosion resistance, abrasion resistance, high strength, thermal conductivity and the like.
Alloys which are used for die casting typically include ALDC12 which is an aluminum-based alloy, and AZ91D which is a magnesium-based alloy. The ALDC12 alloy has a yield strength of 165 MPa and a tensile strength of 331 MPa, and the AZ91D alloy has a yield strength of 150 MPa and a tensile strength of 230 MPa, which are lower than those of the ALDC12 alloy. These commercial alloys for die casting are difficult to apply to current slim products, such as smartphone or tablet cases, which require high strength.
Meanwhile, a ZA27 alloy, a zinc-based alloy, has excellent strength properties, including a yield strength of 365 MPa and a tensile strength of 426 MPa, but has a specific gravity of 5 g/cc, which is higher than those of aluminum-based alloys, indicating that the use of this zinc-based alloy in lightweight applications is limited.
In recent attempts to solve the above-described problems, Korean Patent Registration No. 1133103 (entitled “High-strength aluminum alloy for die casting”) proposes a high-strength aluminum alloy for die casting. The proposed aluminum has increased strength as a result of adding zinc (Zn), magnesium (Mg), copper (Cu), zirconium (Zr) and titanium (Ti) to an aluminum base. However, this alloy has problems in that because aging treatment at 120° C. for 24 hours or more is required, productivity is reduced, and in that an alloy melt rapidly poured into a mold sticks to the inner wall of the mold.
As another example, Korean Patent Application Publication No. 2012-0129458 (entitled “High-strength die casting aluminum alloy for thin-walled product”) proposes a high-strength die casting product for a thin-walled product. The proposed aluminum alloy is produced by adding magnesium (Mg), silicon (Si), iron (Fe), manganese (Mn), copper (Cu), zinc (Zn) and titanium (Ti) to an aluminum base, and has increased strength as well as improved castability due to reduced sticking of an alloy melt, to a mold. However, this alloy has a disadvantage in that it has low corrosion resistance, and thus the surface thereof is easily oxidized and corroded by water or moisture.
Patent Document 1:Korean Patent Registration No. 1133103 (entitled “High-strength aluminum alloy for die casting”);
Patent Document 2: Korean Patent Application Publication No. 2012-0129458 (entitled “High-strength die casting aluminum alloy for thin-walled product”).
Therefore, the present invention has been made in order to fundamentally solve the above-described problems occurring in the present invention, and it is an object of the present invention to provide a high-strength aluminum alloy for die casting having excellent corrosion resistance and thermal conductivity, which can simultaneously exhibit high strength, high corrosion resistance and high thermal conductivity, a method for producing the same, and a method for producing an aluminum alloy casting using the same.
To achieve the above object, one aspect of the present invention is directed to a high-strength aluminum alloy for die casting, which preferably comprises silicon (Si), iron (Fe), magnesium (Mg), nickel (Ni), titanium (Ti), tin (Sn), and the remainder aluminum (Al).
The aluminum alloy of the present invention preferably comprises, based on the total weight of the alley, 5 to 7 wt % of silicon (Si).
The aluminum alloy of the present invention preferably comprises, based on the total weight of the alloy, 0.1 to 1.0 wt % of iron (Fe).
The aluminum alloy of the present invention preferably comprises, based on the total weight of the alloy, 1.0 to 3.0 wt % of magnesium (Mg).
The aluminum alloy of the present invention preferably comprises, based on the total weight of the alloy, 0.1 to 1.0 wt % of nickel (Ni).
The aluminum alloy of the present invention preferably comprises, based on the total weight of the alloy, 0.15 to 0.45 wt % of titanium (Ti).
The aluminum alloy of the present invention preferably comprises, based on the total weight of the alloy, 1.0 to 3.0 wt % of tin (Sn).
The aluminum alloy according to the present invention has a tensile strength of 300 to 320 MPa and a thermal conductivity of 140 to 160 W/m·K.
Another aspect of the present invention is directed to a method for producing a high-strength aluminum alloy for die casting having excellent corrosion resistance and thermal conductivity, the method comprising: a first step of preparing materials comprising, based on the total weight of the materials, 5 to 7 wt % of silicon (Si), 0.1 to 1.0 wt % of iron (Fe), 1.0 to 3.0 wt % of magnesium (Mg), 0.1 to 1.0 wt % of nickel (Ni), 0.15 to 0.45 wt % of titanium (Ti), 1.0 to 3.0 wt % of tin (Sn), and the remainder aluminum (Al); a second step of melting the prepared aluminum (Al) by heating to a temperature of 700 to 750° C., followed by heating to a temperature of 800 to 850° C.; a third step of adding the silicon (Si) to a melt resulting from the second step, followed by heating to a temperature of 900 to 1000° C.; a fourth step of adding the iron (Fe), nickel (Ni) and titanium (Ti) to a mixture resulting from the third step, and then heating the mixture for 4 to 5 hours; a fifth step of reducing the temperature of the mixture of the fourth step to a temperature of 700 to 750° C., and then adding the magnesium (Mg) and tin (Sn) to the mixture, followed by melting; and a sixth step of removing impurities from the mixture of the fifth step, and then tapping the mixture as an ingot, thereby producing the alloy.
Here, the second to sixth steps of the method according to the present invention preferably further comprise analyzing and correcting the components of the mixture.
Furthermore, the sixth step of the method according to the present invention preferably comprises floating the impurities by bubbling an argon or nitrogen gas injected through the bottom of the mixture, and removing the impurities floated on the surface of the mixture.
Moreover, the sixth step of the method according to the present invention preferably further comprises filtering the impurities in a tapping outlet and a tapping channel during tapping of the mixture.
Still another aspect of the present invention is directed to a method for producing a high-strength aluminum alloy casting having excellent corrosion resistance and thermal conductivity by die casting, the method comprising the steps of: preparing an alloy comprising, based on the total weight of the alloy, 5 to 7 wt % of silicon (Si), 0.1 to 1.0 wt % of iron (Fe), 0.1 to 3.0 wt % of magnesium (Mg), 0.1 to 1.0 wt % of nickel (Ni), 0.15 to 0.45 wt % of titanium (Ti), 1.0 to 3.0 wt % of tin (Sn), and the remainder aluminum (Al); and melting the alloy, and pouring the melted alloy into a die casting mold, thereby producing the casting.
The casting produced according to the present invention is preferably an electronic device part or an automotive part.
The casting produced according to the present invention may be a thin-walled molded article having a thickness (T) of 0.38 mm or less.
The terms and words used in the specification and claims should not be interpreted as being limited to typical meanings or dictionary definitions, but should be interpreted as having meanings and concepts relevant to the technical scope of the present invention, based on the principle according to which the inventors can appropriately define the meaning of the terms to describe their invention in the best manner. Accordingly, it should be understood that the embodiments described in the specification and the configurations shown in the drawings are merely preferred examples, but not cover all the technical spirits of the present invention, and thus there may be various equivalents and modifications capable of replacing them at the time of filing of the present invention.
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
One aspect of the present invention is directed to an aluminum alloy for die casting, which comprises silicon (Si), iron (Fe), magnesium (Mg), nickel (Ni), titanium (Ti), tin (Sn), and the remainder aluminum (Al) so as to simultaneously exhibit high strength, high corrosion resistance and high thermal conductivity.
Silicon (Si) functions to increase flowability and strength, and is preferably contained in an amount of 5.0 to 7.0 wt % based on the total weight of the alloy. If the content of silicon is more than 7.0 wt %, cracking may occur due to insufficient heat treatment, and if the content of silicon is less than 5.0 wt %, it cannot achieve the intended object. For this reason, silicon is most preferably contained in an amount of 6.0 wt % so that it can improve all flowability, strength and heat treatment properties.
Iron (Fe) functions to prevent sticking and improve strength, and is preferably contained in an amount of 0.1 to 1.0 wt % based on the total weight of the alloy. If the content of iron is more than 1.0 wt %, it may reduce corrosion resistance and cause precipitates, and if the content of iron is less than 0.01 wt %, it cannot achieve the intended object. For this reason, iron is most preferably contained in an amount of 0.5 wt % so that it can prevent sticking and improve strength and corrosion resistance.
Magnesium (Mg) functions to form a dense surface oxide layer (MgO) that prevents internal corrosion and improves strength. It is preferably contained in an amount of 1.0 to 3.0 wt % based on the total weight of the alloy. If the content of magnesium is more than 3.0 wt %, it may increase flowability, making it difficult to produce a complex shape, and if the content of magnesium is less than 1.0 wt %, it cannot achieve the intended object. For this reason, magnesium (Mg) is most preferably contained in an amount of 2.0 wt % in order to improve corrosion resistance and strength and ensure suitable flowability.
Nickel (Ni) functions to improve corrosion resistance, and is preferably contained in an amount of 0.1 to 1.0 wt % based on the total weight of the alloy. Even if nickel is contained in an amount of more than 1.0 wt %, corrosion resistance will not be significantly improved, and if the content of nickel is less than 0.1 wt %, it cannot achieve the intended object. For this reason, nickel is more preferably contained in an amount of 0.5 wt % so that it can improve corrosion resistance and reduce harmfulness.
Titanium (Ti) functions to improve moldability, corrosion resistance and strength by grain refinement, and is preferably contained in an amount of 0.15 to 0.45 wt % based on the total weight of the alloy. If the content of titanium is more than 0.45 wt %, it may reduce the melt flowability, thus promoting failure, and if the content of titanium is less than 0.15 wt %, it cannot achieve the intended object. For this reason, titanium is most preferably contained in an amount of 0.15 wt % so that it can improve moldability, corrosion resistance and strength.
Tin (Sn) functions to improve moldability and cutting machinability and to compensate for the decrease in thermal conductivity caused by titanium. It is preferably contained in an amount of 1.0 to 3.0 wt % based on the total weight of the alloy. If the content of tin is more than 3.0 wt %, it may reduce corrosion resistance, and if the content of tin is less than 1.0 wt %, it cannot achieve the intended object. For this reason, tin (Sn) is most preferably contained in an amount of 1.0 wt % so that it can improve all moldability, cutting machinabiiity and corrosion resistance.
The aluminum alloy comprising the above-described components and their contents has high corrosion resistance, a tensile strength of 300 to 320 MPa, and a thermal conductivity of 140 to 160 W/m·K.
Another aspect of the present invention is directed to a method of producing a high-strength aluminum alloy for die casting having excellent corrosion resistance and thermal conductivity through a first step (S10) to a sixth step (S60) as shown in
Preferably, materials comprising, based on the total weight of the materials, 6.0 wt % of silicon (Si), 0.5 wt % of iron (Fe), 2.0 wt % of magnesium (Mg), 0.5 wt % of nickel (Ni), 0.15 wt % of titanium (Ti), 1.0 wt % of tin (Sn), and the remainder aluminum, are prepared.
Next, a second step (S20) of melting the prepared aluminum (Al) by heating to a temperature of 700 to 750° C., followed by heating to a temperature of 800 to 850° C., and then a third step (S30) of adding the silicon (Si) to a melt resulting from the second step (S20), followed by heating to a temperature of 900 to 1000° C., is performed.
Thereafter, a fourth step (S40) of adding the iron (Fe), nickel (Ni) and titanium (Ti) to the mixture of step (S30), and then heating the mixture for 4 to 5 hours, is performed, and a fifth step (S50) of reducing the temperature of the mixture of the fourth step to a temperature of 700 to 750° C., and then adding the magnesium (Mg) and tin (Sn) to the mixture, followed by melting, is performed.
Finally, a sixth step (S60) of removing impurities from, the mixture of the fifth step (S50), and then tapping the mixture as an ingot, is performed, thereby producing the alloy. The impurities include oxides, carbides, intermetallic compounds, which comprise hydrogen gas and sodium. The hydrogen gas reduces the mechanical properties and moldability of the alloy and causes corrosion or surface defects such as cracks, and the sodium reduces the flowability and castability of the alloy.
Specifically, as shown in
Meanwhile, as shown in
Still another aspect of the present invention is directed to a method of producing a casting using the aluminum alloy for die casting. First, an alloy comprising, based on the total weight of the alloy, 5 to 7 wt % of silicon (Si), 0.1 to 1.0 wt % of iron (Fe), 0.1 to 3.0 wt % of magnesium (Mg), 0.1 to 1.0 wt % of nickel (Ni), 0.15 to 0.45 wt % of titanium (Ti), 1.0 to 3.0 wt % of tin (Sn), and the remainder aluminum (Al), is prepared.
Preferably, an alloy comprising, based on the total weight of the alloy, 6.0 wt % of silicon (Si), 0.5 wt % of iron (Fe), 2.0 wt % of magnesium (Mg), 0.5 wt % of nickel (Ni), 0.15 wt % of titanium (Ti), 1.0 wt % of tin (Sn), and the remainder aluminum, is prepared. Next, the prepared aluminum alloy is melted, and the melted alloy heated to a temperature of 680 to 750° C. is poured into a die-casting mold under a pressure of 75 MPa, thereby producing the casting.
Since the casting is produced by adding proper amounts of metal elements to aluminum, it has a stable and dense surface oxide layer formed thereon, and thus it has excellent corrosion resistance in a salt water environment or a water or atmospheric environment. In addition, the casting exhibits high tensile strength and yield strength. Furthermore, the alloy melt does not stick to the inner wall of the mold during casting, and the mold-filling ability of the alloy melt is improved. Thus, according to the present invention, a thin sheet-shaped casting having a thickness (T) of 0.38 mm or less can be produced, which is suitable for an electronic device part or an automotive part.
Hereinafter, examples of the present invention will be described in detail, and whether the substantial effects of an alloy of the present invention are effective will be examined.
Alloy Preparation
An alloy of Example 1, which has a representative composition according to the present invention, and alloys of Comparative Example 1 and (ADC12.1) and Comparative Example 2 (S33N), which have conventional compositions, were prepared as shown in Table 1 below.
The alloys prepared as shown in Table 1 above were prepared into ASTM subsize specimens as shown in Table 2 below.
Testing of Physical Properties
The tensile strength and yield strength of each of the prepared specimens were measured using a universal tester (Instron 5982), and the thermal conductivity of each specimen was measured in accordance with ASTM E1461. The results of the measurement are shown in Table 3 below.
From the results of the measurement, it can be seen that the tensile strength of each of Example 1 and Comparative Example 1 is higher than 300 MPa, which satisfies high-strength properties, but the thermal conductivity of Example 1 is 154 W/m·K, which is significantly higher than that of Comparative Example(124 W/m·K).
Test for Corrosion Resistance
First, for each of the prepared specimens which were not surface-treated, salt water was sprayed onto the surface of each specimen under the following conditions according to KS D 9502 (salt spray testing method):
The specimens sprayed with salt water under these conditions were visually observed as shown in Table 4 below. For a specimen for electrochemical testing and a specimen for electrical conductivity testing, an area of 9 cm2 in each specimen was exposed and each specimen was mounted. Next, each specimen was polished with SiC polishing paper #2000, washed with distilled water, and then dried. Using a ZIVE SP1 measurement device shown in
From the results of the observation, it can be seen that Example 1 has a distinct color and a dense surface, compared to Comparative Example 1 or 2.
From the measurement results in Table 5 above, can be seen that the corrosion rate of Example 1 is similar to that of Comparative Example 2, but the electrical conductivity of Example 1 is 32, which is significantly higher than that of Comparative Example 1 (25.2). Namely, higher electrical conductivity indicates lower corrosion-induced resistance, and the fact that the electrical conductivity is higher in the Example than in the Comparative Example indicates that the Example has higher corrosion resistance.
Test for Titanium Content
Titanium (Ti) an important element that influences moldability, corrosion resistance and strength by grain refinement. The tensile strength, yield strength and thermal conductivity of specimens, obtained by adjusting only the content of titanium (Ti) in the alloy of the above-described Example as shown in Table 6 below, were measured. In addition, the electrical conductivity, corrosion potential and corrosion rate of the specimens were measured, and the results are shown in Table 7 below.
From the measurement results in Table 6 above, it can be seen that as the content of titanium (Ti) decreases, the tensile strength and thermal conductivity of the specimen increases and the yield strength decreases, and on the contrary, as the content of titanium increases, the tensile strength and thermal conductivity of the specimen decrease and the yield strength increases.
From the measurement results in Table 7 above, it can be seen. that as the content of titanium (Ti) decreases, the corrosion rate of the specimen decreases and the electrical conductivity increases, and as the content of titanium increases, the corrosion rate increases and the electrical conductivity decreases.
Discussion
In conclusion, referring to Tables 6 and 7 above, it can be confirmed that titanium (Ti) is an important factor for simultaneously achieving high strength, high corrosion resistance and high thermal conductivity according to the present invention. Specifically, it can be confirmed that when the content of titanium (Ti) is less than 0.15 wt %, tensile strength decrease, and when the content of titanium is more than 0.45 wt %, thermal conductivity and corrosion decrease, indicating that the content of titanium (Ti) is preferably 0.15 to 0.45 wt %, more preferably 0.15 wt %.
As described above, the present invention provides the following effects.
First, since the alloy casting of the present invention has a stable and dense surface oxide layer formed thereon, it has excellent water resistance in a salt water environment and a water or atmospheric environment, and thus can increase the life span of an electronic device or automotive part to which the casting is applied.
Second, the alloy of the present invention has excellent heat dissipation performance corresponding to a thermal conductivity of 140 w/m·K or higher, and thus when it is applied to an electronic device, it can guarantee the safety and performance of the device by effectively dissipating the heat generated in the device.
Third, since the alloy of the present invention can be molded into a thin-walled article having a thickness of 0.38 mm or less while having a tensile strength of 300 MPa or higher, it can be widely used for automotive parts and the like, which require safety by high strength and product compactness by thin-wall molding.
It is obvious to those skilled in the art that the scope of the present invention is not limited to the embodiments disclosed herein and various variations and modifications are possible without departing from the spirit and scope of the present invention. Therefore, such variations and modifications should be considered as falling within the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2017-0157968 | Nov 2017 | KR | national |
