Die-cast product and method for producing the same, and sand-cast product and method for producing the same

Abstract

To provide a die-cast product with medium strength and high ductility and a method for producing the same, and a sand-cast product with medium strength and high ductility and a method for producing the same.SOLUTION: The die-cast product contains 6.0 to 11.0 wt.% of Si, 0.51 to 1.00 wt.% of Mg, 0.1 to 1.0 wt.% of Cu, 0.1 to 0.7 wt.% of Mn, 0.50 wt.% or less of Fe, 0.20 wt.% or less of Ti, 0.03 wt.% or less of Sr, and unavoidable impurities in a total amount of 0.50 wt.% or less, with the balance being Al. As Fe compounds, the metallic structure contains Al-Fe-Si-based compounds, Al-Fe-Si-Mn-based compounds, and Al-Fe-Si-Mg-based compounds. As Cu compounds, the metallic structure contains Al-Cu-Mg-based compounds and precipitates containing Cu atoms and Mg atoms. The Vickers hardness is 80 Hv or more and 110 Hv or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a die-cast product and a manufacturing method thereof, and a sand-cast product and a manufacturing method thereof. The present invention relates to a method for manufacturing a thin aluminum casting having a wall thickness of 5 mm or less at least in a portion thereof, made of a medium-strength aluminum alloy with a Vickers hardness of 80 Hv or more. A Vickers hardness of 80 Hv indicates a tensile strength of 230 MPa or more, a yield strength of 130 MPa or more, and an elongation of 5% or more. [Background technology]

[0002] The main alloy compositions for casting and die-casting alloys are Al-Si-Mg, Al-Si-Cu, and Al-Si-Cu-Mg alloys. Forging alloys, the Al-Si-Cu-Mg alloy 4032 is well known, and Ni is added as an essential element for high-temperature strength. Many casting and die-casting alloys contain Cu as an essential element, but the Cu content exceeds 1.5 wt%. While Cu is considered a strength-improving element, it is difficult to achieve sufficient strength without a large Cu content. Furthermore, the higher the Cu content, the worse the corrosion resistance and castability. Furthermore, Mg, which is also included in alloys, is treated as an essential element and added at around 1 wt% when used at high temperatures, such as in pistons. However, when used at room temperature, Mg is treated as an impurity element and is not necessarily controlled to a maximum of 0.5 wt% or less.

[0003] Among die-casting alloys, ADC3 is known as an Al-Si-Mg alloy. This alloy contains trace amounts of Cu as an impurity element. 4032 alloy, a forging alloy, contains Cu, Mg, and Ni as essential elements with an upper limit of 1.3 wt%. Unlike Al-Si-Mg alloys, these Cu-containing alloys all contain Fe as an impurity with an upper limit of around 1% (see, for example, Non-Patent Document 1).

[0004] With the exception of die-cast parts, thick-walled parts have been the norm for most automotive parts. However, with the recent shift toward electric vehicles, there has been active development of thinner die-cast parts for large vehicle bodies, including battery cases, rear and front parts. In parallel with this, development of large, thin sand castings has also progressed as a pre-test for confirming the performance of die-cast parts (see, for example, Patent Document 1).

[0005] When considering application to such fields, if a general die casting method is used, the cast material cannot be expected to have good mechanical properties, particularly ductility, elongation, or bendability. This is because, unless the inside of the mold is evacuated or depressurized, the product will contain numerous air entrapment defects, which will cause blisters to appear on the surface of the product when heat treated, so the elongation of the as-cast product is typically 2% or less (see, for example, Non-Patent Document 2).

[0006] On the other hand, if high ductility is required, a product with medium strength and high ductility of 250 MPa or more can be considered by using an alloy such as Silafont, which has a reduced content of Fe and Cu and the addition of Mn, using a vacuum die casting method. However, there are some cost issues involved.

[0007] To improve the quality of these castings, effective methods include solution treatment to granulate the eutectic silicon, followed by water cooling and artificial aging. However, heat treatment is possible for products manufactured by vacuum die casting and sand castings that do not have air entrapment, so it is possible to improve their mechanical properties.

[0008] However, as mentioned above, when thin and large objects are produced, solution treatment and subsequent quenching are not easy due to the problem of deformation of the casting, and there are issues with the commonly used heat treatment method, i.e., quenching by water cooling from the solution treatment temperature (for example, an average cooling rate of 50°C / second or more).

[0009] For this reason, in the case of thin-walled sand castings, unless high strength is required, forced air cooling from the solution treatment temperature to room temperature is performed using a fan or mist (for example, an average cooling rate of 0.3°C / s to 2.0°C / s). However, this method may not achieve the desired strength. Furthermore, whether after water quenching or fan cooling, distortion correction is required between the time the casting cools to room temperature and the time it is artificially aged. Leaving the casting at room temperature can have well-known negative effects, such as insufficient strength even after artificial aging.

[0010] For example, in the case of JIS AC4C alloy, even a 15-minute artificial aging time after solution treatment and water quenching has been reported to have a negative effect of reducing strength compared to artificial aging immediately after water quenching. Therefore, a simple method to achieve high strength is to raise the artificial aging temperature to a slightly higher level, such as 180°C, or to age for a longer period, such as more than six hours, at 160°C. However, when such heat treatment conditions are selected, the yield strength is somewhat higher than that of die-cast products without heat treatment, and the mechanical properties are not necessarily the same. Thus, there are differences in quality, and the heat treatment process is complicated, leading to increased costs (see, for example, Non-Patent Document 3).

[0011] Regarding heat treatment for die-casting, in order to reduce the complexity of heat treatment work for die-cast products and to eliminate solution treatment, it has been proposed to add several times more Sr than the amount added in general improving treatment agents to exhibit high elongation, and to add aging treatment to achieve the desired mechanical properties of tensile strength. However, in die-cast products, aging treatment should also be avoided if possible (see, for example, Patent Document 2). [Prior art documents] [Non-patent literature]

[0012] [Non-Patent Document 1] Kitaoka et al.: Light Metals, 1988, vol. 38, p. 426 [Non-patent document 2] Japan Light Metal Association, The Actual Strength of Aluminum Alloy Castings [Non-patent document 3] Adachi et al.: Light Metals, 37(1987), 524 [Patent documents]

[0013] [Patent Document 1] Special publication 2023-510881 [Patent Document 2] Japanese Patent Application Publication No. 1-283336 Summary of the Invention [Problem to be solved by the invention]

[0014] The present invention has been made against the above background.

[0015] In mass production methods such as die casting, where production takes place in units of about one minute, it is desirable to avoid heat treatment to obtain the required mechanical properties, as well as the resulting distortion correction work, as much as possible. In this sense, although this alloy has excellent properties with solution treatment, quenching, and artificial aging, it is desirable to avoid solution treatment, i.e., to use it as-cast, or if heat treatment is used, to limit it to T5 treatment (post-cast aging treatment), and the mechanical properties required for this die-cast product are medium strength and high ductility.

[0016] Furthermore, when considering cost reduction for die-cast products, it is desirable to have an alloy that contains a certain amount of Fe to prevent seizure of the die, while still maintaining ductility, rather than an alloy with a low Fe content.

[0017] On the other hand, even in sand casting, where the time from about 10 minutes to about a day until the mold is opened after casting is long, like die casting, it is desirable to avoid heat treatment to obtain the desired mechanical properties, and to avoid the distortion correction work that occurs as a result. In that sense, it is desirable to avoid at least solution treatment that does not involve water quenching, that is, to use the as-cast product, or to perform T5 treatment (post-cast aging treatment).

[0018] However, if solution treatment is required due to mechanical properties, the casting must be left at room temperature for several hours after forced air cooling or water quenching before distortion can be corrected. Even after subsequent artificial aging, the casting is required to have mechanical properties of 230 MPa or more (equivalent to a Vickers hardness of 80 Hv or more), the same level as AC4CH permanent mold castings, a medium-strength, high-ductility alloy generally used in almost all wheels, an important safety component of automobiles. In particular, the casting is required to have tensile properties and hardness close to those of die-cast products. This is because sand mold prototype castings are not simply required to have high strength and ductility, but are also desired to be useful for design considerations of die-cast products and molds.

[0019] The above is from the perspective of improving ductility. However, from the perspective of improving strength, significant challenges remain. The following issues arise when not using the so-called T6 treatment, which consists of solution treatment, water quenching, and aging. When attempting to achieve a moderate strength of 80 Hv or more and 230 MPa or more in the as-cast state or by T5 treatment, whether using sand casting or die casting, Al-Si-Mg alloys tend to over-age, where the Mg-Si compounds that contribute to age hardening precipitate in the mold, resulting in coarse precipitates. This can lead to softening and difficulty in achieving the required strength.

[0020] On the other hand, T6 treatment poses the following challenges. When a casting is solution-treated, it must be water-quenched or forced-air-cooled, then straightened before artificial aging. Because the casting is held in air, it is difficult to achieve the desired strength unless the appropriate aging conditions are selected after the artificial aging at room temperature. As mentioned above, if the appropriate conditions are selected to eliminate the negative effects, the yield strength will be slightly higher than that of a die-cast product without heat treatment, relative to its tensile strength, and it will be difficult to achieve the same mechanical properties. [Means for solving the problem]

[0021] In order to solve the above problems, a first aspect of the present invention provides a die-cast product containing 6.0 to 11.0 wt% Si, 0.51 to 1.00 wt% Mg, 0.1 to 1.0 wt% Cu, 0.1 to 0.7 wt% Mn, 0.50 wt% or less Fe, 0.20 wt% or less Ti, 0.03 wt% or less Sr, and a total of 0.50 wt% or less unavoidable impurities, the balance being Al, and containing, as Fe compounds in the metallographic structure, Al-Fe-Si compounds, Al-Fe-Si-Mn compounds, and Al-Fe-Si-Mg compounds, and as Cu compounds in the metallographic structure, Al-Cu-Mg compounds and precipitates containing Cu atoms and Mg atoms, and having a Vickers hardness of 80 Hv or more and 110 Hv or less.

[0022] Alternatively, the die-cast product according to the first aspect of the present invention contains one or more of 6.0 to 8.9 wt% Si, 0.51 to 0.80 wt% Mg, 0.1 to 0.6 wt% Cu, 0.31 to 0.50 wt% Mn, 0.40 wt% or less Fe, and 0.003 to 0.030 wt% Sr.

[0023] In the method for manufacturing a die-cast product according to the first aspect of the present invention, a molten aluminum alloy is poured into a mold product portion, solidified within the mold product portion, and the time from pouring to removing the casting from the mold product portion is set to within one minute, and age hardening is promoted within this time period to manufacture the die-cast product.

[0024] After die casting, the casting reaches a specified hardness through age hardening before being removed from the mold. However, if the dissolved Cu and Mg atoms still remain in the aluminum matrix, age hardening will progress slightly within the range of 110 Hv or less while the casting is left at room temperature after removal.

[0025] A second aspect of the present invention provides a sand casting product comprising 4.0 to 11.0 wt% Si, 0.51 to 0.80 wt% Mg, 0.1 to 1.0 wt% Cu, 0.2 wt% or less Mn, 0.30 wt% or less Fe, 0.20 wt% or less Ti, 0.005 to 0.030 wt% Sr, and unavoidable impurities in a total amount of 0.50 wt% or less, with the balance being Al, containing eutectic Si independently dispersed in the metallographic structure, containing, as Fe compounds in the metallographic structure, one or more of an Al-Fe-Si compound and an Al-Fe-Si-Mn compound, and an Al-Fe-Si-Mg compound, and containing, as Cu compounds in the metallographic structure, an Al-Cu-Mg compound and precipitates containing Cu atoms and Mg atoms, and having a Vickers hardness of 80 Hv or more and 110 Hv or less.

[0026] Alternatively, the sand casting product according to the second aspect of the present invention contains one or more of 0.51 to 0.70 wt % Mg, 0.1 to 0.6 wt % Cu, 0.15 wt % or less Fe, and 0.005 to 0.020 wt % or less Sr.

[0027] In the method for producing a sand-cast product according to the second aspect of the present invention, a molten aluminum alloy is poured into a sand mold, and the casting removed from the sand mold is subjected to a solution treatment, followed by water quenching or forced air cooling in the atmosphere, and after 15 minutes or more in the atmosphere, an artificial aging treatment at 140°C to 200°C is performed.

[0028] A third aspect of the present invention provides a sand casting product comprising 4.0 to 11.0 wt% Si, 0.51 to 0.80 wt% Mg, 0.1 to 1.0 wt% Cu, 0.2 wt% or less Mn, 0.30 wt% or less Fe, 0.20 wt% or less Ti, 0.005 to 0.030 wt% Sr, and a total of 0.50 wt% or less of unavoidable impurities, with the balance being Al, and containing, as Fe compounds in the metallographic structure, one or more of an Al-Fe-Si compound and an Al-Fe-Si-Mn compound, and an Al-Fe-Si-Mg compound, and containing, as Cu compounds in the metallographic structure, an Al-Cu-Mg compound and precipitates containing Cu atoms and Mg atoms, and having a Vickers hardness of 80 Hv or more and 110 Hv or less.

[0029] Alternatively, the sand casting product according to the third aspect of the present invention contains one or more of 0.51 to 0.70 wt % Mg, 0.1 to 0.6 wt % Cu, 0.15 wt % or less Fe, and 0.005 to 0.020 wt % or less Sr.

[0030] In a method for producing a sand-cast product according to a third aspect of the present invention, a molten aluminum alloy is poured into a sand mold, and the molten aluminum alloy in the sand mold is solidified at an average cooling rate of 0.8°C / second or more in a solidification range from the melting point to the binary eutectic temperature of 577°C. Thereafter, the casting in the sand mold is cooled at an average cooling rate of 0.08°C / second or more in a temperature range from 300°C to 200°C, and the casting is removed from the sand mold and subjected to an artificial aging treatment.

[0031] Alternatively, in the method for producing a sand-cast product according to the third aspect of the present invention, the artificial aging treatment is carried out at a temperature in the range of 140°C to 200°C. [Effects of the Invention]

[0032] According to the present invention, by optimizing the contents of Mg and Cu in die-cast products, a thin die-cast product with medium strength and high ductility is provided using an aluminum alloy containing Fe and Mn without solution treatment, and a method for manufacturing the same.

[0033] According to the present invention, a thin sand-cast product with medium strength and high ductility and a method for manufacturing the same are provided by using an aluminum alloy with an optimized Mg and Cu content, a reduced Fe content, and an added Sr content, followed by solution treatment, water quenching or forced air cooling in the atmosphere, and then artificial aging treatment after 15 minutes or more in the atmosphere.

[0034] According to the present invention, a thin sand-cast product with medium strength and high ductility and a method for manufacturing the same are provided by using an Al alloy with an optimized Mg and Cu content, a reduced Fe content, and added Sr, and by controlling the cooling conditions during and after solidification of the casting cast in the sand mold and performing aging treatment. [Brief explanation of the drawings]

[0035] [Figure 1] FIG. 1 is a photograph showing the metal structure of Comparative Example 2. [Figure 2] FIG. 1 is a photograph showing the metal structure of Example 2. [Figure 3] FIG. 10 is a photograph showing the metal structure of Example 6. [Figure 4] FIG. 1 is a low-magnification photograph showing the metal structure of Example 6. [Figure 5] FIG. 2 is a photograph showing the metal structure of a die-cast product. [Figure 6] 1A and 1B are photographs showing the metal structure of a sand-cast product before and after solution treatment. [Figure 7] FIG. 1 is a photograph showing the effect of the solution treatment temperature on the metal structure of a sand-cast product. [Figure 8] 1 is a graph showing the effect of solution treatment temperature on the tensile strength of a sand-cast product. [Figure 9] 1 is a graph showing the effect of solution treatment temperature on the yield strength of a sand-cast product. [Figure 10] 1 is a graph showing the effect of solution treatment temperature on the elongation of a sand-cast product. [Figure 11] 1 is a graph showing the effect of solution treatment temperature on the hardness of a sand-cast product. DETAILED DESCRIPTION OF THE INVENTION

[0036] Various embodiments of the present invention will now be described in detail.

[0037] [First embodiment] The die-cast product according to the first embodiment of the present invention contains 6.0 to 11.0 weight % Si, 0.51 to 1.00 weight % Mg, 0.1 to 1.0 weight % Cu, 0.1 to 0.7 weight % Mn, 0.50 weight % or less Fe, 0.20 weight % or less Ti, 0.03 weight % or less Sr, and a total of 0.50 weight % or less of unavoidable impurities, with the balance being Al. The die-cast product contains, as Fe compounds in the metallographic structure, Al-Fe-Si compounds, Al-Fe-Si-Mn compounds, and Al-Fe-Si-Mg compounds, and as Cu compounds in the metallographic structure, Al-Cu-Mg compounds and precipitates containing Cu atoms and Mg atoms. The die-cast product has a Vickers hardness of 80 Hv or more and 110 Hv or less.

[0038] In this specification, "unavoidable impurities" refers to elements other than Al, Si, Mg, Cu, Mn, Fe, Ti, and Sr, such as V, Cr, P, Pb, Sn, etc. Note that oxygen is not included in the "unavoidable impurities."

[0039] (Die-cast products) In the die-cast product of this embodiment, if the Si content is too low, the molten metal flow during production is poor, and if it is too high, the ductility is reduced. In this embodiment, the Si content is set to 6.0 to 11.0 wt %. To further improve ductility, the Si content is preferably set to 6.0 to 8.9 wt %.

[0040] In the die-cast product of this embodiment, Mg forms nanometer-sized precipitates with Cu and Al, contributing to improved strength. However, if too much Mg is added, ductility decreases. In this embodiment, the Mg content is set to 0.51 to 1.00 wt%. To further improve ductility, the Mg content is preferably set to 0.51 to 0.80 wt%.

[0041] In the die-cast product of this embodiment, Cu forms nanometer-sized precipitates with Al and Mg, contributing to improved strength. However, if the Cu content is too high, corrosion resistance and ductility decrease. In this embodiment, the Cu content is 0.1 to 1.0 wt %. Preferably, the Cu content is 0.1 to 0.6 wt %.

[0042] The precipitates that contribute to this strength improvement contain Cu and Mg atoms. These precipitates also include at least one of the following: a GP zone consisting of Cu and Mg atoms that is completely coherent with the Al matrix, and a semi-coherent intermediate phase consisting of Al-Cu-Mg precipitates. While micrometer-sized Al-Cu-Mg compounds can be observed in the metal structure using an optical microscope, their role in improving strength is insignificant.

[0043] In the die-cast product of this embodiment, Mn improves ductility by changing the shape of the contained Fe compounds from needle-like to blocky. However, if the amount added is too large, ductility decreases, so the Mn content is set to 0.1 to 0.7 wt%. Preferably, the Mn content is set to 0.31 to 0.50 wt%.

[0044] In the die-cast product of this embodiment, Fe is added to prevent seizure, but if added in excess, it can cause a decrease in ductility, so the Fe content is set to 0.50 wt % or less, preferably 0.40 wt % or less.

[0045] In the die-cast product of this embodiment, Ti is added as a grain refiner to suppress the occurrence of shrinkage cavities in the cast product. Since adding more than 0.20 wt% of Ti does not improve the effect, the amount of Ti is set to 0.20 wt% or less.

[0046] In the die-cast product of this embodiment, the amount of Sr required to refine the eutectic Si varies depending on the amount of P contained in the molten alloy, but considering the reliability of the refinement effect, the amount of Sr is set to 0.03 wt% or less. However, if the amount of Sr is too much, Sr oxides will form and be mixed into the product, degrading the quality, so the amount of Sr is preferably 0.003 to 0.030 wt%.

[0047] (Metal structure of die-cast products) The die-cast product of this embodiment contains, in its metal structure, Fe compounds such as Al-Fe-Si compounds, Al-Fe-Si-Mn compounds, and Al-Fe-Si-Mg compounds, and Cu compounds such as Al-Cu-Mg compounds and precipitates containing Cu and Mg atoms. The Al-Cu-Mg compounds also include Al-Cu-Mg-Si compounds containing Si in addition to Cu and Mg.

[0048] The sizes of Al-Fe-Si compounds, Al-Fe-Si-Mn compounds, Al-Fe-Si-Mg compounds, and Al-Cu-Mg compounds in the metal structure are mainly 2 μm or more, and can be measured by observing the structure using an optical microscope, for example.

[0049] The size of the precipitates containing Cu atoms and Mg atoms in the metal structure is, for example, about 3 nm to 60 nm.The precipitates include, for example, GP zones and intermediate phases as metastable phases.

[0050] The GP zone refers to the atomic arrangement of precipitates after heat treatment. In the GP zone, the aluminum atoms of the parent phase and the Cu and Mg atoms dissolved in the parent phase are aligned in the crystal lattice. For example, in the GP zone, the dissolved Cu and Mg atoms are bonded to the surrounding Al atoms. When a precipitate contains a GP zone, it contributes to age hardening.

[0051] The intermediate phase is a state in which the aluminum of the matrix and the Cu atoms, Mg atoms, etc. that are dissolved in the matrix are partially coherent, which can also be called a semi-coherent state. When precipitates contain an intermediate layer, it also contributes to age hardening.

[0052] The sizes of the GP zone and the intermediate phase in the metal structure can be measured by observing the structure using, for example, a transmission electron microscope.

[0053] When the precipitates are precipitated as a stable phase, they simply disperse in the aluminum matrix as coarse precipitates, and these coarse precipitates do not contribute to age hardening.

[0054] (Manufacturing method for die-cast products) The die casting method involves injecting molten metal into a mold cavity and then removing the casting from the mold cavity within minutes. The manufacturing method is as follows:

[0055] The molten metal is poured into a tube called a sleeve, and then a tip that fits into the sleeve is moved at an injection speed of about several meters per second, filling the mold with the molten metal, which is then pressurized with a metal pressure of, for example, 50 MPa or more to solidify. The solidification time is no longer than 5 seconds. The mold is then opened and the die-cast product is removed from the mold. The mold is opened after the molten aluminum in the biscuit part has solidified. The biscuit part is the part that connects to the mold product part and solidifies more slowly than the mold product part. Therefore, as the volume of the biscuit increases, the solidification time increases, but from a productivity perspective, the removal time is within 1 minute. Note that age hardening progresses during the time until removal.

[0056] The method for manufacturing the die-cast product in this embodiment is, for example, as follows.

[0057] Molten aluminum alloy is poured into a mold and then rapidly cooled in the mold. At the solidification temperature at which the alloy changes from liquid to solid, μm-sized Al-Fe-Si compounds, Al-Fe-Si-Mn compounds, Al-Fe-Si-Mg compounds, and Al-Cu-Mg compounds are crystallized. During this rapid cooling process in the mold, Cu atoms and Mg atoms are dissolved in the primary aluminum crystals that are initially generated as a supersaturated solid solution.

[0058] During the cooling process in the mold, around 200°C, the precipitation of nanometer-sized precipitates is promoted. In particular, in the case of continuous precipitation, age precipitation or phase decomposition is promoted by nucleation and growth or spinodal decomposition. The precipitates contain, for example, Cu and Mg atoms, which contribute to age hardening.

[0059] [Example] (Comparative Examples and Examples of Die-Cast Products) Table 1 shows the chemical composition and mechanical properties of the vacuum-cast die-cast product. The die-cast product has a rectangular cross section, consisting of 1.5 mm, 3.5 mm, and 9.0 mm sections, measuring 50 mm wide and 150 mm long. The casting weight is 230 g. After the molten metal was injected into the mold and filled, the 1.5 mm and 9.0 mm sections lost pressure after the tip-side gate solidified, causing shrinkage cavities. Therefore, the 3.5 mm section, which was sound and had almost no shrinkage cavities, was used for testing. The casting test was conducted as follows: The molten metal was injected into the sleeve using a die-casting machine, a metal pressure of 50 MPa was applied, and the solidified cast product was opened and removed within 10 seconds.

[0060] [Table 1]

[0061] Comparative Example 1 is an Al-Si-Mg alloy that does not contain Cu, unlike the present embodiment. Therefore, when solidified in the mold, it is prone to overaging in the mold, and the Vickers hardness of Comparative Example 1 is low at 75 Hv.

[0062] Comparative Examples 2 and 3 contain 0.30 wt. % Mg, which is lower than the range of chemical compositions of this embodiment. Because Comparative Examples 2 and 3 contain a certain amount of Cu, they also exhibit Vickers hardness of 80 Hv or more and tensile strength of 250 MPa or more. However, when comparing the effects of heat treatment in a test simulating the thermal effects of a product being held in the mold for a long time (400°C x 0 minutes for Comparative Example 2, and 400°C x 2 minutes for Comparative Example 3), the heat-treated Comparative Example 3 is softer than the unheat-treated Comparative Example 2. The chemical compositions of Comparative Examples 2 and 3 leave the product unstable in quality due to the thermal effects of the product wall thickness and time in the mold.

[0063] Comparative Examples 4 and 5 contain 0.26 wt% Cu and 0.45 wt% Mg, which is lower than the present embodiment. Comparative Examples 4 and 5 also have a Vickers hardness of 85 Hv. However, in tests simulating similar thermal effects (Comparative Example 4 at 400°C for 0 minutes, Comparative Example 5 at 400°C for 2 minutes), the heat-treated Comparative Example 5 is softer than the unheat-treated Comparative Example 4. Even with the chemical compositions of Comparative Examples 4 and 5, the quality is unstable due to the thermal effects within the mold.

[0064] Comparative Example 6 contains 1.1 wt % Mg, which is more than in this embodiment. Comparative Example 7 contains 1.2 wt % Cu, which is more than in this embodiment. In Comparative Examples 6 and 7, the Vickers hardness exceeds 100 Hv, but the elongation is low at 3%.

[0065] Comparative Example 8 contains 0.68 wt % of Fe, which is more than the present embodiment. In Comparative Example 8, the high Fe content results in low elongation of 3%.

[0066] On the other hand, all of Examples 1 to 15, which fall within the chemical composition range of this embodiment, exhibit a Vickers hardness of 80 Hv or more, a yield strength of 140 MPa or more, and an elongation of 5% or more.

[0067] Furthermore, in Examples 1 to 15, there is little difference before and after the same test (400°C) as in the Comparative Example, which simulates the thermal effects in the mold. For example, Examples 2 and 3, Examples 4 and 5, Examples 6 and 7, Examples 8 and 9, and Examples 10 and 11 each show the difference between heat treatment (400°C x 0 minutes) and no heat treatment (400°C x 2 minutes) for the same chemical composition. In all cases, there is no significant change in hardness or tensile strength with or without heat treatment, and the impact of heat is minimal, resulting in stable quality.

[0068] In addition, in Examples 1 to 15, it is also possible to improve elongation by reducing the amounts of Mg, Cu, Si, and Fe.

[0069] Fig. 1 shows the metallographic structure of Comparative Example 2. The metallographic structure of Comparative Example 2 contains Al-Fe-Si compounds in the form of large needle-like crystals with lengths of about several tens of µm, and also contains Al-Cu-Mg compounds between the Al-Fe-Si compounds.

[0070] Fig. 2 shows the metallographic structure of Example 2. The metallographic structure of Example 2 contains Al-Fe-Si compounds and Al-Fe-Si-Mg compounds in the form of needle-like crystals having lengths of about 10 µm or less, and contains Al-Cu-Mg compounds between them.

[0071] Fig. 3 shows the metallographic structure of Example 6. Fig. 4 shows the metallographic structure of Example 6 at a low magnification. The metallographic structure of Example 6 contains, as Fe compounds, Al-Fe-Si compounds, Al-Fe-Si-Mn compounds, and Al-Fe-Si-Mg compounds. The metallographic structure also contains, as Cu compounds, Al-Cu-Mg compounds and precipitates containing Cu atoms and Mg atoms.

[0072] Fig. 5 is a photograph showing the metal structure of the die-cast product. The die-cast product shown in Fig. 5 contains 8.7 wt% Si, 0.6 wt% Mg, 0.3 wt% Cu, 0.3 wt% Fe, 0.4 wt% Mn, and the balance Al.

[0073] Generally, the metal structure of die casting consists of primary α-Al, a mixed structure of eutectic Si and eutectic Al, and other compounds. When molten aluminum alloy in a tube called a sleeve is injected and filled into a mold, if the temperature of the molten alloy in the sleeve just before injection is within 50°C of the melting point of the molten alloy, and the lower the temperature, especially if it is within 30°C, the more fine granular Al with a diameter of 10 μm or less will be generated in addition to the petal-shaped or spherical primary α-Al.

[0074] Primary α-Al is the solid that first emerges from the liquid during the solidification process of the molten metal after filling the mold. For example, as shown in Figure 5, the morphology of primary α-Al can be dendritic, petal-like, or spherical. The fine-grained Al is presumably formed from the liquid with a high Si content (approximately 12% by weight of Si) that exists after the formation of primary α-Al during the solidification process, and is thought to be Al that emerged before eutectic Si. After that, eutectic Al and eutectic Si emerge simultaneously, and solidification is complete.

[0075] In Figures 1 to 3, the compounds were identified based on the backscattered electron diffraction (BSE) images obtained by a scanning electron microscope (SEM), crystal orientation analysis using a backscattered electron diffraction (EBSD) device attached to the SEM, and element mapping using an energy dispersive X-ray spectroscopy (EDS) device. Figures 4 and 5 show the results of observations using an optical microscope.

[0076] [Second embodiment] A sand cast product according to a second embodiment of the present invention contains 4.0 to 11.0 wt% Si, 0.51 to 0.80 wt% Mg, 0.1 to 1.0 wt% Cu, 0.2 wt% or less Mn, 0.30 wt% or less Fe, 0.20 wt% or less Ti, 0.005 to 0.030 wt% Sr, and a total of 0.50 wt% or less of unavoidable impurities, with the balance being Al. The product contains eutectic Si independently dispersed in the metallographic structure, and contains, as Fe compounds in the metallographic structure, one or more of an Al-Fe-Si compound and an Al-Fe-Si-Mn compound, and an Al-Fe-Si-Mg compound. The product also contains, as Cu compounds in the metallographic structure, an Al-Cu-Mg compound and precipitates containing Cu and Mg atoms. The product has a Vickers hardness of 80 Hv or more and 110 Hv or less.

[0077] In the method for manufacturing a sand-cast product according to the second embodiment of the present invention, a molten aluminum alloy is poured into a sand mold, and the casting removed from the sand mold is subjected to a solution treatment, followed by water quenching or forced air cooling in the atmosphere, and after 15 minutes or more in the atmosphere, an artificial aging treatment at 140°C to 200°C is performed.

[0078] Among gravity casting methods, the cooling rate of sand casting is 1 / 10 to 1 / 100 of the cooling rate at solidification obtained by die casting. For this reason, the metal structure of castings made by sand casting is not as fine as that obtained by die casting, and it is not easy to achieve high ductility.

[0079] Unlike die casting, sand casting, which does not involve seizure between the mold and molten metal, is best achieved by minimizing the amount of Fe in order to reduce the amount of iron compounds that cause reduced ductility. Reducing the amount of Si is also effective. Furthermore, adding a small amount of Mn, if necessary, can change the shape of the needle-like iron compounds to granular. When performing solution treatment, it is effective to granulate the eutectic Si, which is the starting point for cracks.

[0080] (sand casting products) In the sand casting product of this embodiment, if the Si content is too low, the fluidity during production is poor, and if the Si content is too high, the ductility is reduced. In this embodiment, the Si content is set to 4.0 to 11.0 wt %.

[0081] In the sand-cast product of this embodiment, Mg forms nanometer-sized precipitates with Cu and Al, contributing to improved strength. However, if too much Mg is added, ductility decreases. In this embodiment, the Mg content is 0.51 to 0.80 wt. %. Preferably, the Mg content is 0.51 to 0.70 wt. %.

[0082] In the sand-cast product of this embodiment, Cu forms nanometer-sized precipitates with Al and Mg, contributing to improved strength. However, if the Cu content is too high, corrosion resistance and ductility decrease. In this embodiment, the Cu content is 0.1 to 1.0 wt %. Preferably, the Cu content is 0.1 to 0.6 wt %.

[0083] In the sand casting product of this embodiment, Mn is added to form a compound with Fe to improve ductility. However, since the amount of Fe itself is small in this embodiment, the amount of Mn is set to 0.2 wt% or less.

[0084] In the sand cast product of this embodiment, the Fe content is set to 0.30% by weight or less, preferably 0.15% by weight or less, from the viewpoint of improving ductility.

[0085] In the sand-cast product of this embodiment, Ti is added as a grain refiner for the purpose of suppressing the occurrence of shrinkage cavities in the cast product. Since there is no improvement in the effect even if Ti is added in an amount exceeding 0.20 wt%, the Ti content is set to 0.20 wt% or less.

[0086] In the sand-cast product of this embodiment, the amount of Sr required to refine the eutectic Si grains varies depending on the amount of P contained in the molten alloy, but to ensure the refinement effect, the Sr amount is set to 0.005 to 0.030 wt%. However, if the Sr amount is too high, Sr oxides will form and be mixed into the product, reducing quality. Preferably, the Sr amount is set to 0.005 to 0.020 wt%.

[0087] (Metal structure of sand casting products) The sand casting product of this embodiment contains eutectic Si dispersed independently in the metallographic structure. The Fe compounds contained in the metallographic structure include at least one of an Al-Fe-Si compound and an Al-Fe-Si-Mn compound, as well as an Al-Fe-Si-Mg compound. The Cu compounds contained in the metallographic structure include an Al-Cu-Mg compound and precipitates containing Cu and Mg atoms. The Al-Cu-Mg compounds also include Al-Cu-Mg-Si compounds containing Si in addition to Cu and Mg.

[0088] The eutectic silicon that is dispersed independently in the metal structure is formed, for example, by solution treatment at about 500°C, when the eutectic silicon that was connected in a network state breaks down, becomes granular, and becomes independent.

[0089] Furthermore, by solution treatment at temperatures exceeding 500°C, a certain proportion of Cu atoms and Mg atoms constituting the Al-Cu-Mg compound are temporarily dissolved in the aluminum matrix.

[0090] Figure 6 is a photograph showing the metallographic structure of a sand-cast product before and after solution treatment. Figure 6 shows the results of observation using an optical microscope. As shown in Figure 6, the metallographic structure changes before and after solution treatment. The metallographic structure contains an aluminum matrix, Al-Cu-Mg compounds, and compounds containing iron. In the structure shown in Figure 6, the lightest colored part is the aluminum matrix.

[0091] In the structure shown in Figure 6, the darkest part, indicated by the black arrow, is the Al-Cu-Mg compound. For example, as shown in Figure 6(a), the Al-Cu-Mg compound has a morphology surrounded by a linear outline, e.g., a polygonal shape, before solution treatment. On the other hand, as shown in Figure 6(b), the Al-Cu-Mg compound has a morphology with a smooth outline after solution treatment at, for example, 530°C for 2 hours.

[0092] In the structure shown in Figure 6, the area indicated by the white arrow is an Fe-containing compound, and is intermediate in brightness between the Al-Cu-Mg compound and the aluminum matrix. For example, as shown in Figures 6(a) and 6(b), the Fe-containing compound shows little change in morphology before and after solution treatment.

[0093] The sizes of the Al-Fe-Si compounds, Al-Fe-Si-Mn compounds, Al-Fe-Si-Mg compounds, and Al-Cu-Mg compounds in the metal structure are mainly 2 μm or more.

[0094] The size of the precipitates containing Cu atoms and Mg atoms in the metal structure is, for example, about 3 nm to 60 nm. The precipitates include, for example, GP zones and intermediate phases as metastable phases, similar to those in the first embodiment.

[0095] (Method of manufacturing sand casting products) The method for producing a sand cast product in this embodiment is, for example, as follows.

[0096] Molten aluminum alloy is poured into a sand mold and then solidified within the mold. Within the solidification temperature range where the alloy changes from liquid to solid, Al-Fe-Si compounds, Al-Fe-Si-Mn compounds, Al-Fe-Si-Mg compounds, and Al-Cu-Mg compounds are crystallized. During the cooling process after solidification within the sand mold, coarse precipitates containing Cu and Mg atoms may be generated.

[0097] The castings removed from the sand molds are subjected to solution treatment. Fig. 7 is a photograph showing the effect of the solution treatment temperature on the metal structure of the sand-cast product. Fig. 7 shows the results of observation using an optical microscope. Figs. 8 to 11 are graphs showing the effect of the solution treatment temperature and treatment time on the tensile strength, proof stress, elongation, and Vickers hardness of the sand-cast product.

[0098] For example, as shown in Figure 7(b), when solution treatment is performed up to 530°C, the burning caused by the melting of Cu-containing compounds in the metal structure is small and not very noticeable. However, as shown in Figure 7(c), when solution treatment is performed at 550°C, the burning phenomenon becomes more pronounced. As a result, a large amount of Cu and Mg dissolves in the aluminum matrix, which tends to increase the yield strength (Figure 9) and Vickers hardness (Figure 11). On the other hand, tiny cavities (pores larger than 30 μm) occur after the Al-Cu-Mg compounds dissolve, resulting in a decrease in elongation (Figure 10).

[0099] As shown in Figure 7(a), burning is unlikely to occur with solution treatment at 500°C or below. However, because Al-Cu-Mg compounds are difficult to dissolve in the aluminum matrix, long heat treatment times, such as over 15 hours, are required. Heat treatment times of up to 6 hours are unlikely to improve strength properties (Figures 8, 9, and 11) and elongation (Figure 10).

[0100] For example, as shown in Figure 10, to ensure an elongation of 5% or more, heat treatment is performed in a temperature range of more than 500°C and not more than 540°C. Note that within this temperature range, the required heat treatment time varies depending on the treatment temperature. For example, the heat treatment time for solution treatment is 6 to 12 hours at 510°C, 3 to 10 hours at 520°C, 1 to 8 hours at 530°C, and 0.5 to 2 hours at 540°C.

[0101] Furthermore, as shown in Figure 10, if an even higher elongation of 7% or more is to be achieved by solution treatment, it is effective to perform heat treatment at 520°C or higher and 540°C or lower. In this temperature range, even if minute voids are present, their size will be 10 μm or less. Such minute voids do not adversely affect the mechanical properties, and in fact, they result in good mechanical properties.

[0102] After cooling in the sand mold, the material is subjected to solution treatment. The solution treatment is carried out, for example, at 520 to 540°C. This causes the Cu and Mg atoms in the coarse precipitates to dissolve in the aluminum in an atomic state. Furthermore, by performing solution treatment at temperatures above 500°C, the eutectic Si, which had been connected in a fibrous form, changes to a granular form, both three-dimensionally and two-dimensionally, and becomes independently dispersed.

[0103] After the solution treatment, the steel is water quenched or forced air-cooled in the air, and after 15 minutes or more in the air, it is subjected to artificial aging treatment. The artificial aging treatment is carried out, for example, at 140°C to 200°C. This artificial aging treatment causes nanometer-sized precipitates to precipitate. The precipitates contain, for example, Cu atoms and Mg atoms, and contribute to age hardening.

[0104] [Example] (Comparative Examples and Examples of Sand Cast Products) Table 2 shows the chemical composition and mechanical properties of the sand-cast product. The shape of the sand-cast product is a flat plate with a wall thickness of 3 mm, width of 100 mm, and length of 100 mm, and the casting weight is 400 g. A 3 mm section of this was used for the test.

[0105] [Table 2]

[0106] The sand-cast products were solution treated at 530°C, then removed from the solution furnace and water-cooled or forced air-cooled using a fan (approximately 0.5°C / sec). After that, they were left at room temperature for 2 hours and then subjected to various aging treatments.

[0107] Comparative Examples 9 to 14 differ from the range of chemical compositions of this embodiment in that they do not contain Cu. Comparative Examples 9 to 12 all exhibit a Vickers hardness of 80 Hv or more, but their tensile strengths are 250 to 290 MPa, not reaching 300 MPa. Meanwhile, the tensile strengths of Comparative Examples 9 to 12 are approximately 50 MPa higher than the yield strength (170 to 250 MPa) of Comparative Examples 9 to 12, which are obtained by solution treatment, water quenching, and aging treatment. However, as shown in Comparative Examples 13 and 14, which have the same chemical compositions as Comparative Examples 9 to 12, lowering the aging temperature from 180°C to 160°C to reduce the yield strength results in a decrease in both hardness and tensile strength, which is different from the Vickers hardness of 85 Hv or more, the yield strength equivalent to 150 MPa, and the tensile strength equivalent to 300 MPa obtained in the die-cast product (Table 1).

[0108] Examples 16 to 26 are within the range of the chemical composition of this embodiment. In Examples 16 to 26, by selecting the Mg content, Cu content, and Si content, it is possible to exhibit a yield strength of 136 MPa or more and a Vickers hardness of 85 Hv or more, and it is also possible to ensure a tensile strength equivalent to 300 MPa and good elongation. In Examples 25 and 26, after solution treatment, whether air-cooled or water-cooled, and then left at room temperature, artificial aging at 160°C showed higher tensile strength than Comparative Examples 13 and 14.

[0109] [Third embodiment] A sand cast product according to a third embodiment of the present invention contains 4.0 to 11.0 wt% Si, 0.51 to 0.80 wt% Mg, 0.1 to 1.0 wt% Cu, 0.2 wt% or less Mn, 0.30 wt% or less Fe, 0.20 wt% or less Ti, 0.005 to 0.030 wt% Sr, and a total of 0.50 wt% or less unavoidable impurities, with the balance being Al. The metallographic structure contains, as Fe compounds, one or more of an Al-Fe-Si compound and an Al-Fe-Si-Mn compound, and an Al-Fe-Si-Mg compound. The metallographic structure contains, as Cu compounds, an Al-Cu-Mg compound and precipitates containing Cu and Mg atoms. The metallographic structure has a Vickers hardness of 80 Hv or more and 110 Hv or less.

[0110] In a method for manufacturing a sand-cast product according to a third embodiment of the present invention, a molten aluminum alloy is poured into a sand mold, and the molten aluminum alloy in the sand mold is solidified at an average cooling rate of 0.8°C / second or more in a solidification range from the melting point to the binary eutectic temperature of 577°C. Thereafter, the casting in the sand mold is cooled at an average cooling rate of 0.08°C / second or more in a temperature range from 300°C to 200°C, and the casting is removed from the sand mold and subjected to an artificial aging treatment.

[0111] (Sand casting products with controlled cooling inside the mold) In the sand casting product of this embodiment, if the Si content is too low, the molten metal flow is poor, and if the Si content is too high, the ductility is reduced. In this embodiment, the Si content is set to 4.0 to 11.0 wt %.

[0112] In the sand-cast product of this embodiment, Mg forms nanometer-sized precipitates with Cu and Al, contributing to improved strength. However, if too much Mg is added, ductility decreases. In this embodiment, the Mg content is 0.51 to 0.80 wt. %. Preferably, the Mg content is 0.51 to 0.70 wt. %.

[0113] In the sand-cast product of this embodiment, Cu forms nanometer-sized precipitates with Al and Mg, contributing to improved strength. However, if the Cu content is too high, corrosion resistance and ductility decrease. In this embodiment, the Cu content is 0.1 to 1.0 wt %. Preferably, the Cu content is 0.1 to 0.6 wt %.

[0114] In the sand casting product of this embodiment, Mn is added to form a compound with Fe to improve ductility. However, since the amount of Fe itself is small in this embodiment, the amount of Mn is set to 0.2 wt% or less.

[0115] In the sand cast product of this embodiment, the Fe content is set to 0.30% by weight or less, preferably 0.15% by weight or less, from the viewpoint of improving ductility.

[0116] In the sand-cast product of this embodiment, Ti is added as a grain refiner for the purpose of suppressing the occurrence of shrinkage cavities in the cast product. Since there is no improvement in the effect even if Ti is added in an amount exceeding 0.20 wt%, the Ti content is set to 0.20 wt% or less.

[0117] In the sand casting product of this embodiment, the Sr content is set to 0.005 to 0.030 wt% in consideration of the reliability of the grain refinement effect. However, if the Sr content is too high, Sr oxides are formed and mixed into the product, degrading the quality, so the Sr content is preferably set to 0.005 to 0.020 wt%.

[0118] (Metal structure of sand casting products with in-mold cooling control) The sand casting product of this embodiment contains, in its metal structure, Fe compounds including at least one of Al-Fe-Si compounds and Al-Fe-Si-Mn compounds, as well as Al-Fe-Si-Mg compounds. The metal structure also contains, as Cu compounds, Al-Cu-Mg compounds and precipitates containing Cu and Mg atoms. The precipitates include, for example, the GP zones and intermediate phases described in the first embodiment.

[0119] The sizes of the Al-Fe-Si compounds, Al-Fe-Si-Mn compounds, Al-Fe-Si-Mg compounds, and Al-Cu-Mg compounds in the metal structure are mainly 2 μm or more.

[0120] The size of the precipitates containing Cu atoms and Mg atoms in the metal structure is, for example, about 3 nm to 60 nm. The precipitates include, for example, GP zones and intermediate phases as metastable phases, similar to those in the first embodiment.

[0121] (Manufacturing method of sand casting products by controlling cooling inside the mold) The method for producing a sand cast product in this embodiment is, for example, as follows.

[0122] Molten aluminum alloy is poured into a sand mold, and then cooled inside the sand mold. Cooling control inside the mold is carried out as follows:

[0123] When cooling in the mold, the solidification is performed at an average cooling rate of 0.8°C / s or more in the solidification section from the melting point to the binary eutectic temperature of 577°C. By increasing the average cooling rate in the solidification section, it is possible to solidify a large amount of Cu and Mg in the atomic state in the primary aluminum. Furthermore, in this solidification section and the section up to the final solidification temperature, Al-Fe-Si compounds, Al-Fe-Si-Mn compounds, Al-Fe-Si-Mg compounds, etc. are crystallized. Note that a slower average cooling rate is likely to cause shrinkage cavities inside the casting. Preferably, this average cooling rate is 1.0°C / s or more.

[0124] After passing through the solidification zone, the material is cooled at a relatively fast average cooling rate of 0.08°C / sec or more in the temperature zone from 300°C to 200°C, which suppresses the generation of coarse Al-Cu-Mg precipitates after passing through the solidification zone, thereby preventing a decrease in strength.

[0125] In order to increase the average cooling rate in the solidification section and the temperature section from 300°C to 200°C, it is possible to use sand with high thermal conductivity, sand with fine grain size, suction from outside the sand mold, cooling from outside the sand mold, and passing water through the sand mold.

[0126] After casting, the alloy is subjected to artificial aging treatment. The artificial aging treatment is carried out, for example, at a temperature range of 140°C to 200°C. This artificial aging treatment causes nanometer-sized precipitates to precipitate. The precipitates contain, for example, Cu atoms and Mg atoms, and contribute to age hardening.

[0127] [Example] (Comparative examples and examples of sand casting products with in-mold cooling control) Table 3 shows the chemical composition and mechanical properties of sand-cast products produced by in-mold cooling control. The shape of the sand-cast product is a flat plate with a wall thickness of 3 mm, width of 100 mm, and length of 100 mm, and the casting weight is 400 g. A 3 mm section of this was used for testing.

[0128] [Table 3]

[0129] The sand-cast products shown in Table 3 were not subjected to solution treatment, but were only subjected to artificial aging treatment after casting.

[0130] In Examples 27 to 41, three types of aging treatments (180°C x 6 hours, 160°C x 9 hours, 190°C x 2 hours) were performed. When the solidification rate and post-solidification cooling rate of the casting were to be increased, zircon-based sand was used as the sand material.

[0131] Silica sand was used in Comparative Examples 15 to 17. The passing speed from 300°C to 200°C was slow at 0.06°C / sec or less. Comparative Examples 15 to 17 contained Cu and Mg, but Al-Cu-Mg compounds precipitated coarsely due to the heat effect during the passing from 300°C to 200°C, resulting in a low Vickers hardness of 75Hv or less.

[0132] In Comparative Example 18, zircon-based sand was used. The temperature drop rate from 300°C to 200°C was fast at 0.08°C / sec, but the solidification rate was slow at 0.5°C / sec due to the application of a mold wash. Therefore, the amount of solid solution of Cu and Mg decreased during the temperature drop process, the amount of precipitation hardening during artificial aging treatment (180°C x 6 hours) was small, and the Vickers hardness was low at 70Hv.

[0133] The Cu content in Comparative Example 19 and the Mg content in Comparative Example 20 are less than the range of the chemical composition of this embodiment. In Comparative Examples 19 and 20, even though the solidification rate and post-solidification cooling rate of the casting were increased to 1.0°C / sec and 0.12°C / sec, respectively, by using zircon-based sand, the Vickers hardness was low at 74 Hv or less.

[0134] Examples 27 to 41 are within the range of the chemical composition of this embodiment. In Examples 27 to 41, the Mg content, Cu content, and Si content were selected, and the solidification rate and post-solidification cooling rate were appropriately controlled within the temperature range of this embodiment, so all of them exhibited a Vickers hardness of 80 Hv or more.

[0135] [Fourth embodiment] A die-cast product according to a fourth embodiment of the present invention contains 6.0 to 11.0 weight % Si, 0.51 to 1.00 weight % Mg, 0.1 to 1.0 weight % Cu, 0.1 to 0.7 weight % Mn, 0.50 weight % or less Fe, 0.20 weight % or less Ti, 0.03 weight % or less Sr, 0.0050 weight % or less Be, and a total of 0.50 weight % or less of unavoidable impurities, with the balance being Al. The die-cast product contains, as Fe compounds in the metallographic structure, Al-Fe-Si compounds, Al-Fe-Si-Mn compounds, and Al-Fe-Si-Mg compounds, and as Cu compounds in the metallographic structure, Al-Cu-Mg compounds and precipitates containing Cu atoms and Mg atoms. The die-cast product has a Vickers hardness of 80 Hv or more and 110 Hv or less.

[0136] (Die-cast products) The die-cast product of this embodiment contains Si, Mg, Cu, Mn, Fe, Ti, Sr, and inevitable impurities in the same weight percentages as in the first embodiment, and may further contain Be.

[0137] In the die-cast product of this embodiment, Sr, which is added to improve elongation, has a high oxide-generating ability and therefore reduces the flowability of the molten metal. Furthermore, a high content of Mg also reduces the flowability of the molten metal. Therefore, in order to suppress the oxidation of Sr and Mg and improve the flowability of the molten metal, 0.0050 wt% or less of Be is added. To improve the flowability of the molten metal, the Be content is preferably 0.0005 wt% to 0.0050 wt%.

[0138] (Metal structure of die-cast products) Basically, the die-cast product of this embodiment has the same metal structure as that of the first example.

[0139] (Manufacturing method for die-cast products) Basically, the die-cast product of this embodiment is manufactured in the same manner as in the first embodiment.

[0140] [Example] (Example of die-cast product) Table 4 shows the chemical composition and mechanical properties of the die-cast product according to this embodiment. The test specimens in the examples shown in Table 4 contain Al, 9.0 wt% Si, 0.55 wt% Mg, 0.25 wt% Cu, 0.4 wt% Fe, 0.4 wt% Mn, and 0.11 wt% Ti. The Be and Sr contents for each example are also shown in Table 4.

[0141] [Table 4]

[0142] The test pieces of the examples shown in Table 4 were manufactured in the same manner as in Examples 1 to 15 of the first embodiment, and the casting test procedures were also the same as in the first embodiment. Note that the test pieces for which the Vickers hardness was measured were not subjected to heat treatment.

[0143] Table 4 shows the test results for the presence or absence of poor running of the molten metal in the 3.5 mm thick portion of the test piece.

[0144] Examples 42 to 44 do not contain Sr. As shown in Example 42, when the gate speed is as fast as 82 m / s, there is no poor running of the molten metal even if Be is not contained. As shown in Examples 43 and 44, when the gate speed is as slow as 59 m / s, Example 43, which does not contain Be, experiences poor running of the molten metal, but Example 44, which contains 0.0012 wt% Be, does not experience poor running of the molten metal.

[0145] Examples 45 to 47 contain 0.005 wt% Sr. As shown in Example 45, when the gate speed is as fast as 82 m / s, there is no molten metal running defect even without containing Be. As shown in Examples 46 and 47, when the gate speed is as slow as 59 m / s, Example 46, which does not contain Be, experiences molten metal running defect, but Example 47, which contains 0.0011 wt% Be, does not experience molten metal running defect.

[0146] Examples 48 and 49 contain 0.012 wt% Sr. As shown in Examples 48 and 49, even when the gate speed is as slow as 59 m / s, Examples 48 and 49, which contain 0.0021 wt% and 0.0033 wt% Be, respectively, do not experience poor running.

[0147] As described above, if Be is not added, poor molten metal running occurs when the gate speed is reduced by about 30%. On the other hand, adding 0.0005 wt% or more of Be improves poor molten metal running, regardless of whether Sr is added or not.

[0148] Furthermore, as shown in Examples 45 to 47 in Table 4, there is no difference in hardness depending on the Be content, and all of them show a Vickers hardness of 80 Hv or more.

[0149] [Fifth embodiment] A sand cast product according to a fifth embodiment of the present invention contains 4.0 to 11.0 wt% Si, 0.51 to 0.80 wt% Mg, 0.1 to 1.0 wt% Cu, 0.2 wt% or less Mn, 0.30 wt% or less Fe, 0.20 wt% or less Ti, 0.005 to 0.030 wt% Sr, 0.0050 wt% or less Be, and a total of 0.50 wt% or less unavoidable impurities, with the balance being Al. The metallographic structure contains, as Fe compounds, one or more of an Al-Fe-Si compound and an Al-Fe-Si-Mn compound, and an Al-Fe-Si-Mg compound. The metallographic structure contains, as Cu compounds, an Al-Cu-Mg compound and precipitates containing Cu and Mg atoms. The metallographic structure contains, as Cu compounds, an Al-Cu-Mg compound and precipitates containing Cu and Mg atoms. The Vickers hardness is 80 Hv or more and 110 Hv or less.

[0150] (sand casting products) The sand cast product of this embodiment contains Si, Mg, Cu, Mn, Fe, Ti, Sr, and inevitable impurities in the same weight percentages as those of the second and third embodiments, but may also contain Be.

[0151] In the sand casting product of this embodiment, Sr, which is added to improve elongation, has a high oxide-generating ability and therefore reduces the flowability of the molten metal. Furthermore, a high content of Mg also reduces the flowability of the molten metal. Therefore, in order to suppress the oxidation of Sr and Mg and improve the flowability of the molten metal, 0.0050 wt% or less of Be is added. To improve the flowability of the molten metal, the Be content is preferably 0.0005 wt% to 0.0050 wt%.

[0152] (Metal structure of sand casting products) Basically, the sand cast product of this embodiment has the same metal structure as the second and third examples.

[0153] (Method of manufacturing sand casting products) Basically, it is manufactured in the same manner as in the second and third embodiments.

[0154] [Example] (Example of sand casting product) Table 5 shows the chemical compositions and mechanical properties of the sand casting products according to this embodiment. The test pieces of the comparative examples and examples shown in Table 5 contain Al, 7.0 wt% Si, 0.57 wt% Mg, 0.30 wt% Cu, and 0.14 wt% Ti. The Be and Sr contents of each comparative example and example are also shown in Table 5.

[0155] [Table 5]

[0156] For the in-mold flow length test, the results of which are shown in Table 5, a pouring basin was placed on the top of the mold, the stopper was removed, and the molten metal was filled into the mold in an Ar atmosphere. The length from the center of the spiral to the tip was measured. The dimensions of the in-mold flow length test were 10 mm thick x 10 mm wide x flow length (mm), and the casting temperature was 650°C. The test specimens used to measure Vickers hardness were 10 mm square sand-cast materials that underwent T6 treatment. Specifically, the test was performed at 530°C for 2 hours, followed by water quenching, then left at room temperature for 2 hours, and finally at 160°C for 5 hours.

[0157] Table 5 shows the test results for the flow length and hardness of the test specimens.

[0158] Comparative Examples 21 to 23 do not contain Sr. Comparative Examples 21 to 23 contain 0.0000 to 0.0011 wt % Be. As shown in Comparative Examples 21 to 23, by increasing the Be content, the flow length increases and the molten metal flowability improves.

[0159] Examples 50 to 54 contain 0.012 wt % Sr. Examples 50 to 54 contain 0.0000 to 0.0032 wt % Be. As shown in Examples 50 to 54, the more Be added, the longer the flow length and the more improved the fluidity of the molten metal.

[0160] As shown in Table 5, the addition of 0.0005 wt% or more of Be increases the flow length and improves the fluidity of the molten metal, regardless of whether Sr is added or not. Note that Examples 50 to 54, which contain Sr, require a higher amount of Be to achieve the same flow length compared to Comparative Examples 21 to 23, which do not contain Sr.

[0161] Furthermore, as shown in Examples 50 to 54 in Table 5, there is no difference in hardness depending on the Be content, and all of them show a Vickers hardness of 80 Hv or more.

Claims

1. containing 4.0 to 11.0 mass% Si, 0.51 to 0.80 mass% Mg, 0.1 to 1.0 mass% Cu, 0.2 mass% or less Mn, 0.30 mass% or less Fe, 0.20 mass% or less Ti, 0.005 to 0.030 mass% Sr, and inevitable impurities in a total amount of 0.50 mass% or less, with the balance being Al; Contains eutectic Si independently dispersed in the metal structure, The metal structure contains, as Fe compounds, at least one of an Al—Fe—Si compound and an Al—Fe—Si—Mn compound, and an Al—Fe—Si—Mg compound, The metal structure contains, as Cu compounds, Al-Cu-Mg compounds and precipitates containing Cu atoms and Mg atoms, Vickers hardness is 80Hv or more and 110Hv or less Sand casting products.

2. Contains one or more of 0.51 to 0.70 mass% Mg, 0.1 to 0.6 mass% Cu, 0.15 mass% or less Fe, and 0.005 to 0.020 mass% Sr.

2. The sand-cast product according to claim 1.

3. Molten aluminum alloy is poured into a sand mold, The casting removed from the sand mold is subjected to a solution treatment, and then water quenching or forced air cooling in the atmosphere. After 15 minutes or more in the atmosphere, artificial aging treatment is performed at 140°C to 200°C. A method for producing the sand casting product according to claim 1 or 2 Manufacturing method for sand casting products.

4. containing 4.0 to 11.0 mass% Si, 0.51 to 0.80 mass% Mg, 0.1 to 1.0 mass% Cu, 0.2 mass% or less Mn, 0.30 mass% or less Fe, 0.20 mass% or less Ti, 0.005 to 0.030 mass% Sr, and inevitable impurities in a total amount of 0.50 mass% or less, with the balance being Al; The metal structure contains, as Fe compounds, at least one of an Al—Fe—Si compound and an Al—Fe—Si—Mn compound, and an Al—Fe—Si—Mg compound, The metal structure contains, as Cu compounds, Al-Cu-Mg compounds and precipitates containing Cu atoms and Mg atoms, Vickers hardness is 80Hv or more and 110Hv or less Sand casting products.

5. Contains one or more of 0.51 to 0.70 mass% Mg, 0.1 to 0.6 mass% Cu, 0.15 mass% or less Fe, and 0.005 to 0.02 mass% Sr.

5. The sand-cast product according to claim 4.

6. Molten aluminum alloy is poured into a sand mold, The molten aluminum alloy in the sand mold is solidified at an average cooling rate of 0.8°C / second or more in a solidification section from the melting point to a binary eutectic temperature of 577°C, Thereafter, the casting in the sand mold is cooled in a temperature range from 300°C to 200°C at an average cooling rate of 0.08°C / second or more; The casting removed from the sand mold is subjected to artificial aging treatment. A method for producing the sand casting product according to claim 4 or 5. Manufacturing method for sand casting products.

7. The artificial aging treatment is carried out at a temperature range of 140°C to 200°C. A method for producing a sand-cast product according to claim 6.

8. When the casting is removed from the sand mold, the Al-Cu-Mg compounds are generated as polygonal compounds having linear outer shapes, but are converted into granular compounds having smooth outer shapes by the solution treatment. A method for producing a sand-cast product according to claim 3.

9. The temperature of the solution treatment is higher than 500°C and not higher than 540°C. A method for producing a sand-cast product according to claim 3.

10. The temperature of the solution treatment is 520°C or higher and 540°C or lower. A method for producing a sand-cast product according to claim 3.

11. containing 4.0 to 11.0 mass% Si, 0.51 to 0.80 mass% Mg, 0.1 to 1.0 mass% Cu, 0.2 mass% or less Mn, 0.30 mass% or less Fe, 0.20 mass% or less Ti, 0.005 to 0.030 mass% Sr, 0.0050 mass% or less Be, and inevitable impurities in a total amount of 0.50 mass% or less, with the balance being Al; The metal structure contains, as Fe compounds, at least one of an Al—Fe—Si compound and an Al—Fe—Si—Mn compound, and an Al—Fe—Si—Mg compound, The metal structure contains, as Cu compounds, Al-Cu-Mg compounds and precipitates containing Cu atoms and Mg atoms, Vickers hardness is 80Hv or more and 110Hv or less Sand casting products.

12. Contains one or more of 0.51 to 0.70 mass% Mg, 0.1 to 0.6 mass% Cu, 0.15 mass% or less Fe, and 0.005 to 0.020 mass% Sr. The sand-cast product according to claim 11.

13. Molten aluminum alloy is poured into a sand mold, The casting removed from the sand mold is subjected to a solution treatment, and then water quenching or forced air cooling in the atmosphere. After 15 minutes or more in the atmosphere, artificial aging treatment is performed at 140°C to 200°C. A method for producing the sand casting product according to claim 11 or 12 Manufacturing method for sand casting products.

14. Molten aluminum alloy is poured into a sand mold, The molten aluminum alloy in the sand mold is solidified at an average cooling rate of 0.8°C / second or more in a solidification section from the melting point to a binary eutectic temperature of 577°C, Thereafter, the casting in the sand mold is cooled in a temperature range from 300°C to 200°C at an average cooling rate of 0.08°C / second or more; The casting removed from the sand mold is subjected to artificial aging treatment. A method for producing the sand casting product according to claim 11 or 12 Manufacturing method for sand casting products.

15. The artificial aging treatment is carried out at a temperature range of 140°C to 200°C. A method for producing a sand-cast product according to claim 14.

16. The Al-Cu-Mg compound is characterized in that it has a smooth outline and is not surrounded by a linear outline.

13. The sand-cast product according to claim 11 or 12.

17. The temperature of the solution treatment is higher than 500°C and not higher than 540°C. The method for producing a sand-cast product according to claim 13.

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