Aluminum alloy and method of manufacturing the same

Abstract

To provide an aluminum alloy in which natural aging is suppressed.SOLUTION: An aluminum alloy comprises 5.0 to 12.0 mass% of Si, 0.15 to 0.75 mass% of Mg, 0.05 to 0.20 mass% of Fe, and 0.25 to 1.0 mass% of Mn, the remainder consisting of Al and impurities. The aluminum alloy includes at least precipitates of Al-Si-Fe-Mn compounds and Mg-Si compounds. When Si, Mg, Fe or Mn is observed using TEM mapping at a 400 nm×400 nm field, precipitates of Al-Si-Fe-Mn compounds are observed, along with precipitates of Mg-Si compounds extending from some of the precipitates of Al-Si-Fe-Mn compounds.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an aluminum alloy and a method for producing the same. [Background technology]

[0002] Lighter automobile parts can improve fuel economy and reduce power consumption, so there are currently studies being conducted on replacing conventionally used iron-based materials with aluminum materials or aluminum alloys.

[0003] For example, Patent Document 1 describes a high-strength aluminum alloy with excellent castability and workability, which is characterized by containing, when the whole is taken as 100 mass%, 3.5 mass% to 7.5 mass% silicon (Si), 0.45 mass% to 0.8 mass% magnesium (Mg), and 0.05 mass% to 0.35 mass% chromium (Cr), with the remainder being aluminum (Al) and unavoidable impurities.

[0004] Patent Document 2 describes an aluminum alloy sheet made of an Al-Mg-Si aluminum alloy, characterized in that in a differential scanning calorimetry curve obtained by heating at a rate of 20°C / min, the aluminum alloy sheet has an endothermic peak with a height a of 1.0 to 5.0 mW / g in the temperature range of 150 to 230°C and two or more exothermic peaks in the temperature range of 230 to 270°C, and the ratio b1 / b2 of the peak height b1 on the low-temperature side to the peak height b2 on the high-temperature side of the exothermic peaks is 0.80 or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-18875 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-14541 Summary of the Invention [Problem to be solved by the invention]

[0006] In the prior art, the cast aluminum alloy is subjected to additional heat treatment, such as a solution heat treatment and / or an aging heat treatment. This heat treatment causes Mg-Si precipitates to form in the aluminum alloy. These precipitates provide the necessary hardness for the part and inhibit natural aging. Therefore, in the prior art, the hardness of the aluminum alloy is increased by the precipitates, thereby achieving high strength.

[0007] On the other hand, the heat treatment process has the drawback that it can cause deformation of the parts due to heat treatment strain, and that it can lead to high costs and high CO2 emissions due to the thermal energy consumption.

[0008] Therefore, one object of the present invention is to provide an aluminum alloy in which natural aging is suppressed. Another object of the present invention is to provide a method for producing an aluminum alloy in which natural aging is suppressed even without a heat treatment step after casting. [Means for solving the problem]

[0009] The present inventors have investigated various means for solving the above problems. As a result, they have found that in the production of an aluminum alloy material containing Si, Mg, manganese (Mn), and iron (Fe), an aluminum alloy in which natural aging is suppressed can be produced by controlling the cooling process of the molten alloy during casting, and have completed the present invention. In the aluminum alloy of the present invention, by controlling the cooling process of the molten alloy during casting, Mg-Si compounds precipitate from precipitates of Al-Si-Fe-Mn compounds as the initiation point. In other words, the precipitates of Al-Si-Fe-Mn compounds and precipitates of Mg-Si compounds are in contact with each other.

[0010] That is, an embodiment of the present invention is as follows. (1) An aluminum alloy containing 5.0 to 12.0 mass% Si, 0.15 to 0.75 mass% Mg, 0.05 to 0.20 mass% Fe, and 0.25 to 1.0 mass% Mn, with the remainder being Al and impurities; The alloy contains at least precipitates of Al-Si-Fe-Mn compounds and precipitates of Mg-Si compounds, An aluminum alloy in which, when Si, Mg, Fe, or Mn is observed by TEM mapping in a field of view of 400 nm x 400 nm, precipitates of Al-Si-Fe-Mn-based compounds and precipitates of Mg-Si-based compounds formed so as to extend from part of the precipitates of the Al-Si-Fe-Mn-based compounds are observed. (2) Precipitates of Al-Si-Fe-Mn compounds are observed by the coincidence of the observation positions of Si, Fe, and Mn in TEM mapping. The aluminum alloy according to (1), wherein the precipitates of the Mg—Si compound are observed by the coincidence of the observation positions of Si and Mg in TEM mapping. (3) The aluminum alloy according to (1) or (2), wherein the observed shapes of the precipitates of the Al-Si-Fe-Mn compound and the observed shapes of the precipitates of the Mg-Si compound formed so as to extend from a part of the precipitates of the Al-Si-Fe-Mn compound are needle-like or rod-like, respectively, and have lengths of 10 nm or more. (4) A method for producing the aluminum alloy according to any one of (1) to (3), preparing a raw material for an aluminum alloy containing 5.0 to 12.0 mass% Si, 0.15 to 0.75 mass% Mg, 0.05 to 0.20 mass% Fe, and 0.25 to 1.0 mass% Mn, with the remainder consisting of Al and impurities; a step of heating an aluminum alloy raw material to prepare a molten alloy; Pouring the molten alloy into a mold; and The process of cooling and solidifying the poured molten alloy Including, The step of cooling and solidifying includes a step of holding the molten alloy at a temperature between 380 and 460°C for 5 minutes or more. (5) The manufacturing method according to (4), which does not include a step of heat treating the aluminum alloy after the step of cooling and solidifying it. [Effects of the Invention]

[0011] According to one aspect of the present invention, an aluminum alloy in which natural aging is suppressed can be provided. Also, according to one aspect of the present invention, a method for producing an aluminum alloy in which natural aging is suppressed without performing a heat treatment after casting can be provided. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a graph showing the Vickers hardness of Al—Si-based aluminum alloys of Example 1 and Comparative Examples 1 and 2 after casting and forced aging. [Figure 2] 1 is a diagram showing TEM mapping (400 nm × 400 nm) of the Al-Si-based aluminum alloy of Example 1. [Figure 3] FIG. 2 is a diagram showing TEM mapping (400 nm×400 nm) of the Al—Si-based aluminum alloy of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0013] This embodiment will be described in detail below.

[0014] In this specification, the features of the present invention will be explained with reference to the drawings as appropriate. Note that the aluminum alloy and its manufacturing method of the present invention are not limited to the following embodiments, and can be embodied in various forms incorporating modifications and improvements that can be made by those skilled in the art, without departing from the gist of the present invention. Furthermore, in the present invention, the expression "numerical value (lower limit) to numerical value (upper limit)" indicates a range including the lower limit and the upper limit.

[0015] The present embodiment is an aluminum alloy containing 5.0 to 12.0 mass% Si, 0.15 to 0.75 mass% Mg, 0.05 to 0.20 mass% Fe, and 0.25 to 1.0 mass% Mn, with the remainder being Al and impurities, and containing at least precipitates of Al-Si-Fe-Mn compounds and precipitates of Mg-Si compounds. When Si, Mg, Fe, or Mn is observed by TEM mapping in a field of view of 400 nm × 400 nm, precipitates of Al-Si-Fe-Mn compounds and precipitates of Mg-Si compounds formed so as to extend from part of the precipitates of Al-Si-Fe-Mn compounds are observed.

[0016] This embodiment can provide an aluminum alloy with suppressed natural aging. In the aluminum alloy according to this embodiment, precipitates of Al-Si-Fe-Mn compounds and precipitates of Mg-Si compounds that extend from a portion of the precipitates of the Al-Si-Fe-Mn compounds are observed. When the precipitates of the Al-Si-Fe-Mn compounds and the precipitates of the Mg-Si compounds are formed in this manner, a large amount of Mg-Si compounds that cause natural aging can be precipitated in advance, and the precipitation of Mg-Si compounds that cause natural aging can be suppressed after the aluminum alloy is manufactured. As a result, it is believed that natural aging can be suppressed after the aluminum alloy is manufactured.

[0017] The Si content is 5.0 to 12.0 mass% based on the total mass of the aluminum alloy. By setting the Si content within this range, castability can be improved. The Si content is preferably 6.0 mass% or more, 7.0 mass% or more, or 8.0 mass% or more. The Si content is preferably 11.0 mass% or less, or 10.0 mass% or less. The Si content can be measured by ICP atomic emission spectroscopy.

[0018] The Mg content is 0.15 to 0.75 mass% based on the total mass of the aluminum alloy. Mg contributes to the refinement of eutectic Si. Although the reason for this is not entirely clear, it is believed that the presence of Mg changes the interfacial energy between Al and Si, causing Mg enrichment at the Si growth interface, thereby suppressing the growth of Si. Mg precipitates uniformly in the base material as Mg2Si over time, which can cause natural aging. The precipitation of Mg2Si causes changes in properties, such as reduced ductility and toughness, making it undesirable for materials requiring stability. Therefore, in this embodiment, an aluminum alloy is manufactured so that precipitates of Al-Si-Fe-Mn compounds and precipitates of Mg-Si compounds formed so as to extend from some of the precipitates of Al-Si-Fe-Mn compounds are observed, even while adding Mg. This allows for the advance precipitation of a large amount of Mg-Si compounds, which cause natural aging, and provides an aluminum alloy in which the occurrence of natural aging is suppressed. The Mg content is preferably 0.20% by mass or more, or 0.25% by mass or more. The Mg content is preferably 0.70% by mass or less, 0.60% by mass or less, or 0.50% by mass or less. The Mg content can be measured by ICP atomic emission spectroscopy.

[0019] The Fe content is 0.05 to 0.20 mass% based on the total mass of the aluminum alloy. By setting the Fe content within this range, Al-Si-Fe-Mn compounds can be effectively precipitated. The Fe content is preferably 0.06 mass% or more, or 0.07 mass% or more. The Fe content is preferably 0.18 mass% or less, or 0.16 mass% or less. The Fe content can be measured by ICP atomic emission spectroscopy.

[0020] The Mn content is 0.25 to 1.0 mass% based on the total mass of the aluminum alloy. By setting the Mn content within this range, Al-Si-Fe-Mn compounds can be effectively precipitated. The Mn content is preferably 0.30 mass% or more, or 0.35 mass% or more. The Mn content is preferably 0.80 mass% or less, or 0.60 mass% or less. The Mn content can be measured by ICP atomic emission spectroscopy.

[0021] As described above, in the aluminum alloy according to this embodiment, the Si content is 5.0 to 12.0 mass%, the Mg content is 0.15 to 0.75 mass%, the Fe content is 0.05 to 0.20 mass%, and the Mn content is 0.25 to 1.0 mass%. These contents can also be calculated using software (Thermo-Calc 2020a (hereinafter referred to as ThermoCalc) manufactured by ITOCHU Techno-Solutions Corporation). ThermoCalc is an integrated thermodynamic calculation software that can calculate the phase equilibrium, thermodynamic properties, and various physical properties of any alloy system primarily based on a thermodynamic database. For example, by utilizing an aluminum alloy database, a pseudo-binary phase diagram can be created in which one component of a hexa-component aluminum alloy is changed, and the range of existence of each component can be calculated based on the change points in the component system.

[0022] The aluminum alloy according to this embodiment may further contain other metal elements (i.e., metal elements other than Al, Si, Mg, Fe, and Mn). The content of the other metal elements is 0.10% by mass or less, based on the total mass of the aluminum alloy, and preferably 0.05% by mass or less, 0.03% by mass or less, 0.01% by mass or less, 0.005% by mass or less, 0.003% by mass or less, 0.001% by mass or less, or 0.0001% by mass or less, or preferably not detectable. Other metal elements include, for example, copper (Cu), titanium (Ti), nickel (Ni), zirconium (Zr), cobalt (Co), molybdenum (Mo), tungsten (W), zinc (Zn), lithium (Li), silver (Ag), gallium (Ga), germanium (Ge), scandium (Sc), strontium (Sr), indium (In), vanadium (V), praseodymium (Pr), samarium (Sm), tantalum (Ta), gold (Au), beryllium (Be), chromium (Cr), arsenic (As), selenium (Se), yttrium (Y), niobium (N), and b), ruthenium (Ru), rhodium (Rh), palladium (Pd), cadmium (Cd), tin (Sn), antimony (Sb), tellurium (Te), cerium (Ce), neodymium (Nd), promethium (Pm), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), lutetium (Lu), hafnium (Hf), rhenium (Re), iridium (Ir), platinum (Pt), mercury (Hg), bismuth (Bi), and thorium (Th). The content of other metals can be measured by a method known in the art, and although it varies depending on the alloying element, it can be measured, for example, by ICP atomic emission spectroscopy.

[0023] Examples of impurities include phosphorus (P) and sulfur (S). The content of impurities is usually 0.01% by mass or less, and preferably 0.005% by mass or less, 0.003% by mass or less, 0.001% by mass or less, or 0.0001% by mass or less, based on the total mass of the aluminum alloy. The content of impurities (e.g., phosphorus (P), sulfur (S)) can be measured by a method known in the art, and although the method varies depending on the element being measured, it can be measured, for example, by ICP atomic emission spectroscopy.

[0024] The aluminum alloy according to this embodiment contains at least precipitates of Al-Si-Fe-Mn compounds and precipitates of Mg-Si compounds, and when Si, Mg, Fe, or Mn is observed by TEM mapping in a 400 nm × 400 nm field of view, precipitates of Al-Si-Fe-Mn compounds and precipitates of Mg-Si compounds formed so as to extend from some of the precipitates of Al-Si-Fe-Mn compounds are observed. Note that it is not necessary to confirm the precipitation of Mg-Si compounds originating from all Al-Si-Mn-Fe compounds; it is sufficient to confirm the precipitation of Mg-Si compounds originating from at least some of the Al-Si-Mn-Fe compounds.

[0025] The morphology of Al-Si-Fe-Mn compound precipitates and Mg-Si compound precipitates can be identified by TEM mapping. Precipitates of Al-Si-Fe-Mn compound precipitates can be observed when the observation positions of Si, Fe, and Mn coincide in TEM mapping. Precipitates of Mg-Si compound precipitates can be observed when the observation positions of Si and Mg coincide in TEM mapping.

[0026] The shapes of the observed precipitates of Al-Si-Fe-Mn compounds and the precipitates of Mg-Si compounds formed so as to extend from a part of the precipitates of Al-Si-Fe-Mn compounds are not particularly limited, and may be, for example, needle-like, rod-like, spherical, polygonal, massive, or plate-like.

[0027] The average particle size of precipitates of an Al-Si-Mn-Fe compound is not particularly limited, but is preferably 10 to 300 nm, more preferably 20 to 250 nm, and even more preferably 30 to 200 nm, as the average of the equivalent circle diameters of 100 particles (precipitates) in a TEM photograph. Furthermore, the average particle size of precipitates of an Mg-Si compound is preferably 10 to 300 nm, more preferably 20 to 250 nm, and even more preferably 30 to 200 nm, as the average of the equivalent circle diameters of 100 particles (precipitates) in a TEM photograph. The equivalent circle diameter is the diameter of a circle having an area equal to the area of ​​a particle.

[0028] In this embodiment, the observed precipitates of the Al-Si-Fe-Mn compound and the precipitates of the Mg-Si compound that extend from a part of the Al-Si-Fe-Mn compound precipitate are preferably needle- or rod-shaped and have a length of 10 nm or more. In this embodiment, the length of the needle- or rod-shaped precipitates of the Al-Si-Fe-Mn compound or the Mg-Si compound is preferably 20 nm or more, 30 nm or more, 40 nm or more, or 50 nm or more, or 300 nm or less, 250 nm or less, or 200 nm or less.

[0029] The Vickers hardness of the aluminum alloy according to this embodiment is not particularly limited, but is, for example, 50 HV to 100 HV, and preferably 50 HV to 70 HV.

[0030] The Vickers hardness of the aluminum alloy according to this embodiment after forced aging is not particularly limited. The Vickers hardness of the aluminum alloy according to this embodiment after forced aging (210°C x 90 minutes) is, for example, 50HV to 100HV, and in one embodiment, 50HV to 70HV. In the aluminum alloy according to this embodiment, the change in Vickers hardness before and after forced aging, expressed as {|Vickers hardness after forced aging - Vickers hardness before forced aging| / Vickers hardness before forced aging} x 100, is, for example, 20% or less, preferably 15% or less or 10% or less. The Vickers hardness of the aluminum alloy according to this embodiment can be measured by a Vickers hardness test (JIS B 7725).

[0031] Therefore, the aluminum alloy according to this embodiment has suppressed natural aging. Furthermore, the aluminum alloy according to this embodiment does not need to be subjected to various heat treatments after casting.

[0032] The aluminum alloy according to this embodiment is an alloy casting. A casting refers to a molded product produced by casting. Therefore, the casting includes molded products produced by low-pressure casting, gravity casting, die-casting, and the like. The aluminum alloy according to this embodiment can be molded by casting to be used as a lightweight material to replace iron-based materials, for example, for automobile body parts.

[0033] The aluminum alloy according to this embodiment can be produced by steps (i) to (iv), which will be explained in detail below.

[0034] (i) Raw material preparation process The manufacturing method according to this embodiment includes a raw material preparation step of preparing an aluminum alloy raw material containing 5.0 to 12.0 mass% Si, 0.15 to 0.75 mass% Mg, 0.05 to 0.20 mass% Fe, and 0.25 to 1.0 mass% Mn, with the remainder being Al and impurities.

[0035] In the raw material preparation step, various metals, such as pure metals, compounds, and alloys, can be used as raw materials for the aluminum alloy. For example, aluminum bullion or aluminum scrap can be used as raw materials for the aluminum. Raw materials include those in the form of powder, molten metal, or cast metal (e.g., aluminum alloy ingot). Basically, metals with high melting points can be added as master alloys with other additive elements, and metals with low melting points can be added as pure metals.

[0036] The composition of the raw materials for the aluminum alloy is adjusted so that the contents of the various metals in the aluminum alloy obtained after production fall within the ranges described above. Therefore, the composition of the raw materials for the aluminum alloy will be the same as the composition of the aluminum alloy according to this embodiment, unless the raw materials used are those that are lost due to volatilization or the like during production.

[0037] (ii) Molten metal preparation process The manufacturing method according to this embodiment includes, as a molten metal preparation step, a step of heating raw materials of an aluminum alloy to prepare a molten alloy.

[0038] In the molten metal preparation step, the molten alloy can be prepared, for example, by heating an aluminum alloy raw material in a melting furnace, such as an arc melting furnace, to a temperature at which a liquid phase occurs, typically 680°C to 1200°C, and in one embodiment 1000°C to 1200°C.

[0039] In the molten metal preparation step, the order of addition, addition method, addition temperature, addition time, mixing method, etc. of aluminum and various metals, which are raw materials for the aluminum alloy, are not particularly limited. The molten alloy is prepared so that each metal is uniform.

[0040] For example, in the molten metal preparation process, various metals are added to molten aluminum prepared by heating aluminum to 680°C, and then the temperature of the molten metal is increased to a temperature at which the alloy system melts, for example, 1000°C, to prepare a molten alloy.

[0041] (iii) Pouring process The manufacturing method according to this embodiment includes a step of pouring a molten alloy into a mold as a pouring step.

[0042] In the pouring step, the mold is not limited, and any mold known in the art can be used.

[0043] (iv) Cooling process The manufacturing method according to this embodiment includes a cooling step in which the poured molten alloy is cooled and solidified, and the cooling and solidification step includes holding the molten alloy at a temperature between 380 and 460°C for 5 minutes or more.

[0044] In the cooling step, the molten alloy is cooled to solidify. The cooling step includes a solidification-holding step. The solidification-holding step is a step of holding the molten alloy at a temperature between 380 and 460°C for 5 minutes or more. The time for holding the molten alloy so that the temperature of the molten alloy is 380 to 460°C is preferably 10 minutes or more, 20 minutes or more, 30 minutes or more, 40 minutes or more, 50 minutes or more, 1 hour or more, 2 hours or more, 3 hours or more, 4 hours or more, 5 hours or more, 6 hours or more, 7 hours or more, 8 hours or more, 9 hours or more, or 10 hours or more. The time for holding the molten alloy so that the temperature of the molten alloy is 380 to 460°C is preferably 48 hours or less, 36 hours or less, 24 hours or less, or 18 hours or less. The temperature for holding the molten alloy is preferably 400 to 440°C.

[0045] In the cooling step, the cooling rate of the molten alloy is not particularly limited, but is, for example, 10°C / min to 2000°C / min, and preferably 10°C / min to 1000°C / min.

[0046] In the cooling step of this embodiment, by maintaining the molten alloy within the specific temperature range for the specific time, Al-Si-Fe-Mn compounds are precipitated, and the precipitates act as starting points for the precipitation of large amounts of Mg-Si compounds (mainly MgSi). This prevents the uniform precipitation of Mg-Si compounds, which causes natural aging, and as a result, prevents natural aging in the resulting aluminum alloy. Therefore, the aluminum alloy obtained by the manufacturing method of this embodiment is prevented from experiencing changes in hardness due to aging.

[0047] The manufacturing method according to this embodiment may be a casting method known in the art, except for the solidification and holding step in the cooling step. Casting is a method in which molten metal (including alloys) melted at high temperature is poured into a cavity of a mold made of sand, metal, or the like, and cooled to solidify. Examples of casting include conventional melting and casting methods such as continuous casting, continuous casting and rolling, semi-continuous casting (DC casting), and hot-top casting, as well as die-casting. [Example]

[0048] Hereinafter, several examples relating to this embodiment will be described, but it is not intended that this embodiment be limited to those shown in these examples.

[0049] I. Sample preparation and hardness measurement (i) An Al-Si based aluminum alloy raw material containing the chemical components shown in Table 1 was prepared. (ii) The raw materials prepared in the raw material preparation step (i) were heated to 650°C to prepare a molten alloy. (iii) The molten alloy prepared in the molten alloy preparation step (ii) was poured into a mold. (iv) The molten alloy poured in the pouring step (iii) was cooled until the temperature of the molten alloy reached 440°C (Example 1) or 500°C (Comparative Example 1), and once the temperature of the molten alloy reached each temperature, the molten alloy was held at that temperature for 10 hours. (v) After the solidification and holding step (iv), the mold was cooled to 200°C, the aluminum alloy was removed from the mold, and then air-cooled to room temperature (20°C).

[0050] In addition, a conventional Al-Si-based aluminum alloy (Comparative Example 2) was produced by changing the cooling steps (iv) and (v) of the steps (i) to (v) to "cooling the molten alloy poured in the pouring step (iii) to 200°C, removing the Al-Si-based aluminum alloy from the mold, and further air-cooling it to room temperature (20°C)."

[0051] [Table 1]

[0052] The Vickers hardness of each of the resulting Al-Si based aluminum alloys was measured.

[0053] The presence or absence of natural aging in Al-Si-based aluminum alloys can be confirmed by forced aging, so each Al-Si-based aluminum alloy whose Vickers hardness had been measured was subsequently subjected to heat treatment (forced aging) at 210°C for 90 minutes.

[0054] The Vickers hardness of each of the Al-Si-based aluminum alloys obtained after forced aging was measured again, and the results are shown in Table 2 and Figure 1.

[0055] [Table 2]

[0056] 1, it was found that the aluminum alloy of Example 1, which was held at 380 to 460°C (specifically, 440°C) during the cooling process, showed a suppressed change in Vickers hardness before and after forced aging. Therefore, it was found that the Al-Si-based aluminum alloy produced in this manner showed a suppressed natural aging.

[0057] II. TEM analysis of samples The Al-Si based aluminum alloys of Example 1 and Comparative Example 1 were analyzed by TEM.

[0058] 2, it can be seen that precipitates of Al-Si-Fe-Mn compounds are present in the Al-Si-based aluminum alloy of Example 1, as confirmed by the fact that the observation positions of Si, Fe, and Mn are almost identical. It was confirmed that Mg-Si compounds (MgSi), as confirmed by the fact that the observation positions of Si and Mg are almost identical, are precipitated in relation to these Al-Si-Fe-Mn compounds, extending from part of the precipitates of the Al-Si-Fe-Mn compounds as their starting points.

[0059] 3, in the Al-Si-based aluminum alloy of Comparative Example 1, the observation positions of Si, Fe, and Mn did not coincide, and precipitation of Al-Si-Fe-Mn-based compounds was not confirmed. Moreover, it was found that only Mg-Si-based compounds, confirmed by the observation positions of Si and Mg almost coincided, were precipitated.

[0060] Conventionally, heat treatment (aging treatment) has been used to uniformly precipitate Mg-Si compounds, thereby steadily increasing hardness, thereby imparting to Al-Si aluminum alloys suppressed natural aging and the required hardness as an aluminum alloy characteristic. However, paradoxically, if Mg and Si are present in an aluminum alloy, natural aging will occur and hardness will increase unless heat treatment is performed. Changes in properties due to natural aging are undesirable from the perspective of the required material properties.

[0061] Therefore, in the Al-Si-based aluminum alloy according to this embodiment, a large amount of Mg-Si-based compounds are precipitated starting from precipitates of Al-Si-Fe-Mn-based compounds, thereby suppressing uniform precipitation of Mg2Si compounds. As a result, in an environment of 200°C or less, Si and Mg are less likely to precipitate as Mg2Si compounds, and natural aging, i.e., an increase in hardness, due to the precipitation of Mg2Si compounds is less likely to occur.

[0062] Therefore, the Al-Si-based aluminum alloy according to this embodiment does not require additional heat treatment, such as solution heat treatment and / or aging heat treatment, and as a result, it is possible to suppress the influence of distortion due to heat treatment, and further to suppress an increase in cost and CO2 emissions due to thermal energy consumption.

Claims

1. An aluminum alloy comprising 5.0 to 12.0 mass% Si, 0.15 to 0.75 mass% Mg, 0.05 to 0.20 mass% Fe, and 0.25 to 1.0 mass% Mn, with the balance being Al and impurities; The alloy contains at least precipitates of Al—Si—Fe—Mn-based compounds and precipitates of Mg—Si-based compounds, An aluminum alloy in which, when Si, Mg, Fe, or Mn is observed by TEM mapping within a field of view of 400 nm x 400 nm, precipitates of Al-Si-Fe-Mn-based compounds and precipitates of Mg-Si-based compounds formed so as to extend from parts of the precipitates of Al-Si-Fe-Mn-based compounds are observed.

2. Precipitates of Al-Si-Fe-Mn compounds are observed by the coincidence of the observation positions of Si, Fe, and Mn in TEM mapping.

2. The aluminum alloy according to claim 1, wherein the precipitates of the Mg—Si compound are observed by TEM mapping, where the observation positions of Si and Mg coincide with each other.

3. 2. The aluminum alloy according to claim 1, wherein the observed shapes of the precipitates of the Al-Si-Fe-Mn compound and the observed shapes of the precipitates of the Mg-Si compound formed so as to extend from parts of the precipitates of the Al-Si-Fe-Mn compound are each needle-like or rod-like, and have lengths of 10 nm or more.

4. A method for producing the aluminum alloy according to any one of claims 1 to 3, comprising: preparing a raw material for an aluminum alloy containing 5.0 to 12.0 mass% Si, 0.15 to 0.75 mass% Mg, 0.05 to 0.20 mass% Fe, and 0.25 to 1.0 mass% Mn, with the remainder consisting of Al and impurities; a step of heating an aluminum alloy raw material to prepare a molten alloy; Pouring the molten alloy into a mold; and The process of cooling and solidifying the poured molten alloy Including, The step of cooling and solidifying includes a step of holding the molten alloy at a temperature between 380 and 460°C for 5 minutes or more.

5. The method of claim 4, which does not include a step of heat treating the aluminum alloy after the step of cooling and solidifying.

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