Aluminum alloy and its manufacturing method

Abstract

To provide an aluminum alloy in which natural aging is suppressed and a method for producing the same.SOLUTION: This disclosure relates to an Al-Si-based aluminum alloy that comprises Si, Mg, Mn, Fe, and unavoidable impurities, comprising Al-Si-Mg-Fe-Mn-based compounds, and further to a method for producing the Al-Si-based aluminum alloy by controlling the cooling process of a molten alloy during casting.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, an 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 that has sufficient hardness without performing 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), natural aging can be suppressed by controlling the cooling process of the molten alloy during casting, and an aluminum alloy having sufficient hardness can be produced, and have completed the present invention. In the aluminum alloy of the present invention, it is believed that by controlling the cooling process of the molten alloy during casting, Al-Si-Fe-Mn compounds are preferentially precipitated, and the precipitation of Mg-Si compounds that would normally precipitate is suppressed.

[0010] That is, the gist of the present invention is as follows. (1) An Al-Si-based aluminum alloy containing Si, Mg, Mn, Fe and inevitable impurities, and containing an Al-Si-Mg-Fe-Mn-based compound. (2) An Al-Si-based aluminum alloy according to (1), wherein, when the Al-Si-based aluminum alloy is observed by EPMA mapping in a field of view of 80 μm × 80 μm, in an Al-Si-Mg-Fe-Mn-based compound, for Mg, Mn, and Fe, a region having an intensity of 50% or more of Mg's K-α coincides with a region having an intensity of 10% to 20% of Mn's K-α and a region having an intensity of 5% to 14% of Fe's K-α, and for Mn and Fe, a region having an intensity of 80% or more of Mn's K-α coincides with a region having an intensity of 44% or more of Fe's K-α. (3) (i) a raw material preparation step of preparing a raw material of an Al-Si-based aluminum alloy containing Si, Mg, Mn, Fe, and inevitable impurities; (ii) a molten metal preparation step of preparing a molten alloy by heating the raw materials prepared in the raw material preparation step (i); (iii) a pouring step of pouring the molten alloy prepared in the molten alloy preparation step (ii) into a mold; and (iv) A cooling process in which the molten alloy poured in the pouring process (iii) is cooled and solidified. Including, The cooling step (iv) includes a solidification holding step of holding the molten alloy at a temperature of 510°C to 470°C for 20 minutes to 40 minutes when the temperature of the molten alloy reaches that temperature range. A manufacturing method for Al-Si aluminum alloys. [Effects of the Invention]

[0011] The present invention provides an aluminum alloy with suppressed natural aging. Furthermore, the present invention provides a method for producing an aluminum alloy that has sufficient hardness without requiring a heat treatment step after casting. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a graph showing the Vickers hardness after casting and after forced aging of Al—Si-based aluminum alloys of Comparative Examples 1 and 2 and Examples 1 and 2. [Figure 2] FIG. 1 is a diagram showing EPMA mapping (80 μm×80 μm) of the Al—Si-based aluminum alloy of Example 1. [Figure 3] FIG. 2 is a diagram showing EPMA mapping (80 μm×80 μm) of the Al—Si-based aluminum alloy of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0013] Preferred embodiments of the present invention will now be described in detail. 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.

[0014] The present invention relates to an Al-Si-based aluminum alloy containing Si, Mg, Mn, Fe and inevitable impurities, and the Al-Si-based aluminum alloy contains an Al-Si-Mg-Fe-Mn-based compound.

[0015] The Si content is not limited. The Si content, as metal, is usually 0.1 mass % to 15 mass %, and in one embodiment, 4 mass % to 12 mass %, based on the total mass of the Al-Si-based aluminum alloy. Here, the Si content can be measured by ICP atomic emission spectroscopy.

[0016] The Mg content is not limited. The Mg content, as a metal, is usually 0.01% by mass to 1% by mass, and in one embodiment, 0.1% by mass to 1% by mass, based on the total mass of the Al-Si-based aluminum alloy. Here, the Mg content can be measured by ICP atomic emission spectroscopy.

[0017] The Mn content is not limited. The Mn content, as a metal, is usually 0.01% by mass to 1% by mass, and in one embodiment, 0.1% by mass to 1% by mass, based on the total mass of the Al-Si-based aluminum alloy. Here, the Mn content can be measured by ICP atomic emission spectrometry.

[0018] The Fe content is not limited. The Fe content, as a metal, is usually 0.01% by mass to 1% by mass, and in one embodiment, 0.1% by mass to 1% by mass, based on the total mass of the Al-Si-based aluminum alloy. Here, the Fe content can be measured by ICP atomic emission spectrometry.

[0019] The Al-Si based aluminum alloy of the present invention may further contain other modifying alloy elements, such as 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), The material may contain one or more metals (other metals) selected from the group consisting of niobium (Nb), 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).

[0020] The content of each of the other metals is not limited. The content of each of the other metals, as metals, is typically 0.0001% by mass to 0.1% by mass, and in one embodiment, 0.001% by mass to 0.05% by mass, based on the total mass of the Al-Si-based aluminum alloy. The content of all the other metals, as metals, is typically 0.01% by mass to 1% by mass, and in one embodiment, 0.03% by mass to 0.1% by mass, and in another embodiment, 0.04% by mass to 0.06% by mass, based on the total mass of the Al-Si-based aluminum alloy. The content of the other metals can be measured by a method known in the art, and although it varies depending on the alloying elements, it can be measured, for example, by ICP atomic emission spectroscopy.

[0021] The balance other than the above metals in the Al-Si based aluminum alloy of the present invention consists of aluminum (Al) and unavoidable impurities.

[0022] Here, examples of unavoidable impurities include phosphorus (P) and sulfur (S). The contents of phosphorus (P) and sulfur (S) are not limited. The contents of phosphorus (P) and sulfur (S) are usually 0.01 mass% or less based on the total mass of the aluminum alloy. The contents of phosphorus (P) and sulfur (S) can be measured by methods known in the art, and although the method varies depending on the element being measured, they can be measured, for example, by ICP atomic emission spectroscopy.

[0023] In the Al-Si-based aluminum alloy of the present invention, the Al-Si-based compounds can be identified by EPMA mapping of the Al-Si-based aluminum alloy. In the EPMA mapping of the Al-Si-based aluminum alloy, the Al-Si-based compounds have the following characteristics (i) and (ii): (i) When an Al-Si-based aluminum alloy is observed by EPMA mapping in a field of view of 80 μm × 80 μm, for Mg, Mn, and Fe, a region where the Mg K-α intensity is 50% or more coincides with a region where the Mn K-α intensity is 10% or more, or in one embodiment, 10% to 20%, and a region where the Fe K-α intensity is 5% or more, or in one embodiment, 5% to 14%. (ii) When an Al-Si-based aluminum alloy is observed by EPMA mapping in a field of view of 80 μm × 80 μm, for Mn and Fe, a region where the K-α intensity of Mn is 50% or more, in one embodiment, 80% or more, coincides with a region where the K-α intensity of Fe is 25% or more, in one embodiment, 44% or more.

[0024] Here, the K-α intensity (%) of various metals at a specific location within an 80 μm × 80 μm field of view indicates the proportion (%) of K-α rays from Mg at a specific location within the field of view, for example, in the case of Mg, when the K-α rays from Mg throughout the entire 80 μm × 80 μm field of view are taken as 100%.

[0025] The presence of Si in Al-Si-Mg-Fe-Mn compounds in Al-Si-based aluminum alloys can also be confirmed by EPMA, in the same way as Mg, Mn, and Fe.

[0026] The shape of the Al-Si-Mg-Fe-Mn compound is not limited and may be, for example, spherical, polygonal, or blocky.

[0027] The average particle size of the Al-Si-Mg-Fe-Mn compound is not limited, and is typically 30 nm to 300 nm, and in one embodiment 50 nm to 100 nm, as the average of the circle-equivalent diameters of 100 particles in a TEM photograph.

[0028] The Vickers hardness of the Al-Si based aluminum alloy of the present invention is not limited, and the Vickers hardness of the Al-Si based aluminum alloy of the present invention is usually 40 HV to 100 HV, and in one embodiment, 50 HV to 60 HV.

[0029] The Vickers hardness of the Al-Si-based aluminum alloy of the present invention after forced aging is not limited. The Vickers hardness of the Al-Si-based aluminum alloy of the present invention after forced aging (210°C x 90 minutes) is usually 50HV to 120HV, and in one embodiment, 50HV to 60HV.

[0030] That is, in the Al-Si-based aluminum alloy of the present invention, 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}×100, is usually 4% or less, and in one embodiment, 2% or less.

[0031] Here, the Vickers hardness of the Al-Si based aluminum alloy of the present invention can be measured by a Vickers hardness test.

[0032] Therefore, the Al-Si-based aluminum alloy of the present invention has suppressed natural aging. Furthermore, the Al-Si-based aluminum alloy of the present invention does not need to be subjected to various heat treatments after casting.

[0033] The Al-Si-based aluminum alloy of the present invention is an Al-Si-based aluminum alloy casting. The term "casting" refers to a molded product produced by casting. Therefore, the term "casting" includes molded products produced by low-pressure casting, gravity casting, die casting, etc.

[0034] The aluminum alloy of the present invention can be molded by casting to be used as a lightweight material to replace iron-based materials, for example, for automobile body parts.

[0035] The Al-Si based aluminum alloy of the present invention can be produced by the steps (i) to (iv) described in detail below.

[0036] (i) Raw material preparation process In step (i), the raw material for the Al-Si-based aluminum alloy is not limited. Examples of raw materials for the Al-Si-based aluminum alloy include pure metals, compounds, and alloys of various metals. Aluminum raw materials such as aluminum bullion and aluminum scrap can be used. Furthermore, raw materials for the Al-Si-based aluminum alloy 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 a master alloy with other additive elements, and metals with low melting points can be added as pure metal.

[0037] The composition of the raw materials for the Al-Si-based aluminum alloy is adjusted so that the contents of various metals in the Al-Si-based aluminum alloy obtained after production fall within the ranges explained above. Therefore, the composition of the raw materials for the Al-Si-based aluminum alloy will be the same as the composition of the Al-Si-based aluminum alloy unless the raw materials used are those that are lost during production due to volatilization or the like.

[0038] (ii) Molten metal preparation process In step (ii), the molten alloy can be prepared, for example, by heating a raw material of an Al-Si aluminum alloy in a melting furnace, for example, an arc melting furnace, to a temperature at which a liquid phase is formed, typically 680°C to 1200°C, and in one embodiment, 1000°C to 1200°C.

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

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

[0041] (iii) Pouring process In step (iii), the template is not limited, and any template known in the art can be used.

[0042] (iv) Cooling process In step (iv), the molten alloy is solidified by cooling. Step (iv) includes a solidification holding step. In the solidification holding step, once the temperature of the molten alloy reaches 510°C to 470°C, or in one embodiment 500°C to 480°C, at which solidification begins, the alloy is held at that temperature for 20 to 40 minutes, or in one embodiment 30 minutes.

[0043] In the step (iv), the cooling rate of the molten alloy is not limited, and is typically 50°C / sec to 200°C / sec, and in one embodiment, 80°C / sec to 120°C / sec.

[0044] In step (iv), by holding the molten alloy in the specific temperature range for the specific time, Al-Si-Mg-Fe-Mn compounds are preferentially precipitated in the molten alloy, while precipitation of Mg2Si is suppressed. Because Mg2Si can undergo natural aging, precipitation of Mg2Si is suppressed, and as a result, natural aging is suppressed in the Al-Si-based aluminum alloy obtained after step (iv). Therefore, the Al-Si-based aluminum alloy obtained by the manufacturing method of the present invention can suppress changes in hardness due to aging.

[0045] The method for producing the Al-Si-based aluminum alloy of the present invention may be a casting method known in the art, except for the step of maintaining the solidification in the cooling step (iv).

[0046] Here, casting refers to pouring molten metal (including alloys) melted at high temperatures into the cavity of a mold made of sand, metal, etc., and then cooling and solidifying it.

[0047] Examples of casting include ordinary melt casting methods such as continuous casting, continuous casting and rolling, semi-continuous casting (DC casting) and hot top casting, and die casting. [Example]

[0048] Hereinafter, several examples of the present invention will be described, but it is not intended that the present invention be limited to those shown in these examples.

[0049] I. Sample preparation and hardness measurement (i) Aluminum alloy raw materials containing the chemical compositions shown in Table 1 were prepared. (ii) The raw materials prepared in the raw material preparation step (i) were heated to 700°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 520°C (Comparative Example 1), 500°C (Example 1), 480°C (Example 2), or 460°C (Comparative Example 2), and once the temperature of the molten alloy reached each temperature, the temperature was maintained for 30 minutes. (v) After the solidification and holding step (iv), the mold was cooled to 250°C, the Al-Si based aluminum alloy was taken out of the mold, and further cooled to 25°C in air.

[0050] In addition, a conventional Al-Si-based aluminum alloy (Comparative Example 3) 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 400°C, removing the Al-Si-based aluminum alloy from the mold, and further air-cooling it to 25°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 Al-Si aluminum alloys that were held at 510°C to 470°C, particularly 500°C to 480°C, for 20 to 40 minutes, particularly 30 minutes during the cooling process, showed a suppressed change in Vickers hardness before and after forced aging. Therefore, it was found that the Al-Si aluminum alloys produced in this manner showed a suppressed natural aging.

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

[0058] 2 shows EPMA mapping (80 μm×80 μm) of the Al—Si based aluminum alloy of Example 1. FIG. 3 shows EPMA mapping (80 μm×80 μm) of the Al—Si based aluminum alloy of Comparative Example 1.

[0059] 2, in the Al-Si-based aluminum alloy of Example 1, the K-α peak positions of Si, Mg, Mn, and Fe almost coincided, indicating the precipitation of Al-Si-Mg-Fe-Mn-based compounds. Specifically, in the EPMA mapping of Mg, Mn, and Fe, in an 80 μm × 80 μm field of view, the Mg K-α intensity of 50% or more coincided with the Mn K-α intensity of 10% or more, particularly 10% to 20%, and the Fe K-α intensity of 5% or more, particularly 5% to 14%. Furthermore, in the EPMA mapping of Mn and Fe, in an 80 μm × 80 μm field of view, the Mn K-α intensity of 50% or more, particularly 80% or more, coincided with the Fe K-α intensity of 25% or more, particularly 44% or more.

[0060] On the other hand, as can be seen from FIG. 3, in the Al-Si-based aluminum alloy of Comparative Example 1, the peak positions of the K-α rays of Si, Mg, Mn, and Fe do not coincide, and it is understood that both Fe-Mn-Si-based compounds and MgSi compounds are precipitated.

[0061] Mg2Si compounds stably increase hardness through heat treatment (aging treatment), imparting to the Al-Si-based aluminum alloy suppressed natural aging and the hardness required for the aluminum alloy's properties. In other words, if Mg2Si compounds are present in an aluminum alloy, natural aging will occur and hardness will increase unless heat treatment is performed. In the Al-Si-based aluminum alloy of the present invention, the precipitates are Al-Si-Mg-Fe-Mn-based compounds. In other words, in the Al-Si-based aluminum alloy of the present invention, precipitation of Mg2Si compounds is suppressed in an environment of 200°C or less, so natural aging due to the Mg2Si compounds, i.e., hardness increase, does not occur. Therefore, the Al-Si-based aluminum alloy of the present invention does not require additional heat treatment, such as solution heat treatment and / or aging heat treatment. As a result, the effects of heat treatment distortion can be suppressed, and further, increases in costs and CO2 emissions due to thermal energy consumption can be suppressed.

Claims

1. An Al-Si-based aluminum alloy containing Si, Mg, Mn, Fe, and inevitable impurities, Si: 4% by mass to 12% by mass, Mg: 0.1% by mass to 1% by mass, Mn: 0.1% by mass to 1% by mass and Fe: 0.1% by mass to 1% by mass; Remainder: Al and inevitable impurities It consists of Contains an Al-Si-Mg-Fe-Mn compound, The change in Vickers hardness before and after forced aging (210°C x 90 minutes) is 4% or less, calculated as {|Vickers hardness after forced aging - Vickers hardness before forced aging| / Vickers hardness before forced aging} x 100. Al-Si aluminum alloy.

2. 2. The Al-Si-based aluminum alloy according to claim 1, wherein, when the Al-Si-based aluminum alloy is observed by EPMA mapping in a field of view of 80 μm × 80 μm, in an Al-Si-Mg-Fe-Mn-based compound, for Mg, Mn, and Fe, a region having an intensity of Mg K-α of 50% or more, a region having an intensity of Mn K-α of 10% to 20%, and a region having an intensity of Fe K-α of 5% to 14% coincide with each other, and for Mn and Fe, a region having an intensity of Mn K-α of 80% or more coincides with a region having an intensity of Fe K-α of 44% or more.

3. (i) a raw material preparation step of preparing a raw material of an Al-Si-based aluminum alloy containing Si, Mg, Mn, Fe, and inevitable impurities; (ii) a molten metal preparation step of heating the raw materials prepared in the raw material preparation step (i) to prepare a molten alloy; (iii) a pouring step of pouring the molten alloy prepared in the molten alloy preparation step (ii) into a mold, and (iv) a cooling step of cooling and solidifying the molten alloy poured in the pouring step (iii). Including, Does not include heat treatment after casting In the raw material preparation step (i), the raw material is Si: 4% by mass to 12% by mass, Mg: 0.1% by mass to 1% by mass, Mn: 0.1% by mass to 1% by mass and Fe: 0.1% by mass to 1% by mass; Remainder: Al and inevitable impurities It consists of the cooling step (iv) includes a solidification holding step of, when the temperature of the molten alloy reaches 500°C to 480°C, holding the molten alloy at this temperature range for 30 minutes to precipitate Al—Si—Mg—Fe—Mn-based compounds in the molten alloy; The change in Vickers hardness of the Al-Si-based aluminum alloy after casting before and after forced aging (210°C x 90 minutes) is 4% or less, as calculated as {|Vickers hardness after forced aging - Vickers hardness before forced aging| / Vickers hardness before forced aging} x 100. A method for producing an Al-Si based aluminum alloy.

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