Aluminum-alloy powder, aluminum-alloy sintered body and method of manufacturing aluminum-alloy sintered body

Abstract

To provide an aluminum-alloy powder, aluminum-alloy sintered body and method of manufacturing an aluminum-alloy powder.SOLUTION: An aluminum-alloy powder according to the present invention contains by 0.1 wt.% or more and 2.0 wt.% or less one or two or more of rare earth metal elements consisting of yttrium and lanthanoid, so as to reduce the content of iron to 2.0 wt.% or less. The rare earth metal element is preferably any of praseodymium, neodymium, europium, samarium, terbium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an aluminum alloy powder having excellent sinterability, an aluminum alloy sintered body, and a method for producing the aluminum alloy sintered body. [Background technology]

[0002] Aluminum is used in heat sinks for equipment due to its light weight and good electrical and thermal conductivity, but it is a metallic material that has significant processing constraints because a dense, strong oxide film forms on the surface, protecting the interior. For casting materials, a method is used in which flux (brazing filler metal) is used to break down the oxide film on the surface to join the components and give them the desired shape. However, this method has the problem that it is difficult to achieve sufficient accuracy and spatial resolution for heat exchange materials that require complex and precise shape control, such as pin, fin, and lattice shapes. In contrast, powder sintering allows for near-net-shape manufacturing, and the technology is expected to develop as a means of achieving complex shapes inexpensively. However, even in the powder sintering method, aluminum is difficult to sinter due to the formation of an oxide film, and this remains a major limitation.

[0003] In powder sintering, a method known as hot pressing is to apply pressure to a powder compact to increase the packing of the powder and promote sintering. However, in additive manufacturing processes, which are attracting attention as a method for creating complex shapes with high precision, it is difficult in principle to apply techniques such as pressure. In addition, due to the scale constraints of using particles of only a few tens of micrometers, it is difficult to destroy the oxide film using flux, making it difficult to densify the structure.

[0004] One method to solve this problem is alloying with different elements. By adding elements such as silicon (Si), the liquid phase generation temperature range can be expanded and sintering can be carried out stably, as in the case of Al-Si alloys known as JIS-specified 5000 series aluminum alloys and Al-Si-Mg alloys known as JIS-specified 6000 series aluminum alloys.

[0005] The following Patent Document 1 discloses a technology for additive manufacturing using a mixed powder prepared by adding about 2 mass % of Zr fine particles to A2219 aluminum alloy powder as an alloy powder for laser powder sintering additive manufacturing. Patent Document 2 discloses an aluminum alloy layer containing 4 wt % to 60 wt % of rare earth elements as an aluminum alloy layer to be applied to additive manufacturing technology. Patent Document 3 discloses an aluminum alloy for use in additive manufacturing technology, which contains copper (Cu) and Mg as alloying elements and has a precipitate phase represented by Al3X, which further contains Zr, Y, Er, etc. as element X. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent Application Publication No. 2020 / 0199716 [Patent Document 2] US Patent Application Publication No. 2018 / 0080103 [Patent Document 3] US Patent Application Publication No. 2018 / 0245190 Summary of the Invention [Problem to be solved by the invention]

[0007] In conventional technology, silicon added to aluminum is a semimetal, and while adding silicon is expected to improve sinterability, it also has the problem of impairing the electrical and thermal conductivity that are advantages of aluminum. For this reason, the inventors conducted extensive research into additive elements that can be used in powder sintering to increase the density of the sintered body structure, while selecting additive elements that do not impair the electrical and thermal conductivity that are the advantages of aluminum, and as a result, arrived at the present invention.

[0008] The present invention has been made in view of the above-mentioned problems, and its object is to provide an aluminum alloy powder that can obtain excellent sinterability without impairing the electrical conductivity and thermal conductivity that are advantages of aluminum. Another object of the present invention is to provide an aluminum alloy sintered body and a method for producing the aluminum alloy sintered body. [Means for solving the problem]

[0009] (1) An aluminum alloy powder according to one embodiment of the present invention is characterized in that it contains 0.1 mass % or more and 2.0 mass % or less of one or more metal elements selected from rare earth metal elements consisting of yttrium and lanthanoid elements, and the iron content is suppressed to 2.0 mass % or less. (2) In the aluminum alloy powder according to (1) of the present invention, the rare earth metal element is preferably any one of praseodymium, neodymium, europium, samarium, terbium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

[0010] (3) The aluminum alloy powder according to (1) or (2) of the present invention is preferably used for sintering. (4) With respect to the aluminum alloy powder according to (1) or (2) of the present invention, the median diameter D is the average particle diameter of the 50% cumulative volume based on the volume measured by a laser diffraction / scattering method. 50 However, it is preferable that the thickness is 20 μm or more and 65 μm or less. (5) In the aluminum alloy powder according to (1) or (2) of the present invention, the cross-sectional structure preferably contains precipitates of aluminum rare earth intermetallic compounds having an average width of less than 0.1 μm.

[0011] (6) An aluminum alloy sintered body according to one embodiment of the present invention is characterized in that it contains one or more metal elements selected from the group consisting of yttrium and lanthanoid elements in an amount of 0.1 mass % to 2.0 mass %, and the iron content is suppressed to 2.0 mass % or less. (7) In the aluminum alloy sintered body according to (6) of the present invention, the rare earth metal element is preferably any one of praseodymium, neodymium, europium, samarium, terbium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

[0012] (8) In the aluminum alloy sintered body according to (6) or (7) of the present invention, it is preferable that the cross-sectional structure contains precipitates of an aluminum rare earth intermetallic compound.

[0013] (9) A method for producing an aluminum alloy sintered body according to one embodiment of the present invention is characterized in that an aluminum alloy powder containing one or more metal elements selected from the group consisting of yttrium and lanthanoid elements in an amount of 0.1 mass % to 2.0 mass % and having an iron content of 2.0 mass % or less is used, and is heated in an inert atmosphere at a temperature of 660°C or less. (10) In the method for producing an aluminum alloy sintered body according to (9) of the present invention, the rare earth metal element is any one of praseodymium, neodymium, europium, samarium, terbium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

[0014] (11) In the method for producing an aluminum alloy sintered body according to (9) or (10) of the present invention, the aluminum alloy powder has a median particle diameter D , which is the average particle diameter of 50% of the total particles on a volume basis measured by a laser diffraction / scattering method. 50 However, it is preferable to use an aluminum alloy powder having a particle size of 20 μm or more and 65 μm or less. (12) In the method for producing an aluminum alloy sintered body according to (9) or (10) of the present invention, it is preferable to use an aluminum alloy powder containing precipitates of an aluminum rare earth intermetallic compound having an average width of less than 0.1 μm in the cross-sectional structure. (13) In the method for producing an aluminum alloy sintered body according to (11) of the present invention, it is preferable to use an aluminum alloy powder containing precipitates of an aluminum rare earth intermetallic compound having an average width of less than 0.1 μm in the cross-sectional structure. [Effects of the Invention]

[0015] According to one embodiment of the present invention, an aluminum alloy powder can be provided which contains a suitable amount of rare earth metal elements and has an iron content of 2.0 mass% or less, and therefore has precipitates of aluminum rare earth intermetallic compounds with an average width of less than 0.1 μm in the structure, and which can give a high-density sintered body. Unlike silicon, which is a metalloid, rare earth metal elements are metals, and therefore do not impair the good electrical and thermal conductivity that aluminum inherently possesses, as compared to the addition of silicon. Furthermore, because rare earth metal elements have an atomic weight about five times larger than that of aluminum, even when the amount added is the same as that of silicon that has traditionally been added, it is possible to significantly reduce the composition ratio and atomic ratio. Assuming an amount of Si added equivalent to that traditionally added, the degree to which the electrical conductivity and thermal conductivity of the aluminum itself is impaired can be reduced. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a cross-sectional schematic view showing an example of the metal structure of an aluminum alloy powder according to a first embodiment of the present invention. [Figure 2] 10 is a cross-sectional FE-SEM image showing an example of the aluminum alloy powder obtained in Example 6. [Figure 3] An example of the same metal powder is shown in Figure 2. The cross-sectional SEM image and EDS map image are taken from the corresponding position. [Figure 4] 3 is a graph showing the temperature history in a furnace when a sintered body is produced using an aluminum alloy powder in an example. [Figure 5] FE-SEM image of the structure of an aluminum alloy sintered body produced using the pure aluminum powder of Comparative Example 1, observed at 250x magnification. [Figure 6] FE-SEM image of the structure of an aluminum alloy sintered body produced using the pure aluminum powder of Comparative Example 2, observed at 250x magnification. [Figure 7] FE-SEM image of the structure of an aluminum alloy sintered body produced using the aluminum alloy powder of Comparative Example 3, observed at 250x magnification. [Figure 8] FE-SEM image of the structure of an aluminum alloy sintered body produced using the aluminum alloy powder of Example 1, observed at 250x magnification. [Figure 9] FE-SEM image of the structure of an aluminum alloy sintered body produced using the aluminum alloy powder of Example 2, observed at 250x magnification. [Figure 10] FE-SEM image of the structure of an aluminum alloy sintered body produced using the aluminum alloy powder of Example 3, observed at 250x magnification. [Figure 11] FE-SEM image of the structure of an aluminum alloy sintered body produced using the aluminum alloy powder of Example 4, observed at 250x magnification. [Figure 12] FE-SEM image of the structure of an aluminum alloy sintered body produced using the aluminum alloy powder of Example 5, observed at 250x magnification. [Figure 13] FE-SEM image of the structure of an aluminum alloy sintered body produced using the aluminum alloy powder of Example 6, observed at 250x magnification. [Figure 14] FE-SEM image of the structure of an aluminum alloy sintered body produced using the aluminum alloy powder of Example 7, observed at 250x magnification. [Figure 15] FE-SEM image of the metal structure of the aluminum alloy powder of Comparative Example 3 observed at a magnification of 30,000 times. [Figure 16] FE-SEM image of the metal structure of the aluminum alloy powder of Example 1 observed at a magnification of 30,000 times. [Figure 17]FE-SEM image of the metal structure of the aluminum alloy powder of Example 2 observed at a magnification of 30,000 times. [Figure 18] FE-SEM image of the metal structure of the aluminum alloy powder of Example 3 observed at a magnification of 30,000 times. [Figure 19] FE-SEM image of the metal structure of the aluminum alloy powder of Example 4 observed at a magnification of 30,000 times. [Figure 20] FE-SEM image of the metal structure of the aluminum alloy powder of Example 5 observed at a magnification of 30,000 times. [Figure 21] FE-SEM image of the metal structure of the aluminum alloy powder of Example 6 observed at a magnification of 30,000 times. [Figure 22] FE-SEM image of the metal structure of the aluminum alloy powder of Example 7 observed at a magnification of 30,000 times. [Figure 23] FE-SEM image of the structure of the aluminum alloy sintered body produced from the aluminum alloy powder of Example 6, observed at a magnification of 30,000 times. [Figure 24] 10 is an SEM image of the structure of an aluminum alloy sintered body produced from the aluminum alloy powder of Comparative Example 3, observed at 500x magnification. [Figure 25] Al-K EDS map for the SEM image shown in Figure 24. [Figure 26] Fe-K EDS map for the SEM image shown in Figure 24. [Figure 27] Sm-L EDS map for the SEM image shown in Figure 24. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in detail below based on embodiments, but the present invention is not limited to the embodiments described below. FIG. 1 is an enlarged cross-sectional schematic view showing an example of an aluminum alloy powder according to a first embodiment of the present invention. This aluminum alloy powder 1 is characterized by containing 0.1 mass % to 2.0 mass % of one or more metal elements selected from the rare earth metal elements consisting of yttrium and lanthanoid elements, and having an iron content of 2.0 mass % or less. Furthermore, this aluminum alloy powder 1 preferably contains precipitates of aluminum rare earth intermetallic compounds having an average width of less than 0.1 μm in its cross-sectional structure.

[0018] The rare earth metal element contained in the aluminum alloy powder 1 is preferably any one of praseodymium (Pr), neodymium (Nd), europium (Eu), samarium (Sm), terbium (Tb), gadolinium (Gd), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). The rare earth metal element contained in the aluminum alloy powder 1 is more preferably any one of europium, samarium, terbium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

[0019] These rare earth elements can be described as being composed of yttrium or other lanthanoid elements. The lanthanoid elements can be selected from one or more of praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. In this embodiment, it is more preferable to use elements with an atomic number larger than that of praseodymium among the rare earth metal elements described above. Scandium (Sc), which is generally included in rare earth metal elements, is scarce among rare earth elements and is particularly expensive, so it was not selected in this embodiment in order to reduce powder costs.

[0020] Rare earth metal group element content: 0.1% by mass or more and 2.0% by mass or less The aluminum alloy powder 1 of this embodiment preferably contains 0.1 mass % or more and 2.0 mass % or less of the above-mentioned rare earth metal element in order to generate a necessary and sufficient liquid phase during sintering and obtain good sinterability. If the content of the rare earth metal element is less than 0.1 mass %, it becomes difficult to obtain a good sintered density. To obtain a higher sintered density, it is more preferable to contain 0.3 mass % or more and 2.0 mass % or less of the above-mentioned rare earth metal element. If the content of the rare earth metal element exceeds 2.0 mass %, an excessive liquid phase is generated during sintering, which leads to the collapse of the sintered compact shape and results in a dull luster on the surface of the sintered compact, reducing the aesthetic appeal of the sintered compact. It is believed that an aluminum alloy containing rare earth metal elements in the above-mentioned range melts at a slightly lower temperature than the aluminum matrix due to eutectic melting, making the aluminum alloy particles more likely to melt from the inside and functioning as a liquid phase into which aluminum atoms diffuse.

[0021] Iron (Fe) content: 2.0% by mass or less The aluminum alloy powder 1 of this embodiment contains the rare earth metal elements described above, and the iron content is preferably limited to 2.0 mass% or less. The iron content is more preferably 1.0 mass% or less, and even more preferably 0.5 mass% or less. While 0 mass% is most preferable, the use of raw materials that do not contain iron increases raw material costs industrially, so the iron content may be within the aforementioned range. If the aluminum alloy powder 1 contains more than 2.0 mass% iron, the iron will preferentially alloy with the rare earth metal elements during sintering to form intermetallic compounds, which may inhibit the diffusion of the rare earth metal elements and impair sinterability. In the aluminum alloy powder 1 of this embodiment, the balance is preferably aluminum and inevitable impurities. The other elements contained in the aluminum alloy powder 1 of this embodiment are not particularly limited.

[0022] For example, the aluminum alloy constituting the aluminum alloy powder 1 may have any composition other than the composition containing the above-mentioned rare earth metal elements and having a regulated iron content. For example, aluminum alloys of any composition system represented by the A1000 series, A2000 series, A3000 series, A4000 series, A5000 series, A6000 series, A7000 series, etc. may be used. Alternatively, aluminum alloy powder made of other general aluminum alloys to which elements not specified in these series of alloys have been added may also be used. A1050 is aluminum with a purity of 99.5% or more, and may contain Fe, Si, and other unavoidable impurities in addition to the rare earth metal elements mentioned above. The A1100 series is an aluminum alloy with a purity of 99% or more. For example, A1100 has a composition of 1.0% or less of Fe and Si in total, approximately 0.05 to 0.20% of Cu, 0.05% or less of Mn, 0.1% or less of Zn, and the remainder of impurities. Note that unless otherwise specified, the percentages indicating the element contents are all mass%.

[0023] The A2000 series is an aluminum alloy with a large amount of Cu added. For example, A2024 is an aluminum alloy containing Si: 0.5% or less, Fe: 0.5% or less, Cu: 3.8 to 4.9%, Mn: 0.3 to 0.9%, Mg: 1.2 to 1.8%, Cr: 0.1% or less, and Zn: 0.25% or less. The A3000 series is an AlMn-based aluminum alloy, and one example is A3003, which is an aluminum alloy containing 0.6% or less of Si, 0.7% or less of Fe, 0.05% or less of Cu, 1.0 to 1.5% of Mn, and 0.1% or less of Zn.

[0024] The A4000 series is an aluminum alloy containing added Si. For example, A4032 is an aluminum alloy containing 11.0 to 13.5% Si, 1.0% or less Fe, 0.5 to 1.3% Cu, 0.8 to 1.3% Mg, 0.10% or less Cr, and 0.25% or less Zn. The A5000 series is an aluminum alloy with added Mg. For example, A5052 is an aluminum alloy containing Si: 0.25% or less, Fe: 0.4% or less, Cu: 0.10% or less, Mn: 0.1% or less, Mg: 2.2 to 2.8%, Cr: 0.15 to 0.35%, and Zn: 0.1% or less.

[0025] The A6000 series is an aluminum alloy with added Mg and Si. For example, A6061 is an aluminum alloy containing Si: 0.4 to 0.8%, Fe: 0.7% or less, Cu: 0.15 to 0.4%, Mn: 0.15% or less, Mg: 0.8 to 1.2%, Cr: 0.15 to 0.35%, Zn: 0.25% or less, and Ti: 0.15% or less. The A7000 series is an aluminum alloy with Zn and Mg as the main additives. For example, A7075 is an aluminum alloy containing Si: 0.4% or less, Fe: 0.5% or less, Cu: 1.2 to 2.0%, Mn: 0.3% or less, Mg: 2.1 to 2.9%, Cr: 0.18 to 0.35%, Zn: 5.1 to 6.1%, and Ti: 0.2% or less.

[0026] Fig. 1 is a schematic diagram showing a cross-section of the metallographic structure of a spherical aluminum alloy powder 1 according to this embodiment. When observing the cross-section of the metallographic structure of the aluminum alloy powder 1, the presence of elongated precipitates consisting of the intermetallic compounds of the rare earth metal element and aluminum can be confirmed. Fig. 1 depicts a plurality of elongated precipitates 2 that can be confirmed in the metallographic photograph when the cross-section of the metallographic structure of the aluminum alloy powder 1 is viewed enlarged. Figure 2 shows an SEM image (2000x magnification) of a cross section of the metal structure obtained in the Examples described later. The SEM image shows the presence of precipitates, indicated by bright lines. These precipitates are presumed to be precipitates composed of intermetallic compounds of aluminum and rare earth metal elements, as will be described in detail in the Examples described later. Figure 1 is a schematic diagram showing the outline of the position and shape of precipitate 2, with lines drawn along the precipitates clearly visible in the SEM image shown in Figure 2. In addition, FIG. 1 shows the precipitates 2 as broken lines or curved lines when viewed from a cross section of the metal structure.

[0027] "Average width of precipitates: less than 0.1 μm" The average width of the precipitates 2 is preferably less than 0.1 μm. When precipitates 2 are present inside particles of aluminum alloy powder 1, the aluminum constituting the particles of aluminum alloy powder 1 and the precipitates 2, each less than 0.1 μm wide, are presumably in a thermodynamically metastable state due to the large interfacial energy (interfacial mismatch) between them. Therefore, heating during sintering causes the precipitates to aggregate together in a manner that is closer to thermodynamic stability, i.e., lowers the interfacial energy. This atomic diffusion is believed to contribute to improved sinterability. While there is no specific lower limit for the average width of precipitates 2, the presence of one or more layers of intermetallic compounds of aluminum and rare earth metals is expected to be effective. For example, if the average width of precipitates 2 is approximately 0.5 nm, it can be assumed that precipitates 2 exist as amorphous particles without a long-period structure, but destabilization due to interfacial energy is expected to exist, and therefore similar effects can be expected.

[0028] In this embodiment, the volume-based 50% cumulative average particle diameter (median diameter D 50 ) is preferably 20 μm or more and 65 μm or less.

[0029] Average particle diameter of aluminum alloy powder 1 (D 50 ) is preferably in the above-mentioned range in order to ensure the necessary molding accuracy while maintaining suitable fluidity when using the aluminum alloy powder 1 of this embodiment in powder metallurgy. If the average particle size of the aluminum alloy powder 1 is larger than 65 μm, the fluidity for sintering purposes is improved, but it becomes difficult to obtain a high-density sintered body when sintered in a powder sintering apparatus. From the viewpoint of obtaining a high-density sintered body for sintering purposes, the average particle size of the aluminum alloy powder 1 is preferably 45 μm or less. If the average particle size of the aluminum alloy powder 1 is smaller than 20 μm, the fluidity decreases and the risk of fire and dust scattering, which are inherent to aluminum powder, increases. Taking these into consideration, it is more preferable that the average particle size of the aluminum alloy powder 1 is 20 μm or more and 45 μm or less.

[0030] The aluminum alloy powder 1 can be produced by, for example, gas atomization. Gas atomization is a method of producing powder consisting of rapidly cooled particles of molten metal by ejecting molten metal from the tip of an injection device such as a nozzle at high speed together with an inert gas into air or an inert gas, thereby rapidly cooling the molten metal. When ejecting the molten metal from the nozzle, an inert gas such as argon gas or nitrogen gas can be used. Gas atomization can produce powder of the desired composition with a uniform particle size. The powder produced by gas atomization can be further classified by sieving or other methods to produce aluminum alloy powder with a uniform particle size.

[0031] Aluminum alloy powder 1 having the above-described composition contains a suitable proportion of rare earth metal elements and has iron content of 2.0 mass% or less. Therefore, when sintered, a necessary and sufficient amount of liquid phase is generated from within the particles, exhibiting a favorable sintering promotion effect. As a result, a sintered body with a uniform shape and high sintering density can be obtained. For example, sintering can be performed by heating to 650°C, which is a temperature range of 660°C or less, in an inert atmosphere for a certain period of time. Aluminum alloy sintered bodies can be produced by the manufacturing method described above. Furthermore, since the iron content of the aluminum alloy powder 1 is controlled to 2.0 mass % or less, it is possible to prevent the iron and rare earth metal elements from combining in the matrix to form intermetallic compounds, and therefore a necessary amount of aluminum-rare earth metal element intermetallic compounds with an average width of less than 0.1 μm are formed in the cross-sectional structure. Therefore, when multiple aluminum alloy powders 1 are mixed and sintered, a necessary and sufficient amount of liquid phase can be produced from each aluminum alloy powder 1, and a high sintered density can be achieved as an aluminum alloy sintered body. Therefore, the aluminum alloy powder 1 is an excellent powder for sintering applications. [Example]

[0032] Pure aluminum powders of Comparative Examples 1 and 2, and aluminum alloy powders of Comparative Example 3 and Examples 1 to 7 shown in Table 1 below were produced by nitrogen gas atomization using molten pure aluminum or aluminum alloy. The powder type, rare earth metal element content, iron content (mass%), median diameter D 50 The value of , the width of linear precipitates in the cross section of the metal structure (10-point average / μm), and the sintered density (%) after sintering were measured, and are shown in Table 1 below. The samples of Comparative Examples 1 to 3 and Examples 1 to 7, except for Example 3, were classified to have a particle size of 45 μm or less, and only the sample of Example 3 was classified to have a particle size of 90 μm or less.

[0033] "Measurement of particle size distribution" The particle size distribution of aluminum alloy powder is measured by laser diffraction method, and the volume-based cumulative diameter (median diameter: D 50 ) was calculated as the average particle size.

[0034] "Measurement of sintered density" The true density was calculated by the Archimedes substitution method. The sintered density shown in Table 1 is expressed as a percentage, with the bulk pure aluminum density taken as 1. The test results for each item explained above are summarized in Table 1 below. In Table 1, glow discharge mass spectrometry (GD-MS) was performed to quantify all rare earth elements, including Sc and Y, for Comparative Examples 1 and 2, and it was confirmed that the total amount of all rare earth elements was 1.7 ppm or less in Comparative Example 1 and 3.8 ppm or less in Comparative Example 2. In other examples, the rare earth element content was measured by ICP (inductively coupled plasma) method.

[0035] For each aluminum alloy powder sample, an FE-SEM image was taken at a magnification of 30,000 times for a randomly selected powder sample, and the width of linear precipitates shown in the image was measured at 10 points to calculate the average value. In Table 1, this is expressed as the 10-point average / μm. Each pure aluminum or aluminum alloy powder sample was filled into a cylindrical boron nitride cell with an inner diameter of approximately 5.6 mm and a depth of approximately 3.5 mm. After 300 tap-fills, the sample was collected at a flow rate of 100 mL min -1 The mixture was sintered by heating to 650°C for 1 hour in an argon gas flow, as shown in the furnace temperature history in Figure 4. The sintered density of each of the obtained sintered bodies was measured, with that of pure aluminum being taken as 1. If the sintered density at this point was below 80%, it could be determined that the amount of liquid phase was insufficient.

[0036] [Table 1]

[0037] FIG. 2 shows a cross-sectional SEM image (2000x magnification) obtained for a powder sample randomly selected from the aluminum alloy powder samples shown in Example 6 of Table 1, and FIG. 3 shows an EDS map image for the cross-sectional SEM image shown in FIG. 2. In the cross section of the metal structure of the aluminum alloy powder shown in Figure 2, we were able to observe structures displayed as bright lines and curves. Furthermore, as shown in Figure 3, a strong signal of a rare earth metal (Sm in this example) was detected from the position of the bright lines and curves shown in Figure 2. For this reason, in this specification, the above-mentioned precipitates are referred to as precipitates of aluminum rare earth metal element intermetallic compounds.

[0038] FIG. 5 shows a cross-sectional FE-SEM image (250x magnification) of a sintered body produced using the pure aluminum powder of Comparative Example 1, FIG. 6 shows a cross-sectional FE-SEM image (250x magnification) of a sintered body produced using the pure aluminum powder of Comparative Example 2, and FIG. 7 shows a cross-sectional FE-SEM image (250x magnification) of a sintered body produced using the aluminum alloy powder of Comparative Example 3. Fig. 8 shows a cross-sectional FE-SEM image (250x magnification) of a sintered body produced using the aluminum alloy powder of Example 1, and Fig. 9 shows a cross-sectional FE-SEM image (250x magnification) of a sintered body produced using the aluminum alloy powder of Example 2. Fig. 10 shows a cross-sectional FE-SEM image (250x magnification) of a sintered body produced using the aluminum alloy powder of Example 3, and Fig. 11 shows a cross-sectional FE-SEM image (250x magnification) of a sintered body produced using the aluminum alloy powder of Example 4.

[0039] Fig. 12 shows a cross-sectional FE-SEM image (250x magnification) of a sintered body produced using the aluminum alloy powder of Example 5, and Fig. 13 shows a cross-sectional FE-SEM image (250x magnification) of a sintered body produced using the aluminum alloy powder of Example 6. Fig. 14 shows a cross-sectional FE-SEM image (250x magnification) of a sintered body produced using the aluminum alloy powder of Example 7. The scale bars (white lines) shown in each of Figs. 5 to 14 indicate 100 µm. Comparing Figs. 5 to 14, it can be seen that the sintered bodies of Comparative Examples 1 to 3 have many voids formed between particles, whereas the sintered bodies of Examples 1 to 7 have almost no gaps between particles, and the particles, which are formed by the accumulation of each aluminum alloy powder and are integrated, are closely bonded to each other.

[0040] FIG. 15 shows a cross-sectional FE-SEM image (30,000x magnification) of the aluminum alloy powder of Comparative Example 3, FIG. 16 shows a cross-sectional FE-SEM image (30,000x magnification) of the aluminum alloy powder of Example 1, and FIG. 17 shows a cross-sectional FE-SEM image (30,000x magnification) of the aluminum alloy powder of Example 2. FIG. 18 shows a cross-sectional FE-SEM image (30,000x magnification) of the aluminum alloy powder of Example 3, FIG. 19 shows a cross-sectional FE-SEM image (30,000x magnification) of the aluminum alloy powder of Example 4, and FIG. 20 shows a cross-sectional FE-SEM image (30,000x magnification) of the aluminum alloy powder of Example 5. FIG. 21 shows a cross-sectional FE-SEM image (30,000x magnification) of the aluminum alloy powder of Example 6, FIG. 22 shows a cross-sectional FE-SEM image (30,000x magnification) of the aluminum alloy powder of Example 7, and FIG. 23 shows a cross-sectional FE-SEM image (30,000x magnification) of a sintered body produced using the aluminum alloy powder of Example 6. The scales in FIGS. 15 to 23 have 11 divisions that represent 1.00 μm, and the width between two adjacent divisions represents 0.1 μm.

[0041] Linear precipitates, which are linear structures with strong brightness, were observed in all of the samples shown in Figures 16 to 23. All of these linear precipitates are thought to be aluminum-rare earth metal element intermetallic compounds in which rare earth metal elements are segregated at higher concentrations than the aluminum of the base material. Even in the aluminum alloy powder of Comparative Example 3, the presence of linear precipitates consisting of aluminum rare earth metal element intermetallic compounds was confirmed as shown in Figure 15. Furthermore, as shown in Table 1, the 10-point average value of the width of the linear precipitates was 0.050 µm. The aluminum alloy powder of Comparative Example 3 also contains 0.59 mass% of Sm. However, as shown in Table 1, the sintered body of Comparative Example 3 had a sintered density of 73.1%, which was insufficient compared to the sintered densities of Examples 1 to 7, which were 82.4 to 97.7%.

[0042] To confirm the reason why the sintered density of the sintered body using the aluminum alloy powder of Comparative Example 3 was not improved, the structure of the sintered body of Comparative Example 3 was observed as shown in Fig. 24. As a result, traces of precipitates that were not present in the grains of the other aluminum alloy powders were confirmed within the grains of some of the aluminum alloy powders. Therefore, for the structure of the sintered body shown in FIG. 24, EDS map images for each element were obtained as shown in FIGS. FIG. 25 shows an Al-K EDS map image, FIG. 26 shows an Fe-K EDS map image, and FIG. 27 shows an Sm-L EDS map image.

[0043] 26 and 27, it was found that the distribution of Fe and the distribution of Sm were almost identical. These EDS map images revealed that when the aluminum alloy powder contains iron, rare earth metal elements (Sm) are also present in the locations where iron (Fe) crystallization occurs. This suggests that iron in the aluminum alloy powder matrix has a high affinity with the rare earth metal elements mentioned above, and when a large amount of iron is present in the aluminum alloy powder, the iron and the rare earth metal elements bond together, consuming the rare earth metal elements. As a result, atomic diffusion of the rare earth metal elements is suppressed, preventing the aluminum alloy powder from becoming liquid, and preventing the sintered structure from becoming denser.

[0044] The aluminum alloy powder of Comparative Example 3 contained 2.1 mass % iron, whereas the aluminum alloy powders of Examples 1 to 7 contained only about 0.017 to 0.18 mass % iron, which is thought to be the cause of the different sintered densities. When the rare earth elements are added to aluminum powder to produce an aluminum alloy powder, the iron and rare earth elements are bound together, and the rare earth elements are trapped within the crystal grains. As a result, the amount of rare earth elements that diffuses is reduced, and the amount of liquid phase that forms on the surface of the crystal grains is also reduced. For this reason, the density of the sintered body made of the aluminum alloy powder of Comparative Example 3 is not improved. Therefore, the particle size range mentioned above (median diameter D 50 When the aluminum alloy powder (particle size: 20 μm or more and 65 μm or less) contains the above-mentioned rare earth metal element in an amount of about 0.1 mass % or more and 2.0 mass % or less, by suppressing the iron content to 2.0 mass % or less, it can be presumed that a necessary and sufficient amount of liquid phase is generated during sintering, and the aluminum alloy powder particles are bonded together efficiently, resulting in a sintered body with a high sintering density.

[0045] As shown in the results in Table 1, the samples of Examples 1 to 7 are aluminum alloy powders containing 0.1 mass % to 2.0 mass % of one or more metal elements selected from the rare earth metal elements consisting of yttrium and lanthanoid elements, and containing precipitates of aluminum rare earth intermetallic compounds with an average width of less than 0.1 μm in the cross-sectional structure. 50 However, the particle size is 20 μm or more and 65 μm or less. Furthermore, the aluminum alloy powders of these examples have iron content suppressed to 2.0 mass % or less. The aluminum alloys of Examples 1 to 7 exhibited good sinterability. Furthermore, because the aluminum alloys of Examples 1 to 7 contained small amounts of rare earth metal elements, even when sintered with the aluminum alloy powder, they exhibited the inherent luster of aluminum and retained the inherent electrical and thermal conductivity of aluminum.

[0046] As shown in Table 1, the aluminum alloy powders of Examples 1 to 7 were able to obtain sintered bodies with high sintered densities in the range of 82.4 to 97.7%, and also able to obtain sintered bodies with regular shapes that were not subject to shape collapse due to excessive generation of liquid phase. In contrast to these example samples, the samples of Comparative Examples 1 and 2 had low rare earth metal element contents and were therefore unable to achieve high sintered densities. The sample of Comparative Example 3 contained an appropriate amount of rare earth metal elements and produced precipitates, but the iron content exceeded 2.0 mass %, meaning that the sintered density could not be increased.

[0047] Incidentally, in the case of a structure in which precipitates with an average width of less than 0.1 μm exist inside the metal structure of the aluminum alloy powder, it is believed that there is an influence of interfacial energy, as explained in the embodiment. When precipitates exist within the metal structure of aluminum alloy powder, the aluminum that makes up the particles of the aluminum alloy powder and the precipitates with a width of less than 0.1 μm have a large destabilization energy (interfacial energy) due to interface mismatch, and it is presumed that they are in a thermodynamically metastable state. For this reason, heating during sintering causes them to aggregate together in a thermodynamically more stable state, i.e., with a smaller interfacial energy, and it is thought that the atomic diffusion that occurs at this time contributes to improving sinterability. This can be estimated from the cross-sectional FE-SEM image of the sintered body shown in FIG.

[0048] In the cross-sectional FE-SEM image of Figure 23, the highly bright linear structures (precipitates) in the structure have accumulated together, expanding the cross section to a width of approximately 0.3 μm. Therefore, in order to achieve the above-mentioned effects during sintering, it is believed that the aluminum rare earth metal element intermetallic compound must have an average width of less than 0.1 μm. That is, in the state of aluminum alloy powder before sintering, the precipitates of aluminum-rare earth metal element intermetallic compounds must have an average width of less than 0.1 μm and be in a thermodynamically metastable state with high interfacial energy. If they grow to 0.3 μm or more as shown in Figure 23, the interfacial energy becomes low and they are thought not to exhibit their full functionality.

[0049] For example, in INFridlyander et al., Met. Sci. Heat Treat. 34, 202-205 (1992), a casting alloy having a composition of Al-0.35 wt % Dy was prepared. In this paper, the authors state that "spherical intermetallic compounds with a diameter of approximately 2 μm are formed." When aluminum rare earth intermetallic compounds have a diameter of approximately 2 μm, the interfacial energy is low and is therefore unlikely to be a driving force for inducing atomic rearrangement for sintering. [Explanation of symbols]

[0050] 1...Aluminum alloy powder, 2…precipitates.

Claims

1. An aluminum alloy powder characterized by containing 0.1 mass% or more and 2.0 mass% or less of one or more metal elements selected from rare earth metal elements consisting of yttrium and lanthanoid elements, and having an iron content suppressed to 2.0 mass% or less.

2. 2. The aluminum alloy powder according to claim 1, wherein the rare earth metal element is any one of praseodymium, neodymium, europium, samarium, terbium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

3. The aluminum alloy powder according to claim 1 or 2, which is used for sintering.

4. Median diameter D, which is the average particle diameter of 50% of the total volume measured by laser diffraction / scattering method ５０ The aluminum alloy powder according to claim 1 or 2, characterized in that the particle size is 20 μm or more and 65 μm or less.

5. 3. The aluminum alloy powder according to claim 1, wherein the cross-sectional structure contains precipitates of aluminum rare earth intermetallic compounds having an average width of less than 0.1 μm.

6. An aluminum alloy sintered body characterized by containing 0.1 mass % or more to 2.0 mass % or less of one or more metal elements selected from rare earth metal elements consisting of yttrium and lanthanoid elements, and having an iron content suppressed to 2.0 mass % or less.

7. 7. The aluminum alloy sintered body according to claim 6, wherein the rare earth metal element is any one of praseodymium, neodymium, europium, samarium, terbium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

8. 8. The aluminum alloy sintered body according to claim 6, wherein the cross-sectional structure contains precipitates of an aluminum rare earth intermetallic compound.

9. An aluminum alloy powder containing 0.1 mass% or more to 2.0 mass% or less of one or more rare earth metal elements consisting of yttrium and lanthanoid elements, and an iron content suppressed to 2.0 mass% or less, A method for producing an aluminum alloy sintered body, characterized by heating in an inert atmosphere at a temperature range of 660°C or less.

10. 10. The method for producing an aluminum alloy sintered body according to claim 9, wherein the rare earth metal element is any one of praseodymium, neodymium, europium, samarium, terbium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

11. The aluminum alloy powder has a median diameter D, which is the average particle diameter of 50% cumulative volume measured by a laser diffraction / scattering method. ５０ 11. The method for producing an aluminum alloy sintered body according to claim 9, wherein the aluminum alloy powder has a particle size of 20 μm or more and 65 μm or less.

12. 11. The method for producing an aluminum alloy sintered body according to claim 9, wherein the aluminum alloy powder contains precipitates of an aluminum rare earth intermetallic compound having an average width of less than 0.1 μm in a cross-sectional structure.

13. 12. The method for producing an aluminum alloy sintered body according to claim 11, wherein the aluminum alloy powder contains precipitates of an aluminum rare earth intermetallic compound having an average width of less than 0.1 μm in a cross-sectional structure.

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