Aluminum alloy powder, aluminum alloy sintered body, and method for producing aluminum alloy sintered body

Abstract

Provided is an aluminum alloy powder comprising 0.1-2.0 mass% or one or more metal elements from among rare earth metal elements comprising the lanthanide elements and yttrium, wherein the iron content is suppressed to not more than 2.0 mass%. The rare earth metal element is preferably one of praseodymium, neodymium, europium, samarium, terbium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

Description

Aluminum alloy powder, aluminum alloy sintered body, and method for manufacturing the aluminum alloy sintered body

[0001] The present invention relates to an aluminum alloy powder having excellent sinterability, an aluminum alloy sintered body, and a method for manufacturing the aluminum alloy sintered body. This application claims priority to Japanese Patent Application No. 2024-079403, filed on May 15, 2024, the contents of which are incorporated herein by reference.

[0002] Aluminum is used for heat sinks in equipment due to its light weight and excellent electrical and thermal conductivity. However, the formation of a dense, strong oxide film on its surface, which protects the interior, poses significant processing limitations. For castings, flux (brazing filler metal) is used to break down the surface oxide film and join components to create the desired shape. However, this method poses challenges in achieving sufficient precision 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 (PSS) enables near-net-shape manufacturing, and its technological development is expected to provide a means of inexpensively achieving complex shapes. However, even with PSS, the formation of an oxide film makes aluminum difficult to sinter, which 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 density 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 about 10 μm in size, it is difficult to destroy the oxide film using flux, making it difficult to increase the density of the structure.

[0004] One method for solving this problem is alloying with different elements. 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, the introduction of an additive element such as silicon (Si) widens the liquid phase generation temperature range and ensures stable sintering.

[0005] The following Patent Document 1 discloses a technology for additive manufacturing in which about 2 mass% of Zr fine particles are added to A2219 aluminum alloy powder to form a mixed 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 applied to additive manufacturing technology. Patent Document 3 discloses an aluminum alloy applied to additive manufacturing technology that contains copper (Cu) and Mg as alloy elements and further contains Zr, Y, Er, etc. as element X. ３ An aluminum alloy having a precipitate phase designated X is disclosed.

[0006] U.S. Patent Application Publication No. 2020 / 0199716 (A) U.S. Patent Application Publication No. 2018 / 0080103 (A) U.S. Patent Application Publication No. 2018 / 0245190 (A)

[0007] In conventional technology, silicon is added to aluminum, and because it is a semimetal, adding silicon is expected to improve sinterability, but there is a problem in that it impairs aluminum's advantages of electrical conductivity and thermal conductivity. For this reason, the inventors selected additive elements that do not impair aluminum's advantages of electrical conductivity and thermal conductivity, and conducted extensive research into additive elements that can be used in powder sintering to increase the density of the sintered body structure, and arrived at the present invention.

[0008] The present invention was devised in view of the above-mentioned problems, and its object is to provide an aluminum alloy powder that can achieve excellent sinterability without impairing the electrical 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 manufacturing the aluminum alloy sintered body.

[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 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, it is preferable that the rare earth metal element is 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 regard to the aluminum alloy powder according to (1) or (2) of the present invention, it is preferable that the median diameter D50, which is the cumulative average particle diameter on a volume basis of 50% as measured by a laser diffraction / scattering method, is 20 μm or more and 65 μm or less. (5) With regard to the aluminum alloy powder according to (1) or (2) of the present invention, it is preferable that the cross-sectional structure contains precipitates of an aluminum rare earth intermetallic compound 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 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. (7) In the aluminum alloy sintered body according to (6) of the present invention, it is preferable that the rare earth metal element is 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 aspect of the present invention is characterized in that an aluminum alloy powder containing 0.1 mass % to 2.0 mass % of one or more metal elements selected from rare earth metal elements consisting of yttrium and lanthanoid elements 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) A method for producing an aluminum alloy sintered body according to (9) of the present invention is characterized in that 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, it is preferable to use an aluminum alloy powder having a median diameter D50, which is the cumulative average particle diameter of 50% on a volume basis measured by a laser diffraction / scattering method, 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 aluminum rare earth intermetallic compounds with an average width of less than 0.1 μm in its 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 aluminum rare earth intermetallic compounds with an average width of less than 0.1 μm in its cross-sectional structure.

[0015] According to one embodiment of the present invention, an aluminum alloy powder containing a suitable amount of rare earth metal elements and a suppressed iron content of 2.0 mass% or less can be provided, which has precipitates of aluminum rare earth intermetallic compounds with an average width of less than 0.1 μm in the structure, and can produce a high-density sintered body. Unlike silicon, which is a metalloid, rare earth metal elements are metals, and therefore do not impair the inherently good electrical and thermal conductivity of aluminum compared to the addition of silicon. Furthermore, because rare earth metal elements have an atomic weight approximately five times larger than that of aluminum, even when added in amounts equivalent to conventionally added silicon, the amount can be significantly reduced in terms of composition ratio and atomic ratio. Assuming an amount equivalent to the amount of conventionally added silicon, the degree of impairment of the electrical and thermal conductivity of the aluminum body can be reduced.

[0016] 1 is a cross-sectional schematic diagram showing an example of the metal structure of the aluminum alloy powder according to the first embodiment of the present invention. A cross-sectional FE-SEM image showing an example of the aluminum alloy powder obtained in Example 6. An EDS map image of the same metal powder taken at a position corresponding to the cross-sectional SEM image shown in FIG. 2 . A graph showing the temperature history inside a furnace when a sintered body was produced using the aluminum alloy powder in the examples. An FE-SEM image of the structure of the aluminum alloy sintered body produced using the pure aluminum powder of Comparative Example 1, observed at 250x magnification. An FE-SEM image of the structure of the aluminum alloy sintered body produced using the pure aluminum powder of Comparative Example 2, observed at 250x magnification. An FE-SEM image of the structure of the aluminum alloy sintered body produced using the aluminum alloy powder of Comparative Example 3, observed at 250x magnification. An FE-SEM image of the structure of the aluminum alloy sintered body produced using the aluminum alloy powder of Example 1, observed at 250x magnification. An FE-SEM image of the structure of the aluminum alloy sintered body produced using the aluminum alloy powder of Example 2, observed at 250x magnification. 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. 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. 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. 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. FE-SEM image of the structure of an aluminum alloy sintered body produced using the aluminum alloy powder of Example 7, observed at 30,000x magnification. FE-SEM image of the metal structure of the aluminum alloy powder of Comparative Example 3, observed at 30,000x magnification. FE-SEM image of the metal structure of the aluminum alloy powder of Example 1, observed at 30,000x magnification. FE-SEM image of the metal structure of the aluminum alloy powder of Example 2, observed at 30,000x magnification. FE-SEM image of the metal structure observed at a magnification of 30,000 times for the aluminum alloy powder of Example 3. FE-SEM image of the metal structure observed at a magnification of 30,000 times for the aluminum alloy powder of Example 4.24. FE-SEM image of the metal structure observed at 30,000x magnification for the aluminum alloy powder of Example 5. FE-SEM image of the metal structure observed at 30,000x magnification for the aluminum alloy powder of Example 6. FE-SEM image of the metal structure observed at 30,000x magnification for the aluminum alloy powder of Example 7. FE-SEM image of the metal structure observed at 30,000x magnification for the aluminum alloy powder of Example 6. SEM image of the structure observed at 500x magnification for the aluminum alloy sintered body produced from the aluminum alloy powder of Comparative Example 3. Al-K EDS map for the SEM image shown in FIG. 24. Fe-K EDS map for the SEM image shown in FIG. 24. Sm-L EDS map for the SEM image shown in FIG. 24.

[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 rare earth metal elements consisting of yttrium and lanthanoid elements, and having an iron content suppressed to 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 may 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 atomic numbers larger than that of praseodymium among the rare earth metal elements. Scandium (Sc), which is generally included among rare earth metal elements, is scarce among rare earth elements and particularly expensive, so it was not selected in this embodiment 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% by mass or more and 2.0% by mass or less of the above-mentioned rare earth metal elements in order to generate a sufficient liquid phase during sintering and obtain good sinterability. If the rare earth metal element content is less than 0.1% by mass, it becomes difficult to obtain a good sintered density. To obtain a higher sintered density, it is more preferable to contain 0.3% by mass or more and 2.0% by mass or less of the above-mentioned rare earth metal elements. If the rare earth metal element content exceeds 2.0% by mass, an excessive liquid phase is generated during sintering, which leads to the collapse of the sintered compact shape and the dull luster of the sintered compact surface, thereby reducing the aesthetic appeal of the sintered compact. Although not particularly limited, the rare earth metal element content may be 0.6% by mass or more and 1.8% by mass or less. 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% by mass or less. Furthermore, the iron content is more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less. While 0% by mass is most preferable, the use of iron-free raw materials 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% by mass of iron, the iron may 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 remainder is preferably aluminum and unavoidable impurities. The other elements contained in the aluminum alloy powder 1 of this embodiment are not particularly limited. Although not particularly limited, the lower limit of the iron content may be 0.01% by mass.

[0022] For example, the aluminum alloy constituting the aluminum alloy powder 1 may be any aluminum alloy with any composition, provided that it contains the aforementioned rare earth metal elements and has a regulated iron content. For example, aluminum alloys of any composition system, such as the A1000 series, A2000 series, A3000 series, A4000 series, A5000 series, A6000 series, and A7000 series, may be used. Alternatively, aluminum alloy powders made of other common aluminum alloys to which elements not specified in these series are added may be used. A1050 is aluminum with a purity of 99.5% or higher and may contain, in addition to the aforementioned rare earth metal elements, Fe and Si as inevitable impurities. The A1100 series is an aluminum alloy with a purity of 99% or higher. For example, A1100 has a composition of 1.0% or less Fe and Si in total, approximately 0.05 to 0.20% Cu, 0.05% or less Mn, 0.1% or less Zn, and the remainder being impurities. Unless otherwise specified, the percentages indicating the contents of elements all refer to mass %.

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

[0024] The A4000 series is an aluminum alloy containing Si, such as A4032, which contains 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 containing Mg, such as A5052, which contains 0.25% or less Si, 0.4% or less Fe, 0.10% or less Cu, 0.1% or less Mn, 2.2 to 2.8% Mg, 0.15 to 0.35% Cr, and 0.1% or less Zn.

[0025] The A6000 series is an aluminum alloy containing Mg and Si, such as A6061, which contains 0.4-0.8% Si, 0.7% or less Fe, 0.15-0.4% Cu, 0.15% or less Mn, 0.8-1.2% Mg, 0.15-0.35% Cr, 0.25% or less Zn, and 0.15% or less Ti. The A7000 series is an aluminum alloy containing mainly Zn and Mg, such as A7075, which contains 0.4% or less Si, 0.5% or less Fe, 1.2-2.0% Cu, 0.3% or less Mn, 2.1-2.9% Mg, 0.18-0.35% Cr, 5.1-6.1% Zn, and 0.2% or less Ti.

[0026] FIG. 1 is a schematic diagram showing a metallographic cross-section of a spherical aluminum alloy powder 1 according to this embodiment. Observation of the metallographic cross-section of the aluminum alloy powder 1 confirms the presence of elongated precipitates composed of the intermetallic compounds of rare earth metal elements and aluminum. FIG. 1 depicts a magnified view of the metallographic cross-section of the aluminum alloy powder 1, revealing multiple elongated precipitates 2 that could be seen in the metallographic photograph. The metallographic cross-section may be any cross-section of the aluminum alloy powder 1. The metallographic cross-section may be any cross-section having a cross-sectional area of ​​0.00002% or more of the maximum cross-sectional area of ​​the aluminum alloy powder 1. FIG. 2 shows an SEM image (2000x magnification) of the metallographic cross-section obtained in the Examples described below. The SEM image shows the presence of precipitates indicated by bright lines. These precipitates can be 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 below. FIG. 1 is a schematic diagram showing the outline of the position and shape of precipitates 2, with lines drawn along the precipitates clearly visible in the SEM image shown in FIG. 2. 1 depicts the precipitate 2 as a broken line or a curved line when viewing a cross section of the metal structure. The content of the rare earth metal element relative to the total content of the rare earth metal element and the aluminum content contained in the precipitate 2 may be 5 atomic % or more and 95 atomic % or less, 10 atomic % or more and 75 atomic % or less, or 15 atomic % or more and 67 atomic % or less. The content of aluminum relative to the total content of the rare earth metal element and the aluminum content contained in the precipitate 2 may be 5 atomic % or more and 95 atomic % or less, 25 atomic % or more and 90 atomic % or less, or 33 atomic % or more and 85 atomic % or less.

[0027] "Average width of precipitates: less than 0.1 μm" The average width of precipitates 2 is preferably less than 0.1 μm. When precipitates 2 are present inside particles of aluminum alloy powder 1, it can be assumed that the aluminum constituting the particles of aluminum alloy powder 1 and precipitates 2 with widths less than 0.1 μm have large destabilization energy (interfacial energy) due to interface mismatch, resulting in a thermodynamically metastable state. Therefore, heating during sintering causes the precipitates to aggregate together in a manner that is closer to thermodynamic stability, i.e., reduces the interfacial energy, and atomic diffusion at this time is thought to contribute to improved sinterability. While there is no particular lower limit for the average width of precipitates 2, the presence of one or more layers of an intermetallic compound of aluminum and a rare earth metal can be expected to be effective. For example, when the average width of precipitates 2 is approximately 0.5 nm, it can be assumed that precipitates 2 exist as amorphous with no long-period structure, but destabilization due to interfacial energy is expected to exist, and therefore a similar effect can be expected.

[0028] In this embodiment, the volume-based 50% cumulative average particle diameter (median diameter D50) of the aluminum alloy powder 1 measured by a laser diffraction / scattering method is preferably 20 μm or more and 65 μm or less.

[0029] When using the aluminum alloy powder 1 of this embodiment in powder metallurgy, the average particle size (D50) of the aluminum alloy powder 1 is preferably within the above-mentioned range in order to ensure the necessary molding accuracy while maintaining suitable fluidity. If the average particle size of the aluminum alloy powder 1 is greater than 65 μm, the fluidity for sintering applications 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 higher-density sintered body for sintering applications, 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 less than 20 μm, the fluidity decreases and the risk of fire and dust dispersion, which are specific to aluminum powder, increases. Taking these factors into consideration, the average particle size of the aluminum alloy powder 1 is more preferably 20 μm or more and 45 μm or less.

[0030] The aluminum alloy powder 1 can be produced, for example, by gas atomization. Gas atomization is a method in which molten metal is ejected at high speed from the tip of an injection device such as a nozzle into air or an inert gas at high speed together with an inert gas, thereby rapidly cooling the molten metal and producing powder made of particles formed by 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 a target composition with a uniform particle size. The powder produced by gas atomization can also be further classified by a method such as sieving to produce aluminum alloy powder with a uniform particle size.

[0031] The aluminum alloy powder 1 having the above-described composition contains a suitable proportion of rare earth metal elements and has an 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-promoting effect. As a result, a sintered body with a uniform shape and high sintering density can be obtained. As an 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. The above-described manufacturing method can produce an aluminum alloy sintered body. Furthermore, since the iron content of the aluminum alloy powder 1 is limited to 2.0 mass% or less, the formation of intermetallic compounds due to the combination of iron and rare earth metal elements in the matrix can be suppressed. Therefore, a necessary amount of aluminum-rare earth metal intermetallic compounds with an average width of less than 0.1 μm is generated 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 generated from each aluminum alloy powder 1, resulting in a high sintered density of the aluminum alloy sintered body. Therefore, the aluminum alloy powder 1 is an excellent powder for sintering applications.

[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 D50 value, width of linear precipitates in the cross section of the metal structure (10-point average / μm), and sintered density (%) after sintering were measured for each sample shown in Comparative Examples 1 to 3 and Examples 1 to 7, and the results 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 the aluminum alloy powder was measured by laser diffraction, and the volume-based frequency cumulative diameter (median diameter: D50) was calculated as the average particle size from the obtained results.

[0034] "Measurement of Sintered Density" True density was calculated by Archimedes' substitution method. The sintered density shown in Table 1 is expressed as a percentage, with the density of bulk pure aluminum being set to 1. The test results for each item described above are summarized in Table 1 below. Note that 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 30,000x for a randomly selected powder sample. The width of linear precipitates displayed in the image was measured at 10 locations, and the average value was calculated. Table 1 shows the average value per 10 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 cells were sintered by heating to 650°C for 1 hour in an argon gas flow of 100 mL min-1, as shown in the furnace temperature history shown in Figure 4. The sintered density of each sintered body was measured, with the sintered density of pure aluminum taken as 1. If the sintered density at this point was below 80%, it was determined that the liquid phase was insufficient.

[0036]

[0037] Figure 2 shows a cross-sectional SEM image (2000x magnification) taken of a powder sample randomly selected from the aluminum alloy powder sample shown in Example 6 of Table 1, and Figure 3 shows an EDS map image of the cross-sectional SEM image shown in Figure 2. In the metallographic cross-section of the aluminum alloy powder shown in Figure 2, a structure represented by bright broken lines and curves could be observed. 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 broken 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] Figure 12 shows a cross-sectional FE-SEM image (250x magnification) of a sintered body produced using the aluminum alloy powder of Example 5, and Figure 13 shows a cross-sectional FE-SEM image (250x magnification) of a sintered body produced using the aluminum alloy powder of Example 6. Figure 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 Figures 5 to 14 indicate 100 μm. Comparing Figures 5 to 14 reveals that the sintered bodies of Comparative Examples 1 to 3 have numerous voids formed between particles, whereas the sintered bodies of Examples 1 to 7 have almost no gaps between particles, and the particles are tightly bonded together, with each aluminum alloy powder agglomerating to form an integrated unit.

[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 representing 1.00 µm, with the width between two adjacent divisions representing 0.1 µm.

[0041] In all of the samples shown in Figures 16 to 23, linear precipitates, which are linear structures with strong brightness, were observed. All of these linear precipitates are believed to be aluminum-rare earth metal intermetallic compounds in which rare earth metal elements are segregated at higher concentrations than the aluminum substrate. Even in the aluminum alloy powder of Comparative Example 3, the presence of linear precipitates composed of aluminum-rare earth metal intermetallic compounds was confirmed, as shown in Figure 15. Furthermore, as shown in Table 1, the 10-point average width of the linear precipitates was 0.050 μm. The aluminum alloy powder of Comparative Example 3 also contained 0.59 mass% Sm. However, as shown in Table 1, the sintered compact of Comparative Example 3 had a sintered density of 73.1%, which was insufficient compared to the sintered densities of 82.4 to 97.7% shown for the sintered compacts of Examples 1 to 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 were confirmed within some aluminum alloy powder grains that were not present within other aluminum alloy powder grains. Therefore, EDS map images for each element were obtained for the structure of the sintered body shown in Fig. 24, as shown in Figs. 25 to 27. 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 at the locations where iron (Fe) crystallization is present. This indicates that iron has a high affinity with the rare earth metal elements in the aluminum alloy powder matrix, and when a large amount of iron is present in the aluminum alloy powder, the iron and the rare earth metal elements are bonded together, resulting in the consumption of the rare earth metal elements. As a result, it is believed that the atomic diffusion of the rare earth metal elements is suppressed, preventing the aluminum alloy powder from becoming liquid phase and preventing the densification of the sintered structure.

[0044] The aluminum alloy powder of Comparative Example 3 contained 2.1% by mass of iron, while the aluminum alloy powders of Examples 1 to 7 contained only approximately 0.017 to 0.18% by mass of iron. This is believed to be the cause of the different sintered densities. When the rare earth elements described above are added to aluminum powder to produce aluminum alloy powder, the iron and rare earth metal elements bond together, trapping the rare earth metal elements within the crystal grains. This reduces the amount of rare earth metal elements diffusing and reduces the amount of liquid phase generated on the surface of the crystal grains. For this reason, it is believed that the density of the sintered body made from the aluminum alloy powder of Comparative Example 3 was not improved. Therefore, when the aluminum alloy powder having the particle size range described above (median diameter D50: 20 μm to 65 μm) contains approximately 0.1% to 2.0% by mass of the rare earth metal elements, by limiting the iron content to 2.0% by mass or less, a necessary and sufficient amount of liquid phase is generated during sintering, efficiently bonding the aluminum alloy powder particles together, resulting in a sintered body with a high sintered 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 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. Furthermore, the aluminum alloy powders of these Examples have a median diameter D50 of 20 μm to 65 μm. 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 amount of rare earth metal elements contained in the aluminum alloys of Examples 1 to 7 was small, even when sintered into aluminum alloy powders, 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 capable of producing sintered bodies with high sintered densities in the range of 82.4 to 97.7%, and of producing sintered bodies with regular shapes that were free from shape collapse due to excessive liquid phase generation. In contrast to these example samples, the samples of Comparative Examples 1 and 2 were unable to achieve high sintered densities due to their low rare earth metal element contents. 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%, preventing a high sintered density.

[0047] Incidentally, in the case of a structure in which precipitates with an average width of less than 0.1 μm exist within the metal structure of an aluminum alloy powder, it is believed that the influence of interfacial energy is present, as explained in the embodiment. When precipitates exist within the metal structure of an aluminum alloy powder, it can be assumed that the aluminum constituting the aluminum alloy powder particles and the precipitates with a width of less than 0.1 μm have a large destabilization energy (interfacial energy) due to interface mismatch, resulting in a thermodynamically metastable state. Therefore, it is believed that heating during sintering brings the particles into a more thermodynamically stable state, i.e., aggregates them so that the interfacial energy is smaller, and atomic diffusion at this time contributes to improving sinterability. This assumption can be inferred from the cross-sectional FE-SEM image of the sintered body shown in FIG. 23 .

[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 aforementioned 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 the aluminum alloy powder before sintering, the precipitates of the aluminum rare earth metal element intermetallic compound 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 to not exhibit full functionality.

[0049] For example, I. N. Fridlyander et al., Met. Sci. Heat Treat. 34, 202-205 (1992), reported that a casting alloy having a composition of Al-0.35 wt% Dy was produced. In this document, the authors stated that "spherical intermetallic compounds with a diameter of approximately 2 μm were formed." When aluminum rare earth intermetallic compounds have a diameter of approximately 2 μm, the interfacial energy is low and it is thought that they do not act as a driving force for inducing atomic rearrangement for sintering.

[0050] It is possible to provide an aluminum alloy powder that can give a high-density sintered body having excellent electrical conductivity and thermal conductivity.

[0051] 1 Aluminum alloy powder 2 Precipitate

Claims

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

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, characterized in that it is used for sintering.

4. The aluminum alloy powder according to claim 1 or 2, characterized in that the median diameter D50, which is the cumulative average particle diameter of 50% of the volume as measured by a laser diffraction / scattering method, is 20 μm or more and 65 μm or less.

5. The aluminum alloy powder according to claim 1 or 2, characterized in that 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 and 2.0 mass% or less of one or more rare earth metal elements consisting of yttrium and lanthanoid elements, and having an iron content suppressed to 2.0 mass% or less.

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. The aluminum alloy sintered body according to claim 6 or 7, characterized in that the cross-sectional structure contains precipitates of aluminum rare earth intermetallic compounds.

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

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. A method for producing an aluminum alloy sintered body as set forth in claim 9 or 10, characterized in that the aluminum alloy powder used has a median diameter D50, which is the cumulative average particle diameter of 50% of the volume measured by laser diffraction / scattering method, of 20 μm or more and 65 μm or less.

12. A method for producing an aluminum alloy sintered body as set forth in claim 9 or claim 10, characterized in that the aluminum alloy powder contains precipitates of aluminum rare earth intermetallic compounds having an average width of less than 0.1 μm in the cross-sectional structure.

13. A method for producing an aluminum alloy sintered body as set forth in claim 11, characterized in that the aluminum alloy powder contains precipitates of aluminum rare earth intermetallic compounds having an average width of less than 0.1 μm in the cross-sectional structure.

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