Aluminum alloy molded body and method for producing same

Abstract

[Problem] To provide: an aluminum alloy molded body that is suitable for industrial materials such as automobile parts, mechanical parts, and structural materials and exhibits a Young's modulus of 80 GPa or higher by an aluminum alloy alone without mixing ceramics such as alumina or silicon carbide; and an efficient method for producing the aluminum alloy molded body. [Solution] An aluminum alloy molded body that contains 4-11 mass% of Mn and 1-4 mass% of Cr and satisfies the relationship 1.9 × Cr mass% ≤ Mn mass% ≤ 5.3 × Cr mass%, the balance being inevitable impurities and aluminum, wherein the aluminum alloy molded body is characterized in that the Young's modulus at room temperature (25°C) is 80 GPa or higher.

Description

Aluminum alloy formed body and its manufacturing method

[0001] The present invention relates to an aluminum alloy formed product and a method for producing the same, and more particularly to an aluminum alloy formed product with a high Young's modulus that can be suitably used for automobile parts and the like, and a simple and efficient method for producing the same.

[0002] Aluminum alloys are used in automobile parts, machine parts, structural materials, etc., but their Young's modulus is approximately 70 to 75 GPa, which is significantly smaller than the 200 GPa of steel and the 110 GPa of titanium alloys, and this has limited the applications of aluminum alloys.

[0003] In response to this, for example, Patent Document 1 proposes an aluminum alloy for plastic working that can obtain high tensile strength, high Young's modulus, and high ductility and is useful for high-performance components such as bicycle parts, fishing tackle, golf clubs, and snowboards, and a method for producing the same, proposing "a solidified formed material obtained by mixing an aluminum alloy powder containing 0.4 to 2.0 wt. % of Si, 0.4 to 2.0 wt. % of Mg, and further containing 0.5 to 2.0 wt. % of one or more elements selected from Fe, Mn, and Cr, with the balance being Al containing unavoidable impurities, with 10 to 25 wt. % of alumina, the aluminum alloy for plastic working being characterized by having a Young's modulus of 80 GPa or more at room temperature, a room temperature tensile strength of 300 MPa or more after water quenching, and an elongation of 5% or more."

[0004] The aluminum alloy for plastic processing described in Patent Document 1 has high tensile strength and high Young's modulus, making it useful for high-performance components such as bicycle parts, fishing tackle, golf clubs, and snowboards. While conventional products have an elongation of less than 5% even when the alumina content is 10% by weight, this invention has an elongation of 8% even when the alumina content is 10% by weight or more, and is therefore said to have excellent ductility and be suitable for plastic processing.

[0005] Furthermore, in Non-Patent Document 1, in order to obtain a molded body with excellent properties such as a high Young's modulus by additive manufacturing, a molded body using an AlSi10Mg-10% wtSiC mixed powder as the raw material was investigated, and a Young's modulus of 75 to 90 GPa was obtained.

[0006] Japanese Patent Application Laid-Open No. 2005-298871

[0007] Dongyun Zhang et al. SiC reinforced AlSi10Mg composites fabricated by selective laser melting, Journal of Alloys and Compounds, Volume 894 (2022)

[0008] However, in the aluminum alloy for plastic working described in Patent Document 1, it is necessary to add 10 to 25 mass % of alumina to the aluminum alloy powder and mix them uniformly to obtain a formed material, and if the alumina is not mixed uniformly, the strength of that region will be reduced, and as a result, that region will often become the starting point of fracture.

[0009] Even if the materials are mixed uniformly, the process required for uniform mixing increases costs. Additionally, mixing ceramics results in poor toughness and poor workability. Furthermore, when recycling scrap, the aluminum alloy and alumina must be separated, which poses a problem for recyclability.

[0010] Furthermore, in addition to the recyclability issues mentioned above, the shaped bodies obtained in Non-Patent Document 1 have a low elongation of 1.2% or less for the as-shaped material, so that if the size of the shaped body becomes large, there is a risk of cracks occurring due to thermal stress during shaping.

[0011] In the case of additive manufacturing that does not use ceramics, Young's modulus can be increased by adding large amounts of elements such as iron (Fe) and silicon (Si) to aluminum, but this reduces the ductility of the manufactured object, making it prone to cracks for the same reasons as above, making it difficult to commercialize.

[0012] In view of the problems in the prior art as described above, an object of the present invention is to provide an aluminum alloy formed product that exhibits a Young's modulus of 80 GPa or more using aluminum alloy alone without mixing with ceramics such as alumina or silicon carbide, and is suitable for use as an industrial material such as automobile parts, machine parts, and structural materials, and to provide an efficient method for producing the same.

[0013] In order to achieve the above object, the present inventors have conducted extensive research into the relationship between the composition and microstructure of an aluminum alloy and the Young's modulus of an aluminum alloy formed body, and have found that by optimizing the contents of Mn and Cr and performing an appropriate heat treatment, it is possible to obtain a high Young's modulus of Al. １２ The present inventors have found that forming a G phase, which is a (Mn, Cr) compound, is extremely effective, and have arrived at the present invention.

[0014] That is, the present invention provides an aluminum alloy formed product comprising 4 to 11 mass% of Mn and 1 to 4 mass% of Cr, satisfying the relationship 1.9×Cr mass%≦Mn mass%≦5.3×Cr mass%, with the remainder consisting of unavoidable impurities and aluminum, and having a Young's modulus of 80 GPa or more at room temperature (25°C).

[0015] In the aluminum alloy formed body of the present invention, Al １２ It is preferable that the volume fraction of the G phase, which is a (Mn, Cr) compound, is 10 to 90%. By dispersing a large amount of the G phase in the aluminum alloy molded body, it is possible to impart a high Young's modulus to the aluminum alloy molded body. Furthermore, as a result of intensive studies by the present inventors, it has been found that, for example, ７ Cr / Al １３ Cr ２ It was revealed that a higher Young's modulus can be obtained by forming the G phase compared to the case where the Al--Mn--Si phase or the G phase is formed.

[0016] The aluminum alloy formed product of the present invention preferably has a layered structure consisting of a layer containing particles with a particle size of 1 to 3 μm and a fine-grain layer consisting of particles with a particle size of less than 1 μm. The formation of this layered structure can increase the Young's modulus of the aluminum alloy formed product.

[0017] The present invention also provides a method for producing the aluminum alloy formed product of the present invention, comprising: a molding step of molding an aluminum alloy powder containing 4 to 11 mass% Mn and 1 to 4 mass% Cr, satisfying the relationship 1.9×Cr mass%≦Mn mass%≦5.3×Cr mass%, with the balance being unavoidable impurities and aluminum; and a heat treatment step of heat treating the aluminum alloy formed product obtained in the molding step at a temperature of 350 to 550°C.

[0018] In the method for producing an aluminum alloy compact of the present invention, an aluminum alloy powder containing Mn and Cr necessary for forming the G phase is compacted, and the obtained aluminum alloy compact is subjected to a heat treatment at a temperature of 350 to 550°C, thereby allowing a large amount of G phase to precipitate in the aluminum alloy compact.

[0019] In addition, in the method for manufacturing an aluminum alloy formed product of the present invention, it is preferable to use an additive manufacturing method in the forming step. By using an additive manufacturing method, it is possible to efficiently manufacture aluminum alloy formed products having any shape, such as a complex shape or a hollow shape. Furthermore, according to the present invention, since the as-built material has high ductility, the possibility of cracks occurring during forming is extremely low, and a sound formed product can be obtained.

[0020] Furthermore, in the method for producing an aluminum alloy formed product of the present invention, it is preferable to use an extrusion molding method in the forming step. When the extrusion molding method is used in the forming step, by performing hot extrusion at 350 to 550°C, the temperature history of the hot extrusion can also serve as a heat treatment step.

[0021] Furthermore, the use of extrusion molding allows for efficient production of aluminum alloy compacts having simple shapes, and also allows for efficient formation of a layered structure that contributes to an increase in the Young's modulus of the aluminum alloy compact, and that is composed of a layer containing particles with a particle size of 1 to 3 μm and a fine particle layer containing particles with a particle size of less than 1 μm.

[0022] According to the present invention, it is possible to provide an aluminum alloy formed product that exhibits a Young's modulus of 80 GPa or more using aluminum alloy alone without mixing with ceramics such as alumina or silicon carbide, and is suitable for industrial materials such as automobile parts, machine parts, and structural materials, and an efficient method for producing the same.

[0023] 1 is an example of the results of measuring the circularity of powder using a Morphologi G3 manufactured by Spectris Inc.; FIG. 2 is a schematic diagram showing the shape of a test piece for measuring Young's modulus; FIG. 3 is an image of a cross section of an additive manufacturing product having the alloy composition of Example 2, taken with a microscope; FIG. 4 is an SEM image and EDS mapping results of an extruded material having the alloy composition of Example 4; FIG. 5 is a photograph of the appearance of an additive manufacturing product having the alloy composition of Comparative Example 2; FIG. 6 is a photograph of the appearance of an additive manufacturing product having the alloy composition of Comparative Example 6.

[0024] Representative embodiments of the aluminum alloy formed product and the method for producing the same of the present invention will be described in detail below, but the present invention is not limited to these.

[0025] 1. Manufacturing Method of Aluminum Alloy Compacted Product The manufacturing method of an aluminum alloy compacted product of the present invention is characterized by comprising: a compacting step of compacting an aluminum alloy powder containing 4 to 11 mass% Mn and 1 to 4 mass% Cr, satisfying the relationship 1.9×Cr mass%≦Mn mass%≦5.3×Cr mass%, with the remainder consisting of unavoidable impurities and aluminum, and a heat treatment step of heat treating the aluminum alloy compact obtained in the compacting step at a temperature of 350 to 550° C. Details of the aluminum alloy powder used as a raw material and each step will be described below.

[0026] (1) Aluminum Alloy Powder The aluminum alloy powder used as the raw material for the aluminum alloy compact (hereinafter also simply referred to as "compact") can be produced, for example, by gas atomization (atomizing medium is air, nitrogen gas, Ar gas, He gas, etc.) or water atomization. It can also be produced by other methods such as rotating electrode atomization, plasma atomization, centrifugal atomization, mechanical alloying, and chemical processes. Among these, gas atomization and centrifugal atomization are preferred.

[0027] The composition of the aluminum alloy powder may contain 4 to 11 mass% of Mn and 1 to 4 mass% of Cr, satisfying the relationship 1.9 x Cr mass%≦Mn mass%≦5.3 x Cr mass%, with the remainder being unavoidable impurities and aluminum. Mn, together with Cr, forms the G phase (Al １２ Mn is an element that forms the alloy (Mn, Cr), and Mn alone contributes to improving strength. The Mn content should be 4 to 11 mass%, preferably 5 to 10 mass%, and more preferably 5 to 8 mass%.

[0028] However, in order to efficiently obtain the G phase, it is necessary to satisfy the relationship 1.9 × Cr mass% ≦ Mn mass% ≦ 5.3 × Cr mass%, and preferably the relationship 2.4 × Cr mass% ≦ Mn mass% ≦ 5.3 × Cr mass%. If the Mn content is less than 4 mass%, the strength of the compact will be poor and it will be difficult to form a sufficient amount of G phase to obtain a high Young's modulus. If the Mn content exceeds 11 mass%, the toughness and ductility will be poor and the melting point (liquidus temperature) of the alloy will also be high, which may make it difficult to produce the aluminum alloy powder.

[0029] Cr and Mn form the G phase (Al １２ Cr is an element that forms the alloy (Mn, Cr), and Cr alone contributes to improving strength. The Cr content is preferably 1 to 4 mass%, more preferably 1.5 to 3.5 mass%, and even more preferably 1.8 to 3.2 mass%. If the Cr content is less than 1 mass%, the strength of the compact will be poor and it will be difficult to form a sufficient amount of G phase to obtain a high Young's modulus. If the Cr content exceeds 4 mass%, the toughness and ductility will be poor and the melting point (liquidus temperature) of the alloy will also be high, which may make it difficult to produce the aluminum alloy powder.

[0030] Specific examples of unavoidable impurity elements include iron (Fe), silicon (Si), magnesium (Mg), copper (Cu), zinc (Zn), lithium (Li), nickel (Ni), titanium (Ti), calcium (Ca), sodium (Na), strontium (Sr), yttrium (Y), niobium (Nb), molybdenum (Mo), tungsten (W), antimony (Sb), beryllium (Be), phosphorus (P), vanadium (V), tin (Sn), lead (Pb), bismuth (Bi), cobalt (Co), silver (Ag), gallium (Ga), scandium (Sc), cerium (Ce), boron (B), carbon (C), nitrogen (N), and oxygen (O).

[0031] These inevitable impurity elements may be present inevitably in aluminum ingots, may be mixed inevitably during the production of aluminum alloy powder, or may be modifier elements when grain refinement elements such as titanium, boron, and zirconium are intentionally added. The content of these inevitable impurity elements is not particularly limited as long as it does not impair the effects of the present invention, but each of them is preferably 0.5 mass% or less, more preferably 0.3 mass% or less, and particularly preferably 0.2 mass% or less. The content of each element in the aluminum alloy powder and the aluminum alloy compact can be measured by ICP atomic emission spectroscopy, inert gas fusion-infrared absorption spectroscopy, or the like.

[0032] The average particle size of the aluminum alloy powder is not particularly limited, but may be a volume-based average particle size (median diameter d ５０ ) is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. If the average particle size is less than 5 μm, the fluidity of the powder decreases, and a uniform powder layer may not be formed in the manufacturing process of the molded body. On the other hand, the average particle size is preferably 200 μm or less, more preferably 150 μm or less, even more preferably 100 μm or less, and particularly preferably 80 μm or less. If the average particle size exceeds 200 μm, the powder may get caught on the squeegee during additive manufacturing, making it difficult to spread.

[0033] The average circularity (sphericity) of the aluminum alloy powder is not particularly limited, but is preferably 0.9 or more and 1.0 or less. If the average circularity is less than 0.9, the powder's fluidity may decrease, potentially preventing the formation of a uniform powder layer during the compact manufacturing process. The circularity is a value not exceeding 1, calculated by dividing the equivalent circle diameter calculated from the area by the equivalent circle diameter calculated from the perimeter, and can be determined by image analysis of a photograph of the particles taken with a microscope. If the average circularity of approximately 1,000 particles is 0.90 or more, the required fluidity is ensured and the content of oxides that cause defects tends to be reduced. As an example of measurement results, a photograph and actual measurements of an Al-8Mn-2Cr powder are shown in Figure 1. The circularity of this powder was 0.94, averaged over approximately 1,000 particles.

[0034] (2) Molding Step (2-1) Manufacturing Method of Aluminum Alloy Molded Body by Additive Manufacturing Method A manufacturing method of an aluminum alloy molded body by additive manufacturing method using aluminum alloy powder will be described.

[0035] The layered molding method is a processing method in which molten and solidified regions are stacked layer by layer based on two-dimensional (slice) data obtained from 3D-CAD data. The aluminum alloy compact includes a first step of forming a powder layer containing aluminum alloy powder, and a second step of forming a metal layer by melting and solidifying the aluminum alloy powder at a predetermined position in the powder layer. These first and second steps are sequentially repeated, and multiple metal layers are stacked and joined to produce the aluminum alloy compact.

[0036] Powder bed fusion can be used for the additive manufacturing process, but other additive manufacturing processes can also be used, such as directed energy deposition. Furthermore, indirect additive manufacturing processes such as binder jetting and fused deposition modeling can also be used. While a laser beam can be used as a heat source to melt and solidify the metal powder, the heat source is not limited to a laser beam; for example, an electron beam or plasma can also be used.

[0037] In the first and second steps, the metal layer and the powder layer may be preheated. The preheating temperature is preferably 30°C or higher, more preferably 150°C or higher. Also, a temperature of 500°C or lower is preferable, more preferably 400°C or lower, and even more preferably 250°C or lower. Preheating to 150°C or higher sufficiently suppresses cracks (delamination), while preheating to a temperature higher than 500°C tends to cause the microstructure of the aluminum alloy compact to disappear, resulting in deterioration of mechanical properties. For preheating, an electric heater attached to the lower part of the building platform or base plate is usually used, but a ceramic heater or high-frequency heating may also be used. Heating may also be achieved by scanning a heat source such as a laser beam or an electron beam.

[0038] (2-2) Manufacturing Method of Aluminum Alloy Molded Product by Extrusion Molding A method for manufacturing an aluminum alloy molded product by extrusion molding using aluminum alloy powder will be described.

[0039] As a preliminary step before extrusion molding, it is preferable to cold-form the aluminum alloy powder. Cold-forming methods that can be used include cold pressing and cold isostatic pressing (CIP). The density of the cold-formed body is preferably about 60 to 80%. A density of less than 60% is fragile, and solidifying to a density of more than 80% requires high pressure, which increases costs. To achieve a density of 60% or more, it is preferable to apply a pressure of 9.8 × 10 MPa or more. The cold-formed body may be degassed in a vacuum at 300 to 500°C for about 10 minutes to 24 hours.

[0040] An aluminum alloy formed body can be obtained by hot extruding the cold-formed body preferably at 350 to 550°C, more preferably 400 to 550°C, and even more preferably 450 to 550°C. To precipitate a large amount of G phase and improve Young's modulus, it is desirable to set the temperature as high as possible within these ranges. At temperatures below 350°C, extrusion resistance is high, potentially making extrusion difficult. Conversely, extrusion temperatures above 550°C may cause intermetallic compounds such as precipitates to coarsen, potentially reducing mechanical properties. The holding time at 350 to 550°C can be set appropriately and adjusted depending on the size of the cold-formed body. Typically, it is approximately 5 minutes to 10 hours. The extrusion ratio can be adjusted appropriately depending on the shape and size of the desired formed body, but is typically approximately 5 to 25.

[0041] Although typical forming methods in the forming process have been described above, the forming methods used in the forming process are not limited to these, and various design modifications are possible, all of which are included in the technical scope of the present invention. For example, it goes without saying that hot pressing, HIP (hot isostatic pressing), powder forging, etc. can also be used.

[0042] (3) Heat Treatment Step The aluminum alloy formed body formed by the additive manufacturing method can be subjected to heat treatment to further precipitate the G phase and improve the Young's modulus. Also, in the aluminum alloy formed body formed by the extrusion molding method, if the precipitation of the G phase is insufficient, the G phase can be further precipitated by heat treatment, and the Young's modulus can be improved.

[0043] The heat treatment temperature is preferably 350° C. or higher, more preferably 375° C. or higher, even more preferably 400° C. or higher, and particularly preferably 450° C. or higher. On the other hand, the upper limit is preferably 550° C. or lower, and if the temperature exceeds 550° C., precipitates and crystal grains may become coarse, which may impair mechanical properties.

[0044] The heat treatment time is preferably 0.1 hour or more, more preferably 0.5 hour or more, and even more preferably 1 hour or more. Also, the time is preferably 100 hours or less, more preferably 24 hours or less. If the time is shorter than 0.1 hour, the Young's modulus of the aluminum alloy formed body may not be sufficiently improved. On the other hand, if the time is longer than 100 hours, the strength of the aluminum alloy formed body may be reduced due to overaging. An atmospheric furnace is usually used as the furnace for the heat treatment, but an atmospheric furnace may also be used, and the treatment may be performed in, for example, an inert gas atmosphere such as nitrogen or argon, or a reducing gas atmosphere such as hydrogen.

[0045] 2. Aluminum alloy compact The composition of the aluminum alloy compact of the present invention is substantially the same as the composition of the aluminum alloy powder. When the aluminum alloy powder described above is molded by additive manufacturing, the aluminum alloy powder temporarily melts and resolidifies (rapidly solidifies). However, since the alloy components of the aluminum alloy powder used in the present invention hardly volatilize, the composition of the obtained aluminum alloy compact is the same as the composition of the original aluminum alloy powder within a margin of error.

[0046] The relative density of the aluminum alloy molded body of the present invention is preferably 98% or more, more preferably 99% or more, and even more preferably 99.5% or more. If the relative density is less than 98%, the mechanical properties of the molded body may be significantly deteriorated. This relative density is calculated by binarizing an image (magnification: approximately 100x) obtained with an optical microscope or a microscope of an arbitrary cross section near the center of the molded body, and calculating the area ratio of the metal portion excluding voids. The higher the relative density, the more desirable it is for improving the mechanical strength, ductility, and thermal and electrical conductivity of the layered molded product.

[0047] The Young's modulus of the aluminum alloy molded body is 80 GPa or more. The Young's modulus is preferably 90 GPa or more, more preferably 95 GPa or more, and even more preferably 100 GPa or more. The Young's modulus correlates to some extent with the volume fraction of the G phase, and a Young's modulus of 80 GPa or more is easily obtained when the volume fraction of the G phase is 10% or more. From the viewpoint of improving the Young's modulus, the volume fraction of the G phase is preferably 20% or more, more preferably 30% or more, and even more preferably 35% or more. On the other hand, the upper limit of the volume fraction of the G phase is preferably 90% or less, more preferably 85% or less, and even more preferably 80% or less. If the volume fraction exceeds 90%, the molded body becomes brittle, difficult to process, and tends to have reduced toughness, so it is preferable to avoid it.

[0048] Furthermore, the aluminum alloy formed product preferably has a layered structure consisting of a layer containing particles with a particle size of 1 to 3 μm and a fine-grain layer consisting of particles with a particle size of less than 1 μm. The formation of this layered structure can increase the Young's modulus of the aluminum alloy formed product. The layered structure can be easily observed by SEM observation or the like.

[0049] Furthermore, the as-built molded body obtained by the additive manufacturing method preferably has a breaking elongation of 10% or more at room temperature. By setting the breaking elongation to 10% or more, it is possible to effectively prevent cracks from occurring due to thermal stress generated during manufacturing. This breaking elongation is more preferably 12% or more, and even more preferably 14% or more.

[0050] Representative embodiments of the present invention have been described above, but the present invention is not limited to these, and various design modifications are possible, all of which are included in the technical scope of the present invention.

[0051] Alloys having the nominal compositions shown in Table 1 as examples and comparative examples were prepared, heated to or above the melting point (liquidus temperature) in a high-frequency induction furnace, and thoroughly melted. The alloys were then pulverized by nitrogen gas atomization to obtain aluminum alloy powders.

[0052] The elements of each aluminum alloy powder obtained were measured by ICP atomic emission spectrometry, and the results are shown in Table 1. In addition, the particle size distribution of the powder was measured by a laser diffraction scattering method using a Microtrac, and the particle size of the cumulative 50% particle size from the finest particle side in the volume-based particle size distribution was taken as the average particle size of the aluminum alloy powder. The average particle size was determined by the median diameter "d ５０ The circularity was measured using a Morphologi G3 manufactured by Spectris Corporation as follows. First, about 1,000 particles were selected from each aluminum alloy powder, and the circularity of each particle was read from a photograph of the outer shape of each particle, and the average value was taken as the circularity of the aluminum alloy powder. The obtained average particle diameter and circularity are shown in Table 1.

[0053]

[0054] From Table 1, it can be seen that in all cases, the aluminum alloy powders having the nominal compositions shown as examples contain 4 to 11 mass% of Mn and 1 to 4 mass% of Cr, and satisfy the relationship 1.9×Cr mass%≦Mn mass%≦5.3×Cr mass%.

[0055] The obtained powder was classified by passing it through a sieve with an opening of 63 μm, and 100 g of this powder was placed in a rubber mold and pressed with a cold isostatic press (CIP) at a surface pressure of 3000 kg / cm. ２ The powder compact was formed into a billet, which was heated in an atmospheric furnace at 500°C for 30 minutes and then placed in a container (diameter 32 mm) of an extruder with a maximum load of 100 tons and maintained at 450°C, to obtain an extrusion molded product with a width of 20 mm and a thickness of 4 mm (extrusion ratio 10).

[0056] From this extrusion molded article, a rectangular parallelepiped test piece measuring 60 mm in length, 10 mm in width, and 1.5 mm in thickness was machined to serve as a test piece for Young's modulus measurement. The shape of the test piece for Young's modulus measurement is shown in Figure 2. Using this test piece, the Young's modulus at room temperature (25°C) was measured by the resonance method using a free resonance type Young's modulus measuring instrument (JE-RT manufactured by Nippon Technoplus Co., Ltd.). The obtained values ​​are shown in Table 2.

[0057] When the Young's modulus measurement test pieces were machined, those in which cracks occurred in most (80% or more) of the test pieces were rated as "C" for extrusion workability, those in which cracks occurred in 10% to less than 80% of the test pieces were rated as "B," and those in which almost no cracks occurred (less than 10%) were rated as "A," as shown in Table 2.

[0058]

[0059] Furthermore, an aluminum alloy compact was produced by an additive manufacturing method using the aluminum alloy powder. The aluminum alloy compact was obtained using the aluminum alloy powder as a raw material by a powder bed fusion additive manufacturing method using a laser. The molding machine used for additive manufacturing was a LUMEX Avance-25 manufactured by Matsuura Machinery Works or an EOSINT M280 manufactured by EOS Corporation.

[0060] More specifically, the aluminum alloy molded body was obtained under the following lamination conditions: laser power: 280-480 W, scanning speed: 800-2200 mm / s, scanning pitch: 0.10-0.16 mm, and atmosphere: inert gas. The "molding temperature" shown in Table 2 is the preheating temperature of the base plate during additive manufacturing.

[0061] Test pieces were cut out from each of the resulting molded bodies, and the Young's modulus was measured in the same manner as described above. In addition, for molded bodies produced by the additive manufacturing method, the Young's modulus (at 25°C during measurement) of those heat-treated at 400°C or 500°C was measured in the same manner as described above. The obtained values ​​are shown in Table 2.

[0062] The tensile strength, 0.2% yield strength, and fracture elongation of the laminated molded body were evaluated in accordance with JIS Z 2241, Tensile Testing Method for Metallic Materials. From the obtained molded body, No. 14A test pieces (parallel section φ6 mm, original gauge length 30 mm) specified in the same standard were taken in a direction perpendicular to the molding direction, and tensile tests were performed at room temperature using a Shimadzu 100kNXplus autograph. The crosshead speed during the tensile test was 0.5 mm / min up to 0.2% yield strength and 5 mm / min thereafter. The obtained tensile strength, 0.2% yield strength, and fracture elongation are shown in Table 2. The fracture elongation was calculated in accordance with Section 20.2 of the JIS standard using the final gauge length and original gauge length after fracture, measured by butting two test pieces together after fracture.

[0063] In addition, cracks were evaluated as a measure of the moldability of the layered molded bodies. The obtained molded bodies were visually observed, and for 12 or more molded bodies, the crack occurrence rate was calculated by dividing the number of molded bodies with cracks by the number of molded bodies with cracks + the number of molded bodies without cracks, multiplied by 100. The obtained crack occurrence rate is shown in Table 2.

[0064] Furthermore, X-ray diffraction measurements were performed on each sample of the extruded material and the layered manufactured body, and the main phases and precipitates were identified from the obtained X-ray diffraction profiles. A SmartLab manufactured by Rigaku Corporation was used for the X-ray diffraction measurements. The identification results are shown in Table 2. "G" in Table 2 stands for G-Al. １２ (Mn, Cr) phase, “α” is α-Al phase, “θ” is Al ７ Cr / Al １３ Cr ２ In addition, the volume fraction of the G phase was quantitatively evaluated from the integrated intensity of the X-ray diffraction profile. The obtained volume fractions are shown in Table 2.

[0065] In all cases where the alloy compositions of Examples 1 to 5 were used, the Young's modulus exceeded 80 GPa. Despite being a high-concentration alloy containing Mn and Cr, the extruded test pieces were easily machined.

[0066] Furthermore, the additive manufacturing products having the alloy compositions of Examples 1 to 3 did not exhibit cracks and had good ductility in the as-built state. Furthermore, the relative density calculated by image analysis of cross-sectional observation was 99.5% or higher. A cross section of the additive manufacturing product of Example 2 is shown in Figure 3.

[0067] Furthermore, it can be seen that the Young's modulus of the additively manufactured bodies having the alloy compositions of Examples 2 and 3 increased significantly upon heat treatment at 400°C or 500°C. According to the results of X-ray diffraction measurements, a new G phase was formed by the heat treatment, which is thought to have increased the Young's modulus. On the other hand, the Young's modulus of the extruded material having the alloy composition of Example 3 was even higher, reaching 111 GPa. This is thought to be due to the heat treatment being performed due to the temperature history in the extrusion process, as well as the formation of a layered structure consisting of a layer containing particles with a particle size of 1 to 3 μm and a fine-grain layer consisting of particles with a particle size of less than 1 μm.

[0068] Fig. 4 shows an SEM image and EDS mapping results of the extruded material having the alloy composition of Example 4. From Fig. 4, it can be seen that a layered structure consisting of particles of about 1 µm and fine particles of a size smaller than that has been formed.

[0069] Although the Young's modulus of the extruded material having the alloy composition of Comparative Example 1 exceeds 80 GPa, the extruded product is very brittle and it is difficult to process test specimens, so it cannot be used as a practical alloy.

[0070] In the alloy compositions of Comparative Examples 2 to 5, in addition to the G phase and the aluminum α phase, a large amount of Cr-based θ phase was present. Although the Young's modulus was high, the extruded material became brittle and difficult to machine. Furthermore, cracks occurred in the extruded body when fabricated using the additive manufacturing method, making it impossible to use as a practical alloy. The cracks in the additive manufacturing body of Comparative Example 2 are shown in Figure 5.

[0071] Comparative Example 6 is an alloy to which Fe has been added, but the Young's modulus of the extruded material is low, making it unsuitable for applications requiring rigidity. In additive manufacturing, residual stress causes cracks in the molded body, making it unsuitable for practical use. The appearance of cracks in the additive manufacturing body of Comparative Example 6 is shown in Figure 6.

[0072] From the above results, it is clear that by subjecting an aluminum alloy formed body obtained by molding an aluminum alloy powder containing 4 to 11 mass% Mn and 1 to 4 mass% Cr, satisfying the relationship 1.9×Cr mass%≦Mn mass%≦5.3×Cr mass%, with the remainder being unavoidable impurities and aluminum, to a heat treatment at a temperature of 350 to 550°C, it is possible to obtain an aluminum alloy formed body that exhibits a Young's modulus of 80 GPa or more using the aluminum alloy alone, without mixing with ceramic.

Claims

1. An aluminum alloy formed body containing 4-11 mass% Mn and 1-4 mass% Cr, satisfying the relationship 1.9 x Cr mass% ≦ Mn mass% ≦ 5.3 x Cr mass%, with the remainder consisting of unavoidable impurities and aluminum, and characterized in that the aluminum alloy formed body has a Young's modulus of 80 GPa or more at room temperature (25°C).

2. Al １２ 2. The aluminum alloy formed body according to claim 1, wherein a volume fraction of a G phase which is a (Mn, Cr) compound is 10 to 90%.

3. The aluminum alloy formed product according to claim 1 or 2, characterized in that it has a layered structure consisting of a layer containing particles having a particle size of 1 to 3 μm and a fine-grain layer consisting of particles having a particle size of less than 1 μm.

4. The aluminum alloy formed body according to claim 1 or 2, which is a formed body by an additive manufacturing method, and has a breaking elongation of 10% or more in a state before heat treatment.

5. A method for producing an aluminum alloy formed product according to claim 1 or 2, comprising: a forming step of forming an aluminum alloy powder containing 4-11 mass% Mn and 1-4 mass% Cr, satisfying the relationship 1.9 x Cr mass% <= Mn mass% <= 5.3 x Cr mass%, with the remainder being unavoidable impurities and aluminum; and a heat treatment step of heat treating the aluminum alloy formed product obtained in the forming step at a temperature of 350-550°C.

6. The method for producing an aluminum alloy formed product according to claim 5, characterized in that an additive manufacturing method is used in the forming step.

7. The method for producing an aluminum alloy formed product according to claim 5, wherein an extrusion molding method is used in the forming step.