Additive manufactured aluminum alloy article and method for producing same

Abstract

To provide an aluminum alloy lamination-shaped body which is composed of an aluminum alloy containing 0.5 to 8.0 mass% Mg, has mechanical properties equal to or higher than those of the conventional one, and has small surface roughness, and to provide a simple and efficient method for producing the same.SOLUTION: An aluminum alloy additive manufactured article comprising: 0.5 to 8.0 mass% of Mg; more than 0.0 mass% and 5.0 mass% or less of at least one metal element selected from the group consisting of Fe, Si, Mn, Cr, Ti, Zr, and Sc; and a balance of Al and inevitable impurities, wherein a surface roughness Sa is 22 μm or less, and an oxygen content is 0.015 to 0.048 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aluminum alloy additive manufacturing product (hereinafter also simply referred to as "product") and a manufacturing method thereof. [Background technology]

[0002] Aluminum alloys have long been used for automobile parts, machine parts, structural materials, etc., and are formed by casting, die casting, extrusion, deep drawing, etc. However, all of these forming methods require post-processing, which generates processing waste and offcuts, posing problems not only in terms of yield but also in terms of the environment. In response to this, the recently developed additive manufacturing method (commonly known as "additive manufacturing") makes it possible to manufacture near-net-shape molded products that are close to the shape of the final product.

[0003] For example, Patent Document 1 (JP 2018-184659 A) addresses the issue of "providing an aluminum alloy laminate formed body having higher strength than conventional laminate formed bodies, and a method for manufacturing the same," and discloses "an aluminum alloy laminate formed body and a method for manufacturing the same, which is formed by a layering method from raw metal made of an aluminum alloy containing 0.3 wt% or less of Fe as an unavoidable impurity and one or more of Mn and Cr in a total weight of 0.3 to 10 wt%, and which is characterized by being composed of one or more of an intermetallic compound containing two or more of Al, Mn, Fe, and Cr, and an aluminum alloy solid solution in which one or more elements of Mn, Fe, and Cr are dissolved."

[0004] The aluminum alloy laminate formed body and its manufacturing method in the above Patent Document 1 states that "a high-strength aluminum alloy laminate formed body that is free from cracks inside or outside the laminate formed body and also has little deformation, and a manufacturing method thereof are provided."

[0005] Furthermore, Non-Patent Document 1 (Rhysics Procedia 12 (2011) 369-374) discloses the uses of an aluminum alloy (Scalmalloy (registered trademark)) for additive manufacturing containing scandium (Sc) and the mechanical properties of the resulting aluminum alloy additive manufacturing bodies.

[0006] The above-mentioned Non-Patent Document 1 describes that the static mechanical properties of aluminum alloy additive manufacturing bodies exceed expected levels, and that the strength of aluminum alloy additive manufacturing bodies increases with increasing scandium content, but that ductile behavior is also exhibited. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2018-184659 [Non-patent literature]

[0008] [Non-Patent Document 1] K. Schmidtke, F. Palm, A. Hawkins, C. Emmelmann: Rhysics Procedia 12 (2011) 369-374 Summary of the Invention [Problem to be solved by the invention]

[0009] Aluminum alloys of various compositions have been proposed for additive manufacturing using aluminum alloys as raw materials. Among them, Scalmalloy (trade name) shown in Non-Patent Document 1 is widely used, is easy to additively manufacture, and the resulting additively manufactured bodies have excellent mechanical properties, such as high strength and large elongation.

[0010] However, Scalmalloy contains 4.8% by mass of magnesium, which generates large amounts of magnesium fumes and Al-Mg alloy powder dust when the powder is melted with a laser beam. If these fumes are not properly treated, the dust and fumes will drift inside the molding device, blocking part of the laser beam and making it difficult to obtain a uniform molded object. Furthermore, aluminum alloys containing magnesium have been proposed in addition to Scalmalloy, and these aluminum alloys also have the problem of generating fumes and dust.

[0011] Furthermore, the aluminum alloy laminate molded body and its manufacturing method of Patent Document 1 can produce a high-strength aluminum alloy laminate molded body with a surface roughness Sa of approximately 25 μm, but if a molded body with even smaller surface roughness (a smoother surface) can be obtained, the finishing process can be omitted or simplified, which would be more advantageous in terms of yield and the environment.

[0012] In view of the problems in the prior art as described above, the object of the present invention is to provide an aluminum alloy additive manufacturing product made of an aluminum alloy containing 0.5 to 8.0 mass% Mg, which has mechanical properties equal to or better than those of conventional products and has small surface roughness, and a simple and efficient method for manufacturing the same. [Means for solving the problem]

[0013] In order to achieve the above-mentioned object, the inventors conducted extensive research into aluminum alloy additive manufacturing bodies and methods for manufacturing them, and discovered that it is extremely effective to set the oxygen concentration in the atmosphere during additive manufacturing to 1500 to 8000 ppm, thereby arriving at the present invention.

[0014] That is, the present invention provides: Mg: 0.5~8.0% by mass, At least one metal element selected from the group consisting of Fe, Si, Mn, Cr, Ti, Zr, and Sc: more than 0.0 mass% and not more than 5.0 mass%, The balance is Al and unavoidable impurities, The surface roughness Sa is 22 μm or less, The oxygen content is 0.015 to 0.048% by mass. The present invention provides an aluminum alloy additive manufacturing product characterized by the above.

[0015] The aluminum alloy additive manufacturing product of the present invention has a surface roughness Sa of 22 μm or less, and has a surface condition that is comparable to that of aluminum alloy castings, making it possible to omit or simplify finishing work. Furthermore, the aluminum alloy additive manufacturing product of the present invention has an oxygen concentration in the atmosphere during additive manufacturing of 1500 to 8000 ppm, meaning that it contains 0.015 mass% or more of oxygen, but by keeping the oxygen content to 0.048 mass% or less, deterioration in ductility and toughness is suppressed.

[0016] The aluminum alloy additive manufacturing product of the present invention contains 0.5 to 8.0 mass% Mg, and the solid solution strengthening of this Mg imparts high specific strength and high-temperature strength to the aluminum alloy additive manufacturing product. In addition, the aluminum alloy additive manufacturing product contains more than 0.0 mass% and not more than 5.0 mass% of at least one metal element selected from the group consisting of Fe, Si, Mn, Cr, Ti, Zr, and Sc, further increasing the room-temperature strength and high-temperature strength of the aluminum alloy additive manufacturing product.

[0017] Furthermore, the aluminum alloy additive manufacturing product of the present invention preferably has a relative density of 99.94% or more as determined by cross-sectional observation. A relative density of 99.94% or more as determined by cross-sectional observation can impart excellent mechanical properties to the aluminum alloy additive manufacturing product.

[0018] Furthermore, the aluminum alloy additive manufacturing product of the present invention preferably has a breaking elongation of 15% or more in a tensile test at room temperature, which makes the aluminum alloy additive manufacturing product suitable for use as a component requiring high reliability.

[0019] Furthermore, the aluminum alloy additive manufacturing product of the present invention preferably has a Vickers hardness of 165 Hv or more. When the aluminum alloy additive manufacturing product has a Vickers hardness of 165 Hv or more, the aluminum alloy additive manufacturing product can be suitably used as a member that requires high strength and wear resistance.

[0020] The present invention also provides a method for producing the aluminum alloy additive manufacturing product of the present invention, comprising: Aluminum alloy powder is molded using additive manufacturing, The oxygen concentration in the atmosphere during additive manufacturing is 1500 to 8000 ppm. Also provided is a method for producing an aluminum alloy additive manufacturing product, characterized by the above.

[0021] The aluminum alloy additive manufacturing product of the present invention contains 0.5 to 8.0 mass% Mg, and it is considered preferable to reduce the oxygen in the atmosphere as much as possible in order to suppress oxidation of the Mg contained in the raw material. As a result of extensive research by the inventors into the effect of the oxygen concentration in the atmosphere on additive manufacturing, it has become clear that when additive manufacturing is performed on aluminum alloy raw materials containing Mg, there is an optimal oxygen concentration range from the standpoints of manufacturing accuracy, the density and mechanical properties of the resulting additive manufacturing product, etc.

[0022] More specifically, by maintaining the oxygen concentration in the atmosphere during additive manufacturing at 1500 ppm or higher, it is possible to suppress the generation of dust when the aluminum alloy raw material is in powder form, and fumes caused by Mg contained in the aluminum alloy raw material. On the other hand, by maintaining the oxygen concentration in the atmosphere during additive manufacturing at 8000 ppm or lower, it is possible to suppress not only the generation of dust and fumes, but also the increase in the oxygen content of the resulting aluminum alloy additive manufacturing object. Additionally, by maintaining the oxygen concentration in the atmosphere during additive manufacturing at 1500 to 8000 ppm, it is possible to reduce the surface roughness of the aluminum alloy additive manufacturing object. Furthermore, the relative density of the aluminum alloy additive manufacturing object is also increased, imparting good ductility.

[0023] Furthermore, in the method for producing an aluminum alloy additive manufacturing product of the present invention, it is preferable that the aluminum alloy raw material be aluminum alloy powder, and that powder bed fusion be used for the additive manufacturing method. In powder bed fusion, in which a laser is irradiated onto the raw aluminum alloy powder, if dust or fumes are generated during additive manufacturing, the laser light reaching the powder bed is blocked, resulting in unstable molding behavior. In contrast, in the method for producing an aluminum alloy additive manufacturing product of the present invention, the oxygen concentration in the atmosphere during additive manufacturing is set to 1500 to 8000 ppm, which suppresses the generation of dust and fumes, allowing a good aluminum alloy additive manufacturing product to be obtained using powder bed fusion. [Effects of the Invention]

[0024] According to the present invention, it is possible to provide an aluminum alloy additive manufacturing product made of an aluminum alloy containing 0.5 to 8.0 mass% Mg, which has mechanical properties equal to or better than those of conventional products and has small surface roughness, and a simple and efficient method for manufacturing the same. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 2 is a schematic diagram showing the positions where samples for measuring Vickers hardness are taken. DETAILED DESCRIPTION OF THE INVENTION

[0026] Representative embodiments of the aluminum alloy additive manufacturing product and its manufacturing method according to the present invention will be described in detail below with reference to the drawings, but the present invention is not limited to these.

[0027] 1. Aluminum alloy additive manufacturing body The aluminum alloy additive manufacturing product of the present invention is characterized by containing 0.5 to 8.0 mass% Mg, more than 0.0 mass% and not more than 5.0 mass% of at least one metal element selected from the group consisting of Fe, Si, Mn, Cr, Ti, Zr, and Sc, the balance being Al and unavoidable impurities, having a surface roughness Sa of not more than 22 μm, and an oxygen content of 0.015 to 0.048 mass%. The composition and various properties of the aluminum alloy additive manufacturing product are described in detail below.

[0028] (1) Composition (1-1) Essential additive elements Mg:0.5~8.0% by mass Magnesium (Mg) is easily dissolved in aluminum and has the effect of improving the specific strength and high-temperature strength of the aluminum alloy. If the Mg content is less than 0.5% by mass, the effects of the present invention are poor, while if it exceeds 8.0% by mass, the ductility may be poor and the aluminum alloy may become brittle. The Mg content in the aluminum alloy is preferably 1.0 to 7.0% by mass, and more preferably 2.0 to 6.0% by mass.

[0029] O:0.015~0.048% by mass Oxygen (O) is taken in from the oxide film formed on the surface of the raw material aluminum alloy powder and from the atmosphere during additive manufacturing. By using raw materials and additive manufacturing conditions that result in an oxygen (O) content of 0.015 to 0.048 mass% in the aluminum alloy additive manufacturing product, it is possible to obtain an aluminum alloy additive manufacturing product with an excellent balance of Vickers hardness, surface roughness, relative density, etc. The oxygen content in the aluminum alloy additive manufacturing product is preferably 0.032 to 0.046 mass%. The oxygen content of the aluminum alloy additive manufacturing product can be measured, for example, by inert gas fusion-nondispersive infrared absorption (NDIR) spectroscopy.

[0030] At least one metallic element selected from the group consisting of Fe, Si, Mn, Cr, Ti, Zr, and Sc: more than 0.0 mass% and not more than 5.0 mass% By setting the total content of these elements to more than 0.0% by mass and not more than 5.0% by mass, it is possible to further increase the room temperature strength and high temperature strength. If the total content of these elements exceeds 5% by mass, the ductility of the aluminum alloy additive manufacturing product tends to be poor, and it may become brittle. The total content of these elements is preferably 0.8 to 3.5% by mass. Preferred contents of each element are listed below.

[0031] Fe:0.1~2.0% by mass Iron (Fe) is an element effective in improving high-temperature strength, and is preferably contained in the aluminum alloy in an amount of 0.1 to 2.0 mass %, more preferably 0.2 to 1.5 mass %.

[0032] Si:0.1~2.0% by mass Silicon (Si) mainly forms GP zones, intermediate phases, and compounds (MgSi) with magnesium (Mg), contributing to improving the strength of aluminum alloy additive manufacturing products. The Si content in the aluminum alloy is preferably 0.1 to 2.0 mass%. If the Si content exceeds 2.0 mass%, the aluminum alloy additive manufacturing product may become brittle due to poor ductility.

[0033] Mn:0.1~2.0% by mass Manganese (Mn) is an element that is effective for solid solution strengthening, and is preferably contained in the aluminum alloy in an amount of 0.1 to 2.0 mass %, more preferably 0.2 to 1.5 mass %.

[0034] Cr:0.1~2.0% by mass Chromium (Cr) is an element that contributes to the grain refinement effect and high-temperature strength. The Cr content in the aluminum alloy is preferably 0.1 to 2.0 mass %, and more preferably 0.3 to 1.5 mass %.

[0035] Ti:0.1~2.0% by mass Titanium (Ti) is an element that contributes to the grain refinement effect and high-temperature strength. The Ti content in the aluminum alloy is preferably 0.1 to 2.0 mass %, and more preferably 0.3 to 1.5 mass %.

[0036] Zr:0.1~2.0% by mass Zirconium (Zr) easily forms a compound (AlZr) with aluminum, and this compound also has the effect of improving high-temperature strength. Zr also has the effect of refining crystal grains. The Zr content is preferably 0.1 to 2.0 mass%, more preferably 0.3 to 1.5 mass%.

[0037] Sc:0.3~2.0% by mass Scandium (Sc) easily forms a compound (AlSc) with aluminum, and this compound also has the effect of improving room temperature strength and high temperature strength. The Sc content is preferably 0.3 to 2.0 mass%, more preferably 0.5 to 1.5 mass%.

[0038] (1-2) Inevitable impurities Examples of unavoidable impurities in the aluminum alloy additive manufacturing product of the present invention include zinc (Zn), lithium (Li), nickel (Ni), copper (Cu), 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), cerium (Ce), and boron (B).

[0039] These inevitable impurity elements may be present inevitably in aluminum ingot, may be mixed inevitably during the production of aluminum alloy powder, or may be modifier elements when grain-refining elements such as boron 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 content is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and particularly preferably 0.2% by mass or less.

[0040] The content of each element in the aluminum alloy powder and the aluminum alloy layered manufactured product can be measured, for example, by ICP atomic emission spectrometry.

[0041] (2) Various characteristics (2-1) Surface roughness The aluminum alloy additive manufacturing object of the present invention has an extremely smooth surface with a surface roughness Sa of 22 μm or less, making it possible to produce an object with a shape close to the final shape. The surface roughness Sa is the arithmetic mean height defined in ISO 25178, and can be measured, for example, by a patterned light projection method using a 3D shape measuring instrument VR-3200 manufactured by Keyence Corporation. The surface roughness Sa of the aluminum alloy additive manufacturing object is preferably 20 μm or less, more preferably 18 μm or less, and most preferably 16 μm or less. Note that the surface roughness Sa in the present invention is measured on a surface on the top surface (side) of the object that is as horizontal or as close to horizontal as possible.

[0042] (2-2) Relative density The relative density of the aluminum alloy additive manufacturing product of the present invention is preferably 98.00% or more, more preferably 99.00% or more, even more preferably 99.50% or more, and most preferably 99.94% or more. If the relative density is less than 98.00%, the mechanical properties of the product may be significantly degraded. This relative density can be calculated, for example, by binarizing an optical microscope image (100x magnification) of an arbitrary cross section near the center of the product and calculating the area ratio of the metal portion excluding voids. A higher relative density is desirable to improve the mechanical strength, ductility, and thermal and electrical conductivity of the additive manufacturing product.

[0043] The relative density of the aluminum alloy additive manufacturing product can also be determined by cross-sectional observation using a scanning electron microscope. More specifically, a test piece is embedded in resin, mirror-polished, and then the cross section of the aluminum alloy additive manufacturing product is observed at multiple locations at 100x magnification using a scanning electron microscope. The cross-section is then binarized to calculate the porosity of the cross section, which can then be used as the relative density.

[0044] (2-3) Tensile properties The aluminum alloy additive manufacturing product of the present invention preferably has a breaking elongation of 15% or more, more preferably 18% or more, in a tensile test at room temperature. When the aluminum alloy additive manufacturing product has a breaking elongation of 15% or more at room temperature, the aluminum alloy additive manufacturing product can be suitably used as a component that requires high reliability.

[0045] Furthermore, the tensile strength of the aluminum alloy additive manufacturing product at room temperature is preferably 510 MPa or more, more preferably 515 MPa or more, and most preferably 520 MPa or more. Additionally, the 0.2% proof stress of the aluminum alloy additive manufacturing product at room temperature is preferably 500 MPa or more, more preferably 505 MPa or more, and most preferably 510 MPa or more. The tensile properties of the aluminum alloy additive manufacturing product can be evaluated using a conventionally known tensile testing method; for example, a tensile test piece machined from the aluminum alloy additive manufacturing product using a wire electric discharge machine can be measured using a general-purpose tensile testing machine.

[0046] (2-4) Vickers hardness The aluminum alloy additive manufacturing product of the present invention preferably has a Vickers hardness of 165 Hv or more at room temperature, more preferably 166 Hv or more, and most preferably 167 Hv or more. Since the aluminum alloy additive manufacturing product has a Vickers hardness of 165 Hv or more at room temperature, the aluminum alloy additive manufacturing product can be suitably used as a member that requires high strength and wear resistance.

[0047] The Vickers hardness of an aluminum alloy additive manufacturing product can be measured using a conventionally known measurement method. For example, the aluminum alloy additive manufacturing product can be cut in the thickness direction, the resulting surface can be polished as a measurement surface, and the Vickers hardness can be measured using a general-purpose Vickers hardness tester, and the average of the measured values ​​at 10 points can be used.

[0048] 2. Manufacturing method for aluminum alloy additive manufacturing body The method for producing an aluminum alloy additive manufacturing product of the present invention is a suitable method for producing an aluminum alloy additive manufacturing product of the present invention, and its greatest feature is that the oxygen concentration in the atmosphere during additive manufacturing is set to 1500 to 8000 ppm. The aluminum alloy powder used as a raw material and various production conditions will be described in detail below.

[0049] (1) Aluminum alloy powder The aluminum alloy powder 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 (force) atomization, mechanical alloying, and chemical processes. Among these, gas atomization and centrifugal force atomization are preferred.

[0050] The composition of the aluminum alloy powder can be basically the same as that of the aluminum alloy additive manufacturing body described above, but magnesium has the property of easily evaporating in part when molten at high temperatures, and the magnesium content tends to decrease slightly during additive manufacturing, so it is best to increase the magnesium content in the aluminum alloy by 10 to 20 percent.

[0051] The average particle size of the aluminum alloy powder is not particularly limited, but the volume-based average particle size (median diameter d50) 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 may decrease, making it difficult to form a uniform powder layer during the additive manufacturing process. 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.

[0052] 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 fluidity of the powder may decrease, and a uniform powder layer may not be formed during the manufacturing process of the shaped body. The circularity is a value not exceeding 1 obtained 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 photographs of the particles taken with a microscope. If the average circularity, calculated by averaging the circularities of approximately 1,000 particles, is 0.90 or more, the necessary fluidity is ensured and the content of oxides that cause defects tends to be reduced.

[0053] (2) Additive manufacturing method The additive manufacturing method is a method of processing by stacking molten and solidified regions layer by layer based on two-dimensional (slice) data obtained from 3D-CAD data. Aluminum alloy additive manufacturing involves a first step of forming a powder layer containing aluminum alloy powder, and a second step of forming a metal layer in the powder layer by melting and solidifying the aluminum alloy powder at a predetermined position. These first and second steps are repeated sequentially, and multiple metal layers are stacked and bonded to produce an aluminum alloy additive manufacturing object.

[0054] 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.

[0055] The method for manufacturing an aluminum alloy additive manufacturing product of the present invention is characterized by controlling the oxygen concentration in the atmosphere during additive manufacturing to 1500-8000 ppm in the first and second steps. The oxygen concentration in the atmosphere is preferably 2000-7500 ppm, more preferably 2500-7000 ppm, and most preferably 3000-6000 ppm. Within these ranges, the surface roughness of the Al-Mg alloy additive manufacturing product can be reduced (smoothed), the oxygen content in the product can be kept relatively low, and a high-quality aluminum alloy additive manufacturing product with good dimensional accuracy and balanced mechanical properties can be obtained. When the oxygen concentration in the atmosphere is less than 1500 ppm, there is a tendency for increased dust and fume generation, an increased oxygen content in the product, slightly increased surface roughness, and a slightly lower relative density. On the other hand, if the concentration exceeds 8000 ppm, the generation of dust and fumes is relatively suppressed, but the amount of oxygen in the molded body increases, the surface roughness increases, the relative density decreases, and the ductility tends to decrease.

[0056] The method for adjusting the oxygen concentration in the atmosphere is not particularly limited, but examples include adjusting the degree of vacuum, controlling the purity (oxygen content) or supply amount of N2 gas or Ar gas, a combination of these, etc. For example, a method can be used in which the air in the modeling chamber is evacuated using a vacuum pump such as a rotary pump or an oil diffusion pump, and then replaced with N2 gas or Ar gas of a predetermined purity to control the oxygen concentration.

[0057] In the first and second steps, the metal layer and powder layer may be preheated, although this is not essential. The preheating temperature is preferably 30°C or higher, more preferably 150°C or higher. Also, 400°C or lower is preferable, more preferably 250°C or lower. Preheating to 150°C or higher sufficiently suppresses cracks (delamination), while preheating to a temperature above 400°C tends to cause the microstructure of the aluminum alloy additive manufacturing body 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 ceramic heaters or high-frequency heating may also be used. Heating may also be achieved by scanning a heat source such as a laser beam or electron beam.

[0058] Heat treatment may also be performed after additive manufacturing. Heat treatment is effective for alleviating internal strain in the additively manufactured body and for artificial aging / precipitation strengthening treatment. The heat treatment temperature is preferably 150°C or higher, more preferably 200°C or higher, even more preferably 250°C or higher, and particularly preferably 300°C or higher. On the other hand, the upper limit is preferably 400°C or lower; if the temperature exceeds 400°C, precipitates and crystal grains may become coarse, which may impair mechanical properties.

[0059] The heat treatment time is preferably 0.1 hours or more, more preferably 0.5 hours 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, even more preferably 10 hours or less, and particularly preferably 5 hours or less. If the time is shorter than 0.1 hours, the heat treatment effect is poor, while if it is longer than 100 hours, there is a risk of overaging, resulting in a decrease in the strength of the aluminum alloy additive manufacturing product. An atmospheric furnace is usually used for the heat treatment, but an atmospheric furnace may also be used, and the treatment may be carried out in, for example, an inert gas atmosphere such as nitrogen or argon, or a reducing gas atmosphere such as hydrogen.

[0060] 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. [Example]

[0061] The aluminum alloy compositions shown in Table 1 as examples and comparative examples were prepared, heated to the melting point (liquidus temperature) or higher in a high-frequency induction furnace to melt thoroughly, and pulverized by centrifugal atomization to obtain aluminum alloy powders.

[0062] [Table 1]

[0063] The obtained powder was classified by passing it through a sieve with 63 μm openings and used as raw material powder for additive manufacturing.

[0064] The particle size distribution of the raw material powder was measured using a Microtrac laser diffraction scattering method, 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 is also expressed as the median diameter "d50." The obtained values ​​are shown in Table 1.

[0065] This aluminum alloy powder was used to produce aluminum alloy additive manufacturing objects by additive manufacturing. The aluminum alloy powder was used as a raw material to obtain an aluminum alloy additive manufacturing object by a laser-based powder bed fusion additive manufacturing method. The additive manufacturing machine used for additive manufacturing was a LUMEX Avance-25 manufactured by Matsuura Machinery Works. The chemical composition of each molded object was measured by ICP atomic emission spectroscopy, and the results are shown in Table 1. However, Comparative Examples 1 and 2 show the chemical composition of the raw material powder.

[0066] More specifically, the building conditions were laser power: 340 W, scanning speed: 900 mm / s, scanning pitch: 0.10 mm, no preheating, and N2 gas atmosphere. The oxygen concentration in the building chamber was further adjusted to 500, 1000, 3000, 5000, 6000, 8000, and 10000 ppm. Additive manufacturing was performed on a 12 mm thick aluminum alloy (A5052) base plate at oxygen concentrations of 500, 1000, 3000, 5000, 6000, 8000, and 10000 ppm. The amount of dust generated was measured, and test pieces were obtained at each oxygen concentration. The dust amount in the chamber was measured using a light-scattering digital dust meter (Model 3442) manufactured by Nippon Kanomax. The measurement results are shown in Table 1. Fields where no measurement was performed are left blank.

[0067] The dust amount was evaluated relative to the amount of dust generated when dust first began to generate and when the dust amount was highest, with the dust amount at an oxygen concentration of 5000 ppm in Example 2 set as 1. The dust amount decreased almost linearly as the amount of oxygen in the build chamber increased. A lower amount of dust in the build chamber reduces the probability of dust blocking the laser, resulting in more uniform builds. If part of the laser beam is blocked by dust, the laser intensity becomes insufficient in some areas, resulting in an inconsistent build. The dust amount in the examples tended to be lower than in the comparative examples, demonstrating that the method for manufacturing aluminum alloy additive manufacturing products of the present invention enables uniform builds. In particular, dust amount was effectively suppressed in Example 4, where the oxygen content in the device was 8000 ppm. While the reason for the reduced dust amount in an atmosphere containing an appropriate amount of oxygen is unclear, it is believed that the oxidation of magnesium suppresses fumes caused by magnesium, thereby reducing dust generation.

[0068] The oxygen concentration in the build chamber was adjusted from 3000 to 10000 ppm by filling the build chamber with nitrogen gas whose concentration was adjusted solely by controlling the air supply pressure to the nitrogen gas generator. The oxygen concentration in the build chamber of 500 and 1000 ppm was adjusted by filling the build chamber with nitrogen gas whose concentration was adjusted by changing the mixing ratio of the nitrogen gas from the nitrogen gas generator and the high-purity nitrogen gas from the cylinder.

[0069] Separately, a homemade powder bed fusion manufacturing device consisting of a continuous wave near-infrared laser (YLR-300-AC-Y11 manufactured by IPG Photonics Inc.), a high-speed camera (Fastcam Mini AX200 manufactured by Photoron Inc.), a linear stage (GHR25 manufactured by Jimmc Hillston Inc.), and a build chamber was used. The linear stage equipped with the build chamber had a laser output of 300 W, a spot diameter on the powder bed of 0.1 mm, a laser scanning speed of 500 mm / s, and a base plate made of 10 mm thick aluminum alloy (A5052). The laser irradiation area was observed when the linear stage was scanned in a nitrogen gas atmosphere with varying oxygen concentrations.

[0070] From the obtained video, images were extracted every 3 ms (20 frames) 30 ms after laser irradiation and processed using the image processing software ImageJ. For fume evaluation, the images were binarized in a grayscale range of 0 to 50, and fumes with a diameter of 200 μm or more were calculated as fumes, and the total area was calculated to calculate the fume generation area per frame. The obtained fume generation area is shown in Table 1. Note that if no measurement was made, the area is left blank.

[0071] The fume generation area is large in Comparative Examples 1 to 4 where the oxygen concentration in the manufacturing chamber is low (oxygen concentration: 10 to 1000 ppm), and drops sharply in Examples 2, 5, and 6 where the oxygen concentration is 5000 ppm. Furthermore, in Comparative Example 5 where the oxygen concentration is 10000 ppm, almost no fumes are generated. Furthermore, as shown in Comparative Examples 8 to 10, in aluminum alloys containing almost no Mg, almost no fumes are generated, regardless of the oxygen concentration in the atmosphere.

[0072] These results indicate that when aluminum alloys contain Mg, fumes are generated due to the Mg. However, even with aluminum alloys containing Mg, fume generation can be suppressed by controlling the oxygen concentration in the atmosphere to an appropriate value. Furthermore, similar to when dust blocks the laser beam, fumes can block part of the laser beam, reducing the laser intensity in certain areas and resulting in non-uniformity in the resulting product. However, this can be suppressed by controlling the oxygen concentration in the atmosphere to an appropriate value. It is believed that as the oxygen concentration in the build chamber increases, the amount of oxygen absorbed into the molten pool increases, and Mg forms oxides inside the molten pool, raising its boiling point and reducing the amount of fumes released.

[0073] After removing any adhering powder from the center of the top surface of the object obtained using the LUMEX Avance-25, the surface roughness was measured using a Keyence VR-3200 three-dimensional shape measuring instrument using the pattern light projection method. The obtained surface roughness (Sa) is shown in Table 1. Note that columns where no measurement was performed are left blank.

[0074] The surface roughness was slightly rough in Comparative Example 3 (oxygen concentration: 500 ppm) and Comparative Example 4 (oxygen concentration: 1000 ppm), where the oxygen concentration in the build chamber was low, but after reaching a minimum in Example 1 (oxygen concentration: 3000 ppm), it increased linearly with increasing oxygen concentration in the build chamber. It is thought that a lower oxygen concentration in the build chamber reduces the effect of oxygen and results in a smoother surface, but in Comparative Examples 3 and 4, where the oxygen concentration in the build chamber was low, the laser was partially blocked by the effects of fumes and dust, resulting in a slightly rougher surface.

[0075] The density of the molded body was also determined by cross-sectional observation. The test specimens were cut using a Struers Discotom-100 cutting machine, and then embedded in resin using Clarosit hardener in a cylindrical mold to make it easier to polish the cross-section of the test specimen. The cross-section was then polished using a Struers Tegramin-30 polishing machine. The polished test specimens were observed at multiple points on the cross-section at 100x magnification using a JEOL JCM-7000 scanning electron microscope, and the porosity of the cross-section was calculated by binarization processing, which was used as the relative density. The obtained relative densities are shown in Table 1. Note that fields where measurements were not taken are left blank.

[0076] A relative density of 99.94% or higher is desirable, but the values ​​fell below this target in Comparative Example 3 (oxygen concentration: 500 ppm) and Comparative Example 5 (oxygen concentration: 10,000 ppm). In Comparative Example 3, where the oxygen concentration in the build chamber was low, the laser was partially blocked by fumes and dust, resulting in a decrease in density. In Comparative Example 5, the amount of oxygen was too high, which is thought to be why sufficient density could not be obtained.

[0077] In addition, a molded body for measuring micro Vickers hardness (size: 50 mm length × 20 mm width × 12 mm height) was heat-treated at 325°C for 4 hours, and then cut into three pieces lengthwise as shown in Figure 1. The central molded body was further cut into approximately two equal pieces thicknesswise. The surface obtained by cutting the cut-out base plate side molded body in the thickness direction was polished as the measurement surface, and the Vickers hardness was measured. The test machine used was a Mitutoyo Micro Vickers Hardness Tester HM-221, and the test load was 0.2 kgf, with n = 10, and the average value was calculated. The obtained Vickers hardness is shown in Table 1. Note that if no measurement was performed, the column is left blank.

[0078] In Examples 1 to 4, the Vickers hardness of the molded object was 165 HV or higher. In contrast, the Vickers hardness of the molded object obtained in Comparative Example 3, in which the oxygen concentration in the molding chamber was low (oxygen concentration: 500 ppm), was 164 HV. These results show that by adjusting the oxygen concentration in the molding chamber, it is possible to increase the Vickers hardness of the molded object to 165 HV or higher.

[0079] Next, the shaped bodies for the tensile test specimens (size: length 70 mm x width 20 mm x height 12 mm) were machined into test specimens using a wire electric discharge machine. These were then heat-treated at 325°C for 4 hours and then subjected to tensile testing. The test specimens were JIS-14B test specimens with a parallel section of 24 mm in length, 3 mm in width, and 3 mm in thickness, and a gauge length of 15 mm. The tensile direction was perpendicular to the layer direction, and the test speed was 1.5 mm / min up to the yield strength and 5 mm / min thereafter. The testing machine used was a 100 kN autograph chi manufactured by Shimadzu Corporation. The tensile properties obtained are shown in Table 1. Note that fields not yet measured are left blank.

[0080] The shaped bodies of Examples 1 to 4 have high tensile strength, 0.2% yield strength, and breaking elongation. In particular, the shaped body obtained in Example 1 exhibits a large breaking elongation of 18.6% while having a tensile strength of 522 MPa. On the other hand, the shaped bodies obtained in Comparative Examples 8 to 10, which have a low Mg content, all have low values ​​for tensile strength, 0.2% yield strength, and breaking elongation. Furthermore, even when containing an appropriate amount of Mg, Comparative Example 5, in which the oxygen concentration in the building chamber was too high (oxygen concentration: 10,000 ppm), had a small breaking elongation of 11.0%. The breaking elongation linearly decreased as the oxygen concentration increased, reaching a maximum when the oxygen concentration in the building chamber was 3,000 ppm, indicating that an excessively high oxygen concentration in the building chamber is undesirable.

[0081] A 0.03g lump test piece was also cut out from the end of this tensile test piece with a tool, and the oxygen content of this was measured. The measuring device used was the EMGA-920 manufactured by Horiba, Ltd. The measurement method was inert gas fusion - non-dispersive infrared absorption (NDIR). Note that, because an oxide film forms on the new surface of the shaped body cut with the tool, the test piece cut out with the tool was made into a lump to minimize the effect of this oxide film on the oxygen content measurement results. The obtained oxygen content is shown in Table 1. Note that if no measurement was made, the column is left blank.

[0082] The oxygen content of the molded objects obtained in Comparative Examples 3 and 4 was higher than that of Examples 1 to 4, but it is believed that the oxygen content of the molded objects is basically proportional to the oxygen concentration in the molding chamber.

[0083] The above results show that when additive manufacturing is performed using aluminum alloy powder containing Mg as a raw material, controlling the oxygen concentration in the atmosphere to an appropriate value can suppress the generation of dust and fumes, and produce aluminum alloy additive manufacturing objects with low surface roughness and excellent mechanical properties.

Claims

1. Mg: 0.5 to 8.0% by mass, At least one metal element selected from the group consisting of Fe, Si, Mn, Cr, Ti, Zr, and Sc: more than 0.0 mass% and not more than 5.0 mass%, the balance being Al and inevitable impurities, The surface roughness Sa is 22 μm or less, The oxygen content is 0.015 to 0.048% by mass; An aluminum alloy additive manufacturing body characterized by the above.

2. The relative density determined by cross-sectional observation is 99.94% or more. The aluminum alloy additive manufacturing product according to claim 1,

3. The breaking elongation in a tensile test is 15% or more. The aluminum alloy additive manufacturing product according to claim 1 or 2, characterized in that

4. Vickers hardness is 165Hv or more, The aluminum alloy additive manufacturing product according to claim 1 or 2, characterized in that

5. The method for producing an aluminum alloy additive manufacturing product according to claim 1 or 2, Aluminum alloy powder is molded using additive manufacturing, The oxygen concentration in the atmosphere during additive manufacturing is 1500 to 8000 ppm; A method for manufacturing an aluminum alloy additive manufacturing object, characterized by the above.

6. The aluminum alloy raw material is aluminum alloy powder, using powder bed fusion for said additive manufacturing method; The method for producing an aluminum alloy additive manufacturing object according to claim 5,

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