High-strength aluminium alloys for additive manufacturing of three-dimensional objects

Abstract

To provide an aluminium alloy in powder form that is as cost-effective as possible, is thermally stable and has high-strength properties; a method for producing a three dimensional object; a method for producing an aluminium alloy in powder form; and a three-dimensional object.SOLUTION: The present invention relates to aluminium alloys in powder form with a content of at least two elements M from the group comprising Cr, Fe, Ni and Co and at least one element N from the group comprising Ti, Y and Ce, wherein the alloy has a total quantity of elements M in the range from 1 to 16 wt.%, a total quantity of elements N in the range from 0.5 to 5 wt.% if the aluminium alloy contains Ti or Ce, and 1 to 10 wt.%, if the aluminium alloy contains Y. Aluminium alloys of this kind can be used in additive manufacturing processes, such as selective laser melting, for the production of high-strength three-dimensional objects which can be used in engines for motor vehicles, for instance.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a specific powdered aluminum alloy containing two elements M from the group including Cr, Fe, Ni, and Co and at least one element N from the group including Ti, Y, and Ce, with element M in the range of 1-16 wt.-% and a total amount of element N in the range of 0.5-5 wt.-% if said aluminum alloy contains Ti or Ce, and a total amount of element N in the range of 1-10 wt.-% if said aluminum alloy contains Y. The present invention further relates to a process for the production of such an aluminum alloy, to a process and an apparatus for additive manufacturing of three-dimensional bodies, as well as three-dimensional bodies produced by these processes and the specific aluminum alloy. [Background technology]

[0002] Light metal components have been the subject of intensive research in vehicle, and particularly automobile, manufacturing, with the goal of continually improving vehicle performance and fuel efficiency. Many light metal components for automotive applications today are made from aluminum and / or magnesium alloys. Such light metals can form load-bearing components that must be strong and rigid, with excellent strength and ductility (elongation, etc.). High strength and ductility are particularly important due to the safety requirements and robustness of vehicles such as automobiles. Traditional steel and titanium alloys offer high temperature resistance, but these alloys are either heavy or relatively expensive, respectively.

[0003] A cost-effective alternative to light metal alloys for forming structural vehicle components are aluminum-based alloys, which can be conventionally fabricated into the desired components by bulk forming processes such as extrusion, rolling, forging, stamping, or by casting techniques such as die casting, sand casting, investment casting, chill casting, etc.

[0004] In addition to using light metal alloys for structural components, it is also important to use light metal alloys for components in the engine compartment, but problems arise here due to the high temperatures that tend to occur in the engine compartment, so components for this area of ​​the engine compartment must meet high requirements in terms of strength and heat resistance.

[0005] In recent years, "rapid prototyping" or "rapid tooling" has also gained importance in metal processing. These processes are also known as selective laser sintering and selective laser melting. In this process, thin layers of powder material are repeatedly applied and selectively solidified in each layer in areas where the subsequent production will be located by exposing it to a laser beam, first melting it in place and then solidifying it. In this way, complete three-dimensional bodies can be successively built up.

[0006] A method for producing three-dimensional bodies by selective laser sintering or selective laser melting as well as an apparatus for carrying out this process are disclosed, for example, in EP 1 762 122 A1.

[0007] Various aluminum alloys for selective laser melting are known and available in the market. These engineering materials are mainly AlSi materials such as AlSi10Mg, AlSi12, AlSi9Cu3, etc., which have only moderate strength and structural stability.

[0008] DE 10 2017 200 968 A1 describes aluminum alloys for forming high-temperature-resistant alloys containing aluminum, iron and silicon. These high-temperature-resistant alloys can be processed into three-dimensional bodies by selective laser sintering or selective laser melting. The gist of DE 10 2017 200 968 A1 is that molten precursor material is melted at a concentration of 1.0×10 molten iron to form a solid alloy part with a stable ternary cubic phase with high heat resistance and strength. 5 The advantage is that it cools at a rate of more than 100 K / sec.

[0009] EP 3 181 711 describes high-strength alloys for additive manufacturing of the AlMgSc type. In these alloys, yield strengths of more than 400 MPa are achieved, due to the strong strength-increasing effect of the intermetallic Al-Sc phase. However, the Sc required for these alloys is used in amounts ranging from 0.6 to 3% by weight, making these alloys very costly, and, moreover, this material is highly dependent on the production of sufficient amounts of scandium. A further disadvantage is that the alloys described in EP 3 181 711 are not suitable for application temperatures above 180 °C, due to the tendency of the AlMg matrix to soften and creep.

[0010] Another approach for alloys for additive manufacturing is the concept of Al-MMC (MMC is matrix metal composite), which at room temperature has similar mechanical properties to the AlMgSc alloy of EP 3181711. However, the problem with these materials is that at temperatures above 200 °C, their strength decreases significantly. Another problem with the Al-MMC concept is that the material is composed of a powder mixture of three components, which makes it difficult to transport, store and reuse, since changes in the mixture ratio cannot be eliminated by physical processes. Another drawback is the negative recycling behavior of MMC metal ceramic composites and the fact that mechanical reworking of Al-MMC is more difficult and correspondingly more costly. Summary of the Invention [Problem to be solved by the invention]

[0011] Based on the above-mentioned prior art, there is a need for aluminum alloys that are as cost-effective as possible, thermally stable, and have high strength properties, and can be processed into three-dimensional objects with high strength and stiffness and good corrosion properties by additive manufacturing techniques such as selective laser sintering and selective laser melting. In order to ensure a high level of supply security, rare earth metals that are scarce on the market, such as scandium, should be avoided as much as possible. Furthermore, additional processing steps are required to produce three-dimensional bodies and high-strength three-dimensional bodies produced by these processes. [Means for solving the problem]

[0012] This problem is solved by a powdered aluminum alloy as set forth in claim 1, by a process for producing a three-dimensional body as set forth in claim 10, by a process for producing a powdered aluminum alloy as set forth in claim 12, by a three-dimensional body produced using the powdered aluminum alloy as set forth in claim 13, by an apparatus for carrying out a process for producing a three-dimensional object as set forth in claim 14 and by an aluminum alloy as set forth in claim 15. Preferred embodiments of the invention are set forth in the dependent claims.

[0013] The powdered aluminum alloy of the present invention is a powder for use in the production of a three-dimensional body by an additive manufacturing technique. The powdered aluminum alloy of the present invention contains at least two elements M selected from a group including Cr, Fe, Ni, and Co, and at least one element N selected from a group including Ti, Y, and Ce, the total amount of the elements M being in the range of 1 to 16% by weight, the total amount of the element N being in the range of 0.5 to 5% by weight when the aluminum alloy contains Ti or Ce, and the total amount of the element N being in the range of 1 to 10% by weight when the aluminum alloy contains Y.

[0014] A preferred powdered aluminum alloy contains at least 0.5% and / or at most 8% Fe, at least 0.5% and / or at most 4.0% Cr, and at least 0.5% and / or at most 4.0% Ti, and optionally contains at most 1.0% Si, and / or at most 1% Zr, and / or at most 1% Ce. More preferably, the powdered aluminum alloy contains at least 0.5% and at most 8.0% Fe, at least 0.5% and at most 4.0% Cr, at least 0.5% and at most 4.0% Ti, and optionally contains at most 1.0% Si, at most 1.0% Zr, and at most 1.0% Ce. In one embodiment, the aluminum alloy contains Si, Zr, and Ce in an amount of at least 0.01% by weight.

[0015] As mentioned above, the specific aluminum alloy in powder form advantageously contains at least 0.5% by weight of iron, preferably at least 3% by weight of iron, and more preferably at least 4% by weight of iron. By "specific aluminum alloy in powder form" is meant herein and hereinafter the powdered aluminum alloy as mentioned above according to the general and preferred embodiments. Alternatively or in addition, the specific powdered aluminum alloy preferably contains at most 8% by weight of iron, more preferably at most 7% by weight of iron, and even more preferably at most 6% by weight of iron (or at most 6 atomic % of iron), any of these specified upper limits can be combined with any of the specified lower limits or can define an open range in one direction. The specific powdered aluminum alloy suitably contains at least 0.5% by weight of chromium, preferably at least 2% by weight of chromium, and even more preferably at least 3% by weight of chromium. Alternatively or in addition, certain powdered aluminum alloys of the general and preferred embodiments preferably contain up to 4.5% by weight chromium, more preferably up to 3.8% by weight chromium, each of these specified upper limits may be combined with each of the specified lower limits or may define an open range.

[0016] With regard to the total amount of iron, chromium and / or cobalt contained in the powdered aluminum alloy, a content of 1% by weight or more is considered to be preferred, a content of 1.5% by weight or more is considered to be more preferred, and a content of more than 2% by weight is considered to be even more preferred.

[0017] In a particularly preferred embodiment of the invention, the powdered aluminium alloy does not simultaneously contain relevant amounts of Fe and Co, i.e. when one of these elements Fe and Co is present in the aluminium alloy of the invention in a proportion of 0.5% by weight or more, in particular 1% by weight or more, the other element is present in the aluminium alloy in a proportion of at most 0.1% by weight, preferably at most 0.05% by weight.

[0018] The particular powdered aluminum alloy further suitably comprises at least 0.5 wt.% Ti, more preferably at least 1 wt.% Ti, more preferably at least 1.5 wt.% Ti. Alternatively or in addition, the particular powdered aluminum alloy preferably comprises at most 4.5 wt.% Ti, more preferably at most 3.5 wt.% Ti, each of these specified upper limits can be combined with each of the specified lower limits or can define an open range in one direction.

[0019] The powdered aluminum alloy contains aluminum as the main component, which preferably constitutes at least 90%, more preferably at least 95%, even more preferably at least 98% of the aluminum alloy's 100% content. Further non-aluminum components may be, for example, oxygen, which may be present as an oxide fraction on the surface of the powder particles. Other elements that may be present in the powdered aluminum alloy are, for example, manganese or magnesium.

[0020] With respect to the total powdered aluminum alloy, the proportion of aluminum is preferably at least 80% by weight, more preferably at least 85% by weight. Alternatively, or in addition, the specific powdered aluminum alloy preferably contains up to 93% by weight aluminum, more preferably up to 90.5% by weight aluminum, where any of the specified upper limits can be combined with any of the specified lower limits.

[0021] In the case of silicon, a content of up to 3% by weight can be indicated as preferred, a content of up to 1.5% by weight as more preferred and a content of up to 0.5% by weight as even more preferred, where the expression "up to" can include or exclude a content of 0% by weight (or 0 atomic %, respectively). The same applies to the expression "up to at most 1% by weight" for the zirconium and cerium contents.

[0022] Further preferred powdered aluminium alloys contain at least 3% and / or at most 7% by weight Fe, preferably at least 4% and / or at most 6% by weight Fe, at least 2% and / or at most 4% by weight Cr, preferably at least 3 and / or at most 3.8% by weight Cr (or and / or at most 3.8 atomic % Cr), at least 1% and / or at most 4% by weight Ti, preferably at least 1.5% and / or at most 3.5% by weight Ti (or and / or at most 3.5 atomic % Ti), and at least 80% and / or at most 93% by weight aluminium, preferably at least 85% and / or at most 90.5% by weight aluminium. A more preferred powdered aluminum alloy contains 3-7 wt% Fe, preferably 4-6 wt% Fe, 2-4 wt% Cr, preferably 3-3.8 wt% Cr (or 3-3.8 atomic % Cr), 1-4 wt% Ti, preferably 1.5-3.5 wt% Ti, and 80-93 wt%, preferably 85-90.5 wt% aluminum.

[0023] Among the aforementioned elements, Ni, Y, Co and the rare earth element Ce act as glass formers in aluminum alloys, resulting in the formation of larger amorphous regions in the alloy, which in turn improves the corrosion properties of the alloy.

[0024] Furthermore, Ce, and Zr, or Si, each affect the phase formation of the alloy. In another preferred embodiment, the aluminum alloy of the present invention does not contain a substantial amount of Ce, i.e., less than 1 wt.% Ce, preferably less than 0.5 wt.% Ce, more preferably less than 0.2 wt.% Ce, and even more preferably less than 0.05 wt.% Ce.

[0025] The elements Ti, Fe and Cr have a much lower glass-forming potential in aluminum alloys than Ni, Y and Co. However, by subjecting them to the proper process conditions to harden as quickly as possible, they can produce metastable superstructures with the desired properties.

[0026] Alternative, more preferred powdered aluminum alloys contain at least 1% and / or at most 7.5% Ni, at least 1% and / or at most 5.5% Co, and at least 2% and / or at most 10% Y, and optionally 3.0% Mn and / or 1% Zr. These aluminum alloys preferably contain 1-7.5% Ni, 1-5.5% Co, and 2-10% Y, and optionally 3.0% Mn and 1% Zr. Particularly preferred, these aluminum alloys contain a minimum proportion of 0.01% Mn and / or Zr.

[0027] Further alternative powdered aluminum alloys contain at least 2% and / or up to 10% Ni, at least 0.5% and / or up to 6% Fe, and at least 0.5% and / or up to 5% Ce, and optionally up to 1.0% Zr and / or up to 2.0% each of Gd, Nd, or La. These aluminum alloys preferably contain 2-10% Ni, 0.5-6% Fe, and 0.5-5% Ce, and optionally up to 1% Zr, and / or up to 2% each of Gd, Nd, or La. Particularly preferably, these aluminum alloys contain a minimum proportion of 0.01% Zr and / or Gd and / or Nd and / or La.

[0028] The powdered aluminum alloy of the present invention preferably contains up to 0.3% by weight of oxygen, preferably up to 0.25% by weight of oxygen. Higher oxygen contents within these ranges, for example at least 0.05% by weight of oxygen, in particular 0.1-0.3% by weight of oxygen, preferably 0.15-0.25% by weight of oxygen, impart better flowability to the powder particles (as measured by the Hall Flow Test according to ISO Standard 4490).

[0029] The alloys mentioned above have been found to have a thermally stable nanocrystalline structure reinforced by icosahedral phases and / or amorphous components. Conventionally, it was not possible to manufacture complex parts from these alloys, since they cannot be cast, forged, (traditionally) sintered or welded. Surprisingly, it was found that, despite this background, the alloys of the present invention can be processed by a laser melting process into parts of complex shapes, and therefore can be used for parts with the highest strength, stiffness or creep resistance at temperatures up to 350°C. Furthermore, products manufactured in this way can have improved wear resistance and / or corrosion properties.

[0030] With regard to the particle size, the powdered aluminum alloy of the present invention is not subject to any significant limitations, and the particle size should be in a size range suitable for additive processes for the production of three-dimensional bodies. A suitable particle size can be an average particle size D50 in the range of 0.1 to 500 μm, preferably at least 1 μm and / or at most 200 μm, particularly preferably at least 10 μm and / or at most 80 μm. Particularly preferred is an average particle size D50 in the range of 10 to 80 μm.

[0031] Further, it is preferred that at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight, of the particles have a particle size in the range of 10 to 80 μm.

[0032] In the context of the present invention, the particle size should in particular be determined with the aid of a laser diffraction process (using a HELOS device from Sympatec GmbH, in accordance with ISO standard 13320), where in the case of an average particle size of specification D (number), the number indicates the proportion (percentage) of particles below a certain size (i.e. if D50 is 50 μm, then 50% of the particles have a size below 50 μm). The diameter of a single particle may optionally be the respective maximum diameter (equal to the upper limit of all distances between each two points of the particle), or the sieve diameter or the equivalent spherical diameter related to the volume.

[0033] It is further preferred in the powdered aluminum alloy of the present invention that the aluminum alloy forming the basis of the powder has one or more of the following properties:

[0034] a strength measured at 23 °C, measured as a yield strength of more than 300 MPa, preferably more than 320 MPa; a strength measured at 250 °C, measured as a high temperature (hot) yield strength of more than 200 MPa, preferably more than 250 MPa; A short-term creep strength, measured as a stress at 0.5 creep strain at 260°C and a hold time of 6 minutes, of at least 200 MPa, preferably at least 220 MPa, even more preferably at least 240 MPa.

[0035] "Strength" refers to the ability to withstand mechanical loads before failure occurs and is specified in the DIN standard EN It is measured in the context of the present invention according to the tensile test in accordance with ISO 6892-1:2017 edition A224. "Yield strength" refers to the stress at which a material shows no permanent plastic deformation under a uniaxial, moment-free tensile load.

[0036] The high temperature yield strength refers to the yield strength at a specified temperature and is determined by measurement in the context of the present invention according to DIN standard EN ISO 6892-2: 2011 edition A113.

[0037] The short-term creep strength is determined by measurement in the context of the present invention in accordance with DIN standard EN ISO 6892-2: 2017 edition -05A.

[0038] "Creep" refers to the time- and temperature-dependent deformation of a material due to plasticity and load. Creep strain refers to the plastic strain that occurs when a material creeps.

[0039] The powdered aluminum alloy of the present invention can be produced by known processes used for the production of powdered alloys. A particularly useful process involves the atomization of a liquid aluminum alloy, whereby the aluminum alloy is heated to a suitable temperature and atomized. For atomization, the aluminum alloy should have a temperature above 850°C, preferably above 950°C, and more preferably above 1050°C. Temperatures above 1200°C are not necessary for atomization and are impractical due to higher energy requirements. For this reason, a particularly preferred temperature range for atomization can be specified as greater than 850 and less than 1200°C, preferably greater than 950 and less than 1150°C. To prevent undesirable primary precipitation, it is necessary to ensure that the abovementioned temperatures always prevail at the nozzle, by sufficient overheating of the melt or process control, respectively.

[0040] It was shown that in the powdered aluminum alloys mentioned above, the composition of the starting material may result in the production of high-melting-point particles of intermetallic phases (Al-Ti compounds) larger than 20 μm. Such high-melting-point particles cannot be melted and dissolved together with the surrounding material during subsequent processing as part of the additive manufacturing of three-dimensional bodies. In addition, due to unfavorable process control, coarse high-melting-point intermetallic phases may also be produced during melting in the course of alloying. This can be detected both in the powder particles and in the solidified part in cross sections under an optical microscope. Since these particles may have a negative effect on the use properties of the three-dimensional objects produced from them, a post-processing in which the powdered aluminum alloys are melted under suitable melting conditions and sprayed again may be appropriate.

[0041] Alternatively, the powdered aluminum alloy of the invention can also be produced by mechanical alloying. In this process, the metal powders of the individual components of the subsequent alloy (or its premix) are intensively mechanically processed and homogenized to the atomic level. For particle modification, it is possible to post-treat the particles obtained after mechanical alloying, for example to change the morphology, particle size or particle size distribution, or to carry out surface treatment. The post-treatment can include one or more steps selected from chemical modification of the particles and / or particle surface, classification, grinding, chamfering, plasma spheroidization (i.e. treatment to round particles) and addition. The particle morphology is suitable for a respective modification of the particle size distribution, especially since mechanical alloying usually results in platelets or flakes. This morphology is generally problematic for subsequent additive treatment processes.

[0042] Therefore, in accordance with the above, the present invention relates to a method for the production of a powdered aluminium alloy, in particular a molten aluminium alloy having the above composition, for use in a process in which a powdered aluminium alloy, in particular a molten aluminium alloy having the above composition, is atomised in a suitable device or a powdered aluminium alloy having said composition is prepared by mechanical alloying and optional post-treatment.

[0043] See above for preferred embodiments of atomization, mechanical alloying, and optional post-treatment.

[0044] Furthermore, the present invention relates to powdered aluminum alloys obtained by atomizing the liquid alloy at a temperature preferably above 850°C, more preferably above 1050°C, or by mechanical alloying with optional post-treatment, according to the described process, reference being also made to the above explanations of preferred embodiments of atomization, mechanical alloying and optional post-treatment.

[0045] In another aspect of the invention, the three-dimensional body relates to a process for producing a three-dimensional body produced by selectively solidifying the laminated material by adding a layer of laminated material layer by layer, in particular by supplying radiant energy, scanning positions in each layer corresponding to a cross-section of the three-dimensional body in that layer with at least one area of ​​action, in particular an area of ​​radiation acted on by an energy radiation beam. In the context of the invention described herein, the laminated material comprises a powdered aluminum alloy as mentioned above. Preferably, the laminated material consists of this powdered aluminum alloy itself.

[0046] The three-dimensional body may be an object made of one material (i.e., aluminum alloy) or may be an object made of different materials. When the three-dimensional body is an object made of different materials, the object can be produced, for example, by applying the aluminum alloy of the present invention to a substrate of another material. The material different from the aluminum alloy of the present invention is advantageously an aluminum alloy, for example, AlSi10Mg.

[0047] In the context of this process, it is appropriate to preheat the powdered aluminum alloy before selective solidification, with preheating to a temperature of at least 130°C being indicated as being preferred, with preheating to a temperature of at least 150°C being indicated as being more preferred, and even more preferably with a temperature of at least 190°C being indicated as being more preferred. On the other hand, preheating to very high temperatures, i.e. at least on the vessel in which the three-dimensional body is formed, so that temperatures of up to 400°C can be indicated as reasonable maximum temperatures for preheating, places considerable performance demands on the equipment for the production of the three-dimensional body. The maximum preheating temperature is preferably up to 350°C, more preferably up to 300°C. The specified preheating temperatures respectively indicate the temperatures to which the layering platform on which the powdered aluminum alloy is applied and the powder bed formed by the powdered aluminum alloy are heated.

[0048] Another aspect of the invention relates to a three-dimensional body made with a powdered aluminium alloy as defined above, in particular by the method defined above, which comprises or consists of such an aluminium alloy. The use of the aluminium alloy defined above for the manufacture of such a three-dimensional body results in a very good "as deposited" surface, which allows the subsequent post-treatment of the surface to be minimised.

[0049] Another aspect of the present invention relates to a manufacturing apparatus for carrying out the above-mentioned three-dimensional body manufacturing process, the manufacturing apparatus comprising a laser sintering or laser melting apparatus, a process chamber configured as an open container having a container wall, and a carrier disposed within the process chamber, the process chamber and the carrier being vertically movable relative to one another, a storage container and an application apparatus being horizontally movable, and the storage container being at least partially filled with the above-mentioned powdered aluminum alloy.

[0050] Additive manufacturing devices and related processes for the production of three-dimensional bodies are characterized in that the three-dimensional body is produced therein by solidifying a generally shapeless layer-by-layer of laminated material, which can be brought about, for example, by supplying thermal energy to the laminated material, by irradiating the laminated material with electromagnetic or particle radiation, e.g., for selective laser sintering ("SLS" or "DMLS") or laser or electron beam melting.

[0051] For example, in laser sintering or laser melting, the exposed area of ​​a laser beam ("laser spot") on a layer of laminate material moves over those areas of the layer that correspond to the cross-section of the three-dimensional body to be produced with this layer. Instead of adding energy, selective solidification of the added laminate material can also be performed by 3D printing, for example by adding an adhesive or binder. In general, the invention relates to the production of three-dimensional bodies by adding and selectively solidifying the laminate material in layers, regardless of the way in which the laminate material is solidified.

[0052] In the context of the invention described herein, the individual particles of the laminate material are preferably bonded to one another without the use of adhesives or binders, but only by the application of radiant energy. In this case, the mechanical properties of the aluminum alloy can be adjusted within certain limited ranges by selecting appropriate parameters. For example, DIN standard EN ISO It may be preferred to operate the laser at a power of about 310 W to produce an aluminum alloy of the invention such that the hardness of the aluminum alloy is within the range of 140 to 155 HBW 2.5 / 62.5 Brinell hardness, as measured according to DIN standard EN ISO 6506-1: 2015. Alternatively, in certain manufacturing equipment circumstances, it may be preferred to operate the laser at a power of about 220 W to produce an aluminum alloy of the invention such that the hardness of the aluminum alloy is within the range of 145 to 170 HBW 2.5 / 62.5 Brinell hardness, as measured according to DIN standard EN ISO 6506-1: 2015.

[0053] Various types of lamination materials can be used. In particular, powders such as metal powders, plastic powders, ceramic powders, sand, filler powders or mixed powders can be used as lamination materials. In the context of the present invention, the powdered aluminum alloy of the present invention is used at least proportionately as lamination material.

[0054] Further features and embodiments of the invention can be seen from the description of exemplary embodiments with the aid of the attached drawings. [Brief description of the drawings]

[0055] [Figure 1] FIG. 1 is a partially reproduced schematic cross-sectional view of an apparatus for stacking layer-on-layer of a three-dimensional body according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing a surface comparison of an impeller manufactured by selective laser melting from a powdered aluminum alloy of the present invention. [Diagram 3]FIG. 3 is a graph showing the results of measurement of short-term creep strength of test specimens made from the aluminum alloy powder of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0056] The apparatus shown in Fig. 1 is a known laser sintering or melting apparatus a1. For building an object a2, the apparatus comprises a process chamber a3 having a chamber wall a4. In the process chamber a3, an upwardly opening build vessel a5 having a wall a6 is arranged. A working surface a7 is defined by the upper opening of the build vessel a5, the area of ​​the working surface a7 lying within the opening can be used for building the object a2 and is called the build site a8. A carrier a10 movable in a vertical direction V is arranged in the vessel a5 to which is attached a bottom plate a11, which terminates the build vessel a5 at its bottom and thus forms the bottom of the build vessel.

[0057] The base plate a11 may be a plate formed separately from the carrier a10 and attached to the carrier a10, or may be formed integrally with the carrier a10. Depending on the powder and process used, the base plate a11 may also have a stacking platform a12 on which the objects a2 are stacked. However, the objects a2 may also be stacked on the base plate a11 itself, and the base plate a11 may also function as the stacking platform.

[0058] In Fig. 1 an object a2 to be formed in a build container a5 on a build platform a12 is shown below a working surface a7 in an intermediate state having several solidified layers surrounded by unconsolidated build material a13. The laser sintering apparatus a1 further comprises a storage container a14 for powdered build material a15 which can be solidified by electromagnetic radiation and an application device a16 movable in a horizontal direction H for applying the build material a15 to a build site a8.

[0059] The laser sintering apparatus a1 further comprises an exposure device a20 having a laser device a2 which generates a laser beam a22 as an energy radiation beam which is deflected via a deflection device a23 and focused onto a working surface a7 by a focusing device a24 through a coupling window a25 provided on the upper side within the wall a4 of the processing chamber a2.

[0060] Furthermore, the laser sintering apparatus a1 includes a control unit a29 that coordinates and controls the individual components of the apparatus a1 to execute the lamination process. The control unit a29 may include a CPU whose operation is controlled by a computer program (software). The computer program may be stored in a storage medium that can be mounted in a device, particularly in the control unit, separate from the apparatus.

[0061] In operation, to apply a powder layer, the carrier a10 is first lowered by a height corresponding to the desired layer thickness. A layer of powdered laminate material a15 is then applied by moving the applicator a16 over the working surface a7. For safety, the applicator a16 pushes in front of it a slightly larger amount of laminate material a15 than is required for the layer stack. The applicator a16 systematically pushes the excess amount of laminate material a15 into overflow containers a18. The overflow containers a18 are located on either side of the build container a5.

[0062] The powdered laminate material a15 is applied at least over the entire cross-section of the object a2 to be manufactured, preferably over the entire build site a8, i.e. over the entire area of ​​the working surface a7, which can be lowered by a vertical movement of the carrier a10. The cross-section of the object a2 to be manufactured is then scanned by a laser beam a22 having a radiation exposure area (not shown) which shows diagrammatically the intersection of the energy radiation beam with the working surface a7. As a result, the powdered laminate material a15 solidifies in the position corresponding to the cross-section of the object a2 to be manufactured. These steps are repeated until the object a2 is completed and can be removed from the build container a5.

[0063] To generate a preferably laminar process gas flow a34 in the treatment chamber a3, the laser sintering machine a1 further comprises a gas supply channel a32, a gas inlet nozzle a30, a gas outlet opening a31 and a gas exhaust channel a33. The process gas flow a34 flows horizontally across the build site a8. The gas supply and exhaust may be controlled by a control unit a29 (not shown). The gas extracted from the treatment chamber a3 may be fed to a filter device (not shown) and the filtered gas may be fed back to the treatment chamber a3 via the gas supply duct a32, thus forming a recirculation system with a closed gas loop. Instead of only one gas inlet nozzle a30 and only one gas outlet opening a31, several nozzles or openings may be provided in each case.

[0064] In the apparatus of the present invention, the storage vessel a14 is at least partially filled with powdered aluminum alloy a15 as described above.

[0065] Finally, another aspect of the invention relates to an aluminum alloy containing 2-8% by weight Fe, 0.5-4.0% by weight Cr, and 0.5-4.0% by weight Ti, and optionally 3.0% by weight or less Si and / or 1% by weight or less Zr and / or 1% by weight or less Ce, the total amount of Fe, Cr and Ti in the alloy being at least 10% by weight and / or at most 16% by weight, preferably at least 11% by weight and / or at most 13% by weight. It can be said that a particularly preferred aluminum alloy contains 5.1±1% by weight Fe, 3.5±1% by weight Cr and 2.5±1% by weight Ti, with the total amount of Si, Mg and O being 0.05-1% by weight, more particularly 0.1-6.6% by weight.

[0066] The present invention is further illustrated by a number of examples, which should not be construed as determining the scope of protection of the present application.

[0067] The following aluminum alloys and three-dimensional bodies were characterized using the methods described below:

[0068] The average particle size D50 was measured using a HELOS device (registered trademark) from Sympatex GmbH in accordance with ISO standard 13320.

[0069] Bulk density was measured with a Hall flowmeter according to ISO standard 3923 / 1.

[0070] The flow properties were measured with a Hall flow meter according to ISO standard 4490.

[0071] Density was measured on three-dimensional bodies produced as density cubes by selective laser sintering or selective laser melting using Archimedes' principle according to ISO standard 3369: "Opparent sintered metallic materials and hard metals - Determination of density".

[0072] In this density determination method, the mass of a sample is measured in both air and water, and the measured mass difference between the two measurements is used to estimate the volume of the sample based on the known density of water. The measured weight and volume of the sample can then be used to calculate its density.

[0073] In the test, density cube samples were polished on all sides with Struers Struers SIC #320 sample preparation system using the Labo-Pol-5 sample preparation system The samples were polished manually using sandpaper because air bubbles trapped on the sample surface could alter the test results.

[0074] Weighing in water uses deionized water and a small amount of dishwashing liquid is added to the water to reduce surface tension. The procedure is carried out on a laboratory scale (Köln PLT 650-3M) with a built-in density calculation program. The water temperature is measured before the test for automatic calculation. The measurements are repeated five times for each sample, switching samples between each measurement and allowing the samples to dry completely before a new measurement. The results below show the average value of the five repetitions.

[0075] The measurements of tensile strength, yield strength, elongation at break and modulus of elasticity were carried out according to the tensile test according to the standard DIN standard EN ISO 6892-1: 2016 edition "Metallic materials - Tensile tests - Part 1: Test method at room temperature", respectively. For the tensile tests, three-dimensional bodies produced by selective laser sintering or selective laser melting are used as tensile test specimens (specimens). The cross-sectional diameter of each specimen is reduced on a lathe to a minimum value of approximately 5.0 mm in the center of the specimen. This diameter is checked with a micrometer. The ends of the specimens are threaded for mounting. The tests are carried out, for example, using a universal testing machine with an inspection table 50 kn (Hegewald & Peschke Mess-und Prüftechnik GmbH). The tensile force increases to 10 MPa / s in the elastic phase of the material behavior and decreases to 0.375 MPa / s at the beginning of the plastic deformation phase.

[0076] During the test, the maximum load, yield strength (Rp0.2 limit), tensile strength, E modulus and elongation at break of the specimens are recorded and then the reduction in cross-sectional area at break is measured with calipers.

[0077] The properties high temperature tensile strength, E modulus, high temperature yield strength and elongation at break at 250°C were determined according to DIN standard EN ISO 6892-2:2011 edition A113.

[0078] Hardness tests of three-dimensional bodies produced as samples by selective laser sintering or selective laser melting are carried out using the Brinell method in accordance with the standard DIN standard EN ISO 6506-1: 2015 edition "Hardness testing of metallic materials according to Brinell - Part 1: Test method". Density cube samples are used for the tests. The tests are carried out three times per sample and the measurements are given with an accuracy of 1 HBW. The numerical data given below indicate the ball diameter of the test ball used for the measurements (e.g. 2.5 mm) and the test load (e.g. 63.5 kp).

[0079] The thermal conductivity was determined according to the equation λ = a·cp·ρ from the measured thermal diffusivity aLFA (Laser Flash Method Measurement Apparatus 427 Netch, Ar atmosphere 100 ml / min, two fabricated samples each: disks with diameter 12.6 mm, thickness 3-3.5 mm, plane parallel surface, temperature range 21-250 °C), specific heat capacity cp, and temperature dependent density ρ, taking into account the measured thermal expansion aLFA. The laser flash measurement method is a measurement method for directly measuring thermal diffusivity.

[0080] Here, the sample is heated for a short period of time by a laser. To be able to perform the measurement, the sample is first placed in a sample holder and covered with a graphite layer that absorbs thermal radiation. The sample holder together with the sample is then placed in the system and brought to the desired measurement temperature in an oven. Once the temperature is reached, a defined amount of heat is introduced into the sample with an excitation pulse. A detection laser is then used to measure the thermal reflection of the sample on the other side of the sample holder. This typically shows a rise in the sample temperature after heat input followed by a slower fall. This can be steep or flat depending on the thermal diffusivity of the sample. From this data the thermal conductivity is directly calculated using a mathematical model.

[0081] The specific heat capacity, cp, was measured using a Setaram high-temperature calorimeter with a measurement interval of 80 to 250 °C, a heating rate of 5 K / min, a He atmosphere, and a continuous comparison method, using a cylindrical sample with a diameter of 4.9 mm and a length of 16 mm and two prepared samples with flat parallel surfaces.

[0082] Thermal expansion was measured using a DIL402C dilatometer, with a measurement range of 20 to 250°C, a heating rate of 5 K / min, a He atmosphere, and two prepared specimens with a cylinder of 4 mm diameter and 25 mm length and plane-parallel surfaces.

[0083] The specific heat capacity and thermal expansion values ​​are average values ​​for the measured samples. EXAMPLES

[0084] Example 1: Various aluminum alloy powders were produced with the compositions and properties shown in Table 1 below.

[0085] [Table 1]

[0086] The smaller grain size of aluminum alloy 2 resulted in improved surface quality and reduced crack sensitivity in the production of three-dimensional bodies compared to aluminum alloy 1. Aluminum alloy 2 also has a higher bulk density and better flowability, probably due to the reduced interparticle forces caused by the higher oxygen content. Alloy 3 combines the advantageous properties of alloys 1 and 2.

[0087] The powders were coarse and consisted mainly of spherical particles. Aluminum alloy 1 contained few particles with a size below 10 μm, while aluminum alloy 2 contained a significant amount of fine particles in the powder. Powder 3 was characterized by a lower amount of fines compared to powder 2. Using these powders, layer thicknesses of 20 to 60 μm could be reliably produced.

[0088] Example 2: The three-dimensional test specimen was made of aluminum alloy and was printed on an EOS M290 (EOS Print The samples were fabricated using a 3D laser (Version 2.X, laser power 270 W, linear speed 850 mm / s, hatch distance 0.1 mm, film thickness 0.05 mm). For this purpose, a preheating temperature of 195 °C was set in the sample chamber. Using aluminum alloys, the density of the fabricated objects can be increased to more than 99%. Objects made with aluminum alloy 1 showed a slightly higher sensitivity to brittle cracks.

[0089] Complex test objects can be made from aluminum alloys. Impellers of manufactured dimensions showed a maximum deviation from the specification of ±0.15 mm (see Figure 2).

[0090] Density 2.9g / cm 3 The following properties were measured for samples made of aluminum alloy 3:

[0091] [Table 2]

[0092] Further galvanic corrosion studies were carried out, comparing samples made of aluminum alloy 1 with corresponding samples made of A199.5. A saturated calomel electrode was used as the reference electrode. Measurements were carried out in 0.01 M NaCl solution at 25°C, using a platinum sheet as the counter electrode. This showed a significantly lower negative potential for the aluminum alloy of the present invention, compared to the samples made of Al99.5.

[0093] Example 3: Measurement of short-term creep strength of aluminum alloy 1 The short-term creep strength of one aluminum alloy was determined according to DIN standard EN ISO 6892-2:2011 edition -05 A. For this purpose, the samples were subjected to different stress levels at 260 °C and then kept under constant stress. The permanent elongation occurring after 6 minutes is recorded as the measured value. The stress at which an elongation of 0.5% is obtained is used as the reference value for comparison.

[0094] The results of these tests are shown in Figure 3. For aluminum alloy 1, a short-term creep strength of approximately 260 MPa could be determined, determined as a creep strain of 0.5% at 260 °C and a stress at a holding time of 6 min, which is significantly higher than the short-term creep strengths described for the other aluminum alloys (in the range of 9 to 170 MPa). For the additively manufactured Al-MMC, a short-term creep strength of 170 MPa was determined (not shown).

Claims

1. % and at most 8 wt. % Fe, at least 0.5 wt. % and at most 4.0 wt. % Cr, at least 0.5 wt. % and at most 4.0 wt. % Ti, and at least 0.05 wt. % and at most 0.3 wt. % oxygen, and optionally containing Si, Mg, and Mn, or at most 3.0 wt. % Si and / or not more than 1 wt. % Zr and / or not more than 1 wt. % Ce, wherein the total amount of Si, Mg, Mn, and oxygen is 0.05 to 1 wt. %; A powdered aluminum alloy for additive manufacturing, the balance of which consists of unavoidable impurities and Al.

2. A powdered aluminum alloy as described in claim 1, containing 0.1 to 0.3 weight percent oxygen.

3. 3. A powdered aluminium alloy according to claim 1 or 2, containing at least 3 wt.% and / or at most 7 wt.% Fe, at least 2 wt.% and / or at most 4 wt.% Cr, at least 1 wt.% and / or at most 4 wt.% Ti, and at least 80 wt.% and at most 93 wt.% aluminium.

4. 4. A powdered aluminium alloy according to any one of claims 1 to 3, having an average particle size D50 in the range of 0.1 to 500 μm.

5. 5. A method for producing a powdered aluminium alloy according to any one of claims 1 to 4, wherein the powdered aluminium alloy is processed by atomising a liquid alloy at a temperature above 850°C or by mechanical alloying.

6. 1. A method for producing a three-dimensional body, comprising: the three-dimensional body is formed by adding layer upon layer of a laminate material and selectively solidifying the laminate material; A method for producing a three-dimensional body, wherein the layered material contains the powdered aluminum alloy according to claim 1 .

7. The method of claim 6, wherein the powdered aluminum alloy is preheated to a temperature of at least 130°C and at most 400°C.

8. 1. A method for producing a powdered aluminum alloy, comprising:

5. A method for producing a powdered aluminum alloy, comprising spraying a molten aluminum alloy having the composition according to any one of claims 1 to 4 into an apparatus, or mechanically alloying an aluminum alloy having the composition.

9. A manufacturing apparatus for carrying out the method of claim 6, comprising: a laser sintering or laser melting device; a processing chamber formed as an open vessel having a vessel wall; a carrier disposed within the processing chamber; 5. A manufacturing apparatus characterized in that the processing chamber and the carrier are movable relative to each other in the vertical direction, the storage container and the application device for applying the powdered aluminum alloy are movable in the horizontal direction, and the storage container is at least partially filled with the powdered aluminum alloy according to any one of claims 1 to 4.

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