High strength aluminum alloy with optimized am processability through reactive element addition

Abstract

The invention relates to an aluminum alloy comprising: - about 1.00 % by weight to about 4.00 % by weight magnesium, - about 0.30 % by weight to about 1.20 % by weight of one or more alkaline earth metals other than magnesium, wherein about 0.30 % by weight to about 1.20 % by weight refers to the sum of the one or more alkaline earth metals other than magnesium, - about 0.05 % by weight to about 5.00 % by weight manganese, - about 0.30 % by weight to about 3.00 % by weight zirconium, and - aluminum and unavoidable impurities as the remainder.

Description

[0001] High strength aluminum alloy with optimized AM processability through reactive element addition

[0002] Description

[0003] The invention relates to an aluminum alloy comprising magnesium, manganese, zirconium, aluminum and one or more alkaline earth metals other than magnesium, and to a method for producing a three-dimensional object using said aluminum alloy. The invention further relates to a three-dimensional object obtained by the method. The invention further relates to a device for implementing the method and to a use of the aluminum alloy. The invention further relates to the use of one or more alkaline earth metals selected from strontium and calcium.

[0004] State of the art

[0005] Aluminum alloys, and in particular aluminum alloys providing high strength, are subject of intensive research in the manufacture of vehicles and aeroplanes as there is a continuous aim at improving the performance and efficiency. Such alloys can conventionally be processed by bulk forming processes, such as by extrusion, rolling, forging, stamping, or casting techniques, such as die casting, sand casting, investment casting (fine casting), gravity die casting and the like, to the desired objects.

[0006] For producing prototypes and in series production, additive manufacturing processes become more and more relevant. In general, "additive manufacturing processes", which are also termed "three-dimensional (3D) printing", are those manufacturing processes in which a manufacturing product or three-dimensional object is usually built based on digital 3D design data by depositing a build material of the component layer by layer.

[0007] For creating a three-dimensional object, material is selectively melted and resolidified, whereby this melting can typically be performed by irradiation with radiation energy, e.g. electromagnetic radiation, especially light and / or thermal radiation, but possibly also with particle radiation, e.g. electron radiation. A prominent example is Laser Powder Bed Fusion (LPBF), which is an additive manufacturing method that operates with irradiation, e.g. a laser beam. Here, thin layers of a usually powdered build material are applied one on top of the other repeatedly, wherein the build material in each layer is selectively melted by spatially limited irradiation of the points that, aftermanufacture, are intended to belong to the manufacturing product to be produced. The powder grains or particles of the build material can be partially or completely melted by the local introduction of energy by irradiation. After cooling, these selectively irradiated powder grains are then connected to one another in a solid body.

[0008] Different powders are known as build material, which can be adapted to the field of application of the finished three-dimensional object, e.g. different types of metal alloys. In some areas of application, three-dimensional objects are required that are lightweight and have high strength in combination with high ductility and elevated temperature performance. Materials that meet these requirements and are generally suitable for additive manufacturing are referred to as high-temperature precipitation strengthened metal alloys. This concerns for example applications like aerospace, defense, automotive or structural components. Existing high-temperature precipitation strengthened aluminum (Al) alloys used for additive manufacturing typically comprise magnesium (Mg). Magnesium serves as a solid solution strengthener in these alloys.

[0009] A disadvantage of known high-strength aluminum alloys can be their magnesium content, which can have negative impact on the processability of the aluminum alloy, especially during additive manufacturing processes. Magnesium has one of the highest equilibrium vapor pressures among common solutes in aluminum alloys, so it is prone to vaporization during manufacturing of a powder feedstock for additive manufacturing and during the additive manufacturing process. There are assumptions that significant amounts of the magnesium used in aluminum alloys can be lost due to vaporization regarding additive manufacturing processes and is therefore no longer available for the buildup of the three-dimensional object.

[0010] In many cases, a loss of magnesium from the aluminum alloy may be detrimental to the mechanical properties of the manufactured three-dimensional objects. By way of example, an unintended evaporation of magnesium is likely to reduce strength of the three-dimensional objectand / or can result in the formation of keyhole porosity.

[0011] Additionally, oxidized magnesium vapor or "smoke" can land in the build area of an additive manufacturing machine and become incorporated into the unprocessed build material, compromising the reusability and recyclability of the powdered build material.

[0012] A publication by Q. Tan et al. (Recent understanding of the oxidation and burning of magnesium alloys, Surface Innovations, Volume 7 Issue 2, May 2019, pp. 71-92, ISSN 2050-6252) reviews fundamentals of oxidation and burning of magnesium alloys and provides guidance on developing new oxidation-resistant magnesium alloys.Regarding aluminum alloys, a publication by L. Deillon et al. (A new high strength Al-Mg-Sc alloy for laser powder bed fusion with calcium addition to effectively prevent magnesium evaporation, Journal of Materials Processing Technology, Volume 300, 2022, 117416, ISSN 0924-0136c) states that a precise control of the Mg content in Al-Mg alloys is essential to obtain predictable mechanical properties but that the processing of Al-Mg alloys often suffers Mg losses due to Mg evaporation and oxidation. The publication presents a new high strength Al-Mg-Sc alloy designed for LPBF (laser powder bed fusion) processing, where Mg losses are effectively prevented. The increase in strength observed in the heat-treated condition is attributed to the additional precipitation of numerous finely dispersed Sc-rich precipitates.

[0013] In summary, existing high-strength aluminum alloys for additive manufacturing have non-optimized additive manufacturing processability due to their high Mg content. It is therefore an object of the present invention, to provide an aluminum alloy which has advantageous properties, in particular a high strength, and which can be well processed by an additive manufacturing process. It is an object of the present invention to provide an aluminum alloy, means and a method for producing a three-dimensional object using the aluminum alloy as well as the three-dimensional object, by which at least some of the aforementioned disadvantages can be reduced.

[0014] Description of the invention

[0015] At least one object is solved by an aluminum alloy according to claim 1, by a method according to claim 9, by a three-dimensional object according to claim 10, by a use according to claim 13 or 14 and by a device according to claim 15.

[0016] An aluminum alloy according to the invention comprises based on the total weight of the aluminum alloy

[0017] - about 1.00 % by weight to about 4.00 % by weight magnesium,

[0018] - about 0.30 % by weight to about 1.20 % by weight of one or more alkaline earth metals other than magnesium, wherein about 0.30 % by weight to about 1.20 % by weight refers to the sum of the one or more alkaline earth metals other than magnesium in the aluminum alloy,

[0019] - about 0.05 % by weight to about 5.00 % by weight manganese,

[0020] - about 0.30 % by weight to about 3.00 % by weight zirconium,

[0021] and

[0022] - aluminum and unavoidable impurities as the remainder.The invention provides an aluminum alloy which has advantageous properties, in particular a high strength and a high processability, e.g. during aluminum alloy powder production and additive manufacturing. The invention proposes a novel approach to replace some of the Mg in an aluminum alloy essentially consisting of aluminum, magnesium, manganese and zirconium with an element selected from one or more alkaline earth metals other than magnesium (e.g. Sr and / or Ca) in order to reduce Mg evaporation during additive manufacturing and aluminum alloy powder production. Without wishing to be bound to theory, it is believed that Sr and Ca are surface-active elements in aluminum (Al) and tend to migrate to the surface of liquid metal, thereby reducing surface energy. Without wishing to be bound to theory, it is further believed that this segregation alters the surface composition, thereby influencing the evaporation and oxidation behavior of the liquid metal. Without wishing to be bound to theory, it is further believed that the surface-active element effect can be used to enhance the ignition resistance of magnesium containing aluminum alloys by diminishing Mg vaporization, which is a precursor to Mg ignition. In other words, the additive manufacturing processability challenges with current high-strength Al alloys is resolved by replacing some Mg with a surface active alloying element, which is believed to reside at the surface of the melt and reduces Mg evaporation during processing, and which is believed to reduce Mg evaporation by means of reducing the Mg content. The specific selection of alloying elements and concentrations maintains the relevant material properties and processability. The proposed material enables high elongation values at relatively high tensile strength >390 MPa.

[0023] The aluminum alloy is in particular suitable for additive manufacturing processes (as build material). The aluminum alloy is preferably suitable for heat treatment, especially after consolidating a powdered aluminum alloy in an additive manufacturing process.

[0024] The aluminum alloy preferably provides a high-temperature precipitation strengthened aluminum alloy (HTPSA), especially after heat treatment of the aluminum alloy. In particular, a high-temperature precipitation strengthened aluminum alloy can be obtained by means of heat-treatment or heat aging of the aluminum alloy according to the invention.

[0025] Advantageously, the aluminum alloy according to the invention can also have an improved processability during additive manufacturing (abbreviated to AM) processes compared to other aluminum magnesium alloys, since some of the magnesium in the aluminum alloy is replaced with manganese. Advantageously, by providing a certain part of the solid solution strengthener in the form of manganese instead of magnesium the proportion of magnesium in the aluminum alloy can be reduced. The manganesecan serve as a solid solution strengthener replacing the subtracted magnesium.

[0026] Advantageously, manganese has a lower vapour pressure than magnesium and is therefore less likely to vaporize during additive manufacturing. Further advantageously, manganese turned out to be a suitable substitute for magnesium because, in the composition according to the invention, it should have no adverse effects on the quality of the finished component, wherein e.g. detrimental intermetallic phases can be avoided, and the solidification cracking susceptibility is not affected significantly. Further advantageously, manganese may have a higher solid solution strengthening effect in aluminum than magnesium, especially in the aluminum alloy according to the invention. Given its beneficial combination of solid solubility in aluminum, ability to be super-saturated in aluminum during rapid solidification, and slow diffusivity in aluminum, along with its high solid solution strengthening effect per addition, manganese contributes to provide a build material that can be processed as good as possible in additive manufacturing processes and enables high component quality, wherein the components have high strength and high ductility.

[0027] Advantageously, the addition of zirconium in the given range results in the formation of Ah(Zr) precipitates in the aluminum alloy that provide additional strengthening and have a good thermal stability. The AI3(Zr) precipitates in the aluminum alloy can act as nucleation sites for refined, equiaxed aluminum grains, which contribute to a reduction in hot cracking susceptibility, wherein hot cracking refers to the formation of shrinkage cracks during the solidification of the aluminum alloy in additive manufacturing processes. The addition of zirconium, especially the formation of Zr-based strengthening precipitates in the aluminum alloy, has the advantage, that zirconium is relatively cheap.

[0028] Advantageously the combination of manganese and zirconium as well as the other alloying elements in the composition described above provides an aluminum alloy with particularly improved AM processability (compared to known alloys) and high three-dimensional object quality while providing a particularly high strength and high ductility, especially after heat treatment. It can be assumed that the aluminum alloy also has thermal elevated temperature performance after heat treatment. As the aluminum alloy is also particularly light, it is suitable for additive manufacturing of components for aerospace, defence, automotive or structural components and the like. Advantageously, the aluminum alloy could also be used for heat exchanger applications or for semiconductor applications.

[0029] The alloy can comprise unavoidable impurities, e.g. due to contamination of one or more of the ingredients. Preferably, the amount of a respective impurity is less thanabout 0.10 % by weight, preferably less than about 0.05 % by weight, further preferably less than about 0.02 % by weight, each based on the total weight of the alloy. The total amount of unavoidable impurities in the aluminum alloy can be less than about 0.25 % by weight, preferably less than about 0.15 % by weight, each based on the total weight of the alloy.

[0030] The quantities mentioned here and in other parts of the application refer to the total quantity respectively the total weight of the aluminum alloy, unless otherwise stated.

[0031] Detailed description

[0032] The aluminum alloy does not comprise any intentionally added zinc (Zn). This means that no zinc is added to the aluminum alloy on purpose during manufacture and / or processing of the aluminum alloy. However, the aluminum alloy might comprise metallic or metalloid impurities to a certain extent. Impurity in this context refers to a metallic or metalloid element that does not affect the other intended strengthening mechanisms or significantly degrade the material properties of the aluminum alloy. Accordingly, the aluminum alloy might comprise zinc only as an impurity or in form of a contamination, e.g. due to a contamination of other ingredients of the aluminum alloy.

[0033] In particular, the aluminum alloy is essentially free of zinc. This means that zinc, especially zinc impurities, can be present in the aluminum alloy in an amount that is less than about 0.10 % by weight based on the total weight of the provided aluminum alloy. Preferably, zinc is present in less than about 0.05 % by weight, preferably less than about 0.04 % by weight, further preferably less than about 0.03 % by weight, each based on the total weight of the provided aluminum alloy. The amount of zinc in the alloy can be less than about 0.02 % by weight, less than about 0.01 % by weight, less than about 0.005 % by weight or less than about 0.001 % by weight, each based on the total weight of the provided aluminum alloy.

[0034] Another advantage of the aluminum alloy according to the invention is that the risk of fire associated with vaporized and condensed magnesium particles can be reduced in filter systems of additive manufacturing machines. Fine magnesium particles combined with fine zinc particles are known to have caused temperature rise in atomization plant filters creating a risk of fire in filters of additive manufacturing machines. By not intentionally adding zinc and by substituting some of the magnesium with other elements such as Sr or Ca the risks associated with the vaporization and reactivity ofmagnesium and zinc can be reduced, wherein the operational safety of additive manufacturing machines can be increased.

[0035] Preferably, the aluminum alloy does not comprise any intentionally added scandium (Sc). Accordingly, the alloy might comprise scandium only as an impurity or in form of a contamination, e.g. due to impurities of other ingredients of the aluminum alloy.

[0036] The aluminum alloy may be essentially free of scandium. This means that scandium, especially scandium impurities, can be present in the aluminum alloy in an amount that is less than about 0.10 % by weight based on the total weight of the provided aluminum alloy. Preferred, scandium is present in less than about 0.05 % by weight, preferably less than about 0.04 % by weight, further preferably less than about 0.03 % by weight, each based on the total weight of the alloy. The amount of scandium in the alloy can be less than about 0.02 % by weight scandium, less than about 0.01 % by weight scandium, less than about 0.005 % by weight scandium or less than about 0.001 % by weight scandium, each based on the total weight of the aluminum alloy.

[0037] Preferably, the aluminum alloy essentially consists of aluminum, magnesium, manganese, zirconium and one or more alkaline earth metals other than magnesium. More preferably, the aluminum alloy essentially consists of aluminum, magnesium, manganese, zirconium and one element selected from strontium and calcium.

[0038] In a preferred embodiment, the aluminum alloy comprises at least about 1.00 % by weight zirconium based on the total weight of the aluminum alloy. Preferably, the aluminum alloy comprises at least about 1.20 % by weight zirconium based on the total weight of the aluminum alloy. In a preferred embodiment, the aluminum alloy comprises at most about 2.00 % by weight zirconium based on the total weight of the aluminum alloy. Preferably, the aluminum alloy comprises at most about 1.50 % by weight zirconium based on the total weight of the aluminum alloy.

[0039] Advantageously, the addition of zirconium in the given range results in the formation of Ah(Zr) precipitates in the aluminum alloy that provide additional strengthening and have a good thermal stability. The AI3(Zr) precipitates in the aluminum alloy can act as nucleation sites for refined, equiaxed aluminum grains, which contribute to a reduction in hot cracking susceptibility, wherein hot cracking refers to the formation of shrinkage cracks during the solidification of the aluminum alloy in additive manufacturing processes. The addition of zirconium, especially the formation of Zr-based strengthening precipitates in the aluminum alloy, has the advantage, that zirconium is relatively cheap.Preferably, the aluminum alloy comprises at least about 1.50 % by weight magnesium based on the total weight of the aluminum alloy. More preferably, the aluminum alloy comprises at least about 2.75 % by weight magnesium based on the total weight of the aluminum alloy. Preferably, the aluminum alloy comprises at most about 3.75 % by weight magnesium, more preferably at most about 3.55 % by weight magnesium, each based on the total weight of the aluminum alloy.

[0040] Preferably, the aluminum alloy comprises at least about 0.25 % by weight manganese based on the total weight of the aluminum alloy. Preferably, the aluminum alloy comprises at most about 0.50 % by weight manganese based on the total weight of the aluminum alloy.

[0041] Advantageously, by using a proportion of manganese in the aluminum alloy in combination with other alloying elements, with correspondingly less magnesium being used, the AM processability of the aluminum alloy can be improved particularly effectively (compared to known alloys). As mentioned already, the added manganese can serve as a solid solution strengthener replacing the subtracted magnesium.

[0042] Advantageously, Manganese has a lower vapour pressure than magnesium and is therefore less likely to vaporize during additive manufacturing. Further advantageously, manganese turned out to be a suitable substitute for magnesium because, in the composition described above, it should have no adverse effects on the quality of the finished component, wherein e.g. detrimental intermetallic phases can be avoided, and the solidification cracking susceptibility is not affected significantly. As mentioned already, manganese advantageously may have a higher solid solution strengthening effect in aluminum than magnesium, especially in the aluminum alloy according to the invention. Advantageously, by replacing a certain proportion of magnesium with manganese, a strengthening effect can be achieved. It was found that given its beneficial combination of solid solubility in aluminum, ability to be supersaturated in solution during rapid solidification, and slow diffusivity in aluminum, along with its high solid solution strengthening effect per addition, manganese is an optimal replacement for magnesium in aluminum alloys, especially in HTPSA, to provide a build material that can be processed as good as possible in additive manufacturing processes and enables high component quality, wherein the components have high strength and high ductility.

[0043] Preferably, based on the total weight of the aluminum alloy, the aluminum alloy comprises at least about 0.45 % by weight of one or more alkaline earth metals other than magnesium, wherein at least about 0.45 % by weight refers to the sum of the one or more alkaline earth metals other than magnesium in the aluminum alloy.Preferably, based on the total weight of the aluminum alloy, the aluminum alloy comprises at most about 0.80 % by weight of one or more alkaline earth metals other than magnesium, wherein at most about 0.80 % by weight refers to the sum of the one or more alkaline earth metals other than magnesium in the aluminum alloy.

[0044] Preferably, the one or more alkaline earth metals other than magnesium are selected from strontium and calcium, wherein strontium is preferred in some embodiments.

[0045] In a preferred embodiment, the one or more alkaline earth metals other than magnesium comprises strontium or is strontium.

[0046] In some embodiments, strontium is preferred as the one or more alkaline earth metals other than magnesium, because it does not affect the solidification range of the aluminum alloy. In contrast, e.g. calcium slightly broadens this range. This is described in the example and can be seen in Figure 2. A wider solidification range is generally undesirable for AM processability, as it heightens the propensity for solidification cracking.

[0047] Furthermore, both Sr and Ca are expected to form precipitates at elevated temperatures during rapid solidification. Given that the AI4Sr precipitate forms at about 625 °C out of the melt, whereas Ca precipitates form at about 575 °C, AI4Sr is more likely to contribute to grain refinement by acting as a nucleator for a-AI grains that form in high phase fraction at about 600 °C. Precipitates with high melting points can enhance the strength of the alloy at elevated operating temperatures.

[0048] In another preferred embodiment, the one or more alkaline earth metals other than magnesium comprises calcium or is calcium.

[0049] The aluminum alloy can be in the form of a rod, a wire, a ribbon, a foil, a component, a powder or chips etc.

[0050] In a preferred embodiment, the aluminum alloy is an aluminum alloy powder. The aluminum alloy powder preferably has a powder size distribution (particle diameter) from about 15 pm to about 110 pm (measured per ISO 13322-2, e.g. ISO 13322-2:2021-12). For example, the alloy powder can have a particle size distribution of dlO of at least 25 pm and / or of at most 35 pm and of d50 of at least 35 pm and / or of at most 45 pm and of d90 of at least 50 pm and / or of at most 60 pm. The average diameter of the particles d50 indicates that 50 % of the powder particles or powder grains are below the particle diameter mentioned. Particle sizes can be measured perISO 13322-2, e.g. using a measuring instrument of the Camsizer XT (Retsch Technology, Germany) type.

[0051] The aluminum alloy can be a spherical aluminum alloy powder or a non-spherical aluminum alloy powder or a mixture thereof. The aluminum alloy powder, especially the powder particles, can have a sphericity of at least approximately 0.7, or of at least approximately 0.8, or of at least approximately 0.9, or of at least approximately 0.95, or of approximately 1. The sphericity can, for example, be determined with the aid of microscopy (in accordance with DIN ISO 13322-1) and / or a measuring instrument of the Camsizer XT (Retsch Technology, Germany) type (in accordance with DIN ISO 13322-2).

[0052] The production method of producing an aluminum alloy according to the invention comprises at least one of the following steps. In one step about 1.00 % by weight to about 4.00 % by weight magnesium, about 0.30 % by weight to about 1.20 % by weight of one or more alkaline earth metals other than magnesium, wherein about 0.30 % by weight to about 1.20 % by weight refers to the sum of the one or more alkaline earth metals other than magnesium, about 0.05 % by weight to about 5.00 % by weight manganese, about 0.30 % by weight to about 3.00 % by weight zirconium (each based on the total weight of the aluminum alloy to be produced) and aluminum as the remainder are provided, especially as powder in each case. The materials can be provided separately from each other.

[0053] In one step the provided amounts of magnesium, one or more alkaline earth metals other than magnesium, manganese, zirconium and aluminum are brought together, e.g. alloyed with each other.

[0054] In one step the aluminum alloy is produced, preferably by means of a rapid solidification process. The rapid solidification process can be selected from a group consisting of atomization, spray deposition, melt spinning, melt extraction and beam glazing. In principle, another technique can be used to produce the aluminum alloy.

[0055] In a preferred embodiment, the production method can be performed to provide a powder made of the aluminum alloy, especially to provide a powder available from the aluminum alloy.

[0056] Thus, a further aspect of the present invention concerns a process for the preparation of an aluminum alloy powder of the invention, wherein a molten aluminum alloy of the invention is atomized in an appropriate device or is prepared by dry alloying elementalmetal powders or precursor powders having several elements in them. Also, one or all of the components of the aluminum alloy can be produced by grinding into particles from a solid precursor or by rapid solidification methods such as melt spinning.

[0057] As described above, the novel approach to replace some of the Mg in an aluminum alloy essentially consisting of aluminum, magnesium, manganese and zirconium with a reactive, surface active element selected from one or more alkaline earth metals other than magnesium (e.g. Sr or Ca) reduces Mg evaporation during aluminum alloy powder production, thereby improving quality of the process and product.

[0058] Thus, one aspect of the invention is directed to the use of one or more alkaline earth metals selected from strontium and calcium, preferably strontium, for facilitating the manufacture of an aluminum alloy powder from an aluminum alloy, wherein the aluminum alloy contains aluminum and magnesium, preferably wherein the alloy contains or essentially consists of aluminum, magnesium, manganese and zirconium (as well as strontium and / or calcium).

[0059] A further aspect of the invention is directed to the use of one or more alkaline earth metals selected from strontium and calcium, preferably strontium, for improving the processability by additive manufacturing of an alloy containing aluminum and magnesium, preferably of an alloy containing or essentially consisting of aluminum, magnesium, manganese and zirconium (as well as strontium and / or calcium).

[0060] In a further aspect, the present invention concerns a method for the manufacture of a three-dimensional object, wherein an aluminum alloy according to the invention is provided, preferably in the form of a powder, and the object is prepared by applying the aluminum alloy layer on layer and selectively solidifying (consolidating) the aluminum alloy (powder), in particular by application of electromagnetic radiation or electron beam radiation, at positions in each layer, which correspond to the cross section of the object in this layer, wherein the positions are scanned with an interaction zone, in particular with a radiation interaction zone of an energy beam bundle. Preferably, in this process the aluminum alloy is an aluminum alloy in powder form as defined above.

[0061] The process of the invention can be conducted as a selective laser sintering (SLS) or selective laser melting (SLM) process, which is also sometimes designated as direct metal laser sintering (DMLS) or laser powder bed fusion (LPBF).Alternatively, the process could be conducted such, that the solidification of the powder mixture in the areas, where the three-dimensional object is to be created, is accomplished by application of a binding agent onto the powder, which may optionally be cured, e.g. by application of electromagnetic radiation, to provide a consolidated powder structure (also in some cases designated as "green object"). This object can then be converted to the final three-dimensional object by a sintering process, where the binding agent is degraded and thus removed from the object, while the powder particles form a consolidated dense object. Such process is commercialised e.g. by HP as "Multi jet fusion".

[0062] Irrespective of which of the above indicated processes is used, the application or application layer on layer is preferably carried out in a layer thickness suitable for processing by means of additive manufacturing, for example with a layer thickness in the range from 20 pm to 60 pm, preferably with a thickness of at least 25 pm and / or at most 50 pm and more preferably at a thickness of at least 30 pm and / or at most 40 pm.

[0063] The process according to the invention can also be conducted in a manner that the building material is introduced into the radiation exposure area of an energy source, e.g. a laser, and is melted and applied to a substrate. In such a method, which is also referred to as laser cladding in the mode of powder deposition welding, a powder is sprayed in the form of points onto a substrate via one or more nozzles, and at the same time a laser is aimed at the application point of the laser. The substrate is melted by the radiation energy and the applied alloy powder is melted so that the applied alloy can bond with the melted substrate. In this way, a layer of the particulate material is applied to the workpiece and bonded to a surface layer of the workpiece. A larger workpiece can be produced by sequential "jetting" of melt layers made of particulate material.

[0064] Alternatively, a laser coating process can also be carried out in the mode of wire buildup welding, where a wire is used instead of a powder. Correspondingly, the method according to the invention also comprises an embodiment in which a wire made of an aluminum alloy, as indicated above, is used.

[0065] The aluminum alloy of the invention can be heat treated to generate a high-temperature precipitation strengthened aluminum alloy (HSPTA). The heat treatment or heat aging of the alloy can be an optional step in the method for producing the three-dimensional object. In principle, heat treatment of the alloy can also be carried out independently of the production of the three-dimensional object.Preferably, the heat treatment can be performed at a later time after completion of the three-dimensional object, i.e. heat treatment is not carried out on the feedstock. Preferably, the heat treatment is performed after the three-dimensional object is completely manufactured. In particular, the heat treatment can be performed after the additive manufacturing process being completed. This means that the precipitation hardening can be performed on the additively manufactured three-dimensional object that is made of the alloy. Preferably, the three-dimensional object comprising the alloy has a thermally stable microstructure that remains unchanged by exposure to elevated temperatures for extended times (elevated temperature performance), especially after heat treatment of the three-dimensional object.

[0066] The heat-treatment of the completed three-dimensional object comprising the alloy, especially to achieve precipitation and dispersion hardening, can be performed at a temperature of about 350 °C to about 450 °C. The heat-treatment can be performed for a period of about 1 hour to about 6 hours, preferably to about 7 hours, and especially air quenched. Preferably the heat-treatment can be performed for a period of at least about 5 hours and / or at most about 7 hours especially air quenched. In particular, the heat-treatment can take between about 5 hours and about 7 hours especially air quenched. Preferably heat-treatment is performed under an inert gas atmosphere. Advantageous, thermally stable AI3(Zr) precipitates that act as precipitation strengtheners can be formed in the alloy due to heat treatment.

[0067] A preferred three-dimensional object, especially an additively manufactured object, is obtainable by heat treatment of the three-dimensional object comprising the aluminum alloy. The heat treatment of the three-dimensional object can be performed as described above, especially after the three-dimensional object is manufactured completely. The heat treatment of the alloy as part of the three-dimensional object provides a three-dimensional object that comprises, preferably consists of, a high-temperature precipitation strengthened aluminum alloy (HSPTA).

[0068] For the sake of completeness, it is pointed out that heat treatment could also be performed on the alloy per se, i.e. independently of an AM process or an additively manufactured three-dimensional object. This means that the alloy itself can be heat treated as described above for precipitation hardening of the alloy.

[0069] To adjust the final properties, the process may further comprise any conventional post processing steps (i.e. steps after the preparation of the three-dimensional object), such as e.g. machining and / or painting and / or coating.In a yet further aspect, the present invention concerns a three-dimensional object prepared using an aluminum alloy according to the invention and / or a method according to the invention. Preferably, the aluminum alloy is an aluminum alloy in powder form as defined above. Preferably, the three-dimensional object comprises or consists of the aluminum alloy of the invention. In a preferred embodiment, the particular three-dimensional object is prepared according to the process as described above. Alternatively, the three-dimensional object can also be prepared by isostatic pressing, pressing and sintering or by melting and casting.

[0070] As has been noted above, the aluminum alloy of the invention comprises based on the total weight of the aluminum alloy

[0071] - about 1.00 % by weight to about 4.00 % by weight magnesium,

[0072] - about 0.30 % by weight to about 1.20 % by weight of one or more alkaline earth metals other than magnesium, wherein about 0.30 % by weight to about 1.20 % by weight refers to the sum of the one or more alkaline earth metals other than magnesium in the aluminum alloy,

[0073] - about 0.05 % by weight to about 5.00 % by weight manganese,

[0074] - about 0.30 % by weight to about 3.00 % by weight zirconium,

[0075] and

[0076] - aluminum and unavoidable impurities as the remainder. Accordingly, also for the three-dimensional object it is preferred that it comprises based on the total weight of the aluminum alloy

[0077] - about 1.00 % by weight to about 4.00 % by weight magnesium,

[0078] - about 0.30 % by weight to about 1.20 % by weight of one or more alkaline earth metals other than magnesium, wherein about 0.30 % by weight to about 1.20 % by weight refers to the sum of the one or more alkaline earth metals other than magnesium in the aluminum alloy,

[0079] - about 0.05 % by weight to about 5.00 % by weight manganese,

[0080] - about 0.30 % by weight to about 3.00 % by weight zirconium,

[0081] and

[0082] - aluminum and unavoidable impurities as the remainder.

[0083] The three-dimensional object may have a relative density of 95% or more, 98% or more, 99% or more and 99.5% or more, wherein the relative density is defined as the ratio of the measured density and the theoretical density. The theoretical density is the density of the bulk material (i.e. the cast aluminum alloy). The measured density is the density of the three-dimensional object as determined by the Archimedes Principle according to ISO 3369:2006.A further means to distinguish three-dimensional objects prepared via additive manufacture from conventionally prepared objects is the grain size, which results from only very small areas being melted on activation by the radiation source and being rapidly cooled afterwards. Thus, in a preferred embodiment the inventive three-dimensional objects have grain sizes as conventionally provided by selective laser sintering or selective laser melting. In this case, the processing of the three-dimensional object by an additive manufacturing process is determined form different magnifications of cross section images from etched surfaces, where the melt pool structure and dividing lines between melt pools can be detected. In this case, magnifications of about 50x or lOOx produce tightly cropped images of detail level, from which the trained eye can easily distinguish between a cast microstructure and a microstructure as obtained by additive manufacture.

[0084] Preferably, the aluminum alloy according to the invention and / or the three-dimensional object according to the invention has a tensile strength after heat treatment (e.g. heat treatment as described above) greater than 300 MPa, preferably greater than 350 MPa, further preferably greater than 390 MPa. The tensile strength after heat treatment can be up to 450 MPa.

[0085] Preferably, the aluminum alloy according to the invention and / or the three-dimensional object according to the invention has an elongation of break after heat treatment (e.g. heat treatment as described above) of more than 10 %, preferably more than 12.5 %, further preferably more than 15 %. The elongation of break after heat treatment can be up to 20 MPa.

[0086] The tensile strength and the elongation of break here is determined according to DIN EN ISO 6892-1:2020-06. The tensile strength and elongation at break can also be determined with the aid of the so-called tensile test according to ASTM E8 / E8M and is known to the person skilled in the art.

[0087] In a yet further aspect the present invention concerns a device for implementing the method of the invention for the manufacture of a three-dimensional object, wherein the device comprises an irradiation unit emitting electromagnetic or particle irradiation, preferably a laser sintering or laser melting device, a process chamber having an open container with a container wall, a support, which is inside the process chamber, wherein open container and support are moveable against each other in vertical direction, a storage container and a recoater, which is moveable in horizontal direction, and wherein the storage container is at least partially filled with the aluminum alloy of the invention, preferably in powder form as defined above. Inconnection with this device, it is noted that the device is only claimed in as much as it comprises aluminum alloy of the invention, so that effectively the combination of the device and the aluminum alloy of the invention is claimed as a kit.

[0088] Other features and embodiments of the invention are provided in the following description of an exemplary embodiment of the invention taking account of the appended Figure 1.

[0089] The device represented in Figure 1 is a laser sintering or laser melting apparatus 1 for the manufacture of a three-dimensional object 2. The apparatus 1 contains a process chamber 3 having a chamber wall 4. A container 5 being open at the top and having a container wall 6 is arranged in the process chamber 3. The opening at the top of the container 5 defines a working plane 7. The portion of the working plane 7 lying within the opening of the container 5, which can be used for building up the object 2, is referred to as building area 8. Arranged in the container 5, there is a support 10, which can be moved in a vertical direction V, and on which a base plate 11 which closes the container 5 toward the bottom and therefore forms the base of the container 5 is attached. The base plate 11 may be a plate which is formed separately from the support 10 and is fastened on the support 10, or may be formed so as to be integral with the support 10. A building platform 12 on which the object 2 is built may also be attached to the base plate 11. However, the object 2 may also be built on the base plate 11, which then itself serves as the building platform.

[0090] In Figure 1, the object 2 to be manufactured is shown in an intermediate state. It consists of a plurality of solidified layers and is surrounded by building material 13 which remains unsolidified. The apparatus 1 furthermore contains a storage container 14 for building material 15 in powder form, which can be solidified by electromagnetic radiation, for example a laser, and / or particle radiation, for example an electron beam. The apparatus 1 also comprises a recoater 16, which is movable in a horizontal direction H, for applying layers of building material 15 within the building area 8.

[0091] Optionally, a radiation heater 17 for heating the applied building material 15, e.g. an infrared heater, may be arranged in the process chamber, but for processing of the inventive aluminum alloy this is not necessary.

[0092] The device in Figure 1 furthermore contains an irradiation unit 20 having a laser 21, which generates a laser beam 22 that is deflected by means of a deflecting device 23 and focused onto the working plane 7 by means of a focusing device 24 via an entrance window 25, which is arranged at the top side of the process chamber 3 in the chamber wall 4.The device in Figure 1 furthermore contains a control unit 29, by means of which the individual component parts of the apparatus 1 are controlled in a coordinated manner for carrying out a method for the manufacture of a three-dimensional object. The control unit 29 may contain a CPU, the operation of which is controlled by a computer program (software). During operation of the apparatus 1, the following steps are repeatedly carried out: For each layer, the support 10 is lowered by a height which preferably corresponds to the desired thickness of the layer of the building material 15. The recoater 16 is moved to the storage container 14, from which it receives an amount of building material 15 that is sufficient for the application of at least one layer. The recoater 16 is then moved over the building area 8 and applies a thin layer of the building material 15 in powder form on the base plate 11 or on the building platform 12 or on a previously applied layer. The layer is applied at least across the cross-section of the object 2, preferably across the entire building area 8. The crosssection of the object 2 to be manufactured is then scanned by the laser beam 22 in order to selectively solidify this area of the applied layer. These steps are carried out until the object 2 is completed. The object 2 can then be removed from the container 5.

[0093] According to the invention, an aluminum alloy, preferably a powder, as described above is used as building material 15.

[0094] In the following, the present invention is further illustrated by means of an example, which however should not be construed as limiting the invention thereto in any manner.

[0095] Example

[0096] A high-strength, high-processability aluminum alloy was developed for additive manufacturing.

[0097] For example, spherical powders having powder size distribution 15 pm - 110 pm measured per ISO 13322-2 were prepared with the following composition specifications:

[0098]

[0099] It was found that strontium does not affect the solidification range of the aluminum alloy. In contrast, e.g. calcium slightly broadens this range. This can be seen in Figure 2. A wider solidification range is generally undesirable for AM processability, as it heightens the propensity for solidification cracking. Example 1 ("Ex. 1") in Figure 2 is an aluminum alloy according to the invention containing 0.6 % by weight strontium. Example 2 in Figure 2 is an aluminum alloy according to the invention containing 0.6 % by weight calcium. The reference aluminum alloy ("Ref. 1") contains the same elements in the same amounts as Examples 1-2 with the exception that it does not comprise Sr and Ca but contains more Mg instead.

[0100] From conducted solidification calculations on aluminum alloys of the invention, it can be concluded that both Sr and Ca form precipitates at elevated temperatures during rapid solidification. Given that the AI4Sr precipitate forms at about 625 °C out of the melt, whereas Ca precipitates form at about 575 °C, AI4Sr is more likely to contribute to grain refinement by acting as a nucleator for o-AI grains that form in high phase fraction at about 600 °C. Precipitates with high melting points can enhance the strength of the alloy at elevated operating temperatures.

Claims

Claims1. An aluminum alloy comprising:- about 1.00 % by weight to about 4.00 % by weight magnesium,- about 0.30 % by weight to about 1.20 % by weight of one or more alkaline earth metals other than magnesium, wherein about 0.30 % by weight to about 1.20 % by weight refers to the sum of the one or more alkaline earth metals other than magnesium,- about 0.05 % by weight to about 5.00 % by weight manganese,- about 0.30 % by weight to about 3.00 % by weight zirconium,and- aluminum and unavoidable impurities as the remainder.

2. The aluminum alloy according to claim 1, wherein the aluminum alloy comprises at least about 1.00 % by weight zirconium.

3. The aluminum alloy according to claim 1 or 2, wherein the aluminum alloy comprises about 1.20 % by weight to about 1.50 % by weight zirconium.

4. The aluminum alloy according to any of the preceding claims, wherein the one or more alkaline earth metals other than magnesium are selected from strontium and calcium.

5. The aluminum alloy according to any of the preceding claims, wherein the one or more alkaline earth metals other than magnesium is strontium.

6. The aluminum alloy according to any of the preceding claims 1 to 4, wherein the one or more alkaline earth metals other than magnesium is calcium.

7. The aluminum alloy according to any of the preceding claims, wherein the aluminum alloy is an aluminum alloy powder.

8. The aluminum alloy according to the preceding claim, wherein the aluminum alloy powder has a powder size distribution from about 15 pm to about 110 pm.

9. Method for the manufacture of a three-dimensional object, comprising providing an aluminum alloy as defined in any one of claims 1 to 8, preferably in the form of a powder, and preparing the object by applying the aluminum alloy layer on layer and selectively solidifying the aluminum alloy, in particular by application ofelectromagnetic radiation or electron beam radiation, at positions in each layer, which correspond to the cross section of the object in this layer, wherein the positions are scanned with an interaction zone, in particular with a radiation interaction zone of an energy beam bundle.

10. A three-dimensional object, wherein the three-dimensional object is obtained by a method according to claim 9.

11. The aluminum alloy according to any of claims 1-8 or the three-dimensional object according to claim 10 having a tensile strength after heat treatment greater than 300 MPa, preferably greater than 350 MPa, further preferably greater than 390 MPa.

12. The aluminum alloy according to any of the preceding claims or the three-dimensional object according to any of the preceding claims having an elongation of break after heat treatment of more than 10 %, preferably more than 12.5 %, further preferably more than 15 %.

13. A use of an aluminum alloy according to any of the preceding claims in an additive manufacturing process, preferably in a laser powder bed fusion process, more preferably in a method of claim 9.

14. A use of one or more alkaline earth metals selected from strontium and calcium, preferably strontium, fori) improving the processability by additive manufacturing of an alloy containing aluminum and magnesium, preferably of an alloy containing or essentially consisting of aluminum, magnesium, manganese and zirconium and / orii) facilitating the manufacture of an aluminum alloy powder from an aluminum alloy, the aluminum alloy containing aluminum and magnesium, preferably containing or essentially consisting of aluminum, magnesium, manganese and zirconium.

15. A device for implementing a method according to claim 9, wherein the device comprises an irradiation unit emitting electromagnetic or particle irradiation, preferably a laser sintering or laser melting device, a process chamber having an open container with a container wall, a support, which is inside the process chamber, wherein open container and support are moveable against each other in vertical direction, a storage container and a recoater, which is moveable in horizontal direction, and wherein the storage container is at least partially filled with an aluminum alloy as defined in any one of claims 1 to 8, preferably in the form of a powder.

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