HIGH-STRENGTH ALUMINIUM ALLOYS FOR STRUCTURAL APPLICATIONS, WHICH ARE PROCESSABLE BY ADDITIVE MANUFACTURING

Abstract

The present invention relates to pulverulent aluminium alloys having Cu, Zn or Si/Mg as the most relevant alloying element, the alloy further having a content of 1 to 15 wt. % of metals selected from the group M1 comprising Mo, Nb, Zr, Fe, Ti, Ta, V, and lanthanides. Such aluminium alloys can be used in additive manufacturing processes such as selective laser melting for the production of high-strength and hot-crack-free three-dimensional objects. The present invention further relates to methods and devices for producing three-dimensional objects from such aluminium alloys, methods for producing such pulverulent aluminium alloys, three-dimensional objects also produced from such pulverulent aluminium alloys, and specific aluminium alloys.

Claims

1. A pulverulent aluminum alloy comprising: Cu, Zn or Si/Mg as an alloying element; and a content of 1 to 15 wt. % of metals selected from the group M1 comprising Mo, Nb, Zr, Fe, Ti, Ta, V, and lanthanides.

2. A pulverulent aluminum alloy according to claim 1, wherein the content of metals selected from the group M1 is at least 1.3 wt. %.

3. A pulverulent aluminum alloy according to claim 1, wherein the aluminum alloy has a content of 4 to 6 wt. % Cu, 0.1 to 1.5 wt. % Mg and 0.1 to 1 wt. % Ag, and wherein the up to 99 wt. % missing portion of the alloy is aluminum.

4. A pulverulent aluminum alloy according to claim 3 with a content of at least 4.5 wt. % and/or at most 5.8 wt. %.

5. A pulverulent aluminum alloy according to claim 3, further comprising up to 0.2 wt % oxygen, up to 0.6 wt % silicon.

6. A pulverulent aluminum alloy according to claim 1, wherein the alloy has a mean particle size d50 in the range from 0.1 to 500 μm.

7. A pulverulent aluminum alloy according to claim 1, further comprising a content of metal borides, metal nitrides and metal carbides of less than 0.2 wt. %.

8. A method for producing a pulverulent aluminium alloy according to claim 1, further comprising atomizing the liquid alloy at a temperature greater than 850° C., or a step of mechanical alloying.

9. A method of producing a three-dimensional object, wherein the object is produced by applying a build-up material layer by layer and selectively solidifying the build-up material by the supply of radiation energy, at locations in each layer which are associated with the cross-section of the object in that layer, by scanning the locations with at least one radiation exposure area of an energy beam, or by introducing the build-up material in the radiation exposure area and melting it and applying it to a substrate, wherein the build-up material comprises a pulverulent aluminum alloy according to claim 1 or a corresponding wire-shaped aluminium alloy.

10. The method according to claim 9, further comprising preheating the pulverulent aluminum alloy to a temperature of at least 100° C.

11. The method according to claim 9, further comprising subjecting the produced three-dimensional object to a heat treatment at a temperature of 400° C. to 500° C., and/or for a period of 20 to 200 min.

12. A three-dimensional object produced using a pulverulent aluminum alloy produced by a method according to claim 8, and wherein the three-dimensional object comprises or consists of such an aluminum alloy.

13. The three-dimensional object according to claim 12, wherein a material of the three-dimensional object has a yield strength of at least 400 MPa and/or at most 550 MPa and/or a tensile strength of 450 MPa.

14. A manufacturing device comprising a laser sintering or laser melting device, a process chamber which is designed as an open container with a container wall, a support located in the process chamber, wherein the process chamber and the support are movable relative to one another in the vertical direction, a storage container and a coater which is movable in the horizontal direction, and wherein the storage container is at least partially filled with a pulverulent aluminum alloy according to claim 1.

15. An aluminum alloy having a content of 4 to 6 wt. % Cu, 0.1 to 1.5 wt. % Mg and 0.1 to 1 wt. % Ag, as well as 1.3 to 15 wt. % of metals selected from the group M1 comprising Mo, Nb, Zr, Fe, Ti, Ta, V, and lanthanides, wherein the up to 99 wt. % of the alloy is aluminum and the up to 100 wt. % missing part of the alloy is aluminum, manganese, silicon and oxygen.

Description

[0046] Other features and embodiments of the invention will be found in the description of an exemplary embodiment with the aid of the accompanying drawings.

[0047] FIG. 1 shows a schematic illustration, partially reproduced as a cross-section, of a device for the layer-by-layer build-up of a three-dimensional object according to one embodiment of the present invention.

[0048] The device shown in FIG. 1 is a laser sintering or laser melting device a1 known per se. For the build-up of an object a2 it contains a process chamber a3 with a chamber wall a4. In the process chamber a3, an upwardly open building container a5 with a wall a6 is arranged. A working plane a7 is defined by the upper opening of the building container a5, whereby the area of the working plane a7 lying within the opening, which can be used to build up the object a2, is referred to as the building area a8. In the container a5 a support a10 movable in a vertical direction V is arranged, to which a base plate all is attached, which closes the building container a5 at the bottom and thus forms its base. The base plate all can be a plate formed separately from the support a10 which is attached to the support a10, or it can be formed integrally with the support a10. Depending on the powder and process used, on the base plate all also a building platform a12 on which the object a2 is built may be attached. However, the object a2 can also be built on the base plate all itself, which then serves as a building platform. In FIG. 1, the object a2 to be formed in the building container a5 on the building platform a12 is shown below the working plane a7 in an intermediate state with several solidified layers surrounded by build-up material a13 that has remained unsolidified. The laser sintering device a1 further contains a storage container a14 for a build-up material a15 in powder form which can be solidified by electromagnetic radiation and a coater a16 which can be moved in a horizontal direction H for applying the build-up material a15 to the building area a8. The laser sintering device a1 further contains an exposure device a20 with a laser a21 which generates a laser beam a22 as an energy beam which is deflected via a deflection device a23 and focused onto the working plane a7 by a focusing device a24 via a coupling window a25 which is mounted on the upper side of the process chamber a3 in its wall a4.

[0049] Further, the laser sintering device a1 includes a control unit a29 via which the individual components of the device a1 are controlled in a coordinated manner to perform the building process. The control unit a29 may include a CPU whose operation is controlled by a computer program (software). The computer program may be stored separately from the device on a storage medium from which it can be loaded into the device, in particular into the control unit. In operation, to apply a powder layer, the support a10 is first lowered by a height corresponding to the desired layer thickness. By moving the coater a16 over the working plane a7, a layer of the pulverulent build-up material a15 is then applied. To be on the safe side, the coater a16 pushes a slightly larger amount of build-up material a15 in front of it than is required to build up the layer. The coater a16 pushes the planned excess of build-up material a15 into an overflow container a18. An overflow container a18 is arranged on each side of the building container a5. The application of the pulverulent build-up material a15 happens at least over the entire cross-section of the object a2 to be produced, preferably over the entire building area a8, i.e. the area of the working plane a7, which can be lowered by a vertical movement of the support a10. Subsequently, the cross-section of the object a2 to be produced is scanned by the laser beam a22 with a beam exposure area (not shown), which schematically represents an intersection of the energy beam with the working plane a7. By this the pulverulent build-up material a15 is solidified at points corresponding to the cross-section of the object a2 to be produced. These steps are repeated until the object a2 is completed and can be removed from the building container a5. For generating a preferably laminar process gas flow a34 in the process chamber a3, the laser sintering device a1 further comprises a gas supply channel a32, a gas inlet nozzle a30, a gas outlet opening a31 and a gas discharge channel a33. The process gas flow a34 moves horizontally across the building area a8. The gas supply and discharge may also be controlled by the control unit a29 (not shown). The gas extracted from the process chamber a3 can be fed to a filter device (not shown), and the filtered gas can be fed back to the process chamber a3 via the gas supply channel a32, whereby a recirculation system with a closed gas circuit is formed. Instead of only one gas inlet nozzle a30 and one gas outlet opening a31, several nozzles or openings can be provided in each case.

[0050] In the device according to the invention, the reservoir a14 is at least partially filled with a pulverulent aluminium alloy a15, as indicated above.

[0051] Finally, another aspect of the present invention relates to an aluminium alloy with a content of 4 to 6 wt. % Cu, 0.1 to 1.5 wt. % Mg and 0.1 to 1 wt. % Ag, as well as 1.3 to 15 wt. % of metals selected from the group M1 comprising Mo, Nb, Zr, Fe, Ti, Ta, V, and lanthanides, wherein preferably the up to 99 wt. % missing portion of the alloy is accounted for by aluminium and wherein further preferably the up to 100 wt. % missing portion of the alloy is accounted for by aluminium, manganese, silicon and oxygen.

[0052] The present invention is further illustrated by a number of examples which should not, however, be construed as in any way determining the scope of protection of the present application.

Example 1

[0053] Various aluminium alloys with the compositions given in table 1 were processed into test bodies by means of direct metal laser sintering (DMLS). The test bodies produced in this way were examined with regard to their hardness, yield strength at 23° C. and tensile strength. The results of these tests are also given in Table 1.

TABLE-US-00001 comparison comparison sample 1 sample 1 sample 2 (invention) composition Al remainder remainder remainder to 100% to 100% to 100% Cu 4.8 5.0 5.2 Ag 0.4 0.39 0.33 Mg 0.4 0.4 0.81 Zn 0.11 0.01 Si 0.13 0.07 0.09 Mn 0.4 0.4 0.48 O 0.046 0.019 0.14 Zr 0.13 1.8 Ti 0.24 1.0 rest <0.05 <0.05 <0.05 properties hardness.sup.1 80 HB 120-125 HB 130-145/170 HB.sup.2 yield strength ~250 MPa 480 MPa/510 MPa.sup.2 (Rp 0.2) tensile ~400 MPa 550 MPa/525 MPa.sup.2 strength (Rm) .sup.1= as prepared; .sup.2= after heat treatment.

[0054] To determine the hardness, the manufactured test body was subjected to the Brinell method according to the standard DIN EN ISO 6506-1:2015 “Metallic Werkstoffe—Härteprüfung nach Brinell—Teil 1: Prüfverfahren”. Density cube samples were used for the determination. The tests are performed three times for each sample and the measured values are given with an accuracy of 1 HBW.

[0055] The test body produced in comparison sample 1 showed massive hot cracks. In comparative sample 2, the hot cracks were considerably reduced compared to comparative sample 1, but still visible; a heat treatment of the test body did not lead to an improvement of the hardness of the material. The material according to the invention showed no hot cracks and considerably improved mechanical properties compared to the comparison samples already directly after production. By heat treatment (485° C./40 min and subsequent quenching with water and ageing at 25° C.) these properties could be improved considerably.

Example 2

[0056] A test body (-•-) made of the aluminium alloy according to example 1 was compared with corresponding test bodies made of other materials with regard to its yield strength properties. As comparative materials test bodies made of Scalmalloy (DMLS processed, -⋄-), aluminium alloy AW2618 (forged, T6, -□-), aluminium alloy 7075 (T6, -.box-tangle-solidup.-), aluminium alloy 2024 (T6, -x-) and Addmalloy (DMLS processed, -∘-) were used. The data of the comparison materials are taken from the literature or corresponding data sheets. The yield strengths of test specimens made of these materials are shown in FIG. 2.

[0057] From FIG. 2 it becomes apparent that the aluminium alloy according to the invention had the highest yield strength of all tested materials already at 23° C., whereas only Scalmalloy and the aluminium alloy 7075 had a yield strength in a similarly high range. Compared to the high temperature wrought alloy AW-2618A, the difference was about 27%. Above a temperature of about 100 to 120° C., the yield strength of the aluminium alloy 7075 drops sharply, that of Scalmalloy is even significantly lower at these temperatures. In contrast, the yield strength of the aluminium alloy of the invention decreases only slightly at these temperatures. At about 200° C., the aluminium alloy according to the invention has a yield strength that is about 42% better than the second-best alloy AW 2618A.