Additive manufacturing method for aluminum alloys and lightweight components

Abstract

The present invention relates to an aluminum (Al) alloy, comprising 0.1% to 15% by weight of titanium (Ti), 0.1% to 3.0% by weight of scandium (Sc), 0.1% to 3.0% by weight of zirconium (Zr), 0.1% to 3.0% by weight of manganese (Mn), the balance being aluminum (Al) and unavoidable impurities totaling less than 0.5% by weight. The aluminum (Al) alloy is used in additive manufacturing processes to produce high-strength, high-ductility, lightweight components for aircraft. The aluminum (Al) alloy is initially produced as a powder and remelted during the manufacturing process to achieve the desired characteristics.

Description

Technical Field

[0001] The present invention relates to an aluminum alloy, a method for additive manufacturing lightweight members using powders of this aluminum alloy, and lightweight members manufactured by this method.

[0002] Aluminum alloys are important materials for manufacturing lightweight members for aircraft. Incorporating these lightweight members into an aircraft results in a reduction in the total weight of the aircraft, which enables a reduction in fuel costs. Aluminum alloys used for this purpose need to have high tensile strength, ductility, toughness, and corrosion resistance from the perspective of flight safety.

Background Art

[0003] Examples of aluminum alloys that can be used in aircraft manufacturing are those called AA2024, AA7349, and AA6061. In addition to the base metal, aluminum, magnesium, and copper are included as essential alloy partners, and manganese, zirconium, chromium, iron, silicon, titanium, and / or zinc are also included either essentially or optionally.

[0004] An important further development is shown by scandium-containing aluminum alloys, which are commercially available, for example, under the product name Scalmalloy® from APWorks GmbH. This alloy has higher strength, ductility, and corrosion resistance than the above alloys. Among all transition metals, scandium shows the greatest increase in strength due to precipitation hardening by the precipitation of Al3Sc. Due to the low solubility of scandium in aluminum (about 0.3 wt% at about 660 °C), Scalmalloy® needs to be manufactured by precipitation hardening involving rapid solidification of the melt, such as melt spinning, followed by the formation of secondary Al3Sc precipitates in the aluminum matrix.

[0005] For more information on Scalmalloy®, see the publication "Scalmalloy® - A Unique, High-Strength, Corrosion-Resistant AlMgScZr Material Concept" ("Scalmalloy R See also "A unique high strength and corrosion insensitive AlMgScZr material concept" (AJ Bosch, R. Senden, W. Entelmann, M. Knuewer, F. Palm, "Proceedings of the 11th International Conference on Aluminum Alloys in: "Aluminum Alloys: Their physical and mechanical properties", J. Hirsch, G. Gottstein, B. Skrotzki, Wiley-VCH)) and "Metallurgical peculiarities in hyper-eutectic AlSc and AlMgSc engineering materials prepared by rapid solidification processing" (F. Palm, P. Vermeer, W. von Bestenbostel, D. Isheim, R. Schneider (cited above))).

[0006] Table 1, shown in Figure 1 of the unpublished German patent application 10 2020 131 823.5, lists the chemical compositions of the above aluminum alloys that can be used in the manufacture of lightweight components for aircraft.

[0007] Another advantage of Scalmalloy® is its suitability for additive manufacturing of lightweight components. In addition to processes such as wire arc additive manufacturing (WAAM), it is particularly well-suited for laser powder bed fusion. This additive manufacturing process is also referred to below as the L-PBF process (L-PBF = "Laser Powder Bed Fusion"). The number of alloys that can be used in this process is limited. According to WO2018 / 144323, reliable additive manufacturing is possible with the L-PBF process using alloys such as Scalmalloy®, AlSi10Mg, TiAl6V4, CoCr, and Inconel 718, but the majority of the more than 5,500 alloys currently in use cannot be used in the L-PBF process or 3D printing.

[0008] See the unpublished German patent application No. 10 2020 131 823.5, and incorporate its disclosures herein by reference. [Overview of the project] [Problems that the invention aims to solve]

[0009] The objective of the present invention is to provide an improved aluminum alloy suitable for additive manufacturing, such as laser powder bed fusion (L-PBF process). [Means for solving the problem]

[0010] This objective is achieved by the subject matter of the independent claim. A preferred embodiment is the subject matter of the dependent claim.

[0011] This invention provides an aluminum (Al) alloy comprising the following: Titanium (Ti) in a proportion of 0.1% to 15% by weight, Scandium (Sc) in a proportion of 0.1% to 3.0% by weight, Zirconium (Zr) in a proportion of 0.1% to 3.0% by weight, Manganese (Mn) in a proportion of 0.1% to 3.0% by weight, The remainder consists of aluminum (Al) and, Inevitable impurities totaling less than 0.5% by weight.

[0012] The aluminum (Al) alloy optionally contains at least one first additional alloying element selected from the group consisting of tantalum (Ta), hafnium (Hf), yttrium (Y), and erbium (Er). Here, the individual proportion of each first additional alloying element does not exceed 2.0% by weight, and the total proportion of the first additional alloying elements does not exceed 3.0% by weight.

[0013] The aluminum (Al) alloy optionally contains at least one second additional alloying element selected from the group consisting of vanadium (V), niobium (Nb), chromium (Cr), molybdenum (Mo), silicon (Si), iron (Fe), and cobalt (Co). Here, the individual proportion of each second additional alloying element does not exceed 3.0% by weight, preferably 2.0% by weight, and the total proportion of the second additional alloying elements does not exceed 3.0% by weight.

[0014] The aluminum (Al) alloy optionally contains at least one third additional alloying element selected from the group consisting of magnesium (Mg) or calcium (Ca). Here, the individual proportion of each third additional alloying element is less than 2.0% by weight, and the total proportion of the third additional alloying elements does not exceed 3.0% by weight. [Modes for carrying out the invention]

[0015] Preferably, Mn is present in a proportion of 0.1% to 6% by weight, preferably 0.1% to 4% by weight, preferably 0.1% to 2.5% by weight, preferably 0.1% to 2.0% by weight, and more preferably 1.0% to 2.0% by weight.

[0016] Preferably, Ti is present in a proportion of 0.5% to 5.0% by weight, Sc in a proportion of 0.2% to 1.5% by weight, and Zr in a proportion of 0.20% to 0.70% by weight.

[0017] Preferably, Ti is present in a proportion of 1.0% to 5.0% by weight, Sc in a proportion of 0.5% to 1.0% by weight, and Zr in a proportion of 0.2% to 0.8% by weight.

[0018] Preferably, Ti is present in a proportion of 1.0% to 5.0% by weight, Sc in a proportion of 0.6% to 1.1% by weight, preferably 0.70% to 0.80% or 0.95% to 1.05% by weight, and Zr in a proportion of 0.20% to 0.50% by weight, more preferably 0.30% to 0.40% by weight.

[0019] Preferably, the Ti content is up to 2.0% by weight, more preferably 1.0% to 2.0% by weight, and the aluminum (Al) alloy consists solely of the following metals: namely, Al and Mn, and a metal having a greater enthalpy of vaporization than Al, or a metal having a lower vapor pressure than Al.

[0020] Preferably, Ti is present in a proportion of more than 2.0% by weight up to 5.0% by weight, preferably more than 3.0% by weight up to 5.0% by weight, and Mn is present in a proportion of 0.1% to 2.0% by weight, preferably 1.0% to 2.0% by weight.

[0021] Preferably, the aluminum (Al) alloy consists only of the following metals: namely, exclusively Al and Mn, and a metal greater than Al.

[0022] Preferably, the aluminum (Al) alloy does not contain magnesium (Mg) and / or calcium (Ca) and / or nickel (Ni).

[0023] The present invention provides a method for additively producing a precursor for a lightweight component from a preferred aluminum alloy, the method comprising the following: a) Melt the metals together to form a melt of an aluminum alloy. b) Forcefully cool the melt of the aluminum alloy or leave it to be cooled. At this time, b1) By a rapid solidification process (e.g., melt spinning, powder spraying in gas or water, strip casting, or spray forming, in-situ compaction) at a cooling rate of 1,000 K / s (K per second) to 10,000,000 K / s, particularly at a cooling rate of 100,000 K / s to 1,000,000 K / s, obtain a solidified aluminum alloy, which may be in the form of powder in some cases, and contains scandium in the solid solution. Or, b2) Obtain a solidified aluminum alloy by the cooling process. c) Grind the aluminum alloy obtained in step b1) or b2) into powder.

[0024] In step b) or step b1), it is preferable that the cooling rate is maintained in the temperature range of at least 1,800 K to 500 K.

[0025] The present invention provides a method for additive manufacturing of a precursor of a lightweight member from a preferred aluminum alloy, including the following. d) Manufacture a powder bed from the powder obtained in step c) of the above method. e) In a laser melting process on the powder bed, locally melt the powder with a laser and forcefully cool or allow to be cooled the locally melted area to perform additive manufacturing of a precursor of a three-dimensional lightweight member, thereby obtaining a precursor of a lightweight member from an aluminum alloy containing scandium in the solid solution.

[0026] The present invention provides a method for manufacturing a lightweight member, including heat-treating the precursor of the lightweight member obtained by the above method at a temperature for hardening by precipitation hardening.

[0027] The present invention provides a lightweight component precursor that can be obtained by a preferred method.

[0028] The present invention provides a lightweight member that can be obtained by a preferred method.

[0029] The present invention provides a method for producing lightweight component precursors by selective laser melting, or for producing lightweight components by selective laser melting and subsequent precipitation hardening, using a preferred aluminum alloy or a powder obtained by a preferred method (use of powder).

[0030] The ideas disclosed herein represent further developments and advancements of aluminum alloys containing the following elements, as described in the unpublished German patent application 10 2020 131 823.5. - Ti content of 0.1 to 15.0% by weight, - Sc content of 0.1-3.0% by weight, - Zr content of 0.1 to 3.0% by weight, - The remaining Al and unavoidable impurities.

[0031] By adapting to process boundary conditions, the fine grain structure can be controlled, resulting in superior mechanical properties. Products utilizing this material are suitable for structural applications in lightweight structures and designs (preferably aircraft).

[0032] The alloy design strategies for Al-Mg-Sc (Scalmalloy®) and Al-Cr-Sc (Scancromal®) have already been studied for different aluminum alloys. The alloy design strategy for Al-Ti-Sc (Scantital®) is a process built upon both of the previously considered materials.

[0033] Due to its high Mg content, Scalmalloy® is not always easy to control during the additive manufacturing process. Scancromal® has a relatively coarse microstructure and is not necessarily suitable for all applications, including structural applications. Adding titanium improves the additively manufactured components because there are no alloying elements with high vapor pressure that evaporate during the additive manufacturing process.

[0034] The addition of Ti is associated with several advantages. The L-PBF process is stable because it does not contain metals with high vapor pressure or low enthalpy of vaporization, such as Mg or Zn. Ti increases strength by refining the crystal grains, coupled with the high microstructural supercooling that occurs when Ti is added, by precipitating a coherent primary AhX phase (X=Ti, Zr, Sc) that acts as nucleation sites. Strength is further increased by precipitation hardening of the secondary phase during subsequent post-heat treatment. Ti-added AISc alloys exhibit even better corrosion resistance.

[0035] Ti does not increase the strength of aluminum alloys at room temperature as significantly as Sc or Zr. Most Ti remains dissolved in the solid solution during rapid solidification. Precipitate coarsening occurs more slowly than expected. Creep resistance or fatigue strength ("creep resistance") is increased.

[0036] As a further development, manganese (Mn) has been introduced into aluminum alloys to further improve strength while simultaneously enabling high ductility. Omitting Mg can improve corrosion resistance. Compared to the initial development of Scantital®, the addition of Mn has increased the strength level. Mn has a significant impact on ductility.

[0037] This idea is based on an AITiScMn alloy. This AITiScMn alloy is ultimately manufactured by laser powder bed fusion (L-PBF) additive manufacturing and the rapid cooling exhibited by this process.

[0038] One of the proposed nominal compositions, expressed as a weight percentage (wt%) of the alloy, is AITi(1-5)Sc0.75Zr0.35Mn(0-2).

[0039] The chemical driving force for precipitation, ΔFch, is significantly greater for Al3Zr than for Al3Ti. The elastic strain energy ΔFel (elastic strain energy for precipitation) of Al3Ti during precipitation is seven times that of Al3Zr, preventing nucleation. Under rapid cooling conditions, up to 2 wt% of Ti can be forced to dissolve in the aluminum matrix.

[0040] The advantages of titanium (Ti) in the additive manufacturing of lightweight components using the L-PBF process (or SLM process from "selective laser melting") of aluminum alloys are its low vapor pressure and high enthalpy of vaporization. The vapor pressure of Ti is lower than that of the base metal, aluminum. The enthalpy of vaporization of Ti is higher than that of the base metal, aluminum. As a result, process stability is improved, and a very calm and stable molten pool is created during remelting compared to aluminum alloys containing magnesium.

[0041] Ti ensures strong structural supercooling during solidification. This activates strong primary nucleation sites in the molten material, refining the crystalline grain. The finer microstructure is hall-petch; the strength increases. -1 / 2 The strength of the aluminum alloy is increased in accordance with (inversely proportional to the grain size).

[0042] In the molten state, Zr provides effective nucleation sites even at high temperatures. This is because Al3Zr precipitates as early as around 900°C and can therefore be activated by structural supercooling. In contrast, Al3Sc only precipitates slightly before the solidus temperature.

[0043] When cooling the molten aluminum alloy in step b), if the cooling rate is not too fast, such as when casting the molten material into a crucible, an aluminum matrix is ​​formed in which the alloying elements Ti, Sc, and Zr are mainly present in large primary precipitates. If the above aluminum alloy is cooled very rapidly at a rate of 1,000 K / s to 10,000,000 K / s, the solidified aluminum alloy will substantially contain the above alloying elements in the solid solution. Precipitation of the primary phase is suppressed by rapid cooling. The faster the molten material is cooled, the lower the content of primary precipitates. For example, during subsequent precipitation solidification at a temperature of approximately 250-450°C, nanoscale coherent Al3X phases (X = Ti, Zr, Sc) are precipitated, guaranteeing a significant improvement in the strength of the aluminum alloy.

[0044] In step e), after the powder is melted by the laser beam, a very rapid cooling is performed in which the alloying elements solidify into a substantially solid solution. This process step, as a whole, involves remelting into the desired alloy.

[0045] Next, embodiments of the present invention will be described in more detail.

[0046] A) Manufacturing process of aluminum alloys <Example 1: Production of aluminum alloy in powder form> In an inert crucible, 0.75 wt% Sc, 0.35 wt% Zr, 1.0 wt% Ti, 1.0 wt% Mn, and 96.9 wt% Al are melted. The molten material can be homogenized before further processing.

[0047] The first fraction of the molten material is poured into an inert crucible, where it cools and solidifies. During cooling, primary phases of Al3Sc, Al3Zr, and Al3Ti precipitate. The resulting material is ground into a powder that can be used for selective laser melting in a powder bed.

[0048] The second fraction of the molten material is poured onto rotating water-cooled copper rollers in the melt-spinning process. The molten material is cooled at a rate of 1,000,000 K / s to form strips. Because the molten material cools very rapidly, the formation of Al3Sc, Al3Zr, and Al3Ti is completely or substantially suppressed. The strips are cut into short flakes.

[0049] The alloy material obtained from the two cooling processes is pulverized into powder and can be used for selective laser melting in a powder bed.

[0050] <Example 2: Production of aluminum alloys in powder form with different titanium content> The above procedure is repeated, except that the Ti content is increased to 3.0 wt%, 5.0 wt%, 10.0 wt%, and 15.0 wt%, and the Al content is decreased accordingly. The Sc and Zr content remains unchanged.

[0051] <Example 3: Production of aluminum alloy in powder form containing vanadium> The process of Example 1 is repeated, except that 2.0 wt% vanadium is further added to the crucible, and the Ti, Sc, and Zr content is kept constant.

[0052] <Example 4: Production of nickel-containing aluminum alloy in powder form> The process of Example 1 is repeated, except that 1.2 wt% nickel is further added to the crucible, and the Ti, Sc, and Zr content is kept constant.

[0053] <Example 5: Production of aluminum alloy in powder form containing chromium vanadium> The process of Example 1 is repeated, except that 1.0 wt% vanadium and 2.0 wt% chromium are further added to the crucible, increasing the titanium content to 5 wt%. The Zr content remains unchanged.

[0054] <Example 6: Production of aluminum alloy powders with different Mn content> The process according to Example 1 or 2 is repeated, except that the proportion of Mn is varied to 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 4 wt%, and 6 wt%, and the proportion of Al is adjusted accordingly.

[0055] B) Process for producing lightweight component precursors using the L-PBF process In each case, an aluminum alloy powder from one of the above Examples 1-6 is placed in the equipment for additive manufacturing by selective laser melting to form a powder bed. The laser beam moves across the three-dimensional powder bed according to digital information. During this process, the powder bed is progressively lowered in height, and new powder layers are added. The point-molten aluminum alloy is cooled very rapidly, so as follows: scandium, zirconium, and titanium are frozen (solidified) completely, substantially, or predominantly, to form solid solutions, regardless of the other compositions of the aluminum alloy and regardless of whether the powder was manufactured by normal cooling or rapid cooling (e.g., cooling at a rate of 1,000,000 K / s). After the scanning process is complete, the aluminum alloy component precursor is separated from the powder bed.

[0056] C) Method for manufacturing lightweight components The component precursor produced in B) is heated to a temperature in the range of 250°C to 450°C, preferably 300°C to 400°C, and more preferably 325°C to 350°C. During this process, various Al3X phases (X = Ti, Zr, Sc, or any desired non-stoichiometric mixture of individual elements) precipitate. Al3Ti also precipitates, but compared to Al3Sc and Al3Zr, the main or majority of the titanium component remains in solid solution.

[0057] In summary, the present invention relates to an aluminum (Al) alloy comprising 0.1% to 15% by weight of titanium (Ti), 0.1% to 3.0% by weight of scandium (Sc), 0.1% to 3.0% by weight of zirconium (Zr), 0.1% to 3.0% by weight of manganese (Mn), the remainder being aluminum (Al), and unavoidable impurities totaling less than 0.5% by weight. This aluminum (Al) alloy is used in additive manufacturing methods to produce high-strength, high-ductility lightweight components for aircraft. The aluminum (Al) alloy is initially produced as a powder and then remelted during the manufacturing process to achieve the desired properties.

Claims

1. Titanium (Ti) in a proportion of 1.0% by weight to 5.0% by weight, Scandium (Sc) in a proportion of 0.5% to 1.0% by weight, Zirconium (Zr) in a proportion of 0.2% to 0.8% by weight, Manganese (Mn) in a proportion of 0.1% to 10.0% by weight, An aluminum (Al) alloy consisting of the remainder being aluminum (Al) and unavoidable impurities totaling less than 0.5% by weight.

2. Titanium (Ti) in a proportion of 1.0% by weight to 5.0% by weight, Scandium (Sc) in proportions of 0.6% to 1.1% by weight, or 0.70% to 0.80% by weight, or 0.95% to 1.05% by weight. Zirconium (Zr) in a proportion of 0.20% to 0.50% by weight, or 0.30% to 0.40% by weight. Manganese (Mn) in a proportion of 0.1% to 10.0% by weight, An aluminum (Al) alloy consisting of the remainder being aluminum (Al) and unavoidable impurities totaling less than 0.5% by weight.

3. The aluminum (Al) alloy according to claim 1, wherein the proportion of Mn is 0.1% to 6% by weight, or 0.1% to 4% by weight, or 0.1% to 2.5% by weight, or 0.1% to 2.0% by weight, or 1.0% to 2.0% by weight.

4. The aluminum (Al) alloy according to claim 2, wherein the proportion of Mn is 0.1% to 6% by weight, or 0.1% to 4% by weight, or 0.1% to 2.5% by weight, or 0.1% to 2.0% by weight, or 1.0% to 2.0% by weight.

5. Titanium (Ti) in a proportion exceeding 2.0% by weight up to 5.0% by weight, or exceeding 3.0% by weight up to 5.0% by weight. Scandium (Sc) in a proportion of 0.1% to 3.0% by weight, Zirconium (Zr) in a proportion of 0.1% to 3.0% by weight, Manganese (Mn) in a proportion of 0.1% to 2.0% by weight, or 1.0% to 2.0% by weight. An aluminum (Al) alloy consisting of the remainder being aluminum (Al) and unavoidable impurities totaling less than 0.5% by weight.

6. The aluminum (Al) alloy according to claim 5, wherein the proportion of Sc is 0.2% to 1.5% by weight and the proportion of Zr is 0.20% to 0.70% by weight.

7. The aluminum (Al) alloy according to claim 5, characterized in that the proportion of Sc is 0.5% to 1.0% by weight and the proportion of Zr is 0.2% to 0.8% by weight.

8. The aluminum (Al) alloy according to claim 5, characterized in that the proportion of Sc is 0.6% to 1.1% by weight, or 0.70% to 0.80% by weight, or 0.95% to 1.05% by weight, and the proportion of Zr is 0.20% to 0.50% by weight, or 0.30% to 0.40% by weight.

9. Titanium (Ti) in a proportion of 1.0% by weight to 15.0% by weight, Scandium (Sc) in a proportion of 0.5% to 1.0% by weight, Zirconium (Zr) in a proportion of 0.2% to 0.8% by weight, Manganese (Mn) in a proportion of 0.1% to 10.0% by weight, All of these are present in amounts of 0.1% to 2% by weight: chromium (Cr), cobalt (Co), and / or nickel (Ni). An aluminum (Al) alloy consisting of the remainder being aluminum (Al) and unavoidable impurities totaling less than 0.5% by weight.

10. Titanium (Ti) in a proportion of 1.0% by weight to 5.0% by weight, Scandium (Sc) in a proportion of 0.5% to 1.0% by weight, Zirconium (Zr) in a proportion of 0.2% to 0.8% by weight, Manganese (Mn) in a proportion of 0.1% to 2.0% by weight, or 1.0% to 2.0% by weight. All of these are present in amounts of 0.1% to 2% by weight: chromium (Cr), cobalt (Co), and / or nickel (Ni). An aluminum (Al) alloy consisting of the remainder being aluminum (Al) and unavoidable impurities totaling less than 0.5% by weight.

11. The aluminum (Al) alloy according to claim 1, characterized in that the proportion of Mn is 0.1% by weight to 2.0% by weight, or 1.0% by weight to 2.0% by weight.

12. The aluminum (Al) alloy according to claim 2, characterized in that the proportion of Mn is 0.1% by weight to 2.0% by weight, or 1.0% by weight to 2.0% by weight.

13. An aluminum (Al) alloy according to any one of claims 1 to 12, which does not contain magnesium (Mg) and / or calcium (Ca) and / or nickel (Ni).

14. A method for adding a lightweight component precursor from an aluminum alloy according to any one of claims 1 to 12, comprising the following: a) The metals are melted together to form a molten aluminum alloy. b) Forcibly cool the molten aluminum alloy, or ensure that it is cooled. b1) Obtain a solidified aluminum alloy containing scandium in the solid solution by a rapid solidification process at a cooling rate of 1,000 K / s to 10,000,000 K / s, particularly at a cooling rate of 100,000 K / s to 1,000,000 K / s. Or, b2) A solidified aluminum alloy is obtained by a cooling process. c) Grind the aluminum alloy from step b1) or b2) into a powder.

15. A method for adding a lightweight component precursor from an aluminum alloy according to claim 14, wherein the rapid solidification process is carried out by melt spinning, powder spraying in gas or water, strip casting or spray forming, and the solidified aluminum alloy is in powder form.

16. A method for adding a lightweight component precursor from an aluminum alloy according to any one of claims 1 to 12, comprising the following: d) A powder bed is produced from the powder obtained in step c) of claim 12. e) In a laser melting process on a powder bed, the powder is locally melted with a laser, and the locally melted area is forcibly cooled or otherwise allowed to cool, thereby adding a precursor for a three-dimensional lightweight component to obtain a precursor for a lightweight component from an aluminum alloy containing scandium in a solid solution.

17. A method for producing a lightweight member, characterized by heat-treating a lightweight member precursor obtained by the method described in claim 12 at a temperature at which it hardens by precipitation hardening.

18. Use of an aluminum alloy according to any one of claims 1 to 12 or a powder obtained by the method of claim 12 for producing a lightweight member precursor by selective laser melting, or for producing a lightweight member by producing a lightweight member precursor by selective laser melting and then performing selective laser melting and subsequent precipitation hardening.