Aluminum alloy and additive manufacturing method for lightweight components

Abstract

To provide an improved aluminum alloy which is suitable for additive manufacturing with a sufficiently rapid cooling rate.SOLUTION: The invention relates to an alloy which consists of aluminum, titanium, scandium and zirconium, and other metals selected from hafnium, vanadium, niobium, chromium, molybdenum, silicon, iron, cobalt, nickel and calcium. The aluminum alloy is suitable for the additive manufacture of lightweight components for aircraft. In a first step, a powder of the aluminum alloy of the invention is made to a lightweight component precursor by additive manufacturing such as laser melting in an L-PBF (laser powder bed fusion) process. The precursor comprising titanium, scandium and zirconium in solid solution, as a result of rapid solidification of the laser melt. In a second step, the lightweight component precursor is hardened by precipitation of secondary phases at 250 to 400°C to give a lightweight component. 3D-printed lightweight components of high strength are obtained.SELECTED DRAWING: Figure 4

Description

Technical Field

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

Background Art

[0002] Aluminum alloys are important materials for manufacturing lightweight members for aircraft. The reduction in the total weight of an aircraft associated with incorporating these lightweight members enables the reduction of fuel costs. Aluminum alloys that can be used for this purpose need to have high tensile strength, ductility, toughness, and corrosion resistance from the perspective of flight safety.

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

[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 rapid solidification, such as melt spinning, of the melt, followed by precipitation hardening involving 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, illustrates the chemical composition of the above-mentioned 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. [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The object of the present invention is to provide an improved aluminum alloy suitable for additive manufacturing at a sufficiently fast cooling rate, for example, in an L-PBF process.

[0009] This problem is solved by the aluminum alloy described in claim 1. Advantageous improvements are the subject of the subclaims.

[0010] According to a first aspect, the present invention provides an aluminum alloy comprising the following alloy components. - 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.

[0011] The addition of Ti offers numerous advantages. The LPB-F 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 crystalline grain. In this process, the Al3X phase (X = Ti, Zr, Sc) precipitates coherently as a first step, and this, combined with the high structural supercooling that occurs when Ti is incorporated into the alloy, acts as a nucleation site. During subsequent heat and post-treatment, the secondary phase precipitates and hardens, increasing the strength. AlSc alloys containing Ti exhibit even better corrosion resistance.

[0012] Ti does not cause as significant an increase in strength at room temperature in aluminum alloys as Sc or Zr. During rapid solidification, most of the Ti remains dissolved in the solid solution. Precipitate coarsening is slower than expected. Fatigue resistance or creep resistance is improved.

[0013] 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.

[0014] The advantages of Ti in the additive manufacturing of lightweight components by the L-PBF process (or SLM process from "selective laser melting") of aluminum alloys are its low vapor pressure or high heat 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.

[0015] 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).

[0016] 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.

[0017] The aluminum alloy preferably contains Ti in an amount of 0.5% to 5.0% by weight, Sc in an amount of 0.2% to 1.5% by weight, and Zr in an amount of 0.2% to 1.5% by weight.

[0018] The aluminum alloy preferably contains Ti in an amount of 1.0% to 5.0% by weight, preferably 1.0% to 4.0% by weight, Sc in an amount of 0.5% to 1.0% by weight, and Zr in an amount of 0.2% to 0.8% by weight.

[0019] The aluminum alloy preferably contains one or more metals selected from the group consisting of hafnium (Hf), vanadium (V), niobium (Nb), chromium (Cr), molybdenum (Mo), silicon (Si), iron (Fe), cobalt (Co), and nickel (Ni). The individual content of each of these elements is as follows: - Up to 100% of the Ti content, preferably up to 90%, preferably up to 70%, and more preferably up to 50%. However, the total content of these metals shall be at most 15% by weight, preferably up to 10% by weight, in the aluminum alloy of any of claims 1 to 3. Or, - It is 0.1% by weight to 2% by weight. However, the total content of these metals is at most 15% by weight, preferably at most 10% by weight, in the aluminum alloy according to any one of claims 1 to 3.

[0020] The aluminum alloy preferably contains only metals having a higher heat of vaporization or a lower vapor pressure than aluminum, in addition to aluminum and unavoidable impurities.

[0021] The aluminum alloy preferably contains calcium (Ca) in the range of 0.1 to 5% by weight, preferably in the range exceeding 0.5% by weight to 5% by weight, particularly preferably in the range of 0.7% by weight to 3% by weight. Calcium forms a coating of calcium oxide during laser melting and prevents the undesirable evaporation of alloy elements.

[0022] The aluminum alloy preferably does not contain magnesium and / or manganese.

[0023] The aluminum alloy preferably consists of a combination of the alloy components described above.

[0024] The aluminum alloy preferably consists of Al, Ti, Sc, and Zr, or consists of Al, Ti, Sc, Zr, and one or more of the above metals, excluding unavoidable impurities.

[0025] The aluminum alloy is preferably as follows. That is, excluding unavoidable impurities, it consists of Al, Ti, Sc, Zr, and Cr, and the Cr content is within the range of 0.2% by weight to 3.5% by weight, preferably within the range of 0.5% by weight to 3.0% by weight.

[0026] The aluminum alloy is preferably as follows. That is, excluding unavoidable impurities, it consists of Al, Ti, Sc, Zr, and Ni, and the Ni content is within the range of 0.2% by weight to 2.5% by weight, preferably within the range of 0.5% by weight to 2.0% by weight.

[0027] The aluminum alloy preferably has the following composition. That is, excluding inevitable impurities, it consists of Al, Ti, Sc, Zr, and Mo, and the Mo content is preferably in the range of 0.1% to 1.3% by weight, more preferably in the range of 0.5% to 1.0% by weight.

[0028] The aluminum alloy preferably has the following composition. That is, excluding inevitable impurities, it consists of Al, Ti, Sc, Zr, and Fe, and the Fe content is preferably in the range of 0.1% to 2.5% by weight, more preferably in the range of 0.5% to 2.0% by weight.

[0029] The aluminum alloy preferably has the following composition. That is, excluding inevitable impurities, it consists of Al, Ti, Sc, Zr, and Ca, and the Ca content is preferably in the range of 0.1% to 5% by weight, more preferably in the range exceeding 0.5% to 5% by weight, and particularly preferably in the range of 0.7% to 3% by weight.

[0030] According to a second aspect, the present invention provides a method for additive manufacturing of a precursor of a lightweight structural member, comprising the following steps. a) Melting the metals together to form a melt of an aluminum alloy. b) Either forcibly cooling the melt of the aluminum alloy or leaving it to be cooled. In this case, b1) By a rapid solidification process (e.g., melt spinning, powder spraying in gas or water, strip casting, or spray forming (spray forming, in-situ compaction)) at a cooling rate of 1,000 K / s (K per second) to 10,000,000 K / s, particularly 100,000 K / s to 1,000,000 K / s, to obtain a solidified aluminum alloy, which may be in powder form in some cases, and which contains scandium in the solid solution. Or, b2) Obtaining a solidified aluminum alloy by a cooling process. c) Grind the aluminum alloy from step b1) or b2) into a powder.

[0031] In step b) or step b1), it is preferable that the cooling rate is maintained in a temperature range of at least 1,800K to 500K.

[0032] When cooling the molten aluminum alloy in step b), if the cooling rate is not too fast, 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. During subsequent precipitation solidification at a temperature of approximately 250-450°C, nanoscale coherent Al3X phases (X = Ti, Zr, Sc) precipitate, ensuring a significant improvement in the strength of the aluminum alloy.

[0033] 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.

[0034] According to a third aspect, the present invention provides a method for additively producing a precursor for a lightweight component from the aluminum alloy described above. This method includes the following: d) A powder bed is produced from the powder obtained in step c) of claim 10. e) In a laser melting process on a powder bed, the powder is locally melted with a laser, and the locally melted region is forcibly cooled or allowed to cool, thereby adding a precursor to a three-dimensional lightweight component to obtain a precursor to a lightweight component from an aluminum alloy containing scandium in a solid solution.

[0035] According to a fourth aspect, the present invention provides a method for producing a lightweight member, which includes heat-treating a lightweight member precursor obtained by the method described above at a temperature at which the lightweight member precursor hardens by precipitation hardening.

[0036] According to a fifth aspect, the present invention provides a lightweight component precursor obtained by the additive manufacturing process described above.

[0037] According to a sixth aspect, the present invention provides a lightweight member obtained by the above-described curing process.

[0038] According to a seventh aspect of the present invention, the present invention provides a method for producing a lightweight member by selective laser melting to produce a lightweight member precursor, followed by selective laser melting and subsequent precipitation hardening, using the aluminum alloy described above or a powder obtained by the above method (use of powder).

[0039] Exemplary embodiments are described in more detail below with reference to the attached drawings. [Brief explanation of the drawing]

[0040] [Figure 1] Table 1 shows the chemical compositions of common aluminum alloys used for lightweight aerospace components. [Figure 2] Table 2 shows the physical properties of the most important alloying elements. [Figure 3] This shows the vapor pressure as a function of temperature for the constituent elements of Scalmalloy®. [Figure 4] The vapor pressure as a function of temperature for the constituent elements of the alloy according to the present invention is shown. [Modes for carrying out the invention]

[0041] Figure 1 shows the composition of aluminum alloys used in the manufacture of lightweight components for aircraft, as shown in Table 1. Alloys AA2024, AA7349, AA7010, and AA6061 contain magnesium and copper, similar to duralumin. Duralumin is an aluminum alloy developed by Alfred Wilms in 1906, and it was recognized that the strength of the alloy could be significantly increased through precipitation hardening. This increased strength has made it possible to use aluminum in alloy form for aviation.

[0042] As in the case of Scalmalloy®, the strength of aluminum can be significantly further improved by adding scandium. Due to the low solubility of scandium in aluminum at room temperature, it is necessary to first force the scandium to dissolve in the aluminum using a rapid solidification process such as melt spinning before precipitation hardening can be performed at temperatures ranging from 250°C to 450°C.

[0043] The two aluminum alloys in Table 1, AlSi10Mg and Scalmalloy®, are characterized by their suitability for laser melting in the L-PBF process. Therefore, these two alloys can be processed into lightweight components for aircraft by additive manufacturing.

[0044] Figure 2 shows the physical properties of various alloying elements in Table 2. All alloying elements above aluminum have a higher enthalpy of vaporization than aluminum. All elements below aluminum have a lower enthalpy of vaporization than aluminum.

[0045] Figure 3 is a diagram showing the temperature dependence of the vapor pressure of the alloy components (elements constituting the alloy) of Scalmalloy®.

[0046] Figure 4 is a diagram showing the temperature dependence of the vapor pressure of the aluminum alloy according to the present invention.

[0047] The following describes aluminum alloys, lightweight component precursors, and methods for manufacturing lightweight components.

[0048] 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, and 97.9 wt% Al are melted. The molten material can be homogenized before further processing.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] <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.

[0053] <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.

[0054] <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.

[0055] <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.

[0056] B) Process for producing lightweight component precursors using the L-PBF process Each aluminum alloy powder from each of the above Examples 1 to 5 is placed in a facility 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, 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.

[0057] 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.

Claims

1. - Titanium (Ti) having a content of 0.1% to 15.0% by weight, - Scandium (Sc) in content ranging from 0.1% to 3.0% by weight. - Zirconium (Zr) in a content of 0.1% to 3.0% by weight, - One, two, or more metals selected from the group consisting of vanadium (V), chromium (Cr), and nickel (Ni), and - The remainder consists of aluminum (Al) and unavoidable impurities. The aluminum alloys have the following respective content amounts for vanadium (V), chromium (Cr), and / or nickel (Ni): - Up to 100% of the Ti content, or up to 90%, or up to 70%, or up to 50%. However, the total content of vanadium (V), chromium (Cr), and / or nickel (Ni) may be up to 15% by weight, or up to 10% by weight. Or, - The content of the aluminum alloy is 0.1% to 2% by weight, provided that the total content of vanadium (V), chromium (Cr), and / or nickel (Ni) is a maximum of 15% by weight, or a maximum of 10% by weight, in the aluminum alloy.

2. Ti content ranging from 0.5% to 5.0% by weight, Sc, and, containing 0.2% to 1.5% by weight. The aluminum alloy according to claim 1, characterized by containing Zr in an amount of 0.2% to 1.5% by weight.

3. Ti containing 1.0% to 5.0% by weight, or 1.0% to 4.0% by weight. Sc, and, containing 0.5% to 1.0% by weight. The aluminum alloy according to claim 1 or 2, characterized by containing Zr in an amount of 0.2% to 0.8% by weight.

4. An aluminum alloy according to any one of claims 1 to 3, characterized in that it consists of Al, Ti, Sc, and Zr, with unavoidable impurities removed, and the following: - One or more elements selected from Cr, Ni, and / or V. If Cr is present, the Cr content is in the range of 0.2% to 3.5% by weight, or 0.5% to 3.0% by weight, and if Ni is present, the Ni content is in the range of 0.2% to 2.5% by weight, or 0.5% to 2.0% by weight.

5. A method for adding a lightweight component precursor from an aluminum alloy according to any one of claims 1 to 3, 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, possibly in powder form, containing scandium in a solid solution, by a rapid solidification process at a cooling rate of 1,000 K / s to 10,000,000 K / s, or 100,000 K / s to 1,000,000 K / s, using melt spinning, powder spraying in gas or water, strip casting or spray forming, or other solidification processes. 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.

6. A method for adding a lightweight component precursor from an aluminum alloy according to any one of claims 1 to 3, comprising the following: d) A powder bed is produced from the powder obtained in step c) of claim 5. 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.

7. A method for producing a lightweight member, comprising heat-treating a lightweight member precursor obtained by the method described in claim 6 at a temperature at which the lightweight member precursor hardens by precipitation hardening.

8. The use of an aluminum alloy according to any one of claims 1 to 3 or a powder obtained by the method of claim 5 for producing a lightweight member by selective laser melting to produce a lightweight member precursor, followed by selective laser melting and subsequent precipitation hardening.

Images