ALUMINIUM ALLOY AND PROCESS FOR ADDITIVE MANUFACTURE OF LIGHTWEIGHT COMPONENTS

Abstract

An alloy which consists of aluminum, titanium, scandium and zirconium with or without one, two or more further 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 additive manufacturing step, such as laser melting by the L-PBF process (laser powder bed fusion), a lightweight component precursor is produced from a powder of the aluminum alloy of the invention, this 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 the lightweight component. 3D-printed lightweight components of high strength are obtained.

Claims

1. An aluminum alloy comprising the following alloy components: titanium (Ti) in a fraction of 0.1 wt % to 15.0 wt %, scandium (Sc) in a fraction of 0.1 wt % to 3.0 wt %, zirconium (Zr) in a fraction of 0.1 wt % to 3.0 wt %, aluminum (Al), and unavoidable impurities.

2. The aluminum alloy according to claim 1, wherein the alloy comprises Ti in a fraction of 0.5 wt % to 5.0 wt %, Sc in a fraction of 0.2 wt % to 1.5 wt % and Zr in a fraction of 0.2 wt % to 1.5 wt %.

3. The aluminum alloy according to claim 1, wherein the alloy comprises Ti in a fraction of 1.0 wt % to 5.0 wt %, Sc in a fraction of 0.5 wt % to 1.0 wt % and Zr in a fraction of 0.2 wt % to 0.8 wt %.

4. The aluminum alloy according to claim 1, wherein the alloy comprises one, two 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), a fraction of each of these elements individually corresponding to up to 100%, of the Ti fraction, with a proviso that a total fraction of these metals accounts for, at most, 15 wt % of the aluminum alloy.

5. The aluminum alloy according to claim 1, wherein the alloy comprises one, two 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), a fraction of each of these elements individually being from 0.1 wt % to 2 wt %, with a proviso that a total fraction of these metals accounts for, at most, 15 wt % of the aluminum alloy.

6. The aluminum alloy according to claim 1, wherein the alloy further comprises calcium (Ca) in a fraction in a range from 0.1 wt % to 5 wt %.

7. The aluminum alloy according to claim 1, wherein that as well as aluminum and unavoidable impurities the alloy comprises exclusively metals which have a higher enthalpy of vaporization or a lower vapor pressure than aluminum.

8. The aluminum alloy according to claim 1, wherein the alloy contains no magnesium.

9. The aluminum alloy according to claim 1, wherein the alloy contains no manganese.

10. An aluminum alloy consisting of the alloy components according to claim 1.

11. The aluminum alloy according to claim 1, wherein, apart from unavoidable impurities, the alloy consists of one of the following: Al, Ti, Sc, Zr and one, two 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); Al, Ti, Sc, Zr and Cr, the Cr fraction being in a range from 0.2 wt % to 3.5 wt %; Al, Ti, Sc, Zr and Ni, the Ni fraction being in a range from 0.2 wt % to 2.5 wt %; Al, Ti, Sc, Zr and Mo, the Mo fraction being in a range from 0.1 wt % to 1.3 wt %; Al, Ti, Sc, Zr and Fe, the Fe fraction being in a range from 0.1 wt % to 2.5 wt %; or Al, Ti, Sc, Zr and Ca, the Ca fraction being in a range from 0.1 wt % to 5 wt %.

12. A process for additive manufacture of a lightweight component precursor from an aluminum alloy according to claim 1, which comprises: a) co-melting the alloy components to give an aluminum alloy melt; b) actively or passively cooling the aluminum alloy melt by one of b1) in a rapid solidification process with a cooling rate of 1000 K/s to 10 000 000 K/s, more particularly 100 000 K/s to 1 000 000 K/s, for example melt spinning, powder atomization by means of gas or in water, thin strip casting or spray compacting, to give a solidified aluminum alloy optionally in powder form, with scandium contained in solid solution therein; or b2) in a cooling process, to give a solidified aluminum alloy; c) comminuting the aluminum alloy from step b1) or b2) to give a powder.

13. The process for additive manufacture of a lightweight component precursor from an aluminum alloy according to claim 12, which comprises: d) producing a powder bed from the powder obtained in step c); and e) additively manufacturing a three-dimensional lightweight component precursor in a laser melting process in the powder bed with a laser, with local melting of the powder and active or passive cooling of the local melting, to give a lightweight component precursor composed of an aluminum alloy with scandium obtained in solid solution.

14. The process for producing a lightweight component, which comprises heat-treating the lightweight component precursor obtained in the process according to claim 13 at a temperature at which the lightweight component precursor is hardened by precipitation hardening.

15. A lightweight component precursor obtainable by the process according to claim 13.

16. A lightweight component precursor obtainable by the process according to claim 15.

17. A method of using the aluminum alloy according to claim 1 for producing a lightweight component precursor by selective laser melting and producing a lightweight component by selective laser melting and subsequent precipitation hardening.

18. A method of using the powder obtainable by the process according to claim 10 for producing a lightweight component precursor by selective laser melting and producing a lightweight component by selective laser melting and subsequent precipitation hardening.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] A working example is elucidated in more detail below with reference to the appended drawings, in which:

[0053] FIG. 1 shows the chemical composition of common aluminum alloys for lightweight aeronautical components in table 1;

[0054] FIG. 2 shows the physical properties of the most important alloying elements in table 2;

[0055] FIG. 3 shows the vapor pressure as a function of the temperature of the constituents of Scalmalloy®;

[0056] FIG. 4 shows the vapor pressure as a function of the temperature of the constituents of an alloy of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] FIG. 1 shows in table 1 the composition of aluminum alloys which are used for producing lightweight aeronautical components. Like duralumin, the alloys AA2024, AA7349, AA7010 and AA6061 contain magnesium and copper. Duralumin is an aluminum alloy developed in 1906 by Alfred Wilm, which was found to have a strength that could be boosted significantly by precipitation hardening. With the boost in strength thus achieved it became possible to employ aluminum in alloyed form in aeronautics.

[0058] A further considerable boost to strength of aluminum is possible through the incorporation of scandium, as in the case of Scalmalloy®. Because of the low solubility of scandium in aluminum at room temperature, however, the scandium here first has to be forcibly dissolved in the aluminum in a rapid solidification process, such as melt spinning, before the precipitation hardening can be carried out at a temperature in the range from 250° C. to 450° C.

[0059] A peculiarity of the two aluminum alloys AlSi10Mg and Scalmalloy® in table 1 is that they are suitable for laser melting by the L-PBF process. These two alloys may therefore be processed to lightweight components for aircraft by additive manufacturing.

[0060] FIG. 2 shows in table 2 the physical properties of various alloying elements. The alloying elements above aluminum have a higher enthalpy of vaporization than aluminum. Those below aluminum have a lower enthalpy of vaporization than aluminum.

[0061] FIG. 3 shows, in a diagram, the temperature dependency of the vapor pressure of the alloy constituents of Scalmalloy®.

[0062] FIG. 4 shows, in a diagram, the temperature dependency of the vapor pressure of an aluminum alloy of the invention.

[0063] Described below are processes for producing aluminum alloys, a lightweight component precursor and a lightweight component.

A) PROCESSES FOR PRODUCING ALUMINUM ALLOYS

[0064] Example 1 Production of Aluminum Alloys in Powder Form

[0065] In an inert crucible, 0.75 wt % of Sc, 0.35 wt % of Zr, 1.0 wt % of Ti and 97.9 wt % of Al are melted. The melt may be homogenized prior to further processing.

[0066] A first fraction of the melt is poured into an inert crucible, in which it cools and solidifies. On cooling, primary Al3Sc, Al3Zr and Al3Ti phases are precipitated. The material obtained is comminuted to a powder, which can be used for selective laser melting in a powder bed.

[0067] A second fraction of the melt is poured in a melt spinning process onto a rotating, water-cooled copper roll. The melt cools at a rate of 1 000 000 K/s to form a strip. The cooling of the melt is sufficiently rapid to suppress a substantial part or all of the formation of Al3Sc, Al3Zr and Al3Ti. The strip is cut into short flakes.

[0068] The alloy material obtained in the two cooling processes is comminuted to a powder, which can be used for selective laser melting in a powder bed.

Example 2 Production of Aluminum Alloys in Powder Form with Differing Titanium Content

[0069] The above process is repeated, with the fraction of Ti being increased to 3.0 wt %, 5.0 wt %, 10.0 wt % and 15.0 wt % and the fraction of Al being reduced correspondingly. The fraction of Sc and Zr remains unchanged.

Example 3 Production of an Aluminum Alloy in Powder form Containing Vanadium

[0070] The process of example 1 is repeated, with additionally 2.0 wt % of vanadium being placed into the crucible and with the fraction of Ti, Sc and Zr kept constant.

Example 4 Production of an Aluminum Alloy in Powder form Containing Nickel

[0071] The process of example 1 is repeated, with additionally 1.2 wt % of nickel being placed into the crucible and with the fraction of Ti, Sc and Zr kept constant.

Example 5 Production of an Aluminum Alloy in Powder Form Containing Chromium-Vanadium

[0072] The process of example 1 is repeated, with additionally 1.0 wt % of vanadium and 2.0 wt % of chromium being placed into the crucible, and with the fraction of titanium being increased to 5 wt %. The Zr fraction remains unchanged.

B) PROCESSES FOR PRODUCING A LIGHTWEIGHT COMPONENT PRECURSOR BY THE L-PBF PROCESS

[0073] A respective aluminum alloy powder from each of the above examples 1 to 5 is placed into a plant for additive manufacture by selective laser melting, to form a powder bed. The laser beam is moved over the three-dimensional powder bed in accordance with the digital information, with the powder bed being lowered step by step and with new powder layers being applied. The cooling of the locally melted aluminum alloy is sufficiently rapid but scandium, zirconium and titanium are “frozen” completely or substantially or predominantly in solid solution, irrespective of the composition of the aluminum alloy otherwise and irrespective of whether the powder was produced by normal cooling or by rapid cooling at a rate, for example, of 1 000 000 K/s. When the scanning procedure is at an end, the component precursor composed of the aluminum alloy is removed from the powder bed.

C) PROCESSES FOR PRODUCING A LIGHTWEIGHT COMPONENT

[0074] The component precursor produced in B) is heated to a temperature, such as in the range from 250° C. to 450° C., preferably 300° C. to 400° C. and more preferably 325° C. to 350° C., at which diverse Al3X phases are precipitated (X=Ti, Zr, Sc or any desired non-stochiometric mixture of the individual elements. Al3Ti is likewise precipitated, but by comparison with Al3Sc and Al3Zr there remains a predominant or sizable fraction of the titanium in solid solution.

[0075] While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.