High strength aluminium alloy for rapid solidification manufacturing processes

Abstract

An aluminium based alloy, and a method for production of components by additive manufacturing (AM) or other rapid solidification process with the alloy, is based on the alloy having a composition with from 2.01 wt % to 15.0 wt % manganese, from 0.3 wt % to 2.0 wt % scandium, with a balance apart from minor alloy elements and incidental impurities of aluminium.

Claims

1. An Al—Mn—Sc based alloy, wherein the Al—Mn—Sc based alloy consists of: 2.01 wt % to 15.0 wt % manganese, 0.3 wt % to 2.0 wt % scandium, 0 wt % up to 6.0 wt % magnesium, 0 wt % up to 4.0 wt % zirconium, optionally at least one other alloying element selected from the group consisting of silicon, zinc, magnesium, copper, nickel, cobalt, silver, chromium, lithium, vanadium, titanium, calcium, tantalum, zirconium, hafnium, yttrium, erbium, and combinations thereof, the at least one other alloying element, if present, is in an amount of less than 4 wt % individually and 15 wt % in total, and a balance, apart from incidental impurities, of aluminum, wherein the Al—Mn—Sc alloy has been subjected to a rapid solidification process.

2. The Al—Mn—Sc based alloy of claim 1, wherein the Al—Mn—Sc alloy includes the at least one other alloying element.

3. The Al—Mn—Sc based alloy of claim 2, wherein the Al—Mn—Sc alloy contains at least one of magnesium and zirconium at up to the respective limit of 6.0 wt % magnesium and 4.0 wt % zirconium.

4. The Al—Mn—Sc based alloy of claim 1, wherein the manganese level is from 2.5 wt % to 8 wt %.

5. The Al—Mn—Sc based alloy of claim 4, wherein the manganese level is between 3 wt % and 5 wt %.

6. The Al—Mn—Sc based alloy of claim 1, wherein the scandium level is from 0.4 wt % and 1.5 wt %.

7. The Al—Mn—Sc based alloy of claim 6, wherein the scandium level is from 0.6 wt % to 1.2 wt %.

8. The Al—Mn—Sc based alloy of claim 1, wherein the Al—Mn—Sc alloy is in the form of a grade of powder suitable for use in manufacturing components by an additive manufacturing process.

9. The Al—Mn—Sc-based alloy of claim 1, wherein the rapid solidification process comprises cooling the Al—Mn—Sc-based alloy at a cooling rate in excess of 100 K/s.

10. The Al—Mn—Sc based alloy of claim 1, wherein the Al—Mn—Sc alloy includes zirconium in an amount of from 0.18 wt % to less than 4 wt %.

11. A method for producing a component of an aluminum based alloy, wherein the method uses an additive manufacturing (AM) or other rapid solidification process to produce a component by melting and then rapidly solidifying the aluminum based alloy, and wherein the aluminum based alloy comprises the Al—Mn—Sc based alloy of claim 1.

12. The method of claim 11, wherein the Al—Mn—Sc based alloy includes the at least one other alloying element.

13. The method of claim 11, wherein the component, after recovery from the AM or other rapid solidification process, is subjected to age hardening.

14. The method of claim 11, wherein the cooling rate within the additive manufacturing or other rapid solidification process achieves a supersaturated solid solution for the main elements in order to maintain the properties of the component.

15. The method of claim 14, wherein the cooling rate within the additive manufacturing or other rapid solidification process is in excess of 100 K/s.

16. The method of claim 11, further including a post-heat treatment of the component produced by the AM or other rapid solidification process, wherein the post-heat treatment comprises heating the component to a temperature range between 200° C. and 500° C. for an accumulated time of between 0.10 h and 100 h.

17. An Al—Mn—Sc based component produced by the method of claim 11.

18. An Al—Mn—Sc based alloy, wherein the Al—Mn—Sc based alloy consists of: 2.01 wt % to 15.0 wt % manganese, 0.3 wt % to 2.0 wt % scandium, 0 wt % up to 6.0 wt % magnesium, 0 wt % up to 4.0 wt % zirconium, optionally at least one other alloying element selected from the group consisting of silicon, zinc, magnesium, copper, nickel, cobalt, silver, chromium, lithium, vanadium, titanium, calcium, tantalum, zirconium, hafnium, yttrium, erbium, and combinations thereof, the at least one other alloying element, if present, is in an amount of less than 4 wt % individually and 15 wt % in total, and a balance, apart from incidental impurities, of aluminum, wherein the Al—Mn—Sc alloy is free of precipitates containing manganese or scandium.

19. The Al—Mn—Sc based alloy of claim 18, wherein the Al—Mn—Sc alloy includes zirconium in an amount of from 0.18 wt % to less than 4 wt %.

Description

GENERAL DESCRIPTION OF THE FIGURES

(1) The performance of the samples of the first and second Al—Mn—Sc based alloys produced in the Example 1 is illustrated in the accompanying FIGS. 1 and 2, while performance in accordance with Example 2 is shown in FIGS. 3 and 4. In the Figures:

(2) FIG. 1 is a BSE image showing hardness indentations in a sample of the second Al—Mn—Sc based alloy;

(3) FIG. 2 provides a plot showing the development of hardness with ageing time for each of the first and second Al—Mn—Sc based alloys;

(4) FIG. 3 is a schematic illustration of tensile sample geometries, in accord with ASTM E8M; and

(5) FIG. 4 shows engineering stress/strain curves of non-heat treated samples, as produced by SLM fabrication, and of heat treated samples.

DETAILED DESCRIPTION OF THE FIGURES

(6) FIG. 1 shows the cut surface, of a sample of the second Al—Mn—Sc based alloy, as revealed by metallographic preparation in a backscattered electron micrograph (BSE) image. The lower zone of the image shows the microstructure of the casting of the second alloy, while the upper zone shows the microstructure of the rapidly solidified melt pool produced by remelting of the alloy by laser scanning. As shown, the hardness measurements were taken in the upper, remelted zone. FIG. 1 shows clearly that the upper zone resulting from the laser remelted melt pool is different compared with the initial cast zone, as no white needle or rod shaped primary Al.sub.6Mn or Al.sub.3Sc type precipitates can be observed. This makes clear that manganese and scandium have been successfully trapped within the aluminium matrix after the very fast cooling laser remelting process and a supersaturation status has been achieved.

(7) In FIG. 2, it can be seen that the Al—Mn—Sc based alloy of the invention exhibits very promising results since the hardness values have reached the range of 170-186 HV.sub.0.5. These properties are similar to high strength 7xxx series alloys, but the thermal stability is much improved as the high hardness levels were maintained even after 168 hours at 300° C. Laser processed aluminium alloys, or even casting alloys, cannot commonly achieve such properties, especially compared with those current widely used aluminium alloys for AM technologies. Normal age hardening Al alloys begin to over-age and soften within some minutes of exposure at 300° C. Also, indications are that the results shown by the Examples of the invention can be further improved by even higher cooling rate and other advantages of the AM process. In summary, the Al—Mn—Sc based alloys of the invention show very promising properties and a high potential for application in a wide range of structural, industrial, engineering, aerospace and transportation components made by the AM process, or by other rapid solidification manufacturing processes.

(8) FIG. 3 shows appropriately produced tensile samples from which the stress/strain curves of FIG. 4 were derived. The yield strength of 427 MPa for the as fabricated (non-heat treated) samples itself is excellent, although the markedly enhanced yield strength of 577 MPa for the heat treated samples highlights the potential for the alloys of the present invention. In contrast, the most favourable yield strength quoted for heat treated SCALMALLOY® is believed to be in the range of 459 to 479 MPa (see www.citim.de/en/metal-additive-manufacturing).

(9) Examples 1 and 2, and the results illustrated by FIGS. 1 to 4, highlight a number of important matters relating to the alloy of the present invention. The alloy benefits from the slow diffusion rates referred to earlier herein for both scandium and manganese, as well as certain other added elements such as zirconium. These slow rates facilitate the ability of the alloy after high cooling rates with thermal cycling to undergo precipitation hardening by precipitation of thermally stable nano-sized precipitates or dispersoids. With manganese this is possible from the lower effective limit of 2.01 wt %, up to the relatively high upper limit of 15.0 wt %, without undesirable precipitate coarsening, such as can tend to occur at levels of manganese addition above 15 wt %.

(10) The alloy also is characterised by enhanced property development achievable on the basis of a simple heat treatment, without a requirement for solution treatment as in the complex heat treatment regimes required for some other precipitation hardenable aluminium alloys. The simple heat treatment, which preferably involves only a single stage operation, effectively doubles as a stress relieving step and precipitation hardening heat treatment. In the case of the use of an AM rapid solidification process, such as one based on SLM, the heat treatment can be conducted before or after a resultant component manufactured by the process is cut from the build platform on which it is built up.

(11) While the alloy of the invention is well suited for use in an AM process such as SLM and other rapid solidification processes, Example 1 and FIGS. 1 and 2 show the suitability of the alloy for use in an alternative rapid solidification process. Specifically, with a component made by a subtractive manufacturing process, such as any of a range of casting processes, the component can be scanned by an energy source such as a laser or electron beam to achieve melting of a scanned region of the surface of the component, with the body of the component then providing a heat sink giving rise to rapid solidification to enhance the properties of the alloy of the scanned surface region. This includes surface treatments such as laser cladding or repair of components using the Al—Mn—Sc based alloy of the invention as part of the component and/or deposited surface materials.

REFERENCES

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