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3D printing of high-strength aluminium alloys

Abstract

Metal-based additive manufacturing, or three-dimensional (3D) printing, is a potentially disruptive technology across multiple industries, including the aerospace, biomedical and automotive industries. Building up metal components layer by layer increases design freedom and manufacturing flexibility, thereby enabling complex geometries, increased product customization and shorter time to market, while eliminating traditional economy-of-scale constraints. However, currently only a few alloys, the most relevant being AlSi10Mg, TiAl6V4, CoCr and Inconel 718, can be reliably printed1,2; the vast majority of the more than 5,500 alloys in use today cannot be additively manufactured because the melting and solidification dynamics during the printing process lead to intolerable microstructures with large columnar grains and periodic cracks3,4,5. Here we demonstrate that these issues can be resolved by introducing nanoparticles of nucleants that control solidification during additive manufacturing. We selected the nucleants on the basis of crystallographic information and assembled them onto 7075 and 6061 series aluminium alloy powders. After functionalization with the nucleants, we found that these high-strength aluminium alloys, which were previously incompatible with additive manufacturing, could be processed successfully using selective laser melting. Crack-free, equiaxed (that is, with grains roughly equal in length, width and height), fine-grained microstructures were achieved, resulting in material strengths comparable to that of wrought material. Our approach to metal-based additive manufacturing is applicable to a wide range of alloys and can be implemented using a range of additive machines. It thus provides a foundation for broad industrial applicability, including where electron-beam melting or directed-energy-deposition techniques are used instead of selective laser melting, and will enable additive manufacturing of other alloy systems, such as non-weldable nickel superalloys and intermetallics. Furthermore, this technology could be used in conventional processing such as in joining, casting and injection moulding, in which solidification cracking and hot tearing are also common issues.

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Figure 1: Additive manufacturing of metal alloys via selective laser melting.
Figure 2: Nanoparticle assembly on additive metal feedstock.
Figure 3: Solidification behaviour of additive aluminium alloys.
Figure 4: Mechanical testing of 3D-printed aluminium alloys.

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Acknowledgements

We acknowledge financial support by HRL Laboratories, LLC, and thank D. Martin for her artistic contribution to the figures, as well as B. Carter of HRL Laboratories, LLC, X. Li of the University of California, Los Angeles, and K. Hemker of John Hopkins University for discussions.

Author information

Authors and Affiliations

Authors

Contributions

J.H.M., B.D.Y., J.M.H., T.A.S. and T.M.P. analysed the results and wrote the manuscript. J.H.M., B.D.Y. and T.A.S. designed the experiments. B.D.Y. and J.A.M. functionalized the feedstock material and operated the Concept Laser M2. J.H.M., B.D.Y. and J.A.M. prepared the metallurgical specimens and performed the optical and electron microscopy and the mechanical testing.

Corresponding author

Correspondence to John H. Martin.

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The authors declare no competing financial interests.

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Reviewer Information Nature thanks P. Collins, I. Todd and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Figure 1 SEM image of aluminium alloy 7075 powder.

Extended Data Figure 2 As-printed Al7075 parts for tensile testing and microstructure evaluation.

a, Stock Al7075. b, Al7075 + Zr.

Extended Data Figure 3 Ageing behaviour of additive Al7075.

Extended Data Figure 4 Stress–strain curves for the materials tested in this study, indicating high repeatability in the Al7075 + Zr material.

The colour indicates the material type, with curves of the same colour indicating replicate samples.

Extended Data Figure 5 Scheil solidification curves for aluminium alloys AlSi10Mg, Al7075 and Al6061.

The curve for Al6061 is from ref. 28.

Extended Data Figure 6 Micrographs of etched Al6061, processed as received.

Large cracks are observed in the absence of Zr (left). With the addition of Zr nanoparticles, no cracking is observed, but there is some residual porosity (right). Rows indicate increasing magnification.

Extended Data Figure 7 Micrographs of etched Al7075, processed as received.

Large networks of cracks are observed in the absence of Zr (left). With the addition of Zr nanoparticles, no cracking is observed, but there is some residual porosity (right). Rows indicate increasing magnification.

Extended Data Figure 8 EBSD inverse pole figure of 3D-printed stock 7075 indicating large networks of columnar cracking.

Build direction is vertical to the page.

Extended Data Table 1 Specifications of the Concept Laser M2 selective laser melting system

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Martin, J., Yahata, B., Hundley, J. et al. 3D printing of high-strength aluminium alloys. Nature 549, 365–369 (2017). https://doi.org/10.1038/nature23894

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