Dependence of mechanical properties and microstructure on solidification onset temperature for Al2024–CaB6 alloys processed using laser powder bed fusion

January 19, 2021

Philipp Mair (1), Lukas Kaserer (1), Jakob Braun (1), Janko Stajkovic (1), Christian Klein (1), David Schimback (2), Lukas Perfler (3), Evgeny Zhuravlev (4,5), Olaf Kessler (4,5), Gerhard Leichtfried (1)
Materials Science and Engineering: A, 833, January 2022. DOI: 10.1016/j.msea.2021.142552


Laser powder bed fusion; 2024 aluminum; Additive manufacturing; Selective laser melting; Alloy design; CaB6


The addition of a sufficient amount of the potent heterogeneous nucleating agent CaB6 enables the fabrication of crack-free specimens from the solidification-crack susceptible high-strength 2024 (Al–Cu–Mg) aluminum (Al) alloy using laser powder bed fusion (LPBF). The present work investigates the effects of varying addition contents of CaB6 nanoparticles (0.0–2.0 wt%) on the alloys' solidification behavior as well as the specimens’ solidification-crack volume, microstructure, and mechanical properties.The findings of X-ray microscopy (XRM) analyses on LPBF specimens and in-situ differential fast scanning calorimetry (DFSC) analyses on single powder particles at LPBF-like high heating and cooling rates reveal decreasing crack volumes with decreasing solidification supercooling. A CaB6 content of equal to or greater than 0.5 wt% effectively suppresses solidification cracking. 1.0 wt% is defined as the optimum CaB6 content in terms of mechanical properties. With this content an average grain size of 0.77 μm, an ultimate tensile strength (UTS) of 478 ± 4 MPa and an elongation (A) of 13.2 ± 0.1% are achieved. When the CaB6 content is further increased, the alloy's average grain size asymptotically approaches a minimum size of ∼0.7 μm for the given process parameters. This value corresponds to the nucleation-free zone (NFZ), within which the CaB6 nanoparticles present are not activated as nucleating agents, resulting in deposition along the grain boundaries.

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Author Affiliation

(1) Faculty of Engineering Sciences, University of Innsbruck, Department of Mechatronics, Materials Science, Technikerstrasse 13, 6020, Innsbruck, Austria.
(2) Airbus Central R&T, Airbus Defence and Space GmbH, Willy-Messerschmitt-Straße 1, 82024, Taufkirchen, Germany.
(3) Faculty of Engineering Sciences, University of Innsbruck, Department of Structural Engineering and Material Sciences, Material Technology, Technikerstrasse 13, 6020, Innsbruck, Austria.
(4) Chair of Materials Science, University of Rostock, Rostock, Germany.
(5) Competence Centre °CALOR, Department Life, Light and Matter, University of Rostock, Rostock, Germany.