materials Article Short Heat Treatments for the F357 Aluminum Alloy Processed by Laser Powder Bed Fusion Matteo Vanzetti 1,2, * , Enrico Virgillito 1,2 , Alberta Aversa 1 , Diego Manfredi 1,2 , Federica Bondioli 1,3 , Mariangela Lombardi 1 and Paolo Fino 1   Citation: Vanzetti, M.; Virgillito, E.; Aversa, A.; Manfredi, D.; Bondioli, F.; Lombardi, M.; Fino, P. Short Heat Treatments for the F357 Aluminum Alloy Processed by Laser Powder Bed Fusion. Materials 2021, 14, 6157. https://doi.org/10.3390/ ma14206157 Academic Editor: Daolun Chen Received: 22 September 2021 Accepted: 14 October 2021 Published: 17 October 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Applied Science and Technology (DISAT), Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy; enrico.virgillito@polito.it (E.V.); alberta.aversa@polito.it (A.A.); diego.manfredi@polito.it (D.M.); federica.bondioli@polito.it (F.B.); mariangela.lombardi@polito.it (M.L.); paolo.fino@polito.it (P.F.) 2 Center for Sustainable Future Technologies IIT@Polito, Istituto Italiano di Tecnologia, Via Livorno 60, 10124 Torino, Italy 3 Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali (INSTM), Via G. Giusti 9, 50121 Firenze, Italy * Correspondence: matteo.vanzetti@polito.it Abstract: Conventionally processed precipitation hardening aluminum alloys are generally treated with T6 heat treatments which are time-consuming and generally optimized for conventionally processed microstructures. Alternatively, parts produced by laser powder bed fusion (L-PBF) are characterized by unique microstructures made of very fine and metastable phases. These peculiar features require specifically optimized heat treatments. This work evaluates the effects of a short T6 heat treatment on L-PBF AlSi7Mg samples. The samples underwent a solution step of 15 min at 540 ◦ C followed by water quenching and subsequently by an artificial aging at 170 ◦ C for 2–8 h. The heat treated samples were characterized from a microstructural and mechanical point of view and compared with both as-built and direct aging (DA) treated samples. The results show that a 15 min solution treatment at 540 ◦ C allows the dissolution of the very fine phases obtained during the L-PBF process; the subsequent heat treatment at 170 ◦ C for 6 h makes it possible to obtain slightly lower tensile properties compared to those of the standard T6. With respect to the DA samples, higher elongation was achieved. These results show that this heat treatment can be of great benefit for the industry. Keywords: additive manufacturing; laser powder bed fusion; aluminum; f357; heat treatments; microstructure; mechanical properties 1. Introduction Laser powder bed fusion (L-PBF) can be used to process a wide variety of metallic materials such as steel, titanium, nickel, and aluminum alloys. Aluminum alloys are very interesting for various applications owing to their relatively low cost, light weight, and high strength [1–5]. Among aluminum alloys, traditional cast Al–Si–Mg alloys are the most used and studied ones for the L-PBF technique due to their good laser processability. In particular, AlSi7Mg has attracted by far the greatest interest due to both its nearly eutectic composition that ensures a narrow solidification range and the high Si content that assures a good fluidity in the molten state. These are very important aspects in the L-PBF process as it makes it possible to reach full dense and crack-free parts [6–8]. The large interest in the AlSi7Mg alloy is proved by the large number of scientific papers available in the literature [9–16]. This alloy is also generally called A357 (AMS 4219 standard) or F357 (AMS 4289 standard) depending on the beryllium content, which is lower than 0.002% in the F357 standard. Small quantities of beryllium in the alloy change the precipitates’ shape and dimension, and it is therefore important to strictly control its content to optimize the Materials 2021, 14, 6157. https://doi.org/10.3390/ma14206157 https://www.mdpi.com/journal/materials