Materials Science & Engineering A 778 (2020) 139124 Available online 19 February 2020 0921-5093/© 2020 Elsevier B.V. All rights reserved. Comparison of AlSi7Mg0.6 alloy obtained by selective laser melting and investment casting processes: Microstructure and mechanical properties in as-built/as-cast and heat-treated conditions Juan Carlos Pereira a, * , Emma Gil a , Leire Solaberrieta a , María San Sebasti� an a , Yoana Bilbao b , Pedro Pablo Rodríguez b a LORTEK, Arranomendia Kalea 4A, 20240, Ordizia, Gipuzkoa, Spain b EIPC Research Center, AIE, Torrekua 3, 20600, Eibar, Gipuzkoa, Spain A R T I C L E INFO Keywords: AlSi7Mg0.6 alloy Selective laser melting Investment casting Heat treatment Mechanical properties ABSTRACT AlSi7Mg0.6 alloy is widely used in the automotive and aeronautical industries, and metal additive manufacturing (AM) is a breakthrough technology that motivates foundry companies to explore its potential in these industries; however, there is no deep knowledge of the mechanical properties and their relationship to microstructure in parts obtained by selective laser melting (SLM), as there is for parts obtained by casting. In this work, a com- parison of the microstructure and mechanical properties of AlSi7Mg0.6 alloy obtained by SLM and investment casting processes was made. The mechanical properties of tensile specimens processed by both technologies were evaluated by uniaxial tensile tests and microhardness measurements in as-built/as-cast and heat-treated condi- tions with different build orientations in the case of SLM. An advanced characterization of the microstructure by feld emission scanning electron microscopy (FESEM) and x-ray diffraction (XRD) analysis was also performed. After analyzing the microstructure and mechanical properties obtained with different heat treatments, the strengthening mechanisms of the two processes were identifed. It is possible to obtain improved mechanical properties with SLM processing, exceeding the typical values required for aeronautical parts obtained in in- vestment casting heat-treated (T6), and the ductility is satisfactory. Direct aging after SLM processing can effectively strengthen the AlSi7Mg0.6 alloy and is the more effective way to improve the as-built mechanical properties. 1. Introduction The AlSi7Mg0.6 aluminum alloy (equivalent to A357.0 cast aluminum alloy) is widely used in the automotive and aeronautical in- dustries due to its good weight/resistance ratio, and it can be thermally treated to achieve greater strength, which makes it ideal for the manu- facture of various components such as supports, housings, brackets, panels, actuators, etc. The manufacturing route for A357.0 parts has traditionally been multiple types of casting followed by heat treatment and fnal machining if necessary; SLM could be a good alternative and viable option for this route. Investment casting is a metal casting process. The process uses wax as a material for the pattern. These patterns are subsequently coated with a ceramic shell in the form of an investiture to generate a non- permanent mold with an upper opening through which the wax is frst removed and whose inner hollow serves as a mold or metal container, which, through metal casting, allows faithful copies of the original model to be made. The investment casting process has the following advantages: 1) narrow tolerances and good dimensional accuracy; 2) good surface fnish, better, in general, than traditional casting methods; 3) ability to obtain complex geometries and thin wall thickness (around 1 mm); and 4) design fexibility. Both large and small pieces can be cast, although, of course, within limits. Among the limitations of the process, it is worth highlighting the following: 1) limitation in terms of size and weight of the parts, and 2) limitation in terms of mechanical charac- teristics, since the molten metal is cast into a preheated mold. This factor has an important counterpart, which is that the cooling process is slow, which generates large grain structures and, therefore, mechanical properties (especially elongation) are worse than in other processes, requiring a specifc heat treatment to improve mechanical properties. * Corresponding author. E-mail address: jcpereira@lortek.es (J.C. Pereira). Contents lists available at ScienceDirect Materials Science & Engineering A journal homepage: http://www.elsevier.com/locate/msea https://doi.org/10.1016/j.msea.2020.139124 Received 19 November 2019; Received in revised form 15 February 2020; Accepted 17 February 2020