On the Precipitation Hardening of Selective Laser Melted AlSi10Mg
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manufacturing (AM) techniques are under extensive investigation for their potential to replace conventional manufacturing methods in the production of complex structures. Selective laser melting (SLM) is an AM technology for the production of metal parts from powders using a high intensity infra-red laser.[1,2] Several researchers are interested in material qualification studies for Al alloys in this field,[3,4] and there are numerous studies paying special attention to the mechanical properties of parts manufactured from Al alloys by SLM such as hardness,[5,6] tensile behavior,[4,6–9] creep resistance,[4] impact energy,[6] and fatigue.[10] In most of these studies, a heat treatment has been employed with the aim of enhancing the mechanical behavior of the parts. For the AlSi10Mg alloy, the alloy of interest in this study, annealing is usually used to promote ductility, whereas it is conventionally strengthened through precipitation hardening. NESMA T. ABOULKHAIR, Ph.D Student, and NICOLA M. EVERITT, Associate Professor, are with the Materials, Mechanics and Structures Research Division, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK. Contact e-mail: emxntab@ nottingham.ac.uk CHRIS TUCK, Associate Professor, IAN ASHCROFT, Professor of Mechanics of Solids, and IAN MASKERY, Research Fellow, are with the Manufacturing and Process Technologies Research Division, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK. Manuscript submitted December 11, 2014. Article published online May 28, 2015 METALLURGICAL AND MATERIALS TRANSACTIONS A
Precipitation hardening for AlSi10Mg is divided into two steps; (1) solution heat treatment (SHT) followed by quenching and (2) artificial aging (AA) at 423 K to 453 K (150 C to 180 C).[11] Each step is conducted over duration of time, which is generally provided as a range. The durations are based on studies conducted on conventionally manufactured components from AlSi10Mg that have microstructures that are entirely different from that developed during the SLM process.[3] The duration for each step is of crucial importance to avoid underaging or overaging, which has consequent results in reducing hardness. An example of the importance of the aging process has been shown by Brandl et al.[10] where the fatigue resistance of AlSi10Mg SLM parts was enhanced following a hardening regime. However, whether Brandl et al.[10] selected the most appropriate SHT and AA durations for optimal fatigue resistance requires further investigation. Prashanth et al.[9] reported a mechanical properties dependence on the microstructure evolution of selective laser melted Al-12Si during annealing at different temperatures. Understanding the unique microstructure produced by SLM and its response to precipitation hardening (in hardenable alloys) is essential at this point. This paper shows a method of identifying the optimal heat treatment conditions; SHT and AA for AlSi10Mg for the purposes of optimizing the hardness of components manufactured using SLM. To the authors’
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