Influence on microstructure, strength and ductility of build platform temperature during laser powder bed fusion of AlSi10Mg

AlSi10Mg manufactured by laser powder bed fusion (or selective laser melting) benefits from a very fine microstructure that imparts significant mechanical strength to the material compared to the cast alloy. The build platform temperature stands out as a significant processing parameter influencing the microstructure as it affects the cooling rate and thermal gradient during manufacturing. Setting the build platform temperature to 200 degrees C yields a negligible residual stress level. However, the strength is lower compared to that obtained using a build platform temperature of 35 degrees C, with a similar fracture strain. A detailed 3D microstructural analysis involving focused ion beam/scanning electron microscopy tomography was performed to describe the connectivity and size of the Si-rich eutectic network and link it to the strength and fracture strain. The coarser microstructure of the 200 degrees C build platform material is more prone to damage. The alpha-Al cells as well as the Si-rich precipitates present a larger size in the 200 degrees C material, the latter thus having a lower strengthening effect. The Si-rich eutectic network is also less interconnected and has a larger thickness in the 200 degrees C material. An analytical model is developed to exploit these microstructural features and predict the strength of the two materials. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.