Enhancing microstructure and mechanical properties of laser powder bed fusion-fabricated AlSi10Mg alloy through tailored friction stir processing and post-heat treatment

Abstract

In this study, a series of advanced processing techniques is employed to control the internal structure and improve the mechanical properties of AlSi10Mg alloy fabricated via laser powder bed fusion (L-PBF). In the L-PBF, AlSi10Mg sheets are subjected to friction stir processing (FSP) under low heat input conditions. The main objective of this study is to eliminate microstructural defects and refine the microstructure while maintaining a high tensile strength. FSP effectively refines the grain structure but decreases the strength significantly owing to the thermal cycle. Various post-heat treatment strategies have been proposed to optimize the microstructure and strength of AlSi10Mg alloys as well as to address the strength reduction issue. Samples in different processing stages are characterized using optical microscopy (OM), field-emission scanning electron microscopy (FE-SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), as well as tensile and hardness tests. Notably, the FSP + direct aging (FSP + DA) treatment significantly enhanced both the ultimate tensile strength (UTS) and yield strength (YS) without compromising the ductility achieved after FSP. By applying the strengthening model, the YS contributions of the main strengthening mechanisms in the Al matrix and Si phase at different processing stages are quantitatively analyzed. The estimated YS values are in good agreement with the experimentally measured values.