Microstructural origin of the anisotropic flow stress of laser powder bed fused AlSi10Mg

Abstract

The microstructural origin of anisotropy in the yield stress and ultimate tensile strength of AlSi10Mg tensile specimens produced by laser powder bed fusion (LPBF) is revealed using a combination of micropillar compression tests and microstructure-based numerical simulations. Uniaxial tensile tests demonstrate that specimens with tensile axis parallel to the build direction (vertical specimen) exhibit a higher yield stress and ultimate tensile strength than those perpendicular to the build direction (horizontal specimen). Micropillar compression experiments and a microstructure-based crystal plasticity model together confirm that the anisotropy has its origin in an elongated Al-Si cellular network (nominally 0.7 µm × 1.4 µm with long axis aligned with the build direction) within individual grains. A multiscale microstructure-based model predicts the mechanical properties of LPBF AlSi10Mg tensile specimens by accounting for the hierarchical microstructural features across length scales, which include the Al-Si network, the crystallographic grain structure, and the differences in microstructure between melt pool interiors and melt pool boundaries. The multiscale model over-estimates the yield stress, but correctly predicts the ultimate tensile strength and the anisotropy in the flow strength of tensile specimens. The model is used to computationally predict new microstructures driven by composition and processing parameters for LPBF AlSi10Mg alloys with improved mechanical properties.