Effect of Microstructural Evolution on Mechanical Properties and Fracture Modes of AlSi10Mg Blocks Fabricated by Selective Laser Melting after Stress Relief Annealing

Abstract

AlSi10Mg parts fabricated by selective laser melting (SLM) are frequently reported to have heterogeneous microstructures. How this affects the mechanical properties of SLM parts still requires further study. Herein, AlSi10Mg blocks with simple cuboid shape are printed and annealed at 300 °C. Their microstructure changes significantly from edge to center and from top to bottom. Low‐temperature annealing is not sufficient to eliminate structural heterogeneity. Before annealing, the Si‐rich phase is fine and mainly exists in the form of a eutectic network. The as‐printed blocks have high tensile strength, and the fracture surface exhibits a mix of transcellular pits and pores. After annealing, the network structure is completely broken or disappeared in most locations in the blocks. The Si‐rich phase is significantly coarsened and even segregated locally along the melt pool boundaries. Yield strength is reduced by 25%–47%, but elongation values are doubled. Tensile samples are fractured by an along‐the‐pool boundary fracture mode along the boundary. Micropores formed during the printing process are aggregated in the about 200 μm thick outer surface layer of the block. They also have a significant effect on the local elongation both before and after annealing.

Tensile and fatigue behaviors of additively manufactured AlSi10Mg: Effect of solutionizing and aging heat treatments

“…Due to the unique micro‐/defect‐structures of AlSi10Mg processed by L‐PBF, typical heat treatments (HT) used for wrought counterparts may not always be effective. For instance, the high cooling rates of the L‐PBF process induces cellular networks of Si‐rich inter‐dendritic regions 7,8 which can give rise to improved tensile properties compared to the artificially aged condition 9–11 …”

“…[4][5][6] Due to the unique micro-/defectstructures of AlSi10Mg processed by L-PBF, typical heat treatments (HT) used for wrought counterparts may not always be effective. For instance, the high cooling rates of the L-PBF process induces cellular networks of Si-rich inter-dendritic regions 7,8 which can give rise to improved tensile properties compared to the artificially aged condition. [9][10][11] Despite some improvements in tensile properties, the as-solidified fine dendritic microstructure may make the material more sensitive to surface notches and volumetric defects under cyclic loading.…”