MPB characteristics and Si morphologies on mechanical properties and fracture behavior of SLM AlSi10Mg

In general, melt pool boundary (MPB) characteristics and Si morphologies have strong influences on micromacroscopic plastic behavior and fracture mode. They are the main reasons for the selective laser melting (SLM) AlSi10Mg parts to exhibit anisotropic properties and low ductility. Building strategy is the important step for SLM part design and manufacturing. It can help reducing anisotropic properties of SLM AlSi10Mg parts by distributing MPBs on the load bearing face. In this work, the effects of the MPB characteristics and Si morphologies on mechanical properties and deformability of the microstructure were studied. The SLM AlSi10Mg samples built in three different orientations were tensile tested. The investigated samples had dog bone shape along different building directions such as vertical and horizontal (edge and flat), in two distinct conditions, asbuilt and as-annealed. The anisotropic mechanical properties of parts were discussed in relation to the characteristic MPBs and Si morphologies, micro-macroscopic plastic behavior and predominant fracture mechanisms. By using EOS process AlSi10Mg Flex 2.0 (EOS art.-no. 7202-0261), the mechanical properties of specimens built in different directions showed similar values. This result indicates that the building strategy applied in SLM can reduce anisotropic tensile properties in as-built specimens. However, after heat treatment, the as-annealed parts exhibited anisotropic property, i.e., the as-annealed specimens built in different directions showed significant tensile property difference. Crystal orientation mapping (IPF) and fractography results indicate that the MPB characteristics have a significant impact on the plastic deformation and fracture behavior. MPB characteristics are the main reasons for anisotropic property and low ductility of SLM AlSi10Mg parts. Meanwhile, the eutectic Si phase morphology plays a significant role in ductility of SLM AlSi10Mg parts. Under the annealing heat treatment at 270 degrees C for 1.5 h, the alloy microstructure was transformed from alpha-Al cells surrounded with fibrous Si networks to alpha-Al cells surrounded with discrete Si particles.