On the mechanical behavior of additively manufactured AlSi10Mg processed by post heat treatment: the role of hierarchically heterogeneous microstructure

Abstract

Post heat treatment is an effeicient strategy to tailor the mechanical properties of additively manufactured AlSi10Mg alloy. In-depth understanding of microstructure evolution during heat treatment is critical for optimal microstructure design towards desired mechanical properties. In this work, AlSi10Mg alloy was prepared by laser powder bed fusion (LPBF), followed by two heat treatment routines, namely stress relief (SR) and solution treatment (ST). Microstructure characterization revealed the presence of hierarchically heterogeneous microstructure in the as-built (AB) sample, including the heterogeneous grain structure consisted of columnar grain domains and equiaxed grain bands, the non-uniform distribution of geometrically necessary dislocations (GNDs), and the subgrain cellular structure consisted of soft Al cell and hard eutectic phase network. The heterogeneities at both grain- and subgrain-level contributed to a high ultimate tensile strength and an excellent strain-hardening ability, but the presence of hard eutectic phase network resulted in an unsatisfied ductility. With SR heat treatment, the heterogeneities in the grain structure and GND distribution were slightly reduced, whereas the homogenization of subgrain structure partially occurred due to the fragmentation of eutectic phase network, leading to a moderate strain-hardening ability and a high ductility. With ST heat treatment, the heterogeneities in the grain structure and GND distribution were greatly weakened, accompanied by the elimination of cellular structure, resulting in a low strength and relatively weak strain-hardening ability. This work provides valuable insights into tuning the heat treatment routine to obtain optimal hierarchically heterogeneous microstructure and thus enhanced strength-ductility synergy for the additively manufactured AlSi10Mg alloy.