Microstructural Evolution of PBF-LB AlSi10Mg under Different Heat Treatment Conditions

Laser-based powder bed fusion (PBF-LB) of AlSi10Mg alloys faces non-equilibrium solidification, resulting in a microstructure of α-aluminum phase matrix and an interconnected, fibrous α-silicon-rich phase network. The development of heat treatment (HT) routes tailored specifically for PBF-LB parts are essential, as standardized procedures may not yield optimal results. This study investigates the effect of different HTs on the microstructural characteristics and hardness of AlSi10Mg parts. Analyses revealed that the as-built (AB) microstructure exhibited a typical cellular-dendritic solidification structure. The eutectic α-Si-rich network partially degenerated after direct aging (DA) and stress relieving (SR), while solution annealing (SA), and solution annealing + aging HT erased the solidification microstructure, producing α-Si-rich precipitates dispersed within the α-Al matrix. Columnar grains exhibited preferential epitaxial growth along {001} planes in the <001> direction, with no significant changes observed after HTs. The AB sample displayed a hardness of 122 HV, increasing up to 149 HV after DA. Conversely, SR and SA led to a hardness reduction between 61 and 77 HV. While the DA HT maintains the AB microstructural characteristics with a hardness increase, SR and SA HTs modify the solidification microstructure, reducing hardness.