Investigations of the processing–structure–performance relationships of an additively manufactured AlSi10Mg alloy via directed energy deposition

In this paper, the microstructure formation mechanism of an AlSi10Mg alloy prepared by laser directed energy deposition (DED-LB) and its influence on the mechanical properties was fully studied. The relationships between the microstructure characteristic scale, the molten pool solidification/thermal cycle conditions, and the tensile mechanical properties were established by combining the numerical simulation, theoretical calculation, and experimental validation. The as-deposited microstructure consists of the columnar α-Al dendritic array growing epitaxially along the building direction with the primary dendritic arm spacing of 18 ± 4.5 µm, the dendritic arm cell of 3 ± 1 µm surrounded by the refined eutectic network, and the Si precipitation of 17.7 ± 0.8 nm dispersed in the α-Al dendritic trunk. The feature size of the primary dendritic arm spacing and the dendritic arm cell size can be well predicted using the Kurz-Fisher and KGT dendritic growth models. The formation and size evolution of the Si precipitation was well described by the non-isothermal aging KWN model for the first time. The as-DED-LB-processed AlSi10Mg alloy exhibits a good comprehensive mechanical property with a yield strength of 187 ± 1.5 MPa and elongation to fracture of 7.4 ± 0.5%. The boundary strengthening from the eutectic phase network, the load-bearing capacity for dislocations caused by refined dendritic arms, and the precipitation strengthening of nano-Si particles play a major role in the improvement of the tensile strength and hardening ability. As a result, a quantitative relationship of the processing–microstructure–performance has been systematically investigated and established, which explores a method for the precision control and large-scale application of DED-AlSi10Mg alloys.