Characterization and Analysis of the Thermal Conductivity of AlSi10Mg Fabricated by Laser Powder Bed Fusion

Abstract

Laser-based powder bed fusion (L-PBF) of AlSi10Mg is used to fabricate complex, light-weight structures with high thermal conductivity. Much effort has gone into investigating the mechanical behavior of L-PBF components; however few studies investigated their thermal properties. This investigation characterizes the effect of process parameters on the relative density of AlSi10Mg components fabricated by L-PBF to understand how these parameters contribute to thermal conductivity. Exposure time, laser power, pointwise distance, and build orientation were examined. Results show that these parameters affect the effective thermal conductivity of printed parts by up to 22%. Pointwise distance had the most impact on melt pool size and on effective thermal conductivity compared with other parameters. As the pointwise distance increased, both the conductivity and the melt pool width decreased, whereas the laser power had a negligible effect on both. The effect of exposure time was mainly dependent on the pointwise distance. We show that thermal conductivity is not only related to the relative density of the samples, but the number of the melt pool boundaries in the microstructure also plays a significant role in interrupting the heat flow. A new factor which accounts for the number of melt pool boundaries per unit length in the direction of heat flow is introduced to quantify the phonon scattering associated with the microstructure evolution induced by the process parameter changes. This helps explain the variation in thermal conductivity for samples manufactured with high energy densities which had negligible difference in relative density.

Process-dependent anisotropic thermal conductivity of laser powder bed fusion AlSi10Mg: impact of microstructure and aluminum-silicon interfaces

“…This modeling combined with our TEM and SEM provides strong evidence that electron-phonon interfaces dominate the thermal properties of this alloy system. This refutes the hypothesis found in some literature that phonon scattering at grain boundaries is the dominant factor in thermal conductivity (Elkholy et al, 2022).…”

“…Notably, this literature “propose[d] that the melt pool boundaries and the relative density are the main reasons for the thermal conductivity change.” As will be subsequently shown by our co-located thermal and crystallographic maps, we find evidence that directly contradicts this paper’s hypothesis. Elkholy et al (2022) also states that these melt pool boundaries reduce heat transfer primarily through phonon scattering, while we attribute the dominant source to electron-phonon coupling at the Al-Si interfaces.…”

“…Recently, the bulk thermal conductivity of laser powder bed fusion AlSi10Mg was investigated using an apparatus based on the steady state guard hot-plate method (Elkholy et al , 2022). This literature varied energy density by holding all build variables fixed except laser scanning speed.…”

“…The existing literature has not well examined the role Al-Si interfaces play in L-PBF AlSi10Mg thermal transport. The literature has also provided contradicting explanations regarding the source of L-PBF thermal conductivity reductions at low porosities (Elkholy et al , 2022; Yang et al , 2018). Addressing these knowledge gaps, we make the first coupled thermal conductivity maps for L-PBF AlSi10Mg alloy that were matched to microstructure, and only the second to do so for any additively manufactured material.…”