Unraveling the low thermal conductivity of the LPBF fabricated pure Al, AlSi12, and AlSi10Mg alloys through substrate preheating

Abstract

It is essential to employ post-build heat treatment on the laser powder bed fusion (LPBF) fabricated aluminum (Al) and Al alloys due to their thermal conductivity in the as-built condition being inferior to that of the conventionally manufactured counterparts. In this study, substrate preheating (200 °C) was proposed as a solution to achieve high thermal conductivities in the as-built condition. Pure Al, AlSi12, and AlSi10Mg samples were shown to possess up to 15 %, 25 %, and 80 % higher thermal conductivity values than their non-preheated counterparts reported in the literature. An analytical analysis contingent on calculating electron mean free path in the presence of only intrinsic or a combination of intrinsic and extrinsic scattering phenomena was introduced to justify the thermal behaviors. As per micro X-ray computed tomography, EBSD analysis, and TEM investigations, the extrinsic scattering sites were found to be (i) pores, (ii) grain boundaries, (iii) cell boundaries (Al alloys), (iv) oxides (pure Al), (v) nano-size Si precipitates (AlSi10Mg), (vi) nano-size Mg 2 Si phase (AlSi10Mg), (vii) vacancies, (viii) dislocations and (ix) Si supersaturation in α-Al phase (Al alloys). The dominant scattering site(s) was found for each material based on which the difference between the obtained thermal conductivity and its corresponding nominal value or the one reported for the non-preheated condition was unraveled. The implications of the findings in this study are essential not only for Al/Al alloys but also for other metallic materials (i.e., Cu alloys), requiring high thermal conductivity in the as-built condition.