Effect of remelting on the thermal conductivity of graphene-modified Al-Si alloys fabricated by laser powder bed fusion

Laser powder bed fusion (LPBF) enables the fabrication of complex aluminum components for thermal management applications. Graphene-reinforced Al-Si alloys are promising candidates due to the exceptional thermal conductivity of graphene, although their effective thermal conductivity is strongly limited by graphene agglomeration and associated metallurgical defects that disrupt heat-transfer pathways. In this study, an integrated processing strategy combining ultrasonic powder mixing and laser remelting was developed to simultaneously regulate graphene dispersion and suppress defects in LPBF-fabricated AlSi7Mg alloys. Ultrasonic mixing enhanced the initial dispersion of graphene, while remelting reduced porosity, achieving a relative density exceeding 99.8%, and promoted graphene redistribution. The remelted sample exhibited a thermal conductivity of 168 W/(m·K), representing a ∼29% increase, while maintaining excellent mechanical properties with an ultimate tensile strength of 445 MPa and an elongation of 14.9%. Microstructural analysis reveals that, beyond conventional densification effects, thermal transport is governed by the coupled roles of defect suppression and graphene redistribution, which together reconstruct effective heat-transfer pathways and facilitate both electron and phonon mediated transport. A semi-empirical thermal conductivity model incorporating both porosity and graphene dispersion is established, demonstrating that graphene connectivity provides an additional governing contribution beyond porosity alone. This work establishes a generalizable process-structure-property framework linking graphene dispersion to thermal transport in LPBF-fabricated metal matrix composites.