Laser additive manufactured high thermal conductivity Cu-GNPs/AlSi7Mg composite based on powder preparation and remelting strategy

Coated-graphene nanoplatelets (GNPs) can effectively reduce graphene agglomeration and enhance the thermal conductivity of aluminum metal matrix composites (AMMCs). Thus, laser additive manufacturing (LAM) of coated-GNPs reinforced AMMCs holds great promise for producing lightweight, high thermal conductivity, and complex thermal management structures. However, current powder preparation processes lead to graphene agglomeration, limiting thermal conductivity improvement. Moreover, laser remelting can potentially enhance metallurgical quality and thermal conductivity. Therefore, this study develops LAM-processed Cu-GNPs/AlSi7Mg composite based on optimized powder preparation and remelting strategy. Under combined ultrasonic oscillation and mechanical stirring, 0.5 wt% and 1.5 wt% Cu-GNPs/AlSi7Mg composites (containing 0.1 wt% and 0.3 wt% GNPs) were prepared using chemical Cu plating. The combined mixing ensured uniform graphene dispersion and improved powder flowability, while remelting further reduced defects and enhanced densification. The Cu-GNPs distributed along the grain boundaries promoted component supercooling, resulting in grain refinement and proportion increase of equiaxial grains. Both Cu-GNPs and remelting raised the proportion of heat-affected zones (HAZ) per unit area, where fractured Al-Si eutectic and precipitated Si resulted in lower thermal resistance. In addition, Cu-GNPs established phonon conduction pathways at boundaries, thereby improving grain boundary heat transfer efficiency. Consequently, at 25°C, the thermal conductivity of 1.5 wt% Cu-GNPs/AlSi7Mg reached 156.4 W/(m·K), representing an increase of 23.9 % over AlSi7Mg. Through the synergistic optimization of dispersion, interfacial bonding strength, and metallurgical quality, the thermal conductivity of LAM-ed AlSi7Mg and other Cu-coated GNPs-reinforced systems is effectively improved. This paper provides critical theoretical and technical foundations for engineering applications of thermal management structures.