Graphene nanoplates (GNPs) and carbon nanotubes (CNTs) can construct efficient thermal flux channels in composites, which is becoming one of the effective methods to improve thermal conductivity (TC) of composites. In this paper, an emerging class of GNPs&MWCNTs preform with 3D orientated structures were prepared by using electrostatic self-assembly and directional freeze-drying methods, and then fabricated the GNPs&MWCNTs reinforced AZ91D magnesium (GNPs&MWCNTs/AZ91D) composites by squeeze casting process. To ensure the well preparation of the composites, the GNPs&MWCNTs preforms need to possess enough compression strength to withstand squeezing pressure. Therefore, the effects of the electrostatic self-assembly process, directional freeze drying process and thermal reduction process on the compression strength of 3D structure GNPs&MWCNTs preforms were studied. The compression strength of GNPs&MWCNTs preforms were well improved to 98 KPa, which were used for the fabrication of AZ91D matrix composites. The TC of 0.5 wt.% (1:1) GNPs&MWCNTs/AZ91D composites reached 71.7 W/(m·K) in the freezing direction, which was 41.8% higher than that (50.6 W/(m·K)) of the AZ91D alloy. This work provides a novel method for preparing GNPs&MWCNTs/AZ91D composites with improved TCs.

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