Microstructure and synergistic strengthening mechanisms of carbon nanotubes and Mg2Si nanoparticles hybrid reinforced Mg matrix composites prepared by powder thixoforming

AZ91D Mg-based composites containing carbon nanotubes (CNTs), magnesium silicide (Mg2Sip) nanoparticles, or CNTs-Mg2Sip hybrid reinforcements were synthesized via powder thixoforming using blending and pressing procedures in powder metallurgy, followed by partial remelting and thixoforming technology. The thixoformed microstructure of the CNTs-Mg2Sip hybrid reinforced Mg composite consisted of spheroidal primary α-Mg particles, intergranular secondary solidified structures (SSSs), and hybrid reinforcements homogeneously dispersed within the SSSs. A yield strength of 180 MPa was achieved in the Mg matrix composite reinforced by 0.75CNTs-0.75Mg2Sip hybrids, which was 26% and 12% higher than those of composites reinforced with individual 1.5CNTs and 1.5Mg2Sip, respectively (143 and 161 MPa, respectively). This was attributed to the in situ-synthesized Mg2Sip around the CNTs, which not only restricted the aggregation and pulling out of CNTs but also facilitated the synergistic strengthening effect of the CNTs. This work presents a promising strategy for the synthesis of metal matrix composites with impressive mechanical properties by employing hybrids of CNTs and Mg2Sip as reinforcements.