Achieving ultra-high strength and good ductility in AZ61 alloy composites containing hybrid micron SiC and carbon nanotubes reinforcements

In this work, the multi-scaled micron SiC and carbon nanotubes (CNTs) reinforced AZ61 matrix composites were successfully fabricated by powder metallurgy method followed by hot extrusion. The CNTs were adsorbed onto the surface of the micron SiC particles through hydrogen bonding caused by the groups functionalized on the surface of SiC particles (hydroxyl (-OH)) and CNTs (carboxyl (-COOH)), and then a shift speed ball milling was used to disperse the CNTs uniformly in the matrix. The microstructure characterization showed that this method could maintain the structural integrity of the CNTs, and the hybrid reinforcements could significantly refine the grain size of the matrix. In addition, the basal texture of the composites was weakened gradually as the content of the reinforcement increased. Microstructural investigation revealed that fine MgO formed by in-situ reaction between the oxygen groups and the magnesium matrix resulted in enhanced interfacial bonding. The ultra-high strength and good ductility (ultimate tensile strength: 412 MPa, yield strength: 345 MPa, and elongation: 8.0%) were achieved in the AZ61-5SiC-0.5CNTs composite. The significantly improved strength of the composites was mainly attributed to the synergistic influence of grain refinement, load transfer and increased dislocation density in the matrix due to thermal mismatch while the good ductility can mainly be attributed to the weakened basal texture. This work introduces a method of coupling a novel processing method with hybrid reinforcements approach to develop magnesium matrix composites with high strength and good ductility.