Preparation Mechanism And Process Optimization Of High-performance Carbon Nanotubes Reinforced Magnesium Matrix Composites

Magnesium matrix composites have the advantages of high specific strength and stiffness,and have great application potential in aerospace,transportation and 3C industries.Carbon nanotubes(CNTs)are one of the ideal enhancers for magnesium matrix composites.However,CNTs reinforced magnesia-based(CNTs/Mg)composites are characterized by poor dispersion of CNTs,weak interfacial bonding and the vulnerability of CNTs to damage.Ball-milling could disperse CNTs,and nickel plating of CNTs could improve interfacial bonding,while the combination of the two methods could protect the structural integrity of CNTs.Therefore,CNTs/Mg composites were prepared by combining ball grinding with surface nickel plating.Combining with the calculation of CNTs capacity,the preparation mechanism of high-performance CNTs/Mg composites was studied and the process was optimized.CNTs/Mg composites were prepared from nickel plated CNTs and magnesium powder.The process includes three steps: refining magnesium powder by ball grinding,dispersing by ball grinding and hot pressing sintering.The composite powder and block composite were characterized by optical microscope,X-ray diffraction,scanning electron microscope and energy spectrum analysis.Bulk composites were tested for density,hardness and compression.The study focuses on the preparation mechanism and the influence of sintering process parameters and CNTs content on the structure and properties of CNTs.The results showed that during the preparation of CNTs/Mg composites,the particle size gradually decreased with the extension of ball grinding time,the morphology of magnesium particles changed from spherical to lamellar,and the hardness,compressive strength and yield strength of the composites increased significantly.This is caused by improved dispersion and grain refinement of carbon nanotubes.With the increase of sintering temperature,the grain grows gradually and the relative density increases gradually,resulting in a gradual decrease in the hardness of the composite material,a gradual decrease in the compressive strength and yield strength,and a rise and then a decline in the fracture strain.The hardness,compressive strength and yield strength of the composite decreased gradually as the grain grew with the extension of the insulation time,and the fracture strain increased first and then decreased.With the increase of CNTs content,the grain size of the composites was basically unchanged.When the content of carbon nanotubes is too high,the poor dispersion of carbon nanotubes made the relative density,hardness,compression strength and yield strength of the composites increase first and then decrease.In the range of parameters studied,the composite materials were optimized when the CNTs content was 1vol.%,the refining process of ball grinding was 225r/min for 57 h,and the sintering process was 500? for 0.5h of heat preservation.Its hardness,compressive strength and yield strength are 133 HV,517MPa and 460 MPa,respectively,which are 160%,78% and 146% higher than pure magnesium.