Study On Microstructure And Properties Of AZ31 Magnesium Matrix Composites Reinforced By Carbon Nanotubes And Graphenes

Carbon nanotubes(CNTs),graphenes(GNPs)and their hybrid with different content were used as reinforcement filler to reinforce AZ31 magnesium alloy through powder metallurgy combined with hot extrusion techniques.The composites were characterized by optical microscope,X-ray diffractometer,energy dispersion spectrometer and scanning electron microscope.The effects of the contents of CNTs and GNPs on the microstructure,density,mechanical properties,electrical properties and wear properties of composites were discussed.The effects of the content of process control agent on the milling were studied.In order to further exert the effect of the reinforcement,the microstructure and mechanical properties of the hybrid magnesium matrix composites reinforced with(CNTs+GNPs)were investigated.Equal channel angular extrusion of the composites were tested.The main results are as follows:When the content of process control agent stearic acid was 0.3wt.%,the powder particles after ball milling were the best uniform distribution and the compressive strength,hardness,density and electrical conductivity of the matrix reached the maximum.With the increase of CNTs content,the grain size of the composites decreased first and then increased,and the strength increased first and then decreased,and the elongation and conductivity gradually decreased,and the friction coefficient and wear amount decreased gradually.When the content of CNTs was 1wt.%,the grain size decreased by 19%compared with the matrix,and the hardness and fracture strain increased by 10%and 13%,and the strength increased slightly.When the normal load in the friction is 50N,the friction coefficient and wear decreased by 15%? 39%compared with the matrix,respectively.With the increase of GNPs content,the tensile strength and hardness of the composites gradually increased,and the resistance of friction gradually increased,and the elongation,density and conductivity gradually decreased.When the content of GNPs is 0.5wt.%,the grain size in the extrusion direction decreased by 12%compared with the matrix,and the tensile strength,elongation,compressive strength and hardness of composites were 269MPa,13.8%,480MPa and 83.5HV respectively.When the normal load in the friction is 50N,the friction coefficient and wear decreased by 9%and 23%compared with the matrix,respectively.The composites reinforced with hybrid(CNTs+GNPs)reinforcement exhibited higher comprehensive mechanical properties than those reinforced with individual CNTs and GNPs.In particular,when the hybrid ratio was 1:1(CNTs and GNPs were 0.5wt%),the composites exhibited excellent synergetic coupling effect.The tensile strength,hardness and elongation of the composites were 315MPa,88.7HV and 18.5%,respectively,increased by 11%,9%and 28%compared with the matrix,and the electrical conductivity was 75%of the matrix.When the normal load in the friction is 50N,the friction coefficient and wear of the composites decreased by 10%? 27%compared with the matrix,respectively.After one-step ECAP,the grain size of the composites was obviously refined,and yield strength,the compressive strength have improved significantly,and the ductility maintained the same.When the hybrid ratio was 1:1(CNTs and GNPs were 0.5wt%),the yield strength and compressive strength of the ECAP composites were 247MPa and 507MPa,increased by 14%and 9%compared with the extrusion composites,and increased by 14%and 12%compared with the extrusion matrix.