Study On Microstructure And Mechanical Properties Of Carbon Nanotubes/Alumina Reinforced Magnesium Matrix Composites

Since their discovery,carbon nanotubes?CNTs?have become ideal reinforcement of composite materials by virtue of their unique structure and properties.Magnesium?Mg?matrix composites have many advantages,such as low density,high specific rigidity,high specific strength and easy recovery.Thus,they have broad application prospects in the field of aerospace,medical,electronics and so on.But there are still some defects,for example,low high-temperature strength,deficient creep resistance and poor wear resistance.Therefore,it is significant to study the preparation and properties of CNTs reinforced magnesium matrix composites.The research progress and existing problems of CNTs reinforced magnesium matrix composites were described in this paper.CNTs with homogeneous dispersion and good morphology were synthesized over three kinds of Al₂O₃ particles with Ni as catalyst through chemical vapor deposition?CVD?method.The process factors of synthesizing CNTs on alumina carrier with different grain sizes were discussed.Then magnesium matrix composites reinforced by CNTs/Al₂O₃ were fabricated by powder metallurgy and hot extrusion,followed by the analysis of microstructure and mechanical properties.The reinforcement phase with the best reinforcing effect was selected by comparing the enhanced performance.The innovation point lied in the realization of well dispersed CNTs by alumina particles in the magnesium matrix,and adopting CNTs and Al₂O₃ to jointly reinforce magnesium matrix.The catalyst precursor was prepared by deposition–precipitation process.And then,Ni/Al₂O₃ was obtained after calcination and reduction.CNTs were synthesized on 1?m,23?m and 100?m alumina particles through CVD with acetylene as carbon source and argon as carrier gas.The influences of synthesis temperature,Ni catalyst content and the ratio of reactant gas on the synthesis of CNTs were investigated.The results showed that,when the synthesis temperature was 650°C,the catalyst content was 4wt.%and the ratio of Ar to C₂H₂ is 10:1,CNTs synthesized on alumina had good morphology,complete structure,homogeneous dispersion and high degree of stability and graphitization.CNTs-Al₂O₃/Mg composites were fabricated by the powder metallurgy and hot extrusion processes,using the CNTs/Al₂O₃ in situ composite structure with three different particle sizes of alumina particles,followed by the analysis of microstructure and properties.The results showed that the density of the CNTs/?1?m?Al₂O₃/Mg composites was higher than the other two and reached the highest when the reinforcement content was 4wt.%.The improvement in hardness and tensile strength was the most obvious when CNTs/?1?m?Al₂O₃ composite reinforcements were added into the magnesium matrix.The hardness of the composite was 83.8%higher than that of pure magnesium with the addition amount of 4wt.%,and the tensile strength increased by 26%compared with that of pure magnesium.CNTs/Al2O3 compound reinforcements improved the mechanical properties of magnesium matrix by the combined effects of several reinforcement mechanisms,including refined crystalline strengthening,dislocation strengthening and load strengthening.