Effect Of MWCNTs On Microstructure And Properties Of Reinforced Aluminum Matrix Composites

As it is known to us, the light weight aluminum matrix composite material possesses high strength, good corrosion, good wear-resistance and fatigue durability, along with well dimensional stability. However, with the development of various industries such as aerospace, transportation, construction, electric transporting, machine manufacturing and sports equipment, conventional aluminum matrix composites no longer can meet their industrial demands. However, CNTs own extraordinary mechanical, thermal and electrical properties for their special structure, which hopefully render them an ideal reinforcement for aluminum matrix composites.In this thesis, we used to take high purity aluminum powders and 2024Al alloy powders as matrixes respectively, and utilizing different characteristics multi-walled carbon nanotubes （MWCNTs） which are L-MWCNTs, Ni-MWCNTs and S-MWCNTs as reinforced phases. The MWCNTs reinforced aluminium matrix composite powders were acquired by high energy ball milling. After cold pressing, vacuum sintering and hot extrusion the MWCNTs reinforced aluminium matrix composites were successfully prepared. The effect on microstructure and mechanical properties of different characteristics of MWCNTs/Al matrix composites and MWCNTs/2024Al matrix composites were studied by using scanning electron microscope（SEM）, transmission electron microscope（TEM）, X-Ray Diffraction （XRD）, Raman spectrum, microhardness tester and electronic universal testing machine. The results were as followed:A good dispersion of MWCNTs in the matrix was attained by high energy ball milling. Among the MWCNTs/Al matrix composites, the dispersion of the Ni-MWCNTs/Al matrix composites were best, the S-MWCNTs/Al matrix composites were minor, and the L-MWCNTs/Al matrix composites owns a poor dispersion due to the agglomeration of MWCNTs. Ni-MWCNTs/Al matrix composites present the best density of 99.2%, it was the best mechanical properties, the microhardness and tensile strength were 85.3HV and 247MPa respectively, which achieve great enhancement compared to pure aluminum. As for the MWCNTs/2024Al matrix composites, S-MWCNTs were relatively easy to uniformly disperse in the matrix and combine with the interface of matrix, which lead to the best microhardness （78.5 HV）, tensile strength （389 MPa） and elongation （7.2%）. By contrast, Ni-MWCNTs were poorly disperse in the matrix and badly combine with the interface of matrix, which lead to the bad performance of MWCNTs/2024Al matrix composites.MWCNTs were able to relatively well disperse in the aluminum matrix via the high energy ball milling. Meanwhile, part of damaged MWCNTs locally reacted with the matrix and form Al₄C₃ during sintering and hot extrusion. The formation of Al₄C₃ in the interface between MWCNTs and aluminum were further confirmed by high resolution transmission electron microscope（HRTEM）. After analyzing the experimental procedure, the morphology of Al4C3, along with the strength mechanism of Al4C3, we concluded that:Al₄C₃ were produced by the reaction of damaged MWCNTs and aluminum matrix, and proper amount of Al₄C₃ would increase strength of composites, but too much Al₄C₃ degrade the performance of the composites.