Investigation On The Microstructure And Properties Of Carbon Nanotubes Reinforced Aluminum Matrix Composites

Carbon nanotubes (CNTs) reinforced aluminum matrix composites has low density, antioxidation, wear-resistance and other excellent features. At present, there are many methods of preparation composite material, such as stir-casting process, hot-press sintering, powder metallurgy and so on, but they have some limitations. Therefore, a more efficient new method for preparation of composite materials would be demanded. Friction Stir Processing (FSP) is based on the friction stir welding for the microstructural modification of materials and composite, mainly refining the microstructure. It is a kind of simple manufacturing process which have simple equipment and relatively low cost. In this paper, CNTs reinforced aluminum matrix composite was prepared by FSP. The structures and properties of the composite materials were investigated, and preliminary study on materials prepared by Rotational Extrusion Alloying (REA) was discussed. The results show that:Composite material was prepared by one stir stick. When the volume fraction of CNTs was 1.6%, it was obtained easily for a well formed and homogeneous composite material. When the content of CNTs was high, CNTs in the edge of friction stir zone and shoulder deformation zone were prone to aggregation. It was achieved difficultly for a uniform distribution on macro. When prepared by small stir stick in the first and then large stir stick, it could be obtained well formed and more easily for homogeneous composite material. and could improve aggregation phenomenon on the edge of friction stir zone. On the edge of friction stir zone, the material had undergone plastic deformation and the grains had been distorted and elongated. In the shoulder deformation zone, the grain size was similar to that of the center of friction stir zone which dominated by fine grain. TEM observation shows that CNTs are uniform distributing on the centre of friction stir zone, and embed in aluminum matrix metal. Good combination can be obtained between the CNTs and aluminum matrix.The hardness, wear-resistance and tensile strength of the material are improved by adding CNTs with the increasing of the CNTs content. When used one stir stick and the volume fraction of CNTs was 7%, the average microhardness of friction stir zone was up to 60.8HV, and the tensile strength reached to 201.44MPa; When the volume fraction of CNTs was 5.5%, the wear-resistence improved markedly. When used small stir stick in the first and then large stir stick and the volume fraction of CNTs was 5%, the average microhardness of friction stir zone was 53.8HV, and the tensile strength reached to171.06MPa, the wear-resistance improved obviously too. The main wear mechanism of composites is abrasive wear.When the volume fraction of CNTs was 1.3%-5%, the tensile strength of composite material had improved, but its plasticity lower than that of the base metal. When The volume fraction of CNTs was 5.5%-7%, the "necking" phenomenon disappeared, plasticity was poor and brittleness increased. Composite materials show brittle fracture on macro while ductile fracture on micro.The preliminary study of CNTs reinforced aluminum composite material was prepared by Rotational Extrusion Alloying. The results show that the process can prepare the block composite material and obtain free defect macroscopic cross-section forming. Microhardness is homogeneous distribution.