Preparation And Properties Of Carbon Nanotubes Reinforced Aluminum Matrix Composites By Ultrasonic Welding

6061 aluminum matrix composites reinforced with Multi-walled carbon nanotubes (CNTs) were fabricated successfully by ultrasonic welding technique and there is a good welding interface. The purification of CNTs, ultrasonic welding performance of 6061 aluminum alloy, interface reaction between carbon and aluminum matrix, effects of technological parameters on the mechanical properties and microstructure of composites were deeply studied and analyzed. Preparation technology of composites were assessed, mechanical properties of composites were tested and composites microstructure were observed by optical microscope, scanning electron microscopy, transmission electron microscopy, high resolution electron microscopy, X-ray diffraction, energy spectrum analysis and kinds of mechanical testing machines. The enhancement mechanisms of composites were discussed.It is easier to obtain composites well formed in the welding time 120ms, the welding pressure 17.5MPa and CNTs spraying to aluminum matrix, meanwhile the welding interface is smooth. Flamentous form of CNTs distributed in the composites and dispersed relatively uniform, which almost no reunion phenomenon and there are lots of CNTs around welding, meanwhile CNTs content in relatively reduced away from the position of welding. Its largest peeling force achieve to 195.346N and improve 44%, its tensile shear force is greater than 867.652N and improve 94%, its hardness is up to 73.2HV and improve 78% when compared with that of matrix material.In the constant welding pressure, mechanical properties of composites increase along with the increase of welding time. When the welding time reaching 120ms, peeling strength and tensile shear strength of composites achieve to optimal, but the welding time continue to increase, which will decline, while the hardness of composites will increase. When the welding time is more than 140ms, aluminum matrix will stick on the anvil. In the constant welding time, mechanical properties of composites improve with the increase of welding pressure. When the welding pressure reaching 17.5MPa, mechanical properties of composites also achieve to prominent. When the welding pressure exceeds 21MPa, composites will be crushed by the sonotrode. We found that the hardness of composites increase from surface to welding joint in turn, which the side near sonotrode is higher than near anvil.CNTs in aluminum matrix composites are stable, there is a good bonding interface between CNTs and aluminum matrix where there are no Al4C3 and other impurities phase in. The interface is smooth and there exists the phenomenon of dislocation tangles around some of CNTs. Enhancement mechanisms of composites is mainly dislocation strengthening and second phase strengthening. In addition, fine-grain strengthening has some effects on composite strength improved.