| Carbon nano-tubes(CNTs) reinforced aluminum alloy matrix composites were fabricated by friction stir processing(FSP), The effects of rotation speed, advancing speed and passes of friction stir processing on forming quality of composites were investigated in order to determine the appropriate preparation technology. The effect of preparation technology parameters on the hardness and wear resistance of composites were investigated on this basis by means of testing the hardness and wear resistance of composites fabricated by friction stir processing, The strengthening mechanisms of composites were studied by comprehensive analyzing wear behavior and microstructure of composites via SEM and TEM. Main study results are as follows:CNTs reinforced aluminum alloy matrix composites were successfully fabricated by FSP. It is more easy to obtain well formed composites in high rotation speed(1500r/miin) and low advancing speed(30mm/min); it is also can achieve well formed composites by multiple passes FSP in case of low rotation speed or high advancing speed.Composites can be efficiently strengthen with CNTs and its hardness obviously increase. The average hardness achieves 75.3HV when rotation speed is 750r/min and advancing speed 30mm/min, which is 2.8 and 2.1 times than original substrate and FSP substrate. The hardness of composite increase with the decrease of rotation speed and advancing speed and the increase of passes of FSP, as well as the range of microhardness values decrease.With the same trend as the composites hardness strengthened by CNTs, the wear resistance of composites increase with increase with the decrease of rotation speed and advancing speed and the increase of passes of FSP; Mechanical mixture layer which is composed of broken CNTs and abrasive dust protects the fresh surface of composites from wearing and improves the wear resistance of composites, the main wear mechanism of composites is abrasive wear.ultrafine-grained microstructures are achieved in substrate and composites by FSP, the grain size is 100~300nm, CNTs are well conbined with substrate, which surfaces are coated by substrate alloy. There are some of CNTs Embedded in substrate, which play a effective role in load transfer. The distribution of CNTs in the substrate exist in the direction, Along the direction parallel to the first mixing was "point-like" distribution, along the vertical direction was "linear" distribution. The main strengthen mechanism of composites is fine grain strengthening and second phase strengthening. |
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