| In this paper,the A380-0.9 wt.%Ti O2@CNTs aluminum matrix composites were studied to investigate the effects of different ultrasonic powers on the microstructure and mechanical properties of the composites.Then the composites were subjected to T6 heat treatment to study the effects of different solid solution temperatures and aging times on the microstructure of the composites and the mechanical properties of the composites before and after the T6 heat treatment,and to analyze the strengthening mechanism.Then numerical simulations were used to analyze the effects of different ultrasonic power on carbon nanotube dispersion and aluminum melt nucleation.The microstructure and mechanical properties of Ti O2-coated carbon nanotubes（Ti O2@CNTs）-reinforced A380 aluminum matrix composites prepared by high-energy ultrasonic assisted casting were investigated.The results show that ultrasonic dispersion and its induced fatigue damage can effectively promote the uniform dispersion of Ti O2@CNTs in the matrix alloy.The optimal ultrasonic power was 1.8k W,at which time the tensile strength,yield strength and microhardness of the prepared cast composites were 255 MPa,181 MPa and 121.7 HV,respectively,which increased by 33.5%,32.1%and 39.7%,respectively,compared with the A380 matrix.When Ti O2@CNTs was added,the fracture mechanism of the composites changed from brittle fracture to quasi-dissolution fracture.In addition,the composites were subjected to T6 heat treatment to investigate the effects of different solid solution temperatures and aging times on the microstructure of the composites and the mechanical properties of the composites before and after T6heat treatment.It was found that a semi-coherent interface was formed at the Ti O2/α-Al interface.Coating a layer of Ti O2 particles on the surface of CNTs was beneficial to increase the interfacial bonding between CNTs and the matrix.Solid solution treatment（515°C,2h）and aging treatment（170°C,10h）were the optimal solid solution treatment and optimal aging treatment process parameters for the A380-0.9 wt.%Ti O2@CNTs composites,respectively.The UTS（332 Mpa）,YS（247 Mpa）and EI（2.89%）of A380-0.9wt.%Ti O2@CNTs composites/T6 increased by 30.2%,36.5%and 50.5%,respectively,compared with A380-0.9wt.%Ti O2@CNTs composites.After T6 heat treatment,the precipitation of nanoscale Al2Cu can effectively inhibit the growth ofα-Al grains and hinder the movement of dislocations,which plays a significant role in improving the mechanical properties of the composites.And the fracture mechanism of the composites changed from quasi-dissociative fracture to ductile fracture with small and uniform tough nests.The excellent mechanical properties of A380-Ti O2@CNTs composites can be attributed to the synergistic effects of fine grain strengthening,thermal mismatch strengthening,Orowan strengthening and direct load bearing strengthening.Based on the population equilibrium model（PBM）,the nucleation,growth,aggregation and fragmentation of grains are combined with macroscopic grain size properties to analyze the effect law of different ultrasonic power on carbon nanotube dispersion and aluminum melt nucleation,and the results show that increasing the power of ultrasonic waves can increase the velocity of fluid flow and the region of strong flow increases.However,when the ultrasonic power is too high,the area of strong liquid phase flow decreases slightly instead.The ultrasonic power affects the dispersion of carbon nanotubes within the melt,and the best effect of carbon nanotube dispersion is achieved when the ultrasonic power is 1.8 k W.With the increase of ultrasonic power,the number of nucleation of aluminum melt increases,and the nucleation of aluminum melt can be promoted by the combined effect of high-energy ultrasound and carbon nanotubes enhanced phase. |
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