Microstructure And Mechanical Properties Of CNTs Reinforced 2014Al Composites Fabricated By Powder Sintering

There is increasing attention to CNTs reinforced aluminum matrix composites because of its high strength, high elastic modulus, low coefficient of thermal expansion and good lubrication characteristics, these make it become the ideal reinforced phase to composite. Traditional composite reinforced phase such as Ti C, carbon fiber, etc. due to the limitation of material itself, so the improvement on the properties of the composite materials is very limited, Therefore, study on CNTs enhanced aluminum matrix composites has a very important significance. However, it is difficult to add CNTs to aluminum matrix and the preparation process is complex, this is due to the special physical and chemical properties of CNTs. On the one hand, with a large specific surface area and high surface energy, it is easy to reunite together and difficult to disperse uniformly in the matrix. On the other hand, there is a great difference in density between CNTs and Al matrix, which leads to the poor wettability and the bad bonding property of the interface between CNTs and Al matrix, the interfacial bonding is not ideal. So, to some extent, these factors affect the overall performance of the composites. Therefore, it is very necessary to optimize a good dispersion method and the good interface bonding between CNTs and matrix. Presently, although there are many domestic and foreign scholars have made a lot of research on CNTs reinforced aluminum matrix composites and have obtained many achievements. However, there are still few research on the dispersion of CNTs in the matrix and the interfacial bonding between CNTs and matrix.In this study, the CNTs reinforced 2014 Al composite was fabricated by powder sintering, the effect of different 2014 Al powder size on the microstructure and mechanical properties of CNTs/2014 Al composites was studied, and the effect of CNTs content on the tensile properties of CNTs/2014 Al composites was studied. In addition, the effect of CNTs with different surface properties on the microstructure and mechanical properties of CNTs/2014 Al composites was revealed.The main results are as follows:(1) The CNTs/2014 Al composites prepared by powder metallurgy showed dense microstructure. During the ball milling process, the protection degree to CNTs is different with different size of 2014 Al. Large particles are more conducive to the protection of CNTs, it can reduce the damage of the steel ball to the CNTs, thus, it can improve the structural integrity of the CNTs. Particles size of 9 μm not only can protect the CNTs to a certain extent, the protection of CNTs during the ball milling process, but also can improve the dispersion of CNTs in the matrix, the fabricated composites showed a better mechanical properties.(2) With the addition of CNTs increasing from 0.3 wt.% to 0.7 wt.%, the ultimate tensile strength of CNTs/2014 Al composites firstly increased and then decreased, whereas the elongation decreased all the time. It is revealed that 0.5 wt.% CNTs/2014 Al composites showed the best tensile properties. The yield strength and ultimate tensile strength of the composites increased from 354 MPa and 517 MPa to 418 MPa and 577 MPa, respectively, and the fracture strain decreased from 13.2% to 11.9%.(3) The fabrication of CNTs reinforced 2014 Al composites with different surface properties by powder metallurgy. It was found a large amount of untreated CNTs is still aggregated on the surface of the matrix after ultrasonic dispersion; After 573K/3h treated, the surface of CNTs became smooth, which is an advantage for the CNTs on the matrix surface during the ultrasonic dispersion; The CNTs with carboxyl group treatment was uniformly distributed on the surface of the matrix, which showed a better dispersion. Furthermore, the CNTs with carboxyl group treatment is beneficial to the stress transfer between CNTs and the matrix.(4) By contrast CNTs/2014 Al tensile properties of the composites, we were found CNTs with untreated, oxidation treatment and carboxyl treatment, the tensile strength of the composites was increased by 44 MPa, 70 MPa and 100 MPa compared to the matrix. The composites fabricated by the CNTs with carboxyl treatment showed beet mechanical properties.