Research On Fabrication And Properties Of CNTs/SiCp Magnesium Matrix Composites

CNTs/AZ91 D and SiCp/AZ91 D magnesium matrix composites were fabricated by powder metallurgy combined with hot extrusion. The composites were evaluated with optical microscope, X-ray diffractometer(XRD), energy dispersion spectrometer(EDS) and scanning electron microscope(SEM). The dispersion of CNTs in the alloy powders treated via different mixing process have been investigation. The microstructure, density and mechanical properties for AZ91 D alloy with high adding amount of CNTs and SiCp have been tested. In order to further improve the mechanical properties of composites, the hybrid magnesium matrix composites reinforced with(CNTs+SiCp) were successfully prepared. The microstructure and mechanical properties of hybrid composites were investigated.The experimental results show that: CNTs can be dispersed well in the AZ91 D alloy powders by the ultrasonic based stirring method. With the increase of CNTs content, the average grain size of sintered composites increase first and then decreases, the average grain size reached the minimum at the content of 8wt.%. However, the average grain size of the sintered composites became more finer after hot extrusion, and also the density and microhardness of the extruded composites improved dramatically. In addition, with the increase of CNTs, the tensile strength of the composites increased firstly and then decreased except for the ductility. Moreover, the elastic modulus of composites exhibits no obvious change. The tensile strength of AZ91 alloy with 5.0wt.% CNTs loading was 248.89 MPa, increased by 12.34% compared with the matrix. The tensile fracture analysis shows that the damage mechanism of CNTs/AZ91 D composites is still quasi-cleavage fracture.When the SiCp as reinforcement, the distribution of SiCp in the matrix was evidently improved after hot extrusion, and the grain size of the SiCp/AZ91 D composites became more finer. Moreover, with the increase of SiCp content, the average grain size of composites decreased obviously, however, the density and microhardness as well as elastic modulus were gradually improved. Furthermore, tensile strength increased firstly and then decreased, elongation decreased. As compared to the unreinforced matrix, the maximum tensile strength was 266.61 MPa when adding 15 wt.% SiCp, increased by 21.81%. On the whole, the damage mechanism of SiCp/AZ91 D composites is brittle fracture, and the characteristics of brittle fracture is more obvious with the increase of SiCp content.To further enhance the overall performance of AZ91 alloy, the hybrid reinforced AZ91 alloy with SiCp and CNTs were fabricated by powder metallurgy followed hot extrusion. The results show that the hybrid reinforcements with CNTs and SiCp remarkably enhances the mechanical properties of the as-extruded AZ91 composites. When the weight ratio of CNTs to SiCp was 3:7, the as-extruded hybrid composites showed excellent comprehensive properties. The tensile strength, elastic modulus and microhardness of above hybrid composite improved dramatically, compared to AZ91 alloy reinforced only by 10 wt.% CNTs or 10 wt.% SiCp.