Fabrication And Properties Of CNTs Reinforced Magnesium Matrix Composite

The methods to design and fabricate magnesium matrix composites were reviewed at first in this paper. The properties of magnesium matrix composite were summarized, then the reinforcements and matrix of magnesium matrix composite were introduced. The structure and properties of carbon nano-tubes were introduced, and the advantage of carbon nano-tubes as reinforcement was also discussed. The characteristics and applications of CNTs reinforced magnesium matrix composite were primarily summarized, and the problems of fabricating CNTs/Mg composite and the developing current of CNTs/magnesium composite was reviewed.Carbon nano-tubes and magnesium powder were mixed by ball milling, and the CNTs reinforced magnesium matrix composite was fabricated by hot pressing. In order to improve the wetting property of carbon nano-tubes with magnesium, a nickel film was coated on carbon nano-tubes by electroless plating. The mechanical and physical properties of CNTs/magnesium composite were tested, it showed that the tensile strength is 194.6MPa at room temperature, 81.4MPa at 200℃. Coefficient of heat conduction is 96.8 W/(m·K), coefficient of thermal expansion is 25.02×10-6/k between 30-50℃. The microstructure, fracture pattern and the distribution of CNTs in matrix was observed by optical microscope ,SEM and TEM.The study shows that the nickel coating of carbon nano-tubes improve the wetting properties of carbon nano-tubes with matrix. The parameters of nickel plating process is 40℃, liquor pH 4.5, 20 min. An uniform dispersion of nano-tubes in the magnesium powder surface was observed.The parameters of hot pressed sintering have been studied , and the reasonable parameter of hot pressed sintering were summarized, Content of CNTs 1.0wt%, hot pressing pressure 20 MPa, hot pressing time 20 min, hot pressing temperature 600℃. At last, The properties of composite was observed which was fabricated by oxidized powder. The study showed that the oxidating time has little influence on composite properties at room temperature, but the properties of composite falling rapidly after high temperature oxidation. We found that the blend fracture of magnesium is an inter crystalline cracking, it was inter crystalline cracking and transcrystalline fracture mixed of the composite. There are dimples in the fracture of composite either at room temperature or at high temperature, it shows that composite is ductile rupture. The composite's properties relate with compositing belt in composite. The compositing belt increased the strength of micro interface in composite. TEM study show that CNTs have good associative with magnesium. An uniform dispersion of nano-tubes was observed in magnesium matrix. At last, the strengthen mechanics of composite was studied, it shows that composite belt was formed by CNTs reinforcing magnesium matrix during the recrystallize process. The strengthen mechanics of CNTs reinforced magnesium composite include composite strength, bridging strength and refine grain strength.