The Preparation Of And Interface Research On Continuous Coating C_f/AZ91 Alloy Composite

Continuous C_f/Mg composite not only has properties of low density, high specific strength and specific stiffness, and high temperature resistance, but also has good damping capacities, low coefficient of thermal expansion, good dimensional stability, and high thermal conductivity. With high performance and light-weight property, it’s an ideal structure material which has wide application prospects in aviation, spaceflight, automobile, appliances, energy, transportation, and sports equipment fields. However, continuous C_f/Mg composite is not as accessible as carbon fiber has poor wettability and severe interface reaction with magnesium alloy. Besides the disadvantages of complex manufacturing technology and hard to near-net-shape limit the usage of continuous C_f/Mg composite.To solve the problem of poor wettability and severe interface reaction between carbon fiber and magnesium alloy, Sol-gel Process which controls gelation, coating, and dry sintering process is used to prepare continuous uniform smooth and non-cracking three oxidation coatings of SiO₂, TiO₂ and ZrO₂ on the surface of carbon fiber. Vacuum low pressure infiltration process is used to prepare continuous coating C_f/AZ91 composite, to study effects of different infiltration processes to the density of composite, to reveal the main process where infiltration defects of composite occur and to optimize the infiltration process. Besides, a research done which is about the microstructure, interface structure of composite and the form laws of composite interface, reveals the effects of different coating reactants to composite interface structure.The results are as follows: Carbon fiber with oxidation treatment has obvious effect on coating. The more oxygen-containing groups on the surface of carbon fiber has, the easier the coating process goes. Vacuum low pressure method can be used to prepare C_f/AZ91 magnesium matrix composites with high density and good infiltration. The density of composite increases as the pressure or temperature of infiltration or the pressure-holding time raise. While decreases as volume fraction of carbon fiber increases continuously. The key factors which influence the density of the composite are infiltration pressure and vacuum pressure infiltration. Main infiltration defects of composite are infiltration holes, shrinkage cavity, incomplete infiltration, carbon fiber reunion and uneven distribution of carbon fiber etc. Ways of increasing preheating temperature and infiltration pressure, adding pressure slowly and decreasing the speed of infiltration can be used to reduce infiltration defects and improve infiltration quality. About the surface of composite interface structure: Compared to C_f/Mg composite without coating, carbon fiber of all three coatings enhance the wettability between carbon fiber and AZ91 matrix, protect carbon fiber in infiltration, improve infiltration quality, and avoid or lower carbon fiber reacting with aluminum of alloy matrix on interface. Among those three coatings on carbon fiber, ZrO₂ coating has best effect. SiO₂ coating improve the wettabilty by reacting with magnesium matrix on interface, but on interface around carbon fiber, the reaction produces needle reactant which can’t prevent the interface reaction between carbon fiber and aluminum. TiO₂ coating improve the wettabilty by reacting with magnesium matrix on interface, but the elemental titanium being exchanged gathers around liquid-solid interface on interface and forms a barrier layer. ZrO₂ coating improve the wettabilty by reacting with magnesium matrix on interface, but the remaining ZrO₂ prevents carbon fiber reacting with aluminum on interface in form of coating. The elemental zirconium and MgO have obvious refine organization grain. Therefore, ZrO₂ coating on carbon fiber has better infiltration effect.