The Tensile And Creep Properties Of Pure Al Matrix Composites Reinforced By The Nano-SiCp/TiCp Particles

Due to excellent mechanical properties, easy processing and the demand for thelightweight materials, the nano-particles reinforced aluminum matrix composites hadattracted much attention and were widely used in industrial production. But there were manyproblems about how to prepare the nano-particles reinforced aluminum matrix compositesand have no unified conclusion for strengthening mechanism of nano-particle reinforcedaluminum matrix composites. So it is very important to study the reinforcement mechanismof nano-particles reinforced pure aluminium matrix composite and provide advices how toprepare the nano-particles reinforced aluminum matrix composites.In this thesis, the nano-sized SiC/TiC particles reinforced aluminum matrix compositeswere fabricated by the method of intermediate alloy dissolved in aluminum melt andhigh-energy ultrasonic stirring dispersed. By this way, the dispersion problem of nanoparticles was solved better and the nano-sized SiC/TiC particles reinforced aluminum matrixcomposites have good mechanical properties at room and high temperature andmicrostructure. Therefore, the nano-sized SiC/TiC particles how to impact on the mechanicalproperties and microstructure of particles reinforced aluminum matrix composites and thestrengthening mechanism of composite materials were discussed. The main results arefollows:(1) It was found that the addition of nano-sized SiC/TiC particles makes the α-Aldendrite refined obviously and α-Al dendrite morphology also changed significant.The size of the α-Al dendrite is220-310m in the pure aluminum. The averagesize of the α-Al dendrite is refined to90m in7vol.%nano-sized SiCp/Alcomposites and the average size of the α-Al dendrite is refined to75m in5vol.% nano-TiCp/Al composites. There are some reasons for the α-Al dendrite refinement.Some nano-sized SiC/TiC particles play the role of heterogeneous nucleation andrefine the size of α-Al dendrite. The other nano-sized SiC/TiC particles werepassed to the solid and liquid phase front in the process of solidification and refinethe size of α-Al dendrite.(2) It was found that the addition of nano-SiC/TiC particles improve the mechanicalproperties of particles reinforced aluminum matrix composites at roomtemperature significantly and the elongation of nano-sized SiCp/Al、TiCp/Alcomposites is gradually decline with the content increased of nano-SiC/TiCparticles. The yield strength and tensile strength of7vol.%SiCp/Al and5vol.%TiCp/Al composites at room temperature are101MPa,169MPa and83MPa,175MPa, compared with the pure aluminium (37mpa and66mpa) increased by172%,156%and124%,156%respectively.(3) It was found that the addition of nano-SiC/TiC particles improve the mechanicalproperties of particles reinforced aluminum matrix composites at high temperaturesignificantly. The tensile strength and yield strength of7vol.%SiCp/Al and5vol.%TiCp/Al composite materials under180oC are115MPa,96MPa and121MPa,77MPa, compared with the pure aluminium (36MPa,18MPa) increasedby220%,400%and236%,400%respectively.(4) It was found that the addition of nano-SiC/TiC particles improve the creepresistance of the pure aluminum and the creep resistance of nano-sized SiCp/Al、TiCp/Al composites improved with the increased content of nano-SiC/TiC. Whenthe temperature and the applied stress are180oC and30MPa, the apparentactivation energy and stress exponent of pure aluminum,3vol.%SiCp/Al and3vol.%TiCp/Al are4.60and136.8,6.02and148.8,5.33and143.6. This revealsthat the creep mechanism of nano-SiC/TiC particles reinforced aluminum matrixcomposites mainly are controlled by dislocation climbing and the nano particles.(5) It was found that the fine grain strengthening, Orowan strengthening and thermalmismatch strengthening are all effectively strengthening mechanism for nano SiCp/Al, TiCp/Al composites and the mechanical properties of particles reinforcedaluminum matrix composites are closely related to the distribution of the nanoSiC/TiC particles in pure aluminium matrix.(6) It was found that Ti coated nano-SiC particles can improve the wettability withaluminum melt and improve the distribution of nano-SiC particles in aluminummatrix. It can refine the α-Al dendrite more significantly. The α-Al dendrite size of3vol.%Ti coated nano-sized SiCp/Al reduced by6.5%compare with3vol.%SiCp/Al. The yield strength and tensile strength at room temperature increased by8.0%and3.1%respectively.