Preparation And Mechanical Properties Of In-situ Synthesized A356 Matrix Composites In Al-SiO₂-TiO₂ System

Particle reinforced aluminum matrix composites possess several advantages such as low density, high specific strength and good wear-resistance, high-temperature resistant, and good dimensional stability. These composites can be widely applied to aerial and aerospace industries, electronic industry, automotive industry, etc.In this paper, (Al₂O₃+Al₃Ti) particle reinforced aluminum matrix composites have been prepared by powder metallurgy and diect melt reaction methods, respectively. The solidification microstructure, reaction kinetics and factors influencing the particulate size and distribution have been investigated by modern analysis equipments such as optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometor (XRD), differential scanning calorimeter(DSC) and so on. The reaction kinetics in Al-SiO₂-TiO₂ system, particle size and distribution of the factors are discussed in the research. And pulse magnetic reaction process of composite materials is analyzed. The mechanical properties of composites are tested and the fracture behavior has been analyzed.It is indicated that the exothermic chemical reaction in Al-SiO₂-TiO₂ system can proceed in aluminum melt spontaneously. If the reactants are heated to certain temperature, the chemical reaction will be triggered. The heat released from the reaction can lead a temperature rising and accelerate the reaction. The chemical reaction can start as the temperature is 816℃, the products are generated. However, the reaction is not complete until 920℃to 950℃. The composites consists of Al₂O₃ and Al₃Ti particles for reinforcement,A356 for alloy. Pulsed magnetic field effects the size of particles during the reaction process, very small phase for 5 um, thus to improve the mechanical properties of materials.The optimum parameters of composite fabrication in Al-SiO₂-TiO₂ system are that the reaction temperature is 920℃and the reacton time is 25 minutes. The prefered adding method of (SiO₂+TiO₂) powder is to put them between aluminum ingots and heat to 920℃with aluminum directly. XRD and SEM analysis indicates that the reaction synthesized particles are Al₂O₃ and Al₃Ti. These particles are finer and well-distributed in the aluminum matrix. Pulsed magnetic field treatment during the in-situ synthesis process can increase the volume fraction of in-situ particles, and make them smaller and better distributed in the matrix.The hardness and tensile strength of (Al₂O₃+Al₃Ti)_p/Al composites are higher than those of the corresponding matrix alloy, while the elongation of the composite is lower than that of the matrix alloy. When the (SiO₂+TiO₂) addition content is 10wt%, the hardness of composites is 119 HV, 21.4% more than that of A356. The tensile strength of the composite is 287 MPa, 9.5% more than that of the matrix. The elongation of the composite is 3.7%, 11.9% less than that of A356 matrix .