Study On Reaction Processed Al₂O₃ Particle Reinforced Aluminum Matrix Composites

Particle reinforced metal matrix composites possess several advantages such as low density,high specific strength and stiffness,good wear-resistance and thermal stability.These composites can be applied to aerial and aerospace industries, electronic industry,automotive industry,etc.According to the source difference of reinforcements,the fabrication methods of metal matrix composites can be divided into traditional and in situ ones.The advantage of the traditional method is the simple process,but the particles will be polluted easily.As the reinforcement is formed from the metal matrix,in situ composites has advantages such as fine reinforcement paticles,clean reinforcement surface,and well-bonded interface between the reinforcement and the matrix.In this paper,Al₂O₃ 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 modem analysis equipments such as optical microscope(OM),scanning electron microscope(SEM),X-ray diffractometor (XRD),differential scanning calorimeter(DSC)and so on.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 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 660℃and the products are Al₂O₃ and Si. However,the reaction is not complete until 920℃to 950℃.It is proposed that the reaction process consists of infiltration,reaction and diffusion,reaction terminal,and particle dispersion.It is shown that the size of SiO₂ powders after ball milling is much smaller,which is about 1μm.Smaller size of SiO₂ powder can improve the wettability between SiO₂ and aluminum melt and decrease the reaction temperature.The optimum parameters of composite fabrication in Al-SiO₂ system are that the reaction temperature is 850℃and the reacton time is 30 minutes.The prefered adding method of SiO₂ powders is to put them between aluminum ingots and heat to 850℃with aluminum directly.XRD and SEM analysis indicates that the reaction synthesized particles are Al₂O₃.These particles are finer and well-distributed in the aluminum matrix.Ultrasonic 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/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 addition content is 10wt%,the hardness of composites is 62.6HV,102.6%more than that of pure aluminum.The tensile strength of the composite is 112.3MPa,22.1%more than that of pure aluminum.The elongation of the composite is 10.1%,1.9%less than that of pure aluminum.