The Infiltration Microstructure And Properties Of Si/Al Composites

Si/Al composites were fabricated by pressureless infiltration. The effect ofmatrix alloy, infiltration process and Si particle size on the infiltration microstructureof Si/Al composites was investigated by optical microscope, SEM, EDS. Theformation mechanism of infiltration microstructure was discussed. The effect ofinfiltration microstructure on the thermal conductivity properties, thermal expansionproperties and flexural behavior was investigated. Si/Al composites were milled byNC vertical lathe bed milling machine. The effect of infiltration microstructure on themilling surface morphology and the surface roughness was investigated by SEM andHommel Roughness Tester. The effect of the milling speed n, milling depth apandadvancing speed. f on the machinability of Si/Al composites was investigated by theorthogonal experiment. The empirical equations of mill force were obtained byOrigin.The results show that the sharp corner of the Si particles in the Si/Al compositeswith three kinds of aluminum alloy as matrix were all disappeared. With theincreasing of Si content among matrix alloys, the interspace between Si particlesdecreases, the size of Si particle increases, the number of Si particle connected witheach other increases, the three-dimensional network structure was more likely to beformed between Si particles. With the increasing of infiltration temperature, Siparticle of Si/Al composites evolved from the separation state to the adhesion state,and then to the three-dimensional network structure. With the increasing of infiltrationtime, Si particle of Si/Al composites evolved from the separation state to the adhesionstate, and then to the three-dimensional network structure.The primary Si phase which separates out from aluminum alloy liquid above theeutectic temperature nucleates and grows attaching to the reinforcement Si particles’surface in the cooling course after the end of infiltration. And does the eutectic Siphase which separates out from the eutectic reaction at the eutectic temperature. Theseare similar to the separate-eutectic phenomenon.With the increasing of Si content among matrix alloys, the thermal conductivityand the coefficient of thermal expansion of Si/Al composite decrease, while thebending strength increases. With the increasing of the size of Si particles, the thermalconductivity and the coefficient of thermal expansion of Si/Al composite increase,while the bending strength decreases. With the Si particle of Si/Al composites evolved from the separation state to the adhesion state, and then to the three-dimensionalnetwork structure, the thermal conductivity, the coefficient of thermal expansion andthe bending strength of Si/Al composite decrease.With the Si particle of Si/Al composites evolved from the separation state to theadhesion state, and then to the three-dimensional network structure, the cutting forceand the roughness of milling surface of Si/Al composites increase. The main typicalof the milling surface of Si/Al composites are: the leaving pits because of thebreakage or dropping of Si particles, the coating of matrix aluminum alloy, Siparticles being pressed into the matrix aluminum alloy, Si particles being cutsecondary.The effect of cutting parameters on the machinability of Si/Al composites wasinvestigated by orthogonal experiments. The empirical equations of mill force wereobtained.