Study On Properties Of Silicon Carbide Particle Reinforced Aluminum Composite

For the purpose of accurate optical instrument and electronic packaging applications, SiCp/Al composites were fabricated by pressureless infiltration. The coefficients of thermal expansion, the thermal cycling residual strain and the microyield strength are the evaluations for dimensional stability. Brinell hardness and bending strength is the evaluations for mechanical property. By using scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), dilatometer, thermal mechanical analyzer, tensile test, Brinell hardness and three-point bending tests, the microstructure and the mechanisms of its evolution were studied. The dimensional stability, thermal stress and mechanical properties were examined and their influencing factors were discussed.TEM observations indicate high-density dislocations are found in the matrices of composites, and the SiC-Al interfaces are clean and free from interfacial reaction products. The layer misfit is found inside SiC particle. The thermal stress in SiCp/Al composition is higher than that in unreinforced aluminum alloy. In composite, the thermal residual stress in the matrix is tensile stress, and that in the particle is contract stress. The thermal residual stress of composite is low in cool and thermal cycling pretreatment or with larger diameter reinforcing particle. Considering the distribution of thermal stress in composite, the biggest stress exits at the sharp angle of particle.The studies of thermal expansion and thermal cycling behavior show that CTE of composite is lower than unreinforced aluminum alloy. The dimensional stability of monochromatic temperature change is better. When the volume fraction of particle is higher or the particle diameter is larger, the CTE of composite is lower. Pretreatment has some influence on CTE of composite. The CTE of aged and cooling-heating recycled pretreatment is lower, the CTE of annealed pretreatment is higher. The residual strain of composite appears after thermal cycling, which is induced by the matrix plastic microstrain. With the cyclic number increasing, the residual strain decreases, the dimension is gradually stable. When the matrix is harder or the particle diameter is larger, the thermal cycling dimension stability is higher. The thermal residual strain of cooling-heating cycled pretreatment is the smallest, subsequent is aged pretreatment, the largest is the annealed pretreatment.The studies of microyield behavior indicated that comparing engineering yield strength, plastic mirostrain can take place at low applied stress in SiCp/Al composites. The thermal stress, dislocation structure and moveable dislocations, obstacle to dislocation motion have notable influence on microyield behavior. Thermal residual stress causes mirostrain easier to take place, and can cut down microyield strength. Proper pretreatments increase microyield strength, which reduce thermal residual stress and moveable dislocation, and produce the precipitation of the excess phase to resist dislocation motion. The microyield strength of the composite is higher than the microyield strength of unreinforced aluminum alloy. The microyield strength of aged specimens is the highest, subsequent is cooling-heating cycled specimens, the lowest is annealed specimens.With the particle diameter decreasing, the bending strengths of composites are enhanced. The bending strength of aging pretreatment is higher than annealing pretreatment. The bending strength of cooling-heating cycling pretreatment is between the former and the later. The fracture mode in SiCp/Al composites are mainly brittle fracture, but there are characteristics of ductile fracture in composites.