The Research Of SiCp Reinforced Aluminum Matrix Composite Materials Preparation Process And Property

SiC particle reinforced aluminum matrix composites have a wide range of applications in the aerospace, automotive, sports equipment due to their advantages of high elastic modulus, good wear resistance, high dimensional stability, high specific strength.The preparation method of SiC particle reinforced aluminum matrix composites are mechanical mixing method, powder metallurgy, no pressure impregnation, squeeze casting, and so on. The method in this article is compocasting(the method of mechanical stirring semi-solid liquid aluminum).The method has some advantages of simple process, easy operation, low cost, easy to large-scale industrial production, etc.The current main problem of this method is the bad uniformity of the SiC particle distribution. Therefore this paper mainly studied the SiC particle pretreatment process, influencing factors of SiCp uniformly dispersing process, SiC particle reinforced aluminum matrix composites microstructure and mechanical properties, etc.Good wettability of SiC particles and aluminum liquid is necessary condition for SiC particles uniformly dispersing in the liquid aluminum. In order to improve the wettability of SiC particles and aluminum liquid, this paper introduced the pretreatment of SiC particles. Pretreatment of SiCp have two steps:cleaning, high temperature sintering. The effect of cleaning is to remove impurities on the surface of SiC particles, the mainly study of the cleaning process was the influence of the types of cleaning agents, cleaning time on cleaning effect. Results showed that the cleaning effect of the volume ratio of 1% hydrofluoric acid of SiC particles is best, and the best time of hydrofluoric acid treatment is 12 min. By high temperature sintering, SiC particle surface can form a layer of SiO2 oxide film.The presence of SiO2 is favorable to improve wettability of SiC particles and aluminum liquid. The thickness of SiO2 oxide layer was determined through quality incremental of SiC particles sintering. Explores the thickness of oxide layer by the oxidation temperature and oxidation time. Results showed that the higher oxidation temperature, the faster the oxidation; with oxidation time, oxidation rate gradually reduced, at last the oxide film thickness reached a stable value. Considering the oxidation efficiency, energy saving and equipment service life, etc., the optimal process of the high temperature was sintering 5h under 1200℃.This paper mainly studied three major factors in the preparation process of SiC particle reinforced aluminum matrix composites prepared by the mechanical agitation of semi-solid aluminum liquid:stirring temperature, stirring speed, stirring time. Stirring temperature affected the solid content in the semi-solid liquid aluminum, thus affected the friction between SiC particles and solid phase. To some extent the lower the stirring temperature, the higher solid content, the higher the friction dispersion efficiency between SiC particles and solid phase, and the smaller the volume of gas involving; but too low mixing temperature of liquid aluminum, where is not enough liquid phase for dispersion of SiC particles, results in the decrease of SiC disperse uniformity. With the increase of stirring speed, SiC particles dispersed more uniform, but too high mixing speed resulted in the involving gas of the liquid aluminum increasing dramatically. Proper stirring time is the necessary condition for SiC particles fully dispersing, too long and too short stirring time are unfavorable to the distribution of SiC particles. This article studied that the best preparation process of the uniform distribution of SiC particles in composite materials is the mixing temperature 590℃, the stirring speed 200 r/min and stirring time 2h. Also, this article explored the impact of the different ways of joining SiC particles on the uniformity of the particle dispersion. The SiC particles in situ release by the composite particle got the result of better uniformity of SiC particles in composites.The microstructure of SiC particle reinforced aluminum matrix composites is closely related to the distribution uniformity of SiC particles. SiC particles are mainly distributed on the grain boundary, limiting the growth of the primary phase a-Al, which have the effect of grain refinement. SiC particles in composites also influenced primary silicon and eutectic silicon growth and distribution. The eutectic silicon in the area where SiC particles distribute uniformly are spherical, however the eutectic silicon in the area without SiC particles are needlelike. In the aluminum substrate with high content silicon, a special "1ujube cake type" form primary silicon was formed in composites just because of the uniform distribution of SiC particles. As a result of the existence of interface reaction, the distribution of SiC particles also influenced the formation of the alloy phase in the composites. The mechanical properties of composite material are inseparable with the microstructure of composites, and also closely associated with SiC particle size distribution. The experimental results show that the best mechanical properties of composite materials:maximum tensile strength of 167 Mpa, the elongation of 3.7%. Under the influence of SiC particle distribution and microstructure, composite materials with SiC particles uniformly distributing are mainly ductile fracture, however composite materials without SiC particles uniformly distributing are brittle fracture.