CAST-ALUMINUM ALLOYS - HARD CERAMIC PARTICLES COMPOSITE, A POTENTIAL ENGINEERING MATERIAL

Metal Matrix-Ceramic particulate composites of commercially Al(LMO) an d its eutectic silicon alloys (LM 6) containing up to 25 wt per cent p retreated ceramic particles (Silica and Zircon) were prepared by liqui d metallurgy technique. The particles size ranging from -180 to +90 mi cron were introduced in Al alloys melt followed by pouring the suspens ion into different type of metallic cavities. Quantitative metallograp hic analysis revealed that.particles were uniformly dispersed in both type of gravity die cast composites. Scanning electron microscopic exa mination of the cast fractured composites showed interfacial gap aroun d the both type of particles embedded in the metal matrices. Successfu l attempts have been also made to reduce this gap. Fractured specimen showed an interfacial mode of failure of the composites without affect ing the particles indicating a poor bonding with the matrices. The har dness of LMO metal alloyed with magnesium increased from 52 BHN to 78 BHN, whereas UTS decreased from 92 to 62 MPa as a result of addition o f 20 wt per cent silica particles. In case of LM6 silica particles com posite, the hardness almost remained constant but UTS decreased from 1 84 to 112 MPa due to addition of 20 wt percent silica particles. Compr essive strength of the composites were also decreased as a result of s econd phase particles additions. Similar trends of mechanical properti es (UTS and Hardness) were also observed due to addition of zircon in the above matrices.