INFLUENCE OF EXTRUSION RATIO ON THE MECHANICAL BEHAVIOR OF AA6061/SIC COMPOSITES

The effect of extrusion ratio on the microstructure, mechanical properties, and fracture behavior of metal-matrix composites (MMCs) of AA6061 alloy reinforced with 10 volume percent particulate SiC with an average size of 46 gm was studied. The MMC ingots were fabricated by the stir casting method and were extruded at 450 degrees C at a ram speed of 1mm/s and at the extrusion ratios of 6:1, 12:1, and 18:1. Various techniques including metallography, density measurement, tensile testing, and SEM fractography were utilized to characterize the mechanical behavior of the MMCs. Results demonstrated that extruded composites possessed considerably lower porosity contents, higher strength, and enhanced ductility in comparison with the as-cast samples. In addition, further improvement in the mechanical properties of the extruded composites was noticed by increasing the extrusion ratio. Fractographic observations revealed that the brittle fracture behavior of the as-cast specimens was promoted by cracking of the large SiC particle clusters, whereas, the fracture surfaces of extruded composites showed extensive tear ridge formation by initiation and growth of shallow dimples around the cracked particles, which is characteristic of a ductile fracture process. This change in the fracture behavior and improvement in mechanical properties is attributed to the break up of particle clusters and diminishment of pores during the extrusion process.