INFLUENCE OF SIC PARTICLE-VOLUME FRACTION ON THE COMPRESSIVE BEHAVIOROF PARTIALLY REMELTED AL-SI-BASED COMPOSITES

Al-7%Si-0.3%Mg (A356) matrix composites containing 10, 20 and 30 vol.% of SiC particles were fabricated by the compocasting technique follow ed by rapid reheating up to the liquid state, casting and solidificati on under pressure. The obtained composite ingots were then extruded at 480-degrees-C with an extrusion ratio of 9:1. Specimens obtained from the extruded bars were subjected, after a globularization treatment, to semisolid state filtration to produce samples with various volume f ractions of the liquid phase. These samples were thereafter deformed i n uniaxial compression in the semisolid state at different constant st rain rates ranging from 2.4 x 10(-3) to 3.0 x 10(-1) s-1. The influenc e of the parameters characterizing the volume fractions of the liquid phase and the particles for different strain rates was investigated. A rheological analysis shows that the partially remelted composites beh ave as non-newtonian fluids, following a power-law model of the type s igma = Kepsilon(m) with m in the range 0.25-0.4. Increasing the liquid volume fraction decreases strongly the compressive stress, whereas th e influence of the particle volume fraction is more complex and depend s on the liquid volume fraction.