Tensile properties and superplasticity of hot-extruded Al2O3f/A6061 composites

The effect of the hot-extrusion process on 6061 matrix composites reinforced with alumina short fibers was investigated through the study of microstructures, tensile strength and ductility of the composites before and after the hot-extrusion process. Superplastic behavior of 19 vol% Al2O3f/6061 composites extruded at 783 K at a ratio of 49 was investigated at 803 K. The results show that the grains of the composites became fine equiaxial grains and most of all the alumina fibers turned out to be directional along Extrusion direction after hot-extrusion process. The 6061 matrix composite reinforced with 19% volume fraction of alumina short fiber exhibits superplasticity at a strain rate of 7.2 x 10(-4) s(-1) at 803 K. The tensile strengths of the composites are all lower than that of the unreinforced 6061 alloy at hot-extruded state when the test temperature is lower than 533 K. However, when the volume fraction of alumina fiber exceeds a certain value (12%), the strength of the extruded composite turns to increase with increasing the volume fraction of alumina fiber. Contrarily, the tensile strength of the cast composite turns to decrease with increasing the volume fraction of alumina fiber when the volume fraction of alumina fiber exceeds a certain value (12%) at the lower test temperature than 533 K. Through the extrusion process, the plasticity of the 6061 matrix composites reinforced with alumina short fibers can be improved greatly, especially at ambient temperature.