Microstructure and properties of aluminum silicon/short fibre carbon composites fabricated by semi-solid thixomixing

Abstract

A novel method was developed, based on thixotropic nature of semi-solid slurry of aluminum silicon alloy, for the effective dispersion and distribution of short carbon fibers (Csf) under intensive shear stress (t) into the eutectic without physical or chemical damage. The Csf were distributed homogeneously into the matrix at optimum conditions: a temperature of 576–580 °C, around 48% of solid fraction, and rotation speed of mixing was at 100 rpm. The gas entrapment and porosity was a challenge in the fabrication the aluminum composite by thixomixing, and its size increased when the samples were heat treated. The extruded and heat treated composites had around 24% improvement of mechanical strength as assessed by tensile tests. The predominant deposition of silicon and its intermetallics at the interfacial region improved the wettability and adherence to achieve good mechanical properties. The formation of some intermetallics can be helpful to overcome low wettability effects and their structural evolutions were impressive. The fractography analysis illustrated the ductile fracture with some plastic deformation as the results of dimples and some fiber pull-out in the fractured surface. Ultra-micro hardness evaluation showed good interfacial bonding after heat treatment. The thixomixing process can be developed to produce various composites with different reinforcement.