Microstructure and compression behaviour in the semisolid state of short-fibre-reinforced A356 aluminium alloys

This paper is concerned with the microstructural characterization and compressive behaviour of partially remelted A356 aluminium alloys reinforced with 10 vol.% chopped SiC Nicalon fibres. The composites were fabricated by the compocasting technique and subsequently solidified under pressure, some materials being also extruded at high temperature. It is shown that compocasting leads to breakage of the fibres, which are further fragmented by extrusion and aligned along the extrusion direction. Isothermal holding of the extruded composites in the semisolid state leads to rapid globularization of the structure of the solid phase, with globules coarsening as the holding time increases. The globularization is associated with a decrease in the compression stress at constant strain rate, this stress increasing with increasing strain rate according to a classical power low σ = K ε̇m with values of m close to 0.3. Comparison with the unreinforced alloy and with as-cast composites clearly demonstrates the influence of the presence of the reinforcing elements on the compressive stress of the material together with that of extrusion before partial remelting.