Structural characteristics and extrusion behaviour of Pb–Sn alloys in semisolid state

Abstract

The extrusion behaviour of semisolid Pb–19Sn alloys has been studied on materials with conventionally solidified dendritic structures and with non-dendritic structures obtained through mechanical stirring during solidification. This stirring performed at a constant temperature above the solidus produces a semisolid slurry with approximately spherical primary particles. The volume fraction, particle size, and interparticle spacing of the primary phase decrease as the stirring temperature increases. Whereas the alloy with the non-dendritic structure (rheocast) can be extruded in the semisolid state under low extrusion forces giving a perfectly continuous rod, the alloy with the dendritic structure requires larger forces and produces a fragmented product. These experiments suggest that extrusion can be performed advantageously in the semisolid state with alloys obtained by mechanical stirring during solidification.