A powder-based approach to semisolid processing of metals for fabrication of die-castings and composites

A technique is presented for the generation of a globular (non-dendritic) array of solid fragments surrounded by a solute-enriched liquid. This is based on the premixing, heat treatment and consolidation of different types of powder. The resultant slurries have then been injected into a die at high velocity. The technique offers promise in terms of the versatility with which the slurry microstructure can be controlled and the soundness of the resulting die-castings has been encouraging. Among the effects investigated are the role of solute diffusion, the importance of globule size and the nature of coarsening phenomena. Experiments have also been carried out on the incorporation of ceramic fibres into the product and this appears to offer promise as a composite fabrication route. The work described here concerns only Al base material alloyed with Mg, although the principles outlined are expected to apply to many other systems. 36 ref.--AA(UK/US).