Semi-solid processing of engineering alloys by a twin-screw rheomoulding process

Based on the extensive experience in injection moulding of polymeric materi als, a twin-screw rheomoulding process has been developed in our laboratory for near net-shape production of engineering components. The rheomoulding equipment consists of a liquid metal feeder, a twin-screw extruder with clo sely intermeshing, self-wiping and co-rotating screws, a shot assembly and a central control unit. The fluid flow in the twin-screw rheomoulding proce ss is characterised by high sheer rate and high intensity of turbulence. Th e experimental results of rheomoulded Sn-15wt.% Pb and Mg-30wt.% Zn alloys have demonstrated that the twin-screw rheomoulding process is capable of pr oducing small and near mono-sized solid particles distributed uniformly in a fine-grained eutectic matrix. Compared with other existing semi-solid met al processing techniques, the twin-screw rheomoulding process has the follo wing advantages: small and spherical solid particles of near mono-size, che mical and microstructural uniformity throughout the component, accurate con trol over a large range of solid volume fractions, lower overall component cost due to low cost of feedstock materials, and shorter cycle time. (C) 20 01 Elsevier Science B.V. All rights reserved.