ELABORATION OF METAL-MATRIX COMPOSITES FROM THIXOTROPIC ALLOY SLURRIES USING A NEW MAGNETOHYDRODYNAMIC CASTER

The working principle and the peculiarities of a new electromagnetic r heocaster, which is based on the use of rotating permanent magnets and which allows the production of intense three-dimensional (3-D) multip hase flows in solidifying semisolid alloy slurries and metal matrix co mposites, are described. This process can be applied to the direct con tinuous casting of billets, tubes, and slabs and is characterized by v ery low electric power consumption. Local measurement techniques are a pplied to the study of the evolution of non-Newtonian magnetohydrodyna mic multiphase flow phenomena with the rotational speed of the inducto r, the solid fraction of the aluminum alloy matrix, and the size and v olume percent of SiC particles. An order of magnitude analysis of the various forces acting on the suspended crystals and SiC particles is g iven. The rheological behavior of electromagnetically rheocast ferrous metals, simulated by a lead-tin alloy, is also investigated. Satisfac tory results concerning the microstructure of solidified aluminum slur ries and aluminum matrix composites (homogeneity, crystal shape, grain size, fraction of primary solid, and distribution of SiC particles) w ere obtained. A discussion is presented relating the metallurgical fin dings to the heat and three-phase flow measurements.