1001 MITE-129/elab/ds r6

T Slow cooling and long stirring produce particles that are large and spherical, while fast cooling and short stirring produce small, jagged particles that tend to stick together. As a result, the larger particles slide by each other more easily than the smaller ones do, producing a semisolid with less resistance to flow. High-speed videos show that the semisolid advances smoothly and evenly, producing parts with a consistent microstructure, smooth finish, high reliability, and constant properties. Traditionally, manufacturers of metal components worked with metals that were fully liquid or fully solid. They forged and machined solid pieces, or they cast liquid metals in molds. Using a material that was partly solid and partly liquid was not an option because such semisolids would not flow well enough to fill the nooks and crannies of typical molds. However, in 1971 an MIT doctoral student made a surprising discovery. In the course of studying how molten metals flow as they solidify, the student,