Modern Aspects of Liquid Metal Engineering
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CASTING is the manufacturing process in which a molten metal is injected or poured into a die/mold cavity to create a product being either a raw feedstock for further processing or a final component with a near-net or net-shape configuration. Conventional casting offers a limited part quality at a relatively low cost, in contrast to solid-state forming routes, which provide generally better properties but at substantially higher price.[1] The present techniques offering high-quality parts are associated with complex multistep operations exploring the wrought path with additional hot and cold forming, machining, and other shaping processes after casting. As an intermediate measure, there are efforts aimed at reducing the cost of solid state processing and, independently, at improving quality of casting.[2] It is believed, however, that the ultimate solution may only be achieved through development of a novel technology, which will combine the best features of both processes by offering the highest properties typical for wrought products at the low cost and simplicity of casting (Figure 1). The progress made in the last few decades by the casting industry is associated mainly with the development of new hardware and auxiliaries. This applies, in particular, to high-pressure die casting (HPDC), invented in 1838 for the purpose of producing movable type for the printing industry and since 1894 has been
applied for casting of engineering components, being well suited for mass-scale production of bulk metallic parts.[3] At present, HPDC is the major technology of manufacturing parts for the automotive industry. The new machinery, control electronics, tooling and vacuum, robotics and postcasting treatment automation improved the manufacturing outcome and productivity. So far, the hardware improvement is not matched by understanding and exploring opportunities created by molten alloys. There is, therefore, a renewed interest in the processing side of HPDC and other casting techniques especially in controlling the nature of molten metal supplied to the die/mold. At the center of an effort aimed at casting improvement and a quest for a novel technology of large-scale production is so-called liquid metal engineering (LME).[4] This review provides the fundamentals and applications of LME covering the laboratory- and commercial-scale processes based on both the liquid and semisolid routes. Particular attention is paid to novel elements of LME developed in recent years that combine the melt physical treatment with manipulating its chemistry and temperature to create conditions for optimum nucleation and growth, leading to an improvement of the solidification outcome. A link with conventional treatments aimed mainly at melt alloying, degassing, and purification is emphasized throughout the article.
II. FRANK CZERWINSKI, Innovative Casting Group Leader and Senior Research Scientist, is with CanmetMATERIALS, Natural Resources Canada, 183 Longwood Road South, Hamilton, ON L8P 0A1, Canada. Contact e-mail: [email protected] Manus
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