Thermomechanical Processing of Metal Feedstock for Semisolid Forming: A Review
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TO address the needs of modern manufacturing industry, there is a search for a novel technology allowing large-scale production of net-shape components having high-performance characteristics. Although well-established conventional casting like high-pressure die casting, offers vast advantages in terms of manufacturing simplicity, net-shape capabilities, competitive cost and low energy consumption the product quality in terms of its integrity and properties is still not sufficient for some structural applications required in modern transportation vehicles.[1,2] When semisolid metal processing (SSP) was invented in the early 1970s,[3] it generated high expectations and has been seen as a very promising technology with great potentials and capabilities to revolutionize the manufacturing industry. After almost half century of research and despite valuable findings at a laboratory scale, its
FRANK CZERWINSKI is with the CanmetMATERIALS, Natural Resources Canada, Hamilton, Ontario L8P 0A5, Canada. Contact e-mail: [email protected] Manuscript submitted May 11, 2018.
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global commercialization progress remains rather limited. For a new technology to achieve the commercial acceptance in today’s market, clear advantages of competitive cost and superior product properties must be demonstrated. These elements are so far missing and it is emphasized in the literature that semisolid processing has never advanced to become the major metal casting process anticipated by so many early researchers, it requires further development and the critical breakthrough is still expected. Although the first experiments with semisolid processing involved a product forming from a liquid-state precursor termed as rheocasting, the attention shifted quickly to thixoforming, which on the contrary relies on solid-state precursors. In fact, thixoforming was the first one commercialized and seen as an alternative to complex multistep processes of solid state forming. However, after roughly two decades, rheocasting with then developed a variety techniques of slurry preparations moved again to the center of the research and industrial interest.[4,5] It is claimed that difficulties with manufacturing of suitable feedstock/billet was the main factor leading to reduced interest in thixoforming despite that it offers broader ranges of design options. There are still limitations on potential alloys used—billet manufacturing process represents an extra step that
increases the product cost, and product properties are still lower than those obtained after conventional solid-state forming.[6–8] To overcome this technology gap, understanding and optimizing the billet manufacturing process are required. This review covers all aspects of utilizing solid-state deformation preceding melting to manufacture thixotropic feedstocks for semisolid processing in the form of bulk billets and coarse particulates. Along with theoretical fundamentals, necessary to understand the subject, engineering and commercial details of this proc
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