Validation of Predicted Residual Stresses within Direct Chill Cast Magnesium Alloy Slab
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MAGNESIUM is the lightest of all engineering materials, as it is more than 30 pct lighter than aluminum and 75 pct lighter than steel. For this reason, the demand for magnesium alloys is increasing in situations where weight-saving engineering solutions are required. One example of such an alloy is Elektron WE43 (Magnesium Elektron UK, Manchester, U.K.), which is based on the magnesium-yttrium-neodymiumzirconium alloy system.[1] Elektron WE43 and Elektron 43 (a newly developed alloy for commercial wrought applications, such as rolling, extrusion, and forging) alloys offer high strength at ambient temperature and good creep resistance at increased temperatures, and these alloys have been shown to provide superior ignition resistance.[2] MARK TURSKI, Senior Metallurgist, is with the Magnesium Elektron, Manchester M27 8LJ, U.K., and is also Visiting Academic with the Materials Engineering, The Open University, Milton Keynes MK7 6AA, U.K. Contact e-mail: [email protected] ANNA PARADOWSKA, Instrument Scientist, is with The Bragg Institute, Australian Nuclear Science and Technology Organisation (ANSTO), Menei, NSW 2234, Australia and is also Visiting Scientist with the ISIS facility, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Didcot, Oxfordshire OX11 0QX, U.K. SHU-YAN ZHANG, Instrument Scientist, is with the ISIS facility, Science and Technology Facilities Council, Rutherford Appleton Laboratory. DAG MORTENSEN and HALLVASRD FJAER, Principal Research Scientists, are with the Department of Process and Fluid Flow Technology, Institute for Energy Technology, N-2027 Kjeller, Norway. JOHN GRANDFIELD, Director, is with the Grandfield Technology Pty Ltd, PO BOX 5110, Moreland West, VIC 3055, Australia and is also Adjunct Professor with the Swinburne University of Technology, Faculty of Engineering and Industrial Science, Hawthorn, VIC 3122, Australia. BRUCE DAVIS, Research and Development Program Manager, and RICK DeLORME, Technical Manager, are with Magnesium Elektron North America, Madison, IL 62060. Manuscript submitted February 9, 2011. Article published online February 23, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
Direct chill (DC) casting is a process that allows large volumes of metal to be cast in an efficient manner. The process involves pouring liquid metal into an openbottomed mold; the liquid metal solidifies against the mold wall and is cooled even more by water sprays that impinge on the newly solidified solid shell as it exits the mold. Fast cooling by the water sprays results in steep thermal gradients with associated thermal strains, which can result in significant residual stresses accumulating within the cast material. Such aggressive cooling of the cast material is known to cause hot tearing,[3] during solidification of the metal, or cold cracking,[4] in cases where cracking has occurred after the material has solidified. Initial attempts to DC cast Elektron WE43 in the slab form resulted in catastrophic cold cracking (Figure 1). High-strength aluminum and magnes
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