Solidification of Al Alloys Under Electromagnetic Pulses and Characterization of the 3D Microstructures Using Synchrotro
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ALMOST all metallic alloys are manufactured via the solidification processes, and the mechanical properties of the cast ingots or components, such as the strength, ductility, fatigue life, etc., are predominantly determined by the as-cast grain microstructure formed during the solidification processes.[1,2] The as-cast grain microstructures also affect, to a certain degree, the grain structures formed during any subsequent thermomechanical deformation and/or heat-treatment processes.[1,3] In general, uniformly distributed polygonal grains are desirable for higher strength as revealed by the classical Hall–Petch relationship,[4] i.e., the yield strength (ry) increases linearly with the inverse of square-root of the grain size (p1ffiffid) of the materials (ry p1ffiffid). In industry, the most common practice to control the solidification microstructure is to add external grain refiners during the solidification processes. The typical examples are AlTi-B for Al alloys,[5,6] Zr for Mg-based alloys,[7] B for Ti-based alloys,[8] and Ce for steel.[9] However, there are no universal grain refiners that are suitable for all metallic alloys, and adding grain refiners often result in extra cost, and sometimes contamination to the alloy chemistry. As the environmental impact and sustainable development become important issues in all industry,[10] the metallurgical and metal manufacturing industry has been seeking to develop more environmental friendly technologies for grain refinement without or much less THEERAPATT MANUWONG, WEI ZHANG, PETER LOBO KAZINCZI, and JIAWEI MI, are with the School of Engineering, University of Hull, Hull, East Yorkshire, HU6 7RX, UK. Contact e-mail: [email protected] ANDREW J. BODEY and CHRISTOPH RAU, are with the Diamond Light Source, Oxfordshire, OX11 0DE, UK. Manuscript submitted February 1, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
of adding external grain refiners during the solidification processes.[11] In the past 30 years or so, many physical field-based methods have been investigated with the aim to develop a generic method for grain refinement that is suitable for all metallic alloys regardless of the chemistry. For example, applying ultrasonic wave[12] or electrical current, or magnetic field into the solidifying alloy melts to enhance grain nucleation and control grain growth.[13–16] Technically, the external fields or energy can be applied into the melts via probes that have direct contact with the melts, such as sonotrodes for ultrasonic wave, or electrodes for electrical current; or through a non-contact manner such as electromagnetic inductive coupling.[17] For the direct contact methods, special materials are often needed for making the sonotrodes or electrodes to withstand the erosion of high-temperature melts. So far, no robust solutions have been found to sustain high melting point alloys, e.g., Ni-based alloys, steels, etc. The electromagnetic inductive coupling methods have the advantages of noncontact, but often need high electrical current or voltage inputs to generate enough Lorenz force
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