tailieunhanh - MAGNESIUM ALLOYS DESIGN, PROCESSING AND PROPERTIES_2

Scientists and engineers for decades searched to utilize magnesium, known of its low density, for light-weighting in many industrial sectors. This book provides a broad review of recent global developments in theory and practice of modern magnesium alloys. It covers fundamental aspects of alloy strengthening, recrystallization, details of microstructure and a unique role of grain refinement. | 8 Ultrasonic Grain Refinement of Magnesium and Its Alloys M. Qian1 and A. Ramirez2 1The University of Queensland School of Mechanical and Mining Engineering Australian Research Council ARC Centre of Excellence for Design in Light Metals Brisbane QLD 4072 2Aix-Marseille Université and CNRS UMR 6242 IM2NP Campus de Saint Jérôme Case 142 13397 Marseille Cedex 20 Australia 2France 1. Introduction Achievement of a uniform fine grain structure in cast magnesium Mg alloys is desired as it improves structural uniformity reduces segregation and associated casting defects enhances consistency in performance and facilitates the solid-state forming of various wrought Mg products. Inoculation is a standard grain-refining practice for commercial cast alloys. However many commercial alloy systems do not have an established inoculating agent or chemical grain refiner. In the context of Mg alloys although aluminium-free Mg alloys can be readily grain-refined with zirconium Emley 1966 Qian Das 2006 Qian 2006 it has proved difficult to grain-refine the more common Mg-Al based alloys by inoculation StJohn et al. 2005 Qian Cao 2005 . Alternative approaches to grain-refining these alloys are desirable. Ultrasonic irradiation during solidification is one such alternative that has proved to be effective for Mg-Al based alloys first demonstrated in the former USSR countries Abramov 1994 Eskin 1998 . It is also effective in grain-refining other metallic materials Eskin 1998 Jian et al. 2005 Jian et al. 2006a Liu et al. 2007 Xu et al. 2008 and ice Zhang et al. 2001 . The recent renewed interest in the process for Mg alloys Jian et al. 2006b Ramirez Qian 2007 Zhang et al. 2007 Liu et al. 2008 Ramirez et al. 2008 Ramirez et al. 2009 Qian Ramirez 2009 Qian et al. 2009 Qian et al. 2010a is driven by its potent grain-refining capability ease of operation and requirement for inexpensive equipment. In addition the melt surface is left almost undisturbed during irradiation. As a result there is .

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