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Alloy castings are usually solidified with a coarse columnar grain structure under normal casting conditions unless the mode of the solidification is carefully controlled. It is desirable for the grain structure to be fine and equiaxed to improve their mechanical performance as finished castings. It is possible to develop a fine and equiaxed grain structure either by increasing the number of nucleation sites or by grain multiplication. Immiscible alloys with a microstructure in which a soft phase is dispersed homogeneously in a hard matrix have significant potential applications in advanced bearing systems, especially for the automotive industry. Despite considerable efforts made worldwide, including extensive space experiments, no casting techniques so far can produce the desired immiscible microstructure of alloys. Experimental results on Al-Sn-Cu immiscible alloys have confirmed that intensive shearing using melt conditioning by an advanced shearing technology (MCAST) unit, is an effective way to achieve a fine and uniform dispersion of the soft phase without macro-demixing, and that such a dispersed microstructure can be further refined in alloys with precipitation of the primary Al phase prior to the demixing reaction. In addition, it was found that melt shearing at 200 rpm for 60 s will be adequate to produce a fine and uniform dispersion of the Sn phase, and that a higher shearing speed and prolonged shearing time can only achieve further minor refinement. A study of Al-Si hypoeutectic and hypereutectic alloys presents the effects of the processing temperature and intensive shearing on the microstructural and mechanical properties which have been investigated systematically. Attempts have been made to explain the solidification mechanism with intensive melt shearing. The sheared melt was cast into tensile test samples by high pressure die caster (HPDC) to examine the microstructures and mechanical properties. The experimental results reveal that significant grain refinement and uniformity of grains was achieved by the intensive shearing and also a considerable increase in mechanical properties with pouring temperature by changing intermetallic particles morphology, the position of defect band and reduced microscopic defects.
Eutectic Solidification Processing: Crystalline and Glassy Alloys deals with solidification theory and its application to eutectic processing of crystalline and glassy alloys. The underlying theme is an analysis of the different paths taken by the liquid-solid transformation as the cooling rate increases and a description of the structure and properties of the solid formed, ranging from equilibrium to metastable phase formation in castings, to metallic glass formation in splat quenched ribbons. This text has seven chapters; the first of which describes the main characteristics of the liquid-solid transformation. The chapters that follow show how control over composition, trace impurities, heat flow and cooling rate, and nucleation and growth gives rise to a wide range of solidification structures. Models of the nucleation and growth of eutectic and primary phases are analyzed and used to explain how cast microstructures are formed. Aluminum casting alloys and all types of cast iron are discussed, along with primary phase formation, the dependence of the extent of segregation on solidification conditions, and the practice of segregation prevention during solidification. This book also describes the importance of fluid flow in producing macroscopic segregation in large ingots and considers ways of minimizing this defect. Finally, this book gives a brief account of the various types of metallic glasses, their fabrication, important properties, and potential applications. This book will be of interest to materials scientists and industrial materials engineers.
This book describes in great detail the semi-solid processing of aluminum alloys. The authors examine the fundamentals of semi-solid metal processing, provide guidelines for research, illustrate the tools that are employed, and explain the measured parameters for semi-solid processing characterization.
Semi-solid metal (SSM) processing, as a viable alternative manufacturing route to those of conventional casting and forging, has not yet been fully exploited despite nearly half a century since its introduction to the metal industry. The slow pace of adopting SSM routes may be due to various reasons, including capital costs, profit margins, and, most importantly, the lack of detailed analysis of various SSM processes in open literature to confidently establish their advantages over more conventional routes. Therefore, the SSM community must disseminate their findings more effectively to generate increased confidence in SSM processes in the eyes of our industrial leaders. As such, we have embarked on the task to invite the leaders in SSM research to share their findings in a Special Issue dedicated to semi-solid processing of metals and composites. SSM processing takes advantage of both forming and shaping characteristics usually employed for liquid and solid materials. In the absence of shear forces, the semi-solid metal has similar characteristics to solids, i.e., easily transferred and shaped; by applying a defined force, the viscosity is reduced and the material flows like a liquid. These unique dual characteristics have made SSM routes attractive alternatives to conventional casting on an industrial scale. With the intention of taking full advantage of SSM characteristics, it is crucial to understand SSM processing, including topics such as solidification and structural evolution, flow behavior through modelling and rheology, new processes and process control, alloy development, and properties in general. This Special Issue focuses on the recent research and findings in the field with the aim of filling the gap between industry and academia, and to shed light on some of the fundamentals of science and technology of semi-solid processing.
Semisolid metallurgy (SSM) is now some 37-years-old in terms of time from its conception and ?rst reduction to practice in the laboratory. In the intervening years, there has been a steadily growing body of research on the subject and the beginning of signi?cant industrial applications. The overall ?eld of SSM comprises today a large number of speci?c process routes, almost all of which fall in the category of either “Rheocasting” or Thi- casting.” The former begins with liquid metal and involves agitation during partial solidi?cation followed by forming. The latter begins with solid metal of suitable structure and involves heating to the desired fraction solid and forming. Research over the past 37 years, and particularly over the last decade, has provided a detailed picture of process fundamentals and led to a wide range of speci?c SSM processes and process innovations. Industrial studies and actual p- duction experience are providing a growing picture of the process advantages and limitations. At this time, the conditions for eventual wide adoption of SSM appear favorable, both for nonferrous and ferrous alloys. It must, however, be recognized that major innovations, such as SSM become adopted only slowly by industries where capital costsarehigh,pro?tmarginsaremodest,andfailuretomeetcustomercommitments carries a high penalty.
This book explores the application of external physical fields to the solidification processing of metallic alloys. Leading academics from around the world present comprehensive and critical reviews on state-of-the-art research and discuss possible future directions. Major physical fields, including electromagnetic, electric, acoustic, and thermal, are considered. In addition, the most advanced synchrotron X-ray based real-time and in-situ studies and numerical modeling methodologies are reviewed and discussed, with a special emphasis on their applications to the solidification processes. Throughout, all chapters are illustrated with both historical and very recent research cases, including typical examples of in-situ studies, modeling, and simulation. This book contains essential knowledge and information suitable for a wide audience, from undergraduate and postgraduate students to academics, practicing researchers, and engineers in materials, metallurgy, and manufacturing.
This atlas provides an in-depth understanding of the metallurgy and fracture behavior of aluminum-silicon casting alloys, which are used in a wide variety of automotive, aerospace, and consumer product applications. The atlas includes over 300 high-definition microfractographs of fracture profiles and fracture surfaces, accompanied with detailed descriptions and analysis of the fracture features and their significance in the selection, processing, properties, and performance of the alloy. The microfractographs are described and classified according to criteria described in detail in the introductory chapters in the book. The factors determining the fracture mechanism in these alloys, on the basis of their physical and mechanical properties and fracture mechanics, are described and analyzed. The set of micrographs in this atlas include several unique features: classification according to the alloy and its processing history, detailed analysis of selected microregions of the fracture surface, reference of the fracture features to the phase constituents of the alloy, and high resolution and high microscopic magnification of the SEM images. This book will be of great value to anyone involved in the selection, processing, application, testing, or evaluation of aluminum-silicon castings. The target audience includes metallurgists, foundry personnel, failure analysts, purchasers of castings, researchers in physical and mechanical metallurgy, students, and educators.