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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.
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.
Composite is a material system composed of a mixture or combination of two or more constituents that differ in form and chemical composition and which are essentially insoluble in each other. Metal matrix composites (MMC) are engineered materials composed of an elemental or alloy as a matrix in which an insoluble second phase reinforcer is embedded and distributed to achieve property improvement. Application of MMC comprises a broad range in aircraft, automotive, defence technology and astronautics components. The performance during its work life of MMC is determined by the mechanical properties. The mechanical properties of MMC are linked to microconstituents formed and its characteristics. For MMC processed by casting method, the solidification behaviour will determine the type of microconstituents formed and its properties. In this study, casting via vortex mixing method is employed to produce MMC aluminium-11.8% silicon alloy (LM6) reinforced with different volume percentages (0, 5, 10, 15, 20, 25%) of titanium particulates (TiCp) cast using sand and copper moulds. Temperature measurements during cooling and solidification are used as the main source to analyse solidification properties (fraction solid and latent heat generation) using Fourier thermal analysis method. A metallographic study is performed to observe the particulates distribution and microconstituents present. A hardness test is carried out, the results show that 25% volume addition of TiCp cast using copper mould has the best result. This result correspond to the improved microstructure as particulates are well distributed in the matrix which can be seen on the photomicrographs. From the visual observation of photomicrographs, the increment addition of particulates will promote more nucleation sites and grain size is reduced due to faster solidification of casting using copper mould (high heat extraction capacity). For production using sand mould the maximum mean value of hardness 54.38 Rockwell number is reached by addition of 25% volume content TiCp , solidification time (fraction solid equals to 1) at 195 seconds and volumetric latent heat generated 245.63 103kJ/m3. The best result is obtained by fabrication of LM6-TiCp MMC using copper mould (permanent die), the maximum mean value of hardness 76.82 Rockwell number is reached by addition of 25% TiCp volume content, solidification time (fraction equals to 1) at 5 seconds (fastest) and volumetric latent heat generated 100.77 kJ/m3. From the results, it is concluded that casting of LM6-TiCp MMC is successfully achieved using vortex mixing technique and that addition of particulates influence solidification characteristics which in turn affect the properties of the MMC.
The 14th S2P International Conference (October 23 – 27, 2016, Salt Lake City, USA) was dedicated to the science and processing technologies of the semi-solid metal alloys and composites. Since the discovery of the specific flow behavior of metals in semi-solid state during the early seventies, this fascinating technology has experienced a dynamic and turbulent development history which has led to a whole family of new production processes, new equipments and industrial applications for goals of full use of the technical and economic potential of the flow behaviour, improved materials and process modelling as well as control of processes. All S2P International Conferences have contributed to achieve this goal by providing a forum for scientists to share the common knowledge and to develop a common sense on fundamental topics and industrial requirements.
These proceedings of the 12th International Conference on Semi-Solid Processing of Alloys and Composites contain the papers which were presented at the conference, held in Cape Town (South Africa) between the 8th and 11th October 2012. The aim of these international conferences is to provide a forum where the leading researchers, engineers and industrialists in this field can gather in order to share their work and knowledge, and hold lively discussions concerning current fundamental issues in semi-solid metal processing. Volume is indexed by Thomson Reuters CPCI-S (WoS). The contents are divided into 5 distinct sections: Microstructure and Properties; Process Development; Modeling, Simulation and Rheology; Materials Development and Alloy Design and Industrial Applications.
Volume is indexed by Thomson Reuters CPCI-S (WoS). This volume is dedicated to the science and technology of the semi-solid processing of metals.
Volume is indexed by Thomson Reuters CPCI-S (WoS). This special volume is dedicated to the science and technology of the semi-solid processing of metals. Since the recognition of the possibility of manipulating metals in the semi-solid state, during the seventies, this fascinating technology has experienced dynamic development and has led to a whole family of new production processes, new equipment and industrial applications. In order to exploit fully the technical and economic potential of these new ideas, it is important to achieve a better understanding of the microstructural development and flow behavior in order to improve material and process modelling as well as process control.
Selected peer-reviewed extended articles based on abstracts presented at the 17th International Conference on Semi-Solid Processing of Alloys and Composites (S2P) Aggregated Book