Papers by Keyword: Semi-Solid Processing

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Authors: C.M. Gourlay, T. Nagira, Kentaro Uesugi, Hideyuki Yasuda
Abstract: Synchrotron radiography experiments are overviewed that directly image semi-solid deformation at the globule-scale. Globular Al-15Cu at 50-60% solid was deformed in direct-shear at 10-2 s-1. Deformation is shown to occur by globule rearrangement without discernible deformation of the individual globules. Globules were found to translate and rotate as quasi-discrete bodies in response to forces acting at globule-globule contacts, similar to liquid-saturated granular materials such as water-saturated sand. Rearrangement caused the globule packing-density (the solid fraction) to adjust by local compaction and local dilation of the globule assembly, and deformation is highly inhomogeneous. During shear, there was a net dilation and strain began to localize into a shear band of decreased solid fraction by the end of the experiments.
185
Authors: Zong Ning Chen, Tong Min Wang, Jun Xu, Jing Zhu, Hong Wang Fu, Ting Ju Li
Abstract: Employing a cooling slope technique to produce semisolid slurry, in-situ 3wt%TiB2 particulate reinforced Al-12Si alloy composites have been successfully fabricated by flux-assisted synthesis method. It has been shown that the minute TiB2 particles with size 200-500nm uniformly distribute in the spherical α-Al structure and at the boundary of the eutectic Si. Two groups of contrast experiments with and without flowing on the slope have been performed to investigate the influence of the semisolid processing on the microstructure of the composites. Results have shown that α-Al grain is rather spherical and with an average size of 47.4μm, which indicates semisolid processing can be a potential route to produce metal matrix composites with high strength and good ductility.
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Authors: Zhong Yun Fan, Yu Bo Zuo, Bo Jiang
Abstract: Melt quality is crucial for both continuous and shape casting of light alloys. Gas, oxides and other inclusions in the melt usually deteriorate the quality of the casting products. Conventional refining techniques, such as filtration and rotary degassing, can refine the melt by removing the inclusions although they are costly and time-consuming. A new technology for liquid metal treatment through intensive melt shearing was developed recently to improve the melt quality prior to metal casting. The new technology uses a simple rotor-stator unit to provide intensive melt shearing, which disperses effectively the harmful inclusions into fine particles to enhance nucleation during the subsequent solidification processing. Experimental results have demonstrated that the high shear unit can be used for general melt treatment, physical grain refinement, degassing and preparation of metal matrix composites and semisolid slurries. In this paper we offer an overview of the high shear device and its application in processing light alloys.
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Authors: Roxane Koeune, Jean Philippe Ponthot
Abstract: This paper deals with the simulation of two extrusion tests by thixoforming: a non stationary extrusion test and a double-cup extrusion test. The simulations are based on a thermo-mechanical one-phase constitutive law that has been presented in details in previous papers. A campaign of experimental extrusion testing has been conducted on a steel alloy and the comparison between the numerical and experimental results will validate the model under study. A new feature that has been added to the model is also discussed: the introduction of the phase change thermal effects such as the fusion latent heat and the contraction of the material.
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Authors: Manel Campillo, M. Teresa Baile, Sergi Menargues, Enric Martín, Antonio Forn
Abstract: The A357 Al-Si-Mg cast alloy is commonly used for cast production of automotive components in conventional HPDC and in semi-solid processes. The aim of this work is to study the application of A357 cast alloy in thixoextrusion processes. This technology offers new possibilities of application for cast alloys and several advantages in from of conventional processes of hot-extrusion: lower pressure, minor friction forces, higher material fluidity and longer tool life. The thixoextrusion was experimented in a pilot plant, at different speeds and temperatures, with an induction furnace and a 400 Tn press. With ingots of A357 as cast, a tool with a ratio of 8.5 and with temperatures of extrusion around 560 °C, it is possible to obtain extrusion speeds more than 3 m•s-1. In all cases, when the speed of extrusion increases, the press of extrusion decreases. The effect of heat treatments and extrusion speed in the microstructure of the extruded product is evaluated.
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Authors: Helen V. Atkinson
Abstract: The main alloys which have been semi-solid processed commercially are based on aluminium (particularly the cast compositions) and magnesium. There is a strong drive to broaden the range of alloys to the wrought compositions for aluminium, more creep-resistant magnesium recipes and to higher temperature alloys such as those based on copper, steels, stellites and cast irons. This paper will summarise the issues with such development including the scientific and practical issues for alloy design and the thermodynamic prediction of alloys suitable for semi-solid processing. After an initial introduction to semi-solid processing routes, the most important alloy systems for semi-solid processing from a development point of view (aluminium, magnesium, steels and composites- including nanocomposites) will be discussed. The key issues of alloy design specifically for semi-solid processing will be drawn out through the text.
16
Authors: Qin Yue Pan, Stuart Wiesner, Diran Apelian
Abstract: The continuous rheoconversion process (CRP) is a novel slurry-on-demand process that was developed at MPI/WPI in 2002. The process is based on a passive liquid mixing technique in which the nucleation and growth of the primary phase are controlled using a specially designed “reactor”. The reactor provides heat extraction, copious nucleation, and forced convection during the initial stage of solidification, thus leading to the formation of globular structures. This paper presents our recent work on the scale-up of the CRP for industrial applications. Specifically, we demonstrate an important application of the CRP to low temperature (low fraction solid) HPDC. In Part I of this paper, we present salient results on microstructural characterization of CRP processed castings vs. conventional die castings.
402
Authors: Stuart Wiesner, Qin Yue Pan, Diran Apelian
Abstract: The continuous rheoconversion process (CRPTM) is a novel slurry-on-demand process that was developed at MPI/WPI in 2002. The process is based on a passive liquid mixing technique in which the nucleation and growth of the primary phase are controlled using a specially designed “reactor”. The reactor provides heat extraction, copious nucleation, and forced convection during the initial stage of solidification, thus leading to the formation of globular structures. This paper presents our recent work on the scale-up of the CRPTM for industrial applications. In Part II of this paper, we present salient results on alloy optimization via thermodynamic simulations, as well as validation results obtained from industrial Beta trials.
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Authors: Zbysek Novy, Kateřina Opatová
Abstract: Thanks to innovative processing routes, even conventional materials which have been around for years can be manipulated to obtain unconventional microstructures with specific mechanical and physical properties. This also holds for various semi-solid forming processes, which represent a dynamically developing field. Yet, these processes are still under development due to their technological complexity. One of the innovative methods of semi-solid processing is mini-thixoforming. As it focuses on very small-size products, it offers very steep heating curves and extremely high solidification and cooling rates, unlike conventional thixoforming. These features have profound impact on the evolution of microstructure and the resulting properties of the product. As in the conventional thixoforming process, complex-shaped products can be manufactured with high precision, using a single forming step. The potential and capabilities of the process were explored using the ledeburitic X210Cr12 steel as the experimental material. Once the optimum conditions were found, other tool steels were used for trials as well. Thanks to closely-controlled temperature field, mini-thixoforming was successfully used on a steel with a freezing range of a mere 15 °C. The microstructure evolution in the mini-thixoforming process is an issue of its own. The final microstructure of X210Cr12 after processing consisted of more than 90 % of austenite and chromium carbides. Semi-solid processing of a steel with a high vanadium content led to a microstructure comprising MA matrix and globular vanadium carbides. In a low-alloyed steel, martensitic microstructure was obtained.Keywords: thixoforming, mini-thixoforming, semi-solid processing, tool steels
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Authors: M. Hajian Heidary, M. Bigdeli, A. Mahdavi, F. Khomamizadeh
Abstract: In this study, in order to compare effect of unidirectional compression and rolling on final microstructure of strain induced melt activated (SIMA) A356 aluminum alloy, rectangular samples with dimensions of 3cm×5cm in area and 1cm in thickness and cylindrical specimens with 2.5cm in diameter and 1cm in length, have been prepared for rolling and compressing processes, respectively. Then, these samples were plastically deformed at a same strain in ambient temperature. Afterward, the strained samples were cut into equal quarters. In the next stage, to produce globular microstructure, these specimens were partially remelted in 580°C for different times. Results obtained from light microscopy showed that specimen's thickness and so, its strain affected zones influence on the globulization of dendrites. In addition, it was seen that at a given strain and constant diameter, increase of H/D ratio led to increase of needed time for reaching a certain sphericity in cylindrical samples. Also, it was showed that microstructural evolutions during SIMA processing of both rolled and unidirectional compressed samples were relatively identical. However, at a same condition, ultimate size of globulized dendrites in the rolled samples was smaller than those of compressed ones.
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