Papers by Keyword: Semisolid State

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Authors: Ming-Xu Xia, Hong-xing Zheng, Sen Yuan, Jian Guo Li
Abstract: The phase and morphological transformation during the remelting process was investigated by isothermal soaking and rapidly quenching of preformed AZ91D magnesium alloys in semisolid state. It was revealed that the morphological transformation of preformed alloys is crucial to obtain homogenously fine spheroidal grains and affect the final forming ability. The transformation is divided into two stages, local remelting of the whole experiment and partial remelting of the respective grains, which behave as liquid bands and liquid cells structures, respectively. In the partial melting, the lower melting point phase, β-Mg17Al12, diffused to the grains boundary and center of the grains and separated to Al2Mg and Mg. The Al2Mg and Mg phases with lower melting points melt into cells structures. The final microstructure of the remelting experiments is composed of cells structures, spheroidal grains and liquid phase.
Authors: Carlos Merizalde, Jose María Cabrera, Jose Manuel Prado
Abstract: Semi-solid materials (SSM) in the thixotropic state behave like liquids, i.e they show low or null shear resistance and, at the same time, they behave like solids as do not fall to pieces under applied forces. At present, the potential advantages and industrial applications of these materials are well recognized, in particular for the production of Al-alloy components for the aerospace and automotive sectors. This work is focused on the evaluation and characterization of the thixotropic behaviour of a metal mixture in the semi-solid state obtained by “Compocasting”. The mixture is obtained by mixing spherical solid Cu particles with a liquid eutectic tin-lead alloy. Measurements of the time-dependence of the viscosity of the mixture using an instrumented rheometer showed that, after mechanical stirring, the slurry acquires thixotropic properties. The best conditions to obtain such mixture are presented. Additionally, once the mixture is cooled down, the material is reheated and then tested in a laboratory backward extrusion process. The behaviour of the material is analysed on the basis of the microstructure obtained, and the process parameters considered.
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