Abstract
Shear stress ramp experiments were performed in order to analyze the yield stress of the aluminium alloys AlSi5 and AlSi5Cu03Mg05Ag06 in the semi-solid state with regard to its dependency on time, solid fraction and particle size in the slurry. The experimental results were not influenced by the different chemical compositions of the alloys.
The minimum solid fraction which is required for the occurrence of yield stress is called coherency solid fraction. The yield stress occurring immediately after shearing is called isostructural yield stress. At rest an internal structure is built up and the yield stress increases until the static yield stress is reached. During the transition from isostructural to static, the yield stress is called dynamic yield stress.
The coherency solid fraction was estimated as a function of particle size by means of an extrapolation of the static yield stress to zero. The static yield stress is predominantly influenced by the distance between the particles which can be calculated from the particle size and the solid fraction.
On the basis of dynamic yield stress measurements, the isostructural yield stress was estimated to be smaller than 10 Pa and an empirical model for the development of the dynamic yield stress was set up. Together, the experimental results allow for a complete description of yield stress as a function of particle distance and time.
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Moll, A., Modigell, M. Yield stress phenomena in semi-solid alloys. Int J Mater Form 3 (Suppl 1), 779–782 (2010). https://doi.org/10.1007/s12289-010-0886-x
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DOI: https://doi.org/10.1007/s12289-010-0886-x