Volume Fraction Of Primary Particles Research Articles

Formation of primary intermetallic phases in the interaction of Fe-containing melts of recycled Al-Si alloys with Al2O3 and Al2O3-C filter materials: A µ-CT study

Fe is the most detrimental impurity element in recycled Al-Si alloys due to the formation of brittle, primary, Fe-containing, intermetallic particles during solidification. Their removal from the Al-Si melts e.g. by filtration can reduce the Fe content. New active filter materials can facilitate the formation of these particles for their removal and contribute to the production of high-quality, recycled Al-Si alloys. The interaction of the alloy with the filter material can lead to modification of the thermodynamics of the alloy or of the kinetics of the particle formation. Time-resolved, three-dimensional microstructural investigations have been carried out to study the formation of primary intermetallic particles in Al7.1Si1.5Fe and Al7.1Si0.75Fe0.75Mn alloy melts in contact with Al2O3 and Al2O3-C filter substrate material during a melt conditioning treatment at 620 °C. The microstructures, in particular the primary intermetallic particles αc and αh, have been characterized by computed tomography (CT) and supplementary scanning electron microscopy (SEM). As expected by thermodynamics, the total volume fraction of primary particles remains unchanged by the interaction with the substrate materials. However, kinetic advantages for Fe-removal efficiency can be achieved by an accelerated and preferred selective particle formation in contact with the Al2O3-C material. Furthermore, particle formation is discussed in view of its different stages: nucleation, growth, and ripening.

Semi solid metal processing: The fraction solid dilemma

One of the most challenging aspects in semi solid metal (SSM) processing is to determine the actual volume fraction of the solid at the processing temperature. The fraction has great impact on the SSM slurry viscosity and the subsequent filling of the mold in the casting stage. Three methods, namely quantitative metallography, thermodynamic calculation, and thermal analysis are employed to investigate and clarify the contradictory open literature reports about the real value of the volume fraction of primary particles. It is reported that the discrepancies between the results obtained by different methods are caused mainly by variations in cooling rates and by coarsening of the primaries during the quenching process.

Elastic properties of networks of fractal clusters

Elastic properties of casein gels were followed by dynamic measurements for various volume fractions of casein micelles far above the percolation threshold. Elastic and loss storage moduli versus volume fractions obey a power law with an exponent close to 3. The previous theoretical models for networks made of a homogeneous packing of fractal flocs do not predict the observed behavior. A model is proposed to estimate the vectorial contribution to the network elasticity. This model is in agreement with our experimental results. The value of the fractal dimension of the flocs derived from this analysis is discussed as a function of the volume fraction of primary particles.