Solidification and re-melting phenomena during the slurry preparation stage using the RheoMetalTM process
2016 (English)Report (Other academic)
The melting sequence of the Enthalpy Exchange Material (EEM) and formation of slurry in the RheoMetalTM process was investigated. The EEM was extracted, together with a portion of the slurry at different times before complete melting, and quenched. The EEM initially increased in size due to melt freezing onto its surface, forming a freeze-on layer. The initial growth of this layer was followed by a constant diameter of the EEM and thereafter subsequent melting. Microstructural characterization of the size and morphology of different phases in the EEM and the freeze-on layer was made. Dendritic equiaxed grains and eutectic regions containing Si particles and Cu-bearing particles were observed in the as-cast EEM. The freeze-on layer consisted of dendritic aluminum slightly tilted by about 30° toward the upstream direction, caused by the rotation of the EEM. Energy Dispersion Spectroscopy analysis showed that the freeze-on layer had a composition corresponding to a higher melting point than the EEM.
Microstructural investigation of the EEM showed that the temperature rapidly increased to 495 ºC, causing incipient melting of Al2Cu and Al5Mg8Si6Cu2 phases in grain boundary regions. Following the incipient melting, the temperature in the EEM increased further and binary Al-Si eutectic started to melt to form a region of a fully developed coherent mushy state. Experimental results and a thermal model indicated that as the dendrites spheroidized and the interface at the EEM/freeze-on layer reached a mushy state with 25% solid fraction, coherency was lost and disintegration of the freeze-on layer took place. Subsequently, in the absence of the shielding effect from the freeze-on Layer, the EEM disintegrates at a higher solid fraction, estimated to be 50%. The fast and complex slurry generation in the RheoMetalTM process is a hybrid process with both rheocasting and thixocasting elements in the process.
Place, publisher, year, edition, pages
Jönköping: Jönköping University, School of Engineering , 2016. , 21 p.
JTH research report, ISSN 1404-0018 ; 5
Rheocasting, RheoMetal(TM) process, Slurry fabrication, Solidification, Melting, Heat Transfer Model
Metallurgy and Metallic Materials
IdentifiersURN: urn:nbn:se:hj:diva-31430OAI: oai:DiVA.org:hj-31430DiVA: diva2:954452