The effect of magnetically controlled fluid flow on microstructure Evolution in cast technical Al-alloys: The MICAST project

Abstract

The ESA-MAP research program MICAST (Microstructure Formation in CASTing of Technical Alloys under Diffusive and Magnetically Controlled Convective Conditions) focuses on a systematic analysis of the effect of convection on microstructure evolution in cast Al-alloys. Questions are, for example, how intensity of convection and flow direction act on the evolution of the mushy zone, on macro- and micro-segregations, on dendrite morphology, on the growth mode and on spatial distribution of intermetallic precipitates. In order to simplify the complex interactions between heat and mass transport and microstructure evolution, the experiments performed by the MICAST team are carried out under well-defined thermally and magnetically controlled convective boundary conditions using directional solidification. They are analysed using advanced diagnostics and theoretical modelling, involving micro-modelling and global simulation of heat and mass transport. The MICAST team uses binary, ternary (enriched with Fe and Mn) and technical alloys of the industrially relevant Al Si cast alloys family. In the frame of the MICAST project solidification experiments were performed on the International Space Station (ISS) in the ESA payload Materials Science Laboratory (MSL) with a low gradient furnace (LGF) and a high(er) gradient one (SQF, Solidification and Quenching Furnace) to complement the scanning of a range of solidification times. Binary Al-7wt.%Si and ternary Al-7wt.%Si-1wt.%X (X=Fe, Mn) alloy samples were directionally solidified under both purely diffusive and stimulated convective conditions induced by a Rotating Magnetic Field (RMF). This contribution gives an overview on recent experimental results and theoretical modelling of the MICAST team and gives an outlook for the upcoming years of ISS experimentations by the team and the questions to be addressed with future experiments.