Piotr Mikolajczak

Effect of stirring induced by rotating magnetic field on β-Al5FeSi intermetallic phases during directional solidification in AlSi alloys

Abstract In AlSi alloys, iron plays an important role, and as one of the main impurities, it causes the formation of β-Al5FeSi intermetallics. This study aims to understand the effect of fluid flow on the microstructure and intermetallics in Al–5/7/9 wt-%Si 0·2/0·5/1·0 wt-%Fe alloys directionally solidified in a special furnace facility Artemis-3 under defined thermal and fluid flow conditions (generated through rotating magnetic field). Results showed that forced flow can cause shortening of the β platelets in dendritic regions with increasing their number density. The studies have shown that application of stirring could lead to better results in shortening β-Al5FeSi than lowering Fe content in the range from 1·0 to 0·2 wt-%Fe. It is deduced that the melt flowing together with the β phases reaches the superheated bulk where intermetallics could be fragmented or remelted, and finally, microstructures with shorter β-Al5FeSi and higher number density of β might be obtained.

The role of fluid flow and intermetallic phases in the formation of the primary Al-phase in AlSi alloys

In secondary AlSi alloys, the presence of small amounts of Fe causes the formation of intermetallic phases, which have a negative effect on mechanical and physical properties of castings. To understand the effect of fluid flow on the microstructure and intermetallic phases, Al-5/7/9 wt pet Si 0.2/0.5/1.0 wt pet Fe alloys have been directionally solidified under defined thermal (gradient 3 K/mm, solidification velocity 0.04 mm/s) and fluid flow (rotating magnetic field 6 mT) conditions. The primary α-Al phase and intermetallic phases were studied using light microscopy and SEM with EDX. The influence of fluid flow and intermetallic phases (β-Al5FeSi) on microstructure was characterized by changes of primary and secondary dendrite arm spacing and specific surface area of the dendrites. We observe a pronounced effect of flow on the length of the intermetallic precipitates, a macro-segregation Fe and Si and even small amounts of iron and thus intermetallics reduce possible effects of flow on microstructural parameters.

Three Dimensional Morphology of Mn Rich Intermetallics in AlSi Alloys Investigated with X-Ray Tomography

Elementary Mn has a great importance as neutralizer of Fe intermetallics like β-Al5FeSi, which have detrimental effect on mechanical characteristics of AlSi alloys. Presence of Mn in AlSi alloys causes the formation of other intermetallic phases. To understand the effect of solidification conditions and fluid flow on the microstructure of AlSi-based alloys and the addition of Mn leading to Mn-based intermetallics, Al-5 wt pct Si 0.2/0.4/1.0 wt pct Mn alloys have been directionally solidified under defined thermal (gradient 3 K/mm, solidification velocity 0.02-0.12 mm/s) and fluid flow (rotating magnetic field 6 mT) conditions. The primary Al-phase and Mn-based intermetallic phases were studied using 3D X-ray tomography. The spatial morphology of primary phase and intermetallics were characterized with respect to different fluid flow and solidification conditions. The tomography has showed the 3D complicated structure of Mn phases developed.