Investigation of the effect of solidification rate on microstructure of Al-0.13Si-0.3Fe DC-cast alloy using EBSD and DSC techniques

Abstract

Direct chill (DC) casting is used to cast aluminum alloy ingots. Casting speed influences the distribution and types of iron intermetallics in aluminum ingot microstructure. This study attempted to identify and quantify the iron intermetallic phases in the microstructure of laboratory scale DC Al- 0.13Si-0.3Fe samples using differential scanning calorimetry, scanning electron microscopy, electron backscatter diffraction, and energy dispersive X-ray spectroscopy. Both stable and non-stable iron intermetallic phases were observed but to different extents in all alloy samples’ microstructure. Two different types of iron-rich, AlFeSi globular particles were observed in the alloy samples’ microstructure. As a result, an attempt was made to understand the formation temperature and composition of these small, globular particles. DSC results confirmed that the enthalpy change of phase formation is dependent mainly on the volume fraction of the iron intermetallic phase in the microstructure. A good agreement was observed between the quantitative analysis results and the DSC analysis, which supports the reliability of the quantitative methods used in this study. The results obtained in this study bridge existing gaps in literature on the effect of cooling rate on the selection of iron intermetallic phases, in general, and in the AlSiFe globular particles, in particular.