Investigation of the Formation of Iron-Rich Intermetallic Phases in Al-Si Alloys via Thermal Analysis Cooling Curves, Including a Real-Time Detection for Filtration Process

The formation of iron (Fe)-containing intermetallics during solidification is challenging due to the influences of cooling rate and chemical composition. Differential scanning calorimetry (DSC) is an accurate analysis method but merely replicates adjustable cooling conditions. Thereby, the solidification range is traversed several times before DSC measurement. For this purpose, thermal analysis cooling curves with double thermocouple are conducted to investigate the formation temperature of Fe-rich intermetallics in different AlSi casting alloys. In addition, the influence of chemical composition is examined by increasing the initial contents of iron, manganese, and chromium to 0.8 wt% each. The double thermocouple setup allows determining feeding points and solid fractions of the alloy compounds. To evaluate the data sets, the statistical program R is used to improve data processing and smoothing. The signature of Fe-rich intermetallics in the temperature-time plots corresponds to the detected phases in optical micrographs. In addition, scanning electron microscopy with energy-dispersive spectroscopy and electron backscattering diffraction are used to measure the local chemical composition and identify the iron-rich intermetallics. Real-time evaluation (differential calculation, first derivative, incl. smoothing) for an applicable filtration process can be performed using thermocouples with analog-to-digital converter and Python programs with an interactive graphical interface.