Detektion von Phasen in Aluminiumlegierungen mittels optischer Emissionsspektrometrie mit intensitätsbasierter Einzelfunkenauswertung

Middelmann, Olaf; Bührig-Polaczek, Andreas (Thesis advisor); Senk, Dieter (Thesis advisor)

Aachen : Gießerei-Institut der RWTH Aachen (2022, 2023)
Book, Dissertation / PhD Thesis

In: Ergebnisse aus Forschung und Entwicklung 34
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2021

Abstract

The motivation for this work is the methodical extension of spectral analysis, to additionally determine present phases in the microstructure. In this thesis the three phase types titanium borides, aluminum oxides and AlFeSi phases are considered. With regard to the ferrous phases, the differentiation between the α-Al15(Fe,Mn)3Si2 and β-Al5FeSi modification is the main focus. Samples for spectral analysis are produced in sand casting process. Spectral analysis is performed using the QSG 750-II, SPECTROLAB LAVM12 and Q8 Magellan at the manufacturers facilities. The measured intensities of the element channels were used for method development. Metallographic evaluations serve to control the cast microstructure and to evaluate the influence of the analysis process. Using a scanning electron microscope (REM-EDX) the microstructural constituents are determined. The analysis process of OES-PDA shows a massive influence on the sample surface condition and microstructure. Remelting zones show inhomogeneous compositions based on the mixture of adjacent phases. With regard to the evaluation of titanium borides in the material, the procedure of outlier determination with matching spark numbers for titanium borides is appropriate. A comparison of the considered methods for limit value determination shows a higher sensitivity for the procedures IQR and MAD in comparison to SD and SK_IQR. While quantification depends strongly on the choice of method and parameters. The evaluation of the oxide load requires a prior determination of the measurement error for oxygen. A high-purity aluminum sample was used to define a new zero intensity level. The determination of the percentage deviation of each spark discharge to this zero intensity allows for the definition of a new criterion for the determination of oxides. To distinguish between the two phase types α- and β-AlFeSi the presented method relies on the element intensities of iron, manganese silicon and the ratio of manganese to iron; calculating the minimum squared deviation to defined phase regions. The quantified ratios of these phases do not correspond to the real phase fractions of the microstructure because of a strong influence by the remelting zone. However, the comparison of different samples shows the same tendencies as the metallographic evaluation. The self-learning analysis methods from the field of data mining show themselves to be methods with great potential, but in the studied case the necessary boundary conditions could not be sufficiently fulfilled in order to obtain reliable results. The presented methods successfully extend the functional range of OES PDA.

Institutions

• Division of Materials Science and Engineering [520000]
• Chair for Foundry Science and Foundry Institute [526110]