Casting premium-quality magnesium alloy components for aerospace and automotive applications poses unique challenges. Magnesium alloys are known to freeze rapidly prior to filling a casting cavity, resulting in misruns and cold shuts. In addition, melt oxidation, solute segregation and turbulent metal flow during casting contribute to the formation of fold defects. In this research, formation of fold defects in AZ91D and AE42 magnesium alloys cast via the permanent mold casting process was investigated. Computer simulations of the casting process predicted the development of a turbulent metal flow in a critical casting region with abrupt geometrical transitions. SEM and light optical microscopy examinations revealed the presence of folds in this region for both alloys. However, each alloy exhibited a unique mechanism responsible for fold formation. In the AZ91D alloy, melt oxidation and velocity gradients in the critical casting region prevented fusion of merging metal front streams. In the AE42 alloy, limited solubility of rare-earth intermetallic compounds in the alpha-Mg phase resulted in segregation of Al2RE particles at the leading edge of a metal front and created microstructural inhomogeneity across the fold.
Characterization of fold defects in AZ91D and AE42 magnesium alloy permanent mold castings
Beschreibung von Falzfehlern in Kokillengussteilen aus den Magnesiumlegierungen AZ91D und AE42
Materials Characterization ; 61 , 3 ; 296-304
2010
9 Seiten, 14 Quellen
Aufsatz (Zeitschrift)
Englisch
Alpha-Phase , Anwendung im Fahrzeugbau , Anwendung in der Luft- und Raumfahrt , Dauerformgießen , Faltung , Gießfehler , Inhomogenität , intermetallische Verbindung , Löslichkeit , Magnesiumgusslegierung , MgAlZn-Legierung , optische Mikroskopie , organische Verbindung , Rasterelektronenmikroskopie , Rechnersimulation , Seigerung , Seltenerdmetallzusatz
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