SCANDIUM EFFECTS ON NUCLEATION UNDERCOOLING IN Al-Cu DROPLETS GENERATED BY IMPULSE ATOMIZATION AND ELECTROMAGNETIC LEVITATION

摘要

Development of alloys with increased mechanical properties is an ongoing challenge in the production of materials for Additive Manufacturing. Mechanical properties improvement are achievable through microstructural refinement based on high undercooling induced rapid solidification as well as through alloying elements addition. Transition Metals are usually added to Al-based alloys to yield supersaturated solid solution upon rapid solidification. Nucleation undercooling is one of the most important parameters directly relating solidification processing with microstructural evolution. Therefore, its quantification is key to getting direct information on the specific solidification pathway and thermal history that control microstructures formation. This paper investigates the effects of minor Sc addition (up to 0.4wt %) to Al-4.5wt% Cu on nucleation undercooling during containerless solidification of the alloys under high cooling rate by Impulse Atomization and low cooling rate by Electro-Magnetic Levitation. While direct measurements of primary and eutectic nucleation undercoolings could be made on droplets generated by the Electro-Magnetic Levitation system, the undercooling values in Impulse Atomized droplets have been calculated based on the measured fractions of eutectic and the modeling of secondary dendrite arms coarsening. Analysis of undercooling from both slow (Electro-Magnetic Levitation) and fast (Impulse Atomization) cooled samples allows mapping out of a wide range of solidification microstructures as a function of their processing history.