The Effects of Cooling Rate on Microstructure Formation during Solidification of 319 Alloy

• Published in: International journal of metalcasting 2024-07, Vol.18 (3), p.2079-2091
• Main Authors: da Penha Gomes, Izabel, Barros, André, Brollo, Gabriela Lujan, da Silva, Cássio Augusto Pinto, Cheung, Noé, Zoqui, Eugênio José
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Materials Science; Metallic Materials; Structural Materials; Technical Paper
• ISSN: 1939-5981; 2163-3193
• DOI: 10.1007/s40962-023-01145-z

This work assesses the effect of cooling rate ( T ˙ ) on the solidification kinetics and microstructural evolution of a 319 aluminum alloy with and without the addition of Al–5 wt%Ti–1wt%B grain refiner. Directionally solidified samples were produced under various cooling rates (from 0.05 to 40 °C/s). Microstructure coarsening was then quantitatively analyzed by measuring grain size (GS) and primary ( λ 1 ), secondary ( λ 2 ) and average ( λ L ) dendrite arm spacing. The results show that polarized optical images can be used to identify dendrite fragments between neighboring primary dendrites, allowing a more accurate microstructural analysis after the addition of grain refiner. The results also show that, for a given T ˙ , although GS is reduced after the addition of grain refiner, the respective values of λ 1 , λ 2 and λ L remain practically the same. In other words, the grain refiner only affects nucleation and not grain growth. Experimental growth equations are proposed to represent this behavior. Furthermore, λ L is shown to be a good parameter for evaluating microstructural refinement.