UC Irvine

This study investigates the efficacy of Controlled Diffusion Solidification (CDS) in refining grain structure and improving castability in Al-4.5%Cu and 6061 alloys. Experimental results demonstrate that CDS, in combination with high cooling rates, produces smaller grains than either method alone with only minor reductions in the globular morphology, challenging existing theories on globular grain growth. Chromium additives further refine the grain structure, suggesting avenues to improve fluidity in 6061 cast by CDS. The study also reveals limitations in existing mixing methods, calling for improved techniques for solute homogenization.Hot tearing tests on are conducted on 6061 cast by CDS. Castability is influenced by both hot tearing susceptibility and fluidity; CDS excels in reducing the former but compromises the latter. High-pressure die casting emerges as the most suitable casting process for CDS, consistent with other semi-solid metal processes. Finally, a new mechanistic framework is proposed to explain CDS’s role in grain refinement. The framework considers nucleation dynamics, thermal and chemical equilibration, and solute field impingement, culminating in a globular microstructure. This study serves as a foundation for optimizing CDS for industrial applications, while also highlighting areas that require further research.