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The novelty of the controlled diffusion solidification (CDS) process is the mixing of two precursor alloys with different thermal masses to obtain the resultant desired alloy, which is subsequently cast into a near-net-shaped product. The critical event in the CDS process is the ability to generate a favorable environment during the mixing of the two precursor alloys to enable a well-distributed and copious nucleation event of the primary Al phase leading to a nondendritic morphology in the cast part. The turbulence dissipation energy coupled with the undercooling of the precursor alloy with the higher temperature enables the copious nucleation events, which are well distributed in the resultant mixture.

Controlled diffusion solidification (CDS) is a novel process wherein specific Al alloys can be cast by mixing two precursor alloys of specific compositions and temperature and subsequently casting the resultant mixture. This process enables a nondendritic morphology of the primary Al phase in the cast samples, which is beneficial in mitigating hot tearing tendencies and enabling castability of dilute Al (wrought) alloys to obtain castings with superior mechanical and performance properties. In this study, a hypothesis is proposed to describe the mechanism of the CDS process, specifically the processes of mixing two precursor alloys and a subsequent solidification process. Al -4.5 wt pct Cu was used as an example alloy system to propose a hypothesis and to verify the various features in the mechanism of mixing two alloys. Experimental results show that the mixing process naturally causes copious nucleation of one of the alloys mixed and that the turbulence energy during mixing distributes these nuclei uniformly to enable a favorable solidification condition for a nondendritic cast microstructure. It is critical that the alloy with the higher thermal mass (mass and temperature) is mixed into the alloy with lower thermal mass to obtain a valid CDS process and that the reverse will not yield a favorable homogeneous cast sample. Certain critical parameters during the CDS process have also been identified and quantified for a favorable microstructure of the casting.