Formation of Nondendritic Primary Aluminum Phase in Hypoeutectic Alloys in Controlled Diffusion Solidification (CDS): A Hypothesis |
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Authors: | Abbas A Khalaf Peyman Ashtari Sumanth Shankar |
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Affiliation: | (1) Light Metal Casting Research Centre (LMCRC), McMaster University, Hamilton, ON, Canada, L8S 4L7; |
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Abstract: | 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. |
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