Precipitate Evolution and Strengthening in Supersaturated Rapidly Solidified Al-Sc-Zr Alloys
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UCTION
AGING in dilute Al-Sc alloys has been observed to form coherent L12 precipitates.[1,2] These precipitates demonstrate a higher thermal stability than more traditional precipitation strengthening Al alloys (e.g., Al-2xxx, Al-6xxx), meaning that Al-Sc alloys can be used at higher temperatures than those alloys without the unwanted coarsening and overaging of strength that results. As depicted in Table I, this increased thermal stability is a result of Sc having a relatively low diffusivity in Al when compared to other common precipitating additions such as Cu, Si, and Mg, as the coarsening kinetics are restrained by the low mobility of solute atoms.[3–7] In addition, a mismatch strain of only 1.3 pct between the matrix and the L12 Al3Sc precipitate phase[8] allows for a relatively stable precipitate interface and a reduced driving force for coarsening.[2] Sc has limited solubility below 673 K (400 C) of
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