Abstract
The effects of Mg alloying on the temporal evolution of Al 3Sc (L1 2 structure) nanoscale precipitates are investigated, focusing on the morphology and coarsening kinetics of Al 3Sc precipitates in an Al–2.2 Mg–0.12 Sc at.% alloy aged between 300 and 400 °C. Approximately spheroidal precipitates are obtained after aging at 300 °C and irregular morphologies are observed at 400 °C. The coarsening behavior is studied using conventional and high-resolution transmission electron microscopies to obtain the temporal evolution of the precipitate radius, and atom-probe tomography is employed to measure the Sc concentration in the α-matrix. The coarsening kinetics are analyzed using a coarsening model developed by Kuehmann and Voorhees for ternary systems [Kuehmann CJ, Voorhees PW. Metall Mater Trans A 1996;27:937]. Values of the interfacial free energy and diffusion coefficient for Sc diffusion in this Al–Mg–Sc alloy at 300 °C are independently calculated, and are in good agreement with the calculated value of interfacial free energy [Asta M, Ozolins V, Woodward C. JOM 2001;53:16] and the experimental diffusivity obtained for the Al–Sc system [Marquis EA, Seidman DN. Acta Mater 2001;49:1909; Marquis EA. Ph.D. Thesis. Materials Science and Engineering Department, Northwestern University, 2002; Fujikawa SI. Defect Diffusion Forum 1997;143–147:115].
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