Coarsening Kinetics In Al-Sc-Zr Alloys

A. TOLLEY; V. RADMILOVIC; U. DAHMEN

Phoenix, Arizona, EEUU

Conferencia; Solid to Solid Phase Transformations in INorganic Materials 2005; 2005

We have investigated the coarsening kinetics of Al3X-type phases in binary Al-Sc and ternaryAl-Sc-Zr alloys. Addition of Zr to binary Al-Sc is known to enhance the alloy’s recrystallizationresistance and hardness. This work uses transmission electron microscopy to examine the effectof Zr additions on the precipitation kinetics and morphology of Al3(Sc,Zr) precipitates. Since Zris soluble in Al3Sc, which is isostructural with Al3Zr, it is usually assumed that the precipitates internary Al-Sc-Zr are Al3(Sc,Zr). In this study, we find coherent precipitates with L12 structureand highly anisotropic shapes that consist of a core of Al3Sc surrounded by a thin shell of Al3Zr.The addition of Zr strongly modifies the size of the L12 precipitates during aging by impedingthe coarsening kinetics. The activation energy for coarsening was measured to be ~190kJ/mol forboth Al-Sc and Al-Sc-Zr alloys. The reduced coarsening rate in the ternary alloy is apparentlyrelated to the interfacial energy between the Al matrix and the Al3(Sc,Zr) precipitate.