Effects of Yb and Zr microalloying additions on the microstructure and mechanical properties of dilute Al-Sc alloys

It is known that Zr and Yb partition to the Al3Sc precipitates created during aging when microalloyed separately in dilute binary Al-Sc alloys. Addition of Zr delays precipitate coarsening, thereby improving the coarsening resistance of the ternary Al-Sc-Zr alloys. Addition of Yb increases the resistance against dislocation climb, thereby improving the creep resistances of the ternary Al-Sc-Yb alloys. A combination of microhardness, creep, and atom probe tomography measurements provide evidence that these effects of Zr and Yb additions are cumulative in quaternary dilute Al-Sc-Yb-Zr alloys: Yb increases their creep resistance at 300 degrees C compared with ternary Al-Sc-Zr alloys and Zr improves their coarsening resistance at 300 degrees C compared with ternary Al-Sc-Yb alloys. Additionally, excellent coarsening resistance is observed at 350 and 375 degrees C. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.