Precipitation evolution in Al–Zr and Al–Zr–Ti alloys during isothermal aging at 375–425 C

Formation of Al3Zr or Al3(Zr1 x Tix) precipitates with a metastable L12 structure was investigated in conventionally solidified A1–0.1 Zr, Al–0.2 Zr, Al–0.1 Zr–0.1 Ti, and Al–0.2 Zr–0.2 Ti (at.%) alloys aged isothermally at 375, 400, or 425 C. Pronounced hardening results from nanometer-scale, spheroidal Al3Zr or Al3(Zr1 xTix) (L12) precipitates within solute-enriched dendrites. Interdendritic regions contain a significantly lower number density of coarser cauliflower-, rodand plate-shaped precipitates with the L12 structure. Neither the magnitude of the peak-aged hardness, nor the subsequent loss in hardness due to overaging, is affected by ternary additions of Ti. After extended aging times (1600 h) at 425 C, there is no difference in the mean precipitate radii of spheroidal Al3Zr or Al3(Zr1 xTix) precipitates, confirming that Ti additions do not improve the coarsening resistance. Comparison with prior coarsening studies on Al3Zr, and Al3(Zr1 xVx), Al3(Zr1 xTix) and Al3(Zr1 x yVxTiy) (L12) precipitates at 425 C confirms the lack of an effect from ternary alloying additions. 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.