Mechanical properties and optimization of the aging of a dilute Al-Sc-Er-Zr-Si alloy with a high Zr/Sc ratio

Precipitation strengthening behavior during aging of an Al-0.014Sc-0.008Er-0.08Zr-0.10Si (at.%) alloy was investigated utilizing microhardness, electrical conductivity and scanning electron microscopy. This new composition, with a Sc/Zr ratio (in at.%) smaller than 1/5 represents a significant reduction of the alloy's cost, when compared to more usual Al-0.06Sc (at.%) based alloys with typical Sc/Zr ratios of 3. The research presented herein focuses on identifying the optimal homogenization duration at 640 degrees C and additionally the temperature range at which a single-step aging treatment will achieve the highest possible microhardness in the shortest time. Due to a compromise between dissolution of Er-Si rich primary precipitates, homogenization of the Zr distribution and precipitation of large Al3Zr precipitates, 8 h at 640 degrees C appears to be the optimal homogenization duration for this alloy, leading to an hardness of 571 +/- 22 MPa after aging for 24 h at 400 degrees C. To study the precipitation behavior of this low-Sc concentration alloy, isochronal aging to 575 degrees C with two different heating rates was performed. The small Sc concentration, compensated by a high Zr concentration, permits the alloy to achieve a similar peak microhardness during isochronal aging (587 +/- 20 MPa) as the corresponding Sc-richer and Zr-leaner alloys. The isochronal aging experiments permits us to identify the best aging temperature as between 350 and 425 degrees C. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.