The in fluence of Sc-Si clusters on aging hardening behavior of dilute Al-Sc-(Zr)-(Si) alloy

The aging hardening behaviors of Al-0.12Sc and Al-0.12Sc-0.2Zr (wt.%) alloys with the addition of Si range from 0.05 wt% to 0.3 wt% were investigated by microhardness and transmission electron microscopy. The results indicate that content of similar to 0.15% Si is optimal and Sc-Si clusters forming at the early ageing stage hinder the evolution process of Al3Sc. Upon aging isochronally, Al-Sc-(Zr)-Si alloy shows two stages hardening. The first strengthen stage occurs because of the formation of Sc-Si clusters, and peak hardness of the second stage owes to (Al,Si)(3)Sc evolving from the clusters. During aging isothermally at 275 degrees C, Al-Sc-Si and Al-Sc-Zr-Si show similar hardening characteristics. But ageing at 225 degrees C, the Sc-Si clusters are relatively stable, the second stage increase in the Al-Sc-(0.15, 0.3%)Si alloys have no appearance. Clustering behavior of Sc and Si does not be changed by the addition of Zr. The Al-Sc-Zr-Si alloy exhibits better thermal stability. Because partition of Zr to the preceding formed (Al,Si)(3)Sc reduces the coarsening rate of the precipitates. (C) 2020 Elsevier B.V. All rights reserved.