Understanding grain refinement of Sc addition in a Zr containing Al-Zn-Mg-Cu aluminum alloy from experiments and first-principles

Abstract

In this work, we present a better insight into the grain refining mechanism of Sc addition in an Al-Zn-Mg-Cu-Zr aluminum alloy from experiments and first-principles. It is found a higher concentration of Sc can result in finer grains, but the refining efficiency was sharply decreased when the Sc/Zr ratio(wt.%) exceeds 1. Also, we determined the L12-Al3(Sc, Zr) was formed by Sc displacing Zr in L12-Al3Zr, and those generated particles distributed around L12-Al3Zr. Moreover, the content of Zr was found overwhelmed by Sc within a Sc and Zr containing particle in high Sc/Zr ratio alloys. The calculated surface energy indicates a low Sc doping (<21.4 at.%) tends to stabilize L12-Al3Zr(111) surface, when the doping content in the range of 21.4–35.7%, the clean L12-Al3Zr(111) is energetically favored, when the doping content is higher than 35.7%, the L12-Al3(Sc, Zr)(111) is preferred. Based on the interface energy, the capability of heterogeneous nucleation to α-Al can be ordered as L12-Al3(Sc, Zr) > L12-Al3Zr > L12-Al3Sc. However, in a Sc rich condition, the formation of L12-Al3(Sc, Zr)(111) and Al(111)/L12-Al3(Sc, Zr)(111) interface were hindered by the formation of L12-Al3Sc(111), thus, further refinement of grains was limited, the results well explained the experimental observations.