Repelling effect of Si on Cu atoms enhances the strength and ductility of Al alloys: Atom probe tomography and first-principles analysis

Abstract

This study investigated the ordered transformation of Cu-rich nanophases and Cu–Si clusters in Al alloys using atom probe tomography and first-principles calculations. Initially, thin white films of Cu precipitates were observed within a porous Si structure, with temperature triggering the depletion of high Cu concentrations from Si and the formation of metastable Cu–Si clusters. Strong Cu–Al bonding accelerated the precipitation of Cu-rich nanophases, and the expulsion of Cu from Si and Cu–Si clusters was attributed to the mechanisms of “like charges repel” and “Si-volume repulsion.” Ab initio molecular dynamics simulations revealed that Si enhanced the diffusion of Cu atoms into vacancies at elevated temperatures.