Effects of Zr, Ti and Sc additions on the microstructure and mechanical properties of Al-0.4Cu-0.14Si-0.05Mg-0.2Fe alloys

Abstract

The evolution of microstructure and mechanical properties of Al-0.4Cu-0.14Si-0.05Mg-0.2Fe (wt.%) alloys, micro-alloyed with Zr, Ti and Sc, were investigated. The addition of 0.2%Zr to base alloy accelerates the precipitation of Si-rich nano-phase in α-Al matrix, which plays an important role in improving the mechanical properties of an alloy. The tensile strength increases from 102MPa for the base alloy to 113MPa for the Zr-modified alloy. Adding 0.2%Zr+0.2%Ti to base alloy effectively refines α-Al grain size and accelerates the precipitation of Si and Cu elements, leading to heavy segregation at grain boundary. By further adding 0.2%Sc to Zr+Ti modified alloy, the segregation of Si and Cu elements is suppressed and more Si and Cu precipitates appeared in α-Al matrix. Accompanied with the formation of coherent Al3Sc phase, the tensile strength increases from 108MPa for the Zr+Ti modified alloy to 152MPa for the Sc-modified alloy. Due to excellent thermal stability of Al3Sc phase, the Sc-modified alloy exhibits obvious precipitation hardening behavior at 350°C, and the tensile strength increases to 203MPa after holding at 350°C for 200h.