Effect of iron content on microstructures and mechanical properties of new ultra-high strength Al-Zn-Mg-Cu alloys

The impact of Fe content on the microstructures and mechanical properties of an ultra-high strength aluminum alloy, namely, Al-10.50Zn-2.35Mg-1.25Cu-0.12Cr-0.1Mn-0.1Zr-0.1Ti, was investigated. It is found that the increase of Fe content leads to a notable rise in the volume fraction of microscale secondary phases, including (Cu, Fe, Mn, Cr)Al 7 , σ phase (composed of Al, Zn, Mg, and Cu elements), and Al 3 (Zr, Ti). The formation of these secondary phases results in the depletion of certain phase-forming elements, thereby significantly reducing the quantity of strengthening phases. Fe imposes minimal impact on tensile strength, but it can significantly alter the elongation ( δ ). For instance, the average elongation of the alloy with 0.18 wt.% Fe ( δ =4.5%) is less than half that of the alloy with Fe less than 0.1 wt.% ( δ =9.9%-10.9%). The reduction in elongation is attributed to the combined effects of the formation of coarse secondary phases and the diminished quantity of strengthening phases around these coarse phases.