The Effect of Additions of Mn and Fe on the Structure of an Al-2 at.% Zn-1 at.% Mg Alloy

The structure of an Al-1.9 at.% Zn-1.3-at.% Mg mother alloy with additions of Mn and Fe, respectively, were investigated by TEM and microprobe analysis for two different heat treatments, namely direct quench from 490 °C to 160 °C and a two-step ageing treatment (preageing at RT for 7d before storing at 160 °C), to explain the differences in the course of the hardness obtained during the ageing at 160 °C. The differences of the structure observed are explained in terms of the tendency of the additives to form intermetallic phases, particularly in the grain boundaries.