Influence of cerium on microstructures and mechanical properties of Al-Zn-Mg-Cu alloys

Effect of element cerium (Ce) on microstructure and mechanical properties of Al-Zn-Mg-Cu alloys has been investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and hardness test. The results show that addition of Ce can remarkably refine the as-cast grains and eutectic microstructure. A transformation from Mg(Zn,Cu,Al)₂ phase to Al₂CuMg phase is observed during homogenization. Furthermore, the Ce addition introduces changes in the precipitation process and consequently in the age-hardening behavior of the alloy. Microstructural measurements reveal that the addition of Ce promotes the precipitation of η′ phase, but it also partly retards the precipitation of GP zones. The density of precipitates decreases in a certain degree and rod-like η′ precipitates increase when Ce content is from 0.2% to 0.4% (mass fraction).