The influence of zirconium on decomposition in high strength aluminium alloys

In high strength Al-Zn-Mg and Al-Zn-Mg-Cu alloys dynamical recrystallization during hot working is successfully suppressed by metastable Al 3Zr precipitates that are formed during the homogenization treatment. The density, size and distribution of Al 3Zr particles were varied by using different Zirconium concentrations (0–0,2 wt % Zn) and homogenization procedures. Two calorimetric methods were used to study the influence of Al 3Zr-particles on the precipitation of GP-Zones during cold ageing and of metastable phases (η', R) during warm ageing respectively. Cold ageing was found to be retarded whereas warm ageing turned out to be enhanced by Al 3Zr-partic1es. An explanation is given on the basis of the conservation of dislocations and subgrain boundaries by Al 3Zr-partic1es.