An experimental and theoretical investigation of the formation of Zr-containing dispersoids in Al-4.5Zn-1Mg aluminum alloy

One of the primary objectives of the homogenization treatment applied to direct-chill cast aluminium alloys prior to hot deformation is to create small dispersoids that later act as recrystallization inhibitors during deformation and subsequent solution treatments. The current research concerned the formation of Zr-containing dispersoids during the homogenization treatment of AA7020 aluminium alloy with different Zr contents. A numerical model was applied to simulate the formation of Al3Zr dispersoids. The effects of Zr content and homogenization parameters (i.e., time and temperature) on the sizes and number densities of dispersoids were included in the model. The model predictions were validated with experimental results. An optimum homogenization treatment was proposed on the basis of the results of modelling in terms of Zener drag pressure and verified on the alloy after hot compression testing and annealing.