Microstructural evolution in aluminium alloy 7050 during processing

The microstructural evolution in AA7050 during post homogenization cooling, and its influence on behaviour during preheat, hot rolling, and solution treatment, has been investigated. It is shown that slow cooling, at a rate typical of industrial processing, leads to a complex sequence of large, heterogeneously nucleated precipitates. In particular, S-phase particles grow to over 7 μm in diameter. These particles are retained during preheat to rolling, and are above the critical size required to act as particle stimulated nucleation sites for recrystallization. Furthermore, by removing solute they prevent the formation of fine particles during preheat. This leads to a final recrystallized fraction that is over four times larger in homogenized and slow cooled material than in material quenched rapidly from homogenization.