Evolution of the Cracks, Microstructure, and Properties of AA7020 Twin-Roll Casting Sheets during Warm Rolling Processes

AA7020 twin-roll cast sheets were warm rolled with different processing parameters to investigate the evolution of cracks, microstructure and properties by a single variable method. The as-cast rolled and as-warm rolled sheets were examined by optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), a Vickers hardness tester and an electronic universal testing machine. As the reduction ratio increased, the grains became finer, the mechanical properties improved, and the cracks gradually healed. The grain size, mechanical properties, and cracks first increased and then decreased with increasing warm rolling temperature. The cracks healed by occlusion between grains. When the warm rolling temperature was too high, the grains grew upward, the mechanical properties decreased, and the healed cracks left scars. The optimum process parameters were a warm rolling temperature of 350  °C and a reduction ratio of 80%.