Recrystallization behavior of a co-cast AA3xxx-AA6xxx aluminum alloy laminate - Effect of annealing conditions and cold reduction levels

The annealing behavior of a laminated AA3xxx-AA6xxx alloy system is investigated at temperatures and conditions which represent fine particle presence or dissolution in the AA6xxx (i.e. core) layer, as well as 60 or 80% cold reduction levels. The through-thickness microstructural characteristics of the cold rolled and annealed laminates are analyzed using various methods. It is found that the average grain size of the AA3xxx (i.e. clad) layer is generally finer than that of the core layer and the grains are more equiaxed in that layer for all conditions studied. The annealed microstructure of the core layer is also more strongly affected by the change in the annealing conditions. The dependencies of the average grain size and grain size aspect ratio on the annealing conditions are dictated by the presence, size, distribution and thermal stability of particles. A higher level of cold reduction results in reversing the trend of change in the grain size aspect ratios of both layers with annealing temperature in the range of 380 to 420 °C (1 h), while it yields characteristics similar to that obtained by 60% reduction when annealing is conducted for 30 s at 540 °C. These results are explained through the microstructural evolution parameters that are affected by cold rolling and annealing conditions.