Warm formability and post-forming microstructure/property of high-strength AA 7075-T6 Al alloy

Formability of peak-aged AA 7075-T6 sheet across a temperature range from room temperature to 250 degrees C as well as post-forming microstructure/property were investigated in this paper. It showed that the optimized formability was obtained at 200 degrees C, due to the higher ductility and work hardening capacity at this temperature. The dominant phases in 7075-T6, 200 degrees C warm formed, and 250 degrees C warm formed samples were fines eta' and GP zones, well-developed eta', and coarser eta phases, respectively. Post-forming and post-paint-baking mechanical property of 7075 samples was closely associated with those corresponding microstructures. Specifically, 200 degrees C warm forming caused limited coarsening of matrix precipitates (MPts) and generated a certain number of dislocations, due to the combined effect of the decreased precipitation strengthening and increased dislocation strengthening, the inherent high strength of 7075-T6 was perfectly preserved after 200 degrees C forming. However, 250 degrees C forming led to severely decreased hardness due to the sharply coarsened MPts. Furthermore, the paint-baking treatment exerted little influence to MPts, grain boundary precipitates (GBPs) and precipitate free zone (PFZ), thus the hardness loss caused by paint-baking was unobvious. Overall, 200 degrees C was the appropriate temperature under which the peak-aged 7000 alloys exhibited enhanced formability and maintained high post-forming strength, after paint baking, the drawn component possessed microstructure/property similar to those of retrogression and re-aged (RRA) samples. (C) 2016 Elsevier B.V. All rights reserved.