Fine-grained AA 7075 processed by different thermo-mechanical processings

Grain refinement by two classical thermo-mechanical processings (RI-ITMT and J-ITMT) and an alternative short-cycled thermo-mechanical processing (NTMT) of high strength AA 7075 alloy based on particle-stimulated nucleation of recrystallization (PSN) was investigated. The main difference between those TMPs was investigated in detail, especially the specific grain refining procedure of NTMT was carefully characterized. Their mechanical properties after TMPs were studied as well. The results indicated that the finest grain structure (~8.2 μm) can be achieved by RI-ITMT, and a similar structure (~9 μm) can be obtained by the present NTMT while a much coarser structure (~20 μm) was obtained by J-ITMT. As a result, the strength anisotropy can be eliminated by NTMT and RI-ITMT, and a significant increase in elongation can be achieved by all the processings while maintaining high strength. Warm deformation can accelerate MgZn2 precipitation, coarsening and spheroidization, and more uniform distribution of MgZn2 throughout the Al matrix can be accomplished in reference to the one with only overaging. Deformation-enhanced precipitation and PSN played a key role in grain refinement during NTMT. NTMT combines two ordinary procedures – warm rolling and continuous rolling – in present industry together, which makes grain refinement of age-hardenable Al alloys more time-saving.