Microstructure evolution during homogenization and hot workability of 7055 aluminum alloy produced by twin-roll casting

7055 aluminum alloy was produced by twin-roll casting (TRC) and by conventional mold casting (MC). Homogenization at 465 degrees C for 24 h with natural cooling was applied, followed by uniaxial hot compression tests to verify the hot workability of the alloy. The results show that the TRC sample possessed a lower intermetallics fraction with a smaller size but much larger grain size than the MC sample in both the as-cast and as-homogenized microstructures. In the post-homogenization cooling stage, precipitation of T phase (AlZnMgCu) occurred, Al3Zr acted as nucleation sites for the precipitation of T phase. T phase precipitation-free zone (PFZ) formed at the dendrite arm regions, the formation of the T phase PFZ was based on the Ostwald ripening mechanism. During hot compression test, the MC samples exhibited overall higher flow stress levels than those of TRC samples since the combination of the stronger grain refined strengthening and particle strengthening effects in the MC sample than those in the TRC sample. Macrocracks were developed in the MC sample during hot compression, the source of which was the coarse intermetallic particles in the microstructures. No macrocrack was formed in the TRC sample under the same compression conditions owing to its much finer initial intermetallics, lower accumulation of substructures and local stress. (C) 2021 Published by Elsevier B.V.

Automated summary

The 7055 aluminum alloy was produced by twin-roll casting and conventional mold casting methods, and their hot workability performance showed differences in terms of grain size, intermetallics fraction, and formation mechanism.