High Strength AA7050 Al alloy processed by ECAP: Microstructure and mechanical properties

Commercial AA7050 aluminium alloy in the solution heat-treated condition was processed by ECAP through routes A and BC. Samples were processed in both room temperature and 150 °C, with 1, 3, and 6 passes. The resulting microstructure was evaluated by optical microscopy (OM) and transmission electron microscopy (TEM). Only one pass was possible at room temperature due to the low ductility of the alloy under this condition. In all cases, the microstructure was refined by the formation of deformation bands, with dislocation cells and subgrains inside these bands. The increase of the ECAP temperature led to the formation of more defined subgrain boundaries and intense precipitation of spherical-like particles, identified as η′ and η phases. After the first pass, an increase in the hardness was observed, when compared with the initial condition. After 3 passes the hardness reached a maximum value, higher than the values typically observed for this alloy in the overaged condition. The samples processed by route BC evolved to a more refined microstructure. ECAP also resulted in significant strength improvement, compared to the alloy in the commercial overaged condition.

► ECAP improves the strength of the AA7050 Al alloy with no loss on ductility.
► Room temperature ECAP strengthens the alloy by grain refinement and work hardening.
► ECAP at 150 °C strengthens the alloy by grain refinement and precipitation.
► Second phase precipitation is accelerated by ECAP.
► Precipitates morphology is modified by ECAP.