Effects of heat treatment on the nanoscale precipitation behavior of 7055 aluminum alloy under dynamic shock

This study is intended to examine the effects of heat treatment on the microstructural evolution of 7055 aluminum, an area rarely reached by previous studies. Considering that 7055 aluminum alloy belongs to the aging hardening type, the difference of heat treatment process will lead to a large difference in mechanical properties and microstructure of the materials. Dynamic shock test is conducted on the alloy after treated by T6 and T6I4 processes. The result demonstrates that before dynamic shock, the precipitates on the grain boundary of T4-state alloy are fine, straight and continuously, and the precipitation-free zones (PFZs) around the grain boundary are quite narrow; the precipitates on the grain boundary of T6I4-state alloy are spheroidized and discontinuous, and the PFZs around the grain boundary are quite broad. Under room temperature, the dispersed grains of T4-state alloy are large in size while those of T-6I4-state alloy are finer with concentrated, very dense dislocations around the dispersed grains. The dislocation density displays an obvious positive correlation to the strain rate: The larger the strain rate, the higher the dislocation density. After dynamic shock at 6000s-1, the dislocations are tangled into dislocation walls and the dislocation cells shrink in size. More dislocation cells form in T6I4-state alloy than in T4-state alloy. Under high temperatures, the dislocation density displays an obvious negative correlation to the dynamic shock temperature: As the dynamic shock temperature increases, the dislocation density in the alloy decreases significantly. Under 120 °C, the dislocation density in T4-state specimen increases. A lot of the dislocations are tangled into dislocation walls. Dislocation walls as well as cellular substructures occur in T6I4-state alloy. Under 320 °C, a lot of irregular dislocation networks appear in T6-state alloy, and these dislocations are obstructed by coarsening precipitates; the precipitates in the T6I4-tread alloy are dissolved. Only dislocations beamed into individual single-root structures are observed. The dislocation density is very low.