Effect of a special thermo-mechanical treatment process on microstructure and properties of 7185 alloy

A special thermo-mechanical treatment (ST) process involving two stages of deformation was studied, and the influence mechanism for the first stage of deformation (pre-deformation) on the microstructure evolution and properties of 7185 alloy was researched in detail. The results showed that increasing the amount of pre-deformation could increase the number of spherical precipitates, significantly increase the dislocation density, and form dislocation walls and dislocation cells. The medium-temperature precipitation (MTP) could transform the high-density dislocation cells into ordered dislocation arrays and form many substructures and sub-crystals. After the second stage of deformation (final hot rolling, FHR), the number of precipitates increased again. The sub-crystals were regularly arranged and microscopic shear bands formed. With a weakening of the pinning force, the boundary of the banded microstructure composed of high-density dislocations became straighter. After solution treatment, the movement of low angle grain boundaries (LAGBs) and sub-grain boundaries was blocked due to particle pinning and accumulated strain, which significantly promoted the transition from LAGBs to high angle grain boundaries, thus achieving grain refinement. Therefore, the maximum pre-deformation process (ST3: pre-deformation (250 °C, 60%) + MTP (400 °C, 40 min) + FHR (400 °C, 50%)) could significantly improve the plasticity and corrosion resistance of 7185 alloys.