Evolutions of Microstructure and Mechanical Properties of Cryorolled 7085 Al Alloy After Annealing Treatments

Thermal stability plays an important role in practical applications of Al alloys. The microstructure is unstable because of high internal stress after cryorolling (CR), and the research on thermal stability of CR 7085 Al alloy is still lacking. In this work, solution-treated 7085 Al alloy was subjected to CR with a deformation of 90% and subsequently annealed at temperatures of 150–300°C for 1 h. The microstructure and mechanical properties of annealed samples were investigated. The results show that in the dispersed GP zone, η′ and η precipitates are successively precipitated from the matrix with the increase of annealing temperature, and their size increases gradually. Obvious equiaxed nanograins were formed after annealing at 250°C and 300°C. With the increase of annealing temperature, due to the annihilation of dislocations and coarsening of precipitates, the strength of the samples gradually decreased, and the ductility gradually increased, but the ductility suddenly dropped at 250°C. After annealing at 250°C, η′ precipitates have completely transformed into η ones, while η phase is incoherent with the matrix, so the ductility of the sample decreases despite the sharp decrease in dislocation density.