Fine-grained sheets of AA7055 Al alloy were produced by an improved double-stage rolling thermomechanical treatment (DRTMT) assisted by deformation-enhanced precipitates (DEPs). The DRTMT composed of a low temperature pre-deformation, an intermediate annealing, and a final hot rolling exhibited significantly superior tensile ductility to the conventional rolling thermomechanical treated alloy (CRTMT). Numerous fine spherical DEPs appeared after the pre-deformation. Those DEPs could exert a strong drag force on the migration of boundaries and dislocations. Dislocation cells were formed due to the drag force and dynamic recovery. These dislocation cells become polygon sub-grains by static recovery during the subsequent intermediate annealing. After the final hot deformation, with further deformation and rising temperature, low angle grain boundaries gradually stabilized and transferred to high angle grain boundaries. Due to the transformation, fine equiaxed grains were formed after DRTMT. The DRTMT alloys display superior elongation to the CRTMT alloy while maintaining high strength for grain refinement. Thus, DRTMT would be a good alternative to manufacture different heat-treatable Al alloys with fine grains efficiently.

As heating time, temperature, strain and strain rate are the four most commonly used controllable parameters in thermomechanical treatments of high strength aluminum alloy, which have great influence on microstructures and mechanical properties. 7055 Al alloy was subjected to solution and thermomechanical treatment (4 routes) at different heating time (route 1), temperatures (route 2), strains (route 3) and strain rates (route 4) to investigate their effects on grain structure and precipitation. The results show that MgZn₂ particles are almost completely dissolved back into the matrix after solution treatment, but the coarse Al₇Cu₂Fe and Al₂CuMg remain steady. Particles preferentially precipitate at grain boundaries. Precipitates free zones appear after aging at 300 °C for different time in route 1. With the increased over aging time, precipitates grow and the quantity of rod-shaped increases. After hot deformation, grains are elongated and numerous deformation induced precipitates are formed. Grain width increases with the increase of strain temperature/rate in route 2 and route 4. However, with further strain, grain width first decreases and then increases with the minimum value taken at 60% deformation in route 3. Due to the effect of deformation on spheroidization and refinement of precipitates, the size of precipitates decreases with strain and is spheroidized gradually in route 2 compared with route 1. Strain energy plays the dominant role during over aging or at low strain leading the rod liked precipitates, with the increase of strain, interfacial energy plays the decisive role, and precipitates are spherical.

After different rolling conditions, four 7055 aluminum alloy samples with different precipitation sizes were measured by scanning electron microscope, transmission electron microscope and laser ultrasonic. The attenuation coefficients of ultrasound measured by laser ultrasonic were calculated in the time domain, frequency domain and wavelet denoising, respectively. The relationship between the precipitate size and attenuation coefficient was established. The results show that the attenuation of the ultrasonic wave is related to the size of the precipitated phase; this provides a new method for rapid non-destructive testing of the precipitation of aluminum alloys.

This study explores the hot deformation behavior of Al–Zn–Mg–Cu alloy through uniaxial hot compression (200 °C–450°C) using the Gleeble-1500. True stress–strain curves were corrected, and three models were established: the Arrhenius model, strain compensated (SC) Arrhenius model, and strain compensated recrystallization temperature (RT) segmentation-based (TS-SC) Arrhenius model. Comparative analysis revealed the limited predictive accuracy of the SC Arrhenius model, with a 25.12% average absolute relative error (AARE), while the TS-SC Arrhenius model exhibited a significantly improved to 9.901% AARE. Material parameter calculations displayed variations across the temperature range. The SC Arrhenius model, utilizing an average slope method for parameter computation, failed to consider temperature-induced disparities, limiting its predictive capability. Hot processing map, utilizing the Murty improved Dynamic Materials Model (DMM), indicated optimal conditions for stable forming of the Al–Zn–Mg–Cu alloy. Microstructural analysis revealed MgZn₂ precipitation induced by hot deformation, with crystallographic defects enhancing nucleation rates and precipitate refinement.

In order to obtain fine grained structure efficiently, a new multi-step rolling process (MSR: pre-deformation + intermediate annealing + hot deformation) was applied in Al-Zn-Mg-Cu plates. Conventional hot rolling (CHR) was also carried out as a contrast experiment. The evolution of microstructures and improvement of mechanical properties were analyzed by optical microscope, scanning electron microscope, transmission electron microscope, X-ray diffractometer, and tensile tests. The results show that the MSR process can obtain finer longitudinal grain size and better mechanical properties than CHR, which can be explained as follows: spheroidization of precipitates wrapped by high density dislocations could be promoted by increased pre-deformation; numerous ordered substructures were formed during short-period intermediate annealing at high temperature; in the subsequent hot rolling process, the retained spherical precipitates pinned dislocations and boundaries. With the increase of accumulated strain, low angle grain boundaries gradually transformed into high angle grain boundaries, leading to grain refinement. With the increased pre-deformation (MSR₁ 20 + 60%, MSR₂ 40 + 40%, MSR₃ 60 + 20%), the effect of grain refinement and plasticity improvement gradually weakened. The optimum thermomechanical process (MSR₁ solid solution + pre-deformation (300 °C/20%) + intermediate annealing (430 °C/5 min) + hot deformation (400 °C/60%)) was obtained, which can increase elongation by ~25% compared with the CHR process, while maintaining similar high strength for reduced longitudinal grain size.