Guohui Shi’s research while affiliated with General Research Institute for Nonferrous Metals (GRINM) and other places

Al–Zn–Mg–Cu alloys are widely used in aerospace, with recrystallization significantly influencing their stress corrosion resistance. This study examines the impact of recrystallization morphology on corrosion resistance in a high‐alloying Al–Zn–Mg–Cu alloy, focusing on lath‐shaped and equiaxed recrystallized grains. The findings reveal that, at the same recrystallization fraction, the equiaxed sample has a 2.83 times higher corrosion current density and a 1.15 times higher stress corrosion cracking susceptibility index than the lath sample. However, its critical stress intensity factor is only 89.3% of the lath alloy's. Lath recrystallization demonstrates superior stress corrosion resistance due to larger grain sizes, wider grain boundary precipitate spacing, lower Zn and Mg content, and higher Cu content. Finite element simulations and in‐situ tensile tests show that the equiaxed sample experiences more stress concentration and cracking at grain boundaries under the same applied stress. These results provide insights into optimizing the stress corrosion resistance of Al–Zn–Mg–Cu alloys.

Hot deformation is a crucial process in the manufacturing of aluminum alloy products, as its parameters exert a profound influence on the ultimate properties of the alloys. This work reports on the Al-Zn-Mg-Cu alloys at a deformation temperature of 450°C, a deformation rate of 5 mm/s, and deformation degrees of 50% and 90% in industrial settings. Following that, an extensive assessment of the alloys’ mechanical characteristics, including their fracture toughness, tensile strength, and fatigue performance. Furthermore, a quantitative analysis of the microstructure was undertaken using OM and EBSD, which revealed that both the average and sub-grain sizes of the two alloys exhibited comparable characteristics. However, the recrystallization fraction showed a difference, with the alloy deformed to 90% exhibiting a higher fraction than the alloy deformed to 50%, while these recrystallized grains are distributed in chains. With the increase of deformation degree from 50% to 90%, the yield and ultimate strengths increase slightly. The opposite law is demonstrated by fatigue crack propagation resistance and fracture toughness. Put otherwise, compared to the alloy deformed to 50%, the alloy deformed to 90% exhibited a faster rate of fatigue crack propagation and a lower fracture toughness. In summary, this research examines how the degree of deformation affects the mechanical characteristics and microstructure of Al-Zn-Mg-Cu alloys.

The Al-Zn-Mg-Cu alloy plate is a structural material widely used in aerospace, and its rolling process plays a crucial role in determining its performance. This study investigated the effects of different pass combinations of forward and spread rolling on the grain characteristics, strength, and fracture toughness of Al-Zn-Mg-Cu aluminum alloy plates under industrial conditions. The results show that initially using a small pass reduction followed by a larger one can improve the grain width and thickness on the Long Transverse–Short Transverse surface. Additionally, increasing the spread rolling pass enhances the grain width-to-thickness ratio on the TS surface. Performance tests indicate that grain characteristics have minimal influence on room-temperature tensile properties. However, a higher grain width-to-thickness ratio significantly improves the alloy’s fracture toughness.

In this research, the finite element approach was used to investigate the influence of machining type and machining sequence on the machining deformation of a 7055 aluminum alloy thick plate with an initial residual stress condition. The results reveal that the frame-first machining type produces much less machining distortion than the layer-first machining type. The machining distortion of the thick plate with the end-first connection with the frame-first machining sequence is the smallest. By developing an appropriate machining strategy, the machining distortion of the thick plate may be successfully decreased.

To investigate the dynamic recrystallization behavior of 7xxx aluminum alloys, the isothermal compression tests were carried on the 7056 aluminum alloy in the temperatures range of 320–440 °C and in the strain rates range of 0.001–1 s−1. In addition, the microstructure of samples were observed via electron back scanning diffraction microscope. According to the results, true stress and true strain curves were established and an Arrhenius-type equation was established, showing the flow stress increases with the temperature decreasing and the strain rate increasing. The critical strain (εc) and the critical stress (σc) of the onset of dynamic recrystallization were identified via the strain hardening rate and constructed relationship between deformation parameters as follows: εc=6.71×10−4Z0.137 3 and σp=1.202σc+12.691. The DRX is incomplete in this alloy, whose volume fraction is only 20% even if the strain reaches 0.9. Through this study, the flow stress behavior and DRX behavior of 7056 aluminum alloys are deeply understood, which gives benefit to control the hot working process.

Recrystallization could affect the fatigue performance of aluminum alloys by changing grain structure while the influence mechanism was not clear yet. To issue this problem, a high-alloying Al-Zn-Mg-Cu alloy with various recrystallization fractions obtained by solution treatment was investigated. The results of fatigue crack propagation (FCP) rate tests showed that with the deepening of recrystallization, FCP rate of the alloy decreased firstly and then increased, reaching a minimum FCP rate at a recrystallization fraction of 16.98%. These results are discussed in terms of recrystallization fraction and the size of recrystallization grain with the help of the mathematical model presented by Zheng and Manfred.

The flow behavior of a high-alloying Al–Zn–Mg–Cu alloy was studied by compression tests with the temperature range of 300–440 °C and the strain rates range of 0.001–1 s⁻¹, and the corresponding microstructural evolution was observed. Results show flow stress curves exhibit the peak value at a critical strain, and the peak stress decreases with increasing of deformation temperatures. Numerous precipitated particles with a small size and high-density dislocations should be responsible for the high flow stress. Dynamic recovery is the main way of flow softening while dynamic coarsening of precipitated particles and dynamic recrystallization also play a role in flow softening under low-temperature and high-temperature conditions, respectively. The continuous dynamic recrystallization is the major mechanism for dynamic recrystallization behavior.

Isothermal compression tests of the Al–9.4Zn–1.9Mg–2.0Cu alloy were carried out at the temperature ranging from 300 to 460 °C and the strain rate from 0.001 to 10 s⁻¹, and the deformation degree was 70%. Flow stress curves show that the flow stress decreases with the increasing deformation temperature and the decreasing strain rate. The measured flow stress was corrected because of the effect of friction. The corresponding corrected stress values are lower than measured stress values. The effect of friction is far greater when hot-deformations occurred at lower temperatures or higher strain rates. A constitutive equation considering the effect of strain on material constants (i.e. α, n, Q and A) are established based on the Arrhenius-type equation. Compared with the experimental results, the flow stresses calculated by the constitutive equation have a high precision with the correlation coefficient of 0.95. Results show that higher deformation temperatures and lower strain rates are beneficial for hot deformation of the Al–9.39Zn–1.92Mg–1.98Cu alloy.