Due to their excellent properties, nickel-based superalloys are extensively used in critical parts of modern aero engine and gas turbine. The hot deformation behaviors of a typical nickel-based superalloy are investigated by hot compression tests with strain rate of (0.001-1) 1/s and forming temperature of (920-1040) oC. Results show that the flow stress is sensitive to the forming temperature and strain rate. With the increase of forming temperature or the decrease of strain rate, the flow stress decreases significantly. Under the high forming temperature and low strain rate, the flow stress-strain curves show the obvious dynamic recrystallization. Based on the stress-dislocation relation and kinetics of dynamic recrystallization, a two-stage constitutive model is developed to predict the flow stress of the studied nickel-based superalloy. Comparisons between the predicted and measured flow stress indicate that the established physically-based constitutive model can accurately characterize the hot deformation behaviors for the studied nickel-based superalloy.

The creep-aging behaviors of 7075 aluminum alloy are studied by uniaxial tensile creep experiments under elevated temperatures. The effects of creep-aging temperature and applied stress on the precipitates of 7075-T651 aluminum alloy are investigated using scanning electron microscope (SEM) and transmission electron microscope (TEM). Results show that: (1) Coarse insoluble precipitates ( and ) and intermediate precipitates ( and ) are found in the aluminum matrix, and the effects of creep-aging treatment on these precipitates are not obvious; (2) The main aging precipitates are and phases, and the aging precipitates grow up with the increase of creep-aging temperature and applied stress; (3) With the increase of creep-aging temperature and applied stress, the precipitates are discontinuously distributed on the grain boundary, and the width of precipitate free zone increases with the increase of creep-aging temperature and applied stress; (4) Compared with the microstructure in the traditional stress-free aged sample, the creep-aging process can refine the precipitates and narrow the width of the precipitate free zone.

The hot tensile deformation and fracture behaviors of the hot-rolled AZ31 magnesium alloy were studied by uniaxial tensile tests with the temperature range of 523-723 K and strain rate range of 0.05-0.0005 1/s. Effects of deformation parameters on the strain hardening rate, strain rate sensitivity, microstructural evolution and fracture morphology were discussed. The results show that: (1) The flow curves show a considerable strain hardening stage and no obvious diffuse necking stage under the relatively low temperatures (523 and 573 K). (2) The elongation to fracture increases with the increase of the deformation temperature. But, the sharp drop of the elongation to fracture under 723 K and 0.0005 1/s results from the synthetical effects of the grain growth, inverse eutectic melting reaction (α+β=L) and the incipient melting of α matrix. (3) For the case with the deformation temperature of 623 K and relatively low strain rates, the fracture mechanism is the combination of the void coalescence and intergranular fracture. (4) Under the deformation temperature of 723 K, the fine recrystallized grains experienced a rapid growth and the deformation mechanism is the dislocation creep with the help of inverse eutectic liquid phase. (5) The presence of proper amount of liquid phase on the grain boundary changes the deformation mechanisms, and makes great contribution to the high ductility. However, it will deteriorate the material ductility if the amount of liquid phase is too much.

The effects of the deformation temperature and strain rate on the high-temperature flow behavior of 7075 aluminum alloy were studied by hot compressive tests. Based on the experimental data, the efficiencies of power dissipation and instability parameter were evaluated, and processing maps were constructed by superimposing the instability map over the power dissipation map. Microstructural evolution of 7075 aluminum alloy during the hot compression was analyzed to correlate with the processing maps. Results show that (1) The flow stresses increase with the increase of strain rate and the decrease of deformation temperature; (2) The high-angle boundaries and coarse precipitations distributing in the grain interior/boundaries, which may result in the deep inter-granular corrosion and large areas of denudation layer, should be avoided in the microstructures of the final products; (3) The optimum hot working domain is the temperature range of 623-723 K and strain rate range of 0.001-0.05 s-1.

The uniaxial tensile creep tests of Al–Cu–Mg alloy were carried out over a wide range of temperature and applied stress. The effects of applied stress and creep aging temperature on the precipitation in Al-Cu-Mg alloy were discussed. It is found that the precipitation process is very sensitive to the applied stress and creep aging temperature, and S phase (CuMgAl2) is the main precipitate under the tested creep conditions. With the increase of applied stress and creep aging temperature, S phase easily grows up and becomes sparse. Meanwhile, the creep aging leads to the discontinuous distribution of precipitation phase in grain boundary, which can improve the corrosion-resistance of Al-Cu-Mg alloy. Because the lattice misfit of acicular exudation phase is far less than that of disk-shaped phase, the applied stress/strain fields will alert the competitive precipitation equilibrium between different strengthening phases. So, the large applied stress and high aging temperature easily make the preferential precipitation process as SSS→GPB→S″→S′→S.