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.

Numerical simulations can be truly reliable only when a proper material flow stress relationship is built because of its effective role on metal flow pattern as well as the kinetics of metallurgical transformation. Based on the hot compressive deformation behaviors of 42CrMo steel, a comprehensive constitutive model has been developed to predict stress–strain curve up to the peak stress. A new material parameter L, which is sensitive to the forming temperature and strain rate, was proposed in the developed constitutive model. Additionally, the mathematical models to predict peak stress and peak strain were established based on experimental results. The stress-strain values predicted by the developed model well agree with experimental results, which confirmed that the developed constitutive equation gives an accurate and precise estimate for the flow stress of 42CrMo steel.

The hot tensile deformation behaviors and fracture characteristics of a typical Ni-based superalloy are studied by uniaxial tensile tests under the deformation temperature range of 920-1040 oC and strain rate range of 0.01-0.001 1/s. Effects of deformation parameters on the flow behavior, microstructural evolution and fracture characteristics are discussed in detail. The results show that the flow behaviors are significantly affected by the deformation temperature, strain and strain rate. Under relatively low deformation temperatures (920, 950 and 980 oC), the flow curves are composed of three distinct stages, i.e., work hardening, steady stress and flow softening stages. The flow curves show the typical DRX characteristics under relatively high deformation temperatures (1010 and 1040 oC). With the increase of deformation temperature or the decrease of strain rate, the fraction of recrystallized grains increases. The synthetical effects of localized necking and microvoid coalescence cause the fracture of the studied superalloy under all the deformation conditions. δ phase and carbides are the nucleus for the formation of microvoids. Also, δ phase plays an important role in the coalescence of microvoids.

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.

The high-temperature flow behavior of Al–Cu–Mg alloy is studied by the hot compressive tests over wide range of strain rate and forming temperature. Considering the negative effects of the interfacial friction on the heterogeneous deformation of specimen, the measured flow stress was corrected. The effects of processing parameters on material flow behavior are discussed. Based on the measured stress–strain data, a phenomenological constitutive model, which considers the coupled effects of strain, strain rate and forming temperature on the flow behavior of alloy, was proposed to describe the compressive behavior of the studied Al–Cu–Mg alloy. The proposed constitutive model correlates well with the experimental results, which confirms that the proposed model can give an accurate and precise estimate of flow stress for the studied Al–Cu–Mg alloy.