The mechanical behavior and microstructures of an Al-Zn-Mg-Cu-Cr aluminum alloy during multi-stage hot deformation were investigated by thermal stimulation test, optical microscopy, and transmission electron microscop...The mechanical behavior and microstructures of an Al-Zn-Mg-Cu-Cr aluminum alloy during multi-stage hot deformation were investigated by thermal stimulation test, optical microscopy, and transmission electron microscopy. The true stress vs true strain curves and the microstructure evolution of two hot deformation procedures were gained. The flow stress of the alloy studied decreases with increasing the deforming passes and declining the temperature, and the larger the temperature decline between adjacent stages, the larger the peak stress fall is. The stress-strain behavior mainly result from the dynamic recovery during deformation, the static recovery and recrystallization in the delay time, and the second phases precipitated from the matrix at high temperature.展开更多
The flow stress behavior of Al-3.5Cu-1.5Li-0.25(Sc+Zr) alloy during hot compression deformation was studied by isothermal compression test using Gleeble-1500 thermal-mechanical simulator. Compression tests were prefor...The flow stress behavior of Al-3.5Cu-1.5Li-0.25(Sc+Zr) alloy during hot compression deformation was studied by isothermal compression test using Gleeble-1500 thermal-mechanical simulator. Compression tests were preformed in the temperature range of 653-773 K and in the strain rate range of 0.001-10 s-1 up to a true plastic strain of 0.7. The results indicate that the flow stress of the alloy increases with increasing strain rate at a given temperature,and decreases with increasing temperature at a given imposed strain rate. The relationship between the flow stress and the strain rate and the temperature was derived by analyzing the experimental data. The flow stress is in a hyperbolic sine relationship with the strain rate,and in an Arrhenius relationship with the temperature,which imply that the process of plastic deformation at an elevated temperature for this material is thermally activated. The flow stress of the alloy during the elevated temperature deformation can be represented by a Zener-Hollomon parameter with the inclusion of the Arrhenius term. The values of n,α and A in the analytical expressions of flow stress σ are fitted to be 5.62,0.019 MPa-1 and 1.51×1016 s-1,respectively. The hot deformation activation energy is 240.85 kJ/mol.展开更多
Cu46Zr46Al4.8Ti3.2 bulk metallic glass (BMG) was successfully synthesized by copper-mold casting and the mechanical properties at room temperature were measured by compression tests. The structure and thermal characte...Cu46Zr46Al4.8Ti3.2 bulk metallic glass (BMG) was successfully synthesized by copper-mold casting and the mechanical properties at room temperature were measured by compression tests. The structure and thermal characteristics were analyzed by XRD and DSC, and the fracture surface morphology was examined by SEM. The glassy alloy with 4 mm in diameter shows an high fracture strength of 1960 MPa, with an improvement of about 20% compared to the ultimate compression fracture strength of the Cu46Zr46Al8 BMG, which suggests that the Ti addition improves the compression fracture strength. The different degrees of the adiabatic heating induce four types of fracture features: a vein-like structure, an elongated and striated vein pattern, melting and smooth regions. The elongated and striated vein patterns as well as the melting region show that enormous strain energy is released, which causes significant adiabatic heating. Furthermore, many micro-cracks observed in the smooth region are caused by the strong shear force. In addition, the strong shear force leads to many shear bands as well as the melting in the lateral surface.展开更多
基金supported by the National Key Basic Research and Development Program of China(No.G1999064908)
文摘The mechanical behavior and microstructures of an Al-Zn-Mg-Cu-Cr aluminum alloy during multi-stage hot deformation were investigated by thermal stimulation test, optical microscopy, and transmission electron microscopy. The true stress vs true strain curves and the microstructure evolution of two hot deformation procedures were gained. The flow stress of the alloy studied decreases with increasing the deforming passes and declining the temperature, and the larger the temperature decline between adjacent stages, the larger the peak stress fall is. The stress-strain behavior mainly result from the dynamic recovery during deformation, the static recovery and recrystallization in the delay time, and the second phases precipitated from the matrix at high temperature.
基金Project(2002AA305104) supported by the National High-Tech Research and Development Program of China
文摘The flow stress behavior of Al-3.5Cu-1.5Li-0.25(Sc+Zr) alloy during hot compression deformation was studied by isothermal compression test using Gleeble-1500 thermal-mechanical simulator. Compression tests were preformed in the temperature range of 653-773 K and in the strain rate range of 0.001-10 s-1 up to a true plastic strain of 0.7. The results indicate that the flow stress of the alloy increases with increasing strain rate at a given temperature,and decreases with increasing temperature at a given imposed strain rate. The relationship between the flow stress and the strain rate and the temperature was derived by analyzing the experimental data. The flow stress is in a hyperbolic sine relationship with the strain rate,and in an Arrhenius relationship with the temperature,which imply that the process of plastic deformation at an elevated temperature for this material is thermally activated. The flow stress of the alloy during the elevated temperature deformation can be represented by a Zener-Hollomon parameter with the inclusion of the Arrhenius term. The values of n,α and A in the analytical expressions of flow stress σ are fitted to be 5.62,0.019 MPa-1 and 1.51×1016 s-1,respectively. The hot deformation activation energy is 240.85 kJ/mol.
基金Project(NCET-10-0360) supported by the Program for New Century Excellent Talents in University,ChinaProject supported by the Fundamental Research Funds for the Central Universities,China
文摘Cu46Zr46Al4.8Ti3.2 bulk metallic glass (BMG) was successfully synthesized by copper-mold casting and the mechanical properties at room temperature were measured by compression tests. The structure and thermal characteristics were analyzed by XRD and DSC, and the fracture surface morphology was examined by SEM. The glassy alloy with 4 mm in diameter shows an high fracture strength of 1960 MPa, with an improvement of about 20% compared to the ultimate compression fracture strength of the Cu46Zr46Al8 BMG, which suggests that the Ti addition improves the compression fracture strength. The different degrees of the adiabatic heating induce four types of fracture features: a vein-like structure, an elongated and striated vein pattern, melting and smooth regions. The elongated and striated vein patterns as well as the melting region show that enormous strain energy is released, which causes significant adiabatic heating. Furthermore, many micro-cracks observed in the smooth region are caused by the strong shear force. In addition, the strong shear force leads to many shear bands as well as the melting in the lateral surface.
