Authors: Chang Liang Li, Hua Ding, Yong Qing Zhao, Lian Zhou
Abstract: Superplastic forming provides a good way for Ti alloys which are usually difficult to
be deformed. Ti75 alloy with a nominal composition of Ti-3Al-2Mo-2Zr is a newly developed corrosion resistant alloy, with a middle strength and high toughness. In the present paper, superplastic behavior of the alloy was investigated, the microstructural evolution in superplastic deformation was observed and the superplastic deformation mechanisms were analyzed. The results showed that the strain rate sensitivity, m, of the Ti75 alloy was larger than 0.3 and the strain was over 2.0 without surface cracking at 800°C and 5×10-4s-1 in compressive testing.
During the first stage of superplastic deformation, a phase grains became equiaxed, fine and homogeneous due to the recrystallization in a phase and diffusion in b phase. Newly formed equiaxed a grains then could slide and rotate, exhibiting superplastic features. The stress concentration caused by grain sliding of a grains could be released by slip and diffusion in b phase between the a phase grains, which acted as accommodation mechanisms.
2969
Authors: Zhi Guo Chen, Zi Qiao Zheng, Dong Feng Han
Abstract: The hot deformation behaviors and microstructure in Al-Cu-Li alloy containing small
amount of Ag and Mg were investigated by transmission electron microscopy and isothermal
compression tests.When the strain rate is 0.1, 0.01 and 0.001s-1(the deformation temperature within
the range of 360-520 ) and 1 s-1(deformation temperature 520 )respectively, the flow stress
decreases after a peak value, showing dynamic recrystallization,while the steady-state flow
characteristics exist on the other deformation conditions. The flow stress of Al-Cu-Li-Mg-Ag alloy
during hot deformation can be expressed by a Zener-Hollomon parameter in the hyperbolic-sine
function with the hot deformation activation energyDH of 250.45kJ/mol. The dislocations may
climb with support from many vacancies generated during hot deformation, thus forming lots of
helical dislocations. The dynamic precipitation and successive dynamic particles coarsening during
hot compression have been assumed to be responsible for further flow softening when deformed at
low strain rates.
1925
Authors: Atef S. Hamada, L. Pentti Karjalainen, Mahesh C. Somani, R.M. Ramadan
Abstract: The hot deformation behaviour of two high-Mn (23-24 wt-%) TWIP steels containing 6
and 8 wt-% Al with the fully austenitic and duplex microstructures, respectively, has been
investigated at temperatures of 900-1100°C. In addition, tensile properties were determined over the
temperature range from -80 to 100°C. It was observed that in spite of the lower Al content, the
austenitic steel possessed the hot deformation resistance about twice as high as that of the duplex
steel. Whereas the flow stress curves of the austenitic steel exhibited work hardening followed by
slight softening due to dynamic recrystallisation, the duplex steel showed the absence of work
hardening and discontinuous yielding under similar conditions. Tensile tests at low temperatures
revealed that the austenitic grade had a lower yield strength than that of the duplex grade, but much
better ductility, the elongation increasing with decreasing temperature, contrary to that for the
duplex steel. This can be attributed to the intense mechanical twinning in the austenitic steel, while
in the duplex steel, twinning occurred in the ferrite only and the austenite showed dislocation glide.
217
Authors: Xiao Yu Zhong, Guang Jie Huang, Fang Fang He, Qing Liu
Abstract: Uni-axial tensile plastic deformation behavior of rolled magnesium alloy AZ31B under the temperature range from room temperature(RT) to 250°C with strain rates between 10-3 and 10-1s-1 has been systematically investigated. Microstructure evolution and texture were determined using optical microscopy (OM) and electron back-scattered diffraction (EBSD) techniques, respectively. Our results indicated that the strength and elongation-to-fracture were more sensitive to strain rates at elevated temperature rather than that at room temperature; dynamic recrystallization (DRX) and relaxation of stress at elevated temperature resulted in dramatic change of mechanical properties. Compared with strain rate, the temperature played a more important role in ductility of AZ31B Mg alloy sheet.
219
Authors: Xu Dong Zhou, Xiang Ru Liu
Abstract: The researches of non-oriented silicon steel are mainly focused on the effect of main processing parameters on the microstructure and magnetic properties, but there have been few studied about its flow stress until now. In this paper, the non-oriented silicon steel 50A1300 of hot forming is studied by thermal-mechanical simulation method. The hot deformation behavior of the steel is explored and the flow stress model of the steel is established based on the creep mechanism. The model has good accuracy and is feasible.
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