Papers by Keyword: Dynamic Recrystallization (DRX)

Abstract: Dynamic recrystallization (DRX) behaviour in a newly developed Cu-Sn-P alloy for heat exchangers and tubes was systematically investigated. For this purpose, Cu-Sn-P alloys with different content of Sn were deformed in compression at temperatures between 1073 K and 1213 K and at various strain rates from 2 x 10-4 s-1 to 2 x 10-1 s-1. The onset of DRX was more advanced with increasing temperature and with decreasing strain rate. Full DRX was not achieved at the testing conditions of lower temperature and higher strain rate even after straining to ε = 1.0. This tendency was more significant in the alloy with higher Sn content. With increasing Sn content, the flow stress and the obtained grains size became higher and finer, respectively. These experimental results indicate the important role of Sn for strengthening and microstructual control.

Abstract: Dynamic recrystallization (DRX) behavior in a Cu-0.65Sn-0.025P (mass%) alloy (Cu-Sn-P), which had been newly developed for high strength copper tubes, was systematically investigated. For this purpose, an orientation-controlled bicrystal ( =28o); a model samples of the as-casted billet having coarse columnar grains, was hot deformed in compression at 1073 K at true strain rates from 2 x 10-3 s-1 to 2 x 10-1 s-1 in vacuum. Appearance of peak stress, where DRX sets in, was much delayed in Cu-Sn-P alloy compared with that in Cu and the other copper alloys. While nucleation of new grains preferentially took place at grain boundary, this tendency became more significant with decreasing strain rate. Almost all the new grains were annealing twins (3) formed behind the migrating grain boundary. The more preferential nucleation at grain boundary with decreasing strain rate could be, therefore, reasonably understood by easier and more extensive occurrence of grain boundary migration at lower strain rate.

Abstract: It had been already reported that the resistance of compression at warm condition can be decreased by the preliminary torsion working at AZ31B magnesium alloy. In the present study, it was found that the dynamic recrystallization occured during warm working by torsion. Dynamic recrystallization was slightly seen in the fractured edge of the bar at a rotation speed of 1rpm at temperature 573K and 623K. The amount of torsion to fracture was increased with increasing of deformation temperature. Remarkable dynamic recrystallization could be seen in the center of bar at the rotation speed of 1rpm at temperature of 673K.

Abstract: High strength and ductile Mg96Zn2Y2 (at%) alloys with multi-modal microstructure are developed. Microstructure of the extruded Mg96Zn2Y2 alloy consists of three regions; the dynamically recrystallized -Mg fine-grains region, the hot-worked -Mg coarse-grains region elongated along extrusion direction, and the long-period stacking ordered (LPSO) phase region with kink deformation bands. Bimodal microstructure evolution in -Mg matrix is influenced by the morphology of the LPSO phase in the as-cast state, therefore, the effect of secondary dendrite arm spacing in cast state on the microstructure evolution and mechanical properties of the extruded Mg-Zn-Y alloy is investigated. An increase in the dynamically recrystallized grains improves ductility of the extruded alloys; the effective dispersion of the LPSO phase enhances strengthening of the alloy.

Abstract: Compression tests were performed at temperatures from 350 to 450 °C with different strain rates of 1.0×10−2 and 1.0×10−1 s−1. The microstructures of deformed samples were investigated by electron backscatter diffraction (EBSD). Microstructure observations indicated that under present deformation conditions, fraction of new grains increases with the Z value. It was found that different nucleation mechanisms for DRX were operated in hot deformed 7055 alloy, which was closely related to deformation condition. DRX nucleation and development were discussed in consideration of bulging of original grain boundaries and occasional subgrain rotation near the grain boundaries. Discontinuous dynamic recrystallization (DDRX) which occurred in a local area was also proved to be a nucleation mechanism at higher Z value for 7055 alloy.

Abstract: In this investigation, the dynamic recrystallization phenomenon (DRP) of an Al-Li-Cu-Mg-Zr alloy was studied at two temperatures, 350°C and 400°C. Wedge samples were subjected to hot rolling deformation in both temperature and one passes. For wedge specimens, reduction up to 70% was considered. Results showed that the grain size of the specimens after hot rolling decreases from 100 μm to 30 μm because of DRP. Furthermore, it is observed that critical reduction for starting DR at 400°C is 40% and at 350°C reduction must increase to 50%.

Abstract: Thermal deformation process of H62 brass is studied, multi-scale simulations of macro-forming property and microstructure distribution are carried out for the hot-extrusion process of double cups part with flange utilizing numerical simulation technology, the process parameters are determined and the microstructure of extruded parts is predicted. The constitutive equation of H62 brass under high temperature deformation is established with isothermal compression test, and the results indicate that the flow stress accords to Arrhenius hyperbolic sine functions. The model of microstructure evolution during hot-deformation is founded and the influence of process parameters on microstructure is revealed. The microstructure prediction on extruded part shows that the simulated results agree well with the experimental results. The high-quality products are obtained using the optimal process parameters.

Abstract: Hot-compression and hot-tension experiments were conducted on a Gleeble-1500D thermal-mechanical simulator. The constitutive equation was presented by calculating the stress exponent, activation energy and Zemer-Hollomon parameter during the hot compression. Based on dynamic material model theories and Prasad instability criterion, the hot processing map was developed and the representative microstructure was observed. The total elongation and reduction in area were calculated by the hot tension. These results have shown that P92 steel should be manufactured at higher processing temperature and larger strain rate in practice.

Abstract: In order to obtain a better understanding of mechanisms governing the microstructural evolution of nickel base superalloys during forging, experimental and numerical studies have been undertaken. For the experimental part, isothermal compression tests were performed at 1100°C for several ratio and strain rates to reproduce microstructural evolution during industrial forging. The resulting microstructures were analysed by Electron Back Scattered Diffraction method and Transmission Electron Microscopy to identify the dynamic recrystallization mechanisms. In parallel, numerical studies has been carried out in which a crystalline plasticity modelling implemented in the finite element code Abaqus® coupled to a recrystallization Cellular Automaton code was used to simulate forging. The first model allows us to obtain the local mechanical fields (strain, stress, crystallographic orientation, dislocation density …) and the second one predicts the dynamic recrystallization.

Abstract: The hot working behavior of Mg-3Sn-2Ca alloy has been investigated in the temperature range 300–500 oC and strain rate range 0.0003–10 s-1, with a view to evaluate the mechanisms and optimum parameters of hot working. For this purpose, a processing map has been developed on the basis of the flow stress data obtained from compression tests. The stress-strain curves exhibited steady state behavior at strain rates lower than 0.01 s-1 and at temperatures higher than 350 oC and flow softening occurred at higher strain rates. The processing map exhibited two dynamic recrystallization domains in the temperature and strain rate ranges: (1) 300–420 oC and 0.0003–0.003 s-1, and (2) 420–500 oC and 0.003–1.0 s-1, the latter one being useful for commercial hot working. Kinetic analysis yielded apparent activation energy values of 161 and 175 kJ/mole in domains (1) and (2) respectively. These values are higher than that for self-diffusion in magnesium suggesting that the large volume fraction of intermetallic particles CaMgSn present in the matrix generates considerable back stress. The processing map reveals a wide regime of flow instability which gets reduced with increase in temperature or decrease in strain rate.