Zhi-hui Luo

Bio: Zhi-hui Luo is an academic researcher from Central South University. The author has contributed to research in topics: Transmission electron microscopy & Recrystallization (metallurgy). The author has an hindex of 2, co-authored 2 publications receiving 15 citations.

Formation mechanism of gradient-distributed particles and their effects on grain structure in 01420 Al-Li alloy

Abstract: Fine-grained 01420 Al-Li alloy sheets were produced by thermo-mechanical processing based on the mechanism of particle stimulated nucleation of recrystallization. The thermo-mechanically processed sheets were observed to contain layers of different microstructures along the thickness. The precipitate behavior of the second phase particles and their effects on the distribution of dislocations and layered recrystallized grain structure were analyzed by optical microscopy(OM), scanning electron microscopy(SEM), transmission electron microscopy(TEM) and X-ray diffractometry(XRD). The formation mechanism of the gradient particles was discussed. The results show that after aging, a gradient distribution of large particles along the thickness is observed, the particles in the surface layer(SL) are distributed homogeneously, whereas those in the center layer(CL) are mainly distributed parallel to the rolling direction, and the volume fraction of the particles in the SL is higher than that in the CL. Subsequent rolling in the presence of layer-distributed particles results in a corresponding homogeneous distribution of highly strained regions in the SL and a banded distribution of them in CL, which is the main reason for the formation of layered grain structure along the thickness in the sheets.

Method and mould for producing face-centered cubic metal plate with fine grain

Abstract: The invention opened a process for producing the face-centred cubic metal fine crystalline board. It is 45-80iOangle of the pressed face and the press direction, then press the prepared board. The die of the process has the top die and the low die between which the metal board face is cant. It is 45-80iOangle with the force direction. It can decrease the size of the crystal grain and improve the ND// (111) content, so it improve the deep punching performance of the face-centred cubic metal fine crystalline board, it is fit for the production of the Al and the A-alloy board.

Effect of microstructure on the quench sensitivity of AlZnMgCu alloys

Abstract: The effect of microstructure on the quench sensitivity of 7055 type aluminum alloys was investigated by hardness testing, optical microscopy and transmission electron microscopy. The results showed that the homogenized and hot-rolled alloys without Zr and the homogenized alloy with Zr were not quench sensitive, while the hot-rolled alloy with Zr was quite quench sensitive. The reason was analyzed according to the difference in the microstructure in these alloys, i.e. type of nucleation sites including dispersoids, (sub)grain boundaries and constituent particles for heterogeneous precipitation during slow quenching. Quench-induced η phase was observed mainly on large dispersoids and (sub)grain boundaries. In the homogenized and hot-rolled alloys without Zr, grain boundaries, which were the main heterogeneous precipitation nucleation sites, resulted in low quench sensitivity. In the homogenized alloy with Zr, grain boundaries and fine and coherent Al 3 Zr dispersoids led to low quench sensitivity. In the hot-rolled alloy with Zr, the large number of coarse Al 3 Zr dispersoids and subgrain boundaries were mainly responsible for high quench sensitivity. Constituent particles seemed to have little effect on quench sensitivity.

Influence of initial state and intermediate principal stress on undrained behavior of soft clay during pure principal stress rotation

Abstract: It is important to be fully aware of the dynamic characteristics of saturated soft clays under complex loading conditions in practice. In this paper, a series of undrained tests for soft clay consolidated with different initial major principal stress direction ξ were conducted by a hollow cylinder apparatus (HCA). The clay samples were subjected to pure principal stress rotation as the magnitudes of the mean total stress p, intermediate principal stress coefficient b, and deviator stress q were all maintained constant. The influences of intermediate principal stress coefficient and initial major principal stress direction on the variation of strain components, generation of pore water pressure, cyclic degradation and non-coaxiality were investigated. The experimental observations indicated that the strain components of specimen were affected by both intermediate principal stress coefficient and initial major principal stress direction. The generation of the pore water pressure was significantly influenced by intermediate principal stress coefficient. However, the generation of pore water pressure was merely influenced by initial major principal stress direction when b = 0.5. It was also noted that the torsional stress–strain relationships were affected by the number of cycles, and the effect of intermediate principal stress coefficient and initial major principal stress direction on the torsional stress–strain loops were also significant. Stiffness degradation occur under pure principal stress rotation. Anisotropic behavior resulting from the process of inclined consolidation have considerable effects on the strain components and non-coaxial behavior of soft clay.

Superplastic behavior of an Al–Mg–Li alloy

Abstract: A novel thermomechanical processing has been developed for producing fine-grained Al–Mg–Li alloy 1420 sheet for superplasticity. The refined microstructure had layers of different grain structure through the normal direction of the sheet. The surface layer (SL) had fine, nearly equiaxed grains whereas the center layer (CL) had coarse, elongated grains. The superplastic properties and microstructural evolution of alloy 1420 with such microstructure were investigated using uniaxial tensile tests. It was shown that the refined alloy exhibited considerable elongations of 580–915% when deformed at 510–540 °C and initial strain rates from 5 × 10 −4 to 1 × 10 −3 s −1 . Microstructure observation revealed that the alloy 1420 exhibited unusual cavitation behavior and extensive GBS occurred when tested at 510 °C and above, however, the occurrence of GBS was not uniform. The effects of temperature and strain on grain size and shape, cavity size and volume fraction in the SL and CL were determined, respectively.

Grain structure and microtexture evolution during superplastic deformation of 5A90 Al-Li alloy

Abstract: The microstructural evolution of banded 5A90 Al-Li alloy during superplastic deformation at 475 °C with an initial strain rate of 8×10−4 s−1 was studied using EBSD technique. The results showed that, before deformation, the grain shape appeared to be banded, the most grain boundaries belonged to low-angle boundaries, and the initial sheet had a dominate of {110}«112» brasstexture. During deformation, there were grain growth, grain shape change, misorientation increasing and textural weakening. The fraction of high-angle boundaries increased rapidly once the flow stress reached the peak value. Corresponding deformation mechanism for various stages of deformation was suggested. Dislocation activity was the dominant mechanism in the first stage, then dynamic recrystallization occurred, and grain rotation was expected as an accommodation for grain boundary sliding (GBS). At large strains, GBS was the main mechanism.

A review of vehicle system dynamics in the development of high-speed trains in China

Abstract: The flourishing railway industry in China comes as not only a surprise for the world but also a promoter for the development of high speed railway across the globe. In this paper, a retrospect of China’s high speed railway is introduced, including its railway network plans, construction progress and operation status. A synopsis of the progress made on high speed trains is also presented from their primal stage of technology acquisition to the latter stages of innovative research and development as well as the current types of bullet trains and their uses. The breakthrough of the 500 km/h test train developed by China is also highlighted in this letter inclusive of its design, technical indexes and fundamental testing functionalities. For China to rapidly but yet successfully develop its high speed railway industry and bullet trains, fundamental research will play as much an important role as technical innovation. Sound research on the dynamics is crucial toward the high quality performance and safety operation of high speed trains which include key factors such as vehicle design, operation and maintenance solutions, integration of the track network, and the effects of coupling systems on the dynamics performance of the train system such as airflow, pantograph–catenary and power source–current collection systems. To tackle the problems associated with the increasing of train speed, we have developed a corresponding dynamics coupled system of the track–vehicle–pantograph–catenary–airflow system based on vehicle system dynamics (VSD). Comparing to traditional VSD research, in addition to considering the coupled system dynamics between vehicle and track, wheel and rail, fluid and solid, as well as vehicle and vehicle, the newly developed VSD also vastly increases the degrees of freedom in its calculations, enlarging the traditional VSD to a vast system dynamics (also VSD), giving VSD a new meaning. This paper elaborates the modeling and coupling relations of the track–vehicle–pantograph–catenary–airflow coupled system dynamics. Focusing on high speed trains, the train parameters, track status, and effects of airflow conditions on train dynamics performance was investigated as well as the safety precautions due to limitations from track irregularity and crosswinds.