Papers by Author: Hong Xiao

Abstract: In this paper, a TA2/Q235B composite plate was bonded with a DT4 interlayer by hot-rolling in a vacuum. The resulting interfacial structure and mechanical properties were analyzed. The results show that when the reduction is 25%, the rolling speed is 50 mm/s, and the bonding temperature is between 750 and 850°C, the shear strength of the bonding interface increases with temperature. It is difficult to bond TA2 and DT4 at a bonding temperature of 700°C. Brittle compounds, i.e., TiC, FeTi and Fe2Ti, are formed at the interface when the bonding temperature is 950°C, and the bonding strength significantly decreases. When the bonding temperature is 850°C, the shear strength of the interface reaches a maximum of approximately 237.6 MPa, and the fracture surface presents ductile fracture characteristics.

Abstract: To improve the accuracy of roll flattening calculation based on semi-infinite body model, a more accurate roll flattening model is proposed in this paper, which is derived basing on boundary integral equation method. The lateral surface displacement decay functions are established. Based on the boundary integral equation method, the numerical solution of the finite length semi-infinite body under the distributed force is obtained and verified by Finite Element Method (FEM). Based on the new model, the error of semi-infinite body model is analyzed in different length-diameter ratio and non-contact barrel length. Quantitative relationship and the scope of semi-infinite body model are obtained.

Abstract: Microstructure evolution can cause changes in dislocation density during hot plastic formation of metals and greatly influence the shape of flow curves. Recrystallization kinetics and average grain size were simulated by the coupled flow stress model describing dislocation development and microstructure evolution. The model for microstructure evolution considered different kinds of recrystallization in the same process rooted from nucleation and grain growth. Flow stress was calculated from the average dislocation density determined by the dislocation density model, which took into account hardening and recovery during the hot deformation process. Model parameters were defined by inverse analysis of flow curves obtained from hot compression tests and were completed through solving a nonlinear least-squares problem with constraints using optimization methods. Finally, the results obtained by the proposed model were compared with experimental results.

Abstract: The change of aluminum alloy microstructure before and after strong alternating magnetic treatment in the aluminum alloy LY12 after the thermal plastic figuration is studied in experimental ways using strong alternating magnetic field generator.By comparing microstructure before and after strong alternating magnetic treatment, the changes of microstructure component organization is analyzed to make further analysis of the organizational factors that leads to aluminum alloy LY12 microstructure’s refinement after thermal plastic figuration caused by alternating magnetic field.

Abstract: To reveal the pressure-transfer characteristics of the granular materials in the Solid Granule Medium Forming process, the stainless steel balls with diameter of 1 mm were selected as medium to conduct the axial compression experiment. The particle compression process was simulated by discrete element method, and then the variation law of the microstructure was analyzed from the perspective of force chain. The results showed that: In the gradual compression process of granule medium, its force chains distribution changes from the initial circular shape to the elliptical shape. As the stress increases, the force chains get denser and denser. In addition, the lateral pressure coefficient changes in power law with the compressive stress and it tends to be constant when the internal force chains structure gets stable.

Abstract: For low prediction precision of online model for vertical rolling force in roughing trains of hot strip mill, the process of hot strip roughing trains was simulated by the FEM simulation software DEFORM. The cause of low prediction precision of rolling force during vertical rolling was analyzed. Then the new method for calculating deformation degree when edge rolling was presented by analysis of the FEM simulated results. The formula of external stress status modulus, which is fit for the vertical rolling force calculation, was obtained by analytic regression. Furthermore, a new formula about rolling force calculation was gained. It was approved that the prediction precision was obviously enhanced compared with the practical data for vertical rolling force.

Abstract: Defects of pieces rolled by cross wedge rolling (CWR) have great effect on its practical applications. With reference to the center-pressure method used often in the forging, the effects of non-uniform temperature field on defects were studied by using the three-roll CWR tests under different cooling conditions and the coupled thermo-mechanical finite element models. The porous can be reduced or even eliminated when the billets were rolled with a controlled non-uniform temperature filed. The optimal temperature gradient was determined by FEM, which can be used in practical applications.

Abstract: Improved methods to estimate the kinetics of dynamic and static recrystallization are proposed in this paper. The kinetics for dynamic and static recrystallization can be evaluated by inverse analysis of the flow curves obtained using the single-hit and double-hit hot compression tests carried out on Gleeble 3500. The dynamic and static recrystallization volume fractions can be seen as functions of plastic strain and time, respectively. The mathematical formulations between the recrystallization volume fractions and the dislocation density related to the flow stress are used in incremental forms in the study. The methods are applied to the hot compression tests of plain carbon steel and the kinetics of dynamic and static recrystallization are gained successfully for some conditions at elevated temperature. The results are clarified by comparing them with those reported in previous investigations. It is confirmed that the present methods can provide accurate kinetics for dynamic and static recrystallization with shorter time for experiment and computation.