Papers by Author: Xiao Dong Hu

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Authors: Hong Yang Zhao, Xiao Dong Hu, Dong Ying Ju
Abstract: Experimental study on downstream rolling process for twin roll casting magnesium alloy strip was carried out. The microstructure of the casting and rolling strip were observed by OM, SEM, and TEM. The effects of homogenizing process, the parameters of rolling process and annealing after rolled on secondary rolling of AZ31B casting strip were analyzed. The results show that the twin roll casting strip are suitable for rolling at 380-420 °C after homogenizing at 400 oC for two hours, the reduction rate of each pass should be controlled lower than 18%. Mg alloy sheets with thickness from 0.3-1 mm can be produced in once annealing period in this way. By controlling the pass reduction and rolling temperature, the fabricated AZ31B Mg alloy sheets can achieve both high strength and good plasticity by grain refining below 10μm. The mechanical properties of rolled strip after annealing at 400 oC for 0.5h-1h could get tensile strength 220MPa and meantime elongation rate 20%.
Authors: Dong Ying Ju, Xiao Dong Hu, Hong Yang Zhao
Abstract: Strip casting is a promising route to directly produce magnesium alloy sheet by twin roll casting method. As-cast strips with proper microstructure and good surface quality are requested to serve as next rolling feedstock. In order to restrain the coarse dendrite growth and get uniform grain, a new method of in-line heat treatment was proposed. The as-cast strip was dipped into an oil tank after exiting the rolls and then was quenched with oil at various temperatures. The effect of oil temperature, casting speed and pouring temperature on microstructure and mechanical properties of cast strip was investigated.
Authors: Xiao Dong Hu, Dong Ying Ju
Abstract: Twin-roll thin strip casting process combines casting and hot rolling process into a single step; in which melt and solid states exist in the casting region, so its deformation is more complex than rolling process. In this paper, Anand’s model, a unified visco-plasticity constitutive model, was employed to simulate the highly nonlinear behavior in the twin-roll casting process. Anand model’s parameters were regressed based on compression tests at various temperature and strain rate for magnesium alloy AZ31. To calculate the thermal mechanical stresses, the thermal flow of twin-roll casting process was simulated firstly; then stresses were calculate, in which the temperature field result of thermal flow was imposed as body load, and a small displacement load along roller tangential direction was imposed simultaneously in order to simulate rolling action. The deformation results can well describe the forward slip zone, backward slip zone and melt eddy zone in the casting region. Based on the results, the applicability of Anand’s model on twin-roll casting process was discussed.
Authors: Xiao Dong Hu, Dong Ying Ju, Hong Yang Zhao
Abstract: Twin- roll casting of magnesium alloys is a rapidly solidifying process, which can directly produce thin strips from molten metal. In this paper, based on a pilot vertical type twin-roll caster, 3D models of twin-roll casting process were used for simulation of thermal flow and solidification on depending of casting speed, molten pool level and pouring temperature. The effect of side dams on thermal flow behavior was also considered. Based on the analyzed results, a proper concave slot nozzle was designed to compensate temperature variation across the width of strip. Comparing with parallel type slot nozzle, it can adjust temperature distribution along the roll width continuously by adopting proper concave curves, which is more flexible than rectification boards delivery system. Strips of magnesium alloy AZ31 were produced in the pilot caster with the concave slot nozzle. The experiments show that surface quality of as cast strip was improved by using the new type of nozzle.
Authors: Dong Ying Ju, Hong Yang Zhao, Xiao Dong Hu, Koichi Ohori, Mituo Tougo
Abstract: Strip continuous casting by twin roll method is a rapidly solidifying process, which can directly produce thin strips,reduce energy consumption and product cost of various metal materials. However, the casting of magnesium alloys with large solidifying ranges lead to some problems such as surface and internal defect, variation of solidification finish point for Mg sheet. In this research, the process conditions for a twin roll caster are analyzed by thermal flow simulation. The effect of type and dimension of delivery nozzles on production of Mg alloy are studied. A proper match of the setback distance of thin nozzle and casting speed is studied by thermal flow simulation, based on the characteristics of Mg melt handling, flow dynamics control and solidification.
Authors: Xiao Dong Hu, Hong Yang Zhao, Dong Ying Ju
Abstract: Twin-Roll-Casting process is a rapid solidification process combining with hot rolling deformation. The liquid metal will be squeezed out but not sucked in from the mush zone caused by rolling deformation. This is different from conventional continuous casting process and will greatly affect the microstructure morphology and surface cracks of as-cast strip. In this paper, a 2D FEM model was employed to simulate the thermal mechanical behavior during twin-roll casting process of Mg alloy AZ31. The FEM results were compared with experimental results and show the effect of rolling deformation on the microstructure morphology and surface cracks of as-cast sheet.
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