| Vertical twin-roll strip continuous casting, belonging to near-net-shape processing area, can produce magnesium alloy strips close to the thickness of sheet directly from liquid metal, then through the sutiable following processing the magnesium alloy sheets are obtained. The technics has advantages of short process,low cost. However,the existing casting process stability of vertical twin-roll continuous casting magnesium strip needs to be improved, which to a certain extent restricted the development of vertical twin-roll continuous casting magnesium strips. By introducing the high dam,a new vertical two-roll continuous casting molten pool system is constructed to separate the pool surface of the present continuous casting and the initial solidification point, which can improve the stability of casting process and ensure the quality of magnesium alloy strips. This paper conducted researches on characteristics of the pool of vertical twin-roll continuous casting magnesium alloy strips with the high dam from the three aspects such as the physical and chemical effects of magnesium melt with high dam material and casting rolls, simulation computation of the fluid field and temperature field of the pool,the casting test, in order to provide refrence for the further casting of magnesium alloy strips.The thermal transfer and chemical effects between molten AZ31 and high dam material were studied. The results showed that the heat transfer coefficient of the molt with the selected dam material was 50 W /( m 2? K), and the dam material showed the chemical inertia in the molten magnesium, which can meet the requirement of casting experiment. The heat transfer coefficients of molten AZ31 with carbon steel and stainless steel were tested and were 250 W /( m 2? K), 100 W /( m 2? K) respectively.The fluid field in the pool of vertical twin-roll continuous casting magnesium strip with high dams was investigated by numerical simulation. The effects of parameters such as nozzle's angle, nozzle's depth, rolling speed, touching arc, slit width, dam's height and etc. on the fluid field were studied. From the result, the advisable processes were gotten, including nozzle's angle as oblique down 5°, nozzle's depth as 20mm, touching arc as 46°, slit width as 5mm, dam's height as 80mm, rolling speed as 15r/min. Under the above process, the overall region of the fluid field was mixed well and steady, the speed at the pool level was suitable and fluctuated little, and the effect on the solidification was little. The temperature field in the pool of vertical twin-roll continuous casting magnesium strip with high dams and no dam were investigated by numerical simulation. The effects of parameters such as casting temperature, heat transfer coefficient between molten magnesium and casting rolls, casting speed and etc. on the solidification end point position in the temperature field were studied. From the simulation, the advisable processes were got. The result showed that some laws as the following: when the heat transfer coefficient between magnesium melt and casting rolls increases, the solidification end position decreases; when casting temperature increases, the solidification end position rises; when casting speed increases, the solidification end position rises; the addition of the high dam can result in raising solidification end position. With the high dam, when the casting temperature must be higher than that with no dam, the suitable position of solidification end can be obtained.Casting experiments were conducted separately with dam and no dam. Through observing and analyzing two kinds of thin strip's surfaces and microstructures, the conclusion was made that the surface of the strips casted with dam was more smooth and the grain sizes was more uniform and finer. |
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