Study On Temperature Field And Cast-rolling Force During The Twin-roll Casting Of Wide Magnesium Alloy Sheet

The magnesium alloy sheet production by twin roll casting with advantage of lessinvestment, low energy consumption, low production cost, small space and higher laborproductivity, compared with the traditional methods of sheet production by extrusionand rolling. The twin roll casting is a complicated process with solidification and rollingin a short time, each process parameters will have a heavy effect on the continuity of thecast-rolling process and the sheet quality, especially for the increasing of the width ofthe sheet. So the control of each parameters and the mutual cooperation is particularlyimportant. There are two questions existing in the study of magnesium sheet producedby twin roll casting at present. One is that, the control of process parameters are mainlythrough a single temperature field with the method of numerical simulation in thepresent research, ignoring the effect of cast-rolling force. And the other one is that in thedirection of width uniformity process parameters of the influence of roll casting processresearch has not been reported.The process parameters and the non-uniformity of parameters in the width effecton the temperature field and cast-rolling force was investigated, then the processparameters on the continuity of the cast-rolling process were also studied.(1) A temperature field coupled with flow field mathematical mold was establishedduring the horizontal twin-roll casting of AZ31magnesium alloy sheet with1500mm inwidth and8mm in thickness in this paper. The temperature field in the casting zone wassolved based on the software ANSYS.(2) The cast-rolling force was calculated based on the establishing force model,which can simplify the complex cast-rolling force because of avoiding the solving thehuge stress equations.(3) The yield strength of AZ31which was tested from the Gleeble-1500testmachine in different temperature was obtained. The relationship between yield strengthσ0.2and temperature T isσ0.2=0.1382T+77.882.(4) The process parameters effect on casting zone temperature field and cast-rollingforce were revealed, such as the casting speed, the pouring temperature and the coolingintensity. A quality defect called melt sheet will be produced or the leakage phenomenonwill be happened when the cooling intensity is lower than the minimal critical coolingintensity value; and crack will be produced or rolling suspended will be happened if the cooling intensity is higher than the maximal critical cooling intensity value. When thecasting speed are respectively1m/min,2m/min,3m/min, the minimal and maximalcritical cooling intensity are500,1200,2000W/(m~2.K) and2500,5000,7500W/(m~2.K)respectively.(5) By the use of section method along the width direction, a two-dimensionalmodel was applied on the section, thus the use of2d model instead of complex3d tostudy the process parameters effecting on the temperature field and cast-rolling force.Using the coefficient of variability (CV) characterized the non-uniformity, and thenon-uniformity of the cooling intensity and the pouring temperature effect on thecasting zone temperature field and cast-rolling force was studied. The results show thatthe coefficient of variability of cooling intensity and the pouring temperature are5.5%and2.87%respectively in order to obtain good quality of sheet.