Casting And Rolling Flow Field Of Magnesium Alloy And Solidification Welding Line Characteristic Numerical Simulation Study Of Control

Magnesium alloy is known as"21st century green engineering structural material"due to its excellent characteristics,widely used in aerospace,high-end automotive and 3C fields.The main form of magnesium alloy used in industry is strip,and casting and rolling is considered to be the most ideal way to prepare magnesium alloy sheet and strip,the process has the advantages of short process,high efficiency and low cost.However,due to the uneven cooling rate of the magnesium alloy melt during the casting and rolling process,the strip is prone to defects such as segregation and edge cracking,which restricts the industrialization of cast-rolled magnesium alloy strip.In view of this,this paper proposes to improve the edge cracking problem of magnesium alloy cast and rolled strip by regulating the characteristics of solidification welding line.According to the actual working conditions of the casting and rolling machine,a multi-field coupled casting and rolling numerical simulation model is constructed to investigate the influence of casting and rolling process parameters and electric field parameters on the flow field and solidification welding line characteristics.The main studies are as follows::(1)The effect of casting and rolling process parameters on the flow field and solidification welding line characteristics.Casting and rolling zone to the neutral layer as the critical surface there are two vortices,the metal liquid to play a stirring role.The middle and the side of the casting and rolling area have a large difference in flow rate,resulting in the middle and the edge of the temperature difference,solidification welding line is"tongue"shape,is the main reason for edge cracking of cast and rolled sheet.Increase the rolling speed,the vortex range at the edge slightly increases,but the central vortex almost does not change,the solidification welding line as a whole approaches the exit,the characteristic solidification welding point K and K〞in the rolling direction,the position difference L gradually increases,the suitable rolling speed range is 3-4.2 m/min;increase the casting temperature,the vortex range slightly increases,the solidification welding line as a whole approaches the exit,L first decreases and then increases,the suitable casting temperature range is 918-946 K;increasing the height of the reserved roll seam,the vortex range decreases and the solidification welding line as a whole approaches the exit,L gradually increases and the suitable reserved roll seam height range is 3.8-5.3 mm.(2)The effect of current density on the solidification welding line characteristics for different current loading schemes.Applying DC electric field in the casting and rolling zone,the vortex range increases significantly.Increasing the current density,the solidification welding line as a whole moves closer to the exit.Changing the current density under different loading schemes resulted in different changes in the position and shape of the solidification welding line.Comparison analysis of three current loading scheme(scheme 1:power electrode ends are connected with the upper and lower roll contact brush;scheme 2:power electrode end inserted into the molten pool,one end pressed on the surface of the forming slab;scheme 3:power two electrodes are connected to the copper plate embedded in the side seal plate),scheme 3 in the larger current density conditions,the distance from the characteristic solidification welding point K to the exit is less than K〞to the distance of the exit,the slab side by the casting and rolling force is less than the middle,which is conducive to suppress the magnesium alloy cast and rolled plate strip edge crack.(3)Effect of coupled electric field on flow field and solidification welding line characteristics by casting and rolling process parameters(rolling speed and heat transfer coefficient).Decreasing the rolling speed,the vortex range decreases,the solidification welding line is far from the outlet,the distance from the characteristic solidification welding point K to the outlet is always smaller than the distance from K〞to the outlet,the straight line distance between the two points in the rolling direction increases from 5.3 mm to 12.4 mm;increasing the heat transfer coefficient,the vortex change is not obvious,the solidification welding line is far from the outlet,in the range of 5500-7500 W/(m~2·K),the linear distance between the two points in the rolling direction decreases from 5.3 mm to 0.7 mm.It provides a reference for solving the problem of difficulty in matching the proper position and shape of the solidification welding line with the appropriate current density.