Effect of roll diameter on the thermal-mechanical behaviour of AZ31 strip during twin roll casting

Abstract

Although, the feasibility of producing AZ31 strip and other magnesium alloys via laboratory and pilot scale Twin Roll Casting (TRC) facilities has proven successfully [1, 2], key questions remain in terms of the changes in the thermal mechanical history experienced by the strip and mill force and power requirements as the process is scaled up to a larger TRC machine suitable for industrial production of magnesium strip. A powerful tool to help understand and quantify the effect of this TRC scale up on both the mill requirements and solidification and thermal mechanical history experienced by the strip is to develop and validate a mathematical model of the process. In this study a Thermal-Fluid-Stress model has been developed for TRC of AZ31 magnesium alloy to investigate the effect of roll diameter (355mm, 600mm and 1150mm) using the FEM commercial package ALSIM. Figure 1 illustrates the schematic of the TRC process. The mathematical model includes heat transfer and fluid flow in the liquid metal, heat transfer, fluid flow and latent heat of fusion release in the mushy zone and deformation in the material once the coherency point is reached, Details of the model development and its validation are provided in [3] and a schematic of the TRC process is shown in Figure 1. As expected, the roll diameter has a significant effect on the pressure distribution in the roll bite. The larger diameter roll will lead to an increased arc of contact (L) between the magnesium and the roll. The model-predicted effect of roll diameter on the surface normal stress is shown in Figure 2. By scaling up the caster the amount of solid material in the roll bite region which experiences plastic deformation increases which leads to development of higher level of normal stress on the strip surface. Copyright © 2013 MS&T'13®.

Publication Title

Materials Science and Technology Conference and Exhibition 2013, MS and T 2013

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