低频电磁场对传统热顶铸造6063铝合金凝固过程的影响

Effects of Low-Frequency Electromagnetic Field on Solidification Process of Conventional Hot-Top Casting of 6063 Aluminum Alloy

在传统热顶铸造过程中施加低频电磁场,使用热电偶测量了稳定铸造阶段从铸锭中心到边部不同位置的冷却过程,得到了铸锭内部的温度分布,分析了低频电磁场对传统热顶铸造6063铝合金凝固过程、宏观组织和表面偏析层厚度的影响.实验表明:低频电磁场使铝熔体产生的强制对流使熔池内的温度分布更加均匀,促进了铝熔体过热的散失,使熔池内的温度低于6063铝合金的液相线温度,提高了熔池内部形核质点的数量,在没有添加细化剂条件下使铸锭宏观组织均匀细小,降低了液穴深度.铝熔体流动速度的加快能增强石墨环与铝熔体之间的换热,使结晶器内铸锭表面初始凝壳点位置上移,减小了铝熔体与结晶器的有效接触高度,提高了铸锭的表面质量.

Low-frequency electromagnetic （LFE） field was applied to the conventional hot-top casting process,and thermocouples were used to measure the cooling process from different edge positions to the center of an ingot in the steady-state of casting process,thus getting the cooling curves and temperature distribution within the ingot. The effects of LFE field on the solidification process,macrostructure and thickness of surface segregation layer during the conventional hot-top casting of 6063 aluminum alloy were analyzed. The results showed that the forced convection resulting from Al melt in LFE field makes the temperature distribution more uniform to dissipate the overheat of Al melt so as to enable the temperature in the pool to be lower than the liquidus temperature of 6063 aluminum alloy and to increase the number of nucleating particles inside the pool,thus providing the fine and homogeneous macrostructure without any grain refiner added in and reducing the depth of liquidus cave. Heat transfer between ingot and mold is then intensified by the quickened flow velocity of Al melt. As a result,the initial solidifying point on the ingot surface in mold moves upwards to decrease the height of contact zone between the melt and mold so as to improve the surface quality of ingot.