【摘要】 Al-Bi偏晶合金是潜在的新型汽车轴瓦材料,然而由于偏晶合金的凝固特点,凝固过程中的液-液分离反应极易造成第二相的宏观偏析,很难采用传统凝固方法制备。在水平稳恒磁场下进行Al-Bi偏晶合金的水冷铜模浇铸实验,使熔体内不同位置的温度梯度方向与磁场方向呈不同角度。研究当磁场与富Bi液滴Marangoni运动方向的夹角不同时,磁场对偏晶合金凝固组织影响效果的变化。研究结果表明当磁场方向与富Bi相液滴Marangoni运动方向平行时,磁场对宏观偏析的抑制效果最明显。对本实验条件下磁场在Al-Bi偏晶合金凝固过程中的作用机制进行了分析,Al-Bi偏晶合金富Bi液滴发生了由冷端向热端的Marangoni运动,磁场主要通过电磁拖曳力作用于液滴,降低液滴的迁移速度。当磁场与温度梯度方向垂直时,其对熔体传热的抑制减小了电磁拖曳力的作用效果,加重了富Bi相液滴Marangoni运动造成的偏析。更多还原

【Abstract】 Al-Bi hypermonotectic alloy was a kind of potential bearing material for automotive industry,but due to its solidifying features,the liquid-liquid separation during solidification process always caused serious segregation,thus Al-Bi hypermonotectic alloys were hardly fabricated by conventional solidification methods.The Al-Bi monotectic alloy was casted into water-cooled copper mould with the imposition of horizontal magnetic field,the temperature gradient in different position of the melt got a different angle with the magnetic line,and the effect of magnetic field on solidification structures was studied when it had different angles with the Marangoni motion of Bi-rich droplets.The results showed that the effect of magnetic field was clear when it paralleled to the Marangoni motion of Bi-rich droplets.The mechanism of magnetic field on solidifying process was discussed,the Bi-rich droplets moved from cold side to heat side of the melt under Marangoni effect,and the magnetic field decreased the moving speed of droplets by electromagnetic drag force.The magnetic field decreased the heat transfer in the melt when it was perpendicular to the temperature gradient,which increased the segregation caused by Marangoni motion of Bi-rich droplets.更多还原