螺旋磁场对Pb-Sn合金成分偏析的影响

测试分析新型电磁搅拌器内螺旋磁场和旋转磁场的磁感应强度、分布和作用规律,研究螺旋磁场对Pb-80%Sn过共晶合金凝固组织影响的作用机理,并与无磁场和旋转磁场条件下合金凝固组织的形貌特征及成分分布进行对比分析。结果表明:螺旋磁场相比于旋转磁场可以在铸锭内部更大区域内形成均匀搅拌,更易于破碎和细化枝晶组织,既能促进椭球或球状晶的生成,又能更好地改善宏观偏析;在频率一定的情况下,初生相晶粒尺寸随着励磁电流的增大而减小;当励磁电流为125A时,旋转磁场和螺旋磁场细化晶粒的效果最好;继续增大电流,晶粒产生粗化;螺旋磁场可基本消除成分偏析,并在较小励磁电流(100A)下达到采用旋转磁场(125A)时的最佳搅拌效果。

Effects of spiral magnetic field on composition segregation of Pb-Sn alloy

A new type of electromagnetic stirrer was measured to investigate the spiral and rotating magnetic field with their distributions of magnetic induction and mechanism of action,and the effect of spiral magnetic field on solidification structure of Pb-80%Sn hypereutectic alloy was also studied,with comparison of alloys solidified and component distribution in the conventional condition and rotating magnetic field.The results show that,compared with rotating magnetic field,the spiral magnetic field can lead to a more uniform stirring in a larger zone of the ingot,which is more beneficial to breaking and refining the dendrites structure,thus promoting the formation of ellipsoidal or equiaxed grains and reducing macrosegregation.At a fixed frequency,the grains sizes of the primary phase increase with the excitation current and,an optimal effect can be achieved when the current reaches 125 A for both spiral and rotating magnetic field,while higher excitation current will lead to the growth of grains.The macrosegregation can be substantially eliminated by spiral magnetic field and a lower current(100 A) is effective to obtain the same optimal stirring effect(125 A) of rotating magnetic field.