Effect of Electromagnetic Pulse Waveform on Solidification Process of ZL114A Aluminum Alloys
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摘要: 在脉冲电磁场铸造过程中,由于线圈电感效应会引起脉冲波形的畸变与失真,实际波形引起的电磁效应对铝合金凝固物理场的影响至关重要。本研究建立了电磁场有限元数学模型,结合实验数据,探明了脉冲电流峰值、频率、占空比对磁通密度、电磁力时间和空间分布特性的影响,进而分析其对金属熔体液面波动及凝固组织的作用规律。结果表明,当脉冲电流峰值为100 A、频率为20 Hz、占空比为20%时,线圈有效脉冲加载电流最高、磁通密度最大、磁场分布均匀。此时,电磁力径向分量引起的磁压力对金属液面波动起主导驱动和控制作用,液面形成清晰的波动,ZL114A铝合金中初生α-Al相晶粒得到细化,并形成了细小、分散的二次相;当频率增加至80 Hz后,液面波动振幅减小,合金中的初生Si相粗化和偏聚;当占空比增加至80%后,液面波动振幅显著增加,剧烈的熔体振荡不利于合金凝固组织细化。Abstract: In the cause of pulsed electromagnetic casting, the inductance effect of the coil (Lenz's law) causes distortion and deformation of the pulse waveform, and the electromagnetic effect induced by the actual waveform is crucial for the solidification field of aluminum alloys. In this study, a finite element mathematical model of the electromagnetic field is established in combination with the experimental research to investigate the effects of pulse intensity, frequency, and duty cycle on the filed density and the spatial and temporal distribution characteristics of magnetic flux density and electromagnetic force. Furthermore, the influence of those factors on the melt surface fluctuations and solidification structures are analyzed. Results show that when the peak current is 100 A, the frequency is 20 Hz, and the duty cycle is 20%, the coil's effective pulse loading current and the magnetic flux density are at their maximums, and the magnetic field is evenly distributed. At this point, the magnetic pressure caused by the radial electromagnetic force plays a dominant role in driving and controlling the melt surface fluctuations, leading to clear waves on the liquid surface. The α-Al phase in the ZL114A alloy is refined, and the fine and dispersed secondary phase is formed. As the frequency increases to 80 Hz, the amplitude of surface fluctuations decreases, and the primary Si phase becomes coarser and segregated. When the duty cycle increases to 80%, the amplitude of the surface fluctuations increases significantly, the violent melt oscillation is unfavorable for the refinement of the solidified structure.
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