Effect of temperature field on solidification structure of pure Al under pulse magneto-oscillation

This article discusses the effect of temperature field on the Pulse Magneto-Oscillation(PMO) induced solidification refinement of pure aluminium to provide more information for the industrial application of the PMO solidification technology.The temperature field is altered mainly by applied variable cooling conditions and pulse parameters.Experimental results show that the refinement effect in the case of full sand mould applied is weakened with the decreasing of cooling rate,however,in the alternative case,the sand mould whose sand bottom was replaced by a graphite block is favorable to the survival of equiaxed nucleus.The refinement mechanism is discussed in terms of the relationship between temperature field and the formation process of solidified structure.The formation or survival of nucleus depends on both temperature field and Joule heat produced by PMO,both low pulse frequency and high pulse current were experimentally confirmed to be effective;and PMO was demonstrated high potential in industrial application.

Grain refinement of commercial pure Al treated by Pulsed Magneto-Oscillation on the top surface of melt

Commercial pure Al can be refined by Pulsed Magneto-Oscillation(PMO) treatment applied via a plate induction coil above the top surface of the melt. The proportion of the equiaxed zone area increases with decreasing Height to Diameter(H/D) ratios from 3.5 to1.8 and further to 1.0. Meanwhile, it increases and then decreases with increasing peak current for the three kinds of ingots with H/D ratios of 3.5, 1.8 and 1.0, respectively. However, when the H/D ratio decreases to 0.44, the area proportion of equiaxed zone can reach the maximum value with a lower peak current. FEA software simulation indicates that smaller H/D ratio results in larger current density, electromagnetic force and convection on the top surface of the melt, favoring nucleation and subsequent grain formation. Through evaluating Joule heating effect by PMO, it was found that the proper amount of Joule heating benefits grain refinement. Excessive Joule heating can reduce the size of the equiaxed zone and change the growth morphology of the grains.

Mechanism of pulse magneto-oscillation grain refinement on pure Al

Pulse magneto-oscillation (PMO) was developed as a novel technique to refine the solidification structure of pure aluminium.Its grain refining mechanism was proposed.The PMO refinement mechanism is that the nucleus falls off from the mould wall and drifts into the melt under the action of PMO.The solidification structure of Al melt depends on the linear electric current density,and also the discharge and oscillation frequencies.The radial pressure of PMO sound wave is the major factor that contributes to the migration of nucleus into the melt.

PMO对定向凝固GCr15轴承钢枝晶臂间距的影响

为了解脉冲磁致振荡(pulse magneto-oscillation,PMO)技术对GCr15轴承钢定向凝固组织的作用,通过改变PMO参数和抽拉速率,研究了不同抽拉速率下PMO对定向凝固GCr15轴承钢枝晶臂间距的影响。结果表明:在相同抽拉速率下,PMO的峰值电流依次为150、250、350ki A时,GCr15轴承钢的一次和二次枝晶臂间距先增大后减小。当峰值电流固定为350ki A时,随着PMO频率从90、240、390kf Hz依次增大,一次枝晶臂间距先减小后增大,二次枝晶臂间距逐渐变大。同时,随着抽拉速率的提高,枝晶臂间距减小幅度逐渐降低。通过测量温度梯度发现,在PMO作用下,固-液界面前沿液相中温度梯度的提高和溶质分布的变化,是枝晶臂间距减小的主要原因。

PMO凝固均质化技术在连铸GCr15轴承钢生产中的应用

脉冲磁致振荡(pulse magneto-oscillation,PMO)凝固均质化技术是我国学者原创的连铸坯凝固组织细化和均质化技术。将该技术应用于连铸GCr15轴承钢生产,研究脉冲磁致振荡对GCr15轴承钢连铸坯凝固组织和成分分布的影响。生产实践表明,PMO可以显著细化连铸GCr15轴承钢的凝固组织,改善碳偏析。

PMO对连铸GCr15轴承钢枝晶生长的影响

通过对PMO处理的连铸GCr15轴承钢固/液界面枝晶形貌和微观偏析的观测,探究了施加PMO对铸坯固/液界面前沿枝晶生长的影响。结果表明:PMO作用于固/液界面处,使枝晶间碳富集程度降低,初生相的面积占比增大,一次枝晶间距减小,二次枝晶臂间距增大,且二次臂细长致密,局部枝晶非对称生长。结合PMO的电磁热力效应分析认为,枝晶生长前沿的温度场和溶质场在PMO作用下出现扰动,固/液界面前沿溶质富集减轻,成分过冷度增大,促进枝晶臂生长,导致初生相占比增大;强制对流使液相温度分布均匀,固/液界面处温度梯度增大,故一次枝晶间距减小;由于垂直于拉坯方向的液相温度梯度减小及微区的磁致振荡效应,柱状枝晶的生长方向发生改变,干扰了枝晶间富集溶质的扩散,进而造成了枝晶的非对称生长。

PMO对GCr15钢棒材中带状碳化物评级及分布的影响

脉冲磁致振荡(pulse magneto-oscillation,PMO)是上海大学原创的凝固组织细化及均质化技术。已将PMO技术应用于GCr15轴承钢的工业生产。通过对棒材试样中带状碳化物面积及碳化物平均粒径的测量和统计,研究了该技术对GCr15轴承钢中碳化物带状评级及分布的影响。结果表明:在0.75、0.82 m/min拉速条件下,施加PMO处理后,GCr15钢棒材中心区域碳化物带状得到改善,碳化物平均粒径减小,大尺寸碳化物数量减少。此外,经过PMO处理的GCr15钢棒材中未溶晶界碳化物减少,弥散分布的球状碳化物增多。

应用结晶器PMO提高连铸小方坯质量研究

为了改善某厂螺纹钢小方坯连铸过程中存在的等轴晶率低、中心碳偏析严重、中心疏松和缩孔等内部质量问题,进行了结晶器脉冲磁致振荡(pulse magneto-oscillation,PMO)改善螺纹钢内部质量的试验研究。结果表明:结晶器PMO可以显著细化螺纹钢的凝固组织,扩大中心等轴晶区的范围,减小二次枝晶臂间距,中心缩孔由0.5级降低到0级,中心偏析由2级降低到0.5级,中心碳偏析指数由1.18降低到1.01,铸坯内部质量得到明显改善。

Fine equiaxed dendritic structure of a medium carbon steel cast using pulsed magneto-oscillation melt treatment

The application of a pulsed magneto-oscillation （PMO） technique during the solidification of a commercial high melting point medium carbon steel ingot （φ0140 mm × 450 mm） produced fully equiaxed grains in the cast ingot, indicating that the PMO process significantly promotes heterogeneous nucleation near the solid-liquid interface. The vigorous convection induced by PMO forced the partly solidified grains to move from the solid-liquid interface and became randomly distributed throughout the melt, which resulted in the formation of uniformly sized equiaxed dendrites throughout the whole ingot. Building on the developed nucleation mechanism and a flow field simulation of pure aluminum, a PMO-induced grain refinement model for steel is proposed.

Distributions of Electromagnetic Fields and Forced Flow and Their Relevance to the Grain Refinement in Al–Si Alloy Under the Application of Pulsed Magneto-Oscillation

Distributions of electromagnetic fields and induced forced flow inside a metal melt are crucial to understand the grain refinement of the metal driven by pulsed magneto-oscillation(PMO).In the present study,PMO-induced electromagnetic fields and forced flow in Ga-20 wt%In-12 wt%Sn liquid metal have been systematically investigated by performing numerical simulations and corresponding experimental measurements.The numerical simulations have been confirmed by magnetic and melt flow measurements.According to the simulated distribution of electromagnetic fields under the application of PMO,the strongest magnetic field,electric eddy current and Lorentz force with inward radial direction inside the melt are concentrated adjacent the sidewall of cylindrical melt at the cross section of middle height of coil.As a result,a global forced flow throughout the whole cylindrical column filled with Ga-20 wt%In-12 wt%Snmelt is initiated with a flow structure of two pair of symmetric vortexring.The PMO-induced electromagnetic fields and forced flow in Al-7 wt%Si melt have been numerically simulated.The contribution of electromagnetic fields and forced flow to the grain refinement of Al-7 wt%Sialloy under the application of PMO is discussed.It indicates that the forced flow may play a key role in the grain size reduction.

Distribution of nonmetallic inclusions in molten steel under hot-top pulsed magneto-oscillation treatment

To control the distribution of nonmetallic inclusions in molten developed method, hot-top pulsed magneto-oscillation （HPMO）, steel is of highly commercial importance. A newly was employed to control nonmetallic inclusions in a medium-carbon steel ingot. The experimental results present that the position of nonmetallic inclusions of spinel （Al-Mg-O） and Mn-S inclusions is significantly influenced by HPMO. The number of nonmetallic inclusions gradually increased from the lateral wall to the center of ingot along the radial direction under the impact of HPMO treatment, whereas this distribution trend cannot be observed in the reference sample without HPMO treatment. In addition, the number of inclusions along vertical direction is proportional to the height of ingot, especially for the inclusions with the size of larger than 10 pro. It indicates that the application of HPMO can push away inclusions from lateral to center, and then the expelled inclusions aggregate and rise up to the top of ingot.

Influence of pulsed magneto-oscillation on microstructure and mechanical property of rectangular 65Mn steel ingot

The pulsed magneto-oscillation （PMO） technique has the potential to be applied in the production of heavy steel ingot. In order to confirm it and achieve more insights, the solidification of rectangular 65Mn steel ingot with the size of 220 mm×220 mm × 1000 mm was investigated under the impact of PMO. Experimental results present that PMO treatment can remarkably refine the solidified microstructure of 65Mn steel ingot in comparison with the reference ingot without PMO. The application of PMO not only significantly reduces the grain size, but also promotes the morphology transition of equiaxed grains from well-developed dendritic structures to globular structures. And the resulted globular morphology is mainly due to the fact that the PMO-induced forced flow enhances the stability of crystal growth. As a consequence, the average tensile strength of as-cast samples is enhanced from 643.4 to 762.9 MPa under the application of PMO.

Improving the Solidified Structure by Optimization of Coil Configuration in Pulsed Magneto-Oscillation

Using both numerical and experimental methods, we studied the effect of coil configuration of pulsed magneto-oscillation（PMO） on distribution of electromagnetic field, flow field and solidification structure with the same pulse currentparameters in A1 ingots. We designed and constructed three types of coils： surface pulsed magneto-oscillation, hot-toppulsed magneto-oscillation （HPMO） and combined pulsed magneto-oscillation （CPMO）. PMO treatment refined thesolidification structure in all the ingots. The configuration of the PMO, however, introduced differences in magnetic fieldintensity, electromagnetic force, Joule heat, flow field, equiaxed grain zone, grain size and growth direction of columnargrains. The largest equiaxed grain zone was found in CPMO treated ingot, and the smallest grain size was found in bothHPM0 and CPMO treated ingots. Numerical simulation indicated that difference in electromagnetic field and flow fieldresulted in differences in solidification structure. HPMO is more advantageous over others for large ingot production.

Effects of pulse magneto-oscillation on GCr15 bearing steel continuous casting billet

Pulse magneto-oscillation(PMO)added during solidification could affect the solidification structure and macrosegregation.A modified thermal simulation equipment was applied to prepare GCr15 bearing steel continuous casting billets with different PMO peak currents.Then,metallographic analysis,component analysis and numerical simulation were adopted to study the influence of PMO peak current and its mechanism.The sample with 150 K_(I)A PMO peak current treatment has little difference with the samples without PMO treatment on solidification structure and macrosegregation.As the peak currents are 250 and 350 K_(I)A,the columnar zone increases and macrosegregation aggravated.When 450 K_(I)A peak current is selected,the equiaxed grain ratio is enlarged,and the dendritic grains are refined,and the macrosegregation of C,Cr,Si and Mn is decreased significantly.By analyzing,different convections induced by PMO with various peak currents are the key factor to change the solidification structure and macrosegregation.

阱接触面积对PMOS单粒子瞬态脉冲宽度的影响

使用TCAD模拟工具分析了纳米工艺下阱接触面积对PMOS SET脉冲宽度的影响。结果表明,纳米工艺下,当存在脉冲窄化效应时,增加阱接触面积会导致SET脉冲变宽,这与传统的通过增加阱接触面积可抑制SET脉冲的观点正好相反。同时,还分析了不同入射粒子LET值以及晶体管间距条件对该现象的作用趋势。

PMO作用对60Si2Mn弹簧钢凝固组织的影响

针对中天钢铁在60Si2Mn弹簧钢生产过程中出现的连铸坯凝固组织发达、中心缩孔等级偏高、铸坯初生相非对称性生长等问题开展技术攻关,选用上海大学先进凝固技术中心(CAST)研发的脉冲磁致振荡(简称PMO)凝固均质化技术,对该钢种的连续浇注过程进行干预。结果表明:施加PMO后,60Si2Mn弹簧钢连铸坯柱状枝晶呈对称生长且二次枝晶臂间距减小,内弧侧距离铸坯表面43 mm处发生柱状晶向等轴晶(CET)的转变,中心凝固组织明显细化并球化,中心缩孔基本消除,铸坯凝固组织结构明显优化。

基于PMOS自适应输入输出低压白光LED驱动

白光LED是最被看好的新兴光源产品,其在照明市场的发展潜力值得期待。白光LED具有体积小、发热量低、耗电量小、寿命长、反应速度快、环保、可平面封装易开发成轻薄短小产品等优点。在小功率白光LED驱动电路中,电池(一节电池)供电已经成为一种趋势。在基于标准CMOS工艺条件下,设计了一个可以使用一节电池供电、外围器件极少、无需输出电容、脉冲驱动的白光LED驱动电路,并可以随输入电压不同自适应调节工作状态,适合中小电流条件下白光LED背光照明应用中。

Improving ingot homogeneity by modified hot-top pulsed magneto-oscillation

Heavy ingots,especially the ingot of more than 10 t,often contain detrimental heterogeneous defects,such as macrosegregation,shrinkage pipes,and cracks.Hot-top pulsed magneto-oscillation(HPMO)can refine the solidified structure of ingot and improve their homogeneity.However,it may exacerbate the positive segregation at the upper part of the ingot body.Thus,a round table HPMO riser with a feeding part was designed,and the microstructure and macrosegregation of Al–Si alloy ingots solidified with and without HPMO were investigated.The simulation and experimental results indicated that round table HPMO riser could enable fine and uniform solidified structures in the whole ingot body;in the meantime,feeding part allowed the melt with enriched solute to gather in the upper part of the riser until the last solidification stage of ingot.This provides an effective approach for obtaining highly homogenized ingots.

浇注温度对脉冲磁致振荡细化纯铝凝固组织的影响

采用自制脉冲电源,研究脉冲磁致振荡(pulse magneto-oscillation,PMO)对纯铝凝固组织的作用效果,考察浇注温度对纯铝凝固组织细化的影响.实验结果表明,低的浇注温度有利于铸锭中形成适合晶核生存的温度场,增加晶核存活数量,从而改善铸锭的细化效果.

T/R组件中功放脉冲调制电路的分析与设计

针对相控阵雷达T/R组件中应用广泛的GaN脉冲功率放大器,提出一种高压漏极脉冲调制电路。该电路包含高集成度的PMOS驱动器和高压PMOS管SM6103,并包含快速放电通道,该电路的输入信号为TTL信号、输出信号为+28 V脉冲信号。测试结果显示调制输出信号的上升沿小于40 ns,下降沿小于50 ns,输出电压过冲小于20%,电流驱动能力大于13 A。该脉冲调制电路结构简单、尺寸小,采用裸芯片以及铝丝键合工艺,满足T/R组件小型化的设计要求。