基于DC磁场的磁畴扩大读出技术

MAMMOS(MagneticAMplifyingMagneto-OpticalSystem)是磁畴扩大读出技术之一。该技术是将记录层的微小磁畴扩大复印到读出层,可防止微小磁畴中的信号降低,实现高分辨率的读出。读出时的磁场采用DC磁场,具有利用更简易的系统即可读出的优点。记录层采用RE-rich(富含稀土)的GdFeCo(钆铁钴),读出时施加10ka/m的DC磁场,0.25μm的连续磁畴,可获得43dB的CNR。与CAD-MSR相比,最突出的是0.3μm以下的磁畴的CNR得到了极大的改善,有利于更微小磁畴的读出。

As-cast structure and tensile properties of AZ80 magnesium alloy DC cast with low-voltage pulsed magnetic field

The effects of a low-voltage pulsed magnetic field on the solidified structure and mechanical properties of DC casting AZ80 magnesium alloy were investigated.The results showed that the solidified structure of the DC casting AZ80 magnesium alloy was refined obviously by the low-voltage pulsed magnetic field and significant grain refinement in the DC casting ingot of AZ80 magnesium alloy was achieved.Meanwhile,the morphology of the dentritic in the DC casting ingot was transformed from coarse dentritic to fine rosette with the application of low-voltage pulsed magnetic field.The ability of deformation of the ingot was enhanced and especially the plasticity of the ingot center after upsetting was improved greatly by more than 80%after deformation.

Effective AC and DC Responses of Nonlinear Composites at Higher Concentration

For higher concentration of inclusions, an effective medium approximation （EMA） method is used to investigate the bulk effective response of weakly nonlinear composites, which are subject to the constitutive relation of electric displacement and electric field, Dα = εαE ＋Xα｜E｜^2 E. As an example of three dimensions, under the external AC and DC electric fields Eapp = Eα（1 ＋ sinωt）, we have derived the general effective nonh＇near response of composites by the EMA method for higher concentration of spherical inclusions. Furthermore, the effective nonlinear responses at harmonics are predicted.

Production of super-high strength aluminum alloy billets by low frequency electromagnetic casting

The effects of low frequency electromagnetic field on the macro-physical fields in the semi-continuous casting process of aluminum alloys and the microstructure and crack in the billets were studied and analyzed by the numerical and experimental methods.Comparison of the results for the macro-physical fields in the low frequency electromagnetic casting（LFEC） process with the conventional DC casting process indicates the following characters due to the application of electromagnetic field：an entirely changed direction and remarkably increased velocity of melt flow;a uniform distribution and a decreased gradient of temperature;elevated isothermal lines;a reduced sump depth;decreased stress and plastic deformation.Further,the microstructure of the billets is refined remarkably and the crack in the billets is eliminated in LFEC process because of modification of the macro-physical fields induced by the application of low frequency electromagnetic field.

铝/铜异种材料直流磁场辅助电弧熔钎焊研究

通过添加纵向直流磁场辅助非熔化极惰性气体保护电弧焊(TIG焊)进行铝铜异种材料对接试验,研究焊接电流(I)和磁场强度(B)对接头界面组织及力学性能的影响,对其工艺参数进行优化。结果表明:直流磁场辅助TIG焊可得到成形较好的铝铜接头。磁场促进了界面金属间化合物(IMC)层中的Al_(4.2)Cu_(3.2)Zn_(0.7)三元化合物的形成并抑制硬脆相Al_(2)Cu的生长。随着磁场强度的增加,由于Al_(4.2)Cu_(3.2)Zn_(0.7)的抑制作用,Al_(2)Cu化合物由片状转变为块状,当B=10 mT时,抑制效果最佳,Al_(2)Cu消失;B=20 mT时,抑制效果明显减弱,IMC层中片状的AlCu和Al_(2)Cu重新出现。随着焊接电流的增加,IMC层化合物种类无变化,但其平均厚度呈现先减小后增加的趋势。接头的抗拉强度随着焊接电流和磁场强度的增加呈现先增加后减小的趋势。接头的最佳工艺范围:当焊接电压U=16 V,焊接速度v=140 mm·min^(-1),焊接电流I=90~95 A,磁场强度B=8~15 mT,IMC层平均厚度d<15μm时,接头抗拉强度均大于105 MPa。