电磁振荡强度对半连铸7075铝合金微观组织的影响

在 70 75铝合金半连铸过程中 ,通过同时施加一个稳恒磁场和一个交变磁场 ,使金属熔体产生受迫振荡的方法。实验研究了电磁振荡强度对晶粒细化的影响规律。结果表明 :电磁振荡法获得的铝合金晶粒尺寸较CREM法的小 ,且随着电磁振荡强度的增加 ,铸锭微观组织变得更加细小和均匀。对在电磁振荡作用下 ,合金凝固组织的细化机理进行了探讨。     

电磁振荡对纯铝晶界特征分布及电化学腐蚀性能的影响

向凝固中的纯铝施加强静磁场与交变电流相互作用产生的电磁振荡,获得细化晶粒组织.用EBSD技术观察磁场对其晶界特征分布的影响,发现施加磁场凝固试样的内部出现一定比例的低∑CSL晶界.通过对试样电化学行为的考察得到电磁振荡下凝固的纯铝试样电化学腐蚀电流减小,反映这种特殊晶界的存在会延缓电化学腐蚀过程,亦即提高其抗腐蚀性能.     

电磁振荡下梯度磁场对纯Al凝固组织的影响

研究了梯度磁场对纯Al在强磁场和交流电复合所产生的电磁振荡下凝固组织的影响规律.在不同的梯度磁场中,施加电磁振荡凝固后纵截面细化组织分布发生很大变化,并建立模型进行了分析.结果表明,初生晶核在梯度磁场中所受有效磁悬浮力影响了细化组织分布规律.利用梯度磁场效应,可以控制凝固过程中的"结晶雨"现象和模拟微重力凝固.     

电磁振荡下薄带坯水平连铸的凝固组织

主要研究了静磁场和交流电复合产生的电磁振荡在薄带坯水平连铸上的应用.以纯Sn与Sn-10Pb合金为对象,通过热态物理模拟试验,研究金属薄带坯水平连铸的凝固组织,及其与电磁振荡强度的相互关系.结果显示,在电磁振荡作用下,纯Sn的凝固组织明显细化,并且细化效果随所施加电流的增大而增强;Sn-10Pb合金的凝固组织显示,在凝固前沿施加电磁振荡作用将显著地促进等轴晶组织的形成,使薄带坯中心出现等轴晶区,而且该等轴晶区随电磁振荡的强度增大而扩大.在低强度电磁振荡条件下,凝固组织细化和等轴晶化的原因是:电磁振荡力对金属初生晶的周期性拉伸、压缩、剪切、折弯、扭转等机械作用,使其出现断裂和剥落,增加形核数量;电磁振荡的局部搅拌作用使固/液界面前沿的温度和成分趋于均匀化,导致梯度降低,抑制了柱状晶的生长.     

电磁振荡对铝硅合金凝固组织的影响

研究了直流磁场与交流电同时作用下的Al-Si过共晶合金的凝固组织的变化.试验结果表明,电磁振荡可明显细化合金的宏观组织和显徽组织,随着电磁压力的增加,宏观晶粒尺寸逐渐减小,并且共晶硅相间距减小.     

电磁场对5082铝合金铸轧板材组织的影响

进行了5082铝合金的常规铸轧、静磁场铸轧、交流电场铸轧以及电磁振荡铸轧试验,对比分析各试验条件下获得的铸轧板材的显微组织。结果表明,在5082铝合金板材铸轧过程中施加静磁场可以抑制树枝晶生长、细化晶粒,使晶粒大小分布均匀;施加交流电场使得晶粒分布均匀,但晶粒细化效果不明显,且有助于树枝晶的生长;同时施加静磁场和交流电场,产生电磁振荡效应,使得晶粒细小均匀,晶粒细化效果显著,不再有明显的树枝晶。     

脉冲磁场对Mg-Gd-Y-Zr合金凝固及力学性能的影响

在Mg-Gd-Y-Zr合金凝固过程中施加不同频率的脉冲磁场,研究脉冲磁场对Mg-Gd-Y-Zr合金凝固的影响.实验结果表明,脉冲磁场使Mg-Gd-Y-Zr合金晶粒细化,在频率为5 Hz条件下获得最佳的晶粒细化效果,平均晶粒尺寸从未加脉冲磁场条件下的65 pm细化到37 pm.脉冲磁场的搅拌导致熔体磁过冷及熔体温度梯度降低是晶粒细化的主要原因.脉冲磁场的施加使抗拉强度和延伸率较常规铸造合金分别提高了4.8%、78.5%.     

电磁振荡频率对上引连铸Cu-15Ni-8Sn合金组织及逆偏析的影响

通过在上引连铸Cu-15Ni-8Sn(质量分数,%)合金过程中施加电磁振荡,研究了电磁振荡频率对合金凝固组织及逆偏析的影响。结果表明:当施加的电磁振荡频率为10或30Hz时,合金的宏观凝固组织发生了柱状晶到等轴晶的转变,微观凝固组织由树枝晶转变为蔷薇状组织;当电磁振荡频率从30 Hz增加到50 Hz时,宏观凝固组织又逐渐转变为柱状晶,微观凝固组织也随之转变为发达的树枝晶。电磁振荡频率为10和30 Hz时形成的等轴晶组织有利于改善合金中Sn元素的逆偏析。电磁振荡使合金熔体中产生往复强制对流,10或30 Hz频率的电磁振荡引起的宽幅往复流动使固液界面前沿温度场和溶质场均匀,有利于形成等轴晶,并促使枝晶折断,形成游离晶,消除定向枝晶通道,从而抑制了逆偏析。而在50或100 Hz频率下,电磁振荡频率过高形成了窄幅往复流动,不能有效折断枝晶、达到细化晶粒的目的,从而减弱了抑制逆偏析的作用。     

电磁振荡凝固诱导Al—Cu共晶合金宏观和微观组织的细化

通过在Al-Cu共晶合金凝固过程中同时施加稳恒磁场和交变电场的方式.在熔体中产生了电磁振荡,研究了电磁振荡对Al-Cu共晶合金宏、微观组织的影响.结果表明,适当控制电磁振荡过程参数,可使Al-Cu共晶合金中的宏、微观组织同时得以细化,并分析了组织演化的机理.     

脉冲磁场细晶化技术的研究现状

综述了脉冲磁场细化金属Al、Mg、Cu及其合金等凝固组织的研究进展,从振荡效应、焦耳热效应以及能量起伏三个方面论述了脉冲磁场细化晶粒的机理,并分析了脉冲磁场强度、频率、作用时间对晶粒细化效果的影响。针对目前脉冲磁场细化晶粒的研究现状,指出了未来脉冲磁场细晶技术领域应进一步研究和解决的关键问题。     

Effect of electromagnetic casting process on microstructure and properties of AZ31 magnesium alloy

ABSTRACT

In this paper, AZ31 magnesium alloy is cast by applying the semi-continuous casting process with a low-frequency electromagnetic field. By studying the influence of electromagnetic field frequency, excitation current intensity and casting velocity on the microstructure and mechanical properties, the optimum process under oil-slip electromagnetic casting conditions was determined to improve the degree of grain refinement, yield strength, elongation and tensile strength of AZ31 alloy. An improved microstructure refining effect and higher hardness can be obtained with a current intensity af 60 A. The microstructures and mechanical properties obtained for different casting velocities of V = 200 mm/min and V = 230 mm/min at processing parameters of f = 30 Hz and I = 120 A were compared. Our results suggest that a higher casting speed does not lead to grain refinement or improved mechanical properties. Frequency     

Microstructure formation and grain refinement of Mg-based alloys by electromagnetic vibration technique

The microstructure formation and grains refinement of two Mg-based alloys, i.e. AZ31 and AZ91D, were reported using an electromagnetic vibration （EMV） technique. These two alloys were solidified at various vibration frequencies and the microstructures were observed. The average size of grains was quantitatively measured as a function of vibration frequencies. Moreover, the grain size distribution was outlined versus number fraction. A novel model was proposed to account for the microstructure formation and grain refinement when considering the significant difference of the electrical resistivity properties of the solid and the liquid during EMV processing in the semisolid state. The remarkable difference originates uncoupled movement between the mobile solid and the sluggish liquid, which can activate melt flow. The microstructure evolution can be well explained when the fluid flow intensity versus vibration frequency is taken into account. Moreover, the influence of the static magnetic field on texture formation is also considered, which plays an important role at higher vibration frequencies.     

低频电磁场对7050铝合金铸锭组织的影响

通过在常规半连续铸造过程中施加低频电磁场的方法制备了直径为162mm的7050铝合金铸锭,研究了电磁场对铸锭铸态组织的影响。结果表明,低频电磁场对7050铝合金铸态晶粒尺寸和组织形貌具有显著的影响。施加磁场后铸锭组织变得非常均匀、细小,平均晶粒尺寸由230μm细化至42μm左右,晶粒形貌由粗大枝晶转变等轴晶。电磁场频率和强度对晶粒细化具有重要的影响。对于低频电磁铸造162mm的7050铝合金铸锭,最佳电磁场参数:电磁场频率为25Hz,磁场强度为12800～16000At。     

Refinement mechanism of low voltage pulsed magnetic field on solidification structure of silicon steel

The grain refinement of a silicon steel solidified with a low voltage pulsed magnetic field (LVPMF) was investigated by experiments and modeling. The experiment results show that complete fine equiaxed grains are acquired by applying the LVPMF. The effects of process parameters, such as the melt cooling rate and superheating on the solidification structure, were also studied. Complete fine equiaxed grains can be obtained under a larger range of cooling rate or superheating when the LVPMF is applied. The magnetic force and the melt flow during solidification were modeled and simulated to reveal the grain refinement mechanism. The simulation results show that the LVPMF has a double role in electromagnetic convection and electromagnetic vibration on the alloy melt. We propose the refining mechanism: The melt vibration and convection can promote nucleus multiplication, which contributes to heterogeneous nucleation enhancement and leads to a high nucleation rate and grain refinement.     

Grain refinement of Sn-Pb alloy under a novel combined pulsed magnetic field during solidification

The combined pulsed magnetic field (C-PMF) obtained by simultaneously imposing pulsed and static magnetic field during solidification has been proposed to refine the solidification structure. Compared to the imposition of a single pulsed magnetic field, a more refined structure can be observed under C-PMF. The key factors to affect grain refinement under C-PMF consisted of the vibration frequency characterized by the static magnetic field, pulsed discharge voltage, and the vibration frequency characterized by the pulsed discharge frequency. The microstructure revealed that the grain size decreased with the increasing static magnetic field. The pulsed discharge voltage had an optimum value for obtaining fine grains. Furthermore, when the pulsed discharge frequency was equal to the intrinsic frequency of the liquid metal in a filled cylindrical vessel, resonance vibration occurred in the liquid surface, and grain refinement was promoted.     

Simulation of electromagnetic-flow fields in Mg melt under pulsed magnetic field

The effects of a pulsed magnetic field on the solidified microstructure of pure Mg were investigated.The results show that microstructure of pure Mg is considerably refined via columnar-to-equiaxed growth under the pulsed magnetic field and the average grain size is refined to 260μm under the optimal processing conditions.A mathematical model was built to describe the interaction of the electromagnetic-flow fields during solidification with ANSYS software.The pulsed electric circuit was first solved and the...     

电磁振荡对铝合金半连铸坯微观组织及溶质元素晶内含量的影响

研究了电磁振荡作用下7075铝合金半连铸坯微观组织及溶质元素的晶内分布，对其细化、非枝晶组织形成及溶质元素晶内含量的影响机制进行了探讨。认为在电磁振荡作用下，熔体中结晶核心增加，游离晶粒的枝晶生长方式得到抑制是形成均匀细小的近球形和蔷薇形非枝晶组织的原因，并从电磁场改变7075铝合金凝固过程中的溶质分配系数、结晶间隔、液穴内部温度场、流动场以及微观组织形貌等方面出发，分析了电磁振荡对溶质元素晶内含量的影响。     

脉冲电磁场下铝合金半连续铸造技术研究进展

利用脉冲电磁场引起的力效应、热效应及磁势能可显著改善铝合金半连续铸造组织性能,同时,脉冲电磁铸造技术在绿色生产、智能控制等方面紧密契合“低碳冶金”的国家战略要求。综述了脉冲电磁场在铸造晶粒细化、微观结构演变及析出物细化3方面的研究成果,分析了脉冲电磁场特性与材料相变的耦合机制,提出了脉冲电磁场控制凝固、析出相变组织的初步构想,以满足高性能铝合金的质量要求。着重介绍了基于理论指导开发的熔体表面脉冲电磁场技术及其在7XXX(φ203)、6XXX(φ380)、Al-Si(φ120)等多规格半连续铸造的工业实践,脉冲电磁场有望在今后铸造、热处理等多个冶金环节发挥更大作用。