电磁场对AZ61合金凝固组织的影响

通过对不同电磁场组合作用下AZ61合金的凝固组织的研究,发现在静磁场、静磁场与交流电的组合作用下AZ61合金的凝固组织基本为等轴晶,而在静磁场与直流电组合作用下的快速凝固组织中,枝晶组织增加并且具有一定的方向性;在静磁场单独作用下的晶界形貌,其晶界主要由镁基体和连续的网状化合物组成,在静磁场与交流电组合作用下的晶界形貌主要由镁基体和网状及点状Mg-Al-Zn化合物组成,而在静磁场与直流电组合作用下晶界上的连续网格彻底消失,化合物以不连续的薄片形态分布于镁基体上.     

不同磁场作用下AZ61镁合金的凝固组织

在镁合金的凝固过程中施加低频或静态磁场都能有效细化晶粒,但静磁场的细化效果要优于低频交流磁场,同时随磁场强度的增加,静磁场细化晶粒的效果明显提高;在静磁场条件下,晶界共晶体组织的厚度明显减小,同时在晶内出现了大量细小块状化合物,这有利于提高镁合金的综合性能。     

直流电磁场对AZ80镁合金组织结构的影响

研究了在直流磁场下凝固的AZ80镁合金晶内溶质含量及凝固组织的变化。结果表明:与未施加磁场的试样相比,经过直流磁场处理后,AZ80镁合金中Al、Zn2种溶质元素在晶粒内部的含量均增加,直流磁场作用下,试样宏观组织的变化不明显,晶界有所变窄。     

直流电磁场对AZ80镁合金组织结构的影响

研究了在直流磁场下凝固的AZ80镁合金晶内溶质含量及凝固组织的变化.试验结果表明,与未施加磁场的试样相比,经过直流磁场处理后,AZ80镁合金中Al、Zn二种溶质元素在晶粒内部的含量均增加.此外,直流磁场作用下,试样宏观组织的变化不明显,晶界有所变窄.     

不同电磁场作用下Al-Sn合金的凝固组织

Al-Sn合金由于具有大熔点差和宽结晶温度区间,易出现合金化不充分和晶粒充分生长形成粗大枝晶组织,造成比较严重的偏析。在凝固过程中施加不同电磁场和改变电流大小以获得组织均匀的Al-Sn合金。结果表明,施加电磁场后,Al-Sn合金晶粒明显细化,且行波磁场与复合磁场细化效果更加明显。Al-Sn合金中第二相偏析现象减轻,且随着电流强度增加,第二相分布更加均匀;通过对行波磁场(RMF)、旋转磁场(TMF)、复合磁场(RMF+TMF)处理后Al-Sn合金中的第二相分布比较,发现施加旋转磁场时,部分富Sn相有偏聚现象;而在行波磁场与复合磁场作用下,富Sn相没有明显的偏聚。     

交变磁场下Cu-Fe复合材料的凝固组织与性能

研究了低频交变磁场下Cu-14Fe原位复合材料的凝固行为,讨论了磁场施加和磁场强度对铸锭组织、溶质分布和性能的影响。结果表明,Cu-14Fe复合材料常规凝固组织中Fe相主要呈枝晶和不规则长条状分布,施加交变磁场后,Fe相转化成梅花状或等轴状晶粒,分布更均匀。交变磁场的施加导致Cu基体中Fe溶质含量降低,磁场强度越大,浓度下降越明显。交变磁场的施加大幅降低了铸锭中的氧含量,提高了材料的电导率,降低了基体硬度。交变磁场对Cu-14Fe原位复合材料凝固过程的影响分别从动力学和热力学方面进行了分析,磁场一方面通过力场改变了熔体的热流和溶质分布,另一方面作为能量场作用于熔体影响了晶胚形核的势垒,从而影响了Cu-14Fe原位复合材料的凝固组织与性能。凝固过程中施加交变磁场有利于Cu-14Fe原位复合材料中Fe相的细化和析出。     

交流电磁场对AZ80镁合金组织结构的影响

研究了在交流磁场下凝固的AZ80镁合金晶内溶质含量及凝固组织的变化。实验结果表明:与未施加磁场的试样相比,经过交流磁场处理后,AZ80镁合金中Al、Zn二种溶质元素在晶粒内部的含量均增加。此外,在交流磁场作用下,晶粒细化,夹杂物的尺寸和数量也有所减少,10Hz比30Hz的效果更加明显;晶界有所变窄,其中10 Hz的最显著。     

脉冲磁场对AZ91D镁合金凝固组织的影响

研究了脉冲磁场作用下AZ91D镁合金凝固组织的变化,考察了冷却速度、磁场强度和放电频率对AZ91D镁合金晶粒大小的影响,并对磁场影响凝固组织的机理进行了探讨。试验结果表明:在脉冲磁场的作用下,AZ91D镁合金的凝固组织显著细化,其初生相由发达的树枝晶转变为均匀细小的蔷薇状晶体,共晶网络变得细小且不连续,聚集在晶界上的共晶组织减少;合金的晶粒尺寸随着冷却速度的降低,磁场强度或放电频率的增加而逐渐减小。     

交流磁场对AZ31镁合金凝固组织和压缩性能的影响

对AZ31镁合金凝固过程施加交流磁场,研究不同的交流电压和模具温度对AZ31镁合金凝固组织和压缩性能的影响。结果表明:交流磁场可以有效细化AZ31镁合金的凝固组织;当模具温度一定,交流电压在0~250 V范围内增加,AZ31镁合金的初生枝晶形貌出现先细化后粗化的现象;当交流电压一定,模具温度在20~600℃范围内增加,合金的晶粒尺寸也先减小后增大。交流磁场明显提高合金的压缩性能,当浇注温度720℃,交流电压200 V,模具温度200℃时,合金的抗压强度为251.59 MPa,压缩率为28.78%,与未磁场处理的合金相比,抗压强度、压缩率分别提高了26.33%、34.98%。     

强磁场对Al-4.5Cu合金定向凝固过程中织构和晶界的影响

研究了顺磁性Al-4.5Cu合金添加Al-5Ti-1B细化剂后,在强磁场下定向凝固时凝固组织中织构的形成规律和晶界特征分布.结果表明:当温度梯度为27 K/cm,未施加磁场时,细化后晶粒取向杂乱;施加磁场后,随着磁场强度的提高,晶粒位向发生变化,晶粒沿a-Al易磁化轴〈310〉发生取向排布.伴随〈310〉织构的生成,晶粒中重位点阵(CSL)晶界比例提高.熔体中具有磁晶各向异性的a-Al晶粒在磁场下受磁转矩作用发生转动,是织构生成的主要原因.还讨论了磁场下流体流动对织构生成和晶界的影响.     

The formation of randomly textured magnesium alloy sheet through rapid solidification

The rapid solidification of three magnesium-based alloys has been carried out on copper substrates with four tailored surface morphologies. Increasing surface roughness improved the wetting characteristics of the substrates, as did coating with carbon. Of the alloys tested, AZ31 showed inferior wetting behaviour due to the formation of alumina oxides at the interface between the melt and the copper substrate. This behaviour was obviated by the addition of calcium to the melt. The pure magnesium castings all produced a strongly columnar region and showed a weak crystallographic texture. The alloy castings produced weakly columnar regions with an essentially random texture. The alloys cast onto the carbon-coated substrates produced a fully equiaxed microstructure due to the inhibition of heterogeneous nucleation on the substrate surface. It is demonstrated that a randomly textured microstructure with equiaxed grains can be produced through rapid solidification and the implications of this microstructure for the ductility of magnesium sheet is discussed.     

Effect of magnetostatic field on microstructure of magnesium alloy ZK60

1　INTRODUCTIONNonferrousmaterialshavedisplayedmoreandmoreimportantrolesinthe 2 0 st century .Amongthesenonferrousmaterials ,magnesiumalloyisoneofthelightest practicalmaterial,butmagnesiumisametalwithastrongelectronegativity .Itsstandardelectricpotentialis - 2 .36 3V ,anditserosionresis tanceisnotgood .Becauseoftheoxidizationduringrefining ,deformationandapplication ,theadvantagesofmagnesiumalloysandtheirapplicationislimited .Asthedevelopmentoftherefiningtechnologyandad vancedformationte…     

Simulation of dendritic growth of magnesium alloys with fluid flow

Fluid flow has a significant impact on the microstructure evolution of alloys during solidification. Based on the previous work relating simulation of the dendritic growth of magnesium alloys with hcp (hexagonal close-packed) structure, an extension was made to the formerly established CA (cellular automaton) model with the purpose of studying the effect of fluid flow on the dendritic growth of magnesium alloys. The modified projection method was used to solve the transport equations of flow field. By coupling the flow field with the solute field, simulation results of equiaxed and columnar dendritic growth of magnesium alloys with fluid flow were achieved. The simulated results were quantitatively compared with those without fluid flow. Moreover, a comparison was also made between the present work and previous works conducted by others. It can be concluded that a deep understanding of the dendritic growth of magnesium alloys with fluid flow can be obtained by applying the present numerical model.     

Simulation of dendritic growth of magnesium al oys with fluid flow

Fluid flow has a significant impact on the microstructure evolution of alloys during solidification. Based on the previous work relating simulation of the dendritic growth of magnesium alloys with hcp(hexagonal closepacked) structure, an extension was made to the formerly established CA(cellular automaton) model with the purpose of studying the effect of fluid flow on the dendritic growth of magnesium alloys. The modified projection method was used to solve the transport equations of flow field. By coupling the flow field with the solute field, simulation results of equiaxed and columnar dendritic growth of magnesium alloys with fluid flow were achieved. The simulated results were quantitatively compared with those without fluid flow. Moreover, a comparison was also made between the present work and previous works conducted by others. It can be concluded that a deep understanding of the dendritic growth of magnesium alloys with fluid flow can be obtained by applying the present numerical model.     

Dendrite fragmentation and columnar-to-equiaxed transition during directional solidification at lower growth speed under a strong magnetic field

The effects of strong magnetic fields on the columnar-to-equiaxed transition (CET) have been investigated experimentally. Six alloys have been directionally solidified at low growth speeds (1–10 μm s^?1) under magnetic fields up to 10 T. Experimental results show that the application of a strong magnetic field causes a dendrite fragmentation and then the CET. The thermoelectric magnetic force acting on cells/dendrites and equiaxed grains in the mushy zone has been studied numerically. Numerical results reveal that the value of the thermoelectric magnetic force increases as the magnetic field intensity and the temperature gradient increase. A torque is created on cells/dendrites and equiaxed grains. This torque breaks cells/dendrites and drives the rotation of equiaxed grains. The rotation of equiaxed grains in the mushy zone will further destroy cells/dendrites. Thus, with the increase of the magnetic field intensity and the temperature gradient, the volume fraction of equiaxed grains in front of columnar dendrites increases. When the magnetic field intensity and the temperature gradient reach a critical value, the growth of columnar dendrites is blocked and the CET then occurs. The present work may initiate a new method of inducing the CET via an applied strong magnetic field during directional solidification.     

喷射成形Mg-9Al-xZn合金的微观组织演变

利用喷射成形技术制备AZ91、AZ92和AZ93镁合金沉积柱坯,并对其微观组织演变进行观察.结果表明:铸态普通凝固AZ91合金的晶粒粗大,脆性β-Mg17Al12相连续分布成网状结构;而喷射成形AZ91、AZ92和AZ93合金的组织均匀,晶粒被充分细化,β-Mg17Al12相的网状结构被打破;喷射沉积快速凝固条件下高的冷却速率促进了过饱和α-Mg固溶体组织的形成,使得偏析相减少,形态改善;Zn含量的增加降低了Al在Mg中的溶解极限,促进了β-Mg17Al12相在晶界的析出及α-Mg+β-Mg17Al12离异共晶组织的形成;Zn元素的偏析倾向为激活成分过冷区内的形核质点提供了驱动力,从而阻碍了晶粒长大.     

Microstructure and segregation of magnesium alloy solidified under magnetostatic field

Magnesium alloys are materials with predominant performance, but its formability is needed to be improved. Increasing the content of soluble inside grain, the formability will be improved. The results show that when magnetostatic field is applied to the process of solidification of magnesium alloy, the grain is refined, and the soluble content inside grain increases, on the contrary the content of soluble decreases at grain boundary. Compared with the common solidification, when the magnesium alloy ZK60 is solidified under magnetostatic field, the content of calcium and zinc decrease respectively from 15. 62%, 5. 6% to 14. 85%, 3.7% at grain boundary; the content of zinc increases from 0.68% to 0.91% inside grain. This will increase distortion inside matrix and more dislocation will supply slid deformation, as a result the formability will be improved.     

Columnar to equiaxed transition of eutectic in hypoeutectic aluminium–silicon alloys

Directional solidification of unmodified and strontium modified binary, high-purity, aluminium–7 wt% silicon and commercial A356 alloys has been carried out to investigate the mechanism of eutectic solidification. The microstructure of the eutectic growth interface was investigated with optical microscopy and Electron Backscattering Diffraction (EBSD). In the commercial alloys, the eutectic solidification interface extends in the growth direction and creates a eutectic mushy zone. A planar eutectic growth front is observed in the high-purity alloys. The eutectic aluminium has mainly the same crystallographic orientation as the dendrites in the unmodified alloys and the strontium modified high-purity alloy. A more complex eutectic grain structure is found in the strontium modified commercial alloy. A mechanism involving constitutional undercooling and a columnar to equiaxed transition explains the differences between pure and commercial alloys. It is probably caused by the segregation of iron and magnesium and the activation of nucleants in the commercial alloy.     

时效工艺对WE43镁合金组织与力学性能的影响

研究了WE43稀土镁合金在不同热处理工艺下显微组织、力学性能的变化规律,从而得出最佳的热处理工艺。研究结果表明WE43稀土镁合金铸态组织为等轴状晶粒,比较均匀,平均晶粒尺寸为40 μm;铸造冷却凝固的过程中,在晶界处形成了离异共晶组织;经520 ℃×8 h固溶处理后的组织,共晶相的数量和形态发生了明显的变化,枝晶偏析基本消除,晶界上仍有少量未溶的第二相。230 ℃×8 h时效后稀土第二相的数量增加,并且在晶粒内部析出了点状弥散的稀土相;经过250 ℃×16 h的时效后,合金的硬度达到了峰值,随着时效时间的继续延长,合金的硬度下降。固溶处理后WE43稀土镁合金的抗拉强度为162.59 MPa左右,断后伸长率约为5.0%;而经过250 ℃时效处理后,其抗拉强度明显增加,断后伸长率在4%左右。     

Microstructures and Formability of the As-Rolled Mg-xZn-0.5Er Alloy Sheets at Room TemperatureEI北大核心CSCD

As lightweight requirements rise in transportation, aerospace, and other industries, magnesium alloys have a great application prospect. However, the low formability capabilities of magnesium alloys lead to a severe limit in applications. At present, there are many reports on the influences of texture and second phases on the formability of magnesium alloys at room temperature. Nevertheless, the dominant factors affecting the formability performance of magnesium alloys at room temperature are not clear. In this study, the development of the microstructures and texture of Mg-xZn-0.5Er (x = 0.5, 2.0, 3.0, 4.0, mass fraction, %) alloy sheets were studied, and the impact of the texture and second phases on the formability of these sheets were also investigated. The findings showed that the increase in Zn addition led to an early and complete dynamic recrystallization (DRX) in Mg-Zn-Er alloys sheets, and these recrystallized grains would expand significantly during subsequent hot rolling processes. These recrystallized grains with a large size were typically elongated and then helped to create a strong basal texture. Thus, it was discovered that the microstructures of these sheets were typically made up of equiaxed and elongated grains. The formability performance of these sheets was strongly related to the size of the second phases and the texture. The formability of the sheets containing microscopic second phases mainly depended on the basal texture, while the formability of the sheets which contained coarse second phases was mostly influenced by the second phases and basal texture. Particularly, when the component of the coarse second was larger, the formability would get more inferior due to the predominant role of the second phase at room temperature.