强磁场对Bi-Mn合金半固态凝固过程中MnBi析出相组织的影响

在Bi-6%Mn合金从高于355℃(升温过程中MnBi化合物磁性转变温度)的固液两相区凝固过程中,研究了MnBi析出相组织在无磁场和强磁场条件下的演化过程.结果表明:在无磁场条件下MnBi析出相形态在340℃(MnBi相顺磁-铁磁转变温度)附近发生突变,由较规则的六方块状变为沿ab面长大的不规则片状;10 T磁场条件下析出相形态突变的温度提高到355℃左右.另外,10 T磁场能够控制析出相晶粒以c轴平行磁场取向、定向聚合和熔合长大,使析出相的最终形态又趋向较规则的六方块状.     

稳恒磁场对Al-10Ni合金凝固组织及结晶取向的影响

研究了磁感应强度为0~1.5T的稳恒磁场对Al-10Ni合金凝固组织及结晶取向的影响。结果表明,稳恒磁场能够使合金中Al3Ni初生相均匀分布,在平行于磁场方向的截面上Al3Ni初生相发生定向排列,磁场能显著改变基体Al和Al3Ni相的晶体取向;随着磁感应强度的增加,Al3Ni相的定向排列程度逐渐提高,间距逐渐减小;基体铝相的(311)晶面的生长受到抑制,Al3Ni相在(hk0)面的衍射强度增强,同时以c轴平行磁场方向取向。     

复合静磁场下BiMn合金凝固中的电迁移

为强化电迁移技术的效果,在金属液两端施加恒定电场的同时施加了一个与电流方向平行的稳衡磁场,考察了在磁场作用下BiMn合金中MnBi相的电迁移情况。实验结果表明,在磁场的作用下,MnBi相可以在10A/cm2的电流密度下向阴极发生迁移;当施加的电流密度一定时,MnBi相的偏移率随着磁感应强度的增大而增大,且存在一个临界值;当磁感应强度一定时,只有当电流密度达到一定的值时才能使析出相稳定迁移。     

强磁场下Al-Ni合金凝固初生相Al3Ni的取向行为

进行了10T强磁场下Al-(8%~12%)Ni(质量分数)合金凝固实验,考察了初生相Al3Ni的取向行为。结果表明,加磁场后纤维状初生相Al3Ni在垂直于磁场方向的平面上定向排列聚集,形成层间距基本相同的分层组织。X射线衍射结果表明,施加磁场后,Al3Ni晶体发生了取向,其〈00l〉晶向转向磁场方向。在合金两相区中,当磁感应强度和温度提高到一定值时,初生相的取向程度显著增加,其定向排列因子Г也随之增加。此外,还对晶体在磁场中的取向行为进行了热力学分析。     

磁场对Bi-Mn合金两相区中MnBi相凝固组织的影响

将Bi-3%Mn和Bi-6%Mn合金加热至固液两相区内低于MnBi相Curie点的温度，保温30min后在一定条件下降温凝固，施加0－1．0T磁场，结果表明，磁场对MnBi相凝固组织和材料磁性能有明显的影响，Bi-Mn合金在固液两相区恒温时，MnBi晶体在大于0．1T的磁场作用下沿磁场方向排列和优先长大，定向排列因子г随外磁场强度的增大而提高，在磁场作用下的降温凝固过程中，沿磁场方向MnBi晶体长度增加，其平均长度随磁场的增大和合金在磁场中凝固时间的延长而增加，此外，磁取向试样具有明显的磁各向异性，平行定向排列方向的剩显著增强，而垂直方向的磁性很弱，从铁磁性MnBi晶体的磁各向异性和磁化晶体之间磁相互作用出发，建立了MnBi晶体的磁场中取向和优先长大的理论模型，并利用该模型对实验结果进行了讨论。     

强磁场作用下Al-Ni合金中Al3Ni析出相的凝固行为

用金相显微镜和X射线衍射研究了强磁场条件下Al-8％Ni合金中非铁磁性的Al3Ni析出相的凝固行为，发现强磁场诱导Al3Ni晶粒以C轴平行磁场方向取向，并且晶粒的长轴与C轴垂直；取向的晶粒在垂直磁场方向上形成多个相互平行的Al3Ni聚合面，即形成规则的Al3Ni层状组织：在层状聚合面中随机分布着多个大的Al3Ni聚合体，聚合体内部的晶粒有序排列。     

Bi-Mn合金片状初生MnBi相在强磁场中的凝固组织

进行了强磁场下Bi-Mn合金的全熔和半固态实验,研究了MnBi相在强磁场中的凝固行为．在10T强磁场下从全熔态和Curie点以上半固态开始凝固的实验中,MnBi相在360℃左右逐渐形成片状相,其短轴为易磁化轴;加磁场后易磁化轴转向磁场方向,并沿磁场方向定向排列和聚合,最终形成条状组织;片状相在强磁场的作用下有分裂趋势．结合晶体的磁各向异性和生长各向异性的特点,从磁化理论和晶体学出发,分析了Bi—Mn合金初生MnBi相在磁场中的凝固行为．     

Al-Si-Mg-Y合金消失模铸造振动压力凝固的组织与性能

应用消失模铸造振动压力凝固成形技术制备了Al-7Si-0.8Mg-0.3Y(ASMY)合金。通过SEM、XRD、DSC和TEM等测试方法对其铸态和T6组织进行分析,研究其对力学性能的影响。结果表明:在ASMY合金铸态组织的晶界处生成有少量Al3Y短棒状颗粒相;在T6热处理过程中,稀土Y或Al3Y阻碍Mg2Si相的析出和扩散聚集,使析出相Mg2Si呈弥散分布;Mg2Si相与晶界稳定相Al3Y对合金同时起到钉扎强化作用;采用消失模铸造振动压力凝固技术后,铝合金的孔隙率显著降低,从1.1%降低0.18%;ASMY合金消失模铸造振动压力凝固试样T6态的抗拉强度达到308MPa,比A356普通消失模试样T6态的抗拉强度提高29%。     

T4、T6处理对AZ80镁合金的强化作用

采用拉伸试验、金相实验和XRD等方法测试和分析了AZ80镁合金在铸态、T4态及T6态的力学性能和显微组织。结果表明:T4处理使铸态AZ80镁合金组织中沿晶界处的网状β相分解并溶入到α-Mg基体中,T6处理会析出β-Mg17Al12相,有连续析出和不连续析出,T6处理后材料的抗拉强度和屈服强度最高,T4处理后的断后伸长率较铸态和T6态高。     

Al-7.0Zn-2.9Mg合金板在制备过程中的显微组织及力学性能

采用光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)和差示扫描量热仪(DSC)等分析手段研究了Al-7.0Zn-2.9Mg合金板在制备过程中及不同时效热处理工艺下的显微组织及力学性能。结果表明,Al-7.0Zn-2.9Mg合金铸态组织主要由α(Al)+Mg_(32)(Al,Zn)_(49)(T)相共晶组织、Al(Fe,Mn)Si相和少量过剩T相组成。经均匀化处理后,共晶相基本溶入基体中,基体中又重新析出MgZn_2粒子及少量Al_3Zr相。热轧后的晶粒组织沿轧制方向呈纤维状分布。试验了一种低温时效+常规时效的LTA工艺,结果显示,LTA态的合金强度和伸长率均略高于峰值时效(T6)和回归再时效(RRA)态。同时,析出相尺寸明显大于T6、RRA和双极时效(T73)态,且晶界析出相呈粗大不连续分布,具有较好的抗应力腐蚀开裂(SCC)潜力。     

强磁场对Bi-Mn合金MnBi相形态的影响

研究了强磁场对Bi-Mn合金MnBi相形态的影响,发现在10T的磁场下,在一定温度范围内顺磁相MnBi转变为铁磁相并由一个晶体分裂为许多沿磁场方向取向和聚合的小晶体.并从磁场诱发应变的角度上分析了磁场对相变温度和MnBi相形态的影响.     

Ring--Like Solidification Structure Of Mnbi Phase In Bi—Mn Alloy Under A High Magnetic Field

对强磁场作用下Bi-Mn合金分别从全熔态和从固液两相区开始的凝固过程及其组织的实验研究表明，磁场使初生MnBi相在试样外侧呈环状偏聚，其自身生长为棒状，棒的长轴沿磁场方向呈定向规则排列，而试样心部基本无初生MnBi相。在Curie点以上开始进行较慢的凝固时，由片状聚合而成的棒状MnBi具有单晶特征。对以上现象的形成原因进行了分析。     

Morphology and distribution of Al3Fe phase in hypereutectic Al-Fe alloy solidified under magnetic field

In this study,the (low) DC and AC magnetic fields and the high magnetic field were applied separately during the solidification process of Al-2.89％Fe alloy.The influences of these magnetic fields on the morphology and distribution of Al3Fe phase in Al-2.89％Fe alloy were investigated.The microstructure and macrostructure of the samples were observed using an optical microscope.The results show that the majority of the primary Al3Fe phase particles in the hypereutectic Al-2.89％Fe alloy is gathered at the bottom of the sample under DC and AC magnetic fields or without magnetic field.The primary Al3Fe phase becomes coarse when the alloy solidifies under DC magnetic field,while it are refined and accumulated towards the center of the sample under the AC magnetic field.When the high magnetic field of 12 T is applied,the primary Al3Fe phase distributes throughout the sample homogeneously because the magnetic force acting on the primary Al3Fe phase balances with the gravity force; and the long axis of the Al3Fe phase aligns perpendicularly to the magnetic field direction.Also,the mechanism of the effect of magnetic fields is discussed.     

Variety of solidification structures in Al-2.89%Fe alloy solidified under high magnetic field

考察了冷却速率、磁场强度及高梯度磁场对Al-2.89%Fe(质量分数)过共晶合金中Al3Fe 相形貌及分布规律的影响. 结果表明, 在无磁场条件下, 初生Al3Fe相沉积在试样下部; 施加12 T强磁场后, 初生Al3Fe相所受磁力作用和重力作用相平衡, 在整个试样中均匀分布, 且沿着易磁化方向[121]发生定向排列, 其取向程度不受冷却速率的影响, 但随着磁场强度的增大而加强; 在高梯度磁场中, 初生Al3Fe相所受磁力作用大于重力作用而偏聚在试样的上部, 且多个针状初生Al3Fe相结合在一起, 形成近似星状聚合体. 此外, 对强磁场的作用机理进行了分析和探讨.     

The alignment,aggregation and magnetization behaviors in MnBi–Bi composites solidified under a high magnetic field

Bi–6 wt% Mn alloy is solidified under a high magnetic field and its microstructures and magnetic properties have been investigated. Microstructure results show that three kinds of morphology of MnBi phase appear in different temperature zones. In all these cases, the grains are orientated with the 〈001〉-crystal direction along the magnetic field direction and aggregated. Magnetic measurement shows a pronounced anisotropy in magnetization in directions normal and parallel to the fabrication field, resulting from this alignment. The effect of the magnetic field on the Mn_1.08Bi/MnBi (paramagnetic/ferromagnetic) phase transformation has been studied and the result shows that the phase transformation temperature T_C increases with the increase of the external magnetic field and under a field of 10 T, a typical increase of T_C is 20 °C during heating and 22 °C during cooling. The change in the morphology and in the magnetic properties of MnBi phase is discussed from the phase transformation and the crystal structure change in magnetic field.     

Influence of a high magnetic field on columnar dendrite growth during directional solidification

The influence of a high magnetic field on the growth of MnBi, α-Al and Al₃Ni dendrites in directionally solidified Bi–Mn, Al–Cu and Al–Ni alloys have been investigated. Results indicate that the magnetic field changes the dendrite growth significantly. Indeed, the magnetic field aligns the primary dendrite arm and the effect is different for different dendrites. For the MnBi dendrite, an axial high magnetic field enhanced the growth of the primary dendrite arm along the solidification direction; however, for the α-Al and Al₃Ni dendrites, the magnetic field caused the primary dendrite arm to deviate from the solidification direction. At a lower growth speed, a high magnetic field is capable of causing the occurrence of the columnar-to-equiaxed transition (CET). Moreover, it has also been observed that a high magnetic field affects the growth of the high-order (i.e., secondary and tertiary) dendrite arms of the α-Al dendrite at a higher growth speed; as a consequence, the field enhances the branching of the dendrite and the formation of the (1 1 1)-twin planes. The above results may be attributed to the alignment of the primary dendrite arm under a high magnetic field and the effect of a high magnetic field on crystalline anisotropy during directional solidification.     

强磁场对MnBi/Bi过共晶定向凝固组织的影响

进行了纵向强磁场下MnBi/Bi过共晶定向凝固实验研究.发现磁场使得MnBi相的形态发生了明显变化,对于Bi-0.82wt％ Mn过共晶MnBi/Bi定向凝固组织,在无磁场条件下,当生长速度V=5 μm/s,温度梯度GL =50℃/cm时,MnBi按照小平面生长,形成中空六方形和“V”字形结构;施加磁场条件下,随着磁场强度的提高,MnBi相呈小平面生长的趋势逐渐增强.并且发现磁场的存在使得MnBi相明显粗化,相间距增大.从晶体生长学和磁学的角度分析了强磁场对过共晶MnBi/Bi定向凝固组织的影响.     

Alignment behavior of MnBi phase in Bi-Mn alloy solidified in static magnetic field

1　INTRODUCTIONRegularstructuresinmaterialsarealwayspre paredtoimprovetheirproperties .Itiswellknownthatpowderedferromagneticmaterialscanbeorientedinastaticmagneticfield .Inrecentyearshighmag neticfieldwasappliedtoinducealignmentofparticlesinsomenonferromagneticmaterialswithanisotropicmagneticsusceptibilityinroomtemperature ,suchasparamagneticYBa2 Cu3O7ceramic[1] anddiamagneticgraphite[2 ] .Ifthematerialshavearesidualanisotropyintheirmagneticsusceptibilityatahightemperature ,theycanbetex…     

纵向强磁场对MnBi/Bi共晶定向凝固组织的影响

进行了纵向强磁场下MnBi／Bi共晶定向凝固实验研究，并从热力学的角度分析了强磁场对MnBi／Bi共晶定向凝固组织的影响，发现磁场有利于纤维状MnBi／Bi共晶定向凝固组织的形成，扩大了形成纤维状共晶组织的速度范围；在同一生长速度下随着磁场强度的增加，MnBi／Bi共晶纤维组织变得更加规则，MnBi纤维粗化，纤维间距增大；而且强磁场的施加，使MnBi的形态发生了变化，小平面生长特性增强。