CN110620004A - 永磁体和制造永磁体的方法 - Google Patents

永磁体和制造永磁体的方法 Download PDF

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CN110620004A
CN110620004A CN201910521074.2A CN201910521074A CN110620004A CN 110620004 A CN110620004 A CN 110620004A CN 201910521074 A CN201910521074 A CN 201910521074A CN 110620004 A CN110620004 A CN 110620004A
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alloy
grains
permanent magnet
magnetic field
magnet
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李万锋
梁峰
迈克尔·W·德格纳
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Abstract

本公开提供了“永磁体和制造永磁体的方法”。一种方法，包括：混合第一合金和第二合金，以形成混合物；在第一磁场内压制所述混合物，以形成磁体，使所述第一合金的各向异性粒子与所述磁体的磁矩对齐；以及在第二磁场内对所述磁体进行热处理，以由所述第二合金形成细长晶粒并使所述细长晶粒与所述磁矩对齐。

Description

永磁体和制造永磁体的方法
技术领域
本公开涉及永磁体和制造永磁体的方法。
背景技术
钕铁硼(Nd-Fe-B)合金磁体已用于永磁体电机(诸如马达、发电机或马达/发电机的组合)中。为了满足操作永磁体电机(尤其是电动车辆和混合动力车辆中所用的电机)的高温需求，需要永磁体的高温稳定性。然而，Nd-Fe-B磁体的矫顽力随着温度增加而减小。矫顽力是磁体承受外部磁场而不被去磁的能力。
发明内容
一种方法包括：将Mn-Bi合金与具有Nd-Fe-B各向异性粒子的Nd-Fe-B合金粉末混合，以形成混合物；在第一磁场内压制所述混合物，以形成磁体，使Nd-Fe-B各向异性粒子与磁体的磁矩对齐；以及在第二磁场内对所述磁体进行退火，以形成细长Mn-Bi晶粒并使所述细长Mn-Bi晶粒与所述磁矩对齐。
一种方法包括：混合第一合金和第二合金，以形成混合物；在第一磁场内压制所述混合物，以形成磁体，使所述第一合金的各向异性粒子与磁体的磁矩对齐；以及在第二磁场内对所述磁体进行热处理，以由所述第二合金形成细长晶粒并使所述细长晶粒与所述磁矩对齐。
一种永磁体包括在所述永磁体的磁矩的方向上对齐的Nd-Fe-B各向异性粒子和MnBi LTP晶粒，其中所述MnBi LTP晶粒具有至少为3:2的长宽比。
附图说明
图1示出永磁体；
图2A和图2B示出Mn-Bi在退火之前和之后的磁滞回线；
图3是示出由第一合金和第二合金制造永磁体的方法的流程图；
图4A和图4B示出在磁场内对Nd-Fe-B/Mn-Bi永磁体进行退火的效果；
图5A、图5B和图6是示出实验性磁场退火期间产生的Mn-Bi合金的晶粒结构的示例的灰度图像；并且
图7示出Nd-Fe-B/Mn-Bi永磁体相对于包含大约5重量％镝(Dy)的Nd-Fe-B永磁体的矫顽力变化。
具体实施方式
本文中描述了本公开的实施例。然而，应理解，所公开的实施例仅仅是示例，并且其他实施例可采用各种和替代形式。附图不一定按比例绘制；一些特征可能被放大或最小化以示出特定部件的细节。因此，本文所公开的特定结构细节和功能细节不应被解释为是限制性的，而是仅作为教导本领域技术人员以不同方式采用实施例的代表性基础。如本领域普通技术人员将理解，参考附图中的任一个来示出和描述的各种特征可与一个或多个其他附图中示出的特征相结合，以产生未明确示出或描述的实施例。所示出特征的组合提供用于典型应用的代表性实施例。然而，与本公开的教义一致的特征的各种组合和修改可以是特定应用或实现方式所希望的。
参考图1，示出永磁体10。永磁体10可表示本文所述的任何永磁体。永磁体10具有表示永磁体10的磁场强度和取向的磁矩12。更具体地，磁矩12表示从磁体的南极延伸到北极的磁偶极矩。磁矩12可根据对象在磁场中经历的扭矩来定义。更具体地，具有磁矩的对象上的扭矩等于磁矩乘以磁场的强度。图1所示的永磁体10的磁场由线14表示。
如先前所述，Nd-Fe-B永磁体的矫顽力随着温度增加而减小。为了使永磁体对高温应用稳定并且增加Nd-Fe-B永磁体在较高温度下的矫顽力，可将重稀土元素(诸如镝(Dy)和铽(Tb))添加到Nd-Fe-B永磁体中。然而，由于重稀土元素的稀缺和更高的成本，此类重稀土元素的添加增加了生产Nd-Fe-B永磁体的成本。可替代地，Nd-Fe-B永磁体在较高温度下的稳定性和矫顽力可因Nd-Fe-B合金与不掺入稀土元素的其他合金(诸如MnBi低温相(LTP)，其矫顽力随着温度增加而增大(即，MnBi LTP具有正温度系数))的混合而增加。通过调节这种混合Nd-Fe-B/Mn-Bi永磁体的重量比和处理参数，可将混合永磁体的温度系数调整为增大较高温度下的矫顽力。
可通过各种技术(例如，通过熔融过程)、之后进行退火过程(即，热处理过程)来制备Mn-Bi合金。然后将所制备Mn-Bi合金与Nd-Fe-B粉末混合、之后进行其他过程，以产生混合Nd-Fe-B/Mn-Bi永磁体。所制备Mn-Bi合金的性质取决于Mn-Bi合金的微结构，尤其是晶粒尺寸。退火过程增大MnBi LTP(其为促成Nd-Fe-B/Mn-Bi永磁体的磁性质的Mn-Bi合金的永磁相)的体积比。然而，退火过程还增大MnBi LTP的晶粒尺寸。由于增大了晶粒尺寸，因此所制备Mn-Bi磁体的矫顽力将显著减小。参见示出退火之前的Mn-Bi合金的磁滞回线的图2A、和示出退火之后的Mn-Bi合金(即，MnBi LTP合金)的磁滞回线的图2B。图2B中的矫顽力相对于图2A显著减小(即，在Mn-Bi合金已进行退火并且具有大晶粒尺寸的MnBi LTP的量已增加之后，矫顽力减小)。
退火Mn-Bi合金(即，MnBi LTP合金)的晶粒尺寸，在将MnBi LTP合金(呈粉末形式)与Nd-Fe-B合金粉末混合之前，可通过研磨(例如，球磨研磨、喷射研磨、低温研磨等)或其他粉碎技术来减小，从而增大MnBi LTP合金的矫顽力。然而，通过研磨或其他粉碎技术来减小退火MnBi LTP合金的晶粒尺寸也改变MnBi LTP合金晶粒的特性，使得MnBi LTP合金晶粒是多晶且各向同性的，由于各向同性晶粒的对称形状，它们不具有在磁场中对齐的能力。
参考图3，示出由第一合金和第二合金制造永磁体的方法100的流程图。方法100在框102处开始，其中将第一合金与第二合金混合以形成混合物。混合物内第一合金与第二合金的重量比可在10:1至1:10的范围内。更具体地，第一合金可以是Nd-Fe-B合金，而第二合金可以是Mn-Bi合金。Nd-Fe-B合金可以是任何类型的Nd-Fe-B合金，诸如Nd2Fe14B。Nd-Fe-B还可包含其他元素，诸如Pr、Dy、Tb、Cu、Al、Ga等。Mn-Bi合金可以是任何类型的Mn-Bi合金(诸如MnBi)，并且可与其他元素合金化。在框102处的混合步骤期间，第一合金(例如，Nd-Fe-B)可呈粉末形式，并且优选地为各向异性的氢化歧化脱附复合(HDDR)粉末。
在框102处混合第一合金和第二合金之前，可通过熔融或烧结并以大约1:1的优选摩尔比混合不同的元素(例如，Mn和Bi)来制备第二合金(Mn-Bi合金)。熔融过程可以是任何类型的熔融过程，诸如电弧熔融过程。在熔融或烧结过程之后，可将第二合金熔纺成带或者直接研磨成粉末。也可对第二合金进行退火，之后纺成带或直接研磨成粉末，或者在退火之后研磨成粉末。如果第二合金被熔纺并且是Mn-Bi合金，通过熔纺过程产生的Mn-Bi合金带将包含具有很小晶粒尺寸的极少量的MnBi LTP合金。在熔纺过程之后，可接着将第二合金带(例如，Mn-Bi合金带)研磨(例如，球磨研磨、喷射研磨、低温研磨等)成粉末。然后，在框102处将第二合金带或第二合金粉末(其可以是由熔融或烧结过程之后直接研磨第二合金形成的粉末、由退火过程之后研磨熔融的或烧结的第二合金形成的粉末、或由熔纺过程之后研磨第二合金形成的粉末)与第一合金粉末混合。
一旦框102处将第一合金和第二合金混合，方法100就前进到框104，其中将混合物在压模或模具内并且在第一磁场内压制，以形成永磁体。更具体地，在形成永磁体的压制过程期间，第一合金和第二合金的各向异性粒子和/或晶粒与第一磁场对齐并最终与成型永磁体的磁矩对齐。可将压制操作的压模或模具调整到所需温度。更具体地，压制操作可在足够热以支持永磁体的成型过程而同时低于第一合金的居里温度的温度(即，处于或高于材料失去其永磁特性的温度)下执行，以确保第一合金的各向异性粒子和/或晶粒在第一磁场内对齐。在压制操作期间增加温度可导致成型永磁体的密度增大。可替代地，混合物可首先在第一磁场内在室温下压制，之后进行在增加的温度下且在磁场之外进行的第二压制操作，以支持成型过程。
在框104处，如果第一合金是Nd-Fe-B合金，则压制操作可在低于310℃的温度下执行，310℃是Nd-Fe-B合金的居里温度。应注意，本文所列材料的所有温度相关特性(例如，居里温度、熔点等)指代一个大气压下的温度特性，除非本文另有陈述。然而，更具体地，如果第一合金是Nd-Fe-B合金，则压制过程在300℃或更低的温度下执行。还应注意，如果第二合金是尚未在框104处进行退火的Mn-Bi合金，则Mn-Bi带或粉末将在结构上是多晶的(即，是各向同性的)并且包含极少量的磁性MnBi LTP。因此，Mn-Bi合金的粒子和/或晶粒将不可能在第一磁场中对齐并且建立永磁体品质。然而，如果第二合金是已进行退火和研磨从而实现单晶结构或各向异性MnBi LTP粒子的Mn-Bi合金，则第二合金也可在压制操作期间在第一磁场内对齐。
一旦对第一合金和第二合金进行压制以形成永磁体，则方法100移动到框106，其中成型永磁体在第二磁场内进行退火或热处理，以由第二合金形成细长晶粒(或更具体地，以由第二合金的表现出永磁体的性质的相(例如，MnBi LTP)形成细长晶粒)。在退火过程期间，第二合金的细长晶粒在第二磁场的方向内变得细长或者“生长”。因此，在第二磁场内的退火过程期间，第二合金的细长晶粒与第二磁场对齐并最终与成型永磁体的磁矩对齐。应理解，磁场内对合金进行退火或热处理的过程也可称为磁场退火。更具体地，可在第二磁场内在真空炉或保护气氛中对成型永磁体进行退火。第二磁场将在第一磁场施加到框104处的混合物的相同方向上施加到成型永磁体，使得第二合金的细长晶粒与成型永磁体的磁矩和第一合金的在框104处对齐的各向异性粒子和/或晶粒对齐。
成型永磁体可在高于第一合金的居里温度的温度下进行退火，以便不干扰框104处发生的第一合金的各向异性粒子和/或晶粒的对齐。成型永磁体也可在低于第二合金的居里温度的温度下进行退火，使得退火过程期间由第二合金形成的细长晶粒与第二磁场对齐。成型永磁体可进行退火达在5分钟至4小时的范围内的持续时间。
在框106处，如果第一合金是Nd-Fe-B合金而第二合金是Mn-Bi合金，则退火过程在等于或高于Nd-Fe-B合金的居里温度但低于Mn-Bi合金的居里温度的温度下执行。Mn-Bi合金的居里温度是大约447℃。优选地，退火过程在270℃至400℃的范围内的温度下执行。同样地，在框106处，如果第二合金是Mn-Bi合金，则由Mn-Bi合金形成的细长晶粒包括MnBiLTP材料，这是需要的，因为MnBi LTP是Mn-Bi合金的表现出永磁体的性质的相。
参考图4A和图4B，示出在第二磁场内对成型永磁体107进行退火的效果。图4A示出在第二合金(其可以是Mn-Bi合金)的矩阵110中的第一合金(其可以是Nd-Fe-B合金)的各向异性粒子和/或晶粒108。更具体地，图4A中的第二合金由随机取向的磁晶粒(未示出)构成，因为尚未发生退火过程(即，图4A是其中压制混合物的框104之后的、但在框106处的退火过程之前的永磁体的表示)。图4B示出第二磁场112相对于永磁体的磁矩114的施加以及磁场退火过程对第二合金的效果。在磁场退火过程期间，细长晶粒116(其可包括MnBi LTP)由第二合金形成。细长晶粒是各向异性的。更具体地，在框106处的磁场退火期间，细长晶粒116伸长或“生长”(即，长度增加)并且在第二磁场112的方向上对齐。在磁场退火过程期间，细长晶粒116也可与第一合金的各向异性粒子和/或晶粒以及成型永磁体107的磁矩114对齐。退火过程的持续时间以及第二磁场112到成型磁体107的施加可进行增加，以增大细长晶粒116在第二磁场112的方向上的长度以及最终地增大成型永磁体107的磁矩114，或者可进行减少，以减小细长晶粒116在第二磁场112的方向上的长度以及最终地减小成型永磁体107的磁矩114。一旦在框106处完成退火过程，细长晶粒116的长度L与细长晶粒的宽度W的比可在3:2至100:1的范围内。
如果第一合金是Nd-Fe-B合金而第二合金是Mn-Bi合金，则细长晶粒116将包括MnBi LTP。在框106处的磁场退火期间，Mn-Bi合金的铋将熔融(铋的熔点大约271.4℃)，从而允许MnBi LTP晶粒在第二磁场中对齐。由于磁自由能的贡献，晶粒的生长是各向异性的。细长晶粒116可降低磁静能而增加永磁体107的稳定性。MnBi LTP晶粒将沿着它们的易磁化轴凝聚，并且形成与成型永磁体107的磁矩114对齐的细长晶粒116。另外，将退火温度设定在Nd-Fe-B合金的居里温度处或以上防止来自Nd-Fe-B粒子的杂散场影响MnBi LTP晶粒的对齐过程。细长晶粒形状增大MnBi LTP晶粒的矫顽力并改变晶粒周围的磁场分布，这增大成型磁体107的总体矫顽力。当第一合金是Nd-Fe-B合金而第二合金是Mn-Bi合金时，成型磁体107可称为Nd-Fe-B/Mn-Bi混合磁体。
参考图5A、图5B和图6，示出实验性磁场退火期间所产生的Mn-Bi合金的晶粒结构的示例。图5A和图5B示出MnBi LTP合金的沿着易磁化方向的小晶粒和原子结构的放大的显微图像。图5A和图5B中的较小晶粒是六边形形状，这与MnBi LTP相的晶体学对称性一致并且指示沿着磁场方向118(即，在进行退火时施加到Mn-Bi合金的磁场的方向，其离开图5A、图5B和图6的页面)的各向异性晶粒生长。图6示出在对齐方向上截取的MnBi LTP晶粒的花状磁畴的放大的显微图像。花状畴是永磁体表面的垂直于易磁化轴的典型的畴结构。图5A、图5B和图6的观察结果确认，磁场退火产生MnBi LTP晶粒的对齐。(通过设定磁场退火的持续时间实现的)选择性晶粒生长允许细长晶粒沿着磁场方向118形成，这由于此类细长晶粒的形状各向异性而增大矫顽力。
图7示出Nd-Fe-B/Mn-Bi永磁体相对于钕铁硼/镝(Nd,Dy)-Fe-B永磁体的矫顽力变化。图7包括示出各种磁体的矫顽力对温度的图120。(Nd,Dy)-Fe-B永磁体的矫顽力由线122示出，经磁场退火的Nd-Fe-B/Mn-Bi永磁体的矫顽力由线124示出，并且在磁场之外进行退火的Nd-Fe-B/Mn-Bi永磁体的矫顽力由线126示出。
经磁场退火的Nd-Fe-B/Mn-Bi永磁体和在磁场之外进行退火的Nd-Fe-B/Mn-Bi永磁体两者的矫顽力温度系数(矫顽力随着温度增加而改变的速率)由于退火期间MnBi LTP的体积比增大而在量值上都小于包含大约5％Dy的常规烧结(Nd,Dy)-Fe-B磁体的矫顽力系数。经磁场退火的Nd-Fe-B/Mn-Bi永磁体和在磁场之外进行退火的Nd-Fe-B/Mn-Bi永磁体两者的矫顽力相比烧结(Nd,Dy)-Fe-B磁体随着温度增加都降低得更缓慢。与在磁场之外进行退火的Nd-Fe-B/Mn-Bi永磁体相比，经磁场退火的Nd-Fe-B/Mn-Bi永磁体具有更高的矫顽力。虽然经磁场退火的Nd-Fe-B/Mn-Bi永磁体的矫顽力在室温(大约25℃)下低于烧结(Nd,Dy)-Fe-B磁体的矫顽力，但由于更高的热稳定性，经磁场退火的Nd-Fe-B/Mn-Bi永磁体的矫顽力在180℃下与烧结(Nd,Dy)-Fe-B磁体的矫顽力大致相同。这证明磁场退火能够改进Nd-Fe-B/Mn-Bi混合永磁体的矫顽力和热稳定性，从而在不添加重稀土元素的情况下允许永磁体在更高温度下起作用。
说明书中所用的词语是描述性词语，而不是限制性词语，并且应理解，可在不脱离本公开的精神和范围的情况下作出各种改变。如先前所述，各种实施例的特征可进行组合以形成可能未明确描述或说明的其他实施例。虽然可能关于一个或多个期望特性已将各种实施例描述为提供优点或优于其他实施例或现有技术实现方式，但本领域普通技术人员应认识到，可折衷一个或多个特征或特性以实现取决于特定应用和实现方式的期望总体系统属性。如此一来，关于一个或多个特征被描述相较于其他实施例或现有技术实现方式不期望的实施例并非在本公开的范围之外，并且对于特定应用来说可能是期望的。
根据本发明，一种方法包括：将Mn-Bi合金与具有Nd-Fe-B各向异性粒子的Nd-Fe-B合金粉末混合，以形成混合物；在第一磁场内压制所述混合物，以形成磁体，使Nd-Fe-B各向异性粒子与所述磁体的磁矩对齐；以及在第二磁场内对所述磁体进行退火，以形成细长Mn-Bi晶粒并使所述细长Mn-Bi晶粒与所述磁矩对齐。
根据一个实施例，所述压制在低于Nd-Fe-B的居里温度的温度下执行。
根据一个实施例，所述压制在300℃或更低的温度下执行。
根据一个实施例，所述退火在高于Nd-Fe-B的居里温度但低于Mn-Bi的居里温度的温度下执行。
根据一个实施例，所述退火在270℃至400℃的范围内的温度下执行。
根据一个实施例，执行所述退火达5分钟至4小时的范围内的持续时间。
根据一个实施例，所述细长Mn-Bi晶粒由MnBi低温相(LTP)组成。
根据一个实施例，所述退火增加Mn-Bi晶粒在磁矩方向上的长度。
根据一个实施例，在所述退火之后，所述Mn-Bi晶粒的所述长度与所述Mn-Bi晶粒的宽度的比在3:2至100:1的范围内。
根据本发明，一种方法包括：混合第一合金和第二合金，以形成混合物；在第一磁场内压制所述混合物，以形成磁体，使所述第一合金的各向异性粒子与所述磁体的磁矩对齐；以及在第二磁场内对所述磁体进行热处理，以由所述第二合金形成细长晶粒并使所述细长晶粒与所述磁矩对齐。
根据一个实施例，所述压制在低于所述第一合金的居里温度的温度下执行。
根据一个实施例，所述热处理在高于所述第一合金的居里温度的温度下执行。
根据一个实施例，所述热处理在低于所述第二合金的居里温度的温度下执行。
根据一个实施例，所述第一合金是Nd-Fe-B合金而所述第二合金是MnBi合金。
根据一个实施例，所述细长Mn-Bi晶粒由MnBi LTP组成。
根据一个实施例，所述热处理增加所述细长晶粒在所述磁矩方向上的长度。
根据一个实施例，在所述热处理之后，所述细长晶粒的所述长度与所述细长晶粒的宽度的比在3:2至100:1的范围内。
根据本发明，提供一种永磁体，其具有在所述永磁体的磁矩的方向上对齐的Nd-Fe-B各向异性粒子和MnBi LTP晶粒，其中所述MnBi LTP晶粒具有至少为3:2的长宽比。
根据一个实施例，长宽比在3:2至100:1的范围内。

Claims (15)

1.一种方法，其包括：
将Mn-Bi合金与具有Nd-Fe-B各向异性粒子的Nd-Fe-B合金粉末混合，以形成混合物；
在第一磁场内压制所述混合物，以形成磁体，使Nd-Fe-B各向异性粒子与所述磁体的磁矩对齐；以及
在第二磁场内对所述磁体进行退火，以形成细长Mn-Bi晶粒并使所述细长Mn-Bi晶粒与所述磁矩对齐。
2.如权利要求1所述的方法，其中所述压制在低于Nd-Fe-B的居里温度的温度下执行。
3.如权利要求2所述的方法，其中所述压制在300℃或更低的温度下执行。
4.如权利要求1所述的方法，其中所述退火在高于Nd-Fe-B的所述居里温度但低于Mn-Bi的居里温度的温度下执行。
5.如权利要求1所述的方法，其中所述退火在270℃至400℃的范围内的温度下执行。
6.如权利要求1所述的方法，其中执行所述退火达5分钟至4小时的范围内的持续时间。
7.如权利要求1所述的方法，其中所述细长Mn-Bi晶粒由MnBi低温相(LTP)组成。
8.如权利要求1所述的方法，其中所述退火增加所述Mn-Bi晶粒在所述磁矩方向上的长度。
9.如权利要求8所述的方法，其中在所述退火之后，所述Mn-Bi晶粒的所述长度与所述Mn-Bi晶粒的宽度的比在3:2至100:1的范围内。
10.一种方法，其包括：
将第一合金和第二合金混合，以形成混合物；
在第一磁场内压制所述混合物，以形成磁体，使所述第一合金的各向异性粒子与所述磁体的磁矩对齐；以及
在第二磁场内对所述磁体进行热处理，以由所述第二合金形成细长晶粒并使所述细长晶粒与所述磁矩对齐。
11.如权利要求10所述的方法，其中所述压制在低于所述第一合金的居里温度的温度下执行。
12.如权利要求10所述的方法，其中所述热处理在高于所述第一合金的所述居里温度的温度下执行。
13.如权利要求12所述的方法，其中所述热处理在低于所述第二合金的居里温度的温度下执行。
14.一种永磁体，其包括：
在所述永磁体的磁矩的方向上对齐的Nd-Fe-B各向异性粒子和MnBiLTP晶粒，其中所述MnBiLTP晶粒具有至少为3:2的长宽比。
15.如权利要求14所述的磁体，长宽比在3:2至100:1的范围内。
CN201910521074.2A 2018-06-19 2019-06-17 永磁体和制造永磁体的方法 Pending CN110620004A (zh)

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