JP2004281492A

JP2004281492A - Permanent magnet material

Info

Publication number: JP2004281492A
Application number: JP2003067614A
Authority: JP
Inventors: Hajime Nakamura; 中村　　元; Takehisa Minowa; 武久美濃輪
Original assignee: Shin Etsu Chemical Co Ltd
Current assignee: Shin Etsu Chemical Co Ltd
Priority date: 2003-03-13
Filing date: 2003-03-13
Publication date: 2004-10-07

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small or thin permanent magnet having S/V=6 mm<SP>-1</SP>or above representing good magnetic characteristics without performing a heat treatment for recovering the characteristics after grinding. <P>SOLUTION: The permanent magnet material produces a sintered magnet having an R-Fe-B based composition (R is one kind or more than one kinds being selected from rare earth elements including Y) having mean crystal grain size in main phase of 5 μm or less determined from surface integral rate, ground to have a specific surface area of 6 mm<SP>-1</SP>or above, and having a volume integral rate (%) in the surface deterioration layer not higher than 0.5×S/V (S/V is specific surface area and the unit is mm<SP>-1</SP>). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、焼結磁石体表面の研削加工等に伴う磁気特性の劣化を低減したＲ−Ｆｅ−Ｂ系永久磁石材料に係り、特に磁石体の比表面積（Ｓ（表面積）／Ｖ（体積））が６ｍｍ^−１以上の小型あるいは薄型用高性能永久磁石材料に関する。
【０００２】
【従来の技術】
Ｎｄ−Ｆｅ−Ｂ系永久磁石は、磁気特性が優れているために、ますますその用途が広がってきている。近年、磁石を応用したコンピュータ関連機器やＣＤプレーヤー、ＤＶＤプレーヤー、携帯電話をはじめとする電子機器の軽薄短小化、高性能化、省エネルギー化に伴い、Ｎｄ−Ｆｅ−Ｂ系磁石、中でも特に高性能なＮｄ−Ｆｅ−Ｂ系焼結磁石の小型化、薄型化が要求されており、磁石体の比表面積Ｓ／Ｖが６ｍｍ^−１を超えるような小型あるいは薄型の磁石に対する需要も増大しつつある。
【０００３】
小型あるいは薄型のＮｄ−Ｆｅ−Ｂ系焼結磁石を実用形状に加工し、磁気回路に実装するためには、成形焼結したブロック状の焼結磁石を研削加工する必要があり、この加工には外周刃切断機、内周刃切断機、表面研削機、センタレス研磨機、ラッピングマシンなどが使用される。
【０００４】
しかしながら、上記装置にてＮｄ−Ｆｅ−Ｂ系焼結磁石を研削加工すると、磁石体が小さくなるほど磁気特性が劣化することが知られている。この劣化については、本系磁石の高保磁力の発現に必要な粒界構造が磁石表面では加工により欠損しているため、あるいは加工歪に起因しているためと考えられている。磁気特性の劣化を防止するために、例えば、磁石の焼結過程において結晶粒の成長を防ぐことで、比表面積Ｓ／Ｖが２．６ｍｍ^−１となるまで研削加工しても磁気特性が劣化しない磁石材料が提案されている（特許文献１：特許第２５１４１５５号公報参照）。しかし、Ｓ／Ｖが６ｍｍ^−１を超える場合、磁気特性の劣化が顕著となる問題があった。
【０００５】
そのような極微小磁石体における特性劣化を防止する方法として、例えばスパッタリング等により被研削面に希土類を主成分とする薄膜層を形成し、更に熱処理を施して劣化した被研削面を改質することで、磁石体の特性劣化を防止する方法が提案されている（特許文献２：特公平５−６０２４１号公報、特許文献３：特公平６−６３０８６号公報参照）。しかし、上記方法では、量産に対して極端に生産性が低いために適用は困難であり、磁気特性の劣化が少なく、かつＳ／Ｖが６ｍｍ^−１を超える極微小磁石体の製造は実質不可能と考えられていた。
【０００６】
【特許文献１】
特許第２５１４１５５号公報
【特許文献２】
特公平５−６０２４１号公報
【特許文献３】
特公平６−６３０８６号公報
【０００７】
【発明が解決しようとする課題】
本発明は、上述した従来の問題点に鑑み、研削加工による磁気特性の劣化を低減したＲ−Ｆｅ−Ｂ系焼結磁石材料を提供することを目的とするものである。
【０００８】
【課題を解決するための手段及び発明の実施の形態】
本発明者らは、Ｒ−Ｆｅ−Ｂ系焼結磁石の表面近傍での保磁力について種々検討した結果、加工速度に留意して加工歪の影響を極力抑えた場合、被研削加工面における劣化層の平均厚さｔ（単位はμｍ）は磁石主相の面積率から求められる平均結晶粒径Ｄ（単位はμｍ）と同程度であることを見出した。
そして、この劣化層の平均厚さｔと平均結晶粒径Ｄとの関係から、主相の結晶粒径を可能な限り小さくすることで、被研削加工面における劣化層の平均厚さを小さくできる、即ち小型あるいは薄型の永久磁石の特性劣化を低減できることを見出した。そして、これを達成するためには焼結磁石の作製工程のうち、粉砕工程において磁石原料粒子を十分に細かくし、焼結工程では主相の結晶粒の粗大化を抑制する必要があり、従来のプロセスでは容易には達成されないが、本発明者らは焼結磁石の作製工程での雰囲気、処理温度、合金組成等に鋭意検討を行い、平均結晶粒径が５μｍ以下のＲ−Ｆｅ−Ｂ系焼結磁石を作製することで、該焼結磁石体の表面劣化層の体積分率（％）が０．５×Ｓ／Ｖ（Ｓ／Ｖは比表面積で単位はｍｍ^−１）以下で、該焼結磁石体の最大エネルギー積が、該焼結磁石のバルク状態、即ち比表面積がおおむね０．６ｍｍ^−１未満である磁石体における最大エネルギー積の８５％以上となり、磁気特性の劣化を著しく低減させ得ることを見出し、この発明を完成したものである。
【０００９】
即ち、本発明に係る永久磁石材料は、Ｒ−Ｆｅ−Ｂ系組成（ＲはＹを含む希土類元素から選ばれる１種又は２種以上）からなる焼結磁石で、面積分率から求められる主相の平均結晶粒径が５μｍ以下であり、比表面積が６ｍｍ^−１以上に研削加工され、該焼結磁石体の表面劣化層の体積分率（％）が０．５×Ｓ／Ｖ（Ｓ／Ｖは比表面積で、単位はｍｍ^−１）以下であることを特徴とする。
【００１０】
更に、前記焼結磁石体の最大エネルギー積が、該焼結磁石のバルク状態、即ち、上記研削前の比表面積が０．６ｍｍ^−１未満である磁石体における最大エネルギー積の８５％以上であることを特徴とする。
【００１１】
上記態様に加えて、研削加工した後にアルカリ、酸あるいは有機溶剤のいずれか１種以上により洗浄され、該焼結磁石体の表面劣化層の体積分率（％）が０．５×Ｓ／Ｖ（Ｓ／Ｖは比表面積で単位はｍｍ^−１）以下であること、該焼結磁石体の最大エネルギー積が、該焼結磁石のバルク状態における最大エネルギー積の８５％以上であることを特徴とする。
更には、上記永久磁石体に関して、メッキあるいは塗装による表面処理を施したことを特徴とする。
【００１２】
以下、本発明を更に詳細に説明する。
本発明は、Ｒ−Ｆｅ−Ｂ系焼結永久磁石体表面の研削加工等に伴う磁気特性の劣化を低減した、磁石体の比表面積Ｓ／Ｖが６ｍｍ^−１以上の小型あるいは薄型用高性能永久磁石材料に関するものである。
ここで、Ｒ−Ｆｅ−Ｂ系焼結永久磁石体は、常法に従い、母合金を粗粉砕、微粉砕、成形、焼結することにより得ることができる。
この場合、母合金は、Ｒ、Ｆｅ、Ｂを含有する。ＲはＹを含む希土類元素から選ばれる１種又は２種以上で、具体的にはＹ、Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｔｂ、Ｄｙ、Ｈｏ、Ｅｒ、Ｙｂ及びＬｕが挙げられ、好ましくはＮｄ、Ｐｒ、Ｄｙを主体とする。これらＹを含む希土類元素は合金全体の１０〜２０原子％、特に１２〜１５原子％であることが好ましく、更に好ましくはＲ中にＮｄとＰｒあるいはそのいずれか１種を１０原子％以上、特に５０原子％以上含有することが好適である。Ｂは３〜１５原子％、特に４〜８原子％含有することが好ましい。その他、Ａｌ、Ｃｕ、Ｚｎ、Ｉｎ、Ｓｉ、Ｐ、Ｓ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｎｉ、Ｇａ、Ｇｅ、Ｚｒ、Ｎｂ、Ｍｏ、Ｐｄ、Ａｇ、Ｃｄ、Ｓｎ、Ｓｂ、Ｈｆ、Ｔａ、Ｗの中から選ばれる１種又は２種以上を０〜１１原子％、特に０．１〜５原子％含有してもよい。残部はＦｅ又はＣ、Ｎ、Ｏ等の不可避的な不純物であるが、Ｆｅは５０原子％以上、特に６５原子％以上含有することが好ましい。また、Ｆｅの一部、例えばＦｅの０〜４０原子％、特に０〜１５原子％をＣｏで置換しても差支えない。
【００１３】
母合金は原料金属あるいは合金を、真空あるいは不活性ガス、好ましくはＡｒ雰囲気中で溶解したのち、平型やブックモールドに鋳込む、あるいはストリップキャストにより鋳造することで得られる。なお、本系合金の主相であるＲ_２Ｆｅ_１４Ｂ化合物組成に近い合金と焼結温度で液相助剤となるＲリッチな合金とを別々に作製し、粗粉砕後に秤量混合する、いわゆる２合金法も本発明には適用可能である。但し、主相組成に近い合金に対して、鋳造時の冷却速度や合金組成に依存してα−Ｆｅが残存しやすく、Ｒ_２Ｆｅ_１４Ｂ化合物相の量を増やす目的で必要に応じて均質化処理を施す。その条件は真空あるいはＡｒ雰囲気中で７００〜１，２００℃で１時間以上熱処理する。液相助剤となるＲリッチな合金については上記鋳造法のほかに、いわゆる液体急冷法も適用できる。
【００１４】
上記合金は、通常０．０５〜３ｍｍ、特に０．０５〜１．５ｍｍに粗粉砕される。粗粉砕工程には、ブラウンミルあるいは水素粉砕が用いられ、ストリップキャストにより作製された合金の場合は水素粉砕が好ましい。
このようにして得られた粗粉は、例えば高圧窒素を用いたジェットミルにより微粉砕されるが、このときにレーザー回折法を用いて測定された微粉末の重量中位粒径が５μｍ以下、好ましくは０．２〜５μｍ、更に好ましくは０．５〜４．５μｍになるように粉砕する。但し、重量中位粒径５μｍ以下の粉末は非常に活性であり、大気に触れると発熱を伴って酸化が急激に進行する。従って、微粉砕工程から磁界中圧縮成形を経て焼結工程までの間、微粉末が大気と接触しないようにする必要がある。そのために、微粉末の回収容器内に鉱物油のような微粉末の酸化を阻止可能な溶媒を満たして微粉末をスラリーとし、湿式成形して焼結炉に投入する、あるいは装置全体か金型付近を不活性ガス雰囲気とした圧縮成形機で乾式成形して焼結炉に投入する等の方法が採られる。後者の場合、微粉末及び成形体を次工程に移動する際も容器を不活性ガス雰囲気にする、あるいは装置も含めて微粉末及び成形体の移動するすべての経路を不活性ガス雰囲気にする。上述した酸化を防止する手段を用いても、微粉末の酸化を完全に阻止することは困難であり、微粉末の重量中位粒径が０．２μｍ未満では、不可避的な酸化の影響が大きくなり、良好な磁気特性が得られなくなる場合がある。
【００１５】
上記微粉末は、磁界中に圧縮成形機で成形され、焼結炉に投入される。焼結は真空あるいはＡｒ、Ｈｅ等の不活性ガス雰囲気中、通常９００〜１，２５０℃、特に１，０００〜１，１００℃で行われる。
更に、焼結後、焼結温度未満の低温、好ましくは２００〜９００℃、より好ましくは３５０〜７５０℃の温度で真空あるいはＡｒ、Ｈｅ等の不活性ガス雰囲気中、１０分〜５時間、特に３０分〜２時間程度の熱処理を行うことが好ましく、この熱処理により高い保磁力及び良好な角形性を示す磁石材料を得ることができる。
【００１６】
なお、ここで得られた焼結磁石は、正方晶Ｒ_２Ｆｅ_１４Ｂ化合物を主相として６０〜９９体積％、特に好ましくは８０〜９８体積％含有し、残部は０．５〜２０体積％のＲに富む相、０〜１０体積％のＢに富む相及び不可避的不純物により生成した炭化物、窒化物、酸化物、水酸化物のうち少なくとも１種あるいはこれらの混合物又は複合物からなる。
【００１７】
得られた焼結ブロックは実用形状に研削されるが、加工歪の影響をできるだけ小さくするために、生産性を落とさない範囲で加工速度は小さくすることが好ましい。この場合、研削方法としては、常法に従って行うことができるが、加工速度として具体的には、０．１〜２０ｍｍ／ｍｉｎ、特に０．５〜１０ｍｍ／ｍｉｎであることが好ましい。
【００１８】
この場合、研削量としては、焼結ブロックの比表面積Ｓ／Ｖ（表面積ｍｍ^２／体積ｍｍ^３）が６ｍｍ^−１以上、好ましくは１０ｍｍ^−１以上である。その上限は適宜選定され、特に制限されるものではないが、通常４０ｍｍ^−１以下、特に３０ｍｍ^−１以下である。
【００１９】
なお、上述した研削加工時において、研削加工機の冷却液に水系のものを用いる、あるいは加工時に研削面が高温に曝される場合、被研削面に酸化膜が生じやすい。これを除去するために、アルカリ、酸及び有機溶剤のいずれか１種以上を用いて洗浄する。メッキあるいは塗装による表面処理が必要なとき、この処理はその前処理となる。
【００２０】
なお、アルカリとしては、ピロリン酸カリウム、ピロリン酸ナトリウム、クエン酸カリウム、クエン酸ナトリウム、酢酸カリウム、酢酸ナトリウム、シュウ酸カリウム、シュウ酸ナトリウム等を、酸としては、塩酸、硝酸、硫酸、酢酸、クエン酸、酒石酸等を、有機溶剤としては、アセトン、メタノール、エタノール、イソプロピルアルコール等を使用することができる。この場合、上記アルカリや酸は、磁石体を侵食しない、適宜濃度の水溶液として使用することができる。
【００２１】
本発明の焼結磁石においては、面積分率から求められる主相の平均結晶粒径Ｄが５μｍ以下、好ましくは０．５〜５μｍ、更に好ましくは１〜４．５μｍである。上述したように、被研削加工面における表面劣化層の平均厚さｔ（μｍ）は、磁石主相の面積率から求められる平均結晶粒径（μｍ）と同程度であり、焼結磁石体の表面劣化層の体積分率（％）が０．５×Ｓ／Ｖ（Ｓ／Ｖは比表面積で、単位はｍｍ^−１）以下、好ましくは０．４×Ｓ／Ｖ以下、更に好ましくは０．３×Ｓ／Ｖ以下である。なお、下限は０であり得るが、通常は０．０１×Ｓ／Ｖ以上、特に０．０３×Ｓ／Ｖ以上である。
【００２２】
ここで、上記劣化層の平均厚さｔは、以下の手順で算出される。
まず、研削加工した磁石体の減磁曲線（Ｊ−Ｈカーブ）を測定する。減磁曲線の傾きを印加磁界に対してプロットしたもの（ｄＪ／ｄＨ−Ｈカーブ）を作成すると、２つのピークが認められる。それらのうち絶対値で大きな印加磁界でのピークにおけるピーク位置は磁石体内部の特性劣化していない結晶粒の磁化反転に相当する。もう１つのピークにおけるピーク位置（Ｈ_ｄｍｇと称する）は磁石体の表面劣化層の保磁力に相当し、その位置では劣化層の磁気分極はゼロである。従って、Ｊ−ＨカーブにおけるＨ_ｄｍｇに対応する磁気分極の値（Ｊ_ｂｌｋと称する）を磁石内部の劣化していない粒子の磁気分極と定義できる。磁石体の飽和磁気分極（Ｊ_ｓ）とＪ_ｂｌｋを用いて、研削加工により劣化した領域の体積分率（Ｖ_ｄｍｇと称する、単位はパーセント）は下記式により算出される。
Ｖ_ｄｍｇ＝〔（Ｊ_ｓ−Ｊ_ｂｌｋ）／Ｊ_ｓ〕×１００
【００２３】
一方、例えば、磁石体が直方体であるとし、そのサイズがＡ×Ｂ×Ｃ（単位はμｍ）であるとすると、劣化層の平均厚さｔを用いてＶ_ｄｍｇは下記式のように表現でき、下記式よりｔが算出される。
Ｖ_ｄｍｇ＝［１−（Ａ−２ｔ）×（Ｂ−２ｔ）×（Ｃ−２ｔ）／ＡＢＣ］×１００
【００２４】
磁石体が任意の形状をとる場合でも、その形状に合わせて上記式と同様な式を容易に記述できる。
【００２５】
更に、磁石主相の平均結晶粒径Ｄは以下のようにして求める。まず、磁石体を鏡面研磨した後、腐食液にて粒界にコントラストをつける。それらの任意の視野について撮影した光学顕微鏡像あるいは走査電子顕微鏡像より個々の粒子の面積を測定し、それと等価な円の直径を個々の粒子の結晶粒径とする。続いて粒度分布を示すヒストグラムを作成する際、粒径の範囲に対して範囲内に存在する結晶粒の個数ではなく、結晶粒が占める面積の割合をプロットする。一例を図２に示す。このヒストグラムより求められる面積中位粒径を平均結晶粒径と定義する。
【００２６】
本発明における表面劣化層の体積分率（％）は、上述した通り、０．５×Ｓ／Ｖ以下であるが、この限定理由は以下の通りである。
表面劣化層の平均厚さが一定ならば、比表面積の増大とともに劣化層の占める体積分率は増大する。現在の技術で研削可能な寸法限界は、比表面積でＳ／Ｖ＝３０ｍｍ^−１程度である。Ｓ／Ｖ＝３０ｍｍ^−１の磁石体において劣化層の体積分率が０．５×Ｓ／Ｖを超える、即ち１５％以上となると得られる最大エネルギーが４ＭＧＯｅ以下に低下してしまうので、Ｎｄ−Ｆｅ−Ｂ系焼結磁石に代表されるＲ−Ｆｅ−Ｂ系焼結磁石の高い磁気特性を十分に利用するためには、表面劣化層の体積分率を０．５×Ｓ／Ｖ以下とする。これを達成するためには、前述の通り、焼結磁石の主相の平均結晶粒径を５μｍ以下にすることが必要である。
【００２７】
また、加工に伴う減磁曲線の角形性の低下は、最大エネルギー積の低下に繋がるが、表面劣化層の体積分率を０．５×Ｓ／Ｖ以下とした場合、該焼結磁石体の最大エネルギー積を、該焼結磁石のバルク状態、即ち比表面積が０．６ｍｍ^−１未満である上記研削前の磁石体における最大エネルギー積の８５％以上に高めることが可能となる。
【００２８】
従って、本発明によれば、特性劣化の少ない小型あるいは薄型永久磁石を提供することができる。この場合、この永久磁石の具体的な大きさの一例として、１ｍｍ×１ｍｍ×１ｍｍ（Ｓ／Ｖ＝６ｍｍ^−１）、０．８ｍｍ×０．８ｍｍ×０．２５ｍｍ（Ｓ／Ｖ＝１３ｍｍ^−１）、０．８ｍｍ×０．８ｍｍ×０．１３ｍｍ（Ｓ／Ｖ＝２０ｍｍ^−１）、０．８ｍｍ×０．３ｍｍ×０．１３ｍｍ（Ｓ／Ｖ＝２５ｍｍ^−１）等が挙げられる。
【００２９】
なお、本発明においては、上記磁石にメッキあるいは塗装による表面処理を施すことができる。この場合、メッキとしては、Ｎｉ、Ｃｕ、Ｓｎ、Ｚｎ、Ａｕ、Ａｇの単体及び合金を単層あるいは積層としてメッキを施すことができ、メッキ膜の厚さは０．１〜３０μｍ、特に１〜２０μｍであることが好ましい。塗装としては、水ガラス等の無機系塗装、エポキシ樹脂、アクリル樹脂などの樹脂塗装、あるいはジンクリッチペイント等の処理が挙げられ、その厚さは０．１〜１００μｍ、特に１〜５０μｍであることが好ましい。
【００３０】
【実施例】
以下、本発明の具体的態様について実施例をもって詳述するが、本発明の内容はこれに限定されるものではない。
【００３１】
［実施例１、比較例１］
純度９９重量％以上のＮｄ、Ｄｙ、Ｃｏ、Ａｌ、Ｆｅメタルとフェロボロンを所定量秤量してＡｒ雰囲気中で高周波溶解し、この合金溶湯をＡｒ雰囲気中で銅製単ロールに注湯するストリップキャスト法により薄板状の合金とした。得られた合金の組成は、Ｎｄが１１．０原子％、Ｄｙが２．３原子％、Ｃｏが１．０原子％、Ａｌが１．０原子％、Ｂが４．５原子％、Ｆｅが残部であり、これを合金Ａと称する。合金Ａに水素を吸蔵させた後、真空排気を行いながら５００℃まで加熱して部分的に水素を放出させる、いわゆる水素粉砕により３０メッシュ以下の粗粉とした。更に、純度９９重量％以上のＮｄ、Ｄｙ、Ｆｅ、Ｃｏ、Ａｌ、Ｃｕメタルとフェロボロンを所定量秤量し、Ａｒ雰囲気中で高周波溶解した後、鋳造した。得られた合金の組成はＮｄが２０原子％で、Ｄｙが１０原子％、Ｆｅが２４原子％、Ｂが６原子％、Ａｌが１原子％、Ｃｕが２原子％、Ｃｏが残部であり、これを合金Ｂと称する。合金Ｂは窒素雰囲気中、ブラウンミルを用いて３０メッシュ以下に粗粉砕された。
【００３２】
続いて、合金Ａ粉末を９０重量％、合金Ｂ粉末を１０重量％秤量して、窒素置換したＶブレンダー中で３０分間混合した。この混合粉末は高圧窒素ガスを用いたジェットミルにて、粉末の重量中位粒径４μｍに微粉砕された。得られた混合微粉末を大気に触れさせることなく窒素雰囲気下１５ｋＯｅの磁界中で配向させながら、約１ｔｏｎ／ｃｍ^２の圧力で成形した。次いで、この成形体は大気に触れさせることなくＡｒ雰囲気の焼結炉内に投入され、１，０６０℃で２時間焼結、更に５１０℃で１時間時効処理して急冷し、１０ｍｍ×２０ｍｍ×厚み１５ｍｍ寸法の磁石ブロックを作製した。磁石ブロックは内周刃切断機により比表面積Ｓ／Ｖが２０ｍｍ^−１となるように所定寸法の直方体に全面研削加工され、本発明の磁石体を得た。これを磁石体Ｍ１と称する。
【００３３】
比較のため、同組成混合粉末をジェットミルにて、粉末の重量中位粒径８μｍに微粉砕した。得られた混合微粉末を大気中で１５ｋＯｅの磁界中で配向させながら、約１ｔｏｎ／ｃｍ^２の圧力で成形した。次いで、Ａｒ雰囲気の焼結炉内に投入され、１，０８０℃で２時間焼結、更に５１０℃で１時間時効処理して急冷し、１０ｍｍ×２０ｍｍ×厚み１５ｍｍ寸法の磁石ブロックを作製した。磁石ブロックは内周刃切断機により比表面積Ｓ／Ｖが２０ｍｍ^−１となるように所定寸法の直方体に全面研削加工された。これを磁石体Ｐ１と称する。
【００３４】
磁石体Ｍ１，Ｐ１の減磁曲線をそれぞれ曲線Ｈ，Ｋとして図１に示す。これらの平均結晶粒径、加工前後での磁気特性及び表面劣化層の平均厚さと体積分率を表１に示す。従来技術では、Ｓ／Ｖ＝２０ｍｍ^−１まで加工すると、劣化層の体積分率は４０％近くに達し、最大エネルギー積はバルク磁石の１０％以下しか得られなかったが、本発明では１０％をはるかに超える高いエネルギー積が得られた。
【００３５】
【表１】

【００３６】
［実施例２］
比表面積Ｓ／Ｖが２０ｍｍ^−１となるように全面研削加工された磁石体Ｍ１をアルカリ溶液で洗浄した後、酸洗浄して乾燥させた。これを磁石体Ｍ２と称する。各洗浄の前後には純水による洗浄工程が含まれている。磁石体Ｍ２の磁気特性及び表面劣化層の平均厚さと体積分率を表２に示した。磁石体Ｍ１と比較して、磁気特性が全く劣化していないことがわかる。
【００３７】
［実施例３］
比表面積Ｓ／Ｖが２０ｍｍ^−１となるように全面研削加工され、アルカリ洗浄に次いで酸洗浄された磁石体Ｍ２に対し、無電解銅メッキにより厚さ約５μｍの銅皮膜を被着した。これを磁石体Ｍ３と称する。磁石体Ｍ３の磁気特性及び表面劣化層の平均厚さと体積分率を表２に併記した。磁石体Ｍ１及びＭ２と比較して、磁気特性が殆ど劣化していないことがわかる。
【００３８】
【表２】

【００３９】
【発明の効果】
本発明によれば、研削加工後に特性を回復させるための熱処理を施すことなく良好な磁気特性を示すＳ／Ｖ＝６ｍｍ^−１以上の小型あるいは薄型の永久磁石を提供することができる。
【図面の簡単な説明】
【図１】本発明による磁石体の減磁曲線（曲線Ｈ）及び従来技術による磁石体の減磁曲線（曲線Ｋ）を示した図である。
【図２】本発明による磁石体の結晶粒径分布を示した図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an R—Fe—B permanent magnet material in which deterioration of magnetic properties due to grinding of the surface of a sintered magnet body is reduced, and in particular, specific surface area (S (surface area) / V (volume) of the magnet body. ) Is about 6 mm ⁻¹ or more for small or thin high-performance permanent magnet materials.
[0002]
[Prior art]
Nd-Fe-B-based permanent magnets have been increasingly used because of their excellent magnetic properties. In recent years, Nd-Fe-B magnets, especially high-performance, have been developed with computer-related equipment using magnets, CD players, DVD players, mobile phones, and other electronic devices that are becoming lighter, thinner, smaller, more efficient, and more energy efficient. There is a demand for smaller and thinner Nd-Fe-B based sintered magnets, and the demand for small or thin magnets whose specific surface area S / V exceeds 6 mm ^-1 is also increasing. .
[0003]
In order to process a small or thin Nd-Fe-B based sintered magnet into a practical shape and mount it on a magnetic circuit, it is necessary to grind a shaped and sintered block-shaped sintered magnet. An outer edge cutting machine, an inner edge cutting machine, a surface grinding machine, a centerless polishing machine, a lapping machine and the like are used.
[0004]
However, it is known that when the Nd-Fe-B based sintered magnet is ground by the above-mentioned apparatus, the magnetic properties are deteriorated as the magnet body becomes smaller. This deterioration is considered to be due to the grain boundary structure required for the expression of a high coercive force of the present magnet being lost on the surface of the magnet due to processing or due to processing strain. In order to prevent the magnetic properties from deteriorating, for example, by preventing the growth of crystal grains in the sintering process of the magnet, the magnetic properties are degraded even when the grinding process is performed until the specific surface area S / V becomes 2.6 mm ^−1. There is proposed a magnet material that does not use it (see Patent Document 1: Japanese Patent No. 2514155). However, when the S / V exceeds 6 mm ⁻¹ , there is a problem that the magnetic characteristics are significantly deteriorated.
[0005]
As a method of preventing the characteristic deterioration of such an extremely small magnet body, for example, a thin film layer mainly composed of a rare earth element is formed on the surface to be ground by sputtering or the like, and further subjected to a heat treatment to modify the deteriorated surface to be ground. Thus, there has been proposed a method for preventing the deterioration of the characteristics of the magnet body (see Patent Document 2: Japanese Patent Publication No. 5-60241 and Patent Document 3: Japanese Patent Publication No. 6-63086). However, it is difficult to apply the above method to mass production because of extremely low productivity, there is little deterioration in magnetic properties, and it is practically impossible to produce an extremely small magnet having an S / V exceeding 6 mm ^−1. Was considered possible.
[0006]
[Patent Document 1]
Japanese Patent No. 2514155 [Patent Document 2]
Japanese Patent Publication No. 5-60241 [Patent Document 3]
Japanese Patent Publication No. 6-63086
[Problems to be solved by the invention]
An object of the present invention is to provide an R-Fe-B-based sintered magnet material in which deterioration of magnetic properties due to grinding is reduced in view of the above-described conventional problems.
[0008]
Means for Solving the Problems and Embodiments of the Invention
The present inventors have conducted various studies on the coercive force in the vicinity of the surface of the R—Fe—B based sintered magnet. As a result, when the effect of the processing strain is suppressed as much as possible while paying attention to the processing speed, the deterioration in the surface to be ground is deteriorated. It has been found that the average thickness t (unit: μm) of the layer is approximately the same as the average crystal grain size D (unit: μm) obtained from the area ratio of the magnet main phase.
From the relationship between the average thickness t of the deteriorated layer and the average crystal grain size D, the average grain size of the deteriorated layer on the surface to be ground can be reduced by making the crystal grain size of the main phase as small as possible. That is, it has been found that deterioration of characteristics of a small or thin permanent magnet can be reduced. In order to achieve this, it is necessary to make the magnet raw material particles sufficiently fine in the pulverizing step in the manufacturing step of the sintered magnet, and to suppress the coarsening of the main phase crystal grains in the sintering step. Although the present process is not easily achieved, the present inventors have conducted intensive studies on the atmosphere, processing temperature, alloy composition, and the like in the process of producing a sintered magnet, and have found that the average crystal grain size of R-Fe-B is 5 μm or less. By producing a system-based sintered magnet, the volume fraction (%) of the surface deteriorated layer of the sintered magnet body is 0.5 × S / V (S / V is specific surface area and the unit is mm ⁻¹ ) or less. The maximum energy product of the sintered magnet body is 85% or more of the bulk energy of the sintered magnet, that is, 85% or more of the maximum energy product of the magnet body having a specific surface area of approximately less than 0.6 mm ⁻¹ , which causes deterioration of magnetic characteristics. It has been found that the present invention can be significantly reduced, and the present invention has been completed. It is.
[0009]
That is, the permanent magnet material according to the present invention is a sintered magnet having an R—Fe—B-based composition (R is one or more selected from rare earth elements including Y), and is a main component determined from the area fraction. The average crystal grain size of the phase is 5 μm or less, and the specific surface area is ground to 6 mm ⁻¹ or more, and the volume fraction (%) of the surface deteriorated layer of the sintered magnet body is 0.5 × S / V (S / V is a specific surface area, and the unit is mm- ¹ ) or less.
[0010]
Furthermore, the maximum energy product of the sintered magnet body is 85% or more of the maximum energy product of the bulk state of the sintered magnet, that is, the maximum energy product of the magnet body whose specific surface area before grinding is less than 0.6 mm ^−1. It is characterized by the following.
[0011]
In addition to the above aspect, after the grinding processing, the sintered magnet body is washed with at least one of an alkali, an acid, and an organic solvent, and the volume fraction (%) of the surface deteriorated layer of the sintered magnet body is 0.5 × S / V. (S / V is specific surface area and the unit is mm ⁻¹ ) or less, and the maximum energy product of the sintered magnet body is 85% or more of the maximum energy product in the bulk state of the sintered magnet. And
Further, the present invention is characterized in that the permanent magnet body is subjected to surface treatment by plating or painting.
[0012]
Hereinafter, the present invention will be described in more detail.
The present invention reduces the deterioration of magnetic properties due to the grinding of the surface of an R—Fe—B sintered permanent magnet body and has a high performance for small or thin magnets having a specific surface area S / V of 6 mm ⁻¹ or more. It relates to a permanent magnet material.
Here, the R-Fe-B-based sintered permanent magnet can be obtained by coarsely pulverizing, finely pulverizing, molding, and sintering the master alloy according to a conventional method.
In this case, the master alloy contains R, Fe, and B. R is one or more selected from rare earth elements including Y, and specifically, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu Nd, Pr, and Dy are preferred. The content of the rare earth element containing Y is preferably 10 to 20 atomic%, more preferably 12 to 15 atomic%, and more preferably 10% or more of Nd and Pr or any one of them in R. It is preferable that the content be 50 atomic% or more. B is preferably contained in an amount of 3 to 15 atomic%, particularly 4 to 8 atomic%. In addition, Al, Cu, Zn, In, Si, P, S, Ti, V, Cr, Mn, Ni, Ga, Ge, Zr, Nb, Mo, Pd, Ag, Cd, Sn, Sb, Hf, Ta, One or more selected from W may be contained in an amount of 0 to 11 atomic%, particularly 0.1 to 5 atomic%. The balance is Fe or inevitable impurities such as C, N, and O, but Fe is preferably contained at 50 at% or more, particularly at least 65 at%. Further, a part of Fe, for example, 0 to 40 atomic%, particularly 0 to 15 atomic% of Fe may be replaced with Co.
[0013]
The mother alloy is obtained by melting a raw metal or alloy in a vacuum or an inert gas, preferably an Ar atmosphere, and then casting it in a flat mold or a book mold, or casting it by strip casting. It should be noted that an alloy close to the R ₂ Fe ₁₄ B compound composition, which is the main phase of the present alloy, and an R-rich alloy, which is a liquid phase aid at the sintering temperature, are separately prepared, weighed and mixed after coarse pulverization. The two-alloy method is also applicable to the present invention. However, for an alloy having a composition close to the main phase, α-Fe tends to remain depending on the cooling rate during casting and the alloy composition, and is homogenized as necessary for the purpose of increasing the amount of the R ₂ Fe ₁₄ B compound phase. A chemical treatment is performed. The heat treatment is performed at 700 to 1,200 ° C. for 1 hour or more in a vacuum or Ar atmosphere. For an R-rich alloy serving as a liquid phase aid, a so-called liquid quenching method can be applied in addition to the casting method.
[0014]
The above alloy is usually coarsely pulverized to 0.05 to 3 mm, particularly 0.05 to 1.5 mm. In the coarse grinding step, a brown mill or hydrogen grinding is used. In the case of an alloy produced by strip casting, hydrogen grinding is preferable.
The coarse powder obtained in this manner is finely pulverized by, for example, a jet mill using high-pressure nitrogen. At this time, the weight-median particle size of the fine powder measured by using a laser diffraction method is 5 μm or less, Pulverization is preferably performed so as to be 0.2 to 5 μm, and more preferably 0.5 to 4.5 μm. However, powders having a weight median particle size of 5 μm or less are very active, and when exposed to the air, oxidation proceeds rapidly with heat generation. Therefore, it is necessary to prevent the fine powder from coming into contact with the atmosphere during the period from the pulverization step to the sintering step through compression molding in a magnetic field. For this purpose, the fine powder recovery container is filled with a solvent capable of inhibiting the oxidation of the fine powder such as mineral oil to make the fine powder into a slurry, wet-molded and put into a sintering furnace, or the entire apparatus or a mold is used. Dry molding is performed by a compression molding machine in which the vicinity is an inert gas atmosphere, and the resultant is put into a sintering furnace. In the latter case, the container is kept in an inert gas atmosphere even when the fine powder and the molded body are moved to the next step, or all the paths in which the fine powder and the molded body are moved, including the apparatus, are placed in an inert gas atmosphere. Even with the above-described means for preventing oxidation, it is difficult to completely prevent the oxidation of the fine powder, and if the weight-median particle size of the fine powder is less than 0.2 μm, the influence of unavoidable oxidation is large. In some cases, good magnetic characteristics cannot be obtained.
[0015]
The fine powder is formed by a compression molding machine in a magnetic field, and is put into a sintering furnace. The sintering is performed in a vacuum or in an atmosphere of an inert gas such as Ar or He at a temperature of usually 900 to 1,250 ° C, particularly 1,000 to 1,100 ° C.
Further, after sintering, at a low temperature lower than the sintering temperature, preferably 200 to 900 ° C, more preferably 350 to 750 ° C, in a vacuum or an inert gas atmosphere such as Ar or He for 10 minutes to 5 hours, particularly The heat treatment is preferably performed for about 30 minutes to 2 hours, and a magnetic material having high coercive force and good squareness can be obtained by this heat treatment.
[0016]
The sintered magnet obtained here contains the tetragonal R ₂ Fe ₁₄ B compound as a main phase in an amount of 60 to 99% by volume, particularly preferably 80 to 98% by volume, and the balance is 0.5 to 20% by volume. R-rich phase, 0 to 10% by volume of B-rich phase and at least one of carbides, nitrides, oxides and hydroxides formed by unavoidable impurities, or a mixture or composite thereof.
[0017]
The obtained sintered block is ground into a practical shape. However, in order to minimize the influence of processing strain, it is preferable to reduce the processing speed within a range where productivity is not reduced. In this case, the grinding method can be performed according to a conventional method, but the processing speed is specifically 0.1 to 20 mm / min, particularly preferably 0.5 to 10 mm / min.
[0018]
In this case, as a grinding amount, the specific surface area S / V (surface area mm ² / volume mm ³ ) of the sintered block is 6 mm ⁻¹ or more, preferably 10 mm ⁻¹ or more. The upper limit is appropriately selected and is not particularly limited, but is usually 40 mm ^-1 or less, particularly 30 mm ^-1 or less.
[0019]
In the above-described grinding process, when a water-based coolant is used for the grinding machine, or when the ground surface is exposed to a high temperature during the processing, an oxide film is likely to be formed on the surface to be ground. In order to remove this, washing is performed using at least one of an alkali, an acid and an organic solvent. When a surface treatment by plating or painting is required, this treatment is a pretreatment.
[0020]
Incidentally, as the alkali, potassium pyrophosphate, sodium pyrophosphate, potassium citrate, sodium citrate, potassium acetate, sodium acetate, potassium oxalate, sodium oxalate, etc., as the acid, hydrochloric acid, nitric acid, sulfuric acid, acetic acid, Citric acid, tartaric acid and the like can be used, and as an organic solvent, acetone, methanol, ethanol, isopropyl alcohol and the like can be used. In this case, the alkali or acid can be used as an aqueous solution having an appropriate concentration that does not corrode the magnet body.
[0021]
In the sintered magnet of the present invention, the average crystal grain size D of the main phase determined from the area fraction is 5 μm or less, preferably 0.5 to 5 μm, and more preferably 1 to 4.5 μm. As described above, the average thickness t (μm) of the surface-deteriorated layer on the surface to be ground is approximately the same as the average crystal grain size (μm) obtained from the area ratio of the magnet main phase. The volume fraction (%) of the surface-deteriorated layer is 0.5 × S / V (S / V is a specific surface area, the unit is mm ⁻¹ ) or less, preferably 0.4 × S / V or less, more preferably 0 × S / V. 0.3 × S / V or less. Although the lower limit may be 0, it is usually at least 0.01 × S / V, especially at least 0.03 × S / V.
[0022]
Here, the average thickness t of the deteriorated layer is calculated according to the following procedure.
First, a demagnetization curve (JH curve) of the ground magnet body is measured. When the slope of the demagnetization curve is plotted against the applied magnetic field (dJ / dH-H curve), two peaks are recognized. Among them, the peak position at the peak with the applied magnetic field having a large absolute value corresponds to the magnetization reversal of the crystal grains in the magnet body whose characteristics have not deteriorated. The peak position at the other peak (referred to as _Hdmg ) corresponds to the coercive force of the surface deteriorated layer of the magnet body, and the magnetic polarization of the deteriorated layer is zero at that position. Therefore, the value of magnetic polarization (referred to as J _blk ) corresponding to H _dmg in the JH curve can be defined as the magnetic polarization of undegraded particles inside the magnet. Using the saturation magnetic polarization (J _s ) of the magnet body and J _blk , the volume fraction (referred to as V _dmg , the unit is percent) of the area deteriorated by the grinding is calculated by the following equation.
V _dmg = _{_{_{[(J s -J blk) / J}}} s ] × 100
[0023]
On the other hand, for example, assuming that the magnet body is a rectangular parallelepiped and its size is A × B × C (unit: μm), V _dmg can be expressed as the following equation using the average thickness t of the deteriorated layer. , T is calculated from the following equation.
V _dmg = [1- (A-2t) × (B-2t) × (C-2t) / ABC] × 100
[0024]
Even when the magnet body has an arbitrary shape, an equation similar to the above equation can be easily described according to the shape.
[0025]
Further, the average crystal grain size D of the magnet main phase is determined as follows. First, after the magnet body is mirror-polished, the grain boundaries are contrasted with a corrosive liquid. The area of each particle is measured from an optical microscope image or a scanning electron microscope image taken of the arbitrary field of view, and the diameter of a circle equivalent to this is defined as the crystal particle size of each particle. Subsequently, when creating a histogram showing the particle size distribution, the ratio of the area occupied by the crystal grains is plotted instead of the number of crystal grains existing in the range with respect to the range of the particle size. An example is shown in FIG. The area median grain size obtained from this histogram is defined as the average crystal grain size.
[0026]
The volume fraction (%) of the surface-deteriorated layer in the present invention is 0.5 × S / V or less as described above. The reason for this limitation is as follows.
If the average thickness of the surface deteriorated layer is constant, the volume fraction occupied by the deteriorated layer increases as the specific surface area increases. The dimensional limit that can be ground by the current technology is about S / V = 30 mm ^{−1 in} specific surface area. When the volume fraction of the deteriorated layer exceeds 0.5 × S / V in the magnet body of S / V = 30 mm ⁻¹ , that is, when the volume fraction of the magnet layer is 15% or more, the maximum energy obtained is reduced to 4MGOe or less. In order to make full use of the high magnetic properties of the R-Fe-B based sintered magnet represented by the Fe-B based sintered magnet, the volume fraction of the surface-deteriorated layer should be 0.5 × S / V or less. I do. To achieve this, as described above, the average crystal grain size of the main phase of the sintered magnet needs to be 5 μm or less.
[0027]
Further, a decrease in the squareness of the demagnetization curve due to the processing leads to a decrease in the maximum energy product. However, when the volume fraction of the surface-deteriorated layer is set to 0.5 × S / V or less, the sintered magnet body The maximum energy product can be increased to 85% or more of the maximum energy product of the magnet body before grinding, in which the sintered magnet has a bulk state, that is, the specific surface area is less than 0.6 mm ^-1 .
[0028]
Therefore, according to the present invention, a small or thin permanent magnet with less characteristic deterioration can be provided. In this case, as an example of a specific size of the permanent magnet, 1 mm × 1 mm × 1 mm (S / V = 6 mm ⁻¹ ), 0.8 mm × 0.8 mm × 0.25 mm (S / V = 13 mm ⁻¹⁾ ), 0.8 mm × 0.8 mm × 0.13 mm (S / V = 20 mm ⁻¹ ), 0.8 mm × 0.3 mm × 0.13 mm (S / V = 25 mm ⁻¹ ), and the like.
[0029]
In the present invention, the magnet may be subjected to surface treatment by plating or painting. In this case, the plating may be performed as a single layer or a laminate of a single substance or an alloy of Ni, Cu, Sn, Zn, Au, and Ag, and the thickness of the plating film is 0.1 to 30 μm, particularly 1 to 30 μm. It is preferably 20 μm. Examples of the coating include an inorganic coating such as water glass, a resin coating such as an epoxy resin and an acrylic resin, or a treatment such as a zinc rich paint, and the thickness is 0.1 to 100 μm, particularly 1 to 50 μm. Is preferred.
[0030]
【Example】
Hereinafter, specific embodiments of the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.
[0031]
[Example 1, Comparative Example 1]
Strip casting method in which a predetermined amount of Nd, Dy, Co, Al, Fe metal and ferroboron having a purity of 99% by weight or more and ferroboron are weighed in a high frequency and melted in an Ar atmosphere, and the molten alloy is poured into a copper single roll in an Ar atmosphere. Thus, a thin plate-shaped alloy was obtained. The composition of the obtained alloy is such that Nd is 11.0 atomic%, Dy is 2.3 atomic%, Co is 1.0 atomic%, Al is 1.0 atomic%, B is 4.5 atomic%, and Fe is The remainder is referred to as alloy A. After absorbing hydrogen in the alloy A, the alloy A was heated to 500 ° C. while performing evacuation to partially release hydrogen, so-called hydrogen pulverization to obtain coarse powder of 30 mesh or less. Further, a predetermined amount of Nd, Dy, Fe, Co, Al, Cu metal and ferroboron having a purity of 99% by weight or more was weighed, and after high frequency melting in an Ar atmosphere, casting was performed. The composition of the obtained alloy is 20 atomic% of Nd, 10 atomic% of Dy, 24 atomic% of Fe, 6 atomic% of B, 1 atomic% of Al, 2 atomic% of Cu, and the balance of Co, This is referred to as alloy B. The alloy B was coarsely pulverized to 30 mesh or less using a brown mill in a nitrogen atmosphere.
[0032]
Subsequently, 90% by weight of the alloy A powder and 10% by weight of the alloy B powder were weighed and mixed in a nitrogen-purged V blender for 30 minutes. This mixed powder was finely pulverized by a jet mill using high-pressure nitrogen gas to a powder having a median particle diameter of 4 μm. The obtained mixed fine powder was molded at a pressure of about 1 ton / cm ² while being oriented in a magnetic field of 15 kOe under a nitrogen atmosphere without being exposed to the atmosphere. Next, the molded body was put into a sintering furnace in an Ar atmosphere without being exposed to the air, sintered at 1,060 ° C. for 2 hours, further aged at 510 ° C. for 1 hour, and rapidly cooled to 10 mm × 20 mm × A magnet block having a thickness of 15 mm was manufactured. The magnet block was entirely ground into a rectangular parallelepiped having a predetermined size so that the specific surface area S / V became 20 mm ⁻¹ by an inner peripheral cutting machine, thereby obtaining a magnet body of the present invention. This is called a magnet M1.
[0033]
For comparison, the mixed powder having the same composition was finely pulverized by a jet mill into a powder having a weight median particle diameter of 8 μm. The obtained mixed fine powder was molded at a pressure of about 1 ton / cm ² while being oriented in a magnetic field of 15 kOe in the atmosphere. Then, it was put into a sintering furnace in an Ar atmosphere, sintered at 1,080 ° C. for 2 hours, further aged at 510 ° C. for 1 hour, and quenched to prepare a magnet block having dimensions of 10 mm × 20 mm × 15 mm in thickness. The magnet block was entirely ground into a rectangular parallelepiped of a predetermined size so that the specific surface area S / V became 20 mm ⁻¹ by an inner peripheral blade cutting machine. This is called a magnet P1.
[0034]
FIG. 1 shows the demagnetization curves of the magnet bodies M1 and P1 as curves H and K, respectively. Table 1 shows the average crystal grain size, the magnetic properties before and after the processing, the average thickness of the surface-deteriorated layer, and the volume fraction. In the prior art, when processed to S / V = 20 mm ⁻¹ , the volume fraction of the degraded layer reached close to 40%, and the maximum energy product was only 10% or less of the bulk magnet. And a high energy product far exceeding
[0035]
[Table 1]

[0036]
[Example 2]
The magnet body M1 whose entire surface was ground so that the specific surface area S / V became 20 mm ^-1 was washed with an alkali solution, then washed with an acid, and dried. This is called magnet body M2. Before and after each cleaning, a cleaning step using pure water is included. Table 2 shows the magnetic properties of the magnet M2, the average thickness of the surface-deteriorated layer, and the volume fraction. It can be seen that the magnetic properties are not deteriorated at all as compared with the magnet body M1.
[0037]
[Example 3]
The magnet body M2, which was entirely ground so that the specific surface area S / V became 20 mm ^-1 and washed with alkali and then with acid, was coated with a copper film having a thickness of about 5 μm by electroless copper plating. This is called magnet body M3. Table 2 also shows the magnetic properties of the magnet M3, the average thickness of the surface-deteriorated layer, and the volume fraction. It can be seen that the magnetic properties are hardly deteriorated as compared with the magnet bodies M1 and M2.
[0038]
[Table 2]

[0039]
【The invention's effect】
According to the present invention, it is possible to provide a small or thin permanent magnet of S / V = 6 mm ⁻¹ or more that exhibits good magnetic properties without performing a heat treatment for restoring the properties after grinding.
[Brief description of the drawings]
FIG. 1 is a diagram showing a demagnetization curve (curve H) of a magnet body according to the present invention and a demagnetization curve (curve K) of a magnet body according to the prior art.
FIG. 2 is a view showing a crystal grain size distribution of a magnet body according to the present invention.

Claims

A sintered magnet having an R-Fe-B composition (R is one or more selected from rare earth elements including Y), wherein the average crystal grain size of the main phase determined from the area fraction is 5 µm or less. , the specific surface area is machined on or ^{6 mm -1,} in sintered volume fraction of the magnet body surface deterioration layer (%) is 0.5 × S / V (S / V is the specific surface area, the unit is mm ^{- 1} ) A permanent magnet material characterized by the following.

A sintered magnet having an R-Fe-B composition (R is one or more selected from rare earth elements including Y), wherein the average crystal grain size of the main phase determined from the area fraction is 5 µm or less. And the maximum energy product of the sintered magnet body is ground to 6 mm ⁻¹ or more, and the maximum energy product of the sintered magnet body is less than 0.6 mm ⁻¹ before the grinding. Permanent magnet material characterized by not less than 85% of the product.

A sintered magnet having an R-Fe-B composition (R is one or more selected from rare earth elements including Y), wherein the average crystal grain size of the main phase determined from the area fraction is 5 µm or less. After being ground to have a specific surface area of 6 mm ^-1 or more, the surface area of the sintered magnet body is reduced by washing with at least one of an alkali, an acid and an organic solvent (%). Is 0.5 × S / V (S / V is a specific surface area and a unit is mm ⁻¹ ) or less.

A sintered magnet having an R-Fe-B composition (R is one or more selected from rare earth elements including Y), wherein the average crystal grain size of the main phase determined from the area fraction is 5 µm or less. After being ground to a specific surface area of 6 mm ⁻¹ or more, the sintered body is washed with at least one of an alkali, an acid, and an organic solvent, thereby increasing the maximum energy product of the sintered magnet body. A permanent magnet material characterized in that the specific energy is 85% or more of the maximum energy product of the magnet body having a specific surface area of less than 0.6 mm ^-1 before grinding.

5. The permanent magnet material according to claim 1, wherein the permanent magnet material is subjected to a surface treatment by plating or painting.