JP6497686B2 - Magnesium alloy exhibiting superelastic effect and / or shape memory effect - Google Patents

Magnesium alloy exhibiting superelastic effect and / or shape memory effect Download PDF

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JP6497686B2
JP6497686B2 JP2017545452A JP2017545452A JP6497686B2 JP 6497686 B2 JP6497686 B2 JP 6497686B2 JP 2017545452 A JP2017545452 A JP 2017545452A JP 2017545452 A JP2017545452 A JP 2017545452A JP 6497686 B2 JP6497686 B2 JP 6497686B2
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大輔 安藤
大輔 安藤
須藤 祐司
祐司 須藤
由希子 小川
由希子 小川
小池 淳一
淳一 小池
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CLINO Ltd
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    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C23/00Alloys based on magnesium
    • C22C23/06Alloys based on magnesium with a rare earth metal as the next major constituent
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    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22F1/00Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/06Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of magnesium or alloys based thereon
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22FCHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working

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Description

本発明は、超弾性効果及び/又は形状記憶効果を発現するマグネシウム合金(以下、Mg合金と記載する。)に関する。特に、スカンジウム(Sc)を一定量含むMg合金に関する。本出願は2015年10月13日に出願された日本国特許出願である特願2015−201830の関連出願であり、この日本出願に基づく優先権を主張するものである。また、本発明者らの論文であるAndo, D., et al., Materials Letters, Vol.161, p.5-8、Ogawa, Y., et al., Science, 2016, Vol.353(6297), pp.368-370, Ogawa,
Y., et al., Scripta Materialia, doi.org/10.1016/j.scriptamat.2016.09.024 に記載された全ての内容を援用するものである。
The present invention relates to a magnesium alloy (hereinafter referred to as Mg alloy) that exhibits a superelastic effect and / or a shape memory effect. In particular, the present invention relates to an Mg alloy containing a certain amount of scandium (Sc). This application is a related application of Japanese Patent Application No. 2015-201830, which is a Japanese patent application filed on October 13, 2015, and claims priority based on this Japanese application. In addition, the present inventors' paper, Ando, D., et al., Materials Letters, Vol. 161, p. 5-8, Ogawa, Y., et al., Science, 2016, Vol. 353 (6297 ), pp.368-370, Ogawa,
All contents described in Y., et al., Scripta Materialia, doi.org/10.1016/j.scriptamat.2016.09.024 are incorporated.

Mg合金は構造用材料に用いられる金属では最も低密度で軽量である。したがって、自動車、航空機などの構造材料として用いれば軽量化に寄与し、省エネルギー効果が期待できる。また、Mg合金は、リサイクル性にも優れ、プラスチックに比べて容易にリサイクルできるという利点がある。さらに、比強度も高く、資源も豊富に存在することから、次世代構造材料と呼ばれ注目され始めてから数十年経つ。しかしながら、広く使用されるMg合金が開発されるに至っていない。軽量で、比剛性が高く、衝撃吸収性に優れたMg合金が開発されているにもかかわらず、未だ十分な実用化に至っていない原因の一つに、冷間加工性に乏しい、強度が低いといった機械的性質の不十分さが挙げられる。   Mg alloy has the lowest density and light weight among metals used for structural materials. Therefore, if it is used as a structural material for automobiles, aircraft, etc., it contributes to weight reduction and an energy saving effect can be expected. Further, Mg alloy has an advantage that it is excellent in recyclability and can be easily recycled compared to plastic. Furthermore, since it has a high specific strength and abundant resources, it is called the next generation structural material, and it has been several decades since it began to attract attention. However, widely used Mg alloys have not been developed. Despite the development of lightweight, high specific rigidity and excellent shock absorption Mg alloys, one of the reasons that has not yet been fully put into practical use is poor cold workability and low strength Insufficient mechanical properties.

強度を高くするために、MgにAlを添加した合金が開発されているが、冷間加工性が乏しいという短所がある。例えば、Alが添加された代表的なMg合金には、AZ31(Al3質量%、Zn1質量%、残部Mg)、AZ61(Al6質量%、Zn1質量%、残部Mg)、AZ91(Al9質量%、Zn1質量%、残部Mg)、AM(Al6質量%、Mn1質量%未満、残部Mg)がある。このうち構造材として汎用の高い圧延材を容易に得ることができるのはAZ31のみであるが、AZ31の圧延材にしても250℃程度でしかプレス加工ができず、室温で加工することは難しい。この冷間加工性が乏しいという短所が、様々な用途への実用化を妨げている。   In order to increase the strength, an alloy in which Al is added to Mg has been developed, but it has a disadvantage of poor cold workability. For example, typical Mg alloys to which Al is added include AZ31 (Al 3 mass%, Zn 1 mass%, balance Mg), AZ61 (Al 6 mass%, Zn 1 mass%, balance Mg), AZ91 (Al 9 mass%, Zn1 Mass%, balance Mg), AM (Al 6 mass%, Mn less than 1 mass%, balance Mg). Among them, only AZ31 can easily obtain a general-purpose rolled material as a structural material, but even AZ31 rolled material can only be pressed at about 250 ° C. and is difficult to process at room temperature. . This disadvantage of poor cold workability hinders practical application to various applications.

一般のマグネシウム合金が冷間加工性や強度に乏しい原因として、主相がHCP(hexagonal close−packed)構造であることが挙げられており、変形中に形成される二重双晶内部において局所的大変形が生じるため早期破壊が生じる事が指摘されている。こうした問題の解決策として、結晶粒の微細化やランダム化といった結晶の制御が試みられている(非特許文献1、2)。ただし、結晶粒の微細化などによる結晶組織制御を施しても、その構造はHCPのままであり、構造に起因する異方性が存在するため延性の向上には限界がある。   The reason why general magnesium alloys are poor in cold workability and strength is that the main phase has an HCP (hexagonal close-packed) structure, and it is local in the double twin formed during deformation. It has been pointed out that premature destruction occurs due to large deformation. As a solution to this problem, attempts have been made to control crystals such as refinement and randomization of crystal grains (Non-Patent Documents 1 and 2). However, even if the crystal structure is controlled by refining crystal grains, the structure remains HCP, and there is anisotropy due to the structure, so there is a limit to improving ductility.

Mg合金の冷間加工性を向上させる技術としてMg−Li合金がある(特許文献1、2、非特許文献3)。MgへLiを24.5原子%添加すると結晶構造がHCP構造からBCC(body-centered cubic)構造へと変化し、冷間加工性が向上する。しかしながら、リチウム含有量が多くなるにつれ、耐食性が低下する。また、Mg−Li合金は硬さや強度が低く、熱安定性も悪い。そのため自動車や航空材料のように、強度を必要とする材料として使用することはできない。また、耐食性が悪いことから表面処理が必要であるため用途がきわめて限定されたものとなっている。   As a technique for improving the cold workability of the Mg alloy, there are Mg-Li alloys (Patent Documents 1 and 2 and Non-Patent Document 3). When 24.5 atomic% of Li is added to Mg, the crystal structure changes from an HCP structure to a BCC (body-centered cubic) structure, and cold workability is improved. However, the corrosion resistance decreases as the lithium content increases. In addition, Mg—Li alloy has low hardness and strength and poor thermal stability. Therefore, it cannot be used as a material that requires strength, such as automobiles and aviation materials. In addition, since the corrosion resistance is poor, surface treatment is required, so that the application is extremely limited.

さらに、Mg合金が広く用いられていない原因の二つ目として、Ti合金のような機能性を備えておらず、その応用範囲が広がらないことが挙げられる。Ti合金は、高い比強度を有し、延性にも優れるばかりでなく、特にBCC構造を有するTi合金は超弾性効果を示すことが知られている(特許文献3)。基本的に、応力を負荷することによるマルテンサイト変態に起因して超弾性効果を発現するものは、応力を負荷しない状態での変態温度に依存して形状記憶効果を示すことも知られている。これらの性質を利用して、Ti合金は眼鏡フレームなどの装身具やステント、カテーテル、ガイドワイヤといった医療分野への適用も進んでいる。   Furthermore, the second reason why Mg alloys are not widely used is that they do not have the functionality of Ti alloys and their application range does not widen. It is known that a Ti alloy has a high specific strength and excellent ductility, and in particular, a Ti alloy having a BCC structure exhibits a superelastic effect (Patent Document 3). It is also known that those that exhibit a superelastic effect due to the martensitic transformation by applying stress show a shape memory effect depending on the transformation temperature without stress. . Utilizing these properties, Ti alloys are also being applied to medical fields such as accessories such as eyeglass frames, stents, catheters, and guide wires.

超弾性効果とは、大きな変形ひずみを加えても応力を除くと直ちに元の形状に戻る性質をいう。また、形状記憶効果とは、外力によって変形させても、ある温度以上になると元の記憶した形に戻る性質をいう。超弾性効果を有する形状記憶合金としては、Ni-Ti、Cu-Al-Ni、Cu-Zn、Cu-Zn-Al、Cu−Al−Mn、Ti−Nb−Al、Ni-Al等、様々な金属をベースとした合金が開発されている。   The superelastic effect refers to the property of immediately returning to the original shape when the stress is removed even when a large deformation strain is applied. The shape memory effect refers to the property of returning to the original memorized shape when the temperature rises above a certain temperature even when deformed by an external force. As shape memory alloys having superelastic effects, there are various types such as Ni-Ti, Cu-Al-Ni, Cu-Zn, Cu-Zn-Al, Cu-Al-Mn, Ti-Nb-Al, Ni-Al, etc. Metal-based alloys have been developed.

最近、Mgを主成分とし、合金元素として、Sc、Y、La、Ce、Pr等から選択される少なくとも1種の元素を成分として含有し、一方向結晶構造を有するMg合金が擬弾性を有することが開示されている(特許文献4)。Mg合金が擬弾性を有する機構として、Sc、Y、La、Ce、Pr等を添加することにより、Mgの六方晶の底面すべりを抑制し、双晶の発生を促進する機構が開示されている。特許文献4には、実施例としてYを1.0〜1.7原子%添加したMg合金が開示されており、他の元素を含んだ際の擬弾性については開示されていないが、母相に添加する元素成分は1.0〜6.0原子%の範囲を想定しているものと認められる。ただし、双晶の可逆変化に起因する擬弾性では、残留歪みが多く、90%以上のほぼ完全な形状回復は見込めない。また、良好な形状回復を得るためには単結晶とする必要があり実用には限界がある。   Recently, an Mg alloy having a unidirectional crystal structure having Mg as a main component and containing at least one element selected from Sc, Y, La, Ce, Pr and the like as an alloy element has pseudoelasticity. (Patent Document 4). As a mechanism in which Mg alloy has pseudoelasticity, a mechanism is disclosed in which Sc, Y, La, Ce, Pr, etc. are added to suppress the bottom slip of Mg hexagonal crystal and promote the generation of twins. . Patent Document 4 discloses an Mg alloy to which Y is added in an amount of 1.0 to 1.7 atomic% as an example and does not disclose pseudoelasticity when other elements are included. It is recognized that the elemental component to be added is assumed to be in the range of 1.0 to 6.0 atomic%. However, the pseudoelasticity resulting from the reversible change of twins has many residual strains, and almost complete shape recovery of 90% or more cannot be expected. Further, in order to obtain a good shape recovery, it is necessary to use a single crystal, and there is a limit to practical use.

本発明者らは、Mg合金の結晶構造に着目し研究を行ってきた。Mg合金は異方性の高いHCP構造をとるために冷間加工性が悪いと考え、BCC構造を有するMg合金を探索した。状態図の解析から、Mg-Li合金以外に、Scを加えたMg-Sc合金が高Mg濃度においてBCC構造が存在すると予測された。本発明者らはすでにScを加えたMg合金を製造し、二相組織制御の可能性や機械的特性との関係、さらに結晶配向性について解析し報告している(非特許文献4〜8)。特に、BCC相とHCP相の二相とすることにより、高強度化が可能であることを示している(非特許文献4)。また、175℃〜400℃の温度で時効処理することにより、BCC相内に微細なHCP構造析出物が生成する事によって、硬化する事を見出している(非特許文献5、6)。   The present inventors have conducted research focusing on the crystal structure of the Mg alloy. Since the Mg alloy has a highly anisotropic HCP structure, it is considered that the cold workability is poor, and an Mg alloy having a BCC structure was searched. From the analysis of the phase diagram, it was predicted that the Mg—Sc alloy with Sc added in addition to the Mg—Li alloy has a BCC structure at a high Mg concentration. The present inventors have already manufactured an Mg alloy to which Sc is added, and analyzed and reported the possibility of controlling the two-phase structure, the relationship with the mechanical properties, and the crystal orientation (Non-Patent Documents 4 to 8). . In particular, it is shown that the strength can be increased by using two phases of a BCC phase and an HCP phase (Non-Patent Document 4). Further, it has been found that by performing an aging treatment at a temperature of 175 ° C. to 400 ° C., fine HCP structure precipitates are generated in the BCC phase, thereby hardening (Non-Patent Documents 5 and 6).

特開2011−58089号公報JP 2011-58089 A 特開2001−40445号公報JP 2001-40445 A 特開2004−124156号公報JP 2004-124156 A 特開2015−63746号公報Japanese Patent Laying-Open No. 2015-63746

Miura, H. et al.,2010, Trans. Nonferrous Met. Soc. China, Vol. 20, p.1294-1298.Miura, H. et al., 2010, Trans. Nonferrous Met. Soc. China, Vol. 20, p.1294-1298. Kim, W.J. et al., Acta Materialia, 2003, Vol.51, pp.3293-3307.Kim, W.J. et al., Acta Materialia, 2003, Vol.51, pp.3293-3307. Sanschagrin, A. et al., 1996, Mater. Sci. Eng.A, A220, pp.69-77.Sanschagrin, A. et al., 1996, Mater. Sci. Eng. A, A220, pp. 69-77. 安藤大輔ら、軽金属学会第126回春期大会講演概要(2014)、pp.147−148.Daisuke Ando et al., Abstracts of the 126th Spring Meeting of the Light Metal Society (2014), pp.147-148. 小川由希子ら、軽金属学会第128回春期大会講演概要(2015)、pp.47−48.Yukiko Ogawa et al., The Light Metal Society 128th Spring Conference Outline (2015), pp. 47-48. Ando D. et al.,Materials Letters, 2015, Vol.161, pp.5-8, (available online 17 Jun 2015)Ando D. et al., Materials Letters, 2015, Vol.161, pp.5-8, (available online 17 Jun 2015) Ogawa, Y., et al.,Mater. Sci. Eng.A, 2016, A670, p.335-341.Ogawa, Y., et al., Mater. Sci. Eng. A, 2016, A670, p.335-341. Ogawa, Y., et al.,Scripta Materialia, doi.org/10.1016/j.scriptamat.2016.09.024Ogawa, Y., et al., Scripta Materialia, doi.org/10.1016/j.scriptamat.2016.09.024 Ogawa Y., et al.,Science, 2016, Vol.353(6297), pp.368-370.Ogawa Y., et al., Science, 2016, Vol.353 (6297), pp.368-370. 小川由希子ら、日本金属学会講演大会概要集CD(第159回金属学会秋季大会)、2016年、ISSN 1342−5730、339Yukiko Ogawa et al., The Japan Institute of Metals Conference Summary Collection CD (159th Annual Meeting of the Japan Institute of Metals), 2016, ISSN 1342-5730, 339 マグネシウム技術便覧 日本マグネシウム協会編 カロス出版株式会社 2000年、第4、5章 p71〜129.Magnesium Technical Handbook Japan Magnesium Association, Karos Publishing Co., Ltd. 2000, Chapters 4, 5 p71-129.

上記のようにMg-Sc合金についての解析は行われてきているもののMg-Sc合金の組織制御の方法や、機械的特性の詳細には未だに不明の点が多い。さらに、超弾性、形状記憶特性を備え、かつ冷間加工性に優れたMg合金は未だに開発されていない。本発明は、超弾性効果及び/又は形状記憶効果を有し、かつ冷間加工性に優れたMg合金を提供することを課題とする。   Although analysis of the Mg—Sc alloy has been conducted as described above, there are still many unclear points regarding the method of controlling the structure of the Mg—Sc alloy and the details of the mechanical properties. Furthermore, an Mg alloy having superelasticity and shape memory characteristics and excellent cold workability has not been developed yet. An object of the present invention is to provide an Mg alloy having a superelastic effect and / or a shape memory effect and excellent in cold workability.

本発明者らは、鋭意研究の結果、特定の組成範囲を有するBCC構造を持つMg−Sc合金が、応力誘起変態に付随して超弾性効果を発現する事を見出した。さらに、形状記憶効果を有することを見出した(非特許文献9、10)。本発明は、以下に示すMgにScを一定量添加した合金、及びその製造方法に関する。   As a result of intensive studies, the present inventors have found that an Mg—Sc alloy having a BCC structure having a specific composition range exhibits a superelastic effect accompanying a stress-induced transformation. Furthermore, it discovered that it had a shape memory effect (nonpatent literature 9, 10). The present invention relates to an alloy in which a certain amount of Sc is added to Mg shown below and a method for producing the same.

(1)Mgを主成分とする合金であって、Scを13原子%より多く、30原子%以下の範囲で含有し、残部がMg及び不可避不純物からなり、BCC相を有する超弾性効果及び/又は形状記憶効果を備えたMg合金。
(2)前記組成に加えて、添加元素としてLi、Al、Zn、Y、Ag、In、Sn及びBiからなる群から選ばれる少なくとも一種以上を、合金全体を100原子%として、合計で0.001以上9原子%以下含有する(1)に記載の超弾性効果及び/又は形状記憶効果を備えたMg合金。
(3)前記組成に加えて、添加元素としてCa、Mn、Zr、及びCeからなる群から選ばれる少なくとも一種以上を、合金全体を100原子%として、合計で0.01以上2.0原子%以下、かつ添加元素全量が9原子%以下となるように含有する(1)又は(2)に記載の超弾性効果及び/又は形状記憶効果を備えたMg合金。
(4)超弾性効果及び/又は形状記憶効果を備えたMg合金の製造方法であって、Mgを主成分とし、Scを13原子%より多く、30原子%以下の範囲で含有し、残部がMg及び不可避不純物となるように500℃以上の温度で溶体化し、1000℃/分より速い冷却速度で冷却処理するMg合金の製造方法。
(5)前記組成に加えて、添加元素としてLi、Al、Zn、Y、Ag、In、Sn及びBiからなる群から選ばれる少なくとも一種以上を、合金全体を100原子%として、合計で0.001以上9原子%以下含有させ、溶体化を行う(4)記載のMg合金の製造方法。
(6)前記組成に加えて、添加元素としてCa、Mn、Zr、及びCeからなる群から選ばれる少なくとも一種以上を、合金全体を100原子%として、合計で0.01以上2.0原子%以下、かつ添加元素全量が9原子%以下となるように含有させ、溶体化を行う(4)又は(5)に記載のMg合金の製造方法。
(7)100℃〜400℃の温度範囲にて時効処理する(4)〜(6)いずれか1つに記載のMg合金の製造方法。
(8)(4)〜(7)のいずれか1つに記載の製造方法によって製造されることを特徴とする超弾性効果及び/又は形状記憶効果を備えたMg合金。
(1) An alloy containing Mg as a main component, containing Sc in a range of more than 13 atomic% to 30 atomic% or less, the balance being Mg and inevitable impurities, and having a BCC phase and / or Or Mg alloy with shape memory effect.
(2) In addition to the above composition, at least one or more selected from the group consisting of Li, Al, Zn, Y, Ag, In, Sn, and Bi as additive elements, with the total alloy as 100 atomic%, a total of 0.8. Mg alloy provided with superelastic effect and / or shape memory effect according to (1), which is contained in an amount of 001 to 9 atomic%.
(3) In addition to the above composition, at least one or more selected from the group consisting of Ca, Mn, Zr, and Ce as additive elements, with the total alloy as 100 atomic%, a total of 0.01 or more and 2.0 atomic% The Mg alloy having the superelastic effect and / or shape memory effect according to (1) or (2), which is contained so that the total amount of additive elements is 9 atomic% or less.
(4) A method for producing an Mg alloy having a superelastic effect and / or a shape memory effect, comprising Mg as a main component, containing Sc in a range of more than 13 atomic% and 30 atomic% or less, with the balance being A method for producing an Mg alloy, which is formed into a solution at a temperature of 500 ° C. or higher so as to be Mg and inevitable impurities, and is cooled at a cooling rate faster than 1000 ° C./min.
(5) In addition to the above composition, at least one selected from the group consisting of Li, Al, Zn, Y, Ag, In, Sn, and Bi as an additive element, the total alloy as 100 atomic%, and a total of 0. (4) The manufacturing method of Mg alloy as described in (4) which makes it contain 001 or more and 9 atomic% or less, and performs solution treatment.
(6) In addition to the above composition, at least one or more selected from the group consisting of Ca, Mn, Zr, and Ce as additive elements, with the total alloy as 100 atomic%, a total of 0.01 or more and 2.0 atomic% The method for producing an Mg alloy according to (4) or (5), wherein the additive element is contained so that the total amount of additive elements is 9 atomic% or less and solution treatment is performed.
(7) The method for producing an Mg alloy according to any one of (4) to (6), wherein the aging treatment is performed in a temperature range of 100 ° C to 400 ° C.
(8) An Mg alloy having a superelastic effect and / or a shape memory effect, which is produced by the production method according to any one of (4) to (7).

本発明のMg合金は、冷間加工性に優れると共に、超弾性効果、形状記憶効果を発現する。したがって、様々な分野での応用を期待することができる。特に、Mgは生体内で溶解するため、ステント等生体内に留置する医療用材料に用いれば、再度患者から摘出する必要がないため、患者の負担を軽減することができ非常に有用である。   The Mg alloy of the present invention is excellent in cold workability and exhibits a superelastic effect and a shape memory effect. Therefore, application in various fields can be expected. In particular, since Mg dissolves in the living body, if it is used as a medical material such as a stent that is placed in the living body, it is not necessary to remove it from the patient again, which can reduce the burden on the patient and is very useful.

また、軽量かつ比強度が高いというMg合金の特性に加えて冷間加工性に優れていることから、航空宇宙分野や自動車分野等における種々の構造材料への応用が期待できる。   Further, since it is excellent in cold workability in addition to the properties of Mg alloy that is lightweight and high in specific strength, it can be expected to be applied to various structural materials in the aerospace field, the automobile field, and the like.

実施例1のMg合金の応力―歪み曲線を示すグラフである。3 is a graph showing a stress-strain curve of the Mg alloy of Example 1. 実施例1のMg合金の応力−歪みサイクル試験図である。2 is a stress-strain cycle test diagram of the Mg alloy of Example 1. FIG. 図2Aの応力−歪み曲線により得られたεtとεSEの関係を示すグラフである。It is a graph which shows the relationship between (epsilon) t and (epsilon) SE obtained by the stress-strain curve of FIG. 2A. 実施例1、4、6、比較例3の熱処理後のX線回折結果を示す図である。It is a figure which shows the X-ray-diffraction result after the heat processing of Example 1, 4, 6 and the comparative example 3. FIG. 実施例1のMg合金に応力を負荷しながらX線解析を行った結果を示す図である。It is a figure which shows the result of having performed X-ray analysis, applying stress to Mg alloy of Example 1. FIG. Mg合金のX線回折パターンを示す図。図5AはSc20.5原子%を含むMg合金、図5BはSc19.2原子%を含むMg合金の結果を示す。The figure which shows the X-ray-diffraction pattern of Mg alloy. FIG. 5A shows the result of the Mg alloy containing 20.5 atomic% of Sc, and FIG. 5B shows the result of the Mg alloy containing 19.2 atomic% of Sc. 板状のMg合金試料が温度変化により形状回復する様子を示す写真。The photograph which shows a mode that a plate-shaped Mg alloy sample recovers shape by a temperature change. 降伏応力σy、超弾性回復歪み量εSE i=3と試料の板厚に対する相対結晶粒径の関係を示す図。The figure which shows the relationship between the yield stress (sigma) y, the superelastic recovery strain amount (epsilon) SEi = 3, and the relative crystal grain diameter with respect to the plate | board thickness of a sample.

以下、実施例を示しながら本発明を説明するが、本発明は、以下の実施例によってなんら限定されるものではない。すなわち、本発明の技術思想の範囲における他の例、態様等を当然含むものである。   EXAMPLES Hereinafter, although this invention is demonstrated, showing an Example, this invention is not limited at all by the following Examples. That is, other examples, aspects, and the like within the scope of the technical idea of the present invention are naturally included.

先ず、本発明の合金組成について説明する。本発明のMg合金は、Scを13原子%より多く、30原子%以下の範囲で含む。添加するScは、13原子%以下ではBCC相が得られず超弾性効果、形状記憶効果を得ることができない。また、30原子%以上であると延性に乏しく、粒界破壊が生じてしまう。   First, the alloy composition of the present invention will be described. The Mg alloy of the present invention contains Sc in a range of more than 13 atomic% and 30 atomic% or less. When the added Sc is 13 atomic% or less, a BCC phase cannot be obtained and a superelastic effect and a shape memory effect cannot be obtained. Further, if it is 30 atomic% or more, the ductility is poor, and grain boundary fracture occurs.

本発明のMg合金は、必要に応じて、Li、Al、Zn、Y、Ag、In、Sn及びBiからなる群から選ばれた少なくとも一種以上の添加元素を、合金全体を100原子%として、合計で0.001〜9原子%を含有してもよい。これら元素を含有することにより一層の超弾性効果の向上及び機械的強度の調整が期待できる。添加元素は、9原子%を超えると合金が脆化するために加工性が悪くなる恐れがある。また、0.001原子%より少ない場合には効果を期待することができない。ここで、Liは、BCC構造を安定にする元素であり、加工性向上に有効であると考えられる。Al、Zn、Y、Ag、In及びSnは、固溶硬化あるいは析出硬化により強度を向上させる効果を有し、転位の移動を抑制するため超弾性効果の向上に有効であると考えられる。   The Mg alloy of the present invention, if necessary, at least one or more additive elements selected from the group consisting of Li, Al, Zn, Y, Ag, In, Sn and Bi, with the whole alloy as 100 atomic%, You may contain 0.001-9 atomic% in total. By containing these elements, further improvement of the superelastic effect and adjustment of mechanical strength can be expected. If the additive element exceeds 9 atomic%, the alloy becomes brittle and the workability may deteriorate. In addition, when it is less than 0.001 atomic%, the effect cannot be expected. Here, Li is an element that stabilizes the BCC structure and is considered to be effective in improving workability. Al, Zn, Y, Ag, In, and Sn have the effect of improving the strength by solid solution hardening or precipitation hardening, and are considered to be effective in improving the superelastic effect because they suppress the movement of dislocations.

さらに、超弾性効果は損なわずに、結晶組織を微細にするCa、Mn、Zr、Ceからなる群から選ばれた少なくとも1種以上の元素を添加してもよい。これら元素は結晶粒を微細化する事により、高強度化及び高延性化する事ができることが知られていることから、Mg合金の高強度化、高延性化が期待できる(非特許文献11)。これら添加元素は、合金全体を100原子%として、0.01〜2原子%含有させることができる。添加元素は、2原子%を超えると脆化の恐れがある。また、0.01原子%より少ない場合には高強度化、高延性化の効果を期待することができない。   Furthermore, at least one element selected from the group consisting of Ca, Mn, Zr, and Ce that makes the crystal structure fine may be added without impairing the superelastic effect. Since it is known that these elements can be increased in strength and ductility by refining crystal grains, it is possible to expect an increase in strength and ductility of Mg alloys (Non-patent Document 11). . These additive elements can be contained in an amount of 0.01 to 2 atomic%, with the entire alloy being 100 atomic%. If the additive element exceeds 2 atomic%, there is a risk of embrittlement. On the other hand, when the content is less than 0.01 atomic%, the effect of increasing strength and increasing ductility cannot be expected.

続いて、本発明の合金の製造方法について説明する。本発明のMg合金を製造する場合は、前記各元素を所定量添加し不活性ガス雰囲気中で溶解する。溶解に際しては、高周波加熱溶解が好ましい。溶解した合金を溶解インゴットとし、熱間圧延及び冷間圧延を行い、所定の形状に加工する。   Then, the manufacturing method of the alloy of this invention is demonstrated. When the Mg alloy of the present invention is produced, a predetermined amount of each element is added and dissolved in an inert gas atmosphere. In dissolution, high-frequency heating dissolution is preferable. The melted alloy is used as a melted ingot, and hot rolling and cold rolling are performed and processed into a predetermined shape.

次に、所定の形状に加工したMg合金を溶体化温度範囲まで加熱し、結晶組織をBCC相に変態させた後、急冷する溶体化処理を行う。溶体化処理は500℃以上の温度で行う。溶体化の温度は試料の組成によって異なるが、一般にSc量を多くするにつれて、温度を下げることが可能となる。Sc量が比較的多い合金では500℃程度の温度で完全な溶体化が可能であるが、Sc量が低い合金の場合は、より高温で溶体化をする必要がある。溶体化処理が550℃以上であれば完全に溶体化することから、処理温度は、550℃以上800℃以下であるのが好ましい。550℃以下の温度であると、Sc量の低い合金では、多量のHCP相が形成される場合があり超弾性効果が得られない。一方、800℃以上では材料が溶け始めてしまう。処理温度での保持時間は1分以上あれば良いが、24時間を超えると酸化の影響が無視できなくなる。したがって、処理温度は、1分から24時間の範囲であるのが好ましい。溶体化温度域に加熱後、急冷することにより、BCC相を有するMg−Sc合金を製造することができる。超弾性回復率からは、冷却速度は、1000℃/分以上であることが好ましい。   Next, the Mg alloy processed into a predetermined shape is heated to a solution temperature range to transform the crystal structure into a BCC phase, and then subjected to a solution treatment for rapid cooling. The solution treatment is performed at a temperature of 500 ° C. or higher. The solution temperature varies depending on the composition of the sample, but generally the temperature can be lowered as the amount of Sc is increased. An alloy with a relatively large amount of Sc can be completely solutionized at a temperature of about 500 ° C., but an alloy with a low amount of Sc needs to be solutionized at a higher temperature. If the solution treatment is 550 ° C. or higher, the solution is completely dissolved, so that the processing temperature is preferably 550 ° C. or higher and 800 ° C. or lower. When the temperature is 550 ° C. or lower, an alloy having a low amount of Sc may form a large amount of HCP phase and a superelastic effect cannot be obtained. On the other hand, at 800 ° C. or higher, the material starts to melt. The holding time at the treatment temperature may be 1 minute or longer, but if it exceeds 24 hours, the influence of oxidation cannot be ignored. Accordingly, the treatment temperature is preferably in the range of 1 minute to 24 hours. An Mg—Sc alloy having a BCC phase can be produced by rapid cooling after heating to the solution temperature range. From the superelastic recovery rate, the cooling rate is preferably 1000 ° C./min or more.

さらに、時効処理を施すことにより、材料の硬度を上昇させることが可能である。高硬度となることで超弾性特性、特に、繰り返し特性を改善する事ができる。時効処理温度としては、100℃以上400℃以下であることが好ましい。   Furthermore, it is possible to raise the hardness of material by performing an aging treatment. Super-hardness characteristics, especially repeatability, can be improved by increasing the hardness. The aging treatment temperature is preferably 100 ° C. or higher and 400 ° C. or lower.

次に実施例及び比較例により本発明をさらに詳細に説明する。表1に示す組成で、MgにScを単独で(実施例1〜6)、あるいはさらにLi、Al、Zn、Y、Ag、In、Sn、Biを混合して(実施例7〜16)Mg合金を製造した。   Next, the present invention will be described in more detail with reference to examples and comparative examples. In the composition shown in Table 1, Mg alone is used for Sc (Examples 1 to 6), or Li, Al, Zn, Y, Ag, In, Sn, and Bi are further mixed (Examples 7 to 16). An alloy was produced.

具体的には、下記表1の実施例1〜16の合金組成になるように各材料を秤量し、アルゴンガス雰囲気下、高周波溶解炉を用いて溶解した。坩堝はアルミナ製坩堝を用い、溶解後、坩堝止めし溶解インゴットとした。次に600℃の温度にて2mm程度まで熱間圧延後、600℃の温度で焼鈍を繰り返しながら0.7mmまで冷間圧延を行った。得られた試料を500℃〜700℃の温度で30分の溶体化後、1000℃/分以上で急冷し、Mg合金試料を作製した。溶体化の温度は、BCC相単一相が得られる温度を光学顕微鏡観察を用いて調査し確認する。   Specifically, each material was weighed so as to have the alloy compositions of Examples 1 to 16 in Table 1 below, and melted using a high-frequency melting furnace in an argon gas atmosphere. As the crucible, an alumina crucible was used. After melting, the crucible was fastened to obtain a melting ingot. Next, after hot rolling to about 2 mm at a temperature of 600 ° C., cold rolling was performed to 0.7 mm while repeating annealing at a temperature of 600 ° C. The obtained sample was melted at a temperature of 500 ° C. to 700 ° C. for 30 minutes, and then rapidly cooled at 1000 ° C./min or more to prepare an Mg alloy sample. The solution temperature is confirmed by investigating the temperature at which a single BCC phase is obtained using optical microscope observation.

比較例1〜4の合金は、表1に示す組成で材料を秤量し、実施例と同様にして高周波溶解炉を用いて溶解した。次に、比較例1及び2は、600℃の温度にて、2mm程度まで熱間圧延後、600℃の温度で焼鈍を繰り返しながら0.7mmまで冷間圧延を行った。一方、比較例3及び4は、300℃の温度にて、2mm程度まで熱間圧延後、300℃の温度で焼鈍を繰り返しながら0.7mmまで冷間圧延を行った。得られた試料を300℃の温度にて30分の熱処理、及び1000℃/分以上で急冷し、Mg合金試料を作製した。熱間圧延の温度やその後の熱処理温度が各試料で異なるのは、試料の組成によって溶融温度が異なるためである。   The alloys of Comparative Examples 1 to 4 were weighed with the compositions shown in Table 1 and melted using a high-frequency melting furnace in the same manner as in the Examples. Next, Comparative Examples 1 and 2 were hot-rolled to about 2 mm at a temperature of 600 ° C., and then cold-rolled to 0.7 mm while repeating annealing at a temperature of 600 ° C. On the other hand, Comparative Examples 3 and 4 were hot-rolled to about 2 mm at a temperature of 300 ° C., and then cold-rolled to 0.7 mm while repeating annealing at a temperature of 300 ° C. The obtained sample was heat-treated at a temperature of 300 ° C. for 30 minutes and rapidly cooled at 1000 ° C./min or more to prepare a Mg alloy sample. The reason why the hot rolling temperature and the subsequent heat treatment temperature are different for each sample is that the melting temperature differs depending on the composition of the sample.

次に、各合金で試験片を作製し、超弾性を示すか測定を行った。各試験片は、表面を機械研磨し、最終厚さを0.5mmとした。引張試験片のサイズは、3.5mm幅、0.5mm厚、標点間距離10mmとし、−150℃の試験温度にて、0.5mm/分の引張速度にて試験を行った。4%の予歪みを負荷後、応力を除荷する事により、与えた歪みの超弾性形状回復率を求めた。   Next, a test piece was prepared with each alloy and measured to show superelasticity. The surface of each test piece was mechanically polished to a final thickness of 0.5 mm. The tensile test pieces were 3.5 mm wide, 0.5 mm thick, and the distance between the gauge points was 10 mm, and the test was performed at a test temperature of −150 ° C. and a tensile speed of 0.5 mm / min. After applying a pre-strain of 4%, the stress was unloaded to obtain the superelastic shape recovery rate of the applied strain.

ここで、超弾性形状回復率は、4%の引張歪みの除荷負荷後の超弾性に伴う形状回復量と定義し、次式より評価した。
Here, the superelastic shape recovery rate was defined as the amount of shape recovery accompanying superelasticity after unloading with a tensile strain of 4%, and was evaluated from the following equation.

一例として実施例1の試料において得られた応力―歪み曲線を図1に示す。応力を印加すると、まず、応力に比例して弾性歪みが発生する。降伏点(図1では1%歪み付近)に達すると、その後は応力を大きく増加しなくとも歪みが発生する。4%の予歪みを負荷後、応力を除荷する事により、実施例1の試料では与えた歪みがほぼ元の状態に復元する優れた超弾性効果が出現していることが分かる。   As an example, the stress-strain curve obtained for the sample of Example 1 is shown in FIG. When stress is applied, first, elastic strain is generated in proportion to the stress. When the yield point (in the vicinity of 1% strain in FIG. 1) is reached, after that, strain occurs even if the stress is not increased greatly. It can be seen that by applying the 4% pre-strain and then unloading the stress, the sample of Example 1 has an excellent superelastic effect in which the applied strain is restored almost to its original state.

なお、図1に示すように、εtは「引張負荷歪み量(4%)から弾性変形による回復分を差し引いた予歪み量」及びεSEは「超弾性回復歪み量」である。種々の組成の合金を用い超弾性形状回復率を求めた。結果を表1に示す。
As shown in FIG. 1, ε t is “a pre-strain amount obtained by subtracting a recovery amount due to elastic deformation from a tensile load strain amount (4%)”, and ε SE is a “super elastic recovery strain amount”. Superelastic shape recovery rates were determined using alloys of various compositions. The results are shown in Table 1.

表1に示すように、Mgに13原子%Scを単独で添加した場合(比較例2)では、全く超弾性を示さなかった。一方、14.5原子%Scを添加した場合(実施例3)は、75%の超弾性形状回復率を示した。Sc量が13原子%より少ない場合には、他の元素と併せて14原子%の組成(Sc10原子%−Al4原子%、比較例1)であっても、全く超弾性を示さなかった。したがって、13原子%より多くScを添加することが超弾性効果を有するためには必要であると結論付けた。   As shown in Table 1, when 13 atomic% Sc was added alone to Mg (Comparative Example 2), no superelasticity was shown. On the other hand, when 14.5 atomic% Sc was added (Example 3), the superelastic shape recovery rate was 75%. When the amount of Sc was less than 13 atomic%, even when the composition was 14 atomic% (Sc 10 atomic% -Al 4 atomic%, Comparative Example 1) together with other elements, no superelasticity was exhibited. Therefore, it was concluded that adding more Sc than 13 atomic% is necessary to have a superelastic effect.

また、Sc単独でMgに添加する場合には、Scを20.5原子%以上加えることにより90%以上の超弾性形状回復率を得ることができる(実施例1)。したがって、20.5原子%以上のScを添加した合金組成とすることが好ましい。26.5原子%Scを添加している実施例5と、29.5原子%Scを添加している実施例6を比較すると、Sc量の少ない実施例5の方が超弾性形状回復率は高くなっている。Sc単独で添加する場合には、添加するSc量は26.5原子%付近をピークとして、高い超弾性形状回復率を得ることができるものと考えられる。   When Sc alone is added to Mg, a superelastic shape recovery rate of 90% or more can be obtained by adding 20.5 atomic% or more of Sc (Example 1). Therefore, it is preferable to use an alloy composition to which 20.5 atomic% or more of Sc is added. Comparing Example 5 to which 26.5 atomic% Sc is added and Example 6 to which 29.5 atomic% Sc is added, the superelastic shape recovery rate is higher in Example 5 having a smaller amount of Sc. It is high. In the case of adding Sc alone, it is considered that the amount of Sc to be added can obtain a high superelastic shape recovery rate with a peak at around 26.5 atomic%.

さらに、Scに加えてLi、Al、Zn、Y、Ag、In、Sn及びBiを添加元素として加えた場合も、同様に高い超弾性形状回復率を示す(実施例7〜16)。Sc以外に添加する元素、及び添加量によって超弾性形状回復率は変動するが、Sc単独で添加した場合に比べて超弾性の向上を得ることができる。例えば、実施例10のMg合金のSc添加量は18原子%と少ないが、超弾性回復率は88%である。これに対し、Scを単独で19.5原子%添加した実施例2の合金の超弾性回復率は77%であり、実施例10のMg合金の超弾性回復率の方が高い値となっている。   Further, when Li, Al, Zn, Y, Ag, In, Sn, and Bi are added as additive elements in addition to Sc, a high superelastic shape recovery rate is similarly exhibited (Examples 7 to 16). Although the superelastic shape recovery rate varies depending on the element added in addition to Sc and the addition amount, the superelasticity can be improved as compared with the case of adding Sc alone. For example, the amount of Sc added to the Mg alloy of Example 10 is as small as 18 atomic%, but the superelastic recovery rate is 88%. In contrast, the superelastic recovery rate of the alloy of Example 2 to which 19.5 atomic% of Sc was added alone was 77%, and the superelastic recovery rate of the Mg alloy of Example 10 was higher. Yes.

また、ここでは示さないが、上述のように、Liは、加工性向上に、Al、Zn、Y、Ag、In及びSnは、固溶硬化あるいは析出硬化により強度の向上に寄与することから、これらの添加元素を加えることによって、超弾性効果の向上以外の機械的特性の向上も期待することができる。そのため、複数の添加元素を加えることにより超弾性効果の他に、異なる機械的特性の向上を期待することができる。   Although not shown here, as described above, Li contributes to improving workability, and Al, Zn, Y, Ag, In and Sn contribute to improving strength by solid solution hardening or precipitation hardening. By adding these additive elements, it is possible to expect an improvement in mechanical properties other than an improvement in the superelastic effect. Therefore, the addition of a plurality of additive elements can be expected to improve different mechanical properties in addition to the superelastic effect.

さらに、Ca、Mn、Zr、及びCeからなる群から選ばれる少なくとも一種以上の添加元素を加えてもよい。Ca、Mn、Zr及びCeを添加することにより、結晶組織が微細になることから強度の上昇及び加工性の向上が期待できる。   Further, at least one or more additive elements selected from the group consisting of Ca, Mn, Zr, and Ce may be added. By adding Ca, Mn, Zr and Ce, the crystal structure becomes fine, so that an increase in strength and an improvement in workability can be expected.

実施例1のMg合金試料について、引張サイクル試験を行い、得られる最大超弾性歪み量を評価した。引張サイクル試験は、引張負荷歪み量(ε)を徐々に増加し、超弾性回復歪み量(εSE)を測定した結果である。図2Aに、応力−歪みサイクル試験図を示している。σは降伏応力、ε はサイクルiにおける引張負荷歪み量、εe はサイクルiにおける純弾性回復歪み量、εSE はサイクルiにおける超弾性回復歪み量、ε はサイクルiにおける残留歪み量である。合金試料は、第1サイクルにおいて、歪み量1%まで張力を負荷し、除荷する。第2サイクルにおいて、歪み量2%まで張力を負荷し、徐荷する。これを第8サイクルまで繰り返しながら、応力を測定したものである。図2Bに、引張サイクル試験の測定結果から得られた引張負荷歪み量と超弾性回復歪み量の関係を示しているが、実施例1のMg合金の最大純弾性回復歪み量は、4.4%であった。また、ここでは結果を示さないが、他の実施例のMg合金も同等の最大純弾性回復歪み量であった。The Mg alloy sample of Example 1 was subjected to a tensile cycle test, and the maximum amount of superelastic strain obtained was evaluated. The tensile cycle test is the result of gradually increasing the tensile load strain amount (ε t ) and measuring the superelastic recovery strain amount (ε SE ). FIG. 2A shows a stress-strain cycle test diagram. σ y is the yield stress, ε t i is the tensile load strain amount in cycle i, ε e i is the pure elastic recovery strain amount in cycle i, ε SE i is the super elastic recovery strain amount in cycle i, and ε r i is cycle i. Is the amount of residual strain at. In the first cycle, the alloy sample is unloaded by applying a tension of 1% strain. In the second cycle, the tension is applied to a strain amount of 2% and the load is gradually reduced. The stress was measured while repeating this up to the eighth cycle. FIG. 2B shows the relationship between the tensile load strain amount and the superelastic recovery strain amount obtained from the measurement result of the tensile cycle test. The maximum pure elastic recovery strain amount of the Mg alloy of Example 1 is 4.4. %Met. Further, although the results are not shown here, the Mg alloys of other examples also had the same maximum pure elastic recovery strain amount.

また、Scを全く添加しない既存のMg合金(AZ31:比較例3、ZK60:比較例4)は、表1に示すように超弾性を示さなかった。これら既存のMg合金はHCP構造であることが示されており、BCC構造を有することがMg合金の場合には超弾性の発現に重要であることが示唆される。   Further, as shown in Table 1, the existing Mg alloy (AZ31: Comparative Example 3, ZK60: Comparative Example 4) to which no Sc was added did not exhibit superelasticity. These existing Mg alloys have been shown to have an HCP structure, suggesting that having a BCC structure is important for the development of superelasticity in the case of Mg alloys.

本発明者らは、Mg-Sc合金には、BCC構造を備えたものが存在することをすでに明らかにしているが、超弾性特性を発現するMg合金とBCC構造との関係についてX線回折を行い結晶構造の解析をした。   The present inventors have already clarified that some Mg—Sc alloys have a BCC structure, but X-ray diffraction was performed on the relationship between the Mg alloy exhibiting superelastic characteristics and the BCC structure. The crystal structure was analyzed.

実施例1、4、6、及び比較例3の合金は、上記と同様に熱処理により溶体化し、急冷して試験片を作製した。試験片は、10mm×20mm×0.7mmとし、試料表面を物理研磨にてミラー鏡面に仕上げた。作製した試験片についてX線回折を行った。X線回折装置は、Rigaku社製Ultimaを用い、θ/2θ法で、線源はCu K-αを用いた。結果を図3に示す。ここで、縦軸は対数スケールである。   The alloys of Examples 1, 4, 6 and Comparative Example 3 were formed into a solution by heat treatment in the same manner as described above, and rapidly cooled to prepare test pieces. The test piece was 10 mm × 20 mm × 0.7 mm, and the sample surface was finished to a mirror mirror surface by physical polishing. The produced test piece was subjected to X-ray diffraction. The X-ray diffractometer used was Rigaku's Ultima, the θ / 2θ method, and the radiation source was Cu K-α. The results are shown in FIG. Here, the vertical axis is a logarithmic scale.

実施例1、4及び6では、BCC相を示すピーク(図中○で示す。)の強度が大きく、実質的にBCC相単相であることが分かる。なお、実施例1では、HCP相を示すピーク(図中●で示す。)が若干観察されるが、これは、熱処理後の急冷中に生成したものであり、HCP相の分率は10体積%以下であった。一方、比較例3では、強いHCP相のピークが観察され、HCP相単相であることが分かる。このことから、BCC相が存在することが、超弾性特性の発現には重要であることが示された。
In Examples 1, 4 and 6, it can be seen that the peak (shown by ◯ in the figure) indicating the BCC phase has a large intensity and is substantially a single BCC phase. In Example 1, a peak indicating the HCP phase (indicated by a black circle in the figure) is slightly observed, which is generated during the rapid cooling after the heat treatment, and the HCP phase fraction is 10 vol. % Or less. On the other hand, in Comparative Example 3, a strong HCP phase peak is observed, indicating that the HCP phase is a single phase. From this, it was shown that the presence of the BCC phase is important for the development of superelastic properties.

また、実施例1の試料に応力を負荷しながら、−150℃にてX線回折を行ったところ、BCC構造から斜方晶の構造を有する相が生成する事が分かった。図4は、実施例1の試料に応力を負荷しながら、−150℃でX線回折を行った結果を示す。   Further, when X-ray diffraction was performed at −150 ° C. while applying stress to the sample of Example 1, it was found that a phase having an orthorhombic structure was generated from the BCC structure. FIG. 4 shows the result of X-ray diffraction performed at −150 ° C. while applying stress to the sample of Example 1.

実施例1の試料は、−150℃にて応力負荷無しの状態では、図3の実施例1の結果(室温、応力負荷無しの状態で測定)と同様に、BCC相が主相として観察され、若干、冷却中に生成したHCP相が観察される。一方で、図4に示すように、−150℃にて応力を負荷した状態では、その他に、斜方晶構造と思われる相が観察される(図中矢印)。この斜方晶生成物は、応力除荷後には消失する。この事は、BCC相を持つMg−Sc合金では、通常の形状記憶合金と同様に、応力誘起変態に伴い超弾性効果が得られることを意味している。このように、Mg−Sc合金では、BCC相における応力負荷−除荷に伴う可逆的な変態に伴い優れた超弾性形状回復率が得られる。   In the sample of Example 1, the BCC phase is observed as the main phase in the state without stress load at −150 ° C., similarly to the result of Example 1 in FIG. 3 (measured in the state without room temperature and stress load). Some HCP phases formed during cooling are observed. On the other hand, as shown in FIG. 4, in the state where stress is applied at −150 ° C., a phase that seems to be an orthorhombic structure is observed (arrow in the figure). This orthorhombic product disappears after stress unloading. This means that a Mg—Sc alloy having a BCC phase can obtain a superelastic effect in accordance with a stress-induced transformation, as in a normal shape memory alloy. As described above, in the Mg—Sc alloy, an excellent superelastic shape recovery rate is obtained in association with the reversible transformation accompanying the stress load-unloading in the BCC phase.

次に、溶体化後の冷却速度と超弾性特性の発現との相関について解析を行った。実施例1と同様の組成のMg合金(Sc20.5原子%を含むMg合金)を溶体化後、冷却速度を1000℃/秒、1000℃/分、100℃/分、20℃/分と変えてMg合金を製造した。製造したMg合金は引張試験を行い、超弾性形状回復率を測定した。また、X線回折を行い、相構造を解析した。結果を表2に示す。
Next, the correlation between the cooling rate after solution treatment and the development of superelastic properties was analyzed. After solutionizing the Mg alloy having the same composition as in Example 1 (Mg alloy containing 20.5 at% Sc), the cooling rate was changed to 1000 ° C./second, 1000 ° C./minute, 100 ° C./minute, and 20 ° C./minute. Thus, an Mg alloy was manufactured. The manufactured Mg alloy was subjected to a tensile test to measure the superelastic shape recovery rate. Further, X-ray diffraction was performed to analyze the phase structure. The results are shown in Table 2.

1000℃/秒及び1000℃/分で冷却した場合、70%以上の超弾性回復率が得られるが、100℃/分及び20℃/分で冷却した試料では、超弾性特性が得られなかった。Sc20.5原子%を含むMg合金を用いた場合、X線回折の結果から、1000℃/秒、1000℃/分で急速に冷却しても、少量のHCP相が含まれる。基本的に、熱処理後の冷却が遅くなればなるほど、HCP相が増加する。HCPの増加に伴って、超弾性回復率の発現も低下する。Mg-Sc合金の各組成において冷却温度による超弾性形状回復率は異なるが、1000℃/分より早い速度で冷却を行うことにより実施例に示したいずれの合金でも超弾性を発現することができる。   When cooled at 1000 ° C./second and 1000 ° C./minute, a superelastic recovery rate of 70% or more is obtained, but the samples cooled at 100 ° C./minute and 20 ° C./minute did not provide superelastic properties. . When an Mg alloy containing 20.5 atomic% of Sc is used, a small amount of HCP phase is contained even when rapidly cooled at 1000 ° C./second and 1000 ° C./minute from the results of X-ray diffraction. Basically, the slower the cooling after the heat treatment, the more the HCP phase increases. As the HCP increases, the expression of the superelastic recovery rate also decreases. Although the superelastic shape recovery rate depending on the cooling temperature is different in each composition of the Mg—Sc alloy, the superelasticity can be exhibited in any of the alloys shown in the examples by cooling at a rate faster than 1000 ° C./min. .

上記結果から、Mg合金が超弾性特性を備えるためには、Scを13原子%より多く、30原子%以下の範囲で含有するとともに、結晶構造としてBCC相をとることができるように溶体化後の冷却速度が非常に重要であることが示された。   From the above results, in order for the Mg alloy to have superelastic properties, it is necessary to contain Sc in a range of more than 13 atomic% and 30 atomic% or less, and after solutionization so that a BCC phase can be taken as a crystal structure. The cooling rate of was shown to be very important.

次に、これらMg合金が無応力下においてマルテンサイト変態を生じるか解析を行った。実施例1のMg合金(Sc20.5原子%を含むMg合金)、Sc19.2原子%を含むMg合金の試料を20℃及び−190℃でX線回折を行った(図5)。   Next, it was analyzed whether these Mg alloys cause martensitic transformation under no stress. Samples of the Mg alloy of Example 1 (Mg alloy containing 20.5 at% Sc) and Mg alloy containing 19.2 at% Sc were subjected to X-ray diffraction at 20 ° C. and −190 ° C. (FIG. 5).

図5Aは、BCC相を有するSc20.5原子%を含むMg合金の20℃と190℃のX線回折パターンを示したものである。まず、20℃でX線回折を行い、次に−190℃に冷却しX線回折を行った結果を示している。Sc20.5原子%を含むMg合金試料では、20℃と−190℃との間では変化がなく、この温度ではマルテンサイト変態は生じていないことを示している。   FIG. 5A shows X-ray diffraction patterns at 20 ° C. and 190 ° C. of an Mg alloy containing 20.5 atomic% of Sc having a BCC phase. First, the results of X-ray diffraction at 20 ° C., then cooled to −190 ° C. and X-ray diffraction are shown. In the Mg alloy sample containing 20.5 atomic% of Sc, there is no change between 20 ° C. and −190 ° C., indicating that no martensitic transformation occurs at this temperature.

Sc19.2原子%を含むMg合金の試料は、20℃、−190℃、20℃と温度を推移させ、それぞれの温度でX線回折を行った(図5B)。この組成では、−190℃まで冷却することにより、体心立方構造から斜方晶構造へとマルテンサイト変態(orthorohombic martensite phase、図中ortho−Mと表記)を生じている。マルテンサイト相は、再度温度を20℃まで上昇させることにより、BCC相に可逆的に変化する。この組成のMg合金では20℃と−190℃の間で温度依存的にマルテンサイト変態が起こることから、形状記憶特性を発現することが示唆された。   Samples of the Mg alloy containing Sc19.2 atomic% were subjected to X-ray diffraction at respective temperatures by changing the temperature to 20 ° C., −190 ° C., and 20 ° C. (FIG. 5B). In this composition, by cooling to -190 ° C., a martensitic transformation (orthohomomic martensite phase, expressed as ortho-M in the figure) from a body-centered cubic structure to an orthorhombic structure occurs. The martensite phase reversibly changes to the BCC phase by raising the temperature to 20 ° C. again. In the Mg alloy having this composition, martensitic transformation occurs between 20 ° C. and −190 ° C. in a temperature-dependent manner, suggesting that shape memory characteristics are exhibited.

そこで、Scを含むMg合金の形状記憶特性を発現するか解析を行った。Sc18.3原子%を含むMg合金の板状試料を表面歪み5%程度に液体窒素温度で変形させた後、試料温度をモニターしながら、ゆっくりと昇温した際の形状を観察した(図6)。この組成の試料では−30℃付近から形状回復が始まることが確認された。この結果は、Sc含有量が少ない方が、マルテンサイト変態温度が高くなることを示している。   Then, it analyzed whether the shape memory characteristic of Mg alloy containing Sc was expressed. After deforming a plate-like sample of Mg alloy containing Sc18.3 atomic% to a surface strain of about 5% at liquid nitrogen temperature, the shape when the temperature was slowly increased was observed while monitoring the sample temperature (FIG. 6). ). It was confirmed that shape recovery started from around −30 ° C. in the sample having this composition. This result shows that the one with less Sc content has a higher martensitic transformation temperature.

次に、Sc16.2原子%、Zn1.0原子%、Zr0.1%を含むMg合金の形状記憶特性について解析を行った。当該組成の試料を示差走査熱量計(Differntial scanning calorimetry、DSC)を用いて、マルテンサイト変態開始温度(Ms)、及び終了温度(Mf)、並びにマルテンサイト逆変態開始温度(As)、及び終了温度(Af)を解析した。その結果、Ms=5℃、Mf=−30℃、As=20℃、Af=50℃であった。   Next, the shape memory characteristics of the Mg alloy containing Sc16.2 atomic%, Zn 1.0 atomic%, and Zr 0.1% were analyzed. Using a differential scanning calorimeter (DSC), a martensitic transformation start temperature (Ms), an end temperature (Mf), a martensite reverse transformation start temperature (As), and an end temperature of the sample having the composition are used. (Af) was analyzed. As a result, Ms = 5 ° C., Mf = −30 ° C., As = 20 ° C., and Af = 50 ° C.

さらに、この組成の試料を用いて形状記憶特性について解析を行った。この組成の板材試料を表面歪み3%程度に液体窒素温度下で曲げ変形した後、50℃以上に加熱すると板状試料はほぼ真っ直ぐな形状に回復した。形状回復率は95%以上であり、上記DSCを用いた結果と良い一致を示していた。この結果は、Scを一定量含有していれば、Sc以外の原子を含むものでも形状記憶特性を備えていることを示している。また、この合金組成であれば、室温以上での形状回復が得られており、室温付近の環境温度での使用も可能である。本実施例のように、組成を調整することによって、室温付近の環境温度で形状記憶効果を発現する合金が得られるので応用範囲を広げることができる。   Furthermore, shape memory characteristics were analyzed using a sample having this composition. A plate material sample having this composition was bent and deformed to a surface strain of about 3% under liquid nitrogen temperature, and then heated to 50 ° C. or higher, the plate sample recovered to an almost straight shape. The shape recovery rate was 95% or more, which was in good agreement with the results using the DSC. This result indicates that, if a certain amount of Sc is contained, even those containing atoms other than Sc have shape memory characteristics. Also, with this alloy composition, shape recovery at room temperature or higher is obtained, and use at ambient temperatures near room temperature is also possible. By adjusting the composition as in this example, an alloy that exhibits a shape memory effect at an ambient temperature near room temperature can be obtained, so that the application range can be expanded.

次に、Sc20.5原子%を含むMg合金について、降伏応力σ、純弾性回復歪み量、試料の板厚に対する相対結晶粒径(結晶粒径d/試料板厚t)の関係を検討した。図2に示したような応力−歪みサイクル試験を行い、試料の板厚に対する相対結晶粒径に対する、降伏応力と3%の歪みを印加した後、除荷することによって得られる超弾性歪み量(εSE i=3)をそれぞれプロットした(図7)。Next, regarding the Mg alloy containing 20.5 atomic% of Sc, the relationship between the yield stress σ y , the pure elastic recovery strain, and the relative crystal grain size (crystal grain size d / sample thickness t) with respect to the sample thickness was examined. . A stress-strain cycle test as shown in FIG. 2 is performed, and after applying a yield stress and a strain of 3% to the relative crystal grain size with respect to the thickness of the sample, the amount of superelastic strain obtained by unloading ( ε SE i = 3 ) was plotted (FIG. 7).

試料の板厚に対する相対結晶粒径が大きくなると降伏応力は低下する一方で、超弾性特性は向上することが示された。これは、他の形状記憶合金で見られる性質と同様の傾向であった。図5に−190℃までのXRD結果を示したが、Sc20.5原子%の組成のMg合金の場合、絶対零度温度以上の温度範囲では熱的にマルテンサイト変態を生じない。しかし、絶対零度温度以上の温度範囲では、熱的にマルテンサイト変態を生じない組成のMg合金であっても、図7に示すように他の形状記憶合金で見られる性質と同様の性質が見られたことから、条件によっては形状回復する可能性を有する。   It was shown that when the relative crystal grain size with respect to the plate thickness of the sample increases, the yield stress decreases while the superelastic property improves. This was the same tendency as the properties found in other shape memory alloys. FIG. 5 shows the XRD results up to -190 ° C. In the case of a Mg alloy having a composition of Sc 20.5 atomic%, no martensitic transformation occurs thermally in the temperature range above the absolute zero temperature. However, in the temperature range above the absolute zero temperature, even a Mg alloy having a composition that does not thermally cause martensitic transformation has the same properties as those found in other shape memory alloys as shown in FIG. Therefore, there is a possibility of shape recovery depending on conditions.

本発明のMg合金は、冷間加工性に優れるとともに超弾性特性、及び形状記憶特性を発現する。本発明の超弾性特性、及び形状記憶特性を備えたMg合金は、その「軽い」という特徴から、航空宇宙分野や自動車分野等への利用が可能である。また、Mgは生体分解性を有することから、超弾性効果を備えたMg合金は、ステント等の医療機具に用いた場合には、一定期間体内に留置された後に溶解することが期待され、患者にとって大きなメリットとなる。   The Mg alloy of the present invention is excellent in cold workability and exhibits superelastic characteristics and shape memory characteristics. The Mg alloy having superelastic characteristics and shape memory characteristics of the present invention can be used in the aerospace field, the automobile field, and the like because of its “light” characteristics. In addition, since Mg is biodegradable, Mg alloys with superelastic effects are expected to dissolve after being placed in the body for a certain period of time when used in medical devices such as stents. It is a big merit for me.

Claims (7)

Mgを主成分とする合金であって、
Scを13原子%より多く、30原子%以下の範囲で含有し、
残部がMg及び不可避不純物からなり、
BCC相を有し、
BCC相以外の分率が10体積%以下である超弾性効果及び/又は形状記憶効果を備えたMg合金
An alloy material mainly composed of Mg,
Sc is contained in a range of more than 13 atomic% and 30 atomic% or less,
The balance consists of Mg and inevitable impurities,
Have a BCC phase ,
A Mg alloy material having a superelastic effect and / or a shape memory effect in which the fraction other than the BCC phase is 10% by volume or less .
前記組成に加えて、添加元素としてLi、Al、Zn、Y、Ag、In、Sn及びBiからなる群から選ばれる少なくとも一種以上を、
合金全体を100原子%として、合計で0.001以上9原子%以下含有する請求項1に記載の超弾性効果及び/又は形状記憶効果を備えたMg合金
In addition to the composition, at least one selected from the group consisting of Li, Al, Zn, Y, Ag, In, Sn and Bi as an additive element,
The Mg alloy material having a superelastic effect and / or a shape memory effect according to claim 1, wherein the total alloy material is 100 atomic% and the total content is 0.001 or more and 9 atomic% or less.
前記組成に加えて、添加元素としてCa、Mn、Zr、及びCeからなる群から選ばれる少なくとも一種以上を、
合金全体を100原子%として、合計で0.01以上2.0原子%以下、かつ添加元素全量が9原子%以下となるように含有する請求項1又は2に記載の超弾性効果及び/又は形状記憶効果を備えたMg合金
In addition to the composition, at least one selected from the group consisting of Ca, Mn, Zr, and Ce as an additive element,
The superelastic effect according to claim 1 or 2, wherein the total amount of the alloy material is 100 atomic% and the total content is 0.01 to 2.0 atomic% and the total amount of additive elements is 9 atomic% or less. Alternatively, an Mg alloy material having a shape memory effect.
超弾性効果及び/又は形状記憶効果を備えたMg合金の製造方法であって、
Mgを主成分とし、
Scを13原子%より多く、30原子%以下の範囲で含有し、残部がMg及び不可避不純物となるように500℃以上の温度で溶体化し、
1000℃/分より速い冷却速度で冷却処理し、
BCC相を有しBCC相以外の分率を10体積%以下とするMg合金の製造方法。
A method for producing an Mg alloy material having a superelastic effect and / or a shape memory effect,
Mg as the main component,
Containing Sc in a range of more than 13 atomic% and 30 atomic% or less, and solutionized at a temperature of 500 ° C. or higher so that the balance becomes Mg and inevitable impurities,
Cooling at a cooling rate faster than 1000 ° C / min ,
The manufacturing method of Mg alloy material which has a BCC phase and makes fractions other than a BCC phase 10 volume% or less .
前記組成に加えて、添加元素としてLi、Al、Zn、Y、Ag、In、Sn及びBiからなる群から選ばれる少なくとも一種以上を、
合金全体を100原子%として、合計で0.001以上9原子%以下含有させ、溶体化を行う請求項4記載のBCC相を有しBCC相以外の分率を10体積%以下とするMg合金の製造方法。
In addition to the composition, at least one selected from the group consisting of Li, Al, Zn, Y, Ag, In, Sn and Bi as an additive element,
Mg containing not less than 0.001% and not more than 9% by atom in total with the alloy material as a whole, and having a BCC phase according to claim 4 for solutionization, wherein the fraction other than the BCC phase is not more than 10% by volume. Manufacturing method of alloy material .
前記組成に加えて、添加元素としてCa、Mn、Zr、及びCeからなる群から選ばれる少なくとも一種以上を、
合金全体を100原子%として、合計で0.01以上2.0原子%以下、かつ添加元素全量が9原子%以下となるように含有させ、溶体化を行う請求項4又は5に記載のBCC相を有しBCC相以外の分率を10体積%以下とするMg合金の製造方法。
In addition to the composition, at least one selected from the group consisting of Ca, Mn, Zr, and Ce as an additive element,
6. The solution according to claim 4, wherein the total alloy material is 100 atomic%, and the total alloy material is contained in an amount of 0.01 to 2.0 atomic% and the total amount of additive elements is 9 atomic% or less, and solution treatment is performed. The manufacturing method of Mg alloy material which has a BCC phase and makes fractions other than a BCC phase 10 volume% or less .
100℃〜400℃の温度範囲にて時効処理する請求項4〜6いずれか1項に記載のBCC相を有しBCC相以外の分率を10体積%以下とするMg合金の製造方法。
The manufacturing method of Mg alloy material which has a BCC phase of any one of Claims 4-6 which carries out an aging treatment in the temperature range of 100 to 400 degreeC, and makes fractions other than a BCC phase 10 volume% or less .
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