JP6010366B2 - Al-Mg alloy material for high-pressure hydrogen gas - Google Patents
Al-Mg alloy material for high-pressure hydrogen gas Download PDFInfo
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Description
本発明は、耐水素脆性に優れたＡｌ−Ｍｇ系合金に関し、高圧力の水素ガス環境に直接暴露されて用いられる部材や、高圧水素ガス環境に暴露されると同時に荷重が負荷される状態で長時間用いられる部材に好適なＡｌ−Ｍｇ系合金に関するものである。特に、燃料電池自動車に搭載される高圧水素ガス容器用の部材として好適なＡｌ−Ｍｇ系合金に関する。 The present invention relates to an Al-Mg alloy having excellent hydrogen embrittlement resistance, a member used by being directly exposed to a high-pressure hydrogen gas environment, or a state in which a load is applied at the same time as being exposed to a high-pressure hydrogen gas environment. The present invention relates to an Al—Mg alloy suitable for a member used for a long time. In particular, the present invention relates to an Al—Mg alloy suitable as a member for a high-pressure hydrogen gas container mounted on a fuel cell vehicle.
ＣＯ２排出量規制を背景として、水素エネルギーを利用する燃料電池自動車の開発・実用化が進められ、すでに一部で市販車が公道を走行している。この燃料電池自動車では、燃料となる水素ガスを貯蔵するための高圧水素ガスタンクが搭載される。車載用高圧水素ガスタンクは、燃費性能を高めるために軽量性が必要とされ、アルミニウム合金製又は樹脂製のライナーの周囲に炭素繊維強化樹脂（ＣＦＲＰ）を巻きつけた構造が採用されている。特に、アルミニウム合金は、樹脂に比べて高圧水素ガスに対する気密性に優れ、水素ガスを充填後に長時間保持しても水素ガスの遺漏がほとんど無いため、ガスタンクのライナー素材として好適であるとされている。 Against the background of CO 2 emission regulations, development and commercialization of fuel cell vehicles using hydrogen energy have been promoted, and some commercial vehicles are already running on public roads. This fuel cell vehicle is equipped with a high-pressure hydrogen gas tank for storing hydrogen gas as fuel. The vehicle-mounted high-pressure hydrogen gas tank is required to be lightweight in order to improve fuel efficiency, and employs a structure in which a carbon fiber reinforced resin (CFRP) is wound around an aluminum alloy or resin liner. In particular, aluminum alloy is superior in airtightness to high-pressure hydrogen gas compared to resin, and even if it is held for a long time after filling with hydrogen gas, there is almost no leakage of hydrogen gas. Yes.
高圧水素ガスタンクでは、１回の充填での航続距離を高めるために、７００気圧もの非常に高いガス圧力で水素の充填が行われるのが標準仕様となりつつある。高圧水素ガスタンクでは、ライナーが直接高圧水素ガスと接触して気密保持する構造となっている。このように、高圧の水素ガスに直接暴露され、同時に高圧充填による一定の応力が負荷された状況で長期間使用されるという用途は、アルミニウム合金にとっては比較的新しい用途である。そして、かかる用途に対して、これまでに以下の特許文献に開示された各種のアルミニウム合金が開発されている。 In a high-pressure hydrogen gas tank, in order to increase the cruising distance in one filling, it is becoming standard that hydrogen filling is performed at a very high gas pressure of 700 atm. The high-pressure hydrogen gas tank has a structure in which the liner directly contacts the high-pressure hydrogen gas and is kept airtight. As described above, the application that is directly exposed to high-pressure hydrogen gas and is used for a long time in a state where a constant stress due to high-pressure filling is simultaneously applied is a relatively new application for an aluminum alloy. For such applications, various aluminum alloys disclosed in the following patent documents have been developed so far.
これらの先行技術について、特許文献１及び特許文献２には、耐水素脆性に優れるＡｌ−Ｍｇ−Ｓｉ系合金（６０００系アルミニウム合金）に関する技術が開示されている。また、特許文献３には、Ａｌ−Ｃｕ系合金（２０００系アルミニウム合金）に関する技術が、また、特許文献４にはＡｌ−Ｚｎ−Ｍｇ系合金（７０００系アルミニウム合金）に関する技術がそれぞれ開示されている。 Regarding these prior arts, Patent Literature 1 and Patent Literature 2 disclose technologies relating to an Al—Mg—Si based alloy (6000 based aluminum alloy) excellent in hydrogen embrittlement resistance. Patent Document 3 discloses a technique related to an Al—Cu based alloy (2000 series aluminum alloy), and Patent Document 4 discloses a technique related to an Al—Zn—Mg based alloy (7000 series aluminum alloy). Yes.
これらの合金は、各種のアルミニウム合金の中で、熱処理型アルミニウム合金に分類されており、適切な熱処理を行うことによって材料の強度を高めることができる。この適切な熱処理とは、例えば、Ａｌ−Ｍｇ−Ｓｉ系合金の場合、ライナー形状に加工した後、主要な構成元素であるＭｇとＳｉをマトリクス中に固溶するために５００℃程度の高温に加熱し（溶体化処理）、ライナーを水中に投入するなどして急冷（水焼入れ）した後、さらに１５０〜２００℃の適切な温度で数時間人工時効して、マトリクス中に固溶されたＭｇ・Ｓｉを析出物としてマトリクス中に均一微細に析出させる一連の熱処理を行うことである。この人工時効条件を最適化することによって材料強度を効果的に高めることができる。 These alloys are classified into heat treatment type aluminum alloys among various aluminum alloys, and the strength of the material can be increased by performing an appropriate heat treatment. For example, in the case of an Al—Mg—Si based alloy, this appropriate heat treatment is performed at a high temperature of about 500 ° C. in order to dissolve the main constituent elements Mg and Si in the matrix after processing into a liner shape. After heating (solution treatment), quenching (water quenching) by putting the liner into water, etc., Mg is dissolved in the matrix by artificial aging at an appropriate temperature of 150 to 200 ° C. for several hours. -A series of heat treatments for depositing Si as precipitates in a uniform and fine manner. The material strength can be effectively increased by optimizing the artificial aging conditions.
上記のような熱処理型のアルミニウム合金をライナー材として用いる場合、材料強度を高めることができるので、ライナーの周囲に巻きつけるＣＦＲＰ層の強度負担率を低減することができ、ＣＦＲＰの使用量を減らして高圧水素ガスタンクの製造コストを低減できるメリットがある。 When the heat-treatable aluminum alloy as described above is used as a liner material, the material strength can be increased, so the strength burden ratio of the CFRP layer wound around the liner can be reduced, and the amount of CFRP used can be reduced. This has the advantage of reducing the manufacturing cost of the high-pressure hydrogen gas tank.
しかし一方で、熱処理型のアルミニウム合金を適用する場合、ライナーの形状に加工した後に上記の熱処理を行うことが必要となる。加工後に熱処理を行うと、例えば、溶体化処理後の水焼入れ等による急冷の際に、ライナーの各部位で冷却速度にばらつきが生じて、ライナーに熱ひずみが生じて変形するという問題がある。また、また変形の問題が生じない場合であって、焼入れ時の冷却速度の部位ごとの違いによって、人工時効後の強度にばらつきが生じ、設計よりも短寿命で疲労破壊するなどの問題があった。更に、高圧水素ガスタンクには、水素ガスステーションで用いられる定置式のタンクもある。この場合、長尺のタンクが用いられるためライナーのサイズも長尺となり、車載型のタンクの場合に比べて好適な熱処理（特に焼入れ）を行うことが技術的にさらに困難になるという課題もある。 However, on the other hand, when a heat treatment type aluminum alloy is applied, it is necessary to perform the above heat treatment after processing into a liner shape. When heat treatment is performed after processing, for example, when quenching by water quenching after solution treatment or the like, there is a problem that the cooling rate varies in each part of the liner, and the liner is deformed due to thermal strain. Also, when there is no problem of deformation, there is a problem that the strength after artificial aging varies due to the difference in the cooling rate at the time of quenching, resulting in fatigue failure with a shorter life than the design. It was. Further, the high-pressure hydrogen gas tank includes a stationary tank used in a hydrogen gas station. In this case, since a long tank is used, the size of the liner is also long, and there is a problem that it is technically more difficult to perform a suitable heat treatment (particularly quenching) as compared with the case of a vehicle-mounted tank. .
ところで、アルミニウム合金の中には、上記のような熱処理を行わなくても比較的高い強度が得られる非熱処理型のアルミニウム合金も知られている。その代表的なものがＡｌ−Ｍｇ系合金であり、主成分のＭｇがＡｌマトリクス中に固溶することにより強度を得る。特に、Ｍｇ量を３％（質量）以上含有する場合には、固溶強化により特別な熱処理を行わなくても、中程度の強度を得ることが出来る。またＡｌ−Ｍｇ系合金は成形性、接合性にも優れることから、ライナーの成形・加工に種々の方法を適用することが出来る利点もある。 By the way, among the aluminum alloys, a non-heat-treatable aluminum alloy is also known, which can obtain a relatively high strength without performing the heat treatment as described above. A typical example is an Al—Mg-based alloy, and strength is obtained when Mg as a main component is dissolved in an Al matrix. In particular, when the Mg content is 3% (mass) or more, a medium strength can be obtained without performing a special heat treatment by solid solution strengthening. In addition, since the Al—Mg alloy is excellent in formability and bondability, there is an advantage that various methods can be applied to the molding and processing of the liner.
そこで、高圧水素ガスタンクの材料選定に関する方針として、従来の、ライナー成形・加工後の熱処理を前提とした熱処理型のアルミニウム合金の適用に替えて、Ａｌ−Ｍｇ系合金（非熱処理型のアルミニウム合金）の適用も有用であると考えられる。Ａｌ−Ｍｇ系合金を用いれば、強度は中程度であるものの、成形・加工後に特別な熱処理を行う必要がなくなり、タンクの製造工程が簡略化できるからである。また、ライナーの成形・加工においても、Ａｌ−Ｍｇ系合金の優れた成形性・接合性がより簡略なプロセスの実現に有効である。 Therefore, as a policy for selecting materials for high-pressure hydrogen gas tanks, Al-Mg alloys (non-heat-treatable aluminum alloys) are used instead of the conventional heat-treatable aluminum alloys premised on heat treatment after liner molding and processing. The application of is also considered useful. If an Al—Mg-based alloy is used, although the strength is moderate, it is not necessary to perform a special heat treatment after molding and processing, and the tank manufacturing process can be simplified. Also, in the molding / processing of the liner, the excellent formability / joinability of the Al—Mg alloy is effective for realizing a simpler process.
しかしながら、本発明者等によると、一般的に用いられているＡｌ−Ｍｇ系合金を高圧ガス環境中で荷重が負荷された状態で長期間使用すると、水素脆化を生じる可能性があることが判明している。水素脆化は鉄鋼を初めとして、多くの金属材料で生じることが知られている現象であり、材料の使用環境中において、徐々に材料内部に水素が侵入して、材料の結晶粒界等において脆性的な割れを引き起こすことにより、想定された寿命よりも短い期間で材料が破壊してしまう現象である。本発明者等によれば、アルミニウム合金（Ａｌ−Ｍｇ系合金）は気密保持性に優れるものの、タンクを長期間使用すると極僅かであるが水素がアルミニウム合金中に侵入して、この水素脆化の現象が生じ得ることを見出している。 However, according to the present inventors, hydrogen embrittlement may occur when a commonly used Al-Mg alloy is used for a long time in a high-pressure gas environment under a load. It turns out. Hydrogen embrittlement is a phenomenon that is known to occur in many metal materials, including steel. In the environment where the material is used, hydrogen gradually enters the material, and at the grain boundaries of the material. This is a phenomenon in which the material breaks in a shorter period than the expected life by causing brittle cracks. According to the present inventors, although an aluminum alloy (Al-Mg alloy) is excellent in airtightness retention, hydrogen penetrates into the aluminum alloy when the tank is used for a long time, but this hydrogen embrittlement occurs. It has been found that this phenomenon can occur.
本発明は、上記の背景のもとになされたものであり、高圧水素ガスタンクのライナーをはじめとする高圧水素ガス環境中において、荷重が負荷された状態で長期間使用される部材に好適な、耐水素脆性に優れたＡｌ−Ｍｇ系合金を開発することを目的とするものである。 The present invention was made based on the above background, and is suitable for a member that is used for a long period of time under a load in a high-pressure hydrogen gas environment including a liner of a high-pressure hydrogen gas tank. The object is to develop an Al—Mg alloy having excellent hydrogen embrittlement resistance.
本願発明者等は、上記の課題を解決するために鋭意検討を行い、高圧水素ガス環境中においてＡｌ−Ｍｇ系合金が水素脆化するメカニズムに着目した。その結果、まず、合金成分としてＣｕを添加すると、添加されたＣｕがマトリクス中に固溶元素として存在して、水素原子を補足（トラップ）することによって水素脆化の発生が抑制されて、耐水素脆性が向上することを見出し、その添加量を最適化した。 The inventors of the present application have made extensive studies in order to solve the above-described problems, and have focused on the mechanism by which the Al—Mg-based alloy becomes hydrogen embrittled in a high-pressure hydrogen gas environment. As a result, first, when Cu is added as an alloy component, the added Cu is present as a solid solution element in the matrix, and the occurrence of hydrogen embrittlement is suppressed by capturing (trapping) hydrogen atoms. It was found that hydrogen embrittlement was improved, and the amount added was optimized.
さらに、本願発明者等は、高圧水素ガス中において、脆化の原因となる水素が材料中に侵入する経路を調査したところ、Ａｌ−Ｍｇ系合金の材料表面に存在する主にＡｌ−Ｆｅ−Ｓｉ化合物からなる晶出粒子上で水素ガスが原子状水素に乖離（Ｈ２→２Ｈ）し、この原子状水素が晶出粒子中を経路として、材料内部へと侵入していくことを見出した。そこで、本願発明者等は、晶出粒子の主要な構成元素である不純物Ｆｅ及びＳｉの量について、通常標準的に用いられる材料のレベルよりも低く制限して、材料表面に存在する晶出粒子量を減少させることによって、水素侵入経路自体を減少させ、結果として材料の耐水素脆性を向上させることが可能であることを見出した。 Furthermore, the inventors of the present application have investigated the path of hydrogen that causes embrittlement in the high-pressure hydrogen gas, and found that the Al-Mg-based alloy surface mainly contains Al-Fe-. It was found that hydrogen gas dissociates into atomic hydrogen (H 2 → 2H) on crystallized particles made of Si compound, and this atomic hydrogen penetrates into the material through the crystallized particles as a route. . Therefore, the inventors of the present application limited the amount of impurities Fe and Si, which are the main constituent elements of the crystallized particles, to be lower than the level of the material normally used as a standard, and crystallized particles existing on the material surface. It has been found that by reducing the amount, it is possible to reduce the hydrogen intrusion path itself and consequently improve the hydrogen embrittlement resistance of the material.
即ち、本発明は、質量％で、Ｍｇ：３．０〜６．０％、Ｃｕ：０．０３〜１．０％を含有し、かつ不純物であるＦｅ及びＳｉの含有量が、Ｆｅ：０．１５％未満、及び、Ｓｉ：０．１５％未満に制限され、残部Ａｌと不可避不純物からなる耐水素脆性に優れた高圧水素ガス用のＡｌ−Ｍｇ系合金であって、Ａｌ−Ｆｅ−Ｓｉ化合物からなり、円相当径で１μｍ以上のサイズを有する晶出粒子の分布密度が４０００個/ｍｍ２以下であるＡｌ−Ｍｇ系合金材である。 That is, the present invention contains, in mass%, Mg: 3.0 to 6.0%, Cu: 0.03 to 1.0%, and the contents of Fe and Si as impurities are Fe: 0. Less than 15% and Si: less than 0.15%, an Al—Mg-based alloy for high-pressure hydrogen gas having excellent resistance to hydrogen embrittlement consisting of the remaining Al and inevitable impurities, comprising Al—Fe—Si It is an Al—Mg-based alloy material made of a compound and having a distribution density of crystallized particles having an equivalent circle diameter of 1 μm or more and 4000 pieces / mm 2 or less.
以下、本発明について詳細に説明する。上記の通り、本発明は、Ａｌ−Ｍｇ系合金の耐水素脆性改善のための手段として、（１）耐水素脆性改善に有用な成分元素であるＣｕの添加、及び、（２）合金中の晶出粒子（Ａｌ−Ｆｅ−Ｓｉ化合物）の分布密度の制限及びそのための成分元素の制御の２方向からＡｌ−Ｍｇ系合金の耐水素脆性を一定レベル以上の高い水準とするものである。 Hereinafter, the present invention will be described in detail. As described above, the present invention provides, as means for improving the hydrogen embrittlement resistance of an Al-Mg alloy, (1) addition of Cu, which is a component element useful for improving hydrogen embrittlement resistance, and (2) The hydrogen embrittlement resistance of the Al—Mg alloy is set to a high level above a certain level from the two directions of limiting the distribution density of the crystallized particles (Al—Fe—Si compound) and controlling the constituent elements therefor.
そこで、まず、本発明に係るＡｌ−Ｍｇ系合金について、合金本来の強度を確保しつつ、耐水素脆化性を改善するために組成制御を必須とする元素（Ｍｇ、Ｃｕ、Ｆｅ、Ｓｉ）について、その組成範囲を説明する。尚、本願明細書において、合金組成を示す「％」とは「質量％」を示す。 Therefore, for the Al—Mg alloy according to the present invention, elements that require composition control in order to improve the hydrogen embrittlement resistance while securing the original strength of the alloy (Mg, Cu, Fe, Si) The composition range will be described. In the present specification, “%” indicating the alloy composition indicates “mass%”.
Ｍｇは、Ａｌ−Ｍｇ系合金を構成する主要元素である。ＭｇはＡｌマトリクス中に固溶して、固溶強化によって材料強度を高める役割を果たす。またこの固溶強化に伴って、材料の加工硬化性（ｎ値）が増大し、Ｍｇ量が増大するにつれて材料の延性・成形性が高まる利点がある。本発明ではＭｇ量の下限を３．０％とする。Ｍｇ量が３．０％未満ではＭｇ量が実質的に少ないため、固溶強化による強度上昇が少なく、また延性・成形性が十分でなく、高圧水素ガスタンク等の部材として用いるには不適となる。一方、Ｍｇ量の上限は６．０％とする。Ｍｇ量が６．０％を超えるとＡｌ−Ｍｇ系合金の熱間加工性が大幅に低下して、実質的に材料を製造することが困難となる。また、Ｍｇ量の増大に伴って水素脆化感受性が大幅に増大する。そのため、Ｍｇ量が６．０％を超えると、本発明で規定した方法に従って耐水素性を高める方策を講じても、実用に耐える十分なレベルの耐水素脆性を確保することが出来なくなってしまう。 Mg is a main element constituting the Al—Mg alloy. Mg is dissolved in the Al matrix and plays a role of increasing the material strength by solid solution strengthening. Further, along with this solid solution strengthening, there is an advantage that the work hardenability (n value) of the material is increased, and the ductility / formability of the material is increased as the amount of Mg is increased. In the present invention, the lower limit of the Mg amount is 3.0%. If the Mg content is less than 3.0%, the Mg content is substantially small, so the strength increase due to solid solution strengthening is small, and the ductility and formability are not sufficient, making it unsuitable for use as a member such as a high-pressure hydrogen gas tank. . On the other hand, the upper limit of the amount of Mg is 6.0%. When the amount of Mg exceeds 6.0%, the hot workability of the Al—Mg-based alloy is significantly lowered, and it becomes difficult to manufacture the material substantially. In addition, the hydrogen embrittlement susceptibility greatly increases as the amount of Mg increases. Therefore, if the amount of Mg exceeds 6.0%, even if measures are taken to increase hydrogen resistance according to the method defined in the present invention, a sufficient level of hydrogen embrittlement resistance that can withstand practical use cannot be secured.
ＣｕはＡｌ−Ｍｇ系合金の耐水素脆性を向上させる効果があり、本発明で規定する合金における必須の添加元素である。添加されたＣｕは、Ａｌマトリクス中に固溶元素として存在し、材料中に侵入した微量の水素をＣｕ原子が捕捉（トラップ）して、結晶粒界に集積する水素量を実質的に減少させることにより、耐水素脆性を向上させる効果がある。また、Ｃｕは、強度向上・成形性向上に寄与するという効果も有する。Ｃｕ添加量が０．０３％未満では、マトリクス中に固溶しているＣｕ原子の絶対量が、侵入してくる水素量に比べて少ないため、実質的に耐水素脆性を向上させる効果が認められなくなってしまう。一方、Ｃｕが１．０％を超えると、材料の耐食性が低下して、高圧水素ガス環境に接する部分は問題ないが、外部環境に露出して使用される部分において材料の腐食が問題となる。 Cu has the effect of improving the hydrogen embrittlement resistance of the Al—Mg alloy, and is an essential additive element in the alloy defined in the present invention. The added Cu exists as a solid solution element in the Al matrix, and Cu atoms trap (trap) a very small amount of hydrogen that has entered the material, thereby substantially reducing the amount of hydrogen accumulated at the grain boundaries. This has the effect of improving hydrogen embrittlement resistance. Cu also has the effect of contributing to strength improvement and formability improvement. If the amount of Cu added is less than 0.03%, the absolute amount of Cu atoms dissolved in the matrix is small compared to the amount of hydrogen that enters, so that the effect of substantially improving hydrogen embrittlement resistance is recognized. It will not be possible. On the other hand, if Cu exceeds 1.0%, the corrosion resistance of the material is lowered, and there is no problem in the portion in contact with the high-pressure hydrogen gas environment, but the corrosion of the material becomes a problem in the portion exposed to the external environment. .
Ｆｅ及びＳｉは、アルミニウム合金を製造する上で原料として使用するアルミニウムインゴット中に、不純物元素として含まれているのが通常である。また、近年、アルミニウム飲料缶の使用量が増加し、これに伴いリサイクルされるアルミニウム飲料缶も増加しており、これらの飲料缶を再溶解して原料の一部として用いる場合には、原料コストは低減されるものの、これらの不純物Ｆｅ・Ｓｉ量は増加してしまう場合がある。Ｆｅ及びＳｉはかかる背景で材料中に含有される量が左右される不純物元素である。 Fe and Si are usually contained as impurity elements in an aluminum ingot used as a raw material for producing an aluminum alloy. In recent years, the amount of aluminum beverage cans used has increased, and the number of recycled aluminum beverage cans has also increased. When these beverage cans are redissolved and used as part of the raw materials, the raw material costs are increased. However, the amount of these impurities Fe · Si may increase. Fe and Si are impurity elements whose amount contained in the material depends on such background.
そして、不純物元素であるＦｅ及びＳｉは、上記したように、合金への水素侵入経路として耐水素脆性を低下させるＡｌ−Ｆｅ−Ｓｉ化合物からなる晶出粒子の主要な構成元素である。従って、本発明ではＦｅ・Ｓｉ量を所定の規定量未満になるよう制御し、晶出粒子分布数を制限して、水素の侵入量を減少させることが出来る。具体的には、Ｆｅ量０．１５％未満及びＳｉ量０．１５％未満に制御する。比較的純度の低いアルミニウムインゴットを用いたり、アルミニウム飲料缶等をリサイクルするなどしたりして、Ｆｅ量が０．１５％以上の場合又はＳｉ量が０．１５％以上となってしまった場合は、Ａｌ−Ｆｅ−Ｓｉ化合物からなる晶出粒子の数が多くなり、結果として水素の侵入経路が増大して、材料中に侵入する水素量が増えて、耐水素脆性が低下してしまう。 As described above, impurity elements Fe and Si are main constituent elements of crystallized particles made of an Al—Fe—Si compound that reduces hydrogen embrittlement resistance as a hydrogen intrusion path into the alloy. Therefore, in the present invention, the amount of intrusion of hydrogen can be reduced by controlling the amount of Fe · Si to be less than a predetermined amount, limiting the number of crystallized particle distributions. Specifically, the Fe content is controlled to be less than 0.15% and the Si content is controlled to less than 0.15%. When using an aluminum ingot of relatively low purity, recycling aluminum beverage cans, etc., if the Fe amount is 0.15% or more or the Si amount is 0.15% or more As a result, the number of crystallized particles made of the Al—Fe—Si compound increases, and as a result, the hydrogen penetration path increases, the amount of hydrogen entering the material increases, and the hydrogen embrittlement resistance decreases.
本発明に係るＡｌ−Ｍｇ系合金は、上記のようにＣｕの添加及び各成分元素の制御と共に、材料中のＡｌ−Ｆｅ−Ｓｉ化合物からなる晶出粒子について円相当径で１μｍ以上の存在密度を制限することを特徴とするものである。そこで、次に、本発明における晶出粒子の存在密度の制御について説明する。 The Al—Mg-based alloy according to the present invention has an abundance density of 1 μm or more in terms of the equivalent circle diameter of crystallized particles made of an Al—Fe—Si compound in the material together with addition of Cu and control of each component element as described above. It is characterized by restricting. Then, control of the density of crystallization particles in the present invention will be described next.
Ａｌ−Ｍｇ系合金は、その溶解・鋳造の際の凝固過程においてＡｌ−Ｆｅ−Ｓｉ化合物からなる晶出粒子が生成する。この晶出粒子を構成するＦｅ、Ｓｉの合金への流入経路は上記の通りである。晶出粒子はマトリクス中に分散し一部は材料表面に存在するが、本発明者等の検討結果から、この晶出粒子が水素の侵入経路であり材料内部に水素を侵入させて水素脆化の要因となる。そこで、本発明では、材料表面に存在する円相当径で１μｍ以上のサイズの晶出粒子について、その分布密度を４０００個／ｍｍ２以下に制限することによって、材料中に侵入する水素量を低減して、材料の耐水素脆性を高めている。 In the Al—Mg alloy, crystallized particles made of an Al—Fe—Si compound are generated during the solidification process during melting and casting. The inflow path to the Fe and Si alloys constituting the crystallized particles is as described above. The crystallized particles are dispersed in the matrix and partly exist on the surface of the material. From the results of the study by the present inventors, this crystallized particle is a hydrogen intrusion route, and hydrogen penetrates into the material to cause hydrogen embrittlement. It becomes a factor of. Therefore, in the present invention, the amount of hydrogen penetrating into the material is reduced by limiting the distribution density to 4,000 particles / mm 2 or less for crystallized particles having an equivalent circle diameter of 1 μm or more existing on the material surface. Thus, the hydrogen embrittlement resistance of the material is increased.
ここで晶出粒子のサイズを円相当径で１μｍ以上のものに限定した理由を説明する。通常、晶出粒子は鋳造プロセスの凝固時においては円相当径で約１０μｍのサイズで生成するが、引続いて行われる圧延加工等の製造プロセスの途中に加わる塑性加工によって細かく分断されてより細かい粒子となる。その結果、これらの晶出粒子の大部分は円相当径で１〜５μｍのサイズとなり、１μｍ程度の細かい晶出粒子が最も多く、２μｍ、３μｍと円相当径が大きくなるにつれてそれぞれのサイズの晶出粒子の数は指数関数的に減少する。円相当径で１μｍ未満のサイズの粒子も存在はするが、その数は相対的に少ない上に、そのような微細なものの水素侵入への寄与は小さいため、これを計数する必要はない。そこで、材料中存在割合が高く、水素侵入の影響を有すると考えられる円相当径で１μｍ以上の晶出粒子を制限することとした。尚、晶出粒子が水素侵入サイトとして機能するメカニズムより、より大きな晶出粒子から相対的に水素が侵入しやすくなるが、上述の通り粒子径が１μｍより大きいもの（２μｍ、３μｍ）は、その粒子数が指数的関数的に減少する。そのため、サイズに応じた水素の侵入しやすさよりもその分布密度を重視し、１μｍ以上の晶出粒子数を基準とすることで、その材料固有の水素侵入のしやすさを評価し得るのである。 Here, the reason why the size of the crystallized particles is limited to the equivalent circle diameter of 1 μm or more will be described. Usually, the crystallized particles are produced with a circle equivalent diameter of about 10 μm at the time of solidification in the casting process. However, the crystallized particles are finely divided and finer by plastic processing applied during the manufacturing process such as rolling. Become particles. As a result, most of these crystallized particles have a circle-equivalent diameter of 1 to 5 μm, the largest number of fine crystallized particles of about 1 μm, and 2 μm and 3 μm. The number of exiting particles decreases exponentially. Although there are particles having an equivalent circle diameter of less than 1 μm, the number of particles is relatively small, and the contribution of such fine particles to hydrogen penetration is small, so there is no need to count them. Therefore, it was decided to limit crystallized particles having a high equivalent ratio in the material and having an equivalent circle diameter of 1 μm or more, which is considered to have an influence of hydrogen penetration. In addition, the mechanism in which the crystallized particles function as hydrogen intrusion sites makes it relatively easy for hydrogen to enter from larger crystallized particles. As described above, particles having a particle size larger than 1 μm (2 μm, 3 μm) The number of particles decreases exponentially. Therefore, the distribution density is more important than the ease of hydrogen penetration according to the size, and the ease of hydrogen penetration unique to the material can be evaluated by using the number of crystallized particles of 1 μm or more as a reference. .
そして、円相当径で１μｍ以上のサイズの晶出粒子の分布密度について、４０００個／ｍｍ２以下としたのは、この分布密度以下とすることで水素の侵入経路となる晶出粒子の数が少ないといえるからであり、材料中に侵入する水素が少なく耐水素脆性が高くなる。一方、後述のように不純物であるＦｅ、Ｓｉ量が多く、晶出粒子の分布密度が４０００個／ｍｍ２を超える場合は、水素侵入経路となる晶出粒子数が多く、材料に侵入する水素が多くなるので、耐水素脆性は低くなる。 The distribution density of crystallized particles having an equivalent circle diameter of 1 μm or more is set to 4000 particles / mm 2 or less because the number of crystallized particles serving as hydrogen intrusion paths is set to be equal to or less than this distribution density. This is because the amount of hydrogen penetrating into the material is small and the hydrogen embrittlement resistance is high. On the other hand, as described later, when the amount of Fe and Si as impurities is large and the distribution density of crystallized particles exceeds 4000 particles / mm 2 , the number of crystallized particles serving as a hydrogen intrusion path is large, and hydrogen penetrates into the material. Therefore, hydrogen embrittlement resistance becomes low.
尚、晶出粒子の分布密度の測定方法は、以下のようにして行うことができる。最終工程を経たＡｌ−Ｍｇ系合金について、実際に使用される場合に高圧水素ガスに暴露されることになる面を、通常の金属組織観察のための常法に従って、鏡面研磨仕上げした後、ケラー氏液（塩酸２０ｍｌ、硝酸２０ｍｌ、フッ酸５ｍｌ、蒸留水５０ｍｌの混合液）に１分間浸漬してエッチング後に金属組織観察用の顕微鏡で順光観察することにより、晶出粒子の分布密度を測定することが可能である。さらに具体的には、顕微鏡で１００倍の倍率に設定して観察を行った場合、晶出粒子はマトリクスに対して暗いコントラストで黒点として認識することが可能である。本発明で規定したＡｌ−Ｍｇ系合金の場合、この黒色粒子はほとんど全て晶出粒子であるので、円相当径で１μｍ以上のサイズの粒子を１視野ごとに計数して、１０視野分の合計の粒子数を測定面積で割ることによって、分散粒子数（個／ｍｍ２）を測定することができる。 The method for measuring the distribution density of crystallized particles can be performed as follows. For the Al-Mg based alloy that has undergone the final process, the surface that will be exposed to high-pressure hydrogen gas when actually used is mirror-polished in accordance with a conventional method for observing a normal metal structure, and then Keller. Measure the distribution density of crystallized particles by immersing in liquid (20 ml of hydrochloric acid, 20 ml of nitric acid, 5 ml of hydrofluoric acid, and 50 ml of distilled water) for 1 minute, etching, and direct observation with a microscope for observing the metal structure. Is possible. More specifically, when observation is performed with a microscope set to a magnification of 100 times, the crystallized particles can be recognized as black spots with dark contrast to the matrix. In the case of the Al—Mg-based alloy defined in the present invention, almost all of these black particles are crystallized particles. Therefore, particles having a circle-equivalent diameter of 1 μm or more are counted for each visual field, and the total for 10 visual fields. The number of dispersed particles (number / mm 2 ) can be measured by dividing the number of particles by the measurement area.
以上の通り、本発明に係るＡｌ−Ｍｇ系合金は、耐水素脆性改善に有用なＣｕの添加、及び、水素侵入経路となるＡｌ−Ｆｅ−Ｓｉ晶出粒子の分布密度の制限により、合金の耐水素脆性を向上させるものである。 As described above, the Al—Mg-based alloy according to the present invention has an alloy composition that is limited by the addition of Cu useful for improving hydrogen embrittlement resistance and the distribution density of Al—Fe—Si crystallized particles serving as a hydrogen penetration path. It improves hydrogen embrittlement resistance.
但し、上記のように水素侵入量を制限しつつ、侵入した水素をＣｕにより世ラップした場合でも、非常に苛酷な環境でかつ高い応力が負荷されてより長期間にわたって材料を使用することを想定すると、材料中に侵入した極微量の水素によっても水素脆化を引き起こす可能性が残存する。これは、材料中に侵入した水素が拡散により移動して、材料中の結晶粒界に集積することよって、粒界割れが引き起こされるという水素脆化メカニズムの本質に由来する。 However, even when the intruded hydrogen is wrapped by Cu while limiting the amount of hydrogen intrusion as described above, it is assumed that the material is used for a longer period under a very severe environment and high stress. Then, the possibility of causing hydrogen embrittlement remains even with a very small amount of hydrogen that has entered the material. This originates from the essence of the hydrogen embrittlement mechanism in which the hydrogen that has entered the material moves by diffusion and accumulates at the crystal grain boundaries in the material, thereby causing grain boundary cracking.
そこで、本願発明者等は、耐水素脆性の更なる改善のために鋭意検討を行った。その結果、本発明に係るＡｌ−Ｍｇ系合金について、遷移元素であるＭｎ及びＣｒの含有量を調整しつつ適切な製造プロセスを経て、マトリクス中にＡｌ−Ｍｎ化合物又はＡｌ−Ｍｎ−Ｃｒ化合物を主成分として析出する分散粒子の分布密度を適切に制御することによって、より苛酷な使用環境においても耐水素脆性を確保できる高い耐水素脆性を得ることができることを見出した。このＡｌ−Ｍｎ化合物又はＡｌ−Ｍｎ−Ｃｒ化合物を主成分とする分散粒子の分布密度を最適化することによる耐水素脆性向上メカニズムは、材料中に侵入した微量の水素を、これらの分散粒子によって捕捉（トラップ）させ、結果として結晶粒界に集積する水素量が実質的に減少することである。 Therefore, the inventors of the present application have made extensive studies for further improvement of hydrogen embrittlement resistance. As a result, for the Al-Mg based alloy according to the present invention, an Al-Mn compound or an Al-Mn-Cr compound is added to the matrix through an appropriate manufacturing process while adjusting the contents of transition elements Mn and Cr. It has been found that by appropriately controlling the distribution density of the dispersed particles precipitated as a main component, high hydrogen embrittlement resistance that can ensure hydrogen embrittlement resistance can be obtained even in a more severe use environment. The mechanism for improving hydrogen embrittlement resistance by optimizing the distribution density of the dispersed particles containing the Al-Mn compound or Al-Mn-Cr compound as a main component is that a small amount of hydrogen that has entered the material is absorbed by these dispersed particles. The amount of hydrogen trapped and consequently accumulated at the grain boundaries is substantially reduced.
Ａｌ合金において遷移元素であるＭｎとＣｒは、通常、Ａｌ−Ｍｇ系合金の結晶粒を微細化することを目的として添加されている。これに対し、本発明では、ＭｎとＣｒの含有量調整の意義として、Ａｌ−Ｍｇ系合金の更なる苛酷な環境下での使用を想定し、耐水素脆性向上のための追加的方策として捉えるものである。本発明では、上記のＡｌ−Ｍｎ化合物又はＡｌ−Ｍｎ−Ｃｒ化合物を主成分とする分散粒子の効果を得るためには、Ｍｎ量を０．０２〜０．８％とし、Ｃｒ量を０．０１〜０．２％の範囲として、さらにこれらの合計量について、０．０５％≦Ｍｎ＋Ｃｒ≦０．９％を満たす範囲に調整する。かかるＭｎ、Ｃｒの含有量と後述する製造プロセスに準拠することによって、分散粒子の分布密度を後述する水準を満たすように制御することができる。 In the Al alloy, Mn and Cr, which are transition elements, are usually added for the purpose of refining crystal grains of the Al—Mg alloy. On the other hand, in the present invention, as the significance of the content adjustment of Mn and Cr, it is assumed that the Al—Mg-based alloy is used in a more severe environment, and is regarded as an additional measure for improving hydrogen embrittlement resistance. Is. In the present invention, in order to obtain the effect of the dispersed particles mainly composed of the above Al-Mn compound or Al-Mn-Cr compound, the Mn content is 0.02 to 0.8%, and the Cr content is 0.00. As the range of 01 to 0.2%, the total amount thereof is further adjusted to a range satisfying 0.05% ≦ Mn + Cr ≦ 0.9%. By conforming to the contents of Mn and Cr and the manufacturing process described later, the distribution density of the dispersed particles can be controlled to satisfy the level described later.
上記のＭｎ、Ｃｒの含有量について、Ｍｎ量が０．０２％未満及びＣｒ量が０．０１％未満の場合、又は、これらの合計量（Ｍｎ＋Ｃｒ）が０．０５％未満の場合は、分散粒子密度が不足しその更なる耐水素脆性向上効果を得ることができない。即ち、これらのＭｎとＣｒの含有量においては、１μｍ以上のＡｌ−Ｆｅ−Ｓｉ晶出粒子の分布密度を低減したことによる耐水素脆性向上の効果に止まる。但し、この状態も従来技術に比して耐水素脆性は優れている。 Regarding the above Mn and Cr contents, when the Mn amount is less than 0.02% and the Cr amount is less than 0.01%, or the total amount (Mn + Cr) is less than 0.05%, the dispersion The particle density is insufficient and the further effect of improving hydrogen embrittlement resistance cannot be obtained. That is, in these contents of Mn and Cr, the effect of improving the hydrogen embrittlement resistance by reducing the distribution density of Al—Fe—Si crystallized particles of 1 μm or more is limited. However, this state is also excellent in hydrogen embrittlement resistance as compared with the prior art.
一方、Ｍｎ量が０．８％超及びＣｒ量が０．２％超の場合、又は、これらの合計量（Ｍｎ＋Ｃｒ）が０．９％超の場合は、Ａｌ−Ｆｅ−Ｓｉ晶出粒子の分布密度を増大させ、耐水素脆性を低下させることとなる。これは、Ｍｎ量及びＣｒ量がこれらの範囲を超える場合、余剰分のＭｎ、ＣｒはＡｌ−Ｍｎ−Ｃｒ分散粒子の形成には消費されず、Ａｌ−Ｆｅ−Ｓｉ晶出粒子に固溶することにより、これら晶出粒子の分布密度を増大させることとなる。これにより、増加した晶出粒子を侵入経路として侵入水素量が増加して、耐水素脆性が低下するのである。即ち、ＭｎとＣｒの含有量が多すぎる場合、本発明が第一に意図した１μｍ以上のＡｌ−Ｆｅ−Ｓｉ晶出粒子の分布密度低減の効果までも失する。そのため、ＭｎとＣｒの含有量は前記の上限値以下に調整する必要がある。 On the other hand, when the amount of Mn exceeds 0.8% and the amount of Cr exceeds 0.2%, or when the total amount thereof (Mn + Cr) exceeds 0.9%, the Al—Fe—Si crystallized particles The distribution density is increased and the hydrogen embrittlement resistance is decreased. This is because when the amount of Mn and the amount of Cr exceed these ranges, the excess Mn and Cr are not consumed for the formation of Al—Mn—Cr dispersed particles, but are dissolved in the Al—Fe—Si crystallized particles. As a result, the distribution density of these crystallized particles is increased. As a result, the amount of invading hydrogen increases using the increased crystallization particles as intrusion paths, and the hydrogen embrittlement resistance decreases. That is, when the contents of Mn and Cr are too large, the effect of reducing the distribution density of Al—Fe—Si crystallized particles having a size of 1 μm or more, which is intended by the present invention, is lost. Therefore, it is necessary to adjust the contents of Mn and Cr to the upper limit value or less.
Ａｌ−Ｍｎ化合物又はＡｌ−Ｍｎ−Ｃｒ化合物からなる分散粒子の分布密度を適切に制御することにより耐水素脆性を高めることができる理由は、上記の通りである。即ち、マトリクス中に存在する分散粒子が、高圧水素ガス環境より晶出粒子を経路として侵入してきた水素原子を捕捉することにより、結晶粒界に集積する水素量を実質的に減少させるためである。 The reason why the hydrogen embrittlement resistance can be improved by appropriately controlling the distribution density of the dispersed particles made of the Al—Mn compound or the Al—Mn—Cr compound is as described above. That is, the dispersed particles existing in the matrix trap the hydrogen atoms that have entered from the high-pressure hydrogen gas environment through the crystallized particles as a path, thereby substantially reducing the amount of hydrogen accumulated at the crystal grain boundaries. .
ここで、Ａｌ−Ｍｎ化合物又はＡｌ−Ｍｎ−Ｃｒ化合物からなる分散粒子のサイズを０．５μｍ以下に規定する理由を以下に述べる。分散粒子が水素を捕捉するメカニズムは、分散粒子とマトリクスとの界面において、互いの格子定数の違いに起因して格子ひずみが生じ、その界面の応力場が水素を捕捉するものである。この格子ひずみは分散粒子のサイズが小さいほど大きく、分散粒子のサイズが大きくなるにつれて、格子ひずみは小さくなっていき、同時に水素の捕捉効果も低下する。分散粒子の円相当径が０．５μｍ以下のサイズの場合には、分散粒子とマトリクス界面の格子ひずみが十分に大きく、分散粒子に実質的に水素を捕捉する能力がある。これに対して、分散粒子の円相当径が０．５μｍ超になった場合は、分散粒子とマトリクス界面の格子歪が小さくなり、分散粒子に水素を捕捉する能力が実質的になくなってしまう。このことから、分散粒子のサイズは０．５μｍ以下に規定される。 Here, the reason why the size of the dispersed particles made of the Al—Mn compound or the Al—Mn—Cr compound is regulated to 0.5 μm or less will be described below. The mechanism by which the dispersed particles capture hydrogen is that lattice distortion occurs at the interface between the dispersed particles and the matrix due to the difference in lattice constant between each other, and the stress field at the interface captures hydrogen. The lattice strain increases as the size of the dispersed particles decreases, and the lattice strain decreases as the size of the dispersed particles increases, and at the same time, the effect of trapping hydrogen decreases. When the equivalent-circle diameter of the dispersed particles is 0.5 μm or less, the lattice strain between the dispersed particles and the matrix interface is sufficiently large, and the dispersed particles have the ability to substantially trap hydrogen. On the other hand, when the equivalent circle diameter of the dispersed particles exceeds 0.5 μm, the lattice strain between the dispersed particles and the matrix interface is reduced, and the ability to trap hydrogen in the dispersed particles is substantially lost. For this reason, the size of the dispersed particles is defined to be 0.5 μm or less.
そして、円相当径で０．５μｍ以下の分散粒子の分布密度が１０００００個／ｍｍ２以上の場合は、分散粒子により十分な量の水素を捕捉することが可能であるため、耐水素脆性が高い。これに対して円相当径で０．５μｍ以下の分散粒子の分布密度が１０００００個／μｍ２未満の場合は、分散粒子数が少ないために水素を捕捉する能力が不十分であり、耐水素脆性が低く、材料を苛酷な環境で長期間にわたって使用するためには、信頼性が低い。 When the distribution density of dispersed particles having an equivalent circle diameter of 0.5 μm or less is 100000 particles / mm 2 or more, a sufficient amount of hydrogen can be captured by the dispersed particles, and thus the hydrogen embrittlement resistance is high. . On the other hand, when the distribution density of dispersed particles having an equivalent circle diameter of 0.5 μm or less is less than 100,000 particles / μm 2 , the number of dispersed particles is small, so that the ability to capture hydrogen is insufficient, and hydrogen embrittlement resistance. And is unreliable for long-term use of the material in harsh environments.
Ａｌ−Ｍｎ化合物又はＡｌ−Ｍｎ−Ｃｒ化合物からなる分散粒子の分布密度の測定は、以下の方法により実施することができる。最終工程を経たＡｌ−Ｍｇ系合金について、任意の断面よりスライス状のサンプルを採取して、機械研磨により約１０μｍ程度の薄膜状に加工した後、電解研磨により約３００nm厚の透過型電子顕微鏡（ＴＥＭ）観察用のサンプルを作製して、ＴＥＭにより１００００倍の倍率で観察を行う。 The measurement of the distribution density of the dispersed particles composed of the Al—Mn compound or the Al—Mn—Cr compound can be performed by the following method. For the Al-Mg alloy that has undergone the final process, a sliced sample is taken from an arbitrary cross-section, processed into a thin film of about 10 μm by mechanical polishing, and then a transmission electron microscope having a thickness of about 300 nm by electrolytic polishing ( (TEM) A sample for observation is prepared and observed with a TEM at a magnification of 10,000 times.
本発明で規定された範囲内の合金であれば、上記の条件で結晶粒内のマトリクス中において観察される円相当径０．５μｍ以下のサイズの粒子（ＴＥＭの通常の明視野像では黒くコントラストがついて観察される粒子）のほとんど全ては、分散粒子であると考えて差し支えないが、念のため代表的な粒子に絞った電子線を照射して、放出されるＸ線のエネルギー分布を解析すること（ＴＥＭ−ＥＤＸ装置）により元素解析をして、分散粒子からＭｎ・Ｃｒもしくは他に添加した遷移元素が検出されることを確認しておいても良い。分散粒子の分布密度の測定に関しては、例えば、１００００倍の倍率で１０視野の写真撮影をおこなって、各視野について円相当径０．５μｍ以下の分散粒子数を計測して、１０視野分を合計した粒子を測定した総視野面積で割ることによって、分散粒子の分布密度を測定することが出来る。 In the case of an alloy within the range defined by the present invention, particles having a circle-equivalent diameter of 0.5 μm or less observed in a matrix in a crystal grain under the above conditions (black contrast in a normal bright-field image of TEM) Almost all of the observed particles) can be considered as dispersed particles. However, just in case, an electron beam focused on a representative particle is irradiated to analyze the energy distribution of the emitted X-rays. It is also possible to confirm that the transition element added to Mn · Cr or other elements is detected from the dispersed particles by conducting an elemental analysis using a TEM-EDX apparatus. Regarding the measurement of the distribution density of the dispersed particles, for example, 10 fields of photography are taken at a magnification of 10,000 times, and the number of dispersed particles having an equivalent circle diameter of 0.5 μm or less is measured for each field. The distribution density of the dispersed particles can be measured by dividing the measured particles by the measured total visual field area.
本発明に係るＡｌ−Ｍｇ系合金は、上述のように、Ｍｇ、Ｃｕ、Ｆｅ、Ｓｉを制御必須の成分元素とし、また、更なる耐水素脆性向上のためＭｎ、Ｃｒを添加する。本発明は、これらの成分元素の以外に他の元素を添加制御しても良い。 As described above, the Al—Mg-based alloy according to the present invention uses Mg, Cu, Fe, and Si as essential component elements for control, and further adds Mn and Cr for improving hydrogen embrittlement resistance. In the present invention, other elements may be added and controlled in addition to these component elements.
Ｚｒ、Ｓｃ、Ｖ、Ｎｉの遷移元素は、Ｍｎ、Ｃｒと同様に、各元素を主成分とする微細な分散粒子をマトリクス中に形成して、結晶粒の微細化及び高温での結晶粒の安定化に寄与すると同時に、材料中に侵入した水素を捕捉することによって、耐水素脆性向上にも付加的に寄与する。このため、さらに水素脆化感受性を高めたい場合は、これらの元素のうちの１種又は２種以上を添加しても良い。 As in the case of Mn and Cr, the transition elements of Zr, Sc, V, and Ni form fine dispersed particles mainly composed of each element in the matrix, so that the crystal grains can be refined and the crystal grains at a high temperature can be obtained. Contributing to stabilization, and at the same time, by capturing hydrogen that has entered the material, it additionally contributes to improved hydrogen embrittlement resistance. For this reason, when it is desired to further increase the sensitivity to hydrogen embrittlement, one or more of these elements may be added.
Ｚｒ、Ｓｃ、Ｖ、Ｎｉの１種又は２種以上を添加する場合、Ｚｒ：０．０１〜０．３％、Ｓｃ：０．０１〜０．５％、Ｖ：０．０１〜０．３％、Ｎｉ：０．０２〜０．３％とするのが好ましい。いずれの元素についても規定量未満の場合は、添加量が不十分なために、上記の効果が十分に得られない。一方、いずれの元素も規定量を超えて添加された場合は、これらの元素を主成分とする晶出粒子が多量に生成して水素侵入サイトとなり、侵入する水素量が増大するため、却って耐水素脆性が低下してしまう。 When one or more of Zr, Sc, V and Ni are added, Zr: 0.01 to 0.3%, Sc: 0.01 to 0.5%, V: 0.01 to 0.3 %, Ni: 0.02 to 0.3% is preferable. If any element is less than the specified amount, the above effect cannot be sufficiently obtained because the addition amount is insufficient. On the other hand, if any element is added in excess of the specified amount, a large amount of crystallized particles containing these elements as the main components are generated and become hydrogen intrusion sites, and the amount of invading hydrogen increases. Hydrogen embrittlement is reduced.
また、Ｔｉ及びＢは、合金製造工程のうちの鋳造工程において、鋳塊組織を微細にするために添加される。これらについては、Ｔｉ添加量を０．０１〜０．１５％として単独添加するか、あるいは０．００１〜０．０５％のＢと共添加することにより結晶粒微細化効果が得られる。ここで、Ｔｉ単独添加においても鋳塊組織を微細化するが、ＴｉとＢを共添加することでより効果的に結晶粒微細化される。Ｔｉ量が０．０１％未満の場合は、鋳塊組織を微細にする効果が得られない。同様にＢが０．０００１％未満の場合にも、鋳塊を微細にする効果は得られない。またＴｉ量が０．１５％を超えると、鋳造時にＡｌ−Ｔｉからなる粗大な化合物が晶出し、材料の延性が大幅に低下する。さらにＢが０．０５％を超えると鋳造時にＴｉ−Ｂからなる粗大な化合物が晶出し、材料の延性ならびに靭性が大幅に低下してしまう。 Ti and B are added in order to make the ingot structure fine in the casting process of the alloy manufacturing process. About these, the grain refinement | miniaturization effect is acquired by making Ti addition amount 0.01-0.15% independently, or adding together with 0.001-0.05% B. Here, even when Ti alone is added, the ingot structure is refined, but by adding Ti and B together, crystal grains can be refined more effectively. When the amount of Ti is less than 0.01%, the effect of making the ingot structure fine cannot be obtained. Similarly, when B is less than 0.0001%, the effect of making the ingot fine is not obtained. On the other hand, if the Ti content exceeds 0.15%, a coarse compound composed of Al-Ti is crystallized during casting, and the ductility of the material is greatly reduced. Further, when B exceeds 0.05%, a coarse compound composed of Ti-B is crystallized at the time of casting, and the ductility and toughness of the material are significantly lowered.
尚、以上の添加元素の他、耐食性等を向上させることを目的として微量のＺｎを添加することもある。本発明では１．０％未満の添加量であれば特に所期の目的を損なうことなく添加することが可能である。 In addition to the above additive elements, a trace amount of Zn may be added for the purpose of improving the corrosion resistance and the like. In the present invention, an addition amount of less than 1.0% can be added without impairing the intended purpose.
次に、本発明に係るＡｌ−Ｍｇ系合金の製造方法について説明する。本発明のＡｌ−Ｍｇ系合金材は、一部の製造工程における条件を除いて、基本的に通常のアルミニウム合金材の製造方法に従って製造することができる。即ち、常法に準じて溶解鋳造したアルミニウム合金鋳塊について、均質化処理を行った後に、熱間加工を行ってから、必要に応じて冷間加工、成形加工、焼鈍を適宜組み合わせて、最終的に板・押出材・各種鍛造品のような中間品の形で、耐水素脆性に優れるＡｌ−Ｍｇ系合金素材として製品とする。また、さらに加工や熱処理を適宜行い、高圧水素ガスタンクライナーやその口金等の最終形状まで仕上げて製品としても良い。以下、本発明に係るＡｌ−Ｍｇ系合金の製造工程について、本発明で規定したミクロ組織の形成に関与する製造プロセスについて詳しく述べつつ説明する。 Next, a method for producing an Al—Mg alloy according to the present invention will be described. The Al—Mg-based alloy material of the present invention can be manufactured basically according to a normal method for manufacturing an aluminum alloy material, except for some conditions in the manufacturing process. That is, the aluminum alloy ingot melt-cast according to a conventional method is subjected to a homogenization treatment, followed by hot working, and if necessary, finally combined with cold working, forming processing, and annealing, and finally In particular, it is made into a product as an Al-Mg alloy material with excellent hydrogen embrittlement resistance in the form of intermediate products such as plates, extruded materials, and various forged products. Further, processing and heat treatment may be appropriately performed to finish the final shape such as a high-pressure hydrogen gas tank liner or a die thereof to obtain a product. Hereinafter, the manufacturing process of the Al—Mg alloy according to the present invention will be described in detail with respect to the manufacturing process involved in the formation of the microstructure defined in the present invention.
溶解鋳造工程では、本発明の成分範囲内に溶解調整されたＡｌ−Ｍｇ系合金溶湯を半連続鋳造法（ＤＣ鋳造法、ホットトップ鋳造法）や連続圧延鋳造法等の通常の方法によって鋳造して、鋳塊を製造する。この鋳造時の凝固の際に、晶出粒子が生成してマトリクス中に分布するが、前記の一般的な鋳造法を採用して鋳造を行う場合、晶出粒子の分布状態を本発明で規定する範囲にするため、鋳造工程における鋳塊の凝固時の冷却速度が、０．１℃／ｓｅｃ以上にすることが好ましい。凝固時の冷却速度が０．１℃／ｓｅｃ未満では、粗大な晶出粒子が増加して、晶出粒子の分布密度が本発明の範囲から外れる場合があるからである。凝固鋳造後は、その後に行われる熱間加工に備えて、必要に応じて鋳塊表面の鋳肌を削り取る面削を行っても良い。 In the melt casting process, the Al—Mg alloy molten metal that has been dissolved and adjusted within the component range of the present invention is cast by an ordinary method such as a semi-continuous casting method (DC casting method, hot top casting method) or continuous rolling casting method. To produce an ingot. During solidification at the time of casting, crystallized particles are generated and distributed in the matrix. When casting is performed using the above general casting method, the distribution state of crystallized particles is defined by the present invention. Therefore, the cooling rate during solidification of the ingot in the casting process is preferably 0.1 ° C./sec or more. This is because if the cooling rate during solidification is less than 0.1 ° C./sec, coarse crystallized particles increase and the distribution density of crystallized particles may fall outside the scope of the present invention. After solidification casting, in preparation for the subsequent hot working, chamfering may be performed to scrape the cast surface of the ingot surface as necessary.
次に、Ａｌ−Ｍｎ−Ｃｒ化合物を主成分とする分散粒子を好適なサイズ及び分布密度で析出させることを目的として均質化処理を行う。また、均質化処理はこれと同時に、鋳塊組織中の結晶粒内における偏析を解消し、鋳造後の冷却時に析出した粗大な析出物を固溶させ、材料の機械的特性を向上させる効果もある。 Next, a homogenization treatment is performed for the purpose of precipitating dispersed particles having an Al—Mn—Cr compound as a main component with a suitable size and distribution density. At the same time, the homogenization treatment also eliminates segregation in the crystal grains in the ingot structure, dissolves coarse precipitates precipitated during cooling after casting, and improves the mechanical properties of the material. is there.
そして、分散粒子を最適なサイズ・分布密度で析出させるため、均質化処理は、４５０〜５３０℃の温度範囲から保持温度を適宜選択して、１〜１０時間の保持で行うことが好ましい。均質化処理の保持温度が４５０℃未満では、分散粒子の析出に時間を要し、必要な分布密度を確保することができない。一方、均質化処理の保持温度が５３０℃を超えると、分散粒子のサイズが粗大となり、一部の分散粒子の円相当径が０．５μｍを超えて水素を捕獲する機能が低下するとともに、円相当径０．５μｍ以内の分散粒子の分布密度が規定値未満となり、全体的に分散粒子が捕獲する水素量が低下して、耐水素脆性が低下してしまう。また、保持時間が１時間未満では、分散粒子の析出が不十分であり、必要な分布密度を確保することが出来ない。また保持時間が１０時間を超えると、一部の分散粒子の円相当径が０．５μｍを超えて水素を捕獲する機能が低下するとともに、円相当径０．５μｍ以内の分散粒子の分布密度が規定値未満となり、全体的に分散粒子が捕獲する水素量が低下して、耐水素脆性が低下してしまう。 In order to precipitate the dispersed particles with an optimal size / distribution density, it is preferable that the homogenization treatment is performed by appropriately selecting a holding temperature from a temperature range of 450 to 530 ° C. and holding for 1 to 10 hours. When the holding temperature of the homogenization treatment is less than 450 ° C., it takes time to precipitate the dispersed particles, and a necessary distribution density cannot be ensured. On the other hand, when the holding temperature of the homogenization treatment exceeds 530 ° C., the size of the dispersed particles becomes coarse, the equivalent circle diameter of some dispersed particles exceeds 0.5 μm, and the function of capturing hydrogen decreases. The distribution density of the dispersed particles having an equivalent diameter of 0.5 μm or less becomes less than the specified value, and the amount of hydrogen trapped by the dispersed particles is reduced as a whole, and the hydrogen embrittlement resistance is lowered. Further, if the holding time is less than 1 hour, the precipitation of the dispersed particles is insufficient, and the necessary distribution density cannot be ensured. When the holding time exceeds 10 hours, the equivalent circle diameter of some of the dispersed particles exceeds 0.5 μm and the function of capturing hydrogen decreases, and the distribution density of dispersed particles having an equivalent circle diameter of 0.5 μm or less is reduced. The amount of hydrogen captured by the dispersed particles decreases as a whole, and the hydrogen embrittlement resistance decreases.
均質化処理後、一旦室温まで冷却してから再度熱間加工温度まで加熱するか、もしくは均質化処理温度から、直接、熱間加工温度まで温度を調整した後、熱間加工を行う。この熱間加工は、例えば板を製造する場合は熱間圧延であり、押出材を製造する場合は熱間押出であり、鍛造材を製造する場合は熱間鍛造というように、素材を加熱した状態で行う種々の加工方法を含む。 After the homogenization treatment, it is once cooled to room temperature and then heated again to the hot working temperature, or after the temperature is adjusted directly from the homogenization treatment temperature to the hot working temperature, hot working is performed. This hot working is, for example, hot rolling when producing a plate, hot extrusion when producing an extruded material, and hot forging when producing a forged material, and heating the material. Various processing methods performed in the state are included.
熱間加工の後、最終製品の形状により精度良く近づけるために、さらに冷間加工が行われる。この冷間加工は、例えば板を製造する場合は冷間圧延であり、押出材を製造する場合は冷間引き抜きであり、鍛造材を製造する場合は冷間鍛造というように、素材を室温の状態で行う種々の加工方法を含む。 After hot working, cold working is further performed in order to bring it closer to the shape of the final product with higher accuracy. This cold working is, for example, cold rolling when producing a plate, cold drawing when producing an extruded material, and cold forging when producing a forged material. Various processing methods performed in the state are included.
上記の熱間加工後または、冷間加工の途中、冷間加工が終了した後などに、１回または複数回の焼鈍を行っても良い。焼鈍は、材料を所定の温度に一定時間加熱することにより、材料に導入された加工ひずみを除去して、材料の強度・延性バランスを最適に調整するために行われる。 Annealing may be performed once or a plurality of times after the above hot working or during the cold working or after the cold working is finished. Annealing is performed in order to optimally adjust the strength / ductility balance of the material by heating the material to a predetermined temperature for a certain period of time to remove processing strain introduced into the material.
尚、上記製造工程に追加して行われる成形加工・熱処理プロセスについては、本発明で規定したミクロ組織形態に影響しない範囲であれば全て許容されるものである。また、例えば、高圧水素ガスタンクのライナー形状に成形加工する工程も、基本的に上記の熱間加工・冷間加工・焼鈍を適宜組み合わせることによって行われるものである。 In addition, as long as it does not affect the microstructure form prescribed | regulated by this invention about the shaping | molding process and heat processing process performed in addition to the said manufacturing process, all are accept | permitted. Further, for example, the process of forming into a liner shape of a high-pressure hydrogen gas tank is basically performed by appropriately combining the above hot working / cold working / annealing.
以上説明したいように、本発明に係るＡｌ−Ｍｇ系合金は、成分元素の組成範囲とミクロ組織の最適化によって、耐水素脆性が高められており、非常に高圧の水素ガス中においての長期間の使用に対する信頼性を高めることが出来る。 As described above, the Al-Mg alloy according to the present invention has improved hydrogen embrittlement resistance by optimizing the compositional range and the microstructure of the component elements, and can be used for a long time in a very high pressure hydrogen gas. The reliability for the use of can be increased.
尚、本発明では、Ａｌ−Ｍｇ系合金の耐水素脆性を高めるために上述の最適成分組成としたが、その理由は、水素脆化のメカニズムに基づいて、材料のミクロ組織（晶出粒子分布及び分散粒子分布）を最適に制御するためである。基本的に上述の成分範囲に合金成分を調整し、かつ上述の製造プロセスに従って材料を製造した場合は、このミクロ組織に関する規定から外れる可能性は少ないが、このミクロ組織の関する規定を外れてしまった場合、高い耐水素脆性を有することは期待できず本発明の範囲外となる。 In the present invention, the above-mentioned optimum component composition is used in order to increase the hydrogen embrittlement resistance of the Al-Mg alloy. The reason is that the microstructure of the material (crystallized particle distribution) is based on the mechanism of hydrogen embrittlement. And dispersed particle distribution) are optimally controlled. Basically, when the alloy components are adjusted to the above-mentioned component ranges and the material is manufactured in accordance with the above-described manufacturing process, there is little possibility that it will deviate from the provisions related to this microstructure, but the provisions related to this microstructure are not included. In such a case, it cannot be expected to have high hydrogen embrittlement resistance, which falls outside the scope of the present invention.
以下、本発明の実施形態について、実施例を比較例と共に記す。表１に示す組成に調整した各種Ａｌ−Ｍｇ系合金を溶解して、ＤＣ鋳造法により鋳造して厚み８０ｍｍ×幅２００ｍｍ×長さ８００ｍｍサイズの鋳塊を得た。この鋳塊の凝固時の冷却速度は３℃／ｓｅｃとした。これらの鋳造塊を５００℃の加熱保持温度に加熱して、７時間保持する均質化処理を行った後、厚み方向について上下面各５ｍｍ、幅方向について左右各５ｍｍの厚みで面削を行った。これらのサンプルを４８０℃に加熱保持したのち、熱間圧延を行い、板厚４ｍｍとした。さらに冷間圧延を行い板厚１．２ｍｍとした。その後、この冷間圧延板を５００℃に加熱して１ｍｉｎ保持することにより、完全再結晶組織とした後、１００℃／ｍｉｎの冷却速度で室温まで冷却した。 Hereinafter, about an embodiment of the present invention, an example is described with a comparative example. Various Al—Mg alloys adjusted to the compositions shown in Table 1 were dissolved and cast by a DC casting method to obtain an ingot having a thickness of 80 mm × width of 200 mm × length of 800 mm. The cooling rate during solidification of the ingot was 3 ° C./sec. These cast ingots were heated to a heating and holding temperature of 500 ° C. and subjected to a homogenization treatment for 7 hours, and then were chamfered at a thickness of 5 mm for each of the upper and lower surfaces in the thickness direction and 5 mm for each of the left and right surfaces in the width direction. . These samples were heated and held at 480 ° C. and then hot-rolled to a plate thickness of 4 mm. Further, cold rolling was performed to a plate thickness of 1.2 mm. Thereafter, the cold-rolled sheet was heated to 500 ° C. and held for 1 min to form a complete recrystallized structure, and then cooled to room temperature at a cooling rate of 100 ° C./min.
以上のようにして得た焼鈍板材について、以下に記載する条件で鋭敏化処理を行った。まず、１．２ｍｍ厚の焼鈍板材について板厚１．０ｍｍまで冷間圧延を行ってひずみを導入した後、これを１３０℃×１００時間の条件で熱処理を行った。この鋭敏化処理は、Ａｌ−Ｍｇ系合金を意図的に水素脆化しやすい状態にするための処理で、これによって、引き続き行う湿度制御環境中での低ひずみ速度引張り試験（ＳＳＲＴ試験：Ｓｌｏｗ
Ｓｔｒａｉｎ Ｒａｔｅ Ｔｅｎｓｉｌｅ試験） により、材料毎の耐水素脆性の違いをより明確に区別できるようになる。この鋭敏化処理後の材料について、以下の方法にてミクロ組織評価（晶出粒子及び分散粒子の分布密度測定）を行い、更に、耐水素脆性の評価試験を行った。
The annealed sheet material obtained as described above was sensitized under the conditions described below. First, a 1.2 mm-thick annealed plate was cold-rolled to a thickness of 1.0 mm to introduce strain, and then subjected to heat treatment under conditions of 130 ° C. × 100 hours. This sensitization treatment is a treatment for intentionally making the Al—Mg-based alloy easily hydrogen embrittled, and thereby, a low strain rate tensile test (SSRT test: Slow test) in a humidity control environment to be subsequently performed.
(Strain Rate Tensile test) makes it possible to more clearly distinguish the difference in hydrogen embrittlement resistance for each material. The material after the sensitization treatment was subjected to microstructure evaluation (measurement of distribution density of crystallized particles and dispersed particles) by the following method, and further an evaluation test of hydrogen embrittlement resistance was performed.
晶出粒子の分布密度測定
各供試材の圧延面表面を金属組織観察法の常法に従って鏡面研磨仕上げした後、ケラー氏液（塩酸２０ｍｌ、硝酸２０ｍｌ、フッ酸５ｍｌ、蒸留水５０ｍｌの混合液）に１分間浸漬してエッチング後に金属組織観察用の顕微鏡にて、１００倍の設定で順光観察して、任意の１０視野について写真撮影を行った。円相当径で１μｍ以上のサイズの分散粒子を１視野ごとに計数して、１０視野分の合計の粒子数を測定面積で割ることによって、分散粒子数（個／ｍｍ２）を測定した。
Measurement of distribution density of crystallized particles The surface of the rolled surface of each test material was mirror-polished in accordance with a conventional method for observing the metal structure, and then Keller's solution (
分散粒子の分布密度測定
各供試材より、圧延方向断面が観察面となるようにＴＥＭ観察のためのサンプルを採取して、機械研磨により約１０μｍ程度の薄膜状に加工した後、電解研磨により約３００ｎｍ厚のＴＥＭ観察用のサンプルを作製して、ＴＥＭにより１００００倍の倍率で観察を行った。観察された円相当径０．５μｍ以下のサイズの粒子（ＴＥＭの通常の明視野像では黒くコントラストがついて観察される粒子）のうちいくつかの粒子について、ＴＥＭ−ＥＤＸ装置により絞った電子線を照射して、放出されるＸ線のエネルギー分布を解析して元素解析をして、分散粒子からＭｎ、Ｃｒ（他の添加遷移元素がある合金の場合、当該他の遷移元素も含む）が検出されることを確認した後、１０視野の写真撮影をおこなって、各視野について円相当径０．５μｍ以下の分散粒子数を計測して、１０視野分を合計した粒子を測定した総視野面積で割ることによって、分散粒子の分布密度を測定した。
Measurement of distribution density of dispersed particles Samples for TEM observation were taken from each specimen so that the cross section in the rolling direction was the observation surface, processed into a thin film of about 10 μm by mechanical polishing, and then electropolished. A sample for TEM observation having a thickness of about 300 nm was prepared and observed with a TEM at a magnification of 10,000 times. For some of the observed particles with a circle-equivalent diameter of 0.5 μm or less (particles that are observed with a black contrast in a normal TEM bright field image), an electron beam focused by a TEM-EDX apparatus is used. Irradiate, analyze the energy distribution of the emitted X-rays, analyze the element, and detect Mn and Cr (including other transition elements in the case of alloys with other added transition elements) from the dispersed particles After confirming that the number of dispersed particles having a circle-equivalent diameter of 0.5 μm or less was measured for each visual field, the total visual field area obtained by measuring the total of 10 visual fields was measured. The distribution density of the dispersed particles was measured by dividing.
耐水素脆性評価試験
各種のＡｌ−Ｍｇ系合金の耐水素脆性を評価する試験として、湿度制御環境中でのＳＳＲＴ試験を行った。ＳＳＲＴ試験では、試験雰囲気湿度を制御した環境中にて、アルミニウム合金材を低ひずみ速度で破断するまで引張変形する試験であって、引張変形中に連続的に露出するアルミニウム合金新生面と試験雰囲気中の水蒸気が試験片表面で反応して、この反応に伴い水素が発生してその一部が材料中に侵入する。ＳＳＲＴ試験において試験湿度を高く設定すると、前記反応で発生する水素が増えて、高圧の水素ガス環境を簡便に模擬することができる。一方、試験湿度を非常に低く設定すると、前記反応で発生する水素が少なくなって、材料中に侵入する水素がほとんど無くなるので、水素脆化の影響の無い材料そのものの延性を評価することができる。
As a test for evaluating the resistance to hydrogen embrittlement of the embrittlement resistance evaluation test various Al-Mg-based alloy was subjected to SSRT test at a humidity control environment. The SSRT test is a test in which an aluminum alloy material is subjected to tensile deformation until it breaks at a low strain rate in an environment in which the test atmosphere humidity is controlled, and the aluminum alloy newly exposed surface continuously exposed during tensile deformation and the test atmosphere. The water vapor reacts on the surface of the test piece, and hydrogen is generated along with this reaction, and a part of the hydrogen enters the material. If the test humidity is set high in the SSRT test, the amount of hydrogen generated by the reaction increases, and a high-pressure hydrogen gas environment can be easily simulated. On the other hand, when the test humidity is set very low, the amount of hydrogen generated by the reaction is reduced, and almost no hydrogen penetrates into the material, so that the ductility of the material itself without the influence of hydrogen embrittlement can be evaluated. .
ここでは、各供試材より図１に示す形状のＳＳＲＴ試験用の試験片を、引張方向が圧延直角方向となるように作製して、以下で説明する条件のＳＳＲＴ試験に供した。ＳＳＲＴ試験では、一定のクロスヘッド速度０．００１ｍｍ／ｍｉｎ（初期ひずみ速度１．３９×１０−６／ｓ）で試験片が破断するまで引張変形を付与し、試験雰囲気の湿度は、高圧水素ガス環境を模擬した相対湿度９０％（以下、「ＲＨ９０％」と略記）雰囲気、および水素の影響を受けない乾燥窒素ガス（以下、「ＤＮＧ」と略記）雰囲気の２種類とした。これら２種各々の雰囲気中での材料の破断伸びを、εＲＨ90％およびεＤＮＧと表記して、各材料の水素脆化しやすさ、即ち、「水素脆化感受性指数」を下記の式で定義した。水素脆化感受性指数は、ＤＮＧ環境中の伸びを基準とした場合の、高圧水素ガス模擬環境（ＲＨ９０％）中における低下の度合いを示すものである。 Here, a test piece for the SSRT test having the shape shown in FIG. 1 was prepared from each test material so that the tensile direction was a direction perpendicular to the rolling direction, and was subjected to the SSRT test under the conditions described below. In the SSRT test, tensile deformation was applied until the test piece broke at a constant crosshead speed of 0.001 mm / min (initial strain speed of 1.39 × 10 −6 / s), and the humidity of the test atmosphere was high-pressure hydrogen gas. There are two types of atmospheres: a relative humidity 90% atmosphere (hereinafter abbreviated as “RH 90%”) and a dry nitrogen gas (hereinafter abbreviated as “DNG”) atmosphere that is not affected by hydrogen. The elongation at break of the materials in each of these two atmospheres is expressed as ε RH 90% and ε DNG, and the hydrogen embrittlement susceptibility of each material, that is, the “hydrogen embrittlement susceptibility index” is defined by the following formula: did. The hydrogen embrittlement susceptibility index indicates the degree of decrease in a high-pressure hydrogen gas simulated environment (RH 90%) when the elongation in the DNG environment is used as a reference.
水素脆化感受性指数は、全く水素の影響をうけず脆化しない場合は「０」の値をとり、ＲＨ９０％中で非常に顕著な脆性を示して延性が無くなった場合に「１」の値をとり、中程度の脆性を示す場合に０から１の間の値を示す。尚、本実施形態における水素脆化感受性指数の値は、上述のように、供試材間の耐水素脆性の違いを明確化するために、敢えて供試材に予め水素脆化しやすくなるよう鋭敏化処理を行った材料についての結果である。よって、本実施形態における評価結果は、各材料の耐水素脆性の相対的な比較を示すものであって、各材料の高圧水素ガス容器等の用途での実使用の可否を直接的に示すものではない。 The hydrogen embrittlement susceptibility index takes a value of “0” when it is not affected by hydrogen at all and does not embrittle, and is a value of “1” when ductility disappears in RH 90%, showing very remarkable brittleness. And shows a value between 0 and 1 when it shows moderate brittleness. Note that the value of the hydrogen embrittlement susceptibility index in this embodiment is sharp so that the test material is likely to be easily hydrogen embrittled in advance in order to clarify the difference in hydrogen embrittlement resistance between the test materials as described above. It is a result about the material which performed the chemical treatment. Therefore, the evaluation results in the present embodiment show a relative comparison of the hydrogen embrittlement resistance of each material, and directly show whether or not each material can be used in applications such as a high-pressure hydrogen gas container. is not.
本実施形態で製造したＡｌ−Ｍｇ系合金（合金Ｎｏ．１〜２１）についての、ミクロ組織評価、ＳＳＲＴ試験結果から得られた水素脆化感受性の値について表２に示す。 Table 2 shows the hydrogen embrittlement susceptibility values obtained from the microstructure evaluation and SSRT test results for the Al—Mg-based alloys (alloys Nos. 1 to 21) manufactured in the present embodiment.
表２を参照しつつ評価結果について述べる。まず、実施例である合金Ｎｏ．５と、比較例である合金Ｎｏ．１６、Ｎｏ．１７、Ｎｏ．１８の評価結果を比較しつつ、不純物であるＦｅ、Ｓｉ量及びＡｌ−Ｆｅ−Ｓｉ晶出粒子の分布密度と耐水素脆化性との関係について検討する。本発明例のＮｏ．５は、不純物であるＦｅ、Ｓｉ量がいずれも本発明の範囲内であり、晶出粒子の分布密度が本発明で規定する範囲内となっている。よって、水素脆化感受性指数が比較的低めであり、比較的高い耐水素脆性を有している。 The evaluation results will be described with reference to Table 2. First, Alloy No. which is an example. 5 and alloy No. 5 as a comparative example. 16, no. 17, no. While comparing the 18 evaluation results, the relationship between the Fe and Si amounts as impurities and the distribution density of Al—Fe—Si crystallized particles and hydrogen embrittlement resistance will be examined. No. of the example of the present invention. In No. 5, the amounts of impurities Fe and Si are both within the range of the present invention, and the distribution density of crystallized particles is within the range defined by the present invention. Therefore, the hydrogen embrittlement susceptibility index is relatively low and has a relatively high hydrogen embrittlement resistance.
これに対し、比較例であるＮｏ．１６、Ｎｏ．１７、Ｎｏ．１８は、不純物であるＦｅ又はＳｉ、若しくはその双方が本発明で規制する量よりも多い。このため、晶出粒子の分布密度が本発明で規定する範囲よりも高い。よって、水素脆化感受性指数が高めであり、耐水素脆性が低くなることが確認できた。 On the other hand, No. which is a comparative example. 16, no. 17, no. 18 is more than the amount regulated by the present invention of Fe and / or Si which are impurities. For this reason, the distribution density of the crystallized particles is higher than the range specified in the present invention. Therefore, it was confirmed that the hydrogen embrittlement sensitivity index was high and the hydrogen embrittlement resistance was low.
同様に、実施例であるＮｏ．１、Ｎｏ．２、Ｎｏ．３、Ｎｏ．４は、いずれも不純物Ｆｅ、Ｓｉ量が本発明の範囲内であり、晶出粒子の分布密度が本発明で規定する範囲内である。よって水素脆化感受性が比較的低めであり、比較的高い耐水素脆性を有している。 Similarly, in Example No. 1, no. 2, no. 3, no. In No. 4, the amounts of impurities Fe and Si are both within the range of the present invention, and the distribution density of crystallized particles is within the range defined by the present invention. Accordingly, the hydrogen embrittlement susceptibility is relatively low and the hydrogen embrittlement resistance is relatively high.
また、不純物であるＦｅ、Ｓｉに加えて必須の制御成分であるＭｇ、Ｃｕ量の影響についてみると、比較例のＮｏ．１２は、Ｍｇ量が本発明の規定よりも多い。このため熱間圧延中に割れが発生して、評価サンプルを作製することができず、以降の評価試験を中止した。また、比較例のＮｏ．１３は、Ｍｇ量が本発明の規定よりも少ない。このため本合金はもともと水素脆化感受性が低く、高い耐水素脆性を有している。 In addition to the impurities Fe and Si, in addition to the effects of Mg and Cu, which are essential control components, No. in the comparative example. No. 12 has a larger amount of Mg than specified in the present invention. For this reason, the crack generate | occur | produced during hot rolling, the evaluation sample could not be produced, and the subsequent evaluation test was stopped. Moreover, No. of the comparative example. In No. 13, the amount of Mg is less than that of the present invention. For this reason, this alloy originally has low hydrogen embrittlement susceptibility and high hydrogen embrittlement resistance.
比較例のＮｏ．１４は、Ｃｕ量が本発明の規定よりも少ない。このため本合金は、Ｆｅ及びＳｉ量が本発明の規定の範囲内で、晶出粒子の分布密度が本発明の規定の範囲内であるにも関らず、水素脆化感受性が比較的高めであり、耐水素脆性は比較的低くなることがわかる。そして、比較例のＮｏ．１５は、Ｃｕ量が多いため、水素脆化感受性が低く耐水素脆性が高かった。但し、Ｃｕ量が多すぎ耐食性が劣ることが明らかであり、実用的ではないと推察される。 Comparative Example No. No. 14 has less Cu than prescribed in the present invention. Therefore, this alloy has a relatively high sensitivity to hydrogen embrittlement even though the amount of Fe and Si is within the specified range of the present invention and the distribution density of crystallized particles is within the specified range of the present invention. It can be seen that the hydrogen embrittlement resistance is relatively low. And No. of a comparative example. Since No. 15 had a large amount of Cu, the hydrogen embrittlement sensitivity was low and the hydrogen embrittlement resistance was high. However, it is clear that there is too much Cu content and the corrosion resistance is inferior, and it is assumed that it is not practical.
次に、Ｍｎ、Ｃｒ量及びＡｌ−Ｍｎ化合物又はＡｌ−Ｍｎ−Ｃｒ化合物からなる分散粒子の分布密度と耐水素脆化性との関係について検討する。実施例であるＮｏ．６、Ｎｏ．７、Ｎｏ．８、Ｎｏ．９の合金は、Ｆｅ、Ｓｉ量が本発明の範囲内であることに加えて、Ｍｎ、Ｃｒ量及びその合計量が本発明の範囲内にある。その結果、分散粒子の分布密度が本発明の規定の範囲内である。そして、水素脆化感受性指数が低く耐水素脆性が高い。特に、合金Ｎｏ．５のＭｎ、Ｃｒを含まないものよりも水素脆化感受性指数が更に低くなっておりことから、より高い耐水素脆性を有することがわかる。 Next, the relationship between the amount of Mn, Cr, the distribution density of dispersed particles composed of an Al—Mn compound or an Al—Mn—Cr compound, and hydrogen embrittlement resistance will be examined. No. as an example. 6, no. 7, no. 8, no. In addition to the amount of Fe and Si being within the scope of the present invention, the alloy No. 9 has the amount of Mn and Cr and the total amount within the scope of the present invention. As a result, the distribution density of the dispersed particles is within the specified range of the present invention. The hydrogen embrittlement sensitivity index is low and the hydrogen embrittlement resistance is high. In particular, alloy no. Since the hydrogen embrittlement susceptibility index is further lower than that of No. 5 containing no Mn and Cr, it can be seen that the hydrogen embrittlement resistance is higher.
また、比較例のＮｏ．１９、Ｎｏ．２０は、それぞれＭｎ、Ｃｒ量が本発明で規定される量よりも多い。既に説明したように、Ｍｎ、Ｃｒ量が好適な範囲を超える場合、余剰分のＭｎ、Ｃｒが晶出粒子に固溶し晶出粒子の分布密度を増大させることとなる。このことは表２の結果からも確認することができ、水素脆化感受性が比較的高めであり、耐水素脆性は比較的低めとなっている。 Moreover, No. of the comparative example. 19, no. No. 20 has more Mn and Cr amounts than those specified in the present invention. As already explained, when the amounts of Mn and Cr exceed the preferred ranges, the excess Mn and Cr are dissolved in the crystallized particles, and the distribution density of the crystallized particles is increased. This can also be confirmed from the results in Table 2. The hydrogen embrittlement sensitivity is relatively high, and the hydrogen embrittlement resistance is relatively low.
更に、Ｍｎ、Ｃｒ以外の遷移元素添加の作用について検討すると、実施例のＮｏ．１０、Ｎｏ．１１は、いずれも不純物Ｆｅ・Ｓｉ量が本発明の範囲内であり、規定範囲内のＭｎ、Ｃｒが添加されると共に、他の遷移元素が適宜添加されたものである。これらの合金も水素脆化感受性が低く、耐水素脆性が高い。 Further, when the effect of addition of transition elements other than Mn and Cr is examined, No. of the example. 10, no. In No. 11, the amount of impurities Fe · Si is within the range of the present invention, Mn and Cr within the specified range are added, and other transition elements are added as appropriate. These alloys are also low in hydrogen embrittlement sensitivity and high in hydrogen embrittlement resistance.
尚、Ｍｎ、Ｃｒ及びの遷移元素の添加については、必須ではないことが実施例のＮｏ．２、Ｎｏ．４、Ｎｏ．５の合金が水素脆化感受性が低く、耐水素脆性が高いことから確認できる。このことは、Ｎｏ．１のようにＭｎ、Ｃｒを添加しつつもその合計濃度が不足するものの、水素脆化感受性が低く、耐水素脆性が高いことからも確認できる。即ち、Ｍｎ、Ｃｒは添加しなくとも良いが、添加する場合その添加量を上限以下に管理することが重要である。 It should be noted that the addition of Mn, Cr and transition elements is not essential in the examples No. 2, no. 4, no. It can be confirmed from the fact that the alloy No. 5 has low hydrogen embrittlement susceptibility and high hydrogen embrittlement resistance. This is no. Although the total concentration is insufficient while adding Mn and Cr as in 1, it can be confirmed from the low hydrogen embrittlement susceptibility and high hydrogen embrittlement resistance. That is, Mn and Cr do not have to be added, but when added, it is important to manage the amount added to the upper limit or less.
本発明に係るＡｌ−Ｍｇ系合金は、組成範囲及びミクロ組織（晶出粒子、分散粒子の分布密度）の最適化によって、耐水素脆性を高めたものであり、非常に高圧の水素ガス中においての長期間の使用に対する信頼性を高めることが出来る。本発明に係るＡｌ−Ｍｇ系合金は、熱処理を行わなくても比較的高い強度が得られる非熱処理型のアルミニウム合金であり成形性、接合性にも優れる。本発明は、燃料電池自動車に搭載される高圧水素ガス容器用の部材のように、高圧水素ガス環境に暴露されると同時に荷重が負荷された状態で長時間用いられる部材の構成材料として有用である。
The Al—Mg alloy according to the present invention has improved hydrogen embrittlement resistance by optimization of the composition range and microstructure (the distribution density of crystallized particles and dispersed particles), and in an extremely high pressure hydrogen gas Reliability for long-term use can be increased. The Al—Mg alloy according to the present invention is a non-heat-treatable aluminum alloy that can obtain a relatively high strength without heat treatment, and is excellent in formability and bondability. INDUSTRIAL APPLICABILITY The present invention is useful as a constituent material of a member that is used for a long time in a state in which a load is applied at the same time as being exposed to a high-pressure hydrogen gas environment, such as a member for a high-pressure hydrogen gas container mounted on a fuel cell vehicle. is there.
Claims (4)
Ａｌ−Ｆｅ−Ｓｉ化合物からなり、円相当径で１μｍ以上のサイズを有する晶出粒子の分布密度が４０００個/ｍｍ２以下であるＡｌ−Ｍｇ系合金材。 The content of Fe and Si, which are Mg: 3.0 to 6.0%, Cu: 0.03 to 1.0%, and impurities, is Fe: less than 0.15%, and Si: Al—Mg-based alloy material for high-pressure hydrogen gas that is limited to less than 0.15% and has excellent resistance to hydrogen embrittlement consisting of the balance Al and inevitable impurities,
An Al—Mg-based alloy material comprising an Al—Fe—Si compound and having a distribution density of crystallized particles having an equivalent circle diameter of 1 μm or more and 4000 particles / mm 2 or less.
Ａｌ−Ｍｎ化合物又はＡｌ−Ｍｎ−Ｃｒ化合物からなり、円相当径０．５μｍ以下のサイズを有する分散粒子の分布密度が１０００００個/ｍｍ２以上である請求項１記載の高圧水素ガス用のＡｌ−Ｍｇ系合金材。 % By mass, containing Mn: 0.02-0.8%, or Mn: 0.02-0.8% and Cr: 0.01-0.2%, 0.05% ≦ Mn + Cr Contained in a range satisfying ≦ 0.9%,
2. The Al for high-pressure hydrogen gas according to claim 1, wherein the distribution density of dispersed particles comprising an Al—Mn compound or an Al—Mn—Cr compound and having a circle-equivalent diameter of 0.5 μm or less is 100,000 / mm 2 or more. -Mg-based alloy material.
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