JP5885139B2 - High specific strength magnesium with age hardening properties - Google Patents

High specific strength magnesium with age hardening properties Download PDF

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JP5885139B2
JP5885139B2 JP2012033559A JP2012033559A JP5885139B2 JP 5885139 B2 JP5885139 B2 JP 5885139B2 JP 2012033559 A JP2012033559 A JP 2012033559A JP 2012033559 A JP2012033559 A JP 2012033559A JP 5885139 B2 JP5885139 B2 JP 5885139B2
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正広 久保田
正広 久保田
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Nihon University
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本発明は、強度の高いマグネシウムバルク材及びその製造法に関する。   The present invention relates to a magnesium bulk material having high strength and a method for producing the same.

金属マグネシウムは、非常に軽い軽金属材料として有用であるが、純マグネシウムの強度100MPa以下と非常に低いため、輸送機器をはじめとする構造部材としての使用は皆無に等しいのが現状である。   Metallic magnesium is useful as a very light light metal material, but since the strength of pure magnesium is as low as 100 MPa or less, it is currently used as a structural member including transportation equipment.

金属マグネシウムの強度を向上させる方法としては、熔解・鋳造法で合金を作製する方法が一般的に行なわれている。しかし、このような方法では、工程が煩雑であり、熔解する必要があり、マグネシウムの燃焼という危険を伴うという問題がある。また、マグネシウムの合金化においては、レアアースメタル等の高価な元素を添加する必要がある。   As a method of improving the strength of metallic magnesium, a method of producing an alloy by a melting / casting method is generally performed. However, such a method has a problem that the process is complicated, needs to be melted, and involves a risk of burning magnesium. Further, in alloying magnesium, it is necessary to add an expensive element such as rare earth metal.

一方、金属ナノ結晶粒子に、結晶粒成長抑制物質として金属酸化物などを存在させ、メカニカルミリング処理後、放電プラズマ処理するナノ結晶金属バルク材が報告されている(特許文献1)。   On the other hand, a nanocrystalline metal bulk material in which a metal oxide or the like is present in a metal nanocrystal particle as a crystal grain growth inhibiting substance and subjected to a discharge plasma treatment after mechanical milling treatment has been reported (Patent Document 1).

特開2004−143596号公報JP 2004-143596 A

本発明の課題は、高強度なマグネシウムバルク材を提供することにある。   An object of the present invention is to provide a high-strength magnesium bulk material.

そこで本発明者は、高価なレアメタル等を使用することなくマグネシウムの高強度化を図るべく種々検討した結果、マグネシウム粉末を酸素含有化合物の存在下にメカニカルミリング処理し、焼結し、次に得られた焼結体を加熱処理すれば、該焼結体が加熱処理により強度が飛躍的に向上し、高強度のマグネシウムバルク材が得られることを見出し、本発明を完成した。   Therefore, as a result of various studies to increase the strength of magnesium without using an expensive rare metal or the like, the inventor mechanically milled magnesium powder in the presence of an oxygen-containing compound, sintered, and then obtained. When the sintered body thus obtained was heat-treated, it was found that the strength of the sintered body was dramatically improved by the heat treatment, and a high-strength magnesium bulk material was obtained, and the present invention was completed.

すなわち、本発明は、以下の〔1〕〜〔8〕に関する。
〔1〕マグネシウムの粉末を酸素含有化合物の存在下にメカニカルミリング処理した後、該粉末を焼結し、次いで得られた焼結体を加熱処理することにより得られるマグネシウムバルク材。
〔2〕原料のマグネシウム粉末が、純度99%以上のマグネシウム粉末である〔1〕記載のマグネシウムバルク材。
〔3〕酸素含有化合物が、カルボン酸類、硫酸類、リン酸類及びスルホン酸類から選ばれる酸類である〔1〕又は〔2〕記載のマグネシウムバルク材。
〔4〕メカニカルミリング処理が、カルボン酸類の存在下、ボールミルを用いるメカニカルミリング処理3〜80時間である〔1〕〜〔3〕のいずれかに記載のマグネシウムバルク材。
〔5〕焼結処理が、放電プラズマ焼結である〔1〕〜〔4〕のいずれかに記載のマグネシウムバルク材。
〔6〕加熱処理が、焼結体を150〜300℃に10分〜8時間加熱するものである〔1〕〜〔5〕のいずれかに記載のマグネシウムバルク材。
〔7〕Mg以外にMgOを5〜45質量%含有するものである〔1〕〜〔6〕のいずれかに記載のマグネシウムバルク材。
〔8〕マグネシウムの粉末を酸素含有化合物の存在下にメカニカルミリング処理した後、該粉末を放電プラズマ焼結し、次いで得られた焼結体を加熱処理することを特徴とするマグネシウムバルク材の製造法。
That is, the present invention relates to the following [1] to [8].
[1] A magnesium bulk material obtained by mechanically milling magnesium powder in the presence of an oxygen-containing compound, sintering the powder, and then heat-treating the obtained sintered body.
[2] The magnesium bulk material according to [1], wherein the raw material magnesium powder is a magnesium powder having a purity of 99% or more.
[3] The magnesium bulk material according to [1] or [2], wherein the oxygen-containing compound is an acid selected from carboxylic acids, sulfuric acids, phosphoric acids and sulfonic acids.
[4] The magnesium bulk material according to any one of [1] to [3], wherein the mechanical milling treatment is performed for 3 to 80 hours using a ball mill in the presence of carboxylic acids.
[5] The magnesium bulk material according to any one of [1] to [4], wherein the sintering treatment is discharge plasma sintering.
[6] The magnesium bulk material according to any one of [1] to [5], wherein the heat treatment heats the sintered body to 150 to 300 ° C. for 10 minutes to 8 hours.
[7] The magnesium bulk material according to any one of [1] to [6], which contains 5 to 45% by mass of MgO in addition to Mg.
[8] Manufacture of a magnesium bulk material, characterized in that magnesium powder is mechanically milled in the presence of an oxygen-containing compound, then the powder is subjected to discharge plasma sintering, and then the obtained sintered body is heat-treated. Law.

本発明により得られるマグネシウムバルク材は、メカニカルミリング処理及びプラズマ焼結により得られた焼結体に比べて、加熱処理により強度が飛躍的に向上しており、輸送機器等の構造部材として広範囲に応用可能である。   Magnesium bulk material obtained by the present invention has dramatically improved strength due to heat treatment compared to sintered bodies obtained by mechanical milling and plasma sintering, and is widely used as a structural member for transportation equipment. Applicable.

本発明のマグネシウムバルク材のビッカース硬度と、加熱温度及びMM処理時間との関係を示す図である。It is a figure which shows the relationship between the Vickers hardness of the magnesium bulk material of this invention, heating temperature, and MM processing time. 本発明のマグネシウムバルク材のビッカース硬度と、加熱時間及びMM処理時間との関係を示す図である。It is a figure which shows the relationship between the Vickers hardness of the magnesium bulk material of this invention, a heating time, and MM processing time. 本発明のマグネシウムバルク材のX線回折スペクトルを示す図である。It is a figure which shows the X-ray-diffraction spectrum of the magnesium bulk material of this invention. 加熱時間と、MgO/Mg比との関係を示す図である。It is a figure which shows the relationship between a heating time and MgO / Mg ratio.

本発明のマグネシウムバルク材は、(1)マグネシウムの粉末を酸素含有化合物の存在下にメカニカルミリング処理し、次に(2)該粉末を焼結し、さらに(3)得られた焼結体を加熱処理することにより得られる。   The magnesium bulk material of the present invention is obtained by (1) mechanically milling magnesium powder in the presence of an oxygen-containing compound, then (2) sintering the powder, and (3) obtaining the obtained sintered body. Obtained by heat treatment.

原料としてのマグネシウムは、金属マグネシウムであればよいが、純度98%以上のマグネシウム、特に純度99%以上のマグネシウムを用いるのが好ましい。また用いるマグネシウム粉体の粒子径は800μm以下、さらに500μm以下であるのが、メカニカルミリング、焼結及び加熱処理により高強度のマグネシウムバルク材を得る点で好ましい。   Magnesium as a raw material may be metallic magnesium, but it is preferable to use magnesium having a purity of 98% or more, particularly magnesium having a purity of 99% or more. Further, the particle diameter of the magnesium powder to be used is preferably 800 μm or less, and more preferably 500 μm or less, from the viewpoint of obtaining a high-strength magnesium bulk material by mechanical milling, sintering and heat treatment.

マグネシウム粉末のメカニカルミリングは、酸素含有化合物の存在下に行う。当該酸素含有化合物の存在下にマグネシウムをメカニカルミリングし、放電プラズマ焼結し、次いで加熱することにより、最後の加熱処理時にマグネシウム焼結体の強度が上昇する。酸素含有化合物としては、酸素を含有し、かつ金属を含まない化合物が好ましく、カルボン酸類、硫酸類、リン酸類及びスルホン酸類がより好ましい。これらの酸類のうち、焼結により消失する点から、有機酸がさらに好ましく、脂肪酸類がさらに好ましい。脂肪酸類としては、脂肪酸、脂肪酸エステル、脂肪酸アミド等が好ましく、炭素数1〜30の脂肪酸、炭素数2〜50の脂肪酸エステル、炭素数1〜30の脂肪酸アミドがより好ましく、炭素数1〜30の脂肪酸がさらに好ましく、炭素数6〜30の脂肪酸が特に好ましい。これらの酸素含有化合物の使用量は、加熱処理時の強度向上効果の点から、マグネシウム100質量部に対して0.1〜10質量部が好ましく、0.1〜5質量部がより好ましく、0.5〜5質量部がさらに好ましい。   Mechanical milling of the magnesium powder is performed in the presence of an oxygen-containing compound. By mechanically milling magnesium in the presence of the oxygen-containing compound, discharge plasma sintering, and then heating, the strength of the magnesium sintered body is increased during the final heat treatment. As the oxygen-containing compound, a compound containing oxygen and not containing a metal is preferable, and carboxylic acids, sulfuric acids, phosphoric acids and sulfonic acids are more preferable. Of these acids, organic acids are more preferable, and fatty acids are more preferable from the viewpoint of disappearance by sintering. As fatty acids, fatty acids, fatty acid esters, fatty acid amides and the like are preferable, fatty acids having 1 to 30 carbon atoms, fatty acid esters having 2 to 50 carbon atoms, and fatty acid amides having 1 to 30 carbon atoms are more preferable, and those having 1 to 30 carbon atoms. Are more preferable, and fatty acids having 6 to 30 carbon atoms are particularly preferable. The amount of these oxygen-containing compounds used is preferably from 0.1 to 10 parts by weight, more preferably from 0.1 to 5 parts by weight, based on 100 parts by weight of magnesium, from the viewpoint of improving the strength during heat treatment. More preferably, it is 5-5 mass parts.

メカニカルミリング処理は、機械的エネルギーを付与しながら混合する方法であれば特に限定されるものではないが、例えばボールミル、ターボミル、メカノフュージョン、ディスクミル等を挙げることができ、中でもボールミルが好ましく、特に振動型ボールミル、遊星型ボールミルが好ましい。ボールミルを採用する場合、ボールとしては鋼、セラミックスが用いられるが、鋼が好ましい。その使用量はマグネシウム100質量部に対して100〜5000質量部程度が好ましい。回転数は、100〜800rpmが好ましい。処理時間は1時間〜100時間が好ましく、さらに3〜80時間がより好ましく、8〜50時間がさらに好ましく、20〜40時間がさらに好ましく、28〜36時間が特に好ましい。また、雰囲気は、不活性ガス雰囲気、例えば窒素ガス、アルゴンガス雰囲気で行うのが好ましい。   The mechanical milling process is not particularly limited as long as it is a method of mixing while applying mechanical energy, and examples thereof include a ball mill, a turbo mill, a mechano-fusion, a disk mill, etc. Among them, a ball mill is preferable, A vibration type ball mill and a planetary ball mill are preferable. When a ball mill is employed, steel and ceramics are used as the ball, but steel is preferred. As for the usage-amount, about 100-5000 mass parts is preferable with respect to 100 mass parts of magnesium. The rotation speed is preferably 100 to 800 rpm. The treatment time is preferably 1 hour to 100 hours, more preferably 3 to 80 hours, further preferably 8 to 50 hours, further preferably 20 to 40 hours, and particularly preferably 28 to 36 hours. The atmosphere is preferably an inert gas atmosphere such as a nitrogen gas or argon gas atmosphere.

得られたメカニカルミリング混合物を焼結する。焼結手段は、無加圧焼結法、ホット水圧プレス法、高周波誘導加熱法、放電プラズマ焼結法(SPS)が挙げられるが、放電プラズマ焼結が特に好ましい。放電プラズマ焼結法としては、放電プラズマ装置に黒鉛ダイスを設置し、真空又は不活性ガス(窒素、アルゴン等)雰囲気下、黒鉛ダイスにパルス直流又は短形波を加えた直流を流すか、あるいは最初にパルス直流を流し次いで短形波を加えた直流を流して行う。放電プラズマ条件としては、原料を700〜1200℃、加圧力20〜80MPaに60〜600秒保持するのが好ましい。
また、得られるマグネシウムバルク材の形状は、焼結に用いる装置により調整することができる。
The obtained mechanical milling mixture is sintered. Examples of the sintering means include pressureless sintering, hot hydraulic pressing, high frequency induction heating, and discharge plasma sintering (SPS), with discharge plasma sintering being particularly preferred. As a spark plasma sintering method, a graphite die is installed in a discharge plasma apparatus, and a direct current obtained by applying a pulse direct current or a short wave to a graphite die in a vacuum or an inert gas (nitrogen, argon, etc.) atmosphere, or First, a pulse direct current is applied, and then a direct current with a short wave added is applied. As discharge plasma conditions, it is preferable to hold the raw material at 700 to 1200 ° C. and a pressure of 20 to 80 MPa for 60 to 600 seconds.
Moreover, the shape of the obtained magnesium bulk material can be adjusted with the apparatus used for sintering.

次に得られた焼結体を加熱処理する。当該加熱処理により焼結体の強度が飛躍的に向上する。この強度向上効果の理由は、定かではないが、メカニカルミリング処理においてマグネシウム粉末中に均一に分散された少量の酸素含有化合物が焼結により完全に消失せず、少量酸素の状態で焼結体中に均一に残存し、当該酸素が加熱処理により一部マグネシウムと反応して酸化マグネシウムを生成することによるものと考えられる。なお、焼結体は一度常温に冷却してから、加熱処理に付すのが好ましい。
加熱処理は、大気圧下、150〜300℃に10分〜8時間行うのが好ましく、200〜300℃に10分〜8時間行うのがより好ましく、220〜280℃に10分〜8時間行うのがさらに好ましく、230〜270℃に10分〜8時間行うのがさらに好ましい。また、加熱雰囲気は、大気中でもよいし、不活性ガス中でもよいが、大気中がより好ましく、25〜35質量%がさらに好ましい。
Next, the obtained sintered body is heat-treated. The strength of the sintered body is dramatically improved by the heat treatment. The reason for this strength improvement effect is not clear, but a small amount of oxygen-containing compound uniformly dispersed in the magnesium powder in the mechanical milling process is not completely lost by sintering, and in the sintered body in a small amount of oxygen. It is considered that the oxygen remains uniformly and partly reacts with magnesium by heat treatment to produce magnesium oxide. It is preferable that the sintered body is once cooled to room temperature and then subjected to heat treatment.
The heat treatment is preferably performed at 150 to 300 ° C. for 10 minutes to 8 hours under atmospheric pressure, more preferably 200 to 300 ° C. for 10 minutes to 8 hours, and 220 to 280 ° C. for 10 minutes to 8 hours. More preferably, it is more preferable to carry out at 230-270 degreeC for 10 minutes-8 hours. The heating atmosphere may be in the air or in an inert gas, but is preferably in the air and more preferably 25 to 35% by mass.

得られたマグネシウムバルク材は、マグネシウムの他にMgOを含有する。バルク材全量中のMgOの含有量は5〜45質量%程度であるが、10〜40質量%が好ましく、20〜40質量%がより好ましく、25〜35質量%がさらに好ましい。
また0〜10質量%のMgH2及び0〜10質量%のMg(OH)2を含有していてもよい。
The obtained magnesium bulk material contains MgO in addition to magnesium. The content of MgO in the bulk material is about 5 to 45% by mass, preferably 10 to 40% by mass, more preferably 20 to 40% by mass, and still more preferably 25 to 35% by mass.
Or may contain a 0 to 10 mass% MgH 2 and 0 to 10% by weight of Mg (OH) 2.

得られたマグネシウムバルク材は、純マグネシウムバルク材に比べて、また焼結体に比べても強度が向上している。その硬度は40HV以上であり、50HV以上、さらに80HV以上のものも得られる。従って、本発明のマグネシウムバルク材は、輸送機器や電気電子機器の材料として広く使用することができる。   The obtained magnesium bulk material has improved strength compared to the pure magnesium bulk material and also compared to the sintered body. The hardness is 40 HV or more, and 50 HV or more, and further 80 HV or more can be obtained. Therefore, the magnesium bulk material of the present invention can be widely used as a material for transportation equipment and electrical / electronic equipment.

次に実施例を挙げて本発明を詳細に説明する。   EXAMPLES Next, an Example is given and this invention is demonstrated in detail.

実施例1
純度99.91%、平均粒子径384μmの純Mg粉末25.0gとクロム鋼製ボール400gおよびステアリン酸0.50gをアルゴンガス雰囲気中で500mlのクロム鋼製容器に装入し、遊星型ボールミル(Fritsch,P−5)を用いてメカニカルミリング(MM)処理した。MM処理条件は、ボールミルの公転速度を200rpm一定とし、MM処理時間は2h、4h、8h、16h、32hおよび64hと変化させた。
得られたMM粉末4gをφ20の黒鉛型に装入し、放電プラズマ焼結(SPS)装置を用いて固化成形した。SPS焼結条件は成形温度723K、加圧力45MPa、保持時間180s一定とした。
作製したSPS材は、大気中で473K、523Kおよび573Kで、最大8hまで熱処理した。
SPS材および熱処理材の硬さをビッカース硬度計(荷重1kg,保持時間20s)で10ポイント測定した。SPS材および熱処理材の化合物相を同定するために、X線回折装置(60mA,40kVのCuKα線,回折角度20〜80°,回折速度1.66×10-2deg/s)で測定した。
Example 1
25.0 g of pure Mg powder having a purity of 99.91% and an average particle diameter of 384 μm, 400 g of chromium steel balls and 0.50 g of stearic acid were charged into a 500 ml chromium steel container in an argon gas atmosphere, and a planetary ball mill ( Fritsch, P-5) was used for mechanical milling (MM) treatment. The MM treatment conditions were such that the revolution speed of the ball mill was constant at 200 rpm, and the MM treatment time was changed to 2h, 4h, 8h, 16h, 32h and 64h.
4 g of the obtained MM powder was charged into a φ20 graphite mold and solidified using a spark plasma sintering (SPS) apparatus. The SPS sintering conditions were a molding temperature of 723 K, a pressing force of 45 MPa, and a holding time of 180 s.
The produced SPS material was heat-treated in air at 473K, 523K, and 573K for a maximum of 8 hours.
The hardness of the SPS material and the heat-treated material was measured at 10 points with a Vickers hardness meter (load 1 kg, holding time 20 s). In order to identify the compound phases of the SPS material and the heat-treated material, measurement was performed with an X-ray diffractometer (60 mA, 40 kV CuKα ray, diffraction angle 20 to 80 °, diffraction speed 1.66 × 10 −2 deg / s).

図1に各SPS材の等時加熱(1h)による硬さの変化を示す。未加熱のMM 2hおよびMM 8h SPS材の硬さは、MM未処理のSPS材よりも低い値を示したが、MM 4h、MM 16h、MM 32hおよびMM 64h SPS材は、高い値を示した。MM 16h、MM 32hおよびMM 64h SPSで顕著な硬さの差は認められなかった。これらの結果は、MM処理による粉末への加工ひずみの導入には限界があること、さらに、導入された加工ひずみがSPS焼結中に回復する割合が異なることを示唆している。
473Kで熱処理したMM 2h、MM 4h、MM 16hおよびMM 32h SPS材の硬さは、未加熱のSPS材よりも約5HV高い値を示し、MM 8hおよびMM 64h SPS材では、約15HV高い値を示した。
本発明で作製したSPS材は1hという短時間の熱処理で硬化が認められた。523Kにおける熱処理により、各SPS材の硬さは、さらに高くなった。特に、MM 32h SPS材の硬さは、未加熱と比較して約2倍の85.8HVを示した。熱処理573Kでは、SPS材の硬さは523Kと比較して軟化した。各SPS材の硬さの誤差は、±8HV以内であった。
FIG. 1 shows changes in hardness due to isochronous heating (1 h) of each SPS material. The unheated MM 2h and MM 8h SPS materials showed lower values than the MM untreated SPS materials, while the MM 4h, MM 16h, MM 32h and MM 64h SPS materials showed higher values. . There was no significant difference in hardness between MM 16h, MM 32h and MM 64h SPS. These results suggest that there is a limit to the introduction of processing strain into the powder by MM treatment, and that the rate at which the introduced processing strain recovers during SPS sintering is different.
The hardness of the MM 2h, MM 4h, MM 16h and MM 32h SPS materials heat treated at 473K is about 5 HV higher than the unheated SPS material, and about 15 HV higher for the MM 8h and MM 64h SPS materials. Indicated.
The SPS material produced in the present invention was found to be cured by a short heat treatment of 1 h. By the heat treatment at 523K, the hardness of each SPS material was further increased. In particular, the hardness of the MM 32h SPS material showed 85.8 HV, which is about twice that of unheated. In the heat treatment 573K, the hardness of the SPS material was softened as compared with 523K. The error in hardness of each SPS material was within ± 8 HV.

図1より、硬さの向上が最も顕著に表れた523Kで等温加熱による硬さの変化を図2に示す。MM 2h SPS材は、0.5hでピーク硬さ37.1HVを示し、その後、硬さは一定値を示した。この値は、MM未処理のSPS材よりも高い値である。MM 4h SPS材は、2hでピーク硬さ49.5HVを示し、その後、緩やかに軟化した。一方、MM 8h、MM 16hおよびMM 64h SPS材は、2hでピーク硬さを示し、その後、顕著な硬さの軟化傾向は認められなかった。最も顕著な時効硬化挙動を示したのは、MM 32h SPS材で、1hで85.8HVを示し、その後、緩やかに硬さは高くなり、8hで最高硬さ90.7HVを示した。また、本発明で作製したSPS材は、顕著な軟化が認められず、優れた熱的安定性を示した。時効温度を473Kおよび573Kに変化させても、SPS材の硬さの変化は、図2に示した523Kと同様の傾向を示した。   From FIG. 1, the change in hardness due to isothermal heating at 523 K where the improvement in hardness was most noticeable is shown in FIG. 2. The MM 2h SPS material showed a peak hardness of 37.1 HV at 0.5 h, after which the hardness showed a constant value. This value is higher than that of the MM-untreated SPS material. The MM 4h SPS material showed a peak hardness of 49.5HV in 2h and then softened gently. On the other hand, the MM 8h, MM 16h and MM 64h SPS materials showed a peak hardness at 2 h, and thereafter no significant hardness softening tendency was observed. The MM 32h SPS material showed the most remarkable age hardening behavior, showing 85.8 HV in 1 h, then gradually increasing in hardness, and showing a maximum hardness of 90.7 HV in 8 h. In addition, the SPS material produced in the present invention showed no remarkable softening and showed excellent thermal stability. Even when the aging temperature was changed to 473K and 573K, the change in the hardness of the SPS material showed the same tendency as that of 523K shown in FIG.

明瞭な時効硬化挙動を示した32h SPS材の等温加熱(523)によるX線回折パターンの変化を図3に示す。未加熱の粉末およびSPS材では、純Mgの回折ピークが認められた。一方、0.5h熱処理したSPS材は、Mgの回折ピーク以外にMgO、MgH2およびMg(OH)2の回折ピークが認められた。特に、MgOの回折ピーク強度は、他の化合物の回折ピーク強度より高かった。また、熱処理時間が長くなるにつれてMgH2およびMg(OH)2の回折ピーク強度が高まった。しかし、MgH2およびMg(OH)2の回折ピーク強度に対応した顕著な硬さの変化は認められなかった。このことから、時効硬化挙動の支配的な要因は、MgOの生成であると考えられる。図4から、MgOのマグネシウムバルク材中の含有量は5〜45質量%、さらに10〜40質量%、さらに20〜40質量%であるのが好ましいことがわかる。
また、MgH2は0〜10質量%、Mg(OH)2は0〜10質量%が好ましいことがわかる。
MgH2の生成は、ステアリン酸を構成する水素とMgとの固相反応が誘起されたためであると考えられる。MgOおよびMg(OH)2に関しては、ステアリン酸を構成する酸素もしくは、純Mg粉末の表面に形成されている酸化皮膜およびMg(OH)2がMM処理中に粉末内部に取り込まれたためと考えられる。また、MM処理をしていない純Mg粉末から作製したSPS材を大気中で熱処理してもMgOは生成されなかった。このことから、MgOの生成における酸素の供給源は、ステアリン酸であると推察した。これらの結果は、MgO、MgH2およびMg(OH)2の生成には、水素や酸素を含むステアリン酸を伴ったMM処理およびその後の熱処理が必要であることを示唆している。
The change of the X-ray diffraction pattern by isothermal heating (523) of the 32h SPS material which showed a clear age hardening behavior is shown in FIG. In the unheated powder and SPS material, a pure Mg diffraction peak was observed. On the other hand, the SPS material heat-treated for 0.5 h showed diffraction peaks of MgO, MgH 2 and Mg (OH) 2 in addition to the diffraction peak of Mg. In particular, the diffraction peak intensity of MgO was higher than that of other compounds. In addition, the diffraction peak intensities of MgH 2 and Mg (OH) 2 increased with increasing heat treatment time. However, no significant change in hardness corresponding to the diffraction peak intensities of MgH 2 and Mg (OH) 2 was observed. From this, it is considered that the dominant factor of age hardening behavior is the formation of MgO. FIG. 4 shows that the content of MgO in the magnesium bulk material is preferably 5 to 45% by mass, more preferably 10 to 40% by mass, and further preferably 20 to 40% by mass.
Further, MgH 2 is 0 to 10 mass%, Mg (OH) 2 is found to be preferred 0 to 10% by weight.
It is considered that the production of MgH 2 is due to the induction of a solid phase reaction between hydrogen constituting stearic acid and Mg. Regarding MgO and Mg (OH) 2, it is considered that oxygen constituting stearic acid or an oxide film formed on the surface of pure Mg powder and Mg (OH) 2 were taken into the powder during MM treatment. . In addition, MgO was not generated even when an SPS material made from pure Mg powder not subjected to MM treatment was heat-treated in the atmosphere. From this, it was guessed that the supply source of oxygen in the production of MgO was stearic acid. These results suggest that the production of MgO, MgH 2 and Mg (OH) 2 requires MM treatment with stearic acid containing hydrogen and oxygen and subsequent heat treatment.

図4に各SPS材の等温加熱(523K)によるMgOの回折ピーク強度を純Mgの回折ピーク強度で除した値を回折ピーク強度比として示す。この回折ピーク強度比を相対的なMgO生成量として見積もったるMM 2h SPS材は、0.5hで強度比3.2%を示したが、その後、強度比は、0%であった。一方、MM 4hおよびMM 64h SPS材は、0.5h以後、強度比は一定値(約5%)を示し、MM 8hおよびMM 16h SPS材は、0.5h以後、強度比約10%を示した。特に、MM 32h SPS材は、0.5hで強度比26.1%を示し、その後、わずかに増加し、8hで31.5%を示した。これらの結果は、図2で示した等温加熱による各SPS材の硬さの変化と対応しており、各SPS材の時効硬化挙動の支配的な要因は、MgO生成によるものと考えられる。   FIG. 4 shows a value obtained by dividing the diffraction peak intensity of MgO by isothermal heating (523K) of each SPS material by the diffraction peak intensity of pure Mg as a diffraction peak intensity ratio. The MM 2h SPS material for which the diffraction peak intensity ratio was estimated as the relative amount of MgO produced showed an intensity ratio of 3.2% at 0.5 h, but thereafter the intensity ratio was 0%. On the other hand, the strength ratio of MM 4h and MM 64h SPS materials shows a constant value (about 5%) after 0.5h, and the strength ratio of MM 8h and MM 16h SPS materials shows about 10% after 0.5h. It was. In particular, the MM 32h SPS material showed a strength ratio of 26.1% at 0.5h, then increased slightly and showed 31.5% at 8h. These results correspond to the change in hardness of each SPS material due to isothermal heating shown in FIG. 2, and the dominant factor of the age hardening behavior of each SPS material is considered to be due to MgO generation.

Claims (6)

純度98%以上のマグネシウムの粉末を酸素含有化合物の存在下に16〜80時間メカニカルミリング処理した後、該粉末を焼結し、次いで得られた焼結体を150〜300℃に10分〜8時間加熱処理することを特徴とするマグネシウムバルク材の製造法Magnesium powder having a purity of 98% or more was mechanically milled in the presence of an oxygen-containing compound for 16 to 80 hours , the powder was sintered, and the obtained sintered body was then heated to 150 to 300 ° C. for 10 minutes to 8 minutes. A method for producing a magnesium bulk material , characterized by performing heat treatment for a period of time . 原料のマグネシウム粉末が、純度99%以上のマグネシウム粉末である請求項1記載のマグネシウムバルク材の製造法The method for producing a magnesium bulk material according to claim 1, wherein the raw material magnesium powder is a magnesium powder having a purity of 99% or more. 酸素含有化合物が、カルボン酸類、硫酸類、リン酸類及びスルホン酸類から選ばれる酸類である請求項1又は2記載のマグネシウムバルク材の製造法The method for producing a magnesium bulk material according to claim 1 or 2, wherein the oxygen-containing compound is an acid selected from carboxylic acids, sulfuric acids, phosphoric acids and sulfonic acids. メカニカルミリング処理が、カルボン酸類の存在下、ボールミルを用いるメカニカルミリング処理16〜80時間である請求項1〜3のいずれか1項記載のマグネシウムバルク材の製造法The method for producing a magnesium bulk material according to any one of claims 1 to 3, wherein the mechanical milling treatment is performed for 16 to 80 hours using a ball mill in the presence of carboxylic acids. 焼結処理が、放電プラズマ焼結である請求項1〜4のいずれか1項記載のマグネシウムバルク材の製造法The method for producing a magnesium bulk material according to any one of claims 1 to 4, wherein the sintering treatment is spark plasma sintering. Mg以外にMgOを5〜45質量%含有するものである請求項1〜のいずれか1項記載のマグネシウムバルク材の製造法The method for producing a magnesium bulk material according to any one of claims 1 to 5 , wherein MgO is contained in an amount of 5 to 45 mass% in addition to Mg.
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