JP5336204B2 - Magnesium alloy with excellent balance between anisotropy and yield strength - Google Patents
Magnesium alloy with excellent balance between anisotropy and yield strength Download PDFInfo
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本発明は、異方性と耐力とのバランスが優れたＭｇ−Ａｌ−Ｚｎ系のマグネシウム合金に関する。以下、マグネシウムをＭｇとも言う。 The present invention relates to an Mg—Al—Zn based magnesium alloy having an excellent balance between anisotropy and yield strength. Hereinafter, magnesium is also referred to as Mg.
近年、地球環境の観点から、車輌の燃費向上を目的として、例えば自動車などのフレーム等の強度部材や構造材にマグネシウム合金が適用されている。また、マグネシウム合金は、電気・電子機器の筐体や、自動車、航空機等のエンジン部品（ピストン、コンロッド）などの構成材料としても広く適用されている。 In recent years, from the viewpoint of the global environment, for the purpose of improving the fuel efficiency of vehicles, magnesium alloys have been applied to strength members and structural materials such as frames of automobiles, for example. Magnesium alloys are also widely used as constituent materials for casings of electric and electronic devices and engine parts (pistons, connecting rods) for automobiles, aircrafts and the like.
マグネシウムは、構造材として使用する場合、比重が１．８で実用的に最も軽い金属である（アルミニウムの約２／３、鉄の約１／４の比重）。また、比強度、比剛性、熱伝導性にも優れる。また、実用されている合金中でも密度の小さい、Ｍｇ−Ａｌ−Ｚｎ系などのマグネシウム合金押出材は、軽量でしかも適度の強度を有していることから、各種構造用材料として利用されている（例えば、特許文献１及び特許文献２参照）。 Magnesium, when used as a structural material, has a specific gravity of 1.8 and is the lightest metal practically (about 2/3 of aluminum and about 1/4 of iron). Moreover, it is excellent in specific strength, specific rigidity, and thermal conductivity. In addition, magnesium alloy extruded materials such as Mg—Al—Zn, which have a low density among the alloys in practical use, are used as various structural materials because they are lightweight and have an appropriate strength ( For example, see Patent Literature 1 and Patent Literature 2).
そして、このＭｇ−Ａｌ−Ｚｎ系マグネシウム合金押出材の機械的特性、特に、３００ＭＰａ以上の高い引張強度や、機械的特性の均質性を有するために、押出加工の中でも、特に、熱間静水圧押出加工による押出材とし、合金元素のＡｌのうち４０％以上を固溶Ａｌとして、固溶Ａｌ量を高くすることも提案されている（特許文献３参照）。 And, in order to have the mechanical properties of this Mg-Al-Zn-based magnesium alloy extruded material, in particular, high tensile strength of 300 MPa or more, and homogeneity of mechanical properties, especially in the extrusion process, especially hot isostatic pressure It has also been proposed to increase the amount of solid solution Al by using an extruded material by extrusion processing, with 40% or more of the alloy element Al being solid solution Al (see Patent Document 3).
しかし、このようなマグネシウム合金の押出材を、前記強度部材や構造材として使用する場合には、その異方性が問題となる。この異方性とは、マグネシウム合金押出材の０．２％圧縮耐力が、０．２％引張耐力に比して、著しく低くなる、つまり、引張耐力に対する圧縮耐力の比（ここでは耐力比と呼ぶ）が低くなることである。アルミニウム合金の耐力比に比べて、マグネシウム合金の耐力比は低いため、強度部材や構造材として使用する場合、必要な強度や剛性を満たすために、この異方性を考慮しなければ使用できず、設計自由度が低くなる。さらには、この耐力比が低い（異方性が大きい）と、例えば押出材の押出方向と押出に直角方向とで、即ち押出材の使用方向によって、強度、耐力、伸びなどの機械的な性質が大きく異なることにつながる。また、強度部材や構造材としての信頼性自体も低くなる。更に、強度部材や構造材への成形や機械加工なども難しくなるという問題を有している。そして、これらの問題は、当然ながら、マグネシウム合金押出材の強度部材や構造材用途へと適用を大きく制約することにつながる。 However, when such a magnesium alloy extruded material is used as the strength member or the structural material, the anisotropy becomes a problem. This anisotropy means that the 0.2% compressive yield strength of the extruded magnesium alloy is significantly lower than the 0.2% tensile yield strength, that is, the ratio of the compressive yield strength to the tensile yield strength (here, the yield strength ratio and Is called lower). The strength ratio of magnesium alloy is lower than that of aluminum alloy, so when used as a strength member or structural material, it cannot be used without considering this anisotropy in order to satisfy the required strength and rigidity. , Design freedom is low. Furthermore, when the yield ratio is low (high anisotropy), mechanical properties such as strength, yield strength, elongation, etc., depending on, for example, the direction of extrusion of the extruded material and the direction perpendicular to the extrusion, that is, the direction of use of the extruded material. Leads to a big difference. Moreover, the reliability itself as a strength member or a structural material is also lowered. Furthermore, there is a problem that it becomes difficult to form or machine a strength member or a structural material. These problems naturally lead to significant restrictions on the application of magnesium alloy extruded materials to strength members and structural materials.
これに対して、Ｍｇ−Ａｌ−Ｚｎ系マグネシウム合金押出材の異方性を小さくするために、特許文献４では、集合組織、それも結晶粒の結晶方位の傾きを示すパラメータとしてのシュミット因子を制御することが提案されている。具体的には、３〜１０質量％のＡｌと、０．１〜１．５質量％のＺｎを含むマグネシウム合金押出材において、マグネシウム合金の結晶構造である六方晶（最密六方格子、ｈｃｐ）の底面である（０００１）面をランダムに配向させることで異方性を低減している。より具体的には、六方晶の各結晶粒における（０００１）＜１１−２０＞のシュミット因子の平均値を０．２以上で、且つこのシュミット因子の値が０〜０．２である結晶粒の存在割合を５５％以下としている。 On the other hand, in order to reduce the anisotropy of the Mg—Al—Zn-based magnesium alloy extruded material, in Patent Document 4, a Schmid factor is used as a parameter indicating the texture and the inclination of the crystal orientation of the crystal grains. It has been proposed to control. Specifically, in a magnesium alloy extruded material containing 3 to 10% by mass of Al and 0.1 to 1.5% by mass of Zn, a hexagonal crystal (close-packed hexagonal lattice, hcp) which is a crystal structure of the magnesium alloy Anisotropy is reduced by orienting the (0001) plane, which is the bottom surface of the film, at random. More specifically, a crystal grain having an average value of the Schmit factor of (0001) <11-20> in each hexagonal crystal grain is 0.2 or more and the Schmid factor value is 0 to 0.2. The existing ratio is 55% or less.
このシュミット因子は、マグネシウム合金が有する六方晶結晶構造の変形方向対する、特定のすべり面である（０００１）面と、特定のすべり方向＜１１−２０＞方向、すなわち（０００１）＜１１−２０＞によって規定される。言い換えると、前記六方晶の各結晶粒における変形時の特定のすべり面は底面である（０００１）面で、特定のすべり方向は＜１１−２０＞方向であり、（０００１）＜１１−２０＞とは、これらすべり面とすべり方向との両方を規定しているものである。そして、前記六方晶の各結晶粒における（０００１）＜１１−２０＞のシュミット因子は、マグネシウム合金の製造時における加工方向、たとえば押出材であればその押出方向に対して、（０００１）面の法線方向とのなす角をΦ、（０００１）面内における＜１１−２０＞方向とのなす角をλとした場合に、ｃｏｓΦｃｏｓλで与えられる。このシュミット因子は、他の金属でも種々の特性に関わる因子として公知であり、例えばアルミニウム合金などでは曲げ疲労寿命に関する因子として公知である。また、このシュミット因子は、具体的に後述する通り、ＥＢＳＰ（Electron Back Scatter Diffraction Pattern）による結晶方位の組織解析（広域解析）により、測定が可能である。 This Schmid factor includes a (0001) plane which is a specific slip plane and a specific slip direction <11-20> direction, that is, (0001) <11-20>, with respect to the deformation direction of the hexagonal crystal structure of the magnesium alloy. It is prescribed by. In other words, the specific slip plane at the time of deformation in each crystal grain of the hexagonal crystal is the (0001) plane which is the bottom surface, the specific slip direction is the <11-20> direction, and (0001) <11-20>. Is that both the slip surface and the slip direction are defined. And the Schmid factor of (0001) <11-20> in each crystal grain of the hexagonal crystal is in the (0001) plane with respect to the processing direction at the time of manufacturing the magnesium alloy, for example, the extrusion direction in the case of an extruded material. When the angle formed with the normal direction is Φ and the angle formed with the <11-20> direction in the (0001) plane is λ, it is given by cos Φ cos λ. This Schmitt factor is known as a factor relating to various characteristics even in other metals, and is known as a factor relating to bending fatigue life in, for example, aluminum alloys. Further, this Schmitt factor can be measured by a crystal orientation structure analysis (wide area analysis) by EBSP (Electron Back Scatter Diffraction Pattern), as will be specifically described later.
特許文献４では、自動車の足回り部品などとして、好ましくは、前記マグネシウム合金押出材の平均結晶粒径を５０μｍ以下とし、前記異方性の目安である０．２％圧縮耐力と０．２％引張耐力との比（圧縮耐力／引張耐力）を０．７〜１．２の範囲に高め、前記異方性を小さくしている。また、これらの組織と特性のマグネシウム合金押出材を得るために、前記マグネシウム合金を１５０〜４００℃、好ましくは２００〜３５０℃、押出比４０以上で、直接押出加工し、結晶粒の結晶方位を制御している。 In Patent Document 4, as an automobile undercarriage part or the like, preferably, the average crystal grain size of the magnesium alloy extruded material is set to 50 μm or less, and 0.2% compression proof stress and 0.2% as a guideline for the anisotropy. The ratio to the tensile strength (compression strength / tensile strength) is increased to a range of 0.7 to 1.2 to reduce the anisotropy. Further, in order to obtain a magnesium alloy extruded material having these structures and characteristics, the magnesium alloy is directly extruded at 150 to 400 ° C., preferably 200 to 350 ° C., with an extrusion ratio of 40 or more, and the crystal orientation of the crystal grains is changed. I have control.
前記特許文献４のように、シュミット因子の平均値を高くした場合、異方性は確かに改善できる。しかし、一方で、このシュミット因子の平均値を前記特許文献４のように、０．２以上に高くした場合に、強度や耐力が低くなってしまうことを知見した。この点、前記特許文献４には開示が無く、強度や耐力のデータも一切記載されていない。しかし、本発明者らの知見によれば、シュミット因子の平均値が０．２以上に高いマグネシウム合金押出材は、後述する通り、前記自動車などのフレーム等の強度部材や構造材として必要な１４０ＭＰａ以上の０．２％圧縮耐力を満たさなくなる可能性が高くなる。 As described in Patent Document 4, when the average value of the Schmitt factor is increased, the anisotropy can surely be improved. However, on the other hand, it has been found that when the average value of the Schmitt factor is increased to 0.2 or more as in Patent Document 4, the strength and proof stress are lowered. In this regard, Patent Document 4 has no disclosure and does not describe any data on strength and proof stress. However, according to the knowledge of the present inventors, a magnesium alloy extruded material having an average value of Schmid factor as high as 0.2 or more is 140 MPa required as a strength member and a structural material such as a frame of the automobile as described later. There is a high possibility that the above 0.2% compression strength will not be satisfied.
また、前記特許文献３のようなＭｇ−Ａｌ−Ｚｎ系マグネシウム合金押出材は、強度や耐力は高いものの、異方性が大きすぎる。これに対して、前記特許文献４のようなＭｇ−Ａｌ−Ｚｎ系マグネシウム合金押出材は、異方性は良いものの、強度や耐力が低過ぎる。したがって、Ｍｇ−Ａｌ−Ｚｎ系マグネシウム合金押出材に関するこれら従来技術は、いずれも異方性と耐力とのバランスが良くなかったものである。 Moreover, although the Mg-Al-Zn-based magnesium alloy extruded material as described in Patent Document 3 has high strength and proof stress, the anisotropy is too large. On the other hand, although the Mg-Al-Zn-based magnesium alloy extruded material as in Patent Document 4 has good anisotropy, its strength and proof stress are too low. Therefore, none of these conventional techniques related to the extruded material of Mg—Al—Zn-based magnesium alloy has a good balance between anisotropy and yield strength.
本発明はこのような課題を解決するためになされたものであって、異方性と耐力とのバランスが優れたＭｇ−Ａｌ−Ｚｎ系マグネシウム合金を提供することである。 The present invention has been made to solve such problems, and is to provide an Mg—Al—Zn-based magnesium alloy having an excellent balance between anisotropy and yield strength.
この目的を達成するために、本発明の異方性と耐力とのバランスが優れたマグネシウム合金の要旨は、質量％で、Ａｌ：６〜１２％、Ｚｎ：０．１〜２．０％を各々含有し、残部Ｍｇおよび不可避的不純物からなり、１５０℃以上、２５０℃以下の押出温度と、５ｍｍ／秒以上、７ｍｍ／秒以下の押出速度で熱間押出加工されたマグネシウム合金であって、このマグネシウム合金組織の平均結晶粒径が１５μm 以下であるとともに、このマグネシウム合金が有する六方晶結晶構造の各結晶粒における、このマグネシウム合金の製造時の加工方向を軸とした（０００１）＜１１-２０＞のシュミット因子の平均値が０．１２以上、０．２未満の範囲であることとする。 In order to achieve this object, the gist of the magnesium alloy having an excellent balance between anisotropy and proof stress of the present invention is mass%, Al: 6-12%, Zn: 0.1-2.0%. each contained the remainder Ri Do Mg and unavoidable impurities, 0.99 ° C. or higher, and less of an extrusion temperature of 250 ° C., 5 mm / sec or more, a 7 mm / sec hot extruded magnesium alloy in the following extrusion speed The average grain size of the magnesium alloy structure is 15 μm or less, and each crystal grain of the hexagonal crystal structure of the magnesium alloy has a processing direction at the time of production of the magnesium alloy as an axis (0001) <11 The average value of the Schmid factor of −20> is 0.12 or more and less than 0.2.
本発明は、異方性低減の手段として、集合組織の制御を行い、シュミット因子の平均値を制御すること自体は前記特許文献４と同じである。 In the present invention, as a means for reducing anisotropy, the texture is controlled and the average value of the Schmitt factor itself is the same as that in Patent Document 4.
但し、本発明は、前記シュミット因子の平均値を、前記特許文献４のように０．２以上には高くせず、０．１２〜０．２未満の範囲に規定し、異方性を改善しつつ、前記特許文献４のようにシュミット因子の平均値を高くした場合の強度や耐力の低下を極力防止する。 However, in the present invention, the average value of the Schmitt factor is not set higher than 0.2 as in Patent Document 4, but is defined within a range of 0.12 to less than 0.2 to improve anisotropy. However, a decrease in strength and yield strength when the average value of the Schmitt factor is increased as in Patent Document 4 is prevented as much as possible.
その一方で、本発明は、このマグネシウム合金組織の平均結晶粒径を１５μm 以下、好ましくは１０μm 以下に微細化し、これと前記シュミット因子の平均値制御との相乗効果によって、異方性を改善する。また、この平均結晶粒径の微細化は、当然ながら耐力も向上させるため、この耐力も、この平均結晶粒径の微細化と前記シュミット因子の平均値制御との相乗効果によって、耐力も向上する。 On the other hand, according to the present invention, the average crystal grain size of the magnesium alloy structure is refined to 15 μm or less, preferably 10 μm or less, and the anisotropy is improved by a synergistic effect of this and the Schmid factor average value control. . In addition, since the refinement of the average crystal grain size naturally improves the yield strength, the yield strength is also improved by the synergistic effect of the refinement of the mean crystal grain size and the average value control of the Schmitt factor. .
この結果、本発明では、前記マグネシウム合金の押出材として、０．２％圧縮耐力が１４０ＭＰａ以上であるとともに、０．２％圧縮耐力と０．２％引張耐力との比（圧縮耐力／引張耐力）が０．７以上であるように異方性を抑制することができる。即ち、本発明は、異方性と耐力とのバランスが優れたＭｇ−Ａｌ−Ｚｎ系マグネシウム合金を提供できる。 As a result, in the present invention, as the extruded material of the magnesium alloy, the 0.2% compression strength is 140 MPa or more, and the ratio between the 0.2% compression strength and the 0.2% tensile strength (compression strength / tensile strength). ) Can be suppressed so that it is 0.7 or more. That is, the present invention can provide an Mg—Al—Zn-based magnesium alloy having an excellent balance between anisotropy and yield strength.
(マグネシウム合金成分組成)
本発明では、質量％で、Ａｌ：６〜１２％、Ｚｎ：０．１〜２．０％を各々含有し、残部Ｍｇおよび不可避的不純物からなるマグネシウム合金成分組成とする。
(Magnesium alloy component composition)
In this invention, it is set as the magnesium alloy component composition which contains Al: 6-12% and Zn: 0.1-2.0% by the mass%, respectively, and consists of remainder Mg and an unavoidable impurity.
また、このＡｌ、Ｚｎ以外の元素の許容含有量は、ＪＩＳＨ４２０４に規定されたＭｇ−Ａｌ−Ｚｎ系マグネシウム合金押出形材の成分規格ＭＳ１〜ＭＳ３の上限量が多い方の規格に準じる。即ち、質量％で、Ｍｎ：０．４０％以下、Ｆｅ：０．０３％以下、Ｓｉ：０．１０％以下、Ｃｕ：０．１０％以下、ＮＩ：０．００５％以下、Ｃａ：０．００４％以下の含有が許容される。また、これも前記規格通り、その他存在が予知される場合に限り分析される、これら以外のその他の元素の合計量は０．３０％以下とする。このような元素として、例えば、ランタン、セリウムなどのミッシュメタルが例示される。なお、以下の各元素の説明において記載する％表示は全て質量％である。 In addition, the allowable content of elements other than Al and Zn conforms to the standard having the larger upper limit of the component standards MS1 to MS3 of the Mg—Al—Zn-based magnesium alloy extruded profile defined in JISH4204. That is, by mass%, Mn: 0.40% or less, Fe: 0.03% or less, Si: 0.10% or less, Cu: 0.10% or less, NI: 0.005% or less, Ca: 0.0. A content of 004% or less is allowed. In addition, as described above, the total amount of other elements other than these analyzed only when other existence is predicted is set to 0.30% or less. Examples of such elements include misch metals such as lanthanum and cerium. In addition, all the% display described in description of each following element is the mass%.
Ａｌ：６〜１２％
Ａｌ（アルミニウム）は合金の強化に寄与し、強度、耐力、伸び等の機械的性質を向上させる。Ａｌ含有量が過剰であると、静水圧押出時の押出圧力が上昇して、静水圧による押出性が悪化する。一方、Ａｌ含有量が過少であると耐力が不足する。したがって、Ａｌ含有量は６〜１２％の範囲とする。
Al: 6-12%
Al (aluminum) contributes to strengthening of the alloy and improves mechanical properties such as strength, proof stress and elongation. If the Al content is excessive, the extrusion pressure at the time of hydrostatic extrusion increases, and the extrudability by hydrostatic pressure deteriorates. On the other hand, if the Al content is too low, the yield strength is insufficient. Therefore, the Al content is in the range of 6 to 12%.
Ｚｎ：０．１〜２．０％
Ｚｎ（亜鉛）は固溶強化によって耐力、伸びを向上させるとともに、時効硬化を誘起し、マグネシウム合金押出形材の調質処理時の時効硬化量（強度、耐力の向上）を大きくする効果がある。Ｚｎ含有量が増加するに従って、強度や耐力は大きくなる。しかし、Ｚｎ含有量が過剰であると、却って靱性及び強度が低下する。したがって、Ｚｎ含有量は０．１〜２．０％の範囲とする。
Zn: 0.1 to 2.0%
Zn (zinc) has the effect of improving the yield strength and elongation by solid solution strengthening, inducing age hardening, and increasing the age hardening amount (improvement of strength and yield strength) during the tempering treatment of the extruded magnesium alloy shape. . As the Zn content increases, the strength and yield strength increase. However, if the Zn content is excessive, the toughness and strength are reduced. Therefore, the Zn content is in the range of 0.1 to 2.0%.
（マグネシウム合金組織）
シュミット因子：
先ず、金属多結晶体の塑性変形は、冷間では結晶粒を貫通するすべり変形により生じる。この結晶粒を貫通するすべり変形の場合、結晶面に沿って転位を移動させるのに必要な臨界せん断応力τの大きさは、結晶面と結晶軸方向によって異なる。単結晶円柱体の引張試験を行う場合、引張応力σは、次式：σ＝τ／（ｃｏｓφｃｏｓλ）によって与えられることが公知である。この式において、τは金属結晶のすべり変形が起きるために必要な臨界せん断応力、φはすべり面の法線と引張軸とのなす角度、λはすべり方向と引張軸とのなす角度を各々示す。
(Magnesium alloy structure)
Schmid factor:
First, plastic deformation of a metal polycrystal occurs due to slip deformation penetrating crystal grains in the cold state. In the case of slip deformation penetrating this crystal grain, the magnitude of the critical shear stress τ necessary for moving the dislocation along the crystal plane differs depending on the crystal plane and the crystal axis direction. When conducting a tensile test of a single crystal cylinder, it is known that the tensile stress σ is given by the following equation: σ = τ / (cos φcos λ). In this equation, τ is the critical shear stress required for slip deformation of the metal crystal, φ is the angle between the normal of the slip surface and the tensile axis, and λ is the angle between the slip direction and the tensile axis. .
シュミット因子とは、前記特許文献４にも記載される通り、この式あるいはこの式を変形したτ＝σ（ｃｏｓφｃｏｓλ）における、（ｃｏｓφｃｏｓλ）を示し、引張圧縮方向に対する結晶の傾きを示している。したがって、マグネシウム合金押出材においても、金属結晶のすべり変形が起きるために必要な臨界せん断応力τは、すべり面の法線と押出軸とのなす角度φ、すべり方向と押出軸とのなす角度λとの関係から、（ｃｏｓφｃｏｓλ）によって、シュミット因子の平均値を求めることができる。 As described in Patent Document 4, the Schmitt factor represents (cosφcosλ) in this equation or τ = σ (cosφcosλ) obtained by modifying this equation, and indicates the inclination of the crystal with respect to the tensile and compressive direction. Therefore, in the magnesium alloy extruded material, the critical shear stress τ necessary for slip deformation of the metal crystal is the angle φ formed between the normal of the slip surface and the extrusion axis, and the angle λ formed between the slip direction and the extrusion axis. From the relationship, the average value of the Schmitt factor can be obtained by (cosφcosλ).
前記式の通り、マグネシウム合金押出材の塑性変形で主となるすべり変形が起きるために必要な前記臨界せん断応力τの値は、前記式における右辺のシュミット因子（ｃｏｓφｃｏｓλ）の値によって変化する。マグネシウム合金押出材に外力が加わった場合、シュミット因子の値が最大となるすべり系が最初にすべり変形する（動き出す）。したがって、シュミット因子の偏りが大きいほど、マグネシウム合金押出材の異方性が強くなる。 As described above, the value of the critical shear stress τ necessary for causing the principal slip deformation in the plastic deformation of the magnesium alloy extruded material varies depending on the value of the Schmid factor (cos φ cos λ) on the right side in the equation. When an external force is applied to the magnesium alloy extruded material, the slip system that maximizes the Schmid factor value first slips (starts moving). Therefore, the greater the Schmid factor bias, the stronger the anisotropy of the magnesium alloy extruded material.
シュミット因子の平均値：
六方晶結晶構造有するマグネシウム合金では、主となるすべり系は、すべり面が底面の（０００１）面、この底面のすべり方向が＜１１−２０＞方向である。マグネシウム合金押出材では、押出方向に垂直な方向に（０００１）面が配向しやすく、圧延材では、圧延面に（０００１）面が配向しやすく、これが異方性の原因となっている。このように結晶粒の底面が配向した場合、シュミット因子の平均値が小さくなる。このため、前記特許文献４では、Ｍｇ−Ａｌ−Ｚｎ系合金であるマグネシウム合金押出材の異方性を小さくするために、シュミット因子の平均値を０．２以上と高くして、結晶方位をランダム化し、結晶粒の底面が押出方向に垂直な方向に配向し異方性を低減している。
Average value of Schmid factor:
In the magnesium alloy having a hexagonal crystal structure, the main slip system has a (0001) plane whose bottom surface is the bottom surface and a <11-20> direction in which the bottom surface slides. In the magnesium alloy extruded material, the (0001) plane is easily oriented in the direction perpendicular to the extrusion direction, and in the rolled material, the (0001) plane is easily oriented in the rolled surface, which causes anisotropy. In this way, when the bottom surface of the crystal grains is oriented, the average value of the Schmid factor becomes small. For this reason, in Patent Document 4, in order to reduce the anisotropy of the magnesium alloy extruded material that is an Mg—Al—Zn alloy, the average value of the Schmitt factor is increased to 0.2 or more, and the crystal orientation is changed. Randomized, the bottom surface of the crystal grains is oriented in a direction perpendicular to the extrusion direction to reduce anisotropy.
このようにシュミット因子の平均値を高くした場合、前記特許文献４で開示されている通り、０．２％圧縮耐力と０．２％引張耐力との比（圧縮耐力／引張耐力）を０．７以上とでき、異方性が改善できる。しかし、反面で、前記した通り、シュミット因子の平均値を０．２以上に高くした場合は、Ｍｇ−Ａｌ−Ｚｎ系マグネシウム合金押出材の強度や耐力（絶対値）が下がってしまう。このため、マグネシウム合金押出材が、例えば自動車などのフレーム等の強度部材や構造材として必要な１４０ＭＰａ以上の０．２％圧縮耐力を満たさなくなる可能性が高くなる。したがって、シュミット因子の平均値が０．２以上では、Ｍｇ−Ａｌ−Ｚｎ系マグネシウム合金押出材の異方性は良いものの、強度や耐力が低く、異方性と耐力とのバランスが良くない。 As described above, when the average value of the Schmid factor is increased, the ratio of 0.2% compression strength to 0.2% tensile strength (compression strength / tensile strength) of 0. It can be 7 or more, and anisotropy can be improved. On the other hand, as described above, when the average value of the Schmitt factor is increased to 0.2 or more, the strength and proof strength (absolute value) of the Mg—Al—Zn-based magnesium alloy extruded material are lowered. For this reason, there is a high possibility that the magnesium alloy extruded material will not satisfy the 0.2% compressive proof stress of 140 MPa or more required as a strength member or structural material such as a frame of an automobile, for example. Therefore, when the average value of the Schmitt factor is 0.2 or more, although the anisotropy of the Mg—Al—Zn-based magnesium alloy extruded material is good, the strength and the proof strength are low, and the balance between the anisotropy and the proof strength is not good.
このため、本発明では、マグネシウム合金の製造時の加工方向を軸とした（０００１）＜１１-２０＞のシュミット因子の平均値を０．１２以上、０．２未満（０．１２〜０．２未満）の範囲として、異方性を改善しつつ、強度や耐力（絶対値）の低下を防止する。シュミット因子の平均値が０．１２未満では、異方性が改善されず、０．２％圧縮耐力と０．２％引張耐力との比（圧縮耐力／引張耐力）が０．７以上とならない。一方、シュミット因子の平均値が０．２以上では、後述する平均結晶粒径を微細化させても、０．２％圧縮耐力が１４０ＭＰａ以上とはならない。 For this reason, in this invention, the average value of the Schmid factor of (0001) <11-20> with the processing direction at the time of manufacturing the magnesium alloy as an axis is 0.12 or more and less than 0.2 (0.12 to .0. The range of less than 2) improves anisotropy and prevents a decrease in strength and proof stress (absolute value). When the average value of the Schmitt factor is less than 0.12, the anisotropy is not improved, and the ratio of 0.2% compression strength to 0.2% tensile strength (compression strength / tensile strength) does not become 0.7 or more. . On the other hand, when the average value of the Schmitt factor is 0.2 or more, the 0.2% compressive yield strength does not become 140 MPa or more even if the average crystal grain size described later is refined.
シュミット因子の測定：
このシュミット因子は、電界放射型走査電子顕微鏡ＦＥＳＥＭ（Field Emission Scanning Electron Microscope ）による、後方散乱電子回折像ＥＢＳＰ（ElectronBackscatter Diffraction Pattern）を用いた結晶方位解析方法により測定する。
Schmid factor measurement:
This Schmid factor is measured by a crystal orientation analysis method using a backscattered electron diffraction image EBSP (Electron Backscatter Diffraction Pattern) with a field emission scanning electron microscope FESEM (Field Emission Scanning Electron Microscope).
この結晶方位解析方法は、試料表面に斜めに電子線を当てたときに生じる後方散乱電子回折パターン（菊地パターン）に基づき、結晶方位を解析する。この方法は、高分解能結晶方位解析法（ＦＥＳＥＭ／ＥＢＳＰ法）として、ダイヤモンド薄膜や、銅合金などの他の金属の結晶方位解析でも公知である。 This crystal orientation analysis method analyzes the crystal orientation based on a backscattered electron diffraction pattern (Kikuchi pattern) generated when an electron beam is obliquely applied to the sample surface. This method is also known as a high resolution crystal orientation analysis method (FESEM / EBSP method) for crystal orientation analysis of diamond thin films and other metals such as copper alloys.
この結晶方位解析方法による解析手順は、まず、製造したマグネシウム合金押出材から組織観察用の試験片を採取し、機械研磨およびバフ研磨を行った後、電解研磨して表面を調整する。このように得られた試験片について、例えば日本電子社製のＦＥＳＥＭと、ＴＳＬ社製のＥＢＳＰ測定・解析システムＯＩＭ（Orientation Imaging Macrograph）を用い、同システムの解析ソフトと（ソフト名「ＯＩＭＡｎａｌｙｓｉｓ」）を用いて、各結晶粒の測定視野における方位マッピング（シュミット因子）を求める。 In the analysis procedure by this crystal orientation analysis method, first, a specimen for structure observation is collected from the manufactured magnesium alloy extruded material, subjected to mechanical polishing and buff polishing, and then subjected to electrolytic polishing to adjust the surface. For the specimen obtained in this way, for example, using FESEM manufactured by JEOL Ltd. and EBSP measurement / analysis system OIM (Orientation Imaging Macrograph) manufactured by TSL, analysis software of the system (software name “OIMA Analysis”) Is used to determine the orientation mapping (Schmid factor) in the measurement field of each crystal grain.
より具体的には、測定される材料の測定領域を通常、六角形等の領域に区切り、区切られた各領域について、試料表面に入射させた電子線の反射電子から、菊地パターンを得る。この際、電子線を試料表面に２次元で走査させ、所定ピッチ毎に結晶方位を測定すれば、試料表面の方位分布を測定できる。次に、得られた上記菊池パターンを解析して、電子線入射位置の結晶方位を知る。即ち、得られた菊地パターンを既知の結晶構造のデータと比較し、その測定点での結晶方位を求める。同様にして、その測定点に隣接する測定点の結晶方位を求め、各結晶粒の測定視野における方位マッピング（シュミット因子）を求める。なお、これら互いに隣接する結晶の方位差が±１５°以内（結晶面から±１０°以内のずれ）のものは同一の結晶面に属するものとする（見なす）。 More specifically, the measurement area of the material to be measured is usually divided into hexagonal areas, and a Kikuchi pattern is obtained from the reflected electrons of the electron beam incident on the sample surface for each divided area. At this time, if the electron beam is scanned two-dimensionally on the sample surface and the crystal orientation is measured at every predetermined pitch, the orientation distribution on the sample surface can be measured. Next, the obtained Kikuchi pattern is analyzed to know the crystal orientation at the electron beam incident position. That is, the obtained Kikuchi pattern is compared with data of a known crystal structure, and the crystal orientation at the measurement point is obtained. Similarly, the crystal orientation of the measurement point adjacent to the measurement point is obtained, and the orientation mapping (Schmid factor) in the measurement visual field of each crystal grain is obtained. In addition, those in which the orientation difference between these adjacent crystals is within ± 15 ° (deviation within ± 10 ° from the crystal plane) is assumed to belong to the same crystal plane (deemed).
前記方位マッピングにより、本発明マグネシウム合金の六方晶（最密六方格子、ｈｃｐ）結晶構造の各結晶粒の結晶方位における、（０００１）＜１１−２０＞のシュミット因子は、（０００１）面の法線方向と引張軸（引張試験時の引張方向または圧縮試験時の圧縮方向）とのなす角Φと、（０００１）面内における＜１１−２０＞方向と前記引張軸とのなす角をλとを求め、前記式中の（ｃｏｓφｃｏｓλ）によって、各結晶粒のシュミット因子の値を求める。そして、これら測定した各結晶粒のシュミット因子の値を平均して、本発明で規定するシュミット因子の平均値とする。 According to the orientation mapping, the Schmid factor of (0001) <11-20> in the crystal orientation of each crystal grain of the hexagonal crystal (close-packed hexagonal lattice, hcp) crystal structure of the magnesium alloy of the present invention is the method of the (0001) plane. The angle Φ formed between the linear direction and the tensile axis (the tensile direction during the tensile test or the compression direction during the compression test), and the angle formed between the <11-20> direction in the (0001) plane and the tensile axis is λ. And the value of the Schmid factor of each crystal grain is obtained by (cosφcosλ) in the above formula. And the value of the measured Schmid factor of each crystal grain is averaged to obtain the average value of the Schmit factor defined in the present invention.
平均結晶粒径：
その一方で、本発明は、このマグネシウム合金組織の平均結晶粒径を１５μm 以下、好ましくは１０μm 以下に微細化し、これと前記シュミット因子の平均値制御との相乗効果によって、異方性を改善する。また、この平均結晶粒径の微細化は、当然ながら耐力も向上させるため、この耐力も、この平均結晶粒径の微細化と前記シュミット因子の平均値制御との相乗効果によって、耐力も向上する。
Average grain size:
On the other hand, according to the present invention, the average crystal grain size of the magnesium alloy structure is refined to 15 μm or less, preferably 10 μm or less, and the anisotropy is improved by a synergistic effect of this and the Schmid factor average value control. . In addition, since the refinement of the average crystal grain size naturally improves the yield strength, the yield strength is also improved by the synergistic effect of the refinement of the mean crystal grain size and the average value control of the Schmitt factor. .
この結果、本発明では、前記マグネシウム合金の押出材として、０．２％圧縮耐力が１４０ＭＰａ以上であるとともに、０．２％圧縮耐力と０．２％引張耐力との比（圧縮耐力／引張耐力）が０．７以上であるように異方性を抑制することができる。一方、前記平均結晶粒径が前記した規定を超えて粗大化した場合にはこれらの効果が得られない。 As a result, in the present invention, as the extruded material of the magnesium alloy, the 0.2% compression strength is 140 MPa or more, and the ratio between the 0.2% compression strength and the 0.2% tensile strength (compression strength / tensile strength). ) Can be suppressed so that it is 0.7 or more. On the other hand, these effects cannot be obtained when the average crystal grain size is larger than the above-mentioned regulation.
平均結晶粒径測定方法：
本発明で言う結晶粒径とは、押出後のマグネシウム合金材組織の押出方向の縦断面（押出方向に沿って切断した押出材の断面）における押出方向の結晶粒径（円相当の結晶粒径）である。この結晶粒径は、採取試料における前記押出方向の縦断面を、機械研磨、電解エッチングによって前処理した後に、４００倍の光学顕微鏡を用いて観察する。これを画像解析して、視野内に観察される結晶粒の粒径を、面積が等価な円の直径に換算した大きさとして評価し、これを平均化して、本発明で言う、平均結晶粒径とする。
Average crystal grain size measurement method:
The crystal grain size referred to in the present invention is the crystal grain size in the extrusion direction (cross-section of the extruded material cut along the extrusion direction) in the extrusion direction of the magnesium alloy material structure after extrusion (the crystal grain size equivalent to a circle). ). The crystal grain size is observed using a 400 × optical microscope after pre-processing the longitudinal section of the sample collected in the extrusion direction by mechanical polishing and electrolytic etching. This is image-analyzed, the grain size of the crystal grains observed in the field of view is evaluated as a size converted into a diameter of a circle with an equivalent area, and this is averaged to mean the average crystal grains referred to in the present invention. The diameter.
（製造方法）
本発明マグネシウム合金を得るための好ましい製造方法、条件について以下に説明する。本発明のマグネシウム合金は、特定成分組成に調整したマグネシウム合金溶湯のインゴット鋳造後、インゴットを必要により熱間で押出加工するためのビレットへの機械加工、合金元素を固溶させるための（固溶量を確保するための）溶体化処理、静水圧押出や直接押出などの熱間加工、必要により調質処理（熱処理）を行なって製造する。
(Production method)
A preferable production method and conditions for obtaining the magnesium alloy of the present invention will be described below. The magnesium alloy of the present invention is formed by ingot casting of a magnesium alloy melt adjusted to a specific component composition, followed by machining into a billet for extruding the ingot if necessary, for dissolving the alloy elements (solid solution). It is manufactured by solution treatment (to ensure the amount), hot working such as isostatic pressing or direct extrusion, and tempering treatment (heat treatment) if necessary.
マグネシウム合金の溶体化処理は２００〜５００℃の溶体化処理温度で１〜３０時間行なうことが好ましい。より好ましい溶体化処理温度は２００〜４５０℃である。この温度が低過ぎる、あるいは時間が短過ぎると、Ａｌ、Ｚｎなどの合金元素の固溶量が不足する可能性がある。一方、この温度が高過ぎる、あるいは時間が長過ぎると、結晶粒が粗大化する可能性がある。 The solution treatment of the magnesium alloy is preferably performed at a solution treatment temperature of 200 to 500 ° C. for 1 to 30 hours. A more preferable solution treatment temperature is 200 to 450 ° C. If this temperature is too low or the time is too short, the amount of solid solution of alloy elements such as Al and Zn may be insufficient. On the other hand, if the temperature is too high or the time is too long, the crystal grains may become coarse.
この溶体化処理後のマグネシウム合金ビレットを押出加工するが、前記異方性と耐力とのバランスが優れたマグネシウム合金押出材を得るためには、押出のうちでも静水圧押出することが好ましい。この静水圧押出を用いた、前記異方性と耐力とのバランスが優れたマグネシウム合金押出材の製造方法としては、前記組成からなるマグネシウム合金鋳塊を、１５０〜３５０℃の範囲の低温押出温度で押出して製造する。押出温度は、結晶粒を微細化するためより低温が好ましく、静水圧押出を用いることで、３００℃以下の低温で押出加工を行なうことが可能である。静水圧押出温度は好ましくは低温の１５０〜２５０℃の範囲であり、この温度が１５０℃未満では、Ａｌ、Ｚｎからなるマグネシウム合金の静水圧押出自体が困難となる。また、静水圧押出温度を２５０℃を超えて高くした場合には、１５μm 以下、好ましくは１０μm 以下に、平均結晶粒径を微細化できなくなる可能性がある。 The magnesium alloy billet after the solution treatment is extruded. In order to obtain a magnesium alloy extruded material having an excellent balance between the anisotropy and the yield strength, it is preferable to perform isostatic extrusion among the extrusions. As a method for producing a magnesium alloy extruded material having an excellent balance between anisotropy and yield strength using this hydrostatic extrusion, a magnesium alloy ingot having the above composition is subjected to a low temperature extrusion temperature in the range of 150 to 350 ° C. It is manufactured by extrusion. The extrusion temperature is preferably lower in order to make the crystal grains finer, and the extrusion process can be performed at a low temperature of 300 ° C. or less by using isostatic extrusion. The hydrostatic extrusion temperature is preferably in the low temperature range of 150 to 250 ° C. If this temperature is lower than 150 ° C., the hydrostatic extrusion of the magnesium alloy composed of Al and Zn itself becomes difficult. Further, when the hydrostatic extrusion temperature is increased beyond 250 ° C., there is a possibility that the average crystal grain size cannot be reduced to 15 μm or less, preferably 10 μm or less.
また、押出速度については、シュミット因子の平均値に大きく影響し、押出速度が速すぎると、シュミット因子の平均値が０．１２より小さくなり、シュミット因子の平均値を０．１２以上、０．２未満の範囲とすることができなくなる。したがって、静水圧押出における押出速度は１２ｍｍ／秒以下の低速の押出速度とする。さらには、８ｍｍ／秒以下の低速の押出速度で静水圧押出することが好ましい。これによって、押出されたマグネシウム合金組織の平均結晶粒径を１５μm 以下とし、これら結晶粒の結晶方位の傾きを示すシュミット因子の平均値を０．１２以上、０．２未満の範囲とすることができる。 Further, the extrusion rate greatly affects the average value of the Schmitt factor. If the extrusion rate is too high, the average value of the Schmitt factor becomes smaller than 0.12, and the average value of the Schmitt factor is 0.12 or more, 0. It becomes impossible to make the range less than 2. Therefore, the extrusion speed in the hydrostatic extrusion is a low extrusion speed of 12 mm / second or less. Furthermore, it is preferable to perform isostatic extrusion at a low extrusion speed of 8 mm / second or less. As a result, the average crystal grain size of the extruded magnesium alloy structure is set to 15 μm or less, and the average value of the Schmitt factor indicating the inclination of the crystal orientation of these crystal grains is set to a range of 0.12 or more and less than 0.2. it can.
押出比については、静水圧押出の加工量（加工率）は、歪みの付与による結晶粒の核生成サイトを多数与えて、マグネシウム合金組織の平均結晶粒径を１５μm 以下、好ましくは１０μm 以下に微細化できるだけの十分の量とする。具体的には、押出比１０以上が好ましい。さらには、２０以上がさらに好ましく、静水圧押出を用いることで高押出比が可能となる。
また、押出後の冷却については、空冷さらには水冷することが、結晶粒粗大化防止の点で好ましい。この押出後の押出材は、必要により調質処理（熱処理）を行なう。
Regarding the extrusion ratio, the processing amount (processing rate) of the hydrostatic extrusion gives a large number of crystal grain nucleation sites by imparting strain, and the average crystal grain size of the magnesium alloy structure is finer to 15 μm or less, preferably 10 μm or less. The amount is sufficient to make it easier. Specifically, an extrusion ratio of 10 or more is preferable. Furthermore, 20 or more is more preferable, and a high extrusion ratio is possible by using isostatic pressing.
As for cooling after extrusion, air cooling or water cooling is preferable from the viewpoint of preventing crystal grain coarsening. The extruded material after the extrusion is subjected to a tempering treatment (heat treatment) if necessary.
以下、実施例を挙げて本発明をより具体的に説明するが、本発明はもとより下記実施例によって制限を受けるものではなく、前・後記の趣旨に適合し得る範囲で適当に変更を加えて実施することも勿論可能であり、それらはいずれも本発明の技術的範囲に包含される。 EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.
以下に、本発明の実施例を説明する。マグネシウム合金組成と製造方法、特に溶体化処理条件や熱間押出加工条件を変えて、マグネシウム合金組織中のシュミット因子や平均結晶粒径などを種々変えて、得られたマグネシウム合金押出材の引張や圧縮の耐力や、これらの耐力比（圧縮耐力／引張耐力）などの特性を各々測定、評価した。 Examples of the present invention will be described below. Magnesium alloy composition and manufacturing method, especially solution treatment conditions and hot extrusion conditions are changed, various Schmid factors and average crystal grain sizes in the magnesium alloy structure are changed, Characteristics such as the yield strength of compression and the yield strength ratio (compression strength / tensile strength) were measured and evaluated.
具体的には、下記表１に示す化学成分組成のマグネシウム合金を、それぞれアルゴン不活性雰囲気下の電気溶解炉において溶解し、鋳鉄製ブックモールドに７５０℃の温度で鋳込み、９５ｍｍφ×１００ｍｍ長さのマグネシウム合金鋳塊を得た。そして、これらの鋳塊の表面を機械加工により面削して、各々６８ｍｍφ×１００ｍｍ長さのマグネシウム合金ビレットとした。 Specifically, the magnesium alloys having the chemical composition shown in Table 1 below were melted in an electric melting furnace under an argon inert atmosphere, cast into a cast iron book mold at a temperature of 750 ° C., and a length of 95 mmφ × 100 mm was obtained. A magnesium alloy ingot was obtained. Then, the surfaces of these ingots were chamfered by machining to obtain magnesium alloy billets each having a length of 68 mmφ × 100 mm.
この各ビレットを、表２に示す温度条件で溶体化処理し、この溶体化処理温度で各押出加工を開始し、また、表２に示す押出比や押出速度の条件で、直接押出加工、熱間静水圧押出加工を各々施して、丸棒状の試験材に成形した。肉厚（径）は押出比によって異なり、押出比１０ではφ２２ｍｍであった。このようにして製造した試験材（押出材）に対して、質別Ｈ１１２の調質処理を施した。 Each billet is subjected to a solution treatment under the temperature conditions shown in Table 2, each extrusion process is started at the solution treatment temperature, and direct extrusion, heat treatment is performed under the conditions of extrusion ratio and extrusion speed shown in Table 2. Each was subjected to an isostatic pressing process and formed into a round bar-shaped test material. The wall thickness (diameter) was different depending on the extrusion ratio. The test material (extruded material) produced in this way was subjected to a tempering treatment of quality H112.
各例とも、前記調質処理後の試験材から切り出した試料を使用して、マグネシウム合金組織の平均結晶粒径、シュミット因子を測定した。また、引張試験により、引張や圧縮の耐力や、これらの耐力比（圧縮耐力／引張耐力）などの特性を測定した。これらの結果を表２に示す。 In each example, a sample cut out from the test material after the tempering treatment was used to measure the average crystal grain size and Schmid factor of the magnesium alloy structure. In addition, tensile strength and compression strength and characteristics such as a strength ratio (compression strength / tensile strength) were measured by a tensile test. These results are shown in Table 2.
ここで、表１に示すマグネシウム合金は、記載元素含有量を除いた残部組成は酸素、水素、窒素などの極微量成分を除きマグネシウムである。なお、表１の各元素含有量において示す「−」は、元素含有量が検出限界以下であることを示す。 Here, in the magnesium alloy shown in Table 1, the balance composition excluding the described element content is magnesium except for trace components such as oxygen, hydrogen, and nitrogen. In addition, "-" shown in each element content of Table 1 shows that element content is below a detection limit.
（平均結晶粒径測定方法）
結晶粒径は前記した組織写真を画像解析により測定した。同一試験片の任意の５箇所を測定し、それらの平均値を採用した。
(Average crystal grain size measurement method)
The crystal grain size was measured by image analysis of the above-described structure photograph. The arbitrary five places of the same test piece were measured and those average values were employ | adopted.
（シュミット因子測定方法）
シュミット因子は、前記した高分解能結晶方位解析法（ＦＥＳＥＭ／ＥＢＳＰ法）により、観察試料を研磨した後、ＳＥＭ（走査型電子顕微鏡）室内に試料を入れ、高感度ＳＳ−ＣＣＤカメラにより菊池パターンを取り込んだ。画像収集システムにより、段落００４９で後記する引張試験方向である押出方向に対する（０００１）＜１１−２０＞のシュミット因子を、各結晶粒ごとに評価し、方位マッピング）のデータを収集した。なお、この測定視野範囲は３００μｍ×３００μｍ程度の領域としたが、これらの方位分布は厚み方向に変化しているため、各押出材の厚み方向に５箇所任意に測定し、その平均をとることによって求めた。
(Schmidt factor measurement method)
The Schmitt factor is obtained by polishing an observation sample by the above-described high-resolution crystal orientation analysis method (FESEM / EBSP method), placing the sample in an SEM (scanning electron microscope) chamber, and generating a Kikuchi pattern using a high-sensitivity SS-CCD camera. I took it in. The image collection system evaluated (0001) <11-20> Schmid factor for the extrusion direction, which is the tensile test direction described later in paragraph 0049, for each crystal grain, and collected orientation mapping data. In addition, although this measurement visual field range was made into the area | region of about 300 micrometers x 300 micrometers, since these azimuth | direction distributions are changing in the thickness direction, measure five places arbitrarily in the thickness direction of each extruded material, and take the average. Sought by.
（引張、圧縮試験）
引張試験は、長手方向を押出方向とした試験片を用いて、５８８２型インストロン社製万能試験機により、試験片サイズφ７ｍｍ、ＧＬ＝２５ｍｍ、試験速度０．２ｍｍ／ｍｉｎにて行なった。圧縮試験も同じく、長手方向を押出方向とした試験片を用いて、試験片サイズφ８ｍｍ、高さ１２ｍｍにて行なった。それぞれ同一条件の試験片を３本試験し、０．２％引張耐力と０．２％圧縮耐力（ＭＰａ）の平均値を採用した。
(Tensile, compression test)
The tensile test was performed using a test piece having a longitudinal direction of the extrusion direction and a test piece size of φ7 mm, GL = 25 mm, and a test speed of 0.2 mm / min using a 5882 type Instron universal testing machine. Similarly, the compression test was performed using a test piece having a longitudinal direction of the extrusion direction and a test piece size of φ8 mm and a height of 12 mm. Three test pieces with the same conditions were tested, and average values of 0.2% tensile strength and 0.2% compression strength (MPa) were adopted.
表１、２から明らかな通り、本発明組成内のマグネシウム合金である発明例１〜８（表１の合金番号１〜５）は、溶体化処理が好ましい温度条件範囲内および熱間静水圧押出加工などが好ましい押出比と押出速度範囲内で行なわれて、製品マグネシウム合金押出材を得ている。 As is clear from Tables 1 and 2, Invention Examples 1 to 8 (alloy numbers 1 to 5 in Table 1), which are magnesium alloys in the composition of the present invention, are within the temperature condition range in which solution treatment is preferable and hot isostatic extrusion. Processing and the like are performed within a preferable extrusion ratio and extrusion speed range to obtain a product magnesium alloy extruded material.
このため、前記発明例のマグネシウム合金押出材は、平均結晶粒径が１５μm 以下で、シュミット因子の平均値が０．１２以上、０．２未満の範囲内である。この結果、発明例のマグネシウム合金押出材は、例えば自動車などのフレーム等の強度部材や構造材として必要な１４０ＭＰａ以上の０．２％圧縮耐力を満たし、かつ０．２％圧縮耐力と０．２％引張耐力との比（圧縮耐力／引張耐力）が０．７以上で、異方性と耐力とのバランスが良い。 For this reason, the magnesium alloy extruded material of the above invention example has an average crystal grain size of 15 μm or less, and an average value of Schmid factor within a range of 0.12 or more and less than 0.2. As a result, the magnesium alloy extruded material of the invention example satisfies the 0.2% compression strength of 140 MPa or more required as a strength member or structural material such as a frame of an automobile, for example, and 0.2% compression strength and 0.2 % Tensile strength (compression strength / tensile strength) is 0.7 or more, and the balance between anisotropy and yield strength is good.
これに対して、比較例９〜１３（表１の合金番号１）は、発明例と同じ、本発明組成内のマグネシウム合金であるものの、溶体化処理、熱間静水圧押出加工などの製造条件が外れている。したがって、比較例は平均結晶粒径が１５μm を超えて粗大化するか、シュミット因子の平均値が０．１２以上、０．２未満の範囲を満たさない。この結果、前記比較例は、０．２％圧縮耐力が１４０ＭＰａ未満か、０．２％圧縮耐力と０．２％引張耐力との比（圧縮耐力／引張耐力）が０．７未満で、異方性と耐力とのバランスが悪い。 On the other hand, Comparative Examples 9 to 13 (Alloy No. 1 in Table 1) are the same magnesium alloys within the composition of the present invention as the inventive examples, but the manufacturing conditions such as solution treatment, hot isostatic pressing, etc. Is off. Therefore, in the comparative example, the average crystal grain size becomes larger than 15 μm, or the average Schmid factor does not satisfy the range of 0.12 or more and less than 0.2. As a result, in the comparative example, the 0.2% compression strength is less than 140 MPa, or the ratio of 0.2% compression strength to 0.2% tensile strength (compression strength / tensile strength) is less than 0.7. The balance between directionality and yield strength is poor.
比較例１４、１５は、Ａｌ、Ｚｎなどの合金元素のいずれかの含有量が少なすぎ、本発明組成から外れている。したがって、前記比較例は、溶体化処理や熱間静水圧押出加工などの製造条件が好ましい範囲内で行なわれているにも係わらず、０．２％圧縮耐力が１４０ＭＰａ未満か、０．２％圧縮耐力と０．２％引張耐力との比（圧縮耐力／引張耐力）が０．７未満で、異方性と耐力とのバランスが悪い。 In Comparative Examples 14 and 15, the content of any of the alloy elements such as Al and Zn is too small, and is out of the composition of the present invention. Therefore, in the comparative example, the 0.2% compressive strength is less than 140 MPa or 0.2% even though the production conditions such as solution treatment and hot isostatic pressing are performed within a preferable range. The ratio of compression strength to 0.2% tensile strength (compression strength / tensile strength) is less than 0.7, and the balance between anisotropy and yield strength is poor.
以上の結果から、異方性と耐力とのバランスを優れさせるための、本発明マグネシウム合金における、組成、平均結晶粒径、シュミット因子の平均値の臨界的な意義が裏付けられる。また、これらの組織を得るための、溶体化処理、熱間静水圧押出などの熱間加工条件の意義も裏付けられる。 The above results support the critical significance of the composition, the average crystal grain size, and the average value of the Schmid factor in the magnesium alloy of the present invention for improving the balance between anisotropy and yield strength. In addition, the significance of hot working conditions such as solution treatment and hot isostatic pressing for obtaining these structures is supported.
以上説明したように、本発明によれば、異方性と耐力とのバランスが優れたマグネシウム合金を提供することができる。この結果、これらの特性が要求される、電気・電子機器の筐体や、自動車、航空機のフレーム等の強度部材や構造材に、好適に適用することができる。 As described above, according to the present invention, a magnesium alloy having an excellent balance between anisotropy and yield strength can be provided. As a result, it can be suitably applied to strength members and structural materials such as housings of electric / electronic devices, automobiles, and aircraft frames that require these characteristics.
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