JP2006028548A - Magnesium alloy to be plastic-worked and magnesium alloy member - Google Patents
Magnesium alloy to be plastic-worked and magnesium alloy member Download PDFInfo
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本発明は、鍛造等の塑性加工に用いられる塑性加工用マグネシウム合金、およびマグネシウム合金部材に関する。 The present invention relates to a magnesium alloy for plastic working used for plastic working such as forging, and a magnesium alloy member.
マグネシウム（Ｍｇ）は、実用金属の中で最も軽量で比強度に優れるとともに、資源が豊富でリサイクル性にも優れる。このため、軽量化や環境負荷の低減が求められる自動車分野において、マグネシウム合金製の部品が採用されつつある。 Magnesium (Mg) is the lightest and most specific metal in practical metals, and is rich in resources and excellent in recyclability. For this reason, parts made of magnesium alloy are being adopted in the automotive field where weight reduction and reduction of environmental load are required.
例えば、エンジンを構成する部品のように、自動車用部品には高い強度と優れた耐熱性とが必要となる。高強度のマグネシウム合金としては、Ｍｇ−Ｚｎ系合金が知られている。また、さらなる合金特性の向上を図るべく、種々の元素の添加や、熱処理条件についての検討がなされている。例えば、特許文献１には、耐熱マグネシウム合金として、Ｍｇ−Ｚｎ−Ｃａ系合金が開示されている。また、特許文献２には、高強度マグネシウム合金として、Ｍｇ−Ｚｎ−Ｍｎ系合金とその熱処理について開示されている。
通常、マグネシウム合金製の部品は、主としてダイカスト法等の鋳造法により製造される。したがって、上記特許文献１および特許文献２に開示されたマグネシウム合金は、いずれも鋳造用として開発されたものである。例えば、特許文献１に記載されたＭｇ−Ｚｎ−Ｃａ系合金を鋳造した場合、得られる鋳物の組織では結晶粒径が２０μｍ以上と大きくなる。このため、鋳物の強度は低く、０．２％耐力は１７０ＭＰａ以下となる。このような鋳物では、適用できる部品の種類が限られたものとなる。また、特許文献２に記載されたＭｇ−Ｚｎ−Ｍｎ系合金を加熱すると、Ｚｎを含んだ共晶組成が比較的低温で融解してしまうため、充分に均質化処理を行うことは難しい。
Usually, a magnesium alloy part is manufactured mainly by a casting method such as a die casting method. Therefore, the magnesium alloys disclosed in
一方、最近では、多様な部品のニーズや、部品の高強度化を図るため、鍛造等の各種塑性加工が注目されている。鍛造等の塑性加工用として開発されているマグネシウム合金としては、例えば、Ｍｇ−Ａｌ−Ｚｎ系合金や、Ｍｇ−Ｚｎ−Ｚｒ系合金が知られている。しかし、これらのマグネシウム合金を塑性加工した場合、得られるマグネシウム合金部材の高温下での強度は低く、耐熱性に問題がある。また、上記特許文献２に記載されたＭｇ−Ｚｎ−Ｍｎ系合金を鍛造した場合には、ジルコニウム（Ｚｒ）を含まないため、変形を均一に行うことができない。加えて、Ｍｇ−ＭｇＺｎの共晶組織が鍛造時に融解して、割れを誘引してしまう。
On the other hand, recently, various plastic workings such as forging have attracted attention in order to increase the strength of parts and the needs of various parts. As magnesium alloys developed for plastic working such as forging, for example, Mg—Al—Zn alloys and Mg—Zn—Zr alloys are known. However, when these magnesium alloys are plastically processed, the strength of the obtained magnesium alloy member at a high temperature is low, and there is a problem in heat resistance. In addition, when the Mg—Zn—Mn alloy described in
上述したように、鋳造用のマグネシウム合金については、添加元素の調整により、強度等の合金特性を向上させる試みが種々なされている。しかし、塑性加工用のマグネシウム合金では、合金組成についての検討がほとんどなされていないのが現状である。よって、塑性加工用として、強度と耐熱性とを満足するようなマグネシウム合金は実現されていない。 As described above, various attempts have been made to improve alloy characteristics such as strength by adjusting additive elements for magnesium alloys for casting. However, in the present situation, magnesium alloy for plastic working has not been studied about the alloy composition. Therefore, a magnesium alloy satisfying strength and heat resistance has not been realized for plastic working.
本発明はこのような実状を鑑みてなされたものであり、鍛造等の塑性加工により、高強度かつ耐熱性に優れたマグネシウム合金部材を得ることのできる塑性加工用マグネシウム合金を提供することを課題とする。また、その塑性加工用マグネシウム合金を塑性加工することで、高強度および耐熱性に優れたマグネシウム合金部材を提供することを課題とする。 The present invention has been made in view of such a situation, and it is an object to provide a magnesium alloy for plastic working that can obtain a magnesium alloy member having high strength and excellent heat resistance by plastic working such as forging. And Another object of the present invention is to provide a magnesium alloy member excellent in high strength and heat resistance by plastic working the magnesium alloy for plastic working.
（１）本発明の塑性加工用マグネシウム合金は、全体を１００質量％（以下、単に「％」と表記する。）としたときに、ジルコニウムを０．３％以上１．０％以下、カルシウムおよび希土類元素から選ばれる一種以上を、カルシウムの場合には０．２％以上２．０％以下、希土類元素の場合には０．５％以上４．０％以下、含み、残部がマグネシウムと不可避不純物とからなることを特徴とする。 (1) The magnesium alloy for plastic working of the present invention has a zirconium content of 0.3% or more and 1.0% or less, calcium, and 100% by mass (hereinafter, simply referred to as “%”). Contains at least one element selected from rare earth elements in the case of calcium in the range of 0.2% to 2.0%, in the case of rare earth elements 0.5% to 4.0%, with the balance being magnesium and inevitable impurities It is characterized by the following.
本発明者は、塑性加工に適したマグネシウム合金について検討を重ねた結果、カルシウム（Ｃａ）および希土類元素（以下、適宜「Ｒ．Ｅ．」と称す。）から選ばれる一種以上を含有させることで、塑性加工により合金組織を効果的に微細化することができるという知見を得た。 As a result of repeated studies on a magnesium alloy suitable for plastic working, the present inventor has contained at least one selected from calcium (Ca) and rare earth elements (hereinafter referred to as “RE” as appropriate). The knowledge that the alloy structure can be effectively refined by plastic working has been obtained.
マグネシウム合金の強度は、結晶粒径に依存し、結晶粒が微細化すると強度は高くなる。従来より、α−Ｍｇマトリックスを主相とするマグネシウム合金を高温で鍛造した場合、動的再結晶により結晶粒が微細化することは知られている。しかし、高温下では、一旦微細化した結晶粒が、その後成長して大きくなる。このため、従来のマグネシウム合金を鍛造しただけでは、得られるマグネシウム合金部材の強度はそれほど高くならない。 The strength of the magnesium alloy depends on the crystal grain size, and the strength increases as the crystal grains become finer. Conventionally, when a magnesium alloy having an α-Mg matrix as a main phase is forged at a high temperature, it is known that crystal grains are refined by dynamic recrystallization. However, under high temperature, once refined crystal grains grow later and become larger. For this reason, the intensity | strength of the magnesium alloy member obtained does not become so high only by forging the conventional magnesium alloy.
これに対して、本発明の塑性加工用マグネシウム合金では、ＣａおよびＲ．Ｅ．から選ばれる一種以上の元素の作用により、鍛造等の塑性加工の際に微細化した結晶粒の成長が抑制されると考えられる。このため、塑性加工後にも微細化された組織が得られる。また、後述するように、ＣａおよびＲ．Ｅ．は、マグネシウム合金の耐熱性を向上させる元素である。よって、ＣａおよびＲ．Ｅ．から選ばれる一種以上の元素を含むことで、塑性加工後に得られるマグネシウム合金部材の強度および耐熱性は高くなる。 On the other hand, in the magnesium alloy for plastic working of the present invention, Ca and R.I. E. It is considered that the growth of fine crystal grains during plastic working such as forging is suppressed by the action of one or more elements selected from For this reason, a refined structure can be obtained even after plastic working. As will be described later, Ca and R.I. E. Is an element that improves the heat resistance of the magnesium alloy. Thus, Ca and R.I. E. By including one or more elements selected from the above, the strength and heat resistance of the magnesium alloy member obtained after plastic working are increased.
さらに、本発明の塑性加工用マグネシウム合金は、Ｚｒを含む。Ｚｒの作用により、結晶粒は微細化されるだけでなく、角がなく丸みを帯びた形状になる。つまり、Ｚｒは、結晶粒の微細化および球状化に寄与する。このため、マグネシウム合金部材の強度はより向上する。また、Ｚｒを含むことで塑性加工性が向上する。このように、本発明の塑性加工用マグネシウム合金によれば、高強度および耐熱性に優れたマグネシウム合金部材を得ることができる。また、本発明者が行った試験によれば、同マグネシウム合金部材の靱性も高いことが確認された。 Furthermore, the magnesium alloy for plastic working of the present invention contains Zr. Due to the action of Zr, the crystal grains are not only refined, but also have a rounded shape with no corners. That is, Zr contributes to refinement and spheroidization of crystal grains. For this reason, the strength of the magnesium alloy member is further improved. Moreover, plastic workability improves by containing Zr. Thus, according to the magnesium alloy for plastic working of the present invention, a magnesium alloy member excellent in high strength and heat resistance can be obtained. Moreover, according to the test conducted by the present inventors, it was confirmed that the magnesium alloy member has high toughness.
ここで、マグネシウム合金部材の「強度」は、室温下での引張強さ、０．２％耐力により評価すればよい。例えば、室温下での引張強さおよび０．２％耐力の少なくとも一方が２００ＭＰａ以上であれば、高強度といえる。「耐熱性」は、高温下での引張強さ、０．２％耐力により評価すればよい。例えば、１５０℃下での引張強さおよび０．２％耐力の少なくとも一方が２００ＭＰａ以上であれば、耐熱性に優れるといえる。「靱性」は、室温における破断伸びにより評価すればよい。例えば、室温における破断伸びが５％以上であれば高靱性といえる。 Here, the “strength” of the magnesium alloy member may be evaluated based on the tensile strength at room temperature and the 0.2% proof stress. For example, if at least one of the tensile strength at room temperature and the 0.2% yield strength is 200 MPa or more, it can be said that the strength is high. “Heat resistance” may be evaluated by tensile strength at high temperature and 0.2% proof stress. For example, if at least one of the tensile strength at 150 ° C. and the 0.2% proof stress is 200 MPa or more, it can be said that the heat resistance is excellent. “Toughness” may be evaluated by the elongation at break at room temperature. For example, if the elongation at break at room temperature is 5% or more, it can be said to be high toughness.
（２−１）本発明の第一のマグネシウム合金部材は、上記本発明の塑性加工用マグネシウム合金を塑性加工して得られ、結晶粒の粒径が１０μｍ以下の組織を有することを特徴とする。上述したように、本発明の塑性加工用マグネシウム合金を塑性加工すると、微細化された組織を持つマグネシウム合金部材が得られる。結晶粒の微細化の程度は、塑性加工の方法、条件、加工率等により変化する。本発明の第一のマグネシウム合金部材では、塑性加工後の組織における結晶粒の粒径が１０μｍ以下となる。このように、結晶粒が充分に微細化されているため、本発明の第一のマグネシウム合金部材は、高強度かつ高靱性であり、耐熱性に優れる。 (2-1) The first magnesium alloy member of the present invention is obtained by plastic working the magnesium alloy for plastic working of the present invention, and has a structure in which the grain size of crystal grains is 10 μm or less. . As described above, when the magnesium alloy for plastic working of the present invention is plastically processed, a magnesium alloy member having a refined structure can be obtained. The degree of crystal grain refinement varies depending on the plastic processing method, conditions, processing rate, and the like. In the first magnesium alloy member of the present invention, the grain size of the crystal grains in the structure after plastic working is 10 μm or less. Thus, since the crystal grains are sufficiently refined, the first magnesium alloy member of the present invention has high strength and high toughness, and is excellent in heat resistance.
（２−２）本発明の第二のマグネシウム合金部材は、上記本発明の塑性加工用マグネシウム合金を鋳造したマグネシウム合金製鋳物を塑性加工して得られ、結晶粒の粒径が１０μｍ以下の組織を有することを特徴とする。 (2-2) The second magnesium alloy member of the present invention is obtained by plastic working a magnesium alloy casting obtained by casting the magnesium alloy for plastic working of the present invention, and has a structure in which the grain size of crystal grains is 10 μm or less. It is characterized by having.
すなわち、本発明の第二のマグネシウム合金部材では、本発明の塑性加工用マグネシウム合金を、素材の状態で塑性加工するのではなく、塑性加工の前に、一旦所望の形状に鋳造してマグネシウム合金製鋳物とし、この鋳物を塑性加工する。この点で、上記本発明の第一のマグネシウム合金部材とは、製造工程が異なる。例えば、塑性加工として鍛造法を採用する場合には、本発明の第二のマグネシウム合金部材は、いわゆる鋳造鍛造法により製造されることになる。鋳造鍛造法では、予め鍛造し易いように所望の形状に鋳物を鋳造しておき、その鋳物を鍛造する。このため、鋳造鍛造法によれば、鍛造を行い易く、鍛造工程を簡略化することができる。本発明の塑性加工用マグネシウム合金では、ＣａやＲ．Ｅ．の含有量が所定の範囲に限定される。このため、鋳造した際にも鋳造割れ等の欠陥が少ない。よって、本発明の塑性加工用マグネシウム合金は、鋳造性にも優れ、鋳造鍛造法に好適である。 That is, in the second magnesium alloy member of the present invention, the magnesium alloy for plastic working of the present invention is not subjected to plastic working in the state of the material, but is once cast into a desired shape before plastic working. A casting is made, and the casting is plastically processed. In this respect, the manufacturing process is different from the first magnesium alloy member of the present invention. For example, when a forging method is adopted as the plastic working, the second magnesium alloy member of the present invention is manufactured by a so-called casting forging method. In the casting forging method, a casting is cast into a desired shape in advance so as to facilitate forging, and the casting is forged. For this reason, according to the casting forging method, it is easy to forge and the forging process can be simplified. In the magnesium alloy for plastic working of the present invention, Ca and R.I. E. The content of is limited to a predetermined range. For this reason, there are few defects, such as a casting crack, also when casting. Therefore, the magnesium alloy for plastic working of the present invention is excellent in castability and is suitable for the casting forging method.
マグネシウム合金製鋳物を塑性加工した場合にも、本発明の塑性加工用マグネシウム合金を素材の状態で塑性加工したのと同様に、得られるマグネシウム合金部材の組織は微細化する。本発明の第二のマグネシウム合金部材では、塑性加工後の組織における結晶粒の粒径は１０μｍ以下となる。したがって、上記本発明の第一のマグネシウム合金部材と同様に、高強度かつ高靱性であり、耐熱性に優れる。 Even when a magnesium alloy casting is plastically processed, the structure of the obtained magnesium alloy member is refined in the same manner as when the magnesium alloy for plastic processing of the present invention is plastically processed in the state of the material. In the second magnesium alloy member of the present invention, the grain size of the crystal grains in the structure after plastic working is 10 μm or less. Therefore, like the first magnesium alloy member of the present invention, it has high strength and high toughness and excellent heat resistance.
本発明の塑性加工用マグネシウム合金は、添加元素としてＺｒと、ＣａおよびＲ．Ｅ．から選ばれる一種以上と、を含む。ＣａおよびＲ．Ｅ．から選ばれる一種以上の元素は、鍛造等の塑性加工の際に微細化した結晶粒の成長を抑制する。加えて、マグネシウム合金の耐熱性を向上させる。また、Ｚｒは、結晶粒を微細化および球状化させ、塑性加工性を向上させる。よって、本発明の塑性加工用マグネシウム合金によれば、強度、耐熱性、および靱性が高いマグネシウム合金部材を得ることができる。 In the magnesium alloy for plastic working of the present invention, Zr, Ca and R.I. E. One or more selected from. Ca and R.C. E. One or more elements selected from the above suppress the growth of refined crystal grains during plastic working such as forging. In addition, the heat resistance of the magnesium alloy is improved. Zr also refines the crystal grains and improves the plastic workability. Therefore, according to the magnesium alloy for plastic working of the present invention, a magnesium alloy member having high strength, heat resistance and toughness can be obtained.
本発明の第一、第二のマグネシウム合金部材は、本発明の塑性加工用マグネシウム合金、それを鋳造したマグネシウム合金製鋳物をそれぞれ塑性加工して得られ、組織における結晶粒の粒径が１０μｍ以下である。本発明の第一および第二のマグネシウム合金部材は、いずれも結晶粒が充分に微細化されているため高強度かつ高靱性であり、その上耐熱性にも優れる。 The first and second magnesium alloy members of the present invention are obtained by plastic working the magnesium alloy for plastic working of the present invention and the magnesium alloy casting obtained by casting the same, and the grain size of the crystal grains in the structure is 10 μm or less. It is. Both the first and second magnesium alloy members of the present invention have high strength and high toughness because the crystal grains are sufficiently refined, and also have excellent heat resistance.
以下、実施形態を挙げ、本発明の塑性加工用マグネシウム合金、およびマグネシウム合金部材について詳細に説明する。 Hereinafter, the embodiment will be given and the magnesium alloy for plastic working and the magnesium alloy member of the present invention will be described in detail.
〈塑性加工用マグネシウム合金〉
本発明の塑性加工用マグネシウム合金は、Ｚｒと、ＣａおよびＲ．Ｅ．から選ばれる一種以上の元素と、を含み、残部がＭｇと不可避不純物とからなる。
<Magnesium alloy for plastic working>
The magnesium alloy for plastic working of the present invention comprises Zr, Ca and R.I. E. One or more elements selected from the group consisting of Mg and inevitable impurities.
Ｚｒは、マグネシウム合金の結晶粒を微細化かつ球状化して、マグネシウム合金の強度を向上させる。また、Ｚｒを含むことにより、高温下での塑性加工が可能になる。Ｚｒが多すぎると、マグネシウム合金の融点が高くなるだけでなく、ＺｒがＭｇマトリックス中に均一に分散し難くなる。よって、Ｚｒ量の上限を１．０％以下とする。特に、０．８％以下、さらには０．６％以下とすると好適である。一方、Ｚｒが少なすぎると、結晶粒の微細化および球状化が充分になされない。よって、Ｚｒ量の下限を０．３％以上とする。特に、０．４％以上とすると好適である。 Zr refines and spheroidizes the crystal grains of the magnesium alloy and improves the strength of the magnesium alloy. Further, by including Zr, plastic working at high temperature becomes possible. If there is too much Zr, not only will the melting point of the magnesium alloy increase, but it will also be difficult to disperse Zr uniformly in the Mg matrix. Therefore, the upper limit of the Zr amount is 1.0% or less. In particular, 0.8% or less, further 0.6% or less is preferable. On the other hand, if Zr is too small, crystal grains are not sufficiently refined and spheroidized. Therefore, the lower limit of the amount of Zr is set to 0.3% or more. In particular, 0.4% or more is preferable.
Ｃａは、Ｍｇマトリックス中に固溶してα−Ｍｇ相を強化するとともに、微細な析出物を形成し、粒界化合物を晶出する。また、塑性加工の際に微細化した結晶粒の成長を抑制する。これより、マグネシウム合金の強度および耐熱性を向上させる。Ｃａが多すぎると、粒界化合物が多量に晶出するため、マグネシウム合金が脆くなり、伸びも損なわれる。よって、Ｃａを含む場合には、Ｃａ量の上限を２．０％以下とする。特に、１．５％以下、さらには１．０％以下とすると好適である。一方、Ｃａが少なすぎると、α−Ｍｇ相の強化および結晶粒の成長抑制効果が発揮されない。よって、Ｃａ量の下限を０．２％以上とする。特に、０．４％以上、さらには０．７％以上とすると好適である。 Ca dissolves in the Mg matrix and strengthens the α-Mg phase, forms fine precipitates, and crystallizes the grain boundary compound. In addition, growth of crystal grains refined during plastic working is suppressed. This improves the strength and heat resistance of the magnesium alloy. When there is too much Ca, the grain boundary compound crystallizes in a large amount, so that the magnesium alloy becomes brittle and the elongation is impaired. Therefore, when Ca is contained, the upper limit of the Ca amount is set to 2.0% or less. In particular, 1.5% or less, further 1.0% or less is preferable. On the other hand, when there is too little Ca, the strengthening of the α-Mg phase and the effect of suppressing the growth of crystal grains are not exhibited. Therefore, the lower limit of the Ca content is 0.2% or more. In particular, 0.4% or more, further 0.7% or more is preferable.
Ｒ．Ｅ．は、Ｃａと同様に、Ｍｇマトリックス中に固溶してα−Ｍｇ相を強化するとともに、微細な析出物を形成し、粒界化合物を晶出する。また、塑性加工の際に微細化した結晶粒の成長を抑制する。これより、マグネシウム合金の強度および耐熱性を向上させる。Ｒ．Ｅ．が多すぎると、粒界化合物が多量に晶出するため、マグネシウム合金が脆くなり、伸びも損なわれる。よって、Ｒ．Ｅ．を含む場合には、Ｒ．Ｅ．量の上限を４．０％以下とする。特に、３．０％以下、さらには２．０％以下とすると好適である。一方、Ｒ．Ｅ．が少なすぎると、α−Ｍｇ相の強化および結晶粒の成長抑制効果が発揮されない。よって、Ｒ．Ｅ．量の下限を０．５％以上とする。特に、１．０％以上、さらには１．５％以上とすると好適である。 R. E. Like Ca, it solidifies in the Mg matrix and strengthens the α-Mg phase, forms fine precipitates, and crystallizes the grain boundary compound. In addition, growth of crystal grains refined during plastic working is suppressed. This improves the strength and heat resistance of the magnesium alloy. R. E. If the amount is too large, a large amount of grain boundary compounds are crystallized, so that the magnesium alloy becomes brittle and the elongation is impaired. R. E. When R. is included, R.I. E. The upper limit of the amount is 4.0% or less. In particular, 3.0% or less, further 2.0% or less is preferable. On the other hand, R.I. E. If the amount is too small, the strengthening of the α-Mg phase and the effect of suppressing the growth of crystal grains are not exhibited. R. E. The lower limit of the amount is 0.5% or more. In particular, 1.0% or more, further 1.5% or more is preferable.
Ｒ．Ｅ．は、スカンジウム（Ｓｃ）、イットリウム（Ｙ）、ランタノイド（原子番号５７〜７１）、アクチノイド（原子番号８９〜１０３）である。これらの一種を単独で、あるいは二種以上を混合して用いればよい。例えば、入手が容易で安価であるという理由から、ランタン（Ｌａ）、セリウム（Ｃｅ）等の混合物であるミッシュメタル（Ｍｍ）を用いると好適である。 R. E. Are scandium (Sc), yttrium (Y), lanthanoids (atomic numbers 57 to 71) and actinoids (atomic numbers 89 to 103). One kind of these may be used alone, or two or more kinds may be mixed and used. For example, it is preferable to use misch metal (Mm), which is a mixture of lanthanum (La), cerium (Ce), and the like, because it is easily available and inexpensive.
本発明の塑性加工用マグネシウム合金には、上記ＣａおよびＲ．Ｅ．から選ばれる一種以上を含めばよい。すなわち、ＣａあるいはＲ．Ｅ．のいずれか一方を含む態様であってもよく、また、ＣａおよびＲ．Ｅ．の両方を含む態様であってもよい。α−Ｍｇ相の強化および結晶粒の成長抑制効果を高め、マグネシウム合金の強度および耐熱性をより向上さ
せるためには、ＣａおよびＲ．Ｅ．の両方を含む態様を採用することが望ましい。
In the magnesium alloy for plastic working of the present invention, the above Ca and R.I. E. One or more selected from the above may be included. That is, Ca or R.I. E. The embodiment may include any one of Ca and R. E. The aspect containing both of these may be sufficient. In order to enhance the strengthening of the α-Mg phase and the effect of suppressing the growth of crystal grains, and to further improve the strength and heat resistance of the magnesium alloy, Ca and R.M. E. It is desirable to adopt an embodiment including both of the above.
本発明の塑性加工用マグネシウム合金は、上記Ｚｒ、Ｃａ、Ｒ．Ｅ．に加え、さらにＺｎを含むことが望ましい。Ｚｎは、固溶硬化によりα−Ｍｇ相を強化して、マグネシウム合金の強度をさらに向上させる。この場合、Ｚｎが多すぎると、Ｚｎの固溶量の増加に伴い低融点の粒界化合物が多く晶出する。その結果、クリープ特性の低下を招く。よって、Ｚｎを含む場合には、Ｚｎ量の上限を６．０％以下とすることが望ましい。特に、４．０％以下とすると好適である。一方、Ｚｎによる強度向上効果を充分発揮させるためには、Ｚｎ量の下限を１．０％以上とすることが望ましい。特に、１．５％以上とすると好適である。また、Ｒ．Ｅ．の一種以上を含む場合には、高い固溶線温度を確保するため、Ｚｎの含有量に対するＲ．Ｅ．の含有量（Ｒ．Ｅ．／Ｚｎ）を０．２５より大きくすることが望ましい。 The magnesium alloy for plastic working of the present invention has the above Zr, Ca, R.P. E. In addition to the above, it is desirable to further contain Zn. Zn strengthens the α-Mg phase by solid solution hardening and further improves the strength of the magnesium alloy. In this case, when there is too much Zn, many low-melting-point grain boundary compounds crystallize with an increase in the solid solution amount of Zn. As a result, the creep characteristics are degraded. Therefore, when Zn is contained, it is desirable that the upper limit of the Zn amount is 6.0% or less. In particular, it is preferable to be 4.0% or less. On the other hand, in order to sufficiently exhibit the strength improvement effect by Zn, it is desirable that the lower limit of the Zn amount is 1.0% or more. In particular, 1.5% or more is preferable. R. E. In order to ensure a high solid solution line temperature, the R.S. E. It is desirable to make the content of (RE / Zn) greater than 0.25.
また、本発明の塑性加工用マグネシウム合金は、さらに、ストロンチウム（Ｓｒ）、バリウム（Ｂａ）、マンガン（Ｍｎ）から選ばれる一種以上（以下「Ｓｒ等」と称す。）を含んでいてもよい。Ｓｒ、Ｂａは、Ｍｇマトリックス中へのわずかな固溶により、微細な析出物を形成し、粒界化合物を晶出する。これより、マグネシウム合金の耐熱性を向上させる。Ｍｎは、耐食性に悪影響を与えない元素であり、Ｍｇマトリックス中へのわずかな固溶により、マグネシウム合金の耐熱性を向上させる。この場合、Ｓｒ、Ｂａが多すぎると、晶出化合物が増え、鍛造性および延性が低下する。また、Ｍｎの２％以上の添加は難しく、Ｍｇマトリックス中へＭｎを２％以上固溶させても、耐熱性向上効果は変わらない。よって、Ｓｒ等を含む場合には、これら一種以上の合計量の上限を２％以下とすることが望ましい。特に、１．５％以下とすると好適である。一方、Ｓｒ等による耐熱性向上効果を充分発揮させるためには、これら一種以上の合計量の下限を０．１％以上とすることが望ましい。特に、０．５％以上、さらには１％以上とすると好適である。 Further, the magnesium alloy for plastic working of the present invention may further contain one or more selected from strontium (Sr), barium (Ba), and manganese (Mn) (hereinafter referred to as “Sr etc.”). Sr and Ba form fine precipitates by a slight solid solution in the Mg matrix, and crystallize the grain boundary compound. This improves the heat resistance of the magnesium alloy. Mn is an element that does not adversely affect the corrosion resistance, and improves the heat resistance of the magnesium alloy by a slight solid solution in the Mg matrix. In this case, when there are too many Sr and Ba, the amount of crystallized compounds will increase, and forgeability and ductility will fall. Further, it is difficult to add 2% or more of Mn, and even if 2% or more of Mn is dissolved in the Mg matrix, the effect of improving heat resistance is not changed. Therefore, when Sr etc. are included, it is desirable that the upper limit of the total amount of one or more of these be 2% or less. In particular, 1.5% or less is preferable. On the other hand, in order to sufficiently exhibit the effect of improving heat resistance by Sr or the like, it is desirable that the lower limit of the total amount of one or more of these be 0.1% or more. In particular, 0.5% or more, further 1% or more is preferable.
本発明の塑性加工用マグネシウム合金における不可避不純物は、合金特性に悪影響を与えない限り、その種類や含有量が限定されるものではない。例えば、一般的な不可避不純物として、鉄（Ｆｅ）、ニッケル（Ｎｉ）、銅（Ｃｕ）等が挙げられる。これらの元素は、本発明の塑性加工用マグネシウム合金の耐食性を低下させる。したがって、その含有量を厳しく制限することが望ましい。例えば、Ｆｅの含有量を０．０１５％以下とするとよい。さらに、Ｆｅ、Ｎｉ、Ｃｕの合計量を、０．００５％以下とすると好適である。 The type and content of the inevitable impurities in the magnesium alloy for plastic working of the present invention are not limited as long as they do not adversely affect the alloy characteristics. For example, iron (Fe), nickel (Ni), copper (Cu) etc. are mentioned as a general unavoidable impurity. These elements reduce the corrosion resistance of the magnesium alloy for plastic working of the present invention. Therefore, it is desirable to strictly limit its content. For example, the Fe content is preferably 0.015% or less. Furthermore, it is preferable that the total amount of Fe, Ni, and Cu is 0.005% or less.
本発明の塑性加工用マグネシウム合金の製造方法は、合金の一般的な製造方法に従えばよい。すなわち、マグネシウムの溶湯に上記所定の元素を添加し、凝固させて製造すればよい。本発明の塑性加工用マグネシウム合金は、各種塑性加工に適するよう、インゴット、ビレット等に成形してもよく、また、所望の形状に鋳造してもよい。所望の形状に鋳造した場合は、マグネシウム合金製鋳物としても把握することができる。 The method for producing a magnesium alloy for plastic working according to the present invention may follow a general method for producing an alloy. That is, the predetermined element may be added to a molten magnesium and solidified for production. The magnesium alloy for plastic working of the present invention may be formed into an ingot, billet or the like so as to be suitable for various plastic workings, or may be cast into a desired shape. When it is cast into a desired shape, it can be grasped as a magnesium alloy casting.
〈マグネシウム合金部材〉
本発明の第一のマグネシウム合金部材は、上記本発明の塑性加工用マグネシウム合金を塑性加工して得られる。また、本発明の第二のマグネシウム合金部材は、上記本発明の塑性加工用マグネシウム合金を鋳造したマグネシウム合金製鋳物を塑性加工して得られる。ここで、マグネシウム合金製鋳物を鋳造する鋳造法は、特に限定されるものではなく、通常の重力鋳造、加圧鋳造、高速鋳造等のいずれでもよい。鋳型も砂型、金型等を問わない。
<Magnesium alloy member>
The first magnesium alloy member of the present invention is obtained by plastic working the magnesium alloy for plastic working of the present invention. The second magnesium alloy member of the present invention is obtained by plastic working a magnesium alloy casting obtained by casting the magnesium alloy for plastic working of the present invention. Here, the casting method for casting the magnesium alloy casting is not particularly limited, and may be any of ordinary gravity casting, pressure casting, high speed casting, and the like. The mold may be a sand mold or a mold.
本発明の第一、第二の各合金部材は、本発明の塑性加工用マグネシウム合金を、素材の状態で塑性加工するのか、あるいは所望の形状に鋳造した鋳物の状態で塑性加工するのか、という点においてのみ異なる。それ以外の塑性加工、合金組織等については、何ら異なる点はない。以下、本発明の第一、第二の各合金部材における塑性加工、合金組織等について説明する。 Each of the first and second alloy members of the present invention is whether the magnesium alloy for plastic working of the present invention is plastically processed in a raw material state, or is plastically processed in the state of a casting cast into a desired shape. It differs only in respect. There is no difference in other plastic processing, alloy structure, and the like. Hereinafter, plastic working, alloy structure, etc. in the first and second alloy members of the present invention will be described.
（１）塑性加工
塑性加工の種類は、特に限定されるものではなく、例えば、鍛造、圧延、押出等を行えばよい。なかでも、鍛造は、高強度の多様な部品を容易に製造できることから好適である。例えば、本発明の塑性加工用マグネシウム合金、あるいは塑性加工用マグネシウム合金製鋳物（以下、「本発明のマグネシウム合金等」と称す。）を、液圧プレス、ハンマー等により特定形状に鍛造すればよい。
(1) Plastic processing The type of plastic processing is not particularly limited, and for example, forging, rolling, extrusion, or the like may be performed. Among these, forging is preferable because various parts with high strength can be easily manufactured. For example, the magnesium alloy for plastic working of the present invention or the casting made of a magnesium alloy for plastic working (hereinafter referred to as “magnesium alloy of the present invention”) may be forged into a specific shape by a hydraulic press, a hammer or the like. .
鍛造法には、熱間鍛造、温間鍛造、冷間鍛造、恒温鍛造がある。塑性変形による動的再結晶により結晶粒を効果的に微細化するという観点から、熱間鍛造を採用するとよい。具体的には、鍛造温度を２５０℃以上４５０℃以下とすることが望ましい。加工性や、加工後の強度、伸び等の機械的特性を考慮すると、３００℃以上４００℃以下の温度が好適である。 Forging methods include hot forging, warm forging, cold forging, and isothermal forging. From the viewpoint of effectively refining crystal grains by dynamic recrystallization by plastic deformation, hot forging may be employed. Specifically, it is desirable that the forging temperature be 250 ° C. or higher and 450 ° C. or lower. In consideration of workability, mechanical properties such as strength after processing, and elongation, a temperature of 300 ° C. or higher and 400 ° C. or lower is preferable.
塑性加工の際の加工率は、本発明のマグネシウム合金等を塑性変形させることができれば、特に限定されるものではない。本発明者の実験によると、加工率が１０％以上であれば、合金組織を充分に微細化することができる。より高強度で耐熱性に優れたマグネシウム合金部材を製造するためには、加工率を５０％以上とするとよい。 The processing rate at the time of plastic working is not particularly limited as long as the magnesium alloy of the present invention can be plastically deformed. According to the experiments by the inventors, when the processing rate is 10% or more, the alloy structure can be sufficiently refined. In order to manufacture a magnesium alloy member having higher strength and excellent heat resistance, the processing rate is preferably 50% or more.
（２）熱処理
本発明のマグネシウム合金等を製造した後、温度の低下に伴う溶解度の減少により、添加元素が析出する。したがって、塑性加工の前に再び固溶温度にまで加熱することにより、析出物を固溶させ、合金組織を均質化しておくことが望ましい。すなわち、発明のマグネシウム合金等を塑性加工する前に、４００℃以上の熱処理を施すことが望ましい。熱処理の温度を高くするほど、処理時間を短くすることができる。このため、熱処理の温度を４５０℃以上とすると実用的である。なお、再融解を抑制するという理由から、熱処理の温度を４７５℃以下とすることが望ましい。
(2) Heat treatment After the magnesium alloy or the like of the present invention is produced, the additive element is precipitated due to a decrease in solubility accompanying a decrease in temperature. Therefore, it is desirable that the precipitate is solid-dissolved and the alloy structure is homogenized by heating again to the solid solution temperature before plastic working. That is, it is desirable to perform heat treatment at 400 ° C. or higher before plastic processing the magnesium alloy or the like of the invention. The treatment time can be shortened as the temperature of the heat treatment is increased. Therefore, it is practical to set the heat treatment temperature to 450 ° C. or higher. Note that the temperature of the heat treatment is desirably 475 ° C. or lower for the purpose of suppressing remelting.
（３）人工時効処理
本発明のマグネシウム合金部材は、塑性加工の後、人工時効処理が施されることが望ましい。人工時効処理を行うと、過飽和に固溶されていた原子が拡散、析出して硬化する。また、塑性加工として温間鍛造を行った場合には、人工時効処理により再結晶化し、結晶粒が微細化される。このように、人工時効処理を行うことで、本発明のマグネシウム合金部材の強度をより向上させることができる。人工時効処理は、１５０℃以上２５０℃以下の温度で行うとよい。処理時間等を考慮すると、２００℃以上で行うとよい。
(3) Artificial aging treatment The magnesium alloy member of the present invention is preferably subjected to artificial aging treatment after plastic working. When artificial aging treatment is performed, atoms that have been dissolved in supersaturation diffuse, precipitate, and harden. In addition, when warm forging is performed as plastic working, recrystallization is performed by artificial aging treatment, and crystal grains are refined. Thus, the strength of the magnesium alloy member of the present invention can be further improved by performing the artificial aging treatment. The artificial aging treatment is preferably performed at a temperature of 150 ° C. or higher and 250 ° C. or lower. Considering treatment time and the like, it is preferable to carry out at 200 ° C. or higher.
（４）合金組織
本発明のマグネシウム合金等は、塑性加工され、好ましくは、熱処理→塑性加工→人工時効処理という工程を経て、本発明のマグネシウム合金部材となる。本発明のマグネシウム合金部材は、後に写真で示すように、結晶粒の粒径が１０μｍ以下の組織を有する。つまり、結晶粒は微細化され、個々の結晶粒は丸みを帯びた形状を呈している。このような組織を有するため、本発明のマグネシウム合金部材では、引張強さおよび０．２％耐力の少なくとも一方が２００ＭＰａ以上となる。また、本発明のマグネシウム合金部材の引張強さ、０．２％耐力は、高温下においてもほとんど低下しない。つまり、本発明のマグネシウム合金部材は、高強度であり、かつ耐熱性に優れる。
(4) Alloy structure The magnesium alloy or the like of the present invention is plastically processed, and preferably becomes a magnesium alloy member of the present invention through a process of heat treatment → plastic processing → artificial aging treatment. The magnesium alloy member of the present invention has a structure in which the grain size of crystal grains is 10 μm or less, as shown later in the photograph. That is, the crystal grains are refined and each crystal grain has a rounded shape. Since it has such a structure, in the magnesium alloy member of the present invention, at least one of tensile strength and 0.2% proof stress is 200 MPa or more. Further, the tensile strength and 0.2% proof stress of the magnesium alloy member of the present invention hardly decrease even at high temperatures. That is, the magnesium alloy member of the present invention has high strength and excellent heat resistance.
本発明のマグネシウム合金部材の組織観察は、通常の方法で行えばよく、例えば、光学顕微鏡、走査型電子顕微鏡（ＳＥＭ）、透過型電子顕微鏡（ＴＥＭ）等を用いればよい。本明細書では、ＳＥＭ観察による電子線回折像で合金組織を特定している。そして、結晶粒を２本の平行線で挟んだ場合の最大長さを、「結晶粒の粒径」とする。また、結晶粒界の方位差や集合組織（結晶方位分布状態）は、一般に合金の強度等の機械的性質に関わる重要な因子となる。よって、例えば、ＥＢＳＰ（Electron backscatter diffraction pattern）法による結晶方位解析を行うことも有用である。 Observation of the structure of the magnesium alloy member of the present invention may be performed by an ordinary method. For example, an optical microscope, a scanning electron microscope (SEM), a transmission electron microscope (TEM), or the like may be used. In this specification, the alloy structure is specified by an electron diffraction image obtained by SEM observation. The maximum length when the crystal grain is sandwiched between two parallel lines is defined as “crystal grain size”. Further, the orientation difference and texture (crystal orientation distribution state) of grain boundaries are generally important factors related to mechanical properties such as the strength of the alloy. Therefore, for example, it is also useful to perform crystal orientation analysis by EBSP (Electron backscatter diffraction pattern) method.
以上、本発明のマグネシウム合金部材について説明した。しかし、本発明のマグネシウム合金部材は、「マグネシウム合金部材の製造方法」としても把握することができる。例えば、マグネシウム合金部材の製造方法を、本発明のマグネシウム合金等に４００℃以上の熱処理を施す熱処理工程と、該熱処理後の本発明のマグネシウム合金等を塑性加工する塑性加工工程と、該塑性加工後の加工部材に１５０℃以上２５０℃以下の温度下で人工時効処理を施す人工時効処理工程と、から構成することができる。なお、本マグネシウム合金部材の製造方法においても、前述した好適な態様を適宜採用すればよい。 The magnesium alloy member of the present invention has been described above. However, the magnesium alloy member of the present invention can also be grasped as a “manufacturing method of a magnesium alloy member”. For example, a method for producing a magnesium alloy member includes a heat treatment step of subjecting the magnesium alloy or the like of the present invention to a heat treatment at 400 ° C. or more, a plastic working step of plastically processing the magnesium alloy or the like of the present invention after the heat treatment, and the plastic working And an artificial aging treatment step of subjecting the later processed member to an artificial aging treatment at a temperature of 150 ° C. or more and 250 ° C. or less. Note that, in the manufacturing method of the present magnesium alloy member, the above-described preferred embodiment may be adopted as appropriate.
上記実施形態に基づいて、本発明の塑性加工用マグネシウム合金を鋳造鍛造したマグネシウム合金部材を製造した。製造したマグネシウム合金部材から試料を採取し、組織観察および結晶方位解析を行った。また、同部材から切り出した試験片の引張試験を行い、その引張強さ、０．２％耐力、破断伸びを求めた。以下、マグネシウム合金部材の製造、組織観察等、引張試験および評価について順に説明する。 Based on the said embodiment, the magnesium alloy member which cast-forged the magnesium alloy for plastic working of this invention was manufactured. A sample was collected from the manufactured magnesium alloy member, and the structure was observed and the crystal orientation was analyzed. Moreover, the tensile test of the test piece cut out from the same member was done, and the tensile strength, 0.2% yield strength, and elongation at break were determined. Hereinafter, a tensile test and evaluation, such as manufacture of a magnesium alloy member, structure observation, etc., will be described in order.
〈マグネシウム合金部材の製造〉
（１）Ｍｇ−２％Ｚｎ−２％Ｍｍ−０．８％Ｃａ−０．５％Ｚｒ（単位：質量％、以下同じ）の組成のマグネシウム合金部材を、鋳造鍛造により製造した。まず、電気炉中で予熱した高クロム合金鋼（ＳＵＳ４３０）製るつぼの内周面に、塩化マグネシウム系のフラックスを塗布した。次いで、純Ｍｇ地金をるつぼ中に投入し、７００℃にて溶解した。この溶湯中に、Ｚｎ、Ｍｍ、Ｃａを添加した。その後、溶湯温度を７８０℃まで昇温し、Ｍｇ−Ｚｒ合金を添加した。充分に攪拌し、添加した金属を完全に溶解させた後、溶湯を７８０℃に保持した。その後、この溶湯を金型鋳造し、マグネシウム合金製鋳物（８０ｍｍ×６０ｍｍ×１２ｍｍ）を得た。金型温度は２５〜７０℃とした。なお、溶解作業中は、燃焼防止のため、炭酸ガスとＳＦ6ガスとの混合ガスを溶湯表面に吹きつけるとともに、適宜フラックスを溶湯表面に散布した。また、使用したＭｍは、Ｃｅを５２．２％、Ｌａを２５．４７％、プラセオジム（Ｐｒ）を１６．１％、ネオジム（Ｎｄ）を５．４％、サマリウム（Ｓｍ）を０．１％含む（以下同じ。）。
<Manufacture of magnesium alloy parts>
(1) A magnesium alloy member having a composition of Mg-2% Zn-2% Mm-0.8% Ca-0.5% Zr (unit: mass%, hereinafter the same) was produced by casting forging. First, a magnesium chloride-based flux was applied to the inner peripheral surface of a high chromium alloy steel (SUS430) crucible preheated in an electric furnace. Subsequently, pure Mg metal was put into the crucible and melted at 700 ° C. Zn, Mm, and Ca were added to the molten metal. Thereafter, the molten metal temperature was raised to 780 ° C., and an Mg—Zr alloy was added. After sufficiently stirring and completely dissolving the added metal, the molten metal was kept at 780 ° C. Then, this molten metal was die-cast to obtain a magnesium alloy casting (80 mm × 60 mm × 12 mm). The mold temperature was 25 to 70 ° C. During the melting operation, in order to prevent combustion, a mixed gas of carbon dioxide gas and SF 6 gas was blown onto the molten metal surface, and a flux was appropriately sprayed on the molten metal surface. The Mm used was 52.2% for Ce, 25.47% for La, 16.1% for praseodymium (Pr), 5.4% for neodymium (Nd), and 0.1% for samarium (Sm). Included (the same shall apply hereinafter).
次に、得られたマグネシウム合金製鋳物を、４６５℃で２４時間保持した（熱処理）後、油圧プレスにより据え込み鍛造した。ここで、鍛造温度は３５０℃とし、据え込み率は５０％とした。その後、鍛造により得られた部材を、２００℃で２時間保持し（人工時効処理）、マグネシウム合金部材を得た。得られたマグネシウム合金部材を、実施例１の部材とした。実施例１の部材は、本発明のマグネシウム合金部材に含まれる。 Next, the obtained magnesium alloy casting was kept at 465 ° C. for 24 hours (heat treatment), and then subjected to upset forging with a hydraulic press. Here, the forging temperature was 350 ° C., and the upsetting rate was 50%. Thereafter, the member obtained by forging was held at 200 ° C. for 2 hours (artificial aging treatment) to obtain a magnesium alloy member. The obtained magnesium alloy member was used as the member of Example 1. The member of Example 1 is included in the magnesium alloy member of the present invention.
（２）Ｍｇ−２％Ｍｍ−０．８％Ｃａ−０．５％Ｚｒの組成のマグネシウム合金部材を、上記実施例１と同様に製造した。得られたマグネシウム合金部材を実施例２の部材とした。実施例２の部材と実施例１の部材の相違点は、Ｚｎの有無である。実施例２の部材は、本発明のマグネシウム合金部材に含まれる。 (2) A magnesium alloy member having a composition of Mg-2% Mm-0.8% Ca-0.5% Zr was produced in the same manner as in Example 1 above. The obtained magnesium alloy member was used as the member of Example 2. The difference between the member of Example 2 and the member of Example 1 is the presence or absence of Zn. The member of Example 2 is included in the magnesium alloy member of the present invention.
（３）Ｍｇ−２％Ｚｎ−０．８％Ｃａ−０．５％Ｚｒの組成のマグネシウム合金部材を、上記実施例１と同様に製造した。得られたマグネシウム合金部材を実施例３の部材とした。実施例３の部材と実施例１の部材の相違点は、Ｍｍの有無である。実施例３の部材は、本発明のマグネシウム合金部材に含まれる。 (3) A magnesium alloy member having a composition of Mg-2% Zn-0.8% Ca-0.5% Zr was produced in the same manner as in Example 1 above. The obtained magnesium alloy member was used as the member of Example 3. The difference between the member of Example 3 and the member of Example 1 is the presence or absence of Mm. The member of Example 3 is included in the magnesium alloy member of the present invention.
（４）Ｍｇ−２％Ｚｎ−２％Ｍｍ−０．５％Ｚｒの組成のマグネシウム合金部材を、上記実施例１と同様に製造した。得られたマグネシウム合金部材を実施例４の部材とした。実施例４の部材と実施例１の部材の相違点は、Ｃａの有無である。実施例４の部材は、本発明のマグネシウム合金部材に含まれる。 (4) A magnesium alloy member having a composition of Mg-2% Zn-2% Mm-0.5% Zr was produced in the same manner as in Example 1 above. The obtained magnesium alloy member was used as a member of Example 4. The difference between the member of Example 4 and the member of Example 1 is the presence or absence of Ca. The member of Example 4 is included in the magnesium alloy member of the present invention.
〈組織観察および結晶方位解析〉
製造した実施例１〜４の部材の中央部付近から試料を採取し、それぞれ組織観察を行った。図１（ａ）〜（ｄ）に、各試料の光学顕微鏡写真を示す。図１（ａ）〜（ｄ）に示すように、実施例１〜４の部材では、いずれも結晶粒が微細化かつ球状化されている。これより、少なくともＣａおよびＲ．Ｅ．のいずれか一方と、Ｚｒとを所定の割合で含有するマグネシウム合金を鍛造することで、動的再結晶により結晶粒が微細化かつ球状化されることがわかる。
<Structural observation and crystal orientation analysis>
Samples were collected from the vicinity of the central part of the manufactured members of Examples 1 to 4, and the structure was observed. The optical micrograph of each sample is shown to Fig.1 (a)-(d). As shown to Fig.1 (a)-(d), in all the members of Examples 1-4, the crystal grain is refined | miniaturized and spheroidized. From this, at least Ca and R.I. E. It can be seen that by forging a magnesium alloy containing either one of the above and Zr in a predetermined ratio, the crystal grains are refined and spheroidized by dynamic recrystallization.
次に、実施例１の部材を用いて、塑性変形の有無による組織の違いを調べた。据え込み鍛造では、被鍛造物の中央部付近で塑性変形が大きいのに対して、金型で押圧される上部表面付近はほとんど塑性変形しない。このため、実施例１の部材の中央部付近と、金型で押圧された上部表面付近と、からそれぞれ試料を採取し、組織観察およびＥＢＳＰ法による結晶方位解析を行った。図２に、各試料のＳＥＭ写真および逆極点マップを示す。図２では、上部表面付近の組織を「未変形」として、中央部付近の組織を「据え込み率５０％」として示す。 Next, using the members of Example 1, the difference in structure depending on the presence or absence of plastic deformation was examined. In upsetting forging, plastic deformation is large in the vicinity of the central portion of the forged product, whereas almost no plastic deformation occurs in the vicinity of the upper surface pressed by the mold. For this reason, samples were collected from the vicinity of the central portion of the member of Example 1 and the vicinity of the upper surface pressed by the mold, and the structure was observed and the crystal orientation was analyzed by the EBSP method. In FIG. 2, the SEM photograph and reverse pole map of each sample are shown. In FIG. 2, the structure near the upper surface is shown as “undeformed” and the structure near the center is shown as “upsetting rate 50%”.
図２に示すように、ほとんど塑性変形しない上部表面付近では、結晶粒は微細化されておらず、結晶粒径は１０μｍを超えている。つまり、本発明の塑性加工用マグネシウム合金を単に鋳造しただけでは、結晶粒を微細化することはできない。これに対して、塑性変形された中央部付近では、結晶粒が１０μｍ以下に微細化され、かつ球状化されている。このように、鍛造等の塑性加工を施すことにより、動的再結晶を利用して結晶粒を微細化かつ球状化できることが確認された。 As shown in FIG. 2, in the vicinity of the upper surface that hardly undergoes plastic deformation, the crystal grains are not refined, and the crystal grain size exceeds 10 μm. That is, the crystal grains cannot be refined simply by casting the magnesium alloy for plastic working of the present invention. In contrast, near the plastically deformed central portion, the crystal grains are refined to 10 μm or less and spheroidized. Thus, it was confirmed that crystal grains can be refined and spheroidized using dynamic recrystallization by performing plastic working such as forging.
〈引張試験および評価〉
実施例１の部材から試験片（直径６ｍｍ、平行部長さ３４ｍｍ）を切り出して、引張試験を行った。引張試験の方法は、ＪＩＳ Ｚ ２２４１に従った。図３に、試験片の室温における引張強さ（σB）、０．２％耐力（σ0.2）、破断伸び（ε）を示す。なお、比較のため、図３には、実施例１の部材を製造する過程で得られたマグネシウム合金製鋳物についての各値も示す。
<Tensile test and evaluation>
A test piece (diameter 6 mm, parallel part length 34 mm) was cut out from the member of Example 1 and subjected to a tensile test. The tensile test method was in accordance with JIS Z 2241. FIG. 3 shows the tensile strength (σ B ), 0.2% proof stress (σ 0.2 ), and elongation at break (ε) of the test piece at room temperature. For comparison, FIG. 3 also shows values for the magnesium alloy casting obtained in the process of manufacturing the member of Example 1.
図３に示すように、実施例１の部材では、引張強さが２７０ＭＰａ、０．２％耐力が２２０ＭＰａ、破断伸びが５．８％となった。つまり、本発明のマグネシウム合金部材は、高強度かつ高靱性である。一方、塑性加工されていないマグネシウム合金製鋳物では、引張強さが２３０ＭＰａ、０．２％耐力が１６０ＭＰａ、破断伸びが４％であった。このように、塑性加工により、強度および靱性が大幅に向上することがわかる。 As shown in FIG. 3, in the member of Example 1, the tensile strength was 270 MPa, the 0.2% proof stress was 220 MPa, and the elongation at break was 5.8%. That is, the magnesium alloy member of the present invention has high strength and high toughness. On the other hand, the magnesium alloy casting that was not plastically processed had a tensile strength of 230 MPa, a 0.2% proof stress of 160 MPa, and a breaking elongation of 4%. Thus, it can be seen that the strength and toughness are greatly improved by plastic working.
また、一般に、金属多結晶体の降伏応力σyと平均結晶粒径ｄとの間には、式［σy＝σ0＋ｋyｄ-1/2］で表されるHall-Petchの関係式が成立する。この関係式より、降伏応力σyは結晶粒径ｄの平方根の逆数に比例する。つまり、結晶粒径ｄが小さいほど降伏応力σyは大きくなる。図４に、種々のマグネシウム合金における０．２％耐力の結晶粒径依存性を示す。 In general, the metal polycrystal yield stress sigma y between the average crystal grain size d of the formula [σ y = σ 0 + k y d -1/2] In Hall-Petch relationship represented Is established. From this relational expression, the yield stress σ y is proportional to the reciprocal of the square root of the crystal grain size d. That is, the yield stress σ y increases as the crystal grain size d decreases. FIG. 4 shows the crystal grain size dependence of 0.2% yield strength in various magnesium alloys.
図４には、従来の塑性加工用マグネシウム合金「ＺＫ６０」を押出加工した後、人工時効処理したものの、室温（R.T.）および１５０℃下での０．２％耐力を示す。また、従来の粉末冶金マグネシウム合金「ＡＺ９１Ｐ／Ｍ（Powder Metallugy）」の０．２％耐力を示す。そして、同図に、上記実施例１の部材の室温および１５０℃下における０．２％耐力と、同部材の製造過程で得られたマグネシウム合金製鋳物の室温および１５０℃下における０．２％耐力と、をプロットした。すると、これらは「ＡＺ９１Ｐ／Ｍ」の挙動と一致した。つまり、本発明の塑性加工用マグネシウム合金は、塑性加工を施すことで、粉末冶金合金として高強度の「ＡＺ９１Ｐ／Ｍ」と同等の強度を持つマグネシウム合金部材となることがわかる。さらに、同じ結晶粒径で比較すると、マグネシウム合金部材の強度は、従来の「ＺＫ６０」よりも高くなる。 FIG. 4 shows the 0.2% proof stress at room temperature (R.T.) and 150 ° C. after extruding a conventional magnesium alloy for plastic working “ZK60” and then subjecting it to artificial aging treatment. Moreover, the 0.2% yield strength of the conventional powder metallurgy magnesium alloy “AZ91P / M (Powder Metallugy)” is shown. The figure shows 0.2% proof stress of the member of Example 1 at room temperature and 150 ° C., and 0.2% of the magnesium alloy casting obtained in the manufacturing process of the member at room temperature and 150 ° C. Yield strength was plotted. Then, these agreed with the behavior of “AZ91P / M”. That is, it turns out that the magnesium alloy for plastic working of this invention turns into a magnesium alloy member with the intensity | strength equivalent to high intensity | strength "AZ91P / M" as a powder metallurgy alloy by performing plastic working. Furthermore, when compared with the same crystal grain size, the strength of the magnesium alloy member is higher than that of the conventional “ZK60”.
また、図４に示すように、「ＺＫ６０」の０．２％耐力は、室温下では高いものの、１５０℃下では大幅に低下する。一方、実施例１の部材の０．２％耐力は、１５０℃下であってもほとんど低下しない。このように、本発明のマグネシウム合金部材は、従来の塑性加工用マグネシウム合金に比べて、耐熱性も大きく向上していることがわかる。 Further, as shown in FIG. 4, the 0.2% proof stress of “ZK60” is high at room temperature, but greatly decreases at 150 ° C. On the other hand, the 0.2% yield strength of the member of Example 1 hardly decreases even at 150 ° C. Thus, it can be seen that the magnesium alloy member of the present invention is greatly improved in heat resistance as compared with the conventional magnesium alloy for plastic working.
Claims (12)
ジルコニウムを０．３％以上１．０％以下、
カルシウムおよび希土類元素から選ばれる一種以上を、カルシウムの場合には０．２％以上２．０％以下、希土類元素の場合には０．５％以上４．０％以下、含み、
残部がマグネシウムと不可避不純物とからなることを特徴とする塑性加工用マグネシウム合金。 When the total is 100% by mass (hereinafter simply referred to as “%”),
Zirconium is not less than 0.3% and not more than 1.0%,
Including at least one selected from calcium and rare earth elements, in the case of calcium, 0.2% to 2.0%, in the case of rare earth elements, 0.5% to 4.0%,
A magnesium alloy for plastic working, wherein the balance consists of magnesium and inevitable impurities.
前記亜鉛の含有量に対する該希土類元素の含有量（希土類元素含有量／亜鉛含有量）は０．２５より大きい請求項３に記載の塑性加工用マグネシウム合金。 Including one or more of the rare earth elements,
4. The magnesium alloy for plastic working according to claim 3, wherein a content of the rare earth element (a rare earth element content / a zinc content) with respect to the zinc content is greater than 0.25.
結晶粒の粒径が１０μｍ以下の組織を有するマグネシウム合金部材。 It is obtained by plastic working the magnesium alloy for plastic working according to claim 1,
A magnesium alloy member having a structure having a crystal grain size of 10 μm or less.
結晶粒の粒径が１０μｍ以下の組織を有するマグネシウム合金部材。 It is obtained by plastic working a magnesium alloy casting obtained by casting the magnesium alloy for plastic working according to claim 1,
A magnesium alloy member having a structure having a crystal grain size of 10 μm or less.
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Cited By (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007319895A (en) * | 2006-05-31 | 2007-12-13 | Mitsui Mining & Smelting Co Ltd | Heat-resistant magnesium alloy extruded material, and forged article and manufacturing method therefor |
| WO2008140062A1 (en) | 2007-05-09 | 2008-11-20 | National Institute For Materials Science | Mg-BASED ALLOY |
| WO2009044829A1 (en) * | 2007-10-02 | 2009-04-09 | National Institute For Materials Science | Magnesium alloy |
| JP2009275274A (en) * | 2008-05-16 | 2009-11-26 | National Institute Of Advanced Industrial & Technology | Magnesium alloy and method for producing the same |
| EP2183399A1 (en) * | 2007-08-31 | 2010-05-12 | Cast Crc Limited | Wrought magnesium alloy |
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