JP2017160495A - Magnesium alloy and cast member - Google Patents

Magnesium alloy and cast member Download PDF

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JP2017160495A
JP2017160495A JP2016046346A JP2016046346A JP2017160495A JP 2017160495 A JP2017160495 A JP 2017160495A JP 2016046346 A JP2016046346 A JP 2016046346A JP 2016046346 A JP2016046346 A JP 2016046346A JP 2017160495 A JP2017160495 A JP 2017160495A
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magnesium alloy
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水谷 学
Manabu Mizutani
学 水谷
百合 城野
Yuri Jono
百合 城野
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Sumitomo Electric Industries Ltd
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Abstract

PROBLEM TO BE SOLVED: To provide a magnesium alloy excellent in heat resistance which hardly generates cracks and a cast member.SOLUTION: There is provided a magnesium alloy having a structure containing, by mass%, Al of 1.0% to 3.0%, rare earth element of 1.5% to 3.0%, Ca of 0.5% to 1.5%, Mn of 0.1% to 0.5% and the balance Mg with inevitable impurities and having a compound containing Al and at least one of a rare earth element and Ca dispersed in a grain boundary and having an area ratio of a compound containing Mg and Al in a cross section of 5% or less.SELECTED DRAWING: Figure 1

Description

本発明は、各種の部品の素材などに利用されるマグネシウム合金、マグネシウム合金から構成され、各種の部品などに利用される鋳造部材に関するものである。   The present invention relates to a magnesium alloy used as a raw material for various parts and the like, and a cast member used for various parts.

実用金属で最も比重が小さく、比強度、比剛性に優れるマグネシウム合金は、軽量素材として注目されている。特に、自動車等の輸送機器類では、CO排出量の削減や省エネルギーなどの環境問題に対応するために軽量化への要求が高まっており、従来汎用されているアルミニウム合金に代えて、マグネシウム合金の利用が期待される。 Magnesium alloys, which have the smallest specific gravity among practical metals and are excellent in specific strength and specific rigidity, are attracting attention as lightweight materials. In particular, in transportation equipment such as automobiles, there is an increasing demand for weight reduction in order to cope with environmental problems such as reduction of CO 2 emissions and energy saving. Instead of the conventionally used aluminum alloy, a magnesium alloy Is expected to be used.

マグネシウム合金からなる部品としては、鋳造法の一つであるダイカスト法によって製造されたダイカスト材が挙げられる(特許文献1の[0036])。ダイカスト用マグネシウム合金は、JIS H 5303(2006年)に規定されるMDC1B(ASTM規格のAZ91B合金相当)、MDC1D(同AZ91D相当材)などが代表的である。特許文献2は、Zn,Al,Ca,希土類元素(RE)を添加元素とするダイカスト用マグネシウム合金を開示する。   An example of a part made of a magnesium alloy is a die-cast material manufactured by a die-casting method which is one of casting methods ([0036] of Patent Document 1). Typical examples of the magnesium alloy for die casting include MDC1B (equivalent to AZ91B alloy of ASTM standard) and MDC1D (equivalent to AZ91D) specified in JIS H 5303 (2006). Patent Document 2 discloses a magnesium alloy for die casting using Zn, Al, Ca, and rare earth elements (RE) as additive elements.

特開2012−136727号公報JP 2012-136727 A 特開2002−129272号公報JP 2002-129272 A

耐熱性に優れる上に、ダイカスト法などの金型鋳造法を利用する場合に鋳造部材に割れが生じ難いマグネシウム合金が望まれている。   In addition to excellent heat resistance, there is a demand for a magnesium alloy that is less likely to crack in a cast member when a die casting method such as a die casting method is used.

自動車部品や航空機部品などの部品では、使用環境温度が常温よりも高い場合がある。例えば、エンジンルームの近くに配置される部品では、使用環境温度が100℃〜180℃程度である場合があり、このような用途では耐熱性に優れることが望まれる。特に、これらの部品の使用状態が他の部品や設置対象にボルトなどによって締結された状態である場合には、経時的な変形によって締結状態が緩み、締結力(残留軸力)が低下し難いこと、即ち高温耐クリープ性に優れることが望まれる。   In parts such as automobile parts and aircraft parts, the use environment temperature may be higher than room temperature. For example, in a component arranged near the engine room, the use environment temperature may be about 100 ° C. to 180 ° C., and it is desired that the heat resistance is excellent in such an application. In particular, when these parts are used in a state where they are fastened to other parts or installation targets with bolts or the like, the fastening state is loosened due to deformation over time, and the fastening force (residual axial force) is unlikely to decrease. That is, it is desired to be excellent in high temperature creep resistance.

一方、ダイカスト材などの金型鋳造部材の合金評価を試験的に行う場合などでは、一般に、テストピースの形状を、全体に亘って均一な肉厚を有する、又は肉厚変動が実質的に無い板材、棒材、直方体状の箱材といった単純な形状にする。しかし、実際に鋳造しようとするダイカスト材の形状は、肉厚変動が大きかったり、肉厚変動量が異なる箇所を複数有していたりといった複雑な形状とすることが考えられる。例えば、リブを有する場合には、リブ近傍の肉厚変動が大きい。また、リブの厚さなどによって、肉厚変動量が異なる。本発明者らは、実製品により即した複雑な形状のマグネシウム合金のテストピースを作製した結果、従来のマグネシウム合金ではダイカスト材に熱間割れなどの欠陥が生じ易いとの知見を得た。また、上記熱間割れは、ダイカスト材において、複数の面の継ぎ目である角部を有し、この角部とそれ以外の部分とで厚みが異なる場合にこの角部に生じ易い、との知見を得た。   On the other hand, in the case where the alloy evaluation of a die casting member such as a die-cast material is performed on a test basis, generally, the shape of the test piece has a uniform thickness throughout, or there is substantially no variation in thickness. A simple shape such as a plate material, a bar material, or a rectangular parallelepiped box material is used. However, it is conceivable that the shape of the die cast material to be actually cast has a complicated shape such as a large variation in thickness or a plurality of portions having different thickness variations. For example, when a rib is provided, the thickness variation near the rib is large. Further, the variation in thickness varies depending on the thickness of the rib. As a result of producing a test piece of a magnesium alloy having a complicated shape that is more suitable for an actual product, the inventors have obtained knowledge that defects such as hot cracking are likely to occur in a die-cast material in a conventional magnesium alloy. In addition, in the die-cast material, the above-mentioned hot crack has a corner portion that is a joint of a plurality of surfaces, and knowledge that it is likely to occur in this corner portion when the thickness differs between this corner portion and the other portions. Got.

そこで、本発明の目的の一つは、耐熱性に優れる上に割れが生じ難いマグネシウム合金を提供することにある。本発明の別の目的は、マグネシウム合金から構成され、耐熱性に優れ、外観にも優れる鋳造部材を提供することにある。   Accordingly, one of the objects of the present invention is to provide a magnesium alloy that is excellent in heat resistance and hardly causes cracks. Another object of the present invention is to provide a cast member which is made of a magnesium alloy and has excellent heat resistance and excellent appearance.

本発明の一態様に係るマグネシウム合金は、
質量%で、
Alを1.0%以上3.0%以下、
希土類元素を1.5%以上3.0%以下、
Caを0.5%以上1.5%以下、
Mnを0.1%以上0.5%以下含み、残部がMg及び不可避不純物であり、
Alと、希土類元素及びCaの少なくとも一方の元素とを含む化合物が粒界に分散し、かつ断面におけるMgとAlとを含む化合物の面積割合が5%以下である組織を備える。
The magnesium alloy according to one embodiment of the present invention is
% By mass
Al is 1.0% or more and 3.0% or less,
1.5% to 3.0% rare earth element,
Ca is 0.5% to 1.5%,
Containing 0.1% or more and 0.5% or less of Mn, the balance being Mg and inevitable impurities,
A structure including a compound containing Al and at least one element of rare earth element and Ca is dispersed in the grain boundary, and an area ratio of the compound containing Mg and Al in the cross section is 5% or less.

本発明の一態様に係る鋳造部材は、
内部空間を形成する形状を有し、角部を備える鋳造部材であって、
上記の本発明の一態様に係るマグネシウム合金から構成され、
前記角部と前記角部以外の部分では厚みが異なる。
The cast member according to one aspect of the present invention is
A cast member having a shape that forms an internal space and having corners,
It is composed of the magnesium alloy according to one aspect of the present invention,
The corners and portions other than the corners have different thicknesses.

上記のマグネシウム合金は、耐熱性に優れる上に割れが生じ難い。   The magnesium alloy is excellent in heat resistance and is not easily cracked.

上記の鋳造部材は、耐熱性に優れ、外観にも優れる。   The cast member is excellent in heat resistance and in appearance.

試験例1で作製した試料No.1−1の鋳造部材の断面を走査型電子顕微鏡(SEM)で観察した顕微鏡写真である。Sample No. produced in Test Example 1 It is the microscope picture which observed the section of 1-1 cast member with the scanning electron microscope (SEM). 試験例1で作製した試料No.1−101の鋳造部材の断面をSEMで観察した顕微鏡写真である。Sample No. produced in Test Example 1 It is the microscope picture which observed the cross section of the 1-1101 cast member by SEM. 実施形態1の鋳造部材の概念図である。It is a conceptual diagram of the cast member of Embodiment 1.

本発明者らは、ダイカスト材などの金型鋳造部材を対象として耐熱性に優れるマグネシウム合金を検討した。その結果、耐クリープ性に優れるマグネシウム合金は、Al,希土類元素(RE),Ca,Mnを添加元素とし、Al,Caの含有量が比較的少なく、かつREを特定の範囲で含む組成であると共に、Alが、REを含む化合物やCaを含む化合物(以下、Al−RE化合物、Al−Ca化合物と呼ぶことがある)として結晶粒界に存在し、Mgを含む化合物(以下、Mg−Al化合物と呼ぶことがある)として存在する量が非常に少ない組織を有していた。また、この特定の組成及び特定の組織を有するマグネシウム合金は、鋳造部材本体におけるリブやボス、フランジなどの接続箇所にあたる角部、いわば角部以外の部分とは異なる厚さを有し、複数の面の接続部分である角部に熱間割れが生じ難いとの知見を得た。本発明は、上記の知見に基づくものである。   The present inventors examined a magnesium alloy having excellent heat resistance for a die casting member such as a die-cast material. As a result, the magnesium alloy having excellent creep resistance has a composition containing Al, rare earth elements (RE), Ca, and Mn as additive elements, a relatively low content of Al and Ca, and a specific range of RE. At the same time, Al is present at the grain boundary as a compound containing RE or a compound containing Ca (hereinafter sometimes referred to as an Al-RE compound or an Al-Ca compound), and a compound containing Mg (hereinafter referred to as Mg-Al). (Sometimes referred to as a compound) had a very small amount of tissue present. Further, the magnesium alloy having a specific composition and a specific structure has a thickness different from a corner portion corresponding to a connection portion such as a rib, a boss, and a flange in a cast member body, that is, a portion other than the corner portion. It was found that hot cracks are unlikely to occur at the corners that are the connecting parts of the surfaces. The present invention is based on the above findings.

最初に本発明の実施形態の内容を列記して説明する。
(1)本発明の一態様に係るマグネシウム合金は、
質量%で、
Alを1.0%以上3.0%以下、
希土類元素を1.5%以上3.0%以下、
Caを0.5%以上1.5%以下、
Mnを0.1%以上0.5%以下含み、残部がMg及び不可避不純物であり、
Alと、希土類元素及びCaの少なくとも一方の元素とを含む化合物が粒界に分散し、かつ断面におけるMgとAlとを含む化合物の面積割合が5%以下である組織を備える。
First, the contents of the embodiment of the present invention will be listed and described.
(1) A magnesium alloy according to an aspect of the present invention is
% By mass
Al is 1.0% or more and 3.0% or less,
1.5% to 3.0% rare earth element,
Ca is 0.5% to 1.5%,
Containing 0.1% or more and 0.5% or less of Mn, the balance being Mg and inevitable impurities,
A structure including a compound containing Al and at least one element of rare earth element and Ca is dispersed in the grain boundary, and an area ratio of the compound containing Mg and Al in the cross section is 5% or less.

上記のマグネシウム合金は、Al、希土類元素(RE)、Ca、Mnを特定の範囲で含有する特定の組成であることを一つの理由として、結晶粒界に、Al−RE化合物やAl−Ca化合物が分散して存在すると共に、Mg−Al化合物が非常に少ないという特定の組織を有する。粒界に存在するAl−RE化合物やAl−Ca化合物は、代表的にはMg−Al化合物よりも融点が高い。マグネシウム合金中のAlが、融点がより高い化合物として存在し、融点がより低い化合物が少ないため、上記のマグネシウム合金は使用環境温度が比較的高い部品、例えば100℃以上180℃以下程度である部品を構成する場合に、経時的に変形し難く、耐熱性、特に耐クリープ性に優れる。   One of the reasons that the above magnesium alloy has a specific composition containing Al, rare earth element (RE), Ca, and Mn in a specific range is that an Al-RE compound or an Al-Ca compound is present at the grain boundary. Is present in a dispersed state and has a specific structure in which there are very few Mg-Al compounds. Al-RE compounds and Al-Ca compounds present at grain boundaries typically have a higher melting point than Mg-Al compounds. Since Al in the magnesium alloy exists as a compound having a higher melting point and there are few compounds having a lower melting point, the above magnesium alloy is a component having a relatively high use environment temperature, for example, a component having a temperature of 100 ° C. or more and 180 ° C. or less. When it is constituted, it is difficult to be deformed with time, and is excellent in heat resistance, particularly creep resistance.

また、上記のマグネシウム合金は、Al−RE化合物やAl−Ca化合物が適切に存在するため、割れの起点になり得る化合物が非常に少ないといえる。従って、上記のマグネシウム合金がダイカスト材などの鋳造部材を構成する場合、この鋳造部材は熱間割れなどの欠陥が実質的に無く、外観に優れる。この鋳造部材が上述の角部以外の部分とは異なる厚さを有する角部を備える場合でも、この角部に上記熱間割れなどの欠陥が実質的に無い(後述の試験例参照)。従って、上記のマグネシウム合金は、優れた外観を有するダイカスト材などの鋳造部材を製造でき、このような鋳造部材の製造に供する素材に好適に利用できる。   Further, in the above magnesium alloy, since an Al—RE compound and an Al—Ca compound are appropriately present, it can be said that there are very few compounds that can be a starting point of cracking. Therefore, when the magnesium alloy constitutes a cast member such as a die-cast material, the cast member is substantially free from defects such as hot cracking and is excellent in appearance. Even when this cast member includes a corner having a thickness different from that of the portion other than the above-described corner, the corner is substantially free from defects such as the above-described hot cracking (see test examples described later). Therefore, the magnesium alloy can be used for a material for producing a cast member such as a die-cast material having an excellent appearance, and can be suitably used as a material for producing such a cast member.

(2)上記のマグネシウム合金の一例として、希土類元素とCaとの合計含有量に対するAlの含有量の質量比が0.4以上1.5以下である形態が挙げられる。 (2) As an example of said magnesium alloy, the form whose mass ratio of Al content with respect to the total content of rare earth elements and Ca is 0.4-1.5 is mentioned.

上記形態は、Alに対してRE及びCaを適切に含むため、Al−RE化合物やAl−Ca化合物が粒界に分散して存在すると共に、AlがMg−Al化合物となって存在することを抑制でき、Mg−Al化合物が非常に少ない特定の組織をより確実に有することができる。従って、上記形態は、耐熱性に優れる上に、割れがより生じ難い。   Since the above form appropriately contains RE and Ca with respect to Al, the Al-RE compound and the Al-Ca compound are dispersed in the grain boundary and Al is present as the Mg-Al compound. It can suppress and can have a specific structure | tissue which has very few Mg-Al compounds more reliably. Therefore, the above-mentioned form is excellent in heat resistance and is less susceptible to cracking.

(3)本発明の一態様に係る鋳造部材は、
内部空間を形成する形状を有し、角部を備える鋳造部材であって、
上記(1)又は上記(2)のマグネシウム合金から構成され、
前記角部と前記角部以外の部分では厚みが異なる。
(3) A cast member according to an aspect of the present invention is
A cast member having a shape that forms an internal space and having corners,
Consists of the magnesium alloy of (1) or (2) above,
The corners and portions other than the corners have different thicknesses.

上記の鋳造部材は、上述の特定の組成及び組織を有するマグネシウム合金によって構成されるため、耐熱性、特に耐クリープ性に優れる。また、上記の鋳造部材は、ダイカスト法などの金型鋳造法によって製造されたものである場合に、角部以外の部分とは異なる厚さの角部を備えるものの、この角部及び近傍に熱間割れなどの欠陥が実質的に無く、外観にも優れる。   Since the cast member is composed of the magnesium alloy having the specific composition and structure described above, the cast member is excellent in heat resistance, particularly creep resistance. Further, when the cast member is manufactured by a die casting method such as a die casting method, the cast member has a corner portion having a thickness different from that of the portion other than the corner portion. There are virtually no defects such as cracks, and the appearance is excellent.

[本発明の実施形態の詳細]
以下、本発明の実施形態の形態に係るマグネシウム合金、鋳造部材を具体的に説明する。以下の説明において、元素の含有量の単位は、質量%とする。
[Details of the embodiment of the present invention]
Hereinafter, the magnesium alloy and the cast member according to the embodiment of the present invention will be specifically described. In the following description, the unit of element content is mass%.

[マグネシウム合金]
(組成)
実施形態のマグネシウム合金は、Al,希土類元素(RE),Ca,Mnを添加元素とし、Alを比較的少なく含有すると共に、このAlに対してRE及びCaの双方を特定の範囲で含有する。具体的な組成は、Alを1.0%以上3.0%以下、REを1.5%以上3.0%以下、Caを0.5%以上1.5%以下、Mnを0.1%以上0.5%以下含み、残部がMg及び不可避不純物である。上記の範囲のAlに対して、REとCaとを合計で2.0%以上含む。
[Magnesium alloy]
(composition)
The magnesium alloy of the embodiment contains Al, rare earth elements (RE), Ca, and Mn as additive elements, contains relatively little Al, and contains both RE and Ca in a specific range with respect to this Al. Specifically, Al is 1.0% to 3.0%, RE is 1.5% to 3.0%, Ca is 0.5% to 1.5%, and Mn is 0.1%. % And 0.5% or less, and the balance is Mg and inevitable impurities. The total amount of RE and Ca is 2.0% or more with respect to Al in the above range.

≪アルミニウム(Al)≫
Alは、REを含む化合物やCaを含む化合物を形成して合金組織中に存在することで、耐クリープ性を向上する機能を有する。この効果を良好に有するためにAlの含有量を1.0%以上とする。一方、従来の耐クリープ性に優れるマグネシウム合金では、Alの含有量を4質量%以上としている。Alの含有量がこのように多い場合、RE及びCaの含有量を適切な範囲としなければ、Al-RE化合物やAl−Ca化合物が過剰に存在したり、Mg17Al12などのMg−Al化合物が形成されたりする。過剰なAl-RE化合物やAl−Ca化合物は、より複雑な形状のダイカスト材を製造する場合に熱間割れなどの欠陥の原因になり易い。比較的低融点であるMg−Al化合物は、耐熱性の低下を招く。そこで、実施形態のマグネシウム合金ではAlの含有量を3.0%以下とする。
≪Aluminum (Al) ≫
Al has a function of improving creep resistance by forming a compound containing RE or a compound containing Ca and existing in the alloy structure. In order to have this effect satisfactorily, the Al content is set to 1.0% or more. On the other hand, in the conventional magnesium alloy excellent in creep resistance, the Al content is set to 4% by mass or more. When the content of Al is so high, unless the RE and Ca contents are within an appropriate range, an Al-RE compound or an Al-Ca compound is excessively present, or Mg-Al such as Mg 17 Al 12 is present. A compound is formed. Excessive Al—RE compound and Al—Ca compound are likely to cause defects such as hot cracking when producing a die-cast material having a more complicated shape. An Mg—Al compound having a relatively low melting point causes a decrease in heat resistance. Therefore, in the magnesium alloy of the embodiment, the Al content is set to 3.0% or less.

Alの含有量を更に1.5%以上、2.0%以上とすると、Al-RE化合物やAl−Ca化合物が適切に存在して高い耐クリープ性を有することができる上に、強度の向上、耐食性の向上なども期待できる。Alの含有量を更に2.5%以下、2.0%以下とすると、Mg−Al化合物の含有量をより低減し易く、Mg−Al化合物の含有による耐クリープ性の低下を抑制し易い。   If the Al content is further 1.5% or more and 2.0% or more, the Al-RE compound and the Al-Ca compound can be appropriately present to have high creep resistance, and the strength is improved. Also, improvement in corrosion resistance can be expected. When the Al content is further set to 2.5% or less and 2.0% or less, the content of the Mg—Al compound can be easily reduced, and the deterioration of creep resistance due to the inclusion of the Mg—Al compound can be easily suppressed.

≪希土類元素(RE)≫
REは、AlRE、Al11REなどのAlを含む化合物(Al−RE化合物、代表的には晶出物)を形成して合金組織中に存在することで、耐クリープ性を向上する機能を有する。また、Al−RE化合物の形成によって、Mg−Al化合物の形成(析出)を抑制する機能も有する。上記の効果を良好に有するためにREの含有量を1.5%以上とする。REの含有量が多いほど、Al-RE化合物が十分に形成されて、粒界により多く存在して粒界すべりなどを抑制し易い。一方、REの含有量が多過ぎると、Al-RE化合物が過剰に存在して熱間割れなどの欠陥の原因になり易いため、実施形態のマグネシウム合金では、REの含有量を3.0%以下とする。
≪Rare earth element (RE) ≫
RE forms a compound containing Al (Al-RE compound, typically crystallized product) such as Al 2 RE and Al 11 RE 3 and is present in the alloy structure, thereby improving creep resistance. It has a function. Moreover, it has the function to suppress formation (precipitation) of a Mg-Al compound by formation of an Al-RE compound. In order to have the above effect satisfactorily, the RE content is set to 1.5% or more. The greater the RE content, the more Al-RE compounds are formed and the more they are present at the grain boundaries, the easier it is to suppress grain boundary sliding. On the other hand, if the RE content is too large, the Al-RE compound is excessively present and easily causes defects such as hot cracking. Therefore, in the magnesium alloy of the embodiment, the RE content is 3.0%. The following.

REの含有量を更に2.0%以上、2.5%以上とすると、耐クリープ性の更なる向上が期待できる。REの含有量を更に2.5%以下、2.0%以下とすると、ダイカスト材などの鋳造部材における熱間割れなどの欠陥の更なる低減、抑制を期待できる。また、REの含有量を低減することで、コストの低減も期待できる。
希土類元素は、周期表3族の元素、即ちスカンジウム(Sc)、イットリウム(Y)、ランタノイド、アクチノイド、その他、ミッシュメタルを含む。
When the RE content is further 2.0% or more and 2.5% or more, further improvement in creep resistance can be expected. When the RE content is further 2.5% or less and 2.0% or less, further reduction and suppression of defects such as hot cracking in cast members such as die-cast materials can be expected. In addition, a reduction in cost can be expected by reducing the RE content.
The rare earth element includes elements of Group 3 of the periodic table, that is, scandium (Sc), yttrium (Y), lanthanoid, actinoid, and misch metal.

≪カルシウム(Ca)≫
Caは、AlCa,(Al,Mg)CaなどのAlを含む化合物(Al−Ca化合物、代表的には晶出物)を形成して合金組織中に存在することで、耐クリープ性を向上する機能を有する。また、Al−Ca化合物の形成によって、Mg−Al化合物の形成(析出)を抑制する機能も有する。上記の効果を良好に有するためにCaの含有量を0.5%以上とする。Caの含有量が多いほど、Al-Ca化合物が十分に形成されて、粒界により多く存在して粒界すべりなどを抑制し易い。一方、Caの含有量が多過ぎると、Al-Ca化合物が過剰に存在して熱間割れなどの欠陥の原因になり易いため、実施形態のマグネシウム合金では、Caの含有量を1.5%以下とする。
≪Calcium (Ca) ≫
Ca forms a compound containing Al (Al—Ca compound, typically a crystallized product) such as Al 2 Ca, (Al, Mg) 2 Ca, and is present in the alloy structure. It has a function to improve. Moreover, it has the function to suppress formation (precipitation) of a Mg-Al compound by formation of an Al-Ca compound. In order to have the above effects satisfactorily, the Ca content is set to 0.5% or more. The greater the Ca content, the more Al—Ca compounds are formed and the more they are present at the grain boundaries, the easier it is to suppress grain boundary sliding and the like. On the other hand, if the Ca content is too large, the Al—Ca compound is excessively present and easily causes defects such as hot cracking. Therefore, in the magnesium alloy of the embodiment, the Ca content is 1.5%. The following.

Caの含有量を更に1.0%以上とすると、耐クリープ性の更なる向上、その他難燃性の向上などが期待できる。Caの含有量を更に1.2%以下、1.0%以下とすると、ダイカスト材などの鋳造部材における熱間割れなどの欠陥の更なる低減、抑制を期待できる。   If the Ca content is further 1.0% or more, further improvement in creep resistance and other improvement in flame retardancy can be expected. If the Ca content is further 1.2% or less and 1.0% or less, further reduction and suppression of defects such as hot cracking in cast members such as die cast materials can be expected.

≪マンガン(Mn)≫
Mnは、Alを含む化合物(以下、Al−Mn化合物と呼ぶことがある)を形成することで、Mg−Al化合物の形成を抑制する機能を有する。また、Mnは、マグネシウム合金中に不純物として存在し得るFeを低減して、耐食性の向上にも寄与する。上記の効果を良好に有するためにMnの含有量を0.1%以上とする。Mnの含有量が多いほど、Mg−Al化合物の形成(析出)の抑制、耐食性の向上に寄与する。上記の効果は、Mnの含有量が0.5%程度で飽和するため、実施形態のマグネシウム合金では、Mnの含有量を0.5%以下とする。Mnの含有量を更に0.2%以上0.4%以下とすることができる。
≪Manganese (Mn) ≫
Mn has a function of suppressing the formation of the Mg—Al compound by forming a compound containing Al (hereinafter sometimes referred to as an Al—Mn compound). Further, Mn reduces Fe that may be present as an impurity in the magnesium alloy, and contributes to improvement of corrosion resistance. In order to have the above effects satisfactorily, the Mn content is set to 0.1% or more. The higher the Mn content, the more the formation (precipitation) of the Mg—Al compound is reduced and the corrosion resistance is improved. Since the above effect saturates when the Mn content is about 0.5%, in the magnesium alloy of the embodiment, the Mn content is 0.5% or less. The Mn content can be further made 0.2% to 0.4%.

≪Al/(RE+Ca)≫
RE及びCaの含有量が上述の範囲を満たすことに加えて、REとCaとの合計含有量に対するAlの含有量の質量比をAl/(RE+Ca)とするとき、Al/(RE+Ca)が特定の範囲を満たすことが好ましい。特に、Al/(RE+Ca)が0.4以上であるとAl−RE化合物、Al−Ca化合物が適切に存在すると共に、Mg−Al化合物の含有量を低減できて耐クリープ性に優れる。Al/(RE+Ca)が1.5以下であると、Al-RE化合物及びAl-Ca化合物が過剰に存在せず、ダイカスト材などの鋳造部材における熱間割れなどの欠陥を抑制し易い。Al/(RE+Ca)が更に0.5以上1.0以下であると、耐クリープ性により優れる上に上記欠陥をより抑制し易い。
≪Al / (RE + Ca) ≫
When the mass ratio of the Al content to the total content of RE and Ca is Al / (RE + Ca) in addition to the RE and Ca contents satisfying the above range, Al / (RE + Ca) is specified. It is preferable to satisfy the range. In particular, when Al / (RE + Ca) is 0.4 or more, the Al—RE compound and the Al—Ca compound are appropriately present, and the content of the Mg—Al compound can be reduced, resulting in excellent creep resistance. When Al / (RE + Ca) is 1.5 or less, the Al—RE compound and the Al—Ca compound do not exist excessively, and defects such as hot cracking in a cast member such as a die-cast material can be easily suppressed. When Al / (RE + Ca) is further 0.5 or more and 1.0 or less, it is excellent in creep resistance and the defect is more easily suppressed.

(組織)
実施形態のマグネシウム合金は、上述のAl−RE化合物及びAl−Ca化合物の少なくとも一方、代表的には両方が粒界に分散し、かつMg−Al化合物が少ない又は実質的に存在しない組織を備える(後述の図1参照)。Al−RE化合物の融点は1100℃以上であり、Al−Ca化合物の融点は1000℃以上であり、Mg−Al化合物の融点(462℃)よりも十分に高い。このような高融点化合物であるAl−RE化合物やAl−Ca化合物が粒界に分散して存在し、低融点の化合物が少ないことで、高温に保持された場合でも粒界すべりなどを抑制し、クリープ変形し難くすることができると考えられる。
(Organization)
The magnesium alloy according to the embodiment includes a structure in which at least one of the above-described Al-RE compound and Al-Ca compound, typically both are dispersed at grain boundaries and the Mg-Al compound is low or substantially absent. (See FIG. 1 described later). The melting point of the Al—RE compound is 1100 ° C. or higher, the melting point of the Al—Ca compound is 1000 ° C. or higher, and is sufficiently higher than the melting point of the Mg—Al compound (462 ° C.). Al-RE compounds and Al-Ca compounds, which are such high melting point compounds, are dispersed at the grain boundaries and there are few low melting point compounds, which suppresses grain boundary sliding even when kept at high temperatures. It is thought that creep deformation can be made difficult.

Mg−Al化合物が少ない又は実質的に存在しない組織とは、定量的には、マグネシウム合金の断面におけるMg−Al化合物の面積割合が5%以下である組織とする。上記面積割合が少ないほど、耐熱性に優れる上に上記欠陥を抑制できるため、上記面積割合は4%以下、更に2%以下が好ましい。上記面積割合が0%、即ちMg−Al化合物が存在しないことが最も好ましい。上記面積割合の測定方法は後述する。   The structure in which the Mg—Al compound is small or substantially absent is quantitatively defined as a structure in which the area ratio of the Mg—Al compound in the cross section of the magnesium alloy is 5% or less. The smaller the area ratio, the better the heat resistance and the more the defects can be suppressed. Therefore, the area ratio is preferably 4% or less, and more preferably 2% or less. Most preferably, the area ratio is 0%, that is, no Mg—Al compound is present. The method for measuring the area ratio will be described later.

上述の化合物の組成は、例えば、エネルギー分散X線分析法(EDX)や、オージェ電子分光法(AES)などによって成分分析を行うことで確認できる。   The composition of the above-mentioned compound can be confirmed by performing component analysis by, for example, energy dispersive X-ray analysis (EDX) or Auger electron spectroscopy (AES).

(用途)
実施形態のマグネシウム合金は、ダイカスト材などの金型鋳造部材の製造に供する素材に好適に利用できる。この用途では、所望の大きさの直方体状の塊や、球体状などの塊とすることができる。また、実施形態のマグネシウム合金は、ダイカスト材などの金型鋳造部材自体を構成することができる(実施形態の鋳造部材に相当)。この用途では、後述するように種々の形状、大きさとすることができる。例えば、その全体が均一的な厚さの板材、その全体が均一的な太さの棒材、その全体が均一的な厚さの長方形状の箱材や筒材などとすることができる。即ち、実施形態のマグネシウム合金は、中実体、箱材や筒材のような内部空間を形成すると共に一つの開口部又は連通する開口部を有する中空体のいずれも構成することができる。これら鋳造用素材も鋳造部材も上述の特定の組成及び特定の組織を備える。
(Use)
The magnesium alloy of the embodiment can be suitably used as a material used for manufacturing a die casting member such as a die-cast material. In this application, a rectangular parallelepiped lump having a desired size or a lump such as a sphere can be formed. In addition, the magnesium alloy of the embodiment can constitute a die casting member itself such as a die-cast material (corresponding to the casting member of the embodiment). In this application, various shapes and sizes can be used as described later. For example, a plate material having a uniform thickness as a whole, a bar material having a uniform thickness as a whole, a rectangular box material or a cylinder material having a uniform thickness as a whole can be used. That is, the magnesium alloy according to the embodiment can form any hollow body that forms an internal space such as a solid body, a box material, or a cylindrical material and has one opening or a communicating opening. Both the casting material and the cast member have the above-mentioned specific composition and specific structure.

[鋳造部材]
(形状)
実施形態の鋳造部材1は、実施形態のマグネシウム合金から構成され、上述の特定の組成及び特定の組織を備える。この鋳造部材1は、上述のように熱間割れなどの起点となる化合物が少なく又は実質的に存在せず、割れなどの欠陥が生じ難い実施形態のマグネシウム合金で構成されるため、図3に示すように内部空間を形成する形状を有し、角部を備えるものであって、角部3と角部3以外の部分とでは厚みが異なるものとすることができる。ここでの角部3とは、複数の面が交差する稜線部分である。例えば、図3に示すように内部空間を形成する容器状の本体10を備える場合、天面部や、開口縁がつくる仮想平面に直交する平面で切断した縦断面における隣り合う二つの面が交差する部分が角部3に相当する。角部3は、外方に突出するもの(例、後述の角部30など)、内側に窪んだもの(例、後述の角部31〜36)のいずれでもよい。
[Casting member]
(shape)
The cast member 1 of the embodiment is composed of the magnesium alloy of the embodiment, and includes the specific composition and the specific structure described above. Since the cast member 1 is composed of the magnesium alloy according to the embodiment in which there is little or substantially no starting compound such as hot cracking as described above, and defects such as cracking are unlikely to occur, FIG. As shown, it has a shape that forms an internal space and is provided with corner portions, and the corner portions 3 and portions other than the corner portions 3 can have different thicknesses. The corner | angular part 3 here is a ridgeline part which a some surface cross | intersects. For example, when the container-shaped main body 10 that forms the internal space is provided as shown in FIG. 3, two adjacent surfaces in a longitudinal section cut by a plane orthogonal to a virtual plane formed by the top surface portion and the opening edge intersect each other. The portion corresponds to the corner 3. The corner portion 3 may be either one projecting outward (eg, a corner portion 30 described later) or one recessed toward the inside (eg, corner portions 31 to 36 described later).

図3は、天面部と側壁部とを備え、一方が開口した容器状の本体10を備える鋳造部材1を模式的に示す。図3の右半分は本体10の天面部を上側に、開口部を下側に配置した状態の正面図、左半部はその断面図である。図3に示す鋳造部材1は、上述の割れなどの生じ易い複雑な形状の鋳造部材を概念的に示す。   FIG. 3 schematically shows a casting member 1 having a container-like main body 10 having a top surface portion and a side wall portion, one of which is open. The right half of FIG. 3 is a front view of the state in which the top surface of the main body 10 is arranged on the upper side and the opening is arranged on the lower side, and the left half is a cross-sectional view thereof. A cast member 1 shown in FIG. 3 conceptually shows a cast member having a complicated shape that easily causes the above-described cracking or the like.

図1に示す鋳造部材1は、本体10の開口縁から外方に延設されるフランジ12と、本体10の内天面から開口側に向かって突出する少なくとも一つのボス13と、本体10の天面部から外方に突出する筒部15と、天面部の外面と筒部15の外面との交差部分に設けられる少なくとも一つのリブ14と、側壁部の内側に設けられた凹部16とを備える場合を例示する。フランジ12、ボス13、リブ14、筒部15、及び凹部16から選択される少なくとも一つを備えていれば、その他を省略することができる。また、外方に突出する筒部15に代えて、内部空間に突出する筒部を有することもできる。容器状に代えて、フランジ付きパイプなどとすることができる。   The casting member 1 shown in FIG. 1 includes a flange 12 extending outward from an opening edge of the main body 10, at least one boss 13 protruding from the inner top surface of the main body 10 toward the opening side, A cylindrical portion 15 projecting outward from the top surface portion, at least one rib 14 provided at an intersection of the outer surface of the top surface portion and the outer surface of the cylindrical portion 15, and a concave portion 16 provided inside the side wall portion. The case is illustrated. If at least one selected from the flange 12, the boss 13, the rib 14, the cylindrical portion 15, and the concave portion 16 is provided, the others can be omitted. Moreover, it can replace with the cylinder part 15 which protrudes outward, and can also have the cylinder part which protrudes in internal space. Instead of a container shape, a flanged pipe or the like can be used.

代表的には、フランジ12は、ボルト孔が設けられて、他の部品や設置対象にボルトによって締結される部分として機能する。フランジ12は、開口縁や側壁部の外周面に連続して設けられる環状の形態、開口縁や側壁部の外周面に沿って所定の間隔をあけて複数設けられる形態などが挙げられる。ボス13は天面部などに他の部品を固定や連結などするためにボルトやねじ用の雌ねじを形成したり、ピンなどを圧入する挿入孔などを形成したりするものであり、代表的には筒状である。リブ14は、貫通孔15hが設けられた筒部15を補強するものであり、代表的には板状である。また、代表的には、筒部15の外周に放射状に複数のリブ14が設けられる。ボス13及びリブ14の個数、大きさ、形状などは適宜選択できる。これらの個数が多いほど角部3が多くなり、上述の割れなどが生じ易い複雑な形状といえる。   Typically, the flange 12 is provided with a bolt hole, and functions as a portion fastened to the other component or installation target by the bolt. Examples of the flange 12 include an annular form provided continuously on the outer peripheral surface of the opening edge and the side wall part, and a form provided with a plurality at predetermined intervals along the outer peripheral surface of the opening edge and the side wall part. The boss 13 forms a female screw for a bolt or screw to fix or connect other parts to the top surface portion or the like, or forms an insertion hole for press-fitting a pin or the like. It is cylindrical. The rib 14 reinforces the cylindrical portion 15 provided with the through hole 15h, and is typically plate-shaped. Typically, a plurality of ribs 14 are provided radially on the outer periphery of the cylindrical portion 15. The number, size, shape, and the like of the boss 13 and the rib 14 can be selected as appropriate. It can be said that the larger the number, the more corners 3 and the more complicated the above-mentioned cracks are.

鋳造部材1には、天面部の外面と側壁部の外面とが交差する外側の角部30、外側の角部30に対応する内側の角部31といった本体10自体に設けられる角部、本体10とフランジ12とが交差する角部32、本体10とボス13とが交差する角部33、本体10とリブ14とが交差する角部34、本体10と筒部15とが交差する角部35、凹部16を形成する内底面と内壁面とが交差する角部36などの複数の角部3が存在し得る。そして、この例の鋳造部材1では、各角部3とそれ以外の部分とは厚みが異なる。角部3の厚さtとは、例えば、角部31に示すように上記縦断面において角部30をつくる天面部の外面と側面部の外面との角の二等分線上にとることが挙げられる。図1に示す例では、本体10の角部30,31やボス13近傍の角部33、リブ14近傍の角部34などでは、その周囲の厚さよりも厚く、凹部16における角部36ではその周囲の厚さよりも薄い。また、図1に示す例では、各角部3は実質的に直角である。このような各角部3は、厚さの変化(肉厚変動)、形状の変化が大きい箇所といえ、割れなどが生じ易い箇所と考えられる。定量的には、上記縦断面における隣り合う二つの面が交差する角部3における交差角度が0°超120°以下程度、特に直角及びその近傍であり、角部3における厚さの変化量(その周囲の厚さを基準としたときの変化量)が10%以上、更に25%以上、50%以上である箇所は、割れなどが生じ易い箇所と考えられる。実施形態のマグネシウム合金は、このような割れなどが生じ易い箇所を複数備える複雑な形状の鋳造部材1、特に上述の角部3を1個以上、更に5個以上備える鋳造部材1の製造に供する素材、又は鋳造部材1自体の構成材料に好適である。   The cast member 1 includes a corner 10 provided on the body 10 itself, such as an outer corner 30 where the outer surface of the top surface and the outer surface of the side wall intersect, and an inner corner 31 corresponding to the outer corner 30. Corner 32 where the body 10 and the boss 13 intersect, corner 34 where the body 10 and the rib 14 intersect, corner 35 where the body 10 and the cylinder 15 intersect. There may be a plurality of corners 3 such as a corner 36 where the inner bottom surface and the inner wall surface forming the recess 16 intersect. And in the cast member 1 of this example, each corner | angular part 3 and a part other than that differ in thickness. The thickness t of the corner portion 3 is, for example, taken on the bisector of the corner between the outer surface of the top surface portion and the outer surface of the side surface portion forming the corner portion 30 in the longitudinal section as shown in the corner portion 31. It is done. In the example shown in FIG. 1, the corner portions 30 and 31 of the main body 10, the corner portion 33 near the boss 13, the corner portion 34 near the rib 14, and the like are thicker than the surrounding thickness. Thinner than the surrounding thickness. Moreover, in the example shown in FIG. 1, each corner | angular part 3 is substantially right angle. Each of these corners 3 can be said to be a place where a change in thickness (thickness variation) and a change in shape are large, and a crack is likely to occur. Quantitatively, the intersecting angle at the corner 3 where two adjacent surfaces intersect in the longitudinal section is more than 0 ° and not more than 120 °, particularly right angle and its vicinity, and the amount of change in thickness at the corner 3 ( A portion where the amount of change (based on the surrounding thickness) is 10% or more, more preferably 25% or more, and 50% or more is considered to be a place where cracking or the like is likely to occur. The magnesium alloy according to the embodiment is used for manufacturing a cast member 1 having a complicated shape including a plurality of portions where such cracks or the like are likely to occur, in particular, a cast member 1 including one or more corner portions 3 and five or more corner portions 3 described above. It is suitable for a raw material or a constituent material of the cast member 1 itself.

(大きさ)
実施形態の鋳造部材1は、その全体の厚さが均一的ではなく、上述のように部分的に異なる。各部の厚さは適宜選択できる。例えば、最小厚さは0.5mm〜5mm程度、最大厚さは8mm〜15mm程度が挙げられる。内部空間を形成する容器状などの形状である場合には、その容積は適宜選択できる。例えば、容積は1000cm以上、更に10000cm以上程度が挙げられる。上述の最小厚さ、最大厚さ、及び容積を満たす鋳造部材は、割れなどが生じ易いと考えられるため、上述した実施形態のマグネシウム合金を好適に利用できる。
(size)
The overall thickness of the cast member 1 of the embodiment is not uniform, and is partially different as described above. The thickness of each part can be selected as appropriate. For example, the minimum thickness is about 0.5 mm to 5 mm, and the maximum thickness is about 8 mm to 15 mm. In the case of a shape such as a container that forms the internal space, the volume can be appropriately selected. For example, volume 1000 cm 3 or more, and a degree further 10000 cm 3 or more. Since the cast member satisfying the above-mentioned minimum thickness, maximum thickness, and volume is considered to be easily cracked, the magnesium alloy of the above-described embodiment can be suitably used.

(マグネシウム合金の製造方法)
実施形態のマグネシウム合金は、代表的には、上述した特定の組成のマグネシウム合金溶湯を作製し、鋳造することで製造できる。実施形態の鋳造部材1は、作製した溶湯を用いて、ダイカスト法などの金型鋳造法によって鋳造することで製造できる。成形型には、所望の形状のものが利用できる。
(Manufacturing method of magnesium alloy)
The magnesium alloy of the embodiment can be typically manufactured by producing and casting a molten magnesium alloy having a specific composition described above. The cast member 1 of the embodiment can be manufactured by casting by a die casting method such as a die casting method using the produced molten metal. A mold having a desired shape can be used.

マグネシウム合金溶湯は、以下のように作製することが挙げられる。原料には純度(質量割合、以下純度について同様)が99%以上、好ましくは99.5%以上の純マグネシウムの塊、各添加元素金属の塊又は添加元素を合金化した塊を用いる。   The magnesium alloy melt can be prepared as follows. A pure magnesium lump, a lump of each additive element metal, or a lump obtained by alloying the additive elements is used as the raw material with a purity (mass ratio, hereinafter the same applies to purity) of 99% or more, preferably 99.5% or more.

用意した原料塊を用いて、まず純マグネシウムを完全に溶解して、純マグネシウム溶湯を作製する。雰囲気ガスは、アルゴン(Ar)ガスなどの希ガス、窒素ガス、COガスといった不活性ガスであると、Mgなどの酸化を防止できて好ましい。また、雰囲気ガスは、SFなどの防燃ガスを含むと、発火を防止できて好ましい。 First, pure magnesium is completely dissolved using the prepared raw material lump to produce a pure magnesium molten metal. The atmospheric gas is preferably a rare gas such as argon (Ar) gas, an inert gas such as nitrogen gas, or CO 2 gas because oxidation of Mg or the like can be prevented. In addition, it is preferable that the atmosphere gas contains a flameproof gas such as SF 6 because it can prevent ignition.

純マグネシウム溶湯にAl,RE,Caの順で添加元素を添加する。また、添加する際の純マグネシウム溶湯の温度を650℃以上730℃以下とする。添加後、十分に撹拌する。実施形態のマグネシウム合金は、Al,RE,Caを主として化合物とし、かつ粒界に均一的に分散させて存在させる。このように添加順序、温度、撹拌を特定のものとするマグネシウム合金の製造方法は、純マグネシウム溶湯内に添加元素が均一的に溶解して特定の組成のマグネシウム合金溶湯を精度よく製造でき、工業的な量産に適する方法の一例として好ましいと考えられる。   Add additive elements in the order of Al, RE, and Ca to the pure magnesium melt. Moreover, the temperature of the pure magnesium molten metal at the time of addition shall be 650 degreeC or more and 730 degrees C or less. Stir well after addition. In the embodiment, the magnesium alloy is mainly composed of Al, RE, and Ca and is uniformly dispersed at the grain boundaries. In this way, the manufacturing method of a magnesium alloy with specific addition order, temperature, and stirring can accurately produce a magnesium alloy melt having a specific composition by dissolving the additive elements uniformly in the pure magnesium melt. It is considered preferable as an example of a method suitable for mass production.

Alを最初に添加することでMgの活性度を低下できる。REは、純マグネシウムに完全に溶解するまでの時間が他の元素に比較して長くなり易いため、早めに添加する。Caは、純マグネシウムに溶解し易いため、最後に添加する。REとCaとを同時に添加せず、分けて添加することで、両元素を確実に溶解できる。Mnは、溶解時間が比較的長いため、Alと同時に添加することが好ましい。   The activity of Mg can be reduced by adding Al first. RE is added early because it takes a long time to completely dissolve in pure magnesium as compared with other elements. Since Ca is easily dissolved in pure magnesium, it is added last. By adding RE and Ca separately, but not simultaneously, both elements can be dissolved reliably. Since Mn has a relatively long dissolution time, it is preferable to add Mn simultaneously with Al.

各添加元素を添加するときの純マグネシウム溶湯の温度を650℃以上とすることで、各添加元素を完全に溶解できる。上記温度が高いほど、添加元素の未溶解を防止できると共に、溶解時間を短縮できるため、上記温度を660℃以上、更に680℃以上、690℃以上とすることができる。純マグネシウム溶湯の温度を730℃以下とすることで、マグネシウムの酸化を抑制し易い上に、鉄製の坩堝を用いる場合にFeの溶出に起因するFeの混入を防止し易いため、上記温度を720℃以下、更に700℃以下とすることができる。   By setting the temperature of the pure magnesium molten metal at the time of adding each additive element to 650 ° C. or more, each additive element can be completely dissolved. The higher the temperature, the more the additive element can be prevented from being dissolved, and the dissolution time can be shortened. Therefore, the temperature can be set to 660 ° C. or higher, further 680 ° C. or higher, and 690 ° C. or higher. By controlling the temperature of the pure magnesium molten metal to 730 ° C. or less, it is easy to suppress oxidation of magnesium, and in the case of using an iron crucible, it is easy to prevent Fe contamination due to Fe elution. The temperature can be set to 700 ° C. or lower.

撹拌は、棒状の治具や市販の撹拌機などを用いて機械的に行う。撹拌時間は、撹拌方法や溶湯量などにもよるが、例えば5分以上15分以下程度とすると均一的な成分の溶湯が得られる。撹拌後、例えば10分以上15分以下程度静置することで溶湯の介在物を分離し、その後直ちに鋳造することで添加元素の分離(沈殿又は浮遊)を防止でき、Al−RE化合物、Al−Ca化合物を適切に晶出できる。鋳造工程の冷却速度は0.1℃/秒以上、更に10℃/秒以上、50℃/秒以上とすると、Al−RE化合物、Al−Ca化合物を適切に晶出できる。上記冷却速度となるように冷却条件を調整するとよい。   Stirring is performed mechanically using a rod-shaped jig or a commercially available stirrer. Although the stirring time depends on the stirring method and the amount of molten metal, for example, if the stirring time is about 5 minutes or more and 15 minutes or less, a molten metal having a uniform component can be obtained. After stirring, for example, the inclusions of the molten metal are separated by allowing to stand for about 10 minutes to 15 minutes, and then immediately after casting, separation (precipitation or floating) of the added elements can be prevented, and the Al-RE compound, Al- Ca compound can be appropriately crystallized. When the cooling rate in the casting process is 0.1 ° C./second or more, 10 ° C./second or more, and 50 ° C./second or more, the Al—RE compound and the Al—Ca compound can be appropriately crystallized. It is preferable to adjust the cooling conditions so as to achieve the above cooling rate.

[試験例1]
表1に示す種々の組成(質量%、残部Mg及び不可避不純物)のマグネシウム合金を用いてダイカスト材を作製し、得られたダイカスト材の組織観察を行うと共に、耐熱性及び割れの状態を評価した。
[Test Example 1]
A die-cast material was prepared using magnesium alloys having various compositions (mass%, balance Mg and inevitable impurities) shown in Table 1, and the structure of the obtained die-cast material was observed, and the heat resistance and the state of cracking were evaluated. .

原料として、純度99.9%の純マグネシウムの塊を50kg用意し、Ar雰囲気の溶解炉を用いて690℃で溶解し、純マグネシウム溶湯を作製した。完全に溶解した純マグネシウム溶湯中に、湯温を690℃に保持して以下の添加元素の塊を以下の順序で添加した後、棒状の治具によって10分間撹拌し、表1に示す組成のマグネシウム合金溶湯をそれぞれ作製した。純度は、全て質量%である。
1.純度99.9%の純アルミニウム塊及び純度99.9%の純マンガン塊
2.純度99.9%のミッシュメタル塊
ミッシュメタルの含有元素及びその含有量は、Laが28%、Ceが51%、Ndが16%、Prが5%である。
3.純度99.5%のCa塊
As a raw material, 50 kg of a pure magnesium lump having a purity of 99.9% was prepared and melted at 690 ° C. using a melting furnace in an Ar atmosphere to prepare a pure magnesium molten metal. In the completely melted pure magnesium melt, the hot water temperature was maintained at 690 ° C., and the following additional element lump was added in the following order, followed by stirring for 10 minutes with a rod-shaped jig, and the composition shown in Table 1 was obtained. Each magnesium alloy melt was produced. All the purity is mass%.
1. 1. Pure aluminum mass with a purity of 99.9% and pure manganese mass with a purity of 99.9% Misch Metal Mass with Purity of 99.9% The elements contained in the misch metal and their contents are 28% for La, 51% for Ce, 16% for Nd, and 5% for Pr.
3. 99.5% pure Ca mass

作製した各試料のマグネシウム合金溶湯を用いて、コールドチャンバーダイカストマシン(宇部興産機械株式会社製、型番UB530iS2)でダイカスト材を作製した。この試験では、図3に示す容器状の本体と、本体の開口側に設けられ、ボルト孔を有する環状のフランジと、本体の内部に設けられた5個以上のボスと、本体の天面部から外方に突出する筒部と、本体と筒部との交差部分に放射状に離間して設けられた15個以上のリブとを備えるものを作製した。本体に対してフランジ、ボス、筒部、リブは実質的に直交するように設けられている。また、本体とフランジとが交差する角部、本体とボスとが交差する角部、本体と筒部とが交差する角部、本体とリブとが交差する角部はいずれも、その周囲の厚さと異なる厚さを有する(厚い又は薄い)。本体における角部を除く箇所の平均厚さは4mm、上記角部における厚さの変化量(上記平均厚さ4mmに対する変化量)の最大値は500%(最大厚さ20mm)である。作製した鋳造部材のサイズは、幅200mm×奥行150mm×最大高さ150mm(筒部を含む)程度であり、使用するマグネシウム合金の体積は450cm〜500cm程度である。鋳造過程の冷却速度は、50℃/秒以上とした。 A die-cast material was produced by a cold chamber die casting machine (manufactured by Ube Industries, Ltd., model number UB530iS2) using the magnesium alloy melt of each of the produced samples. In this test, from the container-shaped main body shown in FIG. 3, an annular flange having a bolt hole provided on the opening side of the main body, five or more bosses provided inside the main body, and the top surface portion of the main body. A tube provided with an outwardly projecting cylindrical portion and 15 or more ribs provided radially apart at the intersection of the main body and the cylindrical portion was produced. The flange, the boss, the cylindrical portion, and the rib are provided so as to be substantially orthogonal to the main body. In addition, the corner where the main body and the flange intersect, the corner where the main body and the boss intersect, the corner where the main body and the cylinder intersect, and the corner where the main body and the rib intersect, (Thick or thin). The average thickness of the portion excluding the corners in the main body is 4 mm, and the maximum value of the thickness variation at the corners (the variation with respect to the average thickness of 4 mm) is 500% (maximum thickness 20 mm). Size of the produced cast member is a width of about 200 mm × depth 150 mm × maximum height 150 mm (including a cylindrical portion), the volume of the magnesium alloy used is 450cm 3 ~500cm 3 about. The cooling rate in the casting process was set to 50 ° C./second or more.

作製した各試料のダイカスト材について断面をとり、走査型電子顕微鏡(SEM)で組織観察を行った。断面の採取は、市販のクロスセクションポリッシャ(CP)加工装置を用いて行った。CP断面について任意に観察視野をとる。図1は試料No.1−1の顕微鏡写真、図2は試料No.1−101の顕微鏡写真である。   A cross section was taken of the die-cast material of each prepared sample, and the structure was observed with a scanning electron microscope (SEM). The section was collected using a commercially available cross section polisher (CP) processing apparatus. An observation field is arbitrarily taken for the CP cross section. FIG. 1-1 is a micrograph of FIG. 1-101 micrograph.

図1において、濃い灰色で示される部分はマグネシウム合金の母相、薄い灰色で示される部分は、AlCa,(Al,Mg)CaなどのAl−Ca化合物、白色で示される部分は、AlRE、Al11REなどのAl−RE化合物である。図2において、濃い灰色で示される部分はマグネシウム合金の母相、薄い灰色や白色で示される部分は、AlRE、Al11REなどのAl−RE化合物がラメラ状に晶出している領域であり、薄い灰色部分は微細に晶出している領域、白色部分(大きな粒を含む)は薄い灰色部分に比較して粗大に晶出している領域である。 In FIG. 1, the portion shown in dark gray is the parent phase of a magnesium alloy, the portion shown in light gray is an Al—Ca compound such as Al 2 Ca, (Al, Mg) 2 Ca, and the portion shown in white is Al 2 RE, an Al-RE compound such as Al 11 RE 3. In FIG. 2, the portion shown in dark gray is the parent phase of the magnesium alloy, and the portion shown in light gray or white is the region where Al-RE compounds such as Al 2 RE and Al 11 RE 3 are crystallized in the form of lamellae. The light gray part is a finely crystallized area, and the white part (including large grains) is a coarsely crystallized area compared to the light gray part.

Al,RE,Ca,Mnを特定の範囲で含む試料No.1−1は、図1に示すように、Al−RE化合物及びAl−Ca化合物が結晶粒界に分散して存在することが分かる。また、試料No.1−1は、Mg−Al化合物が確認できず、実質的に存在しない。試料No.1−2〜No.1−5も試料No.1−1と概ね同様な組織を有する。   Sample No. containing Al, RE, Ca, Mn in a specific range. 1-1 shows that the Al-RE compound and the Al-Ca compound are dispersed in the crystal grain boundary as shown in FIG. Sample No. In 1-1, the Mg—Al compound cannot be confirmed, and is substantially absent. Sample No. 1-2-No. Sample No. 1-5 It has almost the same structure as 1-1.

これに対し、図2に示すように、Al及びREを多く含む試料No.1−101は、Al−RE化合物が非常に多い上に粗大なAl−RE化合物が存在することが分かる。   On the other hand, as shown in FIG. 1-101 shows that there are very many Al-RE compounds and there are coarse Al-RE compounds.

上述の顕微鏡写真を用いて、観察視野Sf(350μm×250μm)中に存在するMg−Al化合物(主としてMg17Al12)を抽出してその断面積を求め、更にその合計断面積Smを求める。そして、(Sm/Sf)×100%をその断面におけるMg−Al化合物の面積割合として求め、10個の観察視野における面積割合の平均を各試料の面積割合(%)として表1に示す。Mg−Al化合物の断面積は、画像処理装置によって顕微鏡写真(SEM像)を二値化処理した二値化像などを利用すると容易に測定できる。 Using the above-mentioned micrograph, the Mg—Al compound (mainly Mg 17 Al 12 ) present in the observation visual field Sf (350 μm × 250 μm) is extracted to determine its cross-sectional area, and the total cross-sectional area Sm is further determined. Then, (Sm / Sf) × 100% is obtained as the area ratio of the Mg—Al compound in the cross section, and the average of the area ratios in the 10 observation fields is shown in Table 1 as the area ratio (%) of each sample. The cross-sectional area of the Mg—Al compound can be easily measured by using a binarized image obtained by binarizing a micrograph (SEM image) with an image processing apparatus.

作製した各試料のダイカスト材について亀裂数を調べて、割れの状態を評価した。ここでは、各試料について10個のダイカスト材を用意し、目視確認によってそれぞれの亀裂数を調べ、10個のダイカスト材における亀裂数の平均を各試料の亀裂発生頻度(個)として表1に示す。   The number of cracks was examined for the die cast material of each sample produced, and the state of cracks was evaluated. Here, ten die-cast materials are prepared for each sample, the number of cracks is examined by visual confirmation, and the average number of cracks in the ten die-cast materials is shown in Table 1 as the crack occurrence frequency (number) of each sample. .

作製した各試料のダイカスト材について、以下のようにして耐熱性を評価した。ここでは、アルミニウム製のブロック材の適宜な位置にボルト孔を設け、ブロック材におけるボルト孔を備える取付面と、各試料のダイカスト材に備えるフランジの締付座面とを合わせて、両者のボルト孔に鉄製のボルトを配置し、このボルトによって各試料のダイカスト材と上記ブロック材とを締結した試験部材を作製した。この試験部材を150℃で170時間保持した後、ボルトの締結力(残留軸力)を調べた。残留軸力は、ボルトに市販の歪ゲージを配置し、締結直後であって150℃に加熱する前の歪量S(ここでは初期締付軸力を9Nとして締め付けた際の歪量)、150℃×170時間の熱履歴を与えた後の歪量Stとを調べ、[(St−S)/S]×100(%)を残留軸力(%)として表1に示す。 About the produced die-cast material of each sample, heat resistance was evaluated as follows. Here, bolt holes are provided at appropriate positions on the aluminum block material, and the mounting surface of the block material provided with the bolt holes and the fastening seat surface of the flange provided on the die-cast material of each sample are matched to each other. An iron bolt was placed in the hole, and a test member in which the die-cast material of each sample and the block material were fastened with this bolt was produced. After holding this test member at 150 ° C. for 170 hours, the fastening force (residual axial force) of the bolt was examined. The residual axial force is a strain amount S 0 (here, the strain amount when tightened with an initial tightening axial force of 9 N) immediately after fastening and before heating to 150 ° C. by placing a commercially available strain gauge on the bolt, The strain St after giving a thermal history of 150 ° C. × 170 hours was examined, and [(St−S 0 ) / S 0 ] × 100 (%) is shown in Table 1 as the residual axial force (%).

表1に示すように、Al,RE,Ca,Mnを特定の範囲で含み、かつAl−RE化合物やAl−Ca化合物が粒界に分散して存在すると共にMg−Al化合物が非常に少ない又は実質的に存在しない組織を有する試料No.1−1〜1−5は、残留軸力が高く耐熱性(特に耐クリープ性)に優れる上に、亀裂発生頻度が極めて低く、ダイカスト材に割れが生じ難いことが分かる。定量的には、残留軸力が64%以上であり、65%以上の試料が多い。また、Mg−Al化合物の面積割合が5%以下、ここでは更に4%以下であり、0%である試料もある。試料No.1−3〜No.1−5を比較すると、RE+Caの合計質量に対するAlの含有量が少ないほど(質量比Al/(RE+Ca)が小さいほど)、Mg−Al化合物が形成され難いといえる。また、ここでは試料No.1−1〜1−5の亀裂発生頻度が0個であり、亀裂が生じていない。   As shown in Table 1, Al, RE, Ca, and Mn are included in a specific range, and Al-RE compound and Al-Ca compound are dispersed in the grain boundary and Mg-Al compound is very little or Sample No. having a tissue substantially absent. 1-1 to 1-5 have a high residual axial force and excellent heat resistance (particularly creep resistance), and the crack occurrence frequency is extremely low, so that it is difficult to cause cracks in the die-cast material. Quantitatively, the residual axial force is 64% or more, and there are many samples of 65% or more. In some samples, the area ratio of the Mg—Al compound is 5% or less, further 4% or less, and 0%. Sample No. 1-3 to No. When 1-5 is compared, it can be said that the smaller the Al content with respect to the total mass of RE + Ca (the smaller the mass ratio Al / (RE + Ca)), the harder the Mg-Al compound is formed. Here, the sample No. The crack occurrence frequency of 1-1 to 1-5 is zero, and no crack is generated.

一方、上述の特定の組成及び特定の組織を有していない試料No.1−101〜No.1−105はいずれも、亀裂発生頻度が1個以上であり亀裂が生じている。この亀裂はいずれも上述の角部に生じていた。このことから、周囲の厚さと異なる厚さの角部は、割れが生じ易い箇所であるといえる。Al及びCaの双方が多い試料No.1−102、Caが多い試料No.1−105は、亀裂発生頻度がとりわけ大きく、割れがより生じ易いといえる。Al及びREの双方を多く含み、Caを含まない試料No.1−101,Alを4質量%以上多く含む試料No.1−103,RE及びCaの双方が少ない試料No.1−104は、残留軸力が低く耐熱性に劣る。   On the other hand, sample No. which does not have the above-mentioned specific composition and specific structure. 1-101-No. 1-105 has a crack occurrence frequency of 1 or more and has cracks. All of these cracks occurred at the corners described above. From this, it can be said that the corner | angular part of thickness different from the surrounding thickness is a location which a crack tends to produce. Sample No. with a lot of both Al and Ca. 1-102, Sample No. 1-105 has particularly high crack occurrence frequency, and it can be said that cracks are more likely to occur. Sample No. containing a large amount of both Al and RE and not containing Ca. 1-101, Sample No. 4 containing more than 4% by mass of Al. No. 1-103, sample no. 1-104 has a low residual axial force and is inferior in heat resistance.

詳しくは、試料No.1−101は、Al及びREの双方が多く、Al−RE化合物が優先的に形成されて、Mg−Al化合物を形成し難かったと考えられる。しかし、Al−RE化合物が過剰に存在することで、亀裂が生じ易くなったと考えられる。また、Caを含有しないことで、残留軸力が低くなったと考えられる。
試料No.1−102,No.1−105は、Caが多いことでAl−Ca化合物が多く存在して残留軸力が高くなったと考えられる。しかし、Al−Ca化合物が過剰に存在して、亀裂が非常に生じ易くなったと考えられる。
試料No.1−103,No.1−104は、RE及びCaに対してAlが多いため、低融点であるMg−Al化合物が多く存在することで、クリープ変形し易くなって残留軸力が低くなったと考えられる。特に、No.1−103はAlが4質量%以上と多く、Mg−Al化合物がより多く存在するため、残留軸力が大幅に低くなったと考えられる。
Specifically, sample no. In 1-101, both Al and RE are large, and it is considered that the Al-RE compound was formed preferentially and it was difficult to form the Mg-Al compound. However, it is considered that cracking was likely to occur due to the excessive presence of the Al-RE compound. Moreover, it is thought that residual axial force became low by not containing Ca.
Sample No. 1-102, no. 1-105 is considered to have a high residual axial force due to the presence of a large amount of Al—Ca compound due to the large amount of Ca. However, it is considered that the Al—Ca compound was excessively present and cracks were very easily generated.
Sample No. 1-103, no. Since 1-104 has a large amount of Al relative to RE and Ca, it is considered that a large amount of Mg—Al compound having a low melting point exists, and thus creep deformation easily occurs and the residual axial force is lowered. In particular, no. In 1-103, Al is as high as 4% by mass or more, and a larger amount of Mg-Al compound is present. Therefore, it is considered that the residual axial force was significantly reduced.

以上のことから、耐熱性に優れ、ダイカスト材などの鋳造部材の製造に適したマグネシウム合金は、Al,RE,Ca,Mnを特定の範囲で含み、Al−RE化合物やAl−Ca化合物が粒界に分散して存在し、かつMg−Al化合物が非常に少ない又は実質的に存在しない組織を有することが好ましいことが示された。   In view of the above, a magnesium alloy that is excellent in heat resistance and suitable for manufacturing a cast member such as a die-cast material contains Al, RE, Ca, and Mn in a specific range, and an Al-RE compound or an Al-Ca compound is granular. It has been shown that it is preferable to have a structure that is dispersed in the boundary and has very little or substantially no Mg-Al compound.

本発明は、これらの例示に限定されるものではなく、特許請求の範囲によって示され、特許請求の範囲と均等の意味及び範囲内での全ての変更が含まれることが意図される。
例えば、試験例1において、組成(添加元素の含有量)、鋳造部材の形状や大きさ(厚さ、容積など)、製造条件(湯温、撹拌条件など)などを適宜変更できる。
The present invention is not limited to these exemplifications, but is defined by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.
For example, in Test Example 1, the composition (content of additive element), the shape and size of the cast member (thickness, volume, etc.), manufacturing conditions (hot water temperature, stirring conditions, etc.), etc. can be changed as appropriate.

本発明のマグネシウム合金は、ダイカスト材などの金型鋳造部材の素材に好適に利用できる。本発明の鋳造部材は、種々の部品、特に軽量であることが望まれる部品に利用できる。このような部品として、例えば、自動車や航空機などの輸送機器類、各種の電子・電気機器類(パーソナルコンピュータ(PC)、タブレット型PC、スマートフォンや折り畳み式携帯電話などの携帯電話、デジタルカメラなど)の筐体やカバーなどの外装部材、補強部材、骨格部材などが挙げられる。   The magnesium alloy of the present invention can be suitably used as a material for a die casting member such as a die-cast material. The cast member of the present invention can be used for various parts, particularly parts that are desired to be lightweight. Examples of such parts include transportation equipment such as automobiles and airplanes, various electronic / electrical equipment (personal computers (PCs), tablet PCs, mobile phones such as smartphones and foldable mobile phones, digital cameras, etc.) These include exterior members such as housings and covers, reinforcing members, and skeleton members.

1 鋳造部材 10 本体
12 フランジ 13 ボス 14 リブ 15 筒部 16 凹部
3,30,31,32,33,34,35,36 角部 15h 貫通孔
DESCRIPTION OF SYMBOLS 1 Casting member 10 Main body 12 Flange 13 Boss 14 Rib 15 Cylindrical part 16 Recessed part 3, 30, 31, 32, 33, 34, 35, 36 Corner part 15h Through-hole

Claims (3)

質量%で、
Alを1.0%以上3.0%以下、
希土類元素を1.5%以上3.0%以下、
Caを0.5%以上1.5%以下、
Mnを0.1%以上0.5%以下含み、残部がMg及び不可避不純物であり、
Alと、希土類元素及びCaの少なくとも一方の元素とを含む化合物が粒界に分散し、かつ断面におけるMgとAlとを含む化合物の面積割合が5%以下である組織を備えるマグネシウム合金。
% By mass
Al is 1.0% or more and 3.0% or less,
1.5% to 3.0% rare earth element,
Ca is 0.5% to 1.5%,
Containing 0.1% or more and 0.5% or less of Mn, the balance being Mg and inevitable impurities,
A magnesium alloy comprising a structure in which a compound containing Al and at least one element of a rare earth element and Ca is dispersed at grain boundaries, and an area ratio of the compound containing Mg and Al in a cross section is 5% or less.
希土類元素とCaとの合計含有量に対するAlの含有量の質量比が0.4以上1.5以下である請求項1に記載のマグネシウム合金。   The magnesium alloy according to claim 1, wherein the mass ratio of the Al content to the total content of the rare earth elements and Ca is 0.4 or more and 1.5 or less. 内部空間を形成する形状を有し、角部を備える鋳造部材であって、
請求項1又は請求項2に記載のマグネシウム合金から構成され、
前記角部と前記角部以外の部分では厚みが異なる鋳造部材。
A cast member having a shape that forms an internal space and having corners,
It is comprised from the magnesium alloy of Claim 1 or Claim 2,
Cast members having different thicknesses at the corners and portions other than the corners.
JP2016046346A 2016-03-09 2016-03-09 Magnesium alloy and cast member Pending JP2017160495A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110129644A (en) * 2019-05-23 2019-08-16 山东省科学院新材料研究所 Heat-resisting dissolvable magnesium alloy of one kind and its preparation method and application
US11268173B2 (en) 2017-11-17 2022-03-08 Sumitomo Electric Industries, Ltd. Magnesium alloy and magnesium alloy member

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11268173B2 (en) 2017-11-17 2022-03-08 Sumitomo Electric Industries, Ltd. Magnesium alloy and magnesium alloy member
CN110129644A (en) * 2019-05-23 2019-08-16 山东省科学院新材料研究所 Heat-resisting dissolvable magnesium alloy of one kind and its preparation method and application

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