JP4092255B2 - Al-Si alloy casting having excellent toughness and stress corrosion cracking resistance, and method for producing the same - Google Patents
Al-Si alloy casting having excellent toughness and stress corrosion cracking resistance, and method for producing the same Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、優れた靱性と耐応力腐食割れ性を有するＡｌ−Ｓｉ系合金鋳物、特に、固相と液相とが共存したＡｌ−Ｓｉ系合金材料を凝固させた鋳物およびその製造方法に関する。
【０００２】
【従来の技術】
本出願人は、先に、この種の鋳物として、Ｓｉ含有量が６．５ｗｔ％≦Ｓｉ≦７．５ｗｔ％であるＡｌ−Ｓｉ系合金材料を用い、チクソキャスティングの適用下で製造されたものを提案した（特許文献１参照）。
【０００３】
【特許文献１】
特開平７−３１６７０９号公報
【０００４】
【発明が解決しようとする課題】
前記Ａｌ−Ｓｉ系合金材料を用いてチクソキャスティングを行うと、空孔部等の欠陥の無い高強度な鋳物を得ることができるのであるが、液相に対応した凝固領域について考察を加えた結果、次のような問題のあることが判明した。
【０００５】
即ち、Ａｌ−Ｓｉ系合金材料全体が融液状態にあるときはＳｉ濃度は６．５ｗｔ％≦Ｓｉ≦７．５ｗｔ％であるが、固相と液相とが共存した状態、つまり、固液共存状態にあるときには固相がＡｌより構成されていることから液相中のＳｉ濃度はＡｌ濃度の低下に応じて上昇することになる。そして、液相に対応した液相凝固領域のＳｉ濃度がＳｉ≫１１．７ｗｔ％（共晶点）となる結果として、その部分には多数の初晶Ｓｉが晶出し、これに起因して鋳物における靱性の低下、応力腐食割れの発生等を招いたのである。一方、固相に対応した固相凝固領域の体積分率Ｖｆが低く過ぎると、これは液相が過多であったことから鋳物に偏析が発生してその靱性の低下を招来した。これらの問題はレオキャスティングについても当然に発生する。
【０００６】
【課題を解決するための手段】
本発明は、チクソキャスティングまたはレオキャスティングの適用下で得られたものであって、液相に対応した液相凝固領域における初晶Ｓｉ量を極力減少させ、また偏析の発生を防止した前記Ａｌ−Ｓｉ系合金鋳物を提供することを目的とする。
【０００７】
前記目的を達成するため本発明によれば、固相と液相とが共存したＡｌ−Ｓｉ系合金材料を凝固させて成り、前記Ａｌ−Ｓｉ系合金材料には、初晶Ｓｉの晶出を抑制して靱性と耐応力腐食割れ性を向上させるためにＣｕが添加されているＡｌ−Ｓｉ系合金鋳物であって、前記Ａｌ−Ｓｉ系合金材料は、６．５ｗｔ％≦Ｓｉ≦７．５ｗｔ％、０．５ｗｔ％≦Ｃｕ≦１．５ｗｔ％、０．４ｗｔ％≦Ｍｇ≦０．５ｗｔ％、Ｔｉ＜０．２ｗｔ％および残部Ａｌ（不可避不純物を含む）よりなり、前記固相に対応した固相凝固領域の体積分率Ｖｆが４０％≦Ｖｆ≦６０％であるＡｌ−Ｓｉ系合金鋳物が提供される。
【０００８】
前記Ａｌ−Ｓｉ系合金鋳物において、固相凝固領域の体積分率Ｖｆを前記のように設定すると、偏析の発生を防止することができる。またＣｕ含有量を前記のように設定すると、液相中のＡｌ濃度の減少が融液Ｃｕにより補われてＳｉ濃度の上昇が抑制される。つまり、初晶Ｓｉの晶出が全く無いか、在っても僅少量に抑えられる。これによりＡｌ−Ｓｉ系合金鋳物の靱性および耐応力腐食割れ性を大いに向上させることが可能である。この鋳物は、例えば自動車用サスペンション部品として好適である。
【０００９】
ただし、固相凝固領域の体積分率ＶｆがＶｆ＞６０％では、液相中のＳｉ濃度が上昇して初晶Ｓｉ量が多くなるため鋳物の靱性および耐応力腐食割れ性が低下する。一方、Ｖｆ＜４０％では初晶Ｓｉの晶出は無くなるが、液相が過多であったことから鋳物に偏析が生じる。
【００１０】
各化学成分の添加理由および含有量限定理由は次の通りである。
【００１１】
Ｓｉは、共晶（Ａｌ＋Ｓｉ）を形成し、また湯流れ性を良好にするために添加される。さらにＳｉは、鋳物の強度向上元素として機能する。ただし、Ｓｉ含有量がＳｉ＜６．５ｗｔ％では共晶を形成する液相が少なすぎるため、Ａｌ−Ｓｉ系合金材料の流動が不均一となって鋳物に未充填箇所が生じ易くなる。一方、Ｓｉ＞７．５ｗｔ％では初晶Ｓｉ量が多くなると共に共晶を形成する液相が多すぎるため鋳物に偏析が生じて、その靱性が低下する。
【００１２】
Ｃｕは、前記のように初晶Ｓｉの晶出を抑制するために添加される。ただし、Ｃｕ含有量がＣｕ＞１．５ｗｔ％では耐応力腐食割れ性が低下し、一方、Ｃｕ＜０．５ｗｔ％では添加の意義が無く、初晶Ｓｉ量が多くなって鋳物の靱性が低下する。
【００１３】
Ｍｇは、鋳物において、耐力と靱性を両立させるために添加調整される。ただし、Ｍｇ含有量がＭｇ＜０．４ｗｔ％では鋳物の耐力向上が不十分であり、一方、Ｍｇ＞０．５ｗｔ％では鋳物の耐力は向上するが靱性が低下する。
【００１４】
Ｔｉは、鋳物の金属組織を微細化してその靱性を向上させるために添加される。ただし、Ｔｉ含有量をＴｉ≧０．２ｗｔ％に設定しても効果は変わらない。なお、Ｔｉの過剰添加は金属間化合物の生成を促して鋳物の靱性低下を招来する。
【００１５】
また本発明によれば、固相と液相とが共存したＡｌ−Ｓｉ系合金材料を凝固させて成り、前記Ａｌ−Ｓｉ系合金材料には、初晶Ｓｉの晶出を抑制して靱性と耐応力腐食割れ性を 向上させるためにＣｕが添加されているＡｌ−Ｓｉ系合金鋳物の製造方法であって、６．５ｗｔ％≦Ｓｉ≦７．５ｗｔ％、０．５ｗｔ％≦Ｃｕ≦１．５ｗｔ％、０．４ｗｔ％≦Ｍｇ≦０．５ｗｔ％、Ｔｉ＜０．２ｗｔ％および残部Ａｌ（不可避不純物を含む）よりなり、且つ固相と液相とが共存した固液共存状態を有すると共に固相率Ｓが４０％≦Ｓ≦６０％であるＡｌ−Ｓｉ系合金材料を調製し、次いで前記Ａｌ−Ｓｉ系合金材料を鋳型に注入して冷却し、前記固液共存状態に対応した凝固組織を得るＡｌ−Ｓｉ系合金鋳物の製造方法が提供される。
【００１６】
前記のような手段を採用すると、前記構成の鋳物を容易に量産することができる。
【００１７】
ただし、固相率ＳがＳ＞６０％では、液相中のＳｉ濃度が上昇して初晶Ｓｉ量が多くなるため鋳物の靱性および耐応力腐食割れ性が低下する。一方、Ｓ＜４０％では初晶Ｓｉの晶出は無くなるが、液相が過多であったことから鋳物に偏析が生じる。
【００１８】
各化学成分の添加理由および含有量限定理由は前記の場合と同じである。
【００１９】
【発明の実施の形態】
Ａｌ−Ｓｉ系合金鋳物は、固相と液相とが共存したＡｌ−Ｓｉ系合金材料を凝固させたものであり、図１に示すように、複数の島状をなす、固相に対応した固相凝固領域ＳS と、それらの間を埋める、液相に対応した液相凝固領域ＳL とを有する。Ａｌ−Ｓｉ系合金材料は、６．５ｗｔ％≦Ｓｉ≦７．５ｗｔ％、０．５ｗｔ％≦Ｃｕ≦１．５ｗｔ％、０．４ｗｔ％≦Ｍｇ≦０．５ｗｔ％、Ｔｉ＜０．２ｗｔ％および残部Ａｌ（不可避不純物を含む）よりなる。また固相凝固領域ＳS の体積分率Ｖｆは４０％≦Ｖｆ≦６０％である。
【００２０】
前記Ａｌ−Ｓｉ系合金鋳物において、固相凝固領域ＳS の体積分率Ｖｆを前記のように設定すると、偏析の発生を防止することができる。またＣｕ含有量を前記のように設定すると、液相中のＡｌ濃度の減少が融液Ｃｕにより補われてＳｉ濃度の上昇が抑制される。つまり、初晶Ｓｉの晶出が全く無いか、在っても僅少量に抑えられる。これによりＡｌ−Ｓｉ系合金鋳物の靱性および耐応力腐食割れ性を大いに向上させることが可能である。
【００２１】
以下、具体例について説明する。
【００２２】
表１はＡｌ−Ｓｉ系合金材料の例（１）〜（５）に関する組成を示す。
【００２３】
【表１】
表１において、Ｍｎは不純物であって、鋳物の靱性低下を抑制すべく、その含有量はＭｎ＜０．１ｗｔ％に設定される。Ｆｅは不純物であって、鋳物の耐応力腐食割れ性を改善すべく、その含有量はＦｅ＜０．１ｗｔ％に設定される。Ｆｅ含有量がＦｅ≧０．１ｗｔ％では鋳物の耐食性が低下し、またその耐応力腐食割れ性も低下する。Ｚｎは不純物であって、鋳物の靱性および耐食性の低下を抑制すべく、その含有量はＺｎ＜０．１ｗｔ％に設定される。
【００２５】
表１の例（１）を用いて、固相と液相とが共存した固液共存状態を有し、且つ固相率ＳがＳ＝４５％であるＡｌ−Ｓｉ系合金材料を調製し、次いでそのＡｌ−Ｓｉ系合金材料を鋳型としての金型に注入して冷却し、前記固液共存状態に対応した凝固組織を有するＡｌ−Ｓｉ系合金鋳物の例（１）を得た。次いで、表１の例（２）〜（５）を用いて、前記と同様の方法で、Ａｌ−Ｓｉ系合金鋳物の例（２）〜（５）を得た。
【００２６】
鋳物の例（１）〜（５）について、固相凝固領域ＳS の体積分率Ｖｆおよび液相凝固領域ＳL のＳｉ含有量を測定し、また液相凝固領域ＳL における初晶Ｓｉの有無および個数を調べた。体積分率Ｖｆの測定は、熱力学シュミレーションソフトと急冷による金属組織凍結法との整合によった。Ｓｉ含有量の測定は、熱力学シュミレーションソフトによる定量計算と実物金属組織観察とによった。初晶Ｓｉの有無および個数は顕微鏡写真観察によった。
【００２７】
次いで、鋳物の例（１）〜（５）より、シャルピー衝撃試験用３号試験片を製作して、それらについて試験を行った。また耐応力腐食割れ性に関する試験を行うべく、図２に示すように、鋳物の例（１）〜（５）より、帯板をほぼ円形をなすように折曲げて両端部を対向させたような形状を有する試験片１を製作した。その試験片１の対向部分間に形成された２つの貫通孔２にボルト３を通し、一方の貫通孔２から突出した雄ねじ部４にナット５をねじ込んで、その試験片１を構成するＡｌ−Ｓｉ系合金材料の耐力の９５％分を試験片１に付与した。そして、試験片１を９８〜９９℃のクロム酸試験液中に８０時間浸漬し、その浸漬期間における割れの有無を目視により検査した。クロム酸試験液は、純水１Ｌ当り、３６ｇのＣｒＯ3 と、３０ｇのＫ2 Ｃｒ2 Ｏ7 と、３ｇのＮａＣｌとを含有する。
【００２８】
表２は前記測定および試験結果を示す。
【００２９】
【表２】
表２から明らかなように、鋳物の例（１）〜（５）において、Ａｌ−Ｓｉ系合金材料の固相率Ｓと固相凝固領域ＳS の体積分率Ｖｆとは等しく、したがって鋳物の例（１）〜（５）において固液共存状態に対応した凝固組織が得られていることが判る。
【００３１】
図３は、鋳物の例（４）の金属組織を示す顕微鏡写真の写図であって、本図より液相凝固領域ＳL に１個の初晶Ｓｉが存在することが判る。
【００３２】
図４は、表２に基づいて液相凝固領域ＳL のＳｉ含有量と、シャルピー衝撃値および液相凝固領域ＳL における初晶Ｓｉの個数との関係をグラフ化したものである。表２、図４から明らかなように、鋳物の例（２）〜（４）のごとく、Ａｌ−Ｓｉ系合金材料として、Ｓｉ、ＭｇおよびＴｉをそれぞれ特定量含有し、且つＣｕ含有量を０．５ｗｔ％≦Ｃｕ≦１．５ｗｔ％に設定されたものを用いると、液相凝固領域ＳS における初晶Ｓｉ量を極力減少させ、靱性および耐応力腐食割れ性を向上させることができるものである。
【００３３】
【発明の効果】
本発明によれば、Ａｌ−Ｓｉ系合金鋳物において、初晶Ｓｉの晶出を抑制するために添加されるＣｕの含有量が１．５ｗｔ％を超える領域では耐応力腐食割れ性が低下し、一方、０．５ｗｔ％を下回る領域では添加の意義が無く、初晶Ｓｉ量が多くなって鋳物の靱性が低下する。また固相凝固領域の体積分率Ｖｆ（固相率Ｓ）が６０％を超える領域では、液相中のＳｉ濃度が上昇して初晶Ｓｉ量が多くなるため鋳物の靱性および耐応力腐食割れ性が低下し、一方、４０％を下回る領域では初晶Ｓｉの晶出は無くなるが、液相が過多であることから鋳物に偏析が生じる。従って、Ｃｕの含有量を０．５ｗｔ％≦Ｃｕ≦１．５ｗｔ％に、また体積分率Ｖｆ（固相率Ｓ）４０％≦Ｖｆ（Ｓ）≦６０％に限定したことで、偏析の発生を防止しながら、液相中のＡｌ濃度の減少が融液Ｃｕにより補われてＳｉ濃度の上昇を抑制できて、初晶Ｓｉの晶出を抑制することができ、これにより、靱性および耐応力腐食割れ性を大いに向上させたＡｌ−Ｓｉ系合金鋳物を提供できる。
【００３４】
また特に請求項２の発明によれば、前記構成のＡｌ−Ｓｉ系合金鋳物を量産することが可能な製造方法を提供できる。
【図面の簡単な説明】
【図１】 金属組織の説明図である。
【図２】 応力腐食割れ試験の説明図である。
【図３】 金属組織の一例を示す顕微鏡写真の写図である。
【図４】 液相凝固領域のＳｉ含有量と、シャルピー衝撃値および液相凝固領域における初晶Ｓｉの個数との関係を示すグラフである。
【符号の説明】
ＳS ……固相凝固領域
ＳL ……液相凝固領域[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an Al—Si based alloy casting having excellent toughness and stress corrosion cracking resistance, and more particularly to a casting obtained by solidifying an Al—Si based alloy material in which a solid phase and a liquid phase coexist, and a method for producing the same.
[0002]
[Prior art]
The present applicant previously manufactured an alloy of this type using an Al—Si based alloy material having a Si content of 6.5 wt% ≦ Si ≦ 7.5 wt% under the application of thixocasting. (See Patent Document 1).
[0003]
[Patent Document 1]
JP-A-7-316709 [0004]
[Problems to be solved by the invention]
When thixocasting is performed using the Al-Si-based alloy material, a high-strength casting with no defects such as voids can be obtained. As a result of considering the solidification region corresponding to the liquid phase The following problems were found.
[0005]
That is, when the entire Al—Si based alloy material is in a molten state, the Si concentration is 6.5 wt% ≦ Si ≦ 7.5 wt%, but the solid phase and the liquid phase coexist, that is, solid-liquid When in the coexistence state, since the solid phase is composed of Al, the Si concentration in the liquid phase increases as the Al concentration decreases. As a result of the Si concentration in the liquid phase solidification region corresponding to the liquid phase being Si >> 11.7 wt% (eutectic point), a large number of primary crystal Si is crystallized in the portion, resulting in casting. This led to a decrease in toughness and the occurrence of stress corrosion cracking. On the other hand, when the volume fraction Vf of the solid phase solidification region corresponding to the solid phase is too low, this is because the liquid phase is excessive, so that segregation occurs in the casting and the toughness is reduced. These problems naturally occur with respect to rheocasting.
[0006]
[Means for Solving the Problems]
The present invention is obtained under the application of thixocasting or rheocasting, wherein the amount of primary Si in the liquid phase solidification region corresponding to the liquid phase is reduced as much as possible and segregation is prevented from occurring. It aims at providing Si system alloy casting.
[0007]
In order to achieve the above object, according to the present invention, an Al-Si based alloy material in which a solid phase and a liquid phase coexist is solidified, and the Al-Si based alloy material is crystallized from primary Si. In order to suppress and improve toughness and stress corrosion cracking resistance, it is an Al—Si based alloy casting to which Cu is added, and the Al—Si based alloy material is 6.5 wt% ≦ Si ≦ 7.5 wt %, 0.5 wt% ≦ Cu ≦ 1.5 wt%, 0.4 wt% ≦ Mg ≦ 0.5 wt%, Ti <0.2 wt% and the balance Al (including inevitable impurities), corresponding to the solid phase An Al—Si alloy casting in which the volume fraction Vf of the solid phase solidification region is 40% ≦ Vf ≦ 60% is provided.
[0008]
In the Al—Si alloy casting, when the volume fraction Vf of the solid phase solidification region is set as described above, the occurrence of segregation can be prevented. When the Cu content is set as described above, the decrease in the Al concentration in the liquid phase is compensated by the melt Cu, and the increase in the Si concentration is suppressed. That is, there is no crystallization of primary crystal Si, or even if it exists, it can be suppressed to a very small amount. Thereby, it is possible to greatly improve the toughness and stress corrosion cracking resistance of the Al-Si alloy casting. This casting is suitable, for example, as a suspension part for automobiles.
[0009]
However, when the volume fraction Vf of the solid phase solidification region is Vf> 60%, the Si concentration in the liquid phase increases and the amount of primary Si increases, so the toughness and stress corrosion cracking resistance of the casting deteriorate. On the other hand, in the case of Vf <40%, crystallization of primary Si disappears, but because the liquid phase is excessive, segregation occurs in the casting.
[0010]
The reason for adding each chemical component and the reason for limiting the content are as follows.
[0011]
Si is added to form a eutectic (Al + Si) and to improve the flowability of the hot water. Further, Si functions as an element for improving the strength of the casting. However, when the Si content is Si <6.5 wt%, the liquid phase forming the eutectic is too little, so that the flow of the Al—Si based alloy material becomes non-uniform and uncast portions are likely to occur in the casting. On the other hand, when Si> 7.5 wt%, the amount of primary Si is increased and the liquid phase forming the eutectic is too much, so that segregation occurs in the casting and the toughness is lowered.
[0012]
Cu is added to suppress crystallization of primary crystal Si as described above. However, when the Cu content is Cu> 1.5 wt%, the stress corrosion cracking resistance is lowered. On the other hand, when Cu <0.5 wt%, there is no significance of addition, and the amount of primary Si is increased and the toughness of the casting is lowered. To do.
[0013]
Mg is added and adjusted in the casting in order to achieve both yield strength and toughness. However, when the Mg content is Mg <0.4 wt%, the yield strength of the casting is insufficient, whereas when Mg> 0.5 wt%, the yield strength of the casting is improved but the toughness is lowered.
[0014]
Ti is added to refine the metal structure of the casting and improve its toughness. However, the effect does not change even if the Ti content is set to Ti ≧ 0.2 wt%. It should be noted that excessive addition of Ti promotes the formation of intermetallic compounds and leads to a reduction in the toughness of the casting.
[0015]
According to the present invention comprises solidifying the solid phase and the liquid phase is Al-Si based alloy material coexist, the said Al-Si based alloy material, and toughness by suppressing the crystallization of primary crystal Si In order to improve stress corrosion cracking resistance , Cu is added to produce an Al—Si alloy casting, which is 6.5 wt% ≦ Si ≦ 7.5 wt%, 0.5 wt% ≦ Cu ≦ 1. 5 wt%, 0.4 wt% ≦ Mg ≦ 0.5 wt%, Ti <0.2 wt% and the balance Al (including inevitable impurities), and has a solid-liquid coexistence state in which the solid phase and the liquid phase coexist. An Al—Si based alloy material having a solid phase ratio S of 40% ≦ S ≦ 60% is prepared, and then the Al—Si based alloy material is poured into a mold and cooled to solidify corresponding to the solid-liquid coexistence state. A method for producing an Al—Si based alloy casting to obtain a structure is provided.
[0016]
By adopting the above-described means, it is possible to easily mass-produce the casting having the above configuration.
[0017]
However, when the solid phase ratio S is S> 60%, the Si concentration in the liquid phase increases and the amount of primary Si increases, so the toughness and stress corrosion cracking resistance of the casting deteriorate. On the other hand, in the case of S <40%, crystallization of primary Si is eliminated, but segregation occurs in the casting because the liquid phase is excessive.
[0018]
The reason for adding each chemical component and the reason for limiting the content are the same as in the above case.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
The Al—Si based alloy casting is obtained by solidifying an Al—Si based alloy material in which a solid phase and a liquid phase coexist. As shown in FIG. It has a solid phase solidification region S S and a liquid phase solidification region S L corresponding to the liquid phase filling between them. Al-Si alloy materials are 6.5 wt% ≤ Si ≤ 7.5 wt%, 0.5 wt% ≤ Cu ≤ 1.5 wt%, 0.4 wt% ≤ Mg ≤ 0.5 wt%, Ti <0.2 wt%. And the balance Al (including inevitable impurities). The volume fraction Vf of the solid phase solidification region S S is 40% ≦ Vf ≦ 60%.
[0020]
In the Al—Si alloy casting, when the volume fraction Vf of the solid phase solidified region S S is set as described above, the occurrence of segregation can be prevented. When the Cu content is set as described above, the decrease in the Al concentration in the liquid phase is compensated by the melt Cu, and the increase in the Si concentration is suppressed. That is, there is no crystallization of primary crystal Si, or even if it exists, it can be suppressed to a very small amount. Thereby, it is possible to greatly improve the toughness and stress corrosion cracking resistance of the Al-Si alloy casting.
[0021]
Hereinafter, specific examples will be described.
[0022]
Table 1 shows compositions relating to the examples (1) to (5) of the Al—Si based alloy material.
[0023]
[Table 1]
In Table 1, Mn is an impurity, and its content is set to Mn <0.1 wt% in order to suppress a decrease in toughness of the casting. Fe is an impurity, and its content is set to Fe <0.1 wt% in order to improve the stress corrosion cracking resistance of the casting. When the Fe content is Fe ≧ 0.1 wt%, the corrosion resistance of the casting is lowered, and the stress corrosion cracking resistance is also lowered. Zn is an impurity, and its content is set to Zn <0.1 wt% in order to suppress deterioration of the toughness and corrosion resistance of the casting.
[0025]
Using Example (1) in Table 1, an Al—Si alloy material having a solid-liquid coexistence state in which a solid phase and a liquid phase coexist and having a solid phase ratio S of S = 45% is prepared. Next, the Al—Si based alloy material was poured into a mold as a mold and cooled to obtain an example (1) of an Al—Si based alloy casting having a solidified structure corresponding to the solid-liquid coexistence state. Next, examples (2) to (5) of Al-Si alloy castings were obtained in the same manner as described above using the examples (2) to (5) in Table 1.
[0026]
For examples of castings (1) to (5), solid coagulated region S by measuring the Si content of the volume fraction Vf and liquid coagulation area S L of S, also of primary Si in the liquid phase solidification area S L Existence and number were examined. The volume fraction Vf was measured by matching thermodynamic simulation software with the freezing method of metal structure by rapid cooling. The Si content was measured by quantitative calculation using thermodynamic simulation software and observation of the actual metal structure. The presence and number of primary crystal Si was determined by microscopic observation.
[0027]
Next, No. 3 test pieces for Charpy impact test were produced from the casting examples (1) to (5), and they were tested. Further, as shown in FIG. 2, in order to conduct a test on the resistance to stress corrosion cracking, the strips were folded so as to form a substantially circular shape from the casting examples (1) to (5), and both ends were opposed to each other. A
[0028]
Table 2 shows the measurement and test results.
[0029]
[Table 2]
As is apparent from Table 2, in the casting examples (1) to (5), the solid phase rate S of the Al—Si based alloy material is equal to the volume fraction Vf of the solid phase solidification region S S , and therefore, In Examples (1) to (5), it can be seen that a solidified structure corresponding to the solid-liquid coexistence state is obtained.
[0031]
Figure 3 is a copy view of photomicrographs showing the metal structure of example of the casting (4), it can be seen that one of the primary crystal Si is present in the liquid phase coagulation area S L from the figure.
[0032]
Figure 4 is a graph of the relationship between the Si content of the liquid phase coagulation area S L based on Table 2, the number of primary Si in the Charpy impact value and liquid coagulated region S L. As is apparent from Table 2 and FIG. 4, as in the casting examples (2) to (4), the Al—Si based alloy material contains specific amounts of Si, Mg, and Ti, respectively, and the Cu content is 0. When using the one set to .5 wt% ≦ Cu ≦ 1.5 wt%, the amount of primary Si in the liquid phase solidification region S S can be reduced as much as possible, and the toughness and stress corrosion cracking resistance can be improved. is there.
[0033]
【The invention's effect】
According to the present invention, in the Al-Si alloy casting, the stress corrosion cracking resistance is reduced in a region where the content of Cu added to suppress crystallization of primary Si exceeds 1.5 wt%, On the other hand, in the region below 0.5 wt%, there is no significance of addition, and the amount of primary crystal Si increases and the toughness of the casting decreases. In the region where the volume fraction Vf (solid phase ratio S) of the solid phase solidification region exceeds 60%, the Si concentration in the liquid phase increases and the amount of primary crystal Si increases, so the toughness of the casting and the stress corrosion cracking resistance. On the other hand, in the region of less than 40%, crystallization of primary Si disappears, but the liquid phase is excessive, so that segregation occurs in the casting. Therefore, segregation occurs by limiting the Cu content to 0.5 wt% ≦ Cu ≦ 1.5 wt% and the volume fraction Vf (solid phase ratio S) 40% ≦ Vf (S) ≦ 60%. In the liquid phase, the decrease in the Al concentration in the liquid phase is compensated by the melt Cu, and the increase in the Si concentration can be suppressed, so that the crystallization of primary Si can be suppressed, thereby improving the toughness and stress resistance. It is possible to provide an Al—Si based alloy casting having greatly improved corrosion cracking property.
[0034]
According particularly to the second aspect of the present invention can provide a manufacturing method capable of mass production of Al-Si-based alloy casting before Symbol configuration.
[Brief description of the drawings]
FIG. 1 is an explanatory view of a metal structure.
FIG. 2 is an explanatory diagram of a stress corrosion cracking test.
FIG. 3 is a photomicrograph showing an example of a metal structure.
FIG. 4 is a graph showing the relationship between the Si content in the liquid phase solidification region, the Charpy impact value, and the number of primary crystal Si in the liquid phase solidification region.
[Explanation of symbols]
S S ... Solid phase solidification zone S L ... Liquid phase solidification zone
Claims (2)
前記Ａｌ−Ｓｉ系合金材料は、６．５ｗｔ％≦Ｓｉ≦７．５ｗｔ％、０．５ｗｔ％≦Ｃｕ≦１．５ｗｔ％、０．４ｗｔ％≦Ｍｇ≦０．５ｗｔ％、Ｔｉ＜０．２ｗｔ％および残部Ａｌ（不可避不純物を含む）よりなり、
前記固相に対応した固相凝固領域（ＳS ）の体積分率Ｖｆが４０％≦Ｖｆ≦６０％であることを特徴とする、優れた靱性と耐応力腐食割れ性を有するＡｌ−Ｓｉ系合金鋳物。Solidified Al-Si alloy material that coexists with solid and liquid phases. The Al-Si alloy material improves toughness and stress corrosion cracking resistance by suppressing crystallization of primary Si. An Al-Si alloy casting to which Cu is added to
The Al—Si based alloy material is 6.5 wt% ≦ Si ≦ 7.5 wt%, 0.5 wt% ≦ Cu ≦ 1.5 wt%, 0.4 wt% ≦ Mg ≦ 0.5 wt%, Ti <0.2 wt. % And the balance Al (including inevitable impurities),
Al-Si system having excellent toughness and stress corrosion cracking resistance, wherein volume fraction Vf of solid phase solidification region (S S ) corresponding to the solid phase is 40% ≦ Vf ≦ 60% Alloy casting.
６．５ｗｔ％≦Ｓｉ≦７．５ｗｔ％、０．５ｗｔ％≦Ｃｕ≦１．５ｗｔ％、０．４ｗｔ％≦Ｍｇ≦０．５ｗｔ％、Ｔｉ＜０．２ｗｔ％および残部Ａｌ（不可避不純物を含む）よりなり、且つ固相と液相とが共存した固液共存状態を有すると共に固相率Ｓが４０％≦Ｓ≦６０％であるＡｌ−Ｓｉ系合金材料を調製し、
次いで前記Ａｌ−Ｓｉ系合金材料を鋳型に注入して冷却し、前記固液共存状態に対応した凝固組織を得ることを特徴とする、優れた靱性と耐応力腐食割れ性を有するＡｌ−Ｓｉ系合金鋳物の製造方法。 Solidified Al-Si alloy material that coexists with solid and liquid phases. The Al-Si alloy material improves toughness and stress corrosion cracking resistance by suppressing crystallization of primary Si. A method for producing an Al-Si based alloy casting to which Cu is added to
6.5 wt% ≦ Si ≦ 7.5 wt%, 0.5 wt% ≦ Cu ≦ 1.5 wt%, 0.4 wt% ≦ Mg ≦ 0.5 wt%, Ti <0.2 wt% and the balance Al (including inevitable impurities) And an Al—Si based alloy material having a solid-liquid coexistence state in which a solid phase and a liquid phase coexist and having a solid phase ratio S of 40% ≦ S ≦ 60%,
Next, the Al—Si based alloy material having excellent toughness and stress corrosion cracking resistance is obtained, wherein the Al—Si based alloy material is poured into a mold and cooled to obtain a solidified structure corresponding to the solid-liquid coexistence state. Manufacturing method of alloy castings.
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