JP3801427B2 - Method for preventing coarse primary crystal Si defects in aluminum alloy castings - Google Patents

Description

【００２５】
本予測式の重相関係数は、０．９２５、決定係数は、０．８５６である。式１により、実験的にこの３つのパラメータにより８５％以上の確率で初晶Ｓｉ発生を予測できた。これは、実用上充分な精度といえ、アルミニウム合金鋳物鋳造に際して、どの程度の粒径の初晶Ｓｉ欠陥が発生するかを予測出来る方法を確立できたといえる。なお、式１において、右辺がマイナスの数値となる場合も有り得るが、この場合は零とみなす事で対処できるものである。
【００２６】
上記パラメータのうち、鋳物該当部の溶湯凝固時間については、これまで現物を鋳造して観測しなければ分からない部分であったが、近年、コンピュータを使用する境界要素法もしくは有限要素法を用いた、溶湯の凝固・冷却解析によって、実用上充分な精度で予測値を算出することができるようになり、本式は、より有効に用いることができると考えている。
【００２７】
また、本発明のアルミニウム合金鋳物の粗大初晶Ｓｉ欠陥防止方法は、鋳物に発生する初晶Ｓｉ欠陥の分布割合を、該当欠陥の最大粒度から予測するものである。
【００２８】
請求項１の発明は、発生する初晶Ｓｉの粒径を予測する方法についてのものであるが、実際の鋳物製造では、粒径だけではなく、どのような分布範囲で欠陥が発生するかということも大きなポイントとなる。特に、タイヤ成形においては、その外観品質の要求が高いため、この初晶Ｓｉ欠陥の発生範囲を予測することは重要である。
【００２９】
具体的には、タイヤ成形用金型の様なリング状鋳物を考えた場合、鋳物製品面表面を５０〜１００程度のピッチを単位にして、円周方向に区分けして初晶Ｓｉ欠陥が発生しているピッチの割合が、該当鋳物に発生している初晶Ｓｉ欠陥の最大粒径の二次関数であらわされる、というものである。以下に、該２次関数を示す。
【００３０】
【数２】

【００３１】
なお、式２の相関係数は、０．９４３、決定係数は、０．８９０である。
【００３２】
そして、本発明は、上記したアルミニウム合金鋳物の粗大初晶Ｓｉ欠陥防止方法を用いて、該当鋳物に初晶Ｓｉ欠陥を発生させない臨界Ｓｉ含有量を算出し、これに基づいて鋳造用アルミニウム合金中のＳｉ含有量を調整するというものである。
【００３３】
本発明は、請求項１と請求項２の発明を組み合わせて使用することにより、該当鋳物に発生するであろう初晶Ｓｉ欠陥の最大粒径と、発生割合を事前に予測し、それが、許容限界（閾値）を超えた場合、アルミニウム合金中のＳｉ含有量を意図的に調整して、許容限界内に留められるように制御するものである。
【００３４】
先にも説明した通り、亜共晶型Ｓｉ系アルミニウム合金においては、図１に示されるように、Ｓｉ含有量が高い程、溶湯の凝固温度範囲が狭く、初晶Ｓｉが発生しうる領域が狭くなることから、初晶Ｓｉ（４）発生を抑制するためには好適であるようにみえる。しかしながら、式１の初晶Ｓｉ発生予測式が示すように、Ｓｉ含有量が高くなると初晶Ｓｉ（４）が発生しやすくなるという事実もある。
【００３５】
初晶Ｓｉ（４）発生を減らすには、アルミニウム合金中のＳｉ含有量を少なくした方がよいが、過度に低くしすぎると、鋳造性が悪くなり、引け巣や強度低下等の欠陥を招く事にもつながる。
以上のことを比較考慮して、アルミニウム合金中のＳｉ含有量は、亜共晶組成の範囲内で、且つ初晶Ｓｉ（４）が発生しない範囲で、できるだけ高く設定すべきである。本発明を用いれば、初晶Ｓｉ（４）発生を抑制し、且つ鋳造性に優れるアルミニウム合金中の極大Ｓｉ含有量を算出する事ができるようになる。
【００３６】
具体的な鋳造用アルミニウム合金中のＳｉ含有量の調整プロセスとしては、
(1) 該当鋳物に許容される初晶Ｓｉ欠陥の分布割合を数値化する。
(2) 請求項２に係る発明から、その場合の初晶Ｓｉ欠陥の最大粒径を算出する。
(3) (1) 、 (2)で求めた結果と請求項１に係る発明から、アルミニウム合金中の許容Ｓｉ含有量を計算する。
（この場合、式中の「該当部」とは、製品部内で溶湯凝固時間が遅くなる部位のことである。）
(4) 合金母材のＳｉ含有量を調べ、(3)で求めた値にする為の純Ａｌ添加量を計算し、合金に添加する（必要な第三元素以降の添加元素についても、希釈分を随時追加する。）。
(5) そして、鋳造する。
と言うものである。
【００３７】
また、本発明においては、鋳型表面に溶湯が接触する際の酸化膜をフィルターで除去し、初晶Ｓｉ欠陥の素となる初晶Ｓｉ核を、鋳型に接触させないことが好ましい。
【００３８】
本発明方法により、亜共晶型Ｓｉ系アルミニウム合金の鋳物を製造する際の初晶Ｓｉの発生はかなり抑制することができる。しかしながら、絶対的に初晶Ｓｉの発生を防ぐことは不可能であり、万が一、初晶Ｓｉが発生した場合に、それを除去する方法を準備しておくことが、より健全性の高い鋳物を製造するために好ましい。
【００３９】
初晶Ｓｉ欠陥は、図３に示されるように、鋳造時に溶湯（１６）表面に発生した初晶Ｓｉ（４）の結晶核が鋳型（１４）に貼り付き、溶湯凝固過程でこれが成長することによって起こる。よって、この結晶核を鋳型（１４）に貼り付かないようにすれば、初晶Ｓｉ欠陥は発生しない。大気中鋳造を行う場合、溶湯（１６）表面において非金属性の酸化膜が生成し、溶湯（１６）表面は該被膜で覆われている。この膜は、極めて弱い結合力で一体化された極めて薄いフィルム状のものである。発生した初晶Ｓｉ核は、この膜の直下に存在し、鋳型（１４）へ付着するか否かは、主としてこの酸化膜に支配されている。
【００４０】
従って、鋳造時に、鋳型（１４）直近部をセラミックやステンレス製のメッシュなどのフィルター（１８）でガードし、酸化膜と初晶Ｓｉ核を鋳型に付着しないようにし、初晶Ｓｉ欠陥の発生を防止することが好ましい。酸化膜除去に用いるフィルターは、メッシュのみに限らず、板状、棒状のものであってもよい。
【００４１】
フィルター（１８）の形状は、溶湯（１６）の粘性、溶湯（１６）の充填速度、酸化膜の結合強度特性等が関係するため一概にはいえないが、線径０．６ｍｍ以下程度のもので、メッシュの目の大きさが４ｍｍ×４ｍｍ以下程度のものを、鋳型（１４）から１０ｍｍ以下程度の距離にセットしておくと、酸化膜と初晶Ｓｉを良好に除去することができる。また、フィルター（１８）として、板材、棒材を格子状に設置する場合も同様の方法でセットすればよい。この酸化膜は、メッシュ等への付着性が高い為、一度付着したら鋳型（１４）の方へ移行する可能性は極めて低いと考えられる。
【００４２】
この方法は、鋳造の事前に、鋳型内部にメッシュ等をセットし、アルミニウム合金溶湯充填後に除去するものであり、より多くの労力を必要とする。しかし、このことによりアルミニウム合金中のＳｉ含有量を、安心して高く取る事が可能となり、本発明を補完し、更に健全性の高いアルミニウム合金の鋳物を製造することを可能とするものである。
【００４３】
【実施例】
以下、本発明を実施例に基づいて、更に詳細に説明するが、本発明はこれらの実施例に限定されるものではない。
（実施例１：請求項１及び請求項２の発明の予測式構築の基データ）
表１及び図４に示される実施例１のＮｏ．１〜１５のデータは、全てタイヤ金型（内径φ６００〜１１００ｍｍ、幅１５０〜３００ｍｍ、鋳込み重量３００〜１０００ｋｇ）の鋳造により実測したものである。鋳型材は、ノリタケカンパニーリミテド製Ｇ−６非発泡石膏を、合金材は、日本軽金属製ＡＣ４Ｃ材（Ｓｉ６〜７％、Ｃｕ０．８％、Ｍｇ０．４％）をベースに純ＡｌでＳｉ分を随時希釈したものを使用した。合金材は、７２０℃にて溶解され、高純度Ａｒガスバブリングにて脱ガスした溶湯を用いて、鋳込み開始温度６７０℃狙い、鋳込み時間３〜３０分で鋳造した。
【００４４】
【表１】

【００４５】
（実施例２）
内径φ１０６０ｍｍ、幅２６０ｍｍ、鋳込み重量８５０ｋｇのタイヤ金型を、ＡＣ４Ｃ合金をベースにし、最大初晶Ｓｉ欠陥粒径を０．１ｍｍに、同欠陥の分布割合も４．６％以下におさえることを目標として、鋳造する為の合金中Ｓｉ含有量条件を、請求項１の発明を用いて、次の様に算出した。また、鋳造に先立ち、鋳物製品部の最終凝固部の溶湯凝固時間と、出湯口からの距離をコンピュータ凝固解析（コマツソフト製ＪＳ−ＣＡＳＴ）を用いて算出し、次の様な値を得た。
・ 製品部での溶湯最終凝固時間 ； 1268秒
・ 同部位の出湯口からの距離 ； 308mm
この数値と、先の最大初晶Ｓｉ粒径を請求項１に係る発明の予測式に代入し、合金材の適正Ｓｉ含有量を計算したところ、５．５８質量％である事が判った。
【００４６】
合金母材の初期Ｓｉ含有量は７．０５質量％であった為、ＡＣ４Ｃ母材６７０ｋｇ、純アルミニウム材１８０ｋｇ、金属Ｃｕ１．４ｋｇ、金属Ｍｇ０．８ｋｇと合金を調合し直し、鋳造に使用した。この様にして得られた鋳物から確認された初晶Ｓｉ欠陥の最大粒径は、０．０８ｍｍで、その分布割合も６０ピッチ中２ピッチ(３．３％）となり、予測結果と極めて近いものとなった。
【００４７】
（比較例１）
実施例２で、鋳造に使用する合金材をＡＣ４Ｃ母材（Ｓｉ含有量７．０５質量％）のまま鋳造したところ、鋳物には、最大粒径０．２１ｍｍ、分布割合３０％（６０ピッチ中１８ピッチ）の初晶Ｓｉ欠陥が発生した。本鋳物は外観上の不良判定となった。
【００４８】
（参考例１）
比較例１と同じ材料で、図５に示すように、鋳造時、鋳型から１０ｍｍの位置に、線径０．５ｍｍ、格子間寸法４×４ｍｍのステンレス製金網を設置し、注湯を行った。製品部への鋳込み完了と同時に、金網を速やかに除去し、溶湯を凝固させ、鋳物を作成した。その結果鋳物に確認された初晶Ｓｉ欠陥は、最大粒径０．１ｍｍ、分布割合３．３％（６０ピッチ中２ピッチ）となり、合金中Ｓｉ含有量を調整した、実施例２と、ほぼ同等の改善効果が得られた。
【００４９】
【発明の効果】
以上説明したように、本発明のアルミニウム合金鋳物の粗大初晶Ｓｉ欠陥防止方法によれば、初晶Ｓｉ欠陥を極めて抑制でき、亜共晶型Ｓｉ系アルミニウム合金の鋳物の外観品質の向上が図られるという優れた効果を奏する。これは、特に、タイヤ金型のような溶湯凝固時間が長い大型の鋳造品において極めて高い効果を奏する。
【図面の簡単な説明】
【図１】 Ａｌ−Ｓｉ２元合金の、固液平衡を示す状態図及び各温度における結晶組織状態を示す模式図である。
【図２】 （ａ）０．５重量％、（ｂ）０．２重量％、のＭｇを含むＡｌ−Ｓｉ−Ｍｇ３元合金の固液平衡を示す状態図である。
【図３】 初晶Ｓｉ欠陥の発生メカニズムを示す説明図である。
【図４】 本発明の粗大初晶Ｓｉ欠陥防止方法による、（ａ）初晶Ｓｉ欠陥の粒径の予測値と実測値の関係を示すグラフ及び（ｂ）初晶Ｓｉ欠陥分布割合と最大粒径の関係を示すグラフである。
【図５】 アルミニウム合金鋳物の製造方法におけるフィルターの設置態様の一例を示す模式図である。
【符号の説明】
１…初晶α、２…融液、３…共晶Ｓｉ、４…初晶Ｓｉ、５…α（アルミニウム固体相）、６…Ｌ（液相）、１０…鋳枠、１１…断熱材、１２…ブレード、１３…バックアップ材、１４…鋳型、１５…出湯口、１６…溶湯、１７…初晶Ｓｉ核、１８…金網、１９…定盤。[0001]
BACKGROUND OF THE INVENTION
The present invention is a method for preventing the occurrence of primary Si defects when producing castings using alloy species having a hypoeutectic composition among the alloy species having Si as the main additive element, which is often used as an aluminum alloy for casting. about the law.
[0002]
[Prior art]
Aluminum alloys are often used as casting materials for tire molds and the like because they have moderate mechanical properties, good heat conduction properties, and good castability. Among these, alloy types containing Si as a main additive element are widely used in various fields because of their mechanical properties and good castability.
[0003]
There are basically two types of Si-based aluminum alloys, hypoeutectic and hypereutectic. As shown in the equilibrium diagram of FIG. 1, “hypereutectic type” means that when a molten metal solidifies, aluminum first appears as a solid, and within a solid-liquid coexistence region temperature range, a solid (3 ) Is not generated at all, and an alloy that generates Si solid (3) at the moment when the temperature falls below the eutectic temperature. “Hypereutectic type” means that when the molten metal solidifies, Si is first solid. In the solid-liquid coexistence region temperature range, no aluminum solid is generated, and at the moment when it falls below the eutectic temperature, Si solids (3), (4) and aluminum solid (5) are generated. It is an alloy.
[0004]
In these solidification processes, as shown in FIG. 1, a solid-liquid coexistence region exists in a temperature region sandwiched between a liquidus line and a eutectic line, and in this solid-liquid coexistence region, a hypoeutectic composition is present. Then, the aluminum solid (1) crystallizes first, and the silicon solid (4) crystallizes in the hypereutectic composition. The first appearance of solid in this solid-liquid coexistence region is called primary crystal. This primary crystallized product grows and coarsens as the temperature decreases, and the instant that the eutectic line is reached, the remaining liquid phase becomes solid at once.
[0005]
[Problems to be solved by the invention]
Generally, hypoeutectic aluminum alloys are used as tire mold alloys. This is because the primary crystal Si that occurs first in a hypereutectic Si-based aluminum alloy is polygonal and easily coarsened, and when it appears on the mold surface, it becomes a concave trace. It is because it is easy to generate | occur | produce.
[0006]
In addition to Si, elements such as Cu, Mg, Ti, and Zn are added to an actual aluminum alloy in order to improve various properties. In that case, the eutectic composition is changed by these additive elements, and the equilibrium diagram becomes complicated. Today, aluminum alloys having a Si content of 4 to 8% by mass are most widely used due to good production, but even when an aluminum alloy having a Si content of 4 to 8% by mass is used, in the casting of a relatively large casting of the tire mold, etc., rough skin of the casting by the coarse grain of the primary crystal Si has become a problem.
[0007]
Although it has been known that such a defect is likely to occur as the solidification time of the casting becomes longer, the cause and mechanism of the occurrence are completely unknown, and no effective countermeasures exist. For this reason, primary Si defects have been considered an unavoidable problem in large tire molds.
[0008]
[Means for Solving the Problems]
The present invention has been made in view of the above-described problems, and the object of the present invention is to provide an effect by elucidating the primary Si generation mechanism that occurs when casting a hypoeutectic Si-based aluminum alloy casting. to Ru der to provide a coarse primary crystal Si defect prevention method capable of avoiding primary Si generated.
[0009]
That is, according to the present invention, in a casting aluminum alloy containing Si as a main additive element, a method for preventing coarse primary crystal Si defects in an aluminum alloy casting when producing a casting using an alloy species having a hypoeutectic region side composition Because
The following predictions can approximate the size of primary crystal Si defects generated on the casting surface by a function consisting of three parameters: distance from the pouring gate, molten metal solidification time at the same site, and Si content in the alloy. Formula (1) is constructed in advance, and the maximum grain size of primary Si defects that can be tolerated is set as the primary crystal Si defect grain size in prediction formula (1). By calculating the critical Si content in an aluminum alloy that does not occur and adjusting the Si content in the aluminum alloy based on this critical Si content, a sound casting with few primary crystal Si defects is obtained. A method for preventing coarse primary crystal Si defects in an aluminum alloy casting is provided.
Primary crystal Si defect particle size (mm)
= 0.001238 x distance from the outlet of the casting part (mm)
+0.000139 x molten metal solidification time at the same site (sec)
+ 0.089441 × Si content in alloy (mass%)
-0.956751 (1)
[0010]
In the present invention, the following prediction formula (2) that can approximate the distribution ratio of primary Si defects generated on the casting surface as a function of the maximum grain size of coarse primary Si defects generated in the casting is established in advance. From the predicted value of the maximum grain size of the primary crystal Si defect grain size calculated by this prediction formula (2) and the above formula (1), critical Si in an aluminum alloy that does not generate primary crystal Si defects in the casting is obtained. It is preferable to obtain a healthy casting with few primary crystal Si defects by calculating the content and adjusting the Si content in the aluminum alloy based on the critical Si content.
Ratio of primary crystal Si defect generation pitch to total pitch number (%)
= 1200.1 x (maximum particle size of primary Si defect (mm)) ²
-84.803 × maximum grain size of primary Si defects (mm)
+1.1185 (2)
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The method for preventing coarse primary crystal Si defects in an aluminum alloy casting according to the present invention is for producing a casting using an aluminum alloy species having a hypoeutectic composition in a casting aluminum alloy containing Si as a main additive element. Hereinafter, although embodiment of this invention is described, it cannot be overemphasized that this invention is not limited to the following embodiment.
[0014]
The method for preventing coarse primary Si defects in an aluminum alloy casting according to the present invention is based on the following three parameters: the solidification time of the molten metal, the distance from the outlet, and the Si content of the alloy. Is to predict the size of.
[0015]
This will be described based on the generation mechanism of primary Si in the hypoeutectic Si-based aluminum alloy which has been elucidated for the first time by the present inventors.
As described above, the hypoeutectic Si-based aluminum alloy does not generate primary Si (4) in the solidification process if there is no other additive element. In addition to Si, elements such as Cu and Mg are added to the type Si-based aluminum alloy. According to recent research, it has been reported that due to the addition of Mg, a primary Si generation region also exists in the hypoeutectic region of the Si-based aluminum alloy. As an example, FIG. 3 shows an equilibrium diagram of a Si-based aluminum alloy containing 0.5 mass% and 0.2 mass% of Mg.
[0016]
As shown in FIG. 2 , by the addition of Mg element, a primary crystal Si (4) generation region is generated in the co-eutectic type region in the solid-liquid coexistence region. The same is confirmed when Cu element is added, and it is theoretically confirmed that primary crystal Si (4) is generated in the hypoeutectic solidification process due to the influence of the third additive element. .
[0017]
In simple terms, the generation of primary Si defects is a combination of the basic mechanism of an equilibrium diagram as shown in FIG. 2 and the dynamic characteristics from the start of casting in casting to the completion of molten metal filling and thereafter solidification. Can be considered to be determined.
[0018]
In casting, as shown in FIG. 3 , the molten aluminum alloy (16) is poured from the lower outlet (15) of the mold (14) and gradually filled upward. Among them, the molten aluminum alloy (16) is deprived of heat from the casting mold (14), the casting frame (10), etc. from the beginning of casting, and the temperature decreases. This temperature decreases rapidly as the middle and later stages of filling from the initial stage of filling the molten metal. In terms of the part of the mold (14), the temperature of the molten metal is high at the part close to the pouring gate (15), and the temperature rapidly decreases toward the middle and upper side of the mold (14).
[0019]
In the initial stage of casting, the molten metal (16) is preliminarily overheated, and the entire molten metal is in a liquid phase state. However, it will fall to the primary crystal Si (4) generation temperature range. This is a factor for generating primary Si nuclei. Since the primary crystal Si nucleus is lighter than the molten aluminum (16), it floats on the surface of the molten metal (16), which sticks to the surface of the mold (14) and grows in the process of solidifying the molten metal (16). It is considered that Si defects are generated.
[0020]
In the case of a tire mold, the primary Si defect is uneven and occurs. This is because, in the case of a tire mold, there are many protrusions such as grooves and blades in the mold, so that the semi-solid phase containing primary Si generated on the surface of the molten metal is likely to stick to the mold, and the semi-solid phase is formed by the grooves and blades. When the solidified layer is hooked, primary Si aggregates and appears uneven.
[0021]
More specifically, as shown in the enlarged view on the right side of FIG. 3 , when the temperature of the molten metal (16) is close to the solidification temperature, primary Si nuclei are formed. On the surface of the molten metal (16), a film such as an oxide film is stretched together with the primary Si nuclei and spreads laterally as in the group A. Therefore, if a projection such as a blade is present on the surface of the mold (14), the coating is caught by the projection as the molten metal (16) rises, and the coating and the coating conform to the shape as in the group B. The primary crystal Si nuclei gather together and stick to the surface of the mold (14). The Si primary crystal nuclei thus fixed grow and become coarse before the melt is solidified, so that primary crystal Si defect clusters, so-called unevenness, are formed.
[0022]
From the above, the parameters that determine the occurrence of primary Si defects in the primary Si defect generation mechanism are as follows: (1) Melt solidification time of the relevant part, (2) Distance from the hot water outlet of the relevant part, (3) The conclusion was reached that the Si content.
[0023]
The present inventors have repeated experiments based on this conclusion, and have found that the grain size of the generated primary crystal Si defects can be accurately predicted by the following formula.
[0024]
[Expression 1]

[0025]
The multiple correlation coefficient of this prediction formula is 0.925, and the determination coefficient is 0.856. According to Equation 1, primary Si generation can be predicted with a probability of 85% or more by using these three parameters experimentally. This can be said to be sufficient accuracy for practical use, and it can be said that a method capable of predicting the size of primary Si defects having a grain size during casting of an aluminum alloy casting can be established. In Equation 1, there may be a case where the right side is a negative numerical value, but in this case, it can be dealt with by regarding it as zero.
[0026]
Of the above parameters, the melt solidification time of the relevant part of the casting was a part that had to be observed until the actual product was cast and observed, but recently the boundary element method using computers or the finite element method has been used. As a result of the solidification / cooling analysis of the molten metal, the predicted value can be calculated with sufficient accuracy in practical use, and it is considered that this equation can be used more effectively.
[0027]
Moreover, the coarse primary crystal Si defect prevention method of the aluminum alloy casting of the present invention predicts the distribution ratio of primary crystal Si defects generated in the casting from the maximum grain size of the corresponding defect.
[0028]
The invention of claim 1 relates to a method for predicting the grain size of the primary Si generated, but in actual casting production, not only the grain size but in what distribution range the defects occur. That is also a big point. In particular, in tire molding, the demand for appearance quality is high, so it is important to predict the generation range of this primary crystal Si defect.
[0029]
Specifically, when considering a ring-shaped casting such as a tire mold, the surface of the casting product is divided in the circumferential direction with a pitch of about 50 to 100 as a unit, and primary Si defects are generated. The ratio of the pitch being expressed is expressed as a quadratic function of the maximum grain size of the primary Si defects generated in the casting. The quadratic function is shown below.
[0030]
[Expression 2]

[0031]
In addition, the correlation coefficient of Formula 2 is 0.943, and the determination coefficient is 0.890.
[0032]
Then, the onset Ming, using coarse primary crystal Si defect prevention method of an aluminum alloy casting as described above, to calculate the critical Si content that does not generate a primary crystal Si defects to the appropriate casting, casting aluminum alloys based thereon This is to adjust the Si content.
[0033]
The present invention predicts in advance the maximum grain size of primary Si defects that will occur in the corresponding casting and the generation ratio by using the inventions of claim 1 and claim 2 in combination, When the allowable limit (threshold value) is exceeded, the Si content in the aluminum alloy is intentionally adjusted so as to be kept within the allowable limit.
[0034]
As described above, in the hypoeutectic Si-based aluminum alloy, as shown in FIG. 1, the higher the Si content, the narrower the solidification temperature range of the molten metal, and there is a region where primary Si can be generated. Since it becomes narrow, it seems suitable for suppressing the generation of primary crystal Si (4). However, as shown in the primary crystal Si generation prediction formula of Formula 1, there is also a fact that primary Si (4) is likely to be generated when the Si content is high.
[0035]
In order to reduce the generation of primary crystal Si (4), it is better to reduce the Si content in the aluminum alloy, but if it is too low, the castability deteriorates, leading to defects such as shrinkage and strength reduction. It also leads to things.
In consideration of the above, the Si content in the aluminum alloy should be set as high as possible within the range of the hypoeutectic composition and the generation of primary Si (4). By using the present invention, it is possible to calculate the maximum Si content in an aluminum alloy that suppresses generation of primary crystal Si (4) and is excellent in castability.
[0036]
As a specific adjustment process of the Si content in the aluminum alloy for casting,
(1) Quantify the distribution ratio of primary Si defects allowed in the casting.
(2) From the invention according to claim 2, the maximum grain size of primary Si defects in that case is calculated.
(3) The allowable Si content in the aluminum alloy is calculated from the results obtained in (1) and (2) and the invention according to claim 1 .
(In this case, the "corresponding portion" in the formula is that sites molten metal solidification time Naru rather slow in the product section.)
(4) Investigate the Si content of the alloy base material, calculate the pure Al addition amount to obtain the value obtained in (3) , and add it to the alloy. Add minutes from time to time.)
(5) And cast.
It is what you say.
[0037]
Further, in the present invention , it is preferable that the oxide film when the molten metal contacts the mold surface is removed by a filter so that the primary Si nuclei that are elements of primary Si defects do not contact the mold.
[0038]
According to the method of the present invention, the generation of primary Si during the production of a hypoeutectic Si-based aluminum alloy casting can be considerably suppressed. However, it is impossible to absolutely prevent the generation of primary Si, and in the unlikely event that primary Si is generated, preparing a method for removing it will result in a more sound casting. Preferred for manufacturing.
[0039]
As shown in FIG. 3 , primary crystal Si defects are caused by crystal nuclei of primary crystal Si (4) generated on the surface of the molten metal (16) during casting sticking to the mold (14) and growing in the molten metal solidification process. Caused by. Therefore, if this crystal nucleus is not attached to the template (14), primary Si defects will not occur. When casting in the atmosphere, a nonmetallic oxide film is generated on the surface of the molten metal (16), and the surface of the molten metal (16) is covered with the coating. This membrane is in the form of a very thin film integrated with a very weak bonding force. The generated primary Si nuclei exist immediately below this film, and whether or not they adhere to the template (14) is mainly governed by this oxide film.
[0040]
Therefore, during casting, the immediate vicinity of the mold (14) is guarded by a filter (18) such as a ceramic or stainless steel mesh so that the oxide film and primary Si nuclei do not adhere to the mold, and primary Si defects are generated. It is preferable to prevent. The filter used for removing the oxide film is not limited to a mesh, but may be a plate shape or a rod shape.
[0041]
The shape of the filter (18) is not unequivocally related to the viscosity of the molten metal (16), the filling speed of the molten metal (16), the bond strength characteristics of the oxide film, etc., but the wire diameter is about 0.6 mm or less. If a mesh having a mesh size of about 4 mm × 4 mm or less is set at a distance of about 10 mm or less from the mold (14), the oxide film and the primary crystal Si can be removed satisfactorily. Moreover, what is necessary is just to set by the same method also when installing a board | plate material and a bar in a grid | lattice form as a filter (18). Since this oxide film has high adhesion to a mesh or the like, it is considered that the possibility of shifting to the mold (14) once attached is extremely low.
[0042]
In this method, a mesh or the like is set in the mold before casting, and is removed after filling with the molten aluminum alloy, which requires more labor. However, this makes it possible to secure a high Si content in the aluminum alloy, which complements the present invention and makes it possible to produce a cast aluminum alloy with higher soundness.
[0043]
【Example】
EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these Examples.
(Example 1: Basic data for construction of prediction formulas of inventions of claims 1 and 2)
Table 1 and Example 1 shown in FIG. 4 No. All the data of 1 to 15 are actually measured by casting a tire mold (inner diameter φ600 to 1100 mm, width 150 to 300 mm, casting weight 300 to 1000 kg). The mold material is G-6 non-foamed gypsum made by Noritake Company Limited, and the alloy material is made of Nippon Light Metal's AC4C material (Si6-7%, Cu0.8%, Mg0.4%) based on pure Al. Those diluted as needed were used. The alloy material was cast at a casting start temperature of 670 ° C. and a casting time of 3 to 30 minutes using a molten metal melted at 720 ° C. and degassed by high-purity Ar gas bubbling.
[0044]
[Table 1]

[0045]
(Example 2)
The goal is to use a tire mold with an inner diameter of φ1060mm, width of 260mm, and casting weight of 850kg, based on AC4C alloy, maximum primary crystal Si defect particle size of 0.1mm, and the distribution ratio of the defects to 4.6% or less. Then, the Si content condition in the alloy for casting was calculated as follows using the invention of claim 1. Prior to casting, the melt solidification time of the final solidified part of the cast product part and the distance from the outlet were calculated using computer solidification analysis (JS-CAST manufactured by Komatsu Soft), and the following values were obtained. .
-Final solidification time of molten metal in the product section; 1268 seconds-Distance from the outlet of the same part; 308mm
Substituting this numerical value and the above-mentioned maximum primary crystal Si particle size into the prediction formula of the invention according to claim 1 and calculating the appropriate Si content of the alloy material, it was found to be 5.58% by mass.
[0046]
Since the initial Si content of the alloy base material was 7.05 mass%, the alloy was remixed with 670 kg of AC4C base material, 180 kg of pure aluminum material, 1.4 kg of metal Cu, and 0.8 kg of metal Mg, and used for casting. The maximum grain size of primary Si defects confirmed from the casting thus obtained is 0.08 mm, and the distribution ratio is 2 pitches (3.3%) in 60 pitches, which is very close to the predicted result. It became.
[0047]
(Comparative Example 1)
In Example 2, when the alloy material used for casting was cast with an AC4C base material (Si content 7.05 mass%), the casting had a maximum particle size of 0.21 mm and a distribution ratio of 30% (in 60 pitches). 18 pitch) primary Si defects were generated. This casting was judged as defective in appearance.
[0048]
( Reference Example 1 )
As shown in FIG. 5 , a stainless steel wire mesh having a wire diameter of 0.5 mm and an interstitial dimension of 4 × 4 mm was installed at the position of 10 mm from the mold at the time of casting as shown in FIG. . At the same time as casting into the product part, the wire mesh was quickly removed, the molten metal was solidified, and a casting was created. As a result, the primary Si defects confirmed in the casting became a maximum particle size of 0.1 mm, a distribution ratio of 3.3% (2 pitches in 60 pitches), and almost the same as Example 2 in which the Si content in the alloy was adjusted. The same improvement effect was obtained.
[0049]
【The invention's effect】
As described above, according to the coarse primary crystal Si defect prevention how the aluminum alloy casting of the present invention, can very suppressed primary crystal Si defects, to improve the appearance quality of castings hypoeutectic Akiragata Si aluminum alloy There is an excellent effect of being planned. This is extremely effective particularly in a large-sized cast product having a long molten metal solidification time such as a tire mold.
[Brief description of the drawings]
FIG. 1 is a phase diagram showing a solid-liquid equilibrium and a schematic diagram showing a crystal structure state at each temperature of an Al—Si binary alloy.
FIG. 2 is a phase diagram showing a solid-liquid equilibrium of an Al—Si—Mg ternary alloy containing (a) 0.5 wt% and (b) 0.2 wt% of Mg.
FIG. 3 is an explanatory view showing a generation mechanism of primary crystal Si defects.
FIG. 4 shows (a) a graph showing the relationship between the predicted value of the grain size of primary crystal Si defects and the actual measurement value, and (b) the distribution ratio of primary crystal Si defects and the maximum grain size by the coarse primary crystal Si defect prevention method of the present invention. It is a graph which shows the relationship of a diameter.
5 is a schematic diagram showing an example of a filter installation mode in the method of manufacturing the A aluminum alloy casting.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Primary crystal alpha, 2 ... Melt, 3 ... Eutectic Si, 4 ... Primary crystal Si, 5 ... alpha (aluminum solid phase), 6 ... L (liquid phase), 10 ... Cast frame, 11 ... Heat insulation material, DESCRIPTION OF SYMBOLS 12 ... Blade, 13 ... Backup material, 14 ... Mold, 15 ... Outlet, 16 ... Molten metal, 17 ... Primary crystal Si nucleus, 18 ... Wire mesh, 19 ... Surface plate.

Claims (2)

In a casting aluminum alloy having Si as a main additive element, a method for preventing a coarse primary crystal Si defect in an aluminum alloy casting when producing a casting using an alloy species having a hypoeutectic region side composition,
The following predictions can approximate the size of primary crystal Si defects generated on the casting surface by a function consisting of three parameters: distance from the pouring gate, molten metal solidification time at the same site, and Si content in the alloy. Formula (1) is constructed in advance, and the maximum grain size of primary Si defects that can be tolerated is set as the primary crystal Si defect grain size in prediction formula (1). By calculating the critical Si content in an aluminum alloy that does not occur and adjusting the Si content in the aluminum alloy based on this critical Si content, a sound casting with few primary crystal Si defects is obtained. A method for preventing coarse primary crystal Si defects in aluminum alloy castings.
Primary crystal Si defect particle size (mm)
= 0.001238 x distance from the outlet of the casting part (mm)
+0.000139 x molten metal solidification time at the same site (sec)
+ 0.089441 × Si content in alloy (mass%)
-0.956751 (1) The following prediction formula (2) that can approximate the distribution ratio of primary crystal Si defects generated on the casting surface as a function of the maximum grain size of coarse primary crystal Si defects generated in the casting is established in advance. From the predicted value of the maximum grain size of the primary crystal Si defect grain size calculated by (2) and claim 1, the critical Si content in the aluminum alloy that does not generate primary crystal Si defects in the casting is calculated. The method for preventing coarse primary crystal Si defects in an aluminum alloy casting according to claim 1, wherein a sound casting with few primary crystal Si defects is obtained by adjusting the Si content in the aluminum alloy based on the Si content .
Ratio of primary crystal Si defect generation pitch to total pitch number (%)
= 1200.1 x (maximum particle size of primary Si defect (mm)) ²
-84.803 × maximum grain size of primary Si defects (mm)
+1.1185 (2)

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