JPH0813054A - Additive for molten aluminum alloy - Google Patents

Abstract

PURPOSE:To obtain an additive for a molten Al alloy for producing defectless Al alloy castings and die castings having excellent airtightness by incorporating a specific amt. of hydrogen into a metals or alloy. CONSTITUTION:This additive for the molten Al alloy is obtd. by incorporating <=0.05wt.% H to the metal or alloy, more preferably Ti, Zr or their alloy and further, incorporating <=1% metal hydride, more preferably Ti or Zr hydride thereto at need. The additive is preferably used in the form of a compression molding or in the form of sealing the additive into an Al vessel in a reduced pressure atmosphere and or inert gaseous atmosphere. The H is added to the Al alloy without oxidizing the alloy by using such additive, by which occurrence of casting defects, such as shrinks, of the thick parts is obviated and the connection of pores to each other is prevented by dispersing the pores. The excellent castings and die castings are thus obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy molten metal for producing an aluminum alloy casting and an aluminum alloy die casting which are excellent in airtightness, for example, an engine component for automobiles which requires airtightness and strength such as a manifold and a cylinder head. Regarding additives.

[0002]

2. Description of the Related Art When an aluminum alloy is melted and an aluminum alloy casting and an aluminum alloy die casting are cast from the molten metal, hydrogen gas or pores due to shrinkage are often generated inside the casting. When such a casting is used for parts such as gas passages and containers, if defects such as pores inside the casting are connected, leakage may occur inside and outside the parts. That is, regardless of whether the internal defect of the casting is a pore due to hydrogen gas or a pore due to shrinkage, if it exists independently, leakage inside and outside the component does not occur.

As shown in FIG. 3, the pores generated inside an aluminum casting obtained by a usual casting method such as gravity casting or low pressure casting are non-circular, and the pores 3a and 3b are easily connected. When the aluminum alloy casting having the pores 3 having such a shape is used for parts that generate a pressure difference between the inside and the outside, for example, engine parts for automobiles such as a manifold and a cylinder head, intake air and cooling water leak to the outside to improve engine performance. There is a risk of damage. Therefore, conventionally, various measures have been taken to prevent the generation of pores due to hydrogen gas, such as degassing treatment for removing gas in the molten aluminum alloy.

However, when casting with a degassed molten metal, the generation of pores in the aluminum alloy casting is surely reduced, but on the contrary, shrinkage or dents are likely to occur in the thick portion of the portion where the thickness change is large. For example, as shown in FIG. 4, when a boss portion 7 such as a manifold or a cylinder head, which is an engine component, is contracted or has a zigzag 10, the inside and outside of the boss portion 7 are connected to each other after screwing, and as a result, Intake air will leak outside. Therefore, paying attention to the generation of pores due to hydrogen gas, performing degassing causes other casting defects,
It is difficult to stably obtain an aluminum alloy casting having excellent airtightness.

Japanese Patent Publication No. 5-65573 discloses Al-
Si-Mg type or Al-Si-Mg-Cu type alloy,
There is a disclosure that by adding 0.001 to 0.01% of Ca, shrinkage cavities due to the presence of the impurity Fe are prevented and an aluminum alloy for casting having excellent airtightness is obtained.

However, even if Ca is added to reduce shrinkage cavities, the shape of the shrinkage cavities becomes non-circular and pores may be connected to each other. For example, there is a pressure difference between the inside and outside of such an aluminum alloy casting. There still remains a problem for use as an engine part for automobiles.

As a method of preventing shrinkage cavities from occurring in the thick-walled portion of a casting, hydrogen is added to the molten metal to disperse the shrinkage cavities. Hydrogen dissolved in the molten aluminum alloy has a drastic decrease in the solubility of hydrogen when the molten metal solidifies. Therefore, as shown in the following formula, the hydrogen is gasified into bubbles and remains in the aluminum alloy casting to form fine pores. Two
H (dissolution) → H ₂ (gas) From this, it can be seen that hydrogen has an effect of relaxing solidification shrinkage and dispersing shrinkage cavities in fine pores.

Conventionally, as a manufacturing method of adding hydrogen to an aluminum alloy molten metal, a method of utilizing decomposition of water as shown in the following equation, by immersing a cloth containing potatoes or water in the molten metal, etc. It has been implemented. 2Al + 3H ₂ O → Al ₂ O ₃ + 6H (dissolved)

Among them, potatoes containing a proper amount of water are often used because of their excellent workability. However, in the addition method using the decomposition of water such as potatoes,
As shown in the above equation, a large amount of slag is generated because aluminum oxide is generated, and a slag work for removing the slag is required. Also, since this oxide is mixed in the molten metal, the film oxide in castings cast from this molten metal becomes the starting point of gas generation, and the pores become elongated, making it easier for them to connect together and reducing the airtightness. To do.

On the other hand, in Japanese Patent Publication No. 51-44084, 1 to 25% of magnesium is added and melted in order to prevent the molten aluminum from rapidly solidifying and to control the size of crystal grains, and then foaming. In order to improve the viscosity of the alloy and to increase the viscosity of the alloy, there is disclosed a method for producing a porous aluminum alloy casting in which a titanium hydride that generates gas at a temperature below the liquidus and above the solidus of the alloy is added and stirred.
According to the present invention, a foamable aluminum alloy casting is obtained, and the porosity of the foam is about 30 to about 60%, and the size of the pores is about 0.05 to about 0.20 mm. However, in Japanese Patent Publication No. 51-44084, the porosity is
The pores are too large to have airtightness and lack mechanical strength, so that they cannot be applied to automobile engine parts.

The present invention relates to the manufacture of parts used at sites where there is a pressure difference inside and outside, for example, automobile engine parts such as manifolds and cylinder heads, by adding hydrogen without oxidizing the molten aluminum alloy. We provide an aluminum alloy molten metal additive for obtaining aluminum alloy castings and aluminum alloy die castings that have excellent airtightness by generating casting defects such as shrinkage at the meat part and generating pores dispersedly without connecting pores to each other. The purpose is to do.

[0012]

In order to achieve the above object, the molten aluminum alloy additive of the present invention is characterized by being composed of a metal or alloy containing 0.05% by weight or more of hydrogen. The metal is preferably titanium or zirconium, and the alloy is preferably titanium alloy or zirconium alloy. The molten aluminum alloy additive preferably contains metal hydride in an amount of 1% by weight or more, and titanium hydride or zirconium hydride is preferable as the metal hydride. This molten aluminum alloy additive is preferably molded by compression, or enclosed in an aluminum container under reduced pressure or in an inert gas atmosphere.

[0013]

Since the metals and alloys containing hydrogen have the property of releasing hydrogen as the temperature rises, it is possible to contain hydrogen by adding it to the molten aluminum alloy. If the hydrogen content of these metals and alloys is 0.05% or more by weight, the amount of hydrogen required for dispersion of shrinkage (about 0.4 pp without lowering the melt temperature).
m or more) can be contained in the molten metal. If the hydrogen content of metals and alloys is less than 0.05% by weight, a sufficient amount of hydrogen cannot be obtained, or increasing the amount of addition will lower the melt temperature and complicate addition work. Become.
Therefore, the hydrogen content of the metal and alloy used as the molten aluminum alloy additive is preferably 0.05% or more by weight.

As such metals and alloys, titanium, zirconium, magnesium or the like, which easily absorbs hydrogen, can be used. In particular, it is preferable to use titanium or zirconium. This is because titanium and zirconium have the function of refining the crystal grains of the aluminum alloy and improving the mechanical strength.

When the hydrogen content of the metal is increased, it becomes a metal hydride. Since this metal hydride contains a large amount of hydrogen of several percent by weight, as used as a hydrogen storage alloy, the metal hydride is contained in the additive by 1% by weight.
If it is contained above, hydrogen can be sufficiently added to the molten metal. Further, when a metal hydride is used alone, it is 0.0
Hydrogen can be sufficiently contained in the melt by adding a small amount of about 1% to 0.1%, and the pores are finely dispersed.

Examples of such metal hydrides include TiH ₂ ,
ZrH ₂ , MgH ₂ , Mg ₂ NiH ₂ or the like can be used. In particular, it is preferable to use TiH ₂ or ZrH ₂ . TiH ₂ and ZrH ₂ have the function of refining the crystal grains of the aluminum alloy and improving the mechanical strength.
Alternatively, it contains Zr.

When hydrogen absorbs hydrogen, the metal becomes brittle and becomes granular or powder. Even if it is attempted to add such an additive as it is to the molten metal, it floats on the molten metal and the addition efficiency is very poor. Therefore, it is better to wrap it in an aluminum foil or the like for addition. However, since the size wrapped with aluminum foil or the like becomes uneven, the addition device cannot be used and automation is difficult. Therefore, if a granular or powdered hydrogen-containing metal or metal hydride is compression-molded into a constant shape, the addition operation becomes easy and automation is possible.

When the hydrogen-containing metal or metal hydride is left in the atmosphere, hydrogen is diffused and oxidized. When hydrogen is dissipated, the target amount of hydrogen cannot be added, and when the additive oxidizes, oxides are mixed in the molten metal and the strength of the cast product decreases. Therefore, if a hydrogen-containing metal or metal hydride is enclosed in an aluminum container in a depressurized state or in an inert atmosphere, such a problem does not occur, and since the shape of the additive becomes constant, addition work becomes easier. , Can be automated.

[0019]

EXAMPLES Examples of the present invention will be described in detail below. (Example 1) (JIS) AC4B aluminum alloy 10
Kg was melted in a graphite crucible and kept at 700 ° C., and various additives were added by wrapping the granular ones and powders in an aluminum foil as they were. Then, casting was performed in a copper mold and a flat plate mold with a boss to prepare a sample.

Table 1 shows the amount of hydrogen in a cast product prepared by a copper mold from the melt before addition, the melt containing the additive of the present invention, and the melt containing the conventional potato, and the boss shown in FIG. It shows the state of shrinkage of the cast product produced by the attached flat plate mold. The amount of hydrogen was measured by a Lansley hydrogen analysis method by collecting an analytical sample from the lower part of the cast product that was quenched with a copper mold, and the shrinkage was evaluated by the dispersion state of the shrinkage of the cross section of the bossed flat plate cast product. Was done.
As shown in the figure, the distribution of shrinkage is indicated by x when the shrinkage is concentrated on the boss as shown in (a), as △ when the shrinkage is dispersed as in (b), and as shown in (c). Very finely dispersed particles are indicated by ◯.

[0021]

[Table 1] Additives Additives Additives Remarks for sinking in molten metal Hydrogen amount Hydrogen amount Dispersion (wt%) (wt%) (ppm) Before addition − − − 0.18 × Inventive Example 1 Hydrogen-containing Ti 0.05 0.1 0.43 △ 2 Hydrogen-containing Ti 0.9 0.01 0.44 △ 3 Hydrogen-containing Ti 0.9 0.1 0.53 ○ 4 Ti + TiH ₂ 0.05 0.1 0.42 △ TiH ₂ content 1.3% 5 Ti + TiH ₂ 0.4 0.1 0.49 ○ TiH ₂ content 10% 6 TiH ₂ 3.8 0.01 0.54 ○ 7 TiH ₂ 3.8 0.1 0.63 ○ 8 Ti-5Al 0.1 0.1 0.40 △ 9 Ti-5Al 1.2 0.01 0.45 △ 10 Ti-5Al 1.2 0.1 0.51 ○ 11 Hydrogen content Zr 0.05 0.1 0.40 ○ 12 Hydrogen content Zr 0.8 0.01 0.44 ○ 13 Hydrogen content Zr 0.8 0.1 0.50 ○ 14 ZrH ₂ 2.2 0.01 0.49 ○ 15 ZrH ₂ 2.2 0.1 0.57 ○ Comparative example 1 Hydrogen content Ti 0.03 0.1 0.23 × 2 Hydrogen-containing Ti 0.03 1.0 0.49 ○ Melt temperature drop 3 Ti + TiH ₂ 0.02 0.1 0.21 × TiH ₂ content 0.5% Conventional example Potato −0.05 0.47 × Noro

As shown in Examples 1 to 3 of the present invention, 0.05%
With Ti containing hydrogen as described above, the amount of hydrogen in the molten aluminum can be 0.4 ppm or more, and shrinkage can be dispersed. Further, as shown in Examples 4 and 5 of the present invention, even with Ti containing 1% or more of TiH ₂ , the hydrogen content of the molten aluminum can be 0.4 ppm or more, and shrinkage can be dispersed. As shown in Examples 6 and 7 of the present invention, T
When TiH ₂ containing 3.8% of hydrogen in i is added alone, hydrogenation can be sufficiently performed even if the addition amount is as small as 0.01%, and shrinkage dispersion is very good. As shown in Examples 8 to 13 of the present invention, even in the case of Ti-5Al alloy and Zr, 0.4 ppm of hydrogen is contained at a hydrogen content of 0.05% or more like Ti.
The above can be added. As shown in Examples 14 and 15 of the present invention,
Similar to TiH ₂ , ZrH ₂ containing 2.2% hydrogen in Zr can be added at least in a sufficient amount and the shrinkage dispersion is very good. On the other hand, as shown in Comparative Examples 1 and 2, when the hydrogen content of Ti is less than 0.05%, 1.0% or more must be added in order to sufficiently add hydrogen. Then, the addition will lower the temperature of the molten metal, which will hinder the casting operation. Comparative Example 3
As shown in (3), when the content of TiH ₂ is less than 1.0%, the hydrogen content of the entire additive is small and the hydrogen addition to the molten metal is insufficient. Even with the addition of potatoes in the conventional example, the hydrogen content is 0.47 ppm, but since a large amount of slag is generated, a removing operation is required and the shrinkage is not finely dispersed because the oxide increases.

Example 2 A molded body having a diameter of 20 mm obtained by compression molding a hydrogen-containing metal and a metal hydride at a pressure of 200 MPa was maintained at 700 ° C. in the same manner as in Example 1.
It was added to the 4B aluminum alloy melt and cast in a copper mold and a flat plate mold with a boss to prepare a sample. Table 2 shows the amount of hydrogen in the molten metal before the addition and the molten metal to which the additive of the present invention was added by the copper mold and the shrinkage condition of the cast product made by the flat plate mold with the boss. is there. The amount of hydrogen and the dispersion state of shrinkage were determined in Example 1.
Was evaluated in the same way as

[0024]

[Table 2] Additives Additives Additives Amount of hydrogen in sink in molten metal Hydrogen amount Dispersion (wt%) (wt%) (ppm) Before addition − − − 0.18 × Inventive Example 16 Hydrogen-containing Ti 0.9 0.1 0.50 ○ 17 TiH ₂ 3.8 0.01 0.54 ○ 18 Ti-5Al 1.2 0.1 0.51 ○ 19 Hydrogen-containing Zr 0.8 0.1 0.50 ○ 20 ZrH ₂ 2.2 0.01 0.49 ○

The addition operation is facilitated by using a compression molded body, and as shown in Table 2, the hydrogen content and the shrinkage dispersion effect similar to those of aluminum foil can be obtained with any of the additives. It was

(Example 3) TiH ₂ and ZrH ₂ sealed in an aluminum container under reduced pressure or an argon atmosphere were left for 1 month in the atmosphere, and then, as in Example 1,
A sample was prepared by adding it to an AC4B aluminum alloy melt held at 700 ° C. and casting it in a copper mold and a flat plate mold with a boss.

Table 3 shows the amounts of hydrogen in the melt before addition, the melt containing the additive of the present invention and the melt containing TiH ₂ and ZrH ₂ left for 1 month in the air without being enclosed in the container of the comparative example. It shows the situation of closing.

[0028]

[Table 3] Additives to containers Additives Additives Filled in molten metal Filled hydrogen Amount of hydrogen Dispersion (wt%) (wt%) (ppm) Before addition − − − − 0.18 × Inventive Example 21 Reduced pressure TiH ₂ 3.8 0.01 0.54 ○ 22 Ar TiH ₂ 3.8 0.01 0.55 ○ 23 Reduced pressure ZrH ₂ 2.2 0.01 0.50 ○ 24 Ar ZrH ₂ 2.2 0.01 0.49 ○ Comparative Example 4 None TiH ₂ 3.8 0.01 0.44 △ 5 None ZrH ₂ 2.2 0.01 0.42 △

As shown in Examples 21 and 23 of the present invention, when the metal hydride was enclosed in an aluminum container under a reduced pressure, hydrogen could be sufficiently contained in the molten metal even if the molten metal additive was left for one month. The dispersion state of shrinkage is also good. In addition, in Invention Examples 22 and 24 sealed in an argon atmosphere, the same effect as in the case of the reduced pressure sealing was obtained. On the other hand, in Comparative Examples 4 and 5 which were left as they were without being sealed in the container, the amount of hydrogen and the dispersion of shrinkage were slightly inferior to those in the case of vacuum packing and argon packing.

Example 4 (JIS) AC4B aluminum alloy was melted in a graphite crucible and kept at 700 ° C., and 0.2% by weight of titanium containing 0.05% of hydrogen was added. Using this molten metal, the thickness of the thin portion shown in FIG. 7 is 5 mm.
100 of the manifolds 4 were cast by gravity casting. Then, the openings 6a and 6b of the manifold 4 were closed and submerged in water, and an air pressure of 0.3 MPa was applied to the inside to inspect for the occurrence of leakage. As a result, it was found that no leakage occurred in all 100 cast pieces, that they had good airtightness and that they were excellent as engine parts. Further, FIG. 1 shows the state of pores in the cross section of the wall thickness portion of 5 mm, but there are few film oxides and the pores 3c are fine spherical. On the other hand, FIG. 2 shows the state of pores in a cross section of a 5 mm-thick portion of a casting made from the molten metal by adding the potato of the conventional example.
c is coarse and elongated.

(Example 5) (JIS) AC2A aluminum alloy was melted in a graphite crucible, and 0.01% by weight of titanium hydride containing 3.8% of hydrogen was added. This molten metal was distributed to the holding furnace of the low-pressure casting machine, and the thin wall thickness was 5 m.
100 m cinder heads were cast by the low pressure casting method.
Then, it was submerged in the same manner as in Example 4 and had 0.3 MPa inside.
Air pressure was applied to inspect for leaks. As a result, it was found that no leakage occurred in all 100 cast pieces, that they had good airtightness and that they were excellent as engine parts.

(Example 6) (JIS) ADC12 aluminum alloy was melted in a graphite crucible and held at 680 ° C, and a mixed additive of titanium and titanium hydride containing 1.5% by weight of titanium hydride was added to the molten metal. Was added. Using this molten metal, 100 oil pans with a thickness of 2 mm at the thin portion were cast by the die casting method. Then, in the same manner as in Example 4, submersion in water was performed and an air pressure of 0.3 MPa was applied to the inside to inspect for occurrence of leakage. As a result, it was found that no leakage occurred in all 100 cast pieces, that they had good airtightness and that they were excellent as engine parts. As described above, it was found that the melt additive of the present invention is effective for shrinkage cavity dispersion even in die casting.

In the above examples of the present invention, titanium is used as the metal,
Although titanium hydride (TiH ₂ ) is shown as the metal hydride, similar effects can be obtained with other metals, alloys and metal hydrides.

[0034]

As described above in detail, the aluminum alloy melt additive for obtaining the aluminum alloy casting having excellent airtightness of the present invention is a metal or alloy containing 0.05% by weight or more of hydrogen. However, by adding this to the molten aluminum alloy, hydrogen can be added without oxidizing the molten metal, and slag work such as slag is unnecessary,
It is possible to disperse the shrinkage cavities of the casting into fine pores without increasing oxides. The aluminum alloy casting using the molten metal additive of the present invention is useful as a manifold, a cylinder head or the like as an automobile engine part.

[Brief description of drawings]

FIG. 1 is a diagram showing a state of an internal cross section of an aluminum alloy casting obtained by adding hydrogen-containing titanium to a molten aluminum alloy for casting according to an embodiment of the present invention.

FIG. 2 is a view showing a state of an internal cross section of an aluminum alloy casting obtained by adding the potato of Comparative Example to a molten aluminum alloy for casting.

FIG. 3 is a diagram showing pores generated at a grain boundary of an aluminum alloy casting.

FIG. 4 is a diagram showing a form of a shrinkage cavity or a zest cavity generated in a boss portion such as a manifold or a cylinder head of an automobile engine component.

FIG. 5 is a view showing a flat plate mold with a boss for evaluation of shrinkability.

FIG. 6 is a view showing a typical situation of shrinkage occurring in a flat plate casting with a boss.

FIG. 7 is a view showing an outer appearance of a manifold as an automobile engine part.

[Explanation of symbols]

1: Crystal grains, 3: Pores, 4: Manifold, 6: Opening, 7: Boss, 10: Zaku nest.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location C22C 16/00 (72) Inventor Hitoshi Goto 11 Kinugaoka, Moka-shi, Tochigi Hitachi Metals Co., Ltd. Moka factory

Claims (8)

[Claims] 1. An aluminum alloy melt additive, comprising a metal or an alloy containing 0.05% by weight or more of hydrogen. 2. The molten aluminum alloy additive according to claim 1, wherein the metal is titanium or zirconium. 3. The molten aluminum alloy additive according to claim 1, wherein the alloy is a titanium alloy or a zirconium alloy. 4. The molten aluminum alloy additive according to claim 1, which contains a metal hydride in an amount of 1% by weight or more. 5. The molten aluminum alloy additive according to claim 4, wherein the metal hydride is titanium hydride. 6. The molten aluminum alloy additive according to claim 4, wherein the metal hydride is zirconium hydride. 7. The molten aluminum alloy additive according to any one of claims 1 to 6, which is a compression molded body. 8. A molten aluminum alloy additive according to any one of claims 1 to 7, wherein the molten aluminum alloy additive is sealed in an aluminum container in a reduced pressure atmosphere and / or an inert gas atmosphere.