JP2020152996A - Method for making alp compounds finer and aluminum alloy casting - Google Patents

Abstract

To provide convenient and efficient methods for making AlP compounds in aluminum finer, and an aluminum alloy casting in which AlP compounds and eutectic structures are both made finer.SOLUTION: A method for making AlP compounds finer includes setting a molten metal temperature of aluminum to the temperature equal to or higher than a crystallization temperature of the AlP compounds in an atmosphere containing oxygen. Preferably, it is held for 5-60 minutes at the molten metal temperature, and aluminum is preferably an Al-Si alloy.SELECTED DRAWING: None

Description

The present invention relates to a method for refining an AlP compound in aluminum and an aluminum alloy casting in which the AlP compound is miniaturized.

P (phosphorus) is a typical unavoidable impurity contained in aluminum, and is often mixed with Al—Si alloys in particular. Here, the main causes of P being mixed as an impurity in the Al—Si based alloy are a path caused by metallic Si and a path caused by scrap of the hypereutectic Al—Si alloy.

Specifically, P is often mixed with metallic Si as an unavoidable impurity, and when the metallic Si is used as a raw material, P is mixed with the aluminum alloy containing Si. Further, since P has an action of refining primary crystal Si, it is often added to a hypereutectic Al-Si based alloy or the like in which primary crystal Si is easily crystallized. Even when scraps such as the above are used as raw materials, P will be mixed.

When P is present in the molten metal, an AlP compound is generated, and the AlP compound acts as an effective heterogeneous nucleus of the primary crystal Si, so that the primary crystal Si is refined. From the viewpoint of ensuring the microstructure, ductility and toughness of the aluminum alloy, it is desirable to avoid coarsening of the AlP compound, but an appropriate method for refining the AlP compound has not been proposed, and basically P. A method of ensuring the strength and reliability of an Al—Si alloy by reducing the content of Al—Si is being studied.

For example, in Patent Document 1 (Japanese Unexamined Patent Publication No. 2002-80920), Mg is added to an aluminum molten metal containing P and / or Sb at a molten metal temperature of 650 to 850 ° C., and chlorine gas is blown into the molten aluminum to provide P and in the molten metal. A method for removing P and / or removing Sb from the molten aluminum, which comprises removing / or Sb, has been proposed.

In the P-depletion method disclosed in Patent Document 1, by adding Mg to the molten aluminum, P and Mg in the molten metal react with each other to form a Pated Mg compound, and chlorine gas is blown into the molten aluminum. , Mg in the molten metal reacts with chlorine gas to form MgCl, absorbs the P-modified Mg compound in the molten metal and removes it as dross, so that the amount of P in the molten metal can be reduced. It is said.

JP-A-2002-80920

However, chlorine has extremely high toxicity, and in addition to being designated as a deleterious substance by the Poisonous and Deleterious Substances Control Law, it has also been pointed out as a causative substance of ozone layer holes. Therefore, sufficient care must be taken when handling chlorine, and when chlorine is used, a separate facility for treating the chlorine is required. Furthermore, chlorine is highly corrosive, and corrosion of equipment used and leakage of chlorine are also serious problems.

Further, as described above, P has an action of refining primary crystal Si, and if the AlP compound can be sufficiently miniaturized, it imparts good mechanical properties to the aluminum alloy without removing P. It is thought that it can be done. At the same time, if the eutectic structure can be miniaturized, further improvement in strength can be expected.

In view of the above problems in the prior art, an object of the present invention is a simple and efficient method for refining an AlP compound in aluminum, and an aluminum alloy casting in which both the AlP compound and the eutectic structure are miniaturized. Is to provide.

As a result of intensive research on a method for treating molten aluminum in order to achieve the above object, the present inventors have found that it is extremely effective to heat the molten aluminum to a certain temperature or higher in an atmosphere containing oxygen. , The present invention has been reached. In addition, "aluminum" includes aluminum and various aluminum alloys.

That is, the present invention provides a method for refining an AlP compound, which comprises setting the molten aluminum temperature to be equal to or higher than the crystallization temperature of the AlP compound in an atmosphere containing oxygen. P is removed when the molten aluminum temperature is set to be equal to or higher than the crystallization temperature of the AlP compound in an inert gas atmosphere, reduced pressure and vacuum atmosphere. However, in the method for refining the AlP compound of the present invention, the surface of the molten aluminum is coated with an oxide film. Therefore, P is trapped in the oxide film, becomes a gas, and stays in the molten metal without being removed from the molten metal. Here, by setting the molten metal temperature to 1250 ° C. or lower, it is possible to suppress the energy consumption required for the molten metal treatment and the deterioration of the equipment due to the high temperature.

Generally, when casting aluminum as an actual operation, the molten aluminum is held in a temperature range of 700 to 800 ° C., and after performing in-core treatment such as degassing, slag removal, and component adjustment, gold having a predetermined shape is used. Pour hot water into the mold. On the other hand, in the method for refining an AlP compound of the present invention, the molten aluminum is heated and held at a high temperature equal to or higher than the crystallization temperature of the AlP compound, so that the dissolved AlP compound is not melted before being re-solidified. It is considered that it will be smaller than that of.

Further, in the method for refining the AlP compound of the present invention, not only the AlP compound is miniaturized, but also the miniaturized AlP compound reduces the action of the eutectic Si as a coagulation nucleus, so that the eutectic structure is also present. It will be miniaturized.

Here, the effect of the method for refining the AlP compound of the present invention lasts even if the molten metal is held at a high temperature for a long time after the treatment, and is finally obtained even if it is held at 750 ° C. for 60 minutes, for example. The AlP compound of the aluminum alloy casting is miniaturized.

In the method for refining an AlP compound of the present invention, it is preferable to keep the AlP compound at a crystallization temperature or higher for 5 to 60 minutes. By keeping the molten aluminum at a high temperature equal to or higher than the crystallization temperature of the AlP compound for 5 minutes or more, the AlP compound can be sufficiently dissolved and finely divided. On the other hand, if the holding time is 60 minutes or less, the effect of miniaturizing the AlP compound is not lost, and it is possible to suppress an increase in energy consumption and deterioration of equipment such as a melting furnace.

Further, in the method for refining an AlP compound of the present invention, it is preferable that the aluminum is an Al—Si alloy. In the Al—Si alloy, scrap such as a hypereutectic Al—Si alloy having a high P content may be used as a raw material, but even when the raw material has a high P content, the AlP compound of the present invention may be used as a raw material. Good strength and reliability can be imparted to the aluminum alloy by using the micronization method of.

In addition, the present invention
The primary α (Al) phase crystallizes,
The content of P is 15 ppm or less,
The average particle size of AlP particles is 4 μm or less.
Also provided are aluminum alloy castings, characterized by.

In the aluminum alloy casting of the present invention, the P content is 15 ppm or less, the P content is extremely low, the AlP particles (AlP compound) are refined, and the eutectic Si is refined. It is being promoted. The average particle size (diameter equivalent to a circle) of eutectic Si is preferably 10 μm or less. Here, the AlP particles act as heterogeneous nuclei of Si, and when there are many AlP particles, eutectic solidification occurs without supercooling. In the case of the general solidification, the eutectic Si becomes coarse, but since the P content is reduced in the aluminum alloy casting of the present invention, the AlP particles are reduced and the AlP particles are dissolved. When the AlP particles are crystallized again, the AlP particles become fine (the average particle size is 4 μm or less), and the eutectic Si becomes fine due to supercooling.

Further, in the aluminum alloy casting of the present invention, the Si content is preferably 5 to 30% by mass. By setting the Si content to 5% by mass or more, the fluidity and mold filling property of the molten aluminum alloy when manufacturing the aluminum alloy casting can be ensured, and the strength and abrasion resistance of the aluminum alloy casting can be ensured. Can be improved. On the other hand, by setting the Si content to 30% by mass or less, it is possible to reduce the mixing of P due to the raw material to which Si is added. The more preferable Si content is 5 to 15% by mass.

Further, in the aluminum alloy casting of the present invention, it is preferable that the average particle size of the AlP particles does not become 4 μm or more even after the remelting / solidification heat treatment. If the mechanism is that "dissolved AlP particles crystallize finely during solidification, which reduces the size of AlP particles that act as heterogeneous nuclei at low supercooling, which causes eutectic Si coarsening." There is a concern that the AlP particles may be coarsened by repeating melting and casting a plurality of times, but in the aluminum alloy casting of the present invention, the coarsening of the AlP particles is suppressed even after the remelting and solidification heat treatment. Here, in the aluminum alloy casting of the present invention, it is preferable that the average particle size of the AlP particles does not become 4 μm or more even after the redissolution / solidification heat treatment is repeated twice or more.

Further, in the aluminum alloy casting of the present invention, it is preferable that the layer spacing of the eutectic Si is 7 μm or less. By setting the layer spacing of eutectic Si to 7 μm or less, high strength can be imparted to the aluminum alloy casting. Here, the layer spacing of eutectic Si is preferably 7 μm or less even after the remelting / solidifying heat treatment, and the layer spacing of eutectic Si is even after repeating the remelting / solidifying heat treatment twice or more. It is more preferably 7 μm or less.

According to the present invention, it is possible to provide a simple and efficient method for refining an AlP compound in aluminum, and an aluminum alloy casting in which both the AlP compound and the eutectic structure are miniaturized.

It is a microstructure photograph of the implemented aluminum alloy casting 1. It is a microstructure photograph of the implemented aluminum alloy casting 2. It is a microstructure photograph of the implementation aluminum alloy casting 3. It is a microstructure photograph of the comparative aluminum alloy casting 1. It is a microstructure photograph of the comparative aluminum alloy casting 2. It is a microstructure photograph of the comparative aluminum alloy casting 3. It is a graph which shows the particle size distribution of an AlP compound. It is a microstructure photograph of the aluminum alloy casting 4 (holding time 10 minutes). It is a microstructure photograph of the aluminum alloy casting 4 (holding time 30 minutes). It is a microstructure photograph of the aluminum alloy casting 4 (holding time 60 minutes). 6 is a microstructure photograph of the case where the AlP compound is not subjected to the miniaturization treatment in Example 4. It is a microstructure photograph of the aluminum alloy casting 5 (holding time 20 minutes). It is a microstructure photograph of the aluminum alloy casting 5 (holding time 60 minutes). It is a microstructure photograph of the aluminum alloy casting 5 (holding time 120 minutes). It is a microstructure photograph of the aluminum alloy casting 5 (holding time 180 minutes). It is a microstructure photograph of the aluminum alloy casting 5 (without holding time). 6 is a microstructure photograph of Example 6 in the case where the AlP compound is not subjected to the miniaturization treatment (condition 1). It is a microstructure photograph of the aluminum alloy casting 6 (condition 2). It is a microstructure photograph of the aluminum alloy casting 6 (condition 3). It is a microstructure photograph of the aluminum alloy casting 6 (condition 4). It is a microstructure photograph of the aluminum alloy casting 6 (condition 5). It is a graph which shows the layer spacing of the eutectic structure of an aluminum alloy casting.

Hereinafter, the method for refining the AlP compound of the present invention and the aluminum alloy casting will be described in detail, but the present invention is not limited to these.

1. 1. Method for refining AlP compound The method for refining an AlP compound of the present invention is characterized in that the molten aluminum temperature is set to be equal to or higher than the crystallization temperature of the AlP compound in an oxygen-containing atmosphere, and the AlP compound is extremely simple and efficient. It is a miniaturization method of. By forming an oxide film on the surface of the molten metal, it is possible to suppress the release of P to the outside of the system, and in the recoagulation process, the dissolved AlP compound can be made smaller than that before dissolution.

The atmosphere containing oxygen is not particularly limited as long as an appropriate oxide film is formed on the surface of the molten metal. For example, the treatment may be performed in the atmosphere, or a mixed gas atmosphere of oxygen and an inert gas may be used. Good. Further, the heating means for the molten aluminum is not particularly limited as long as the effect of the present invention is not impaired, and various conventionally known heating methods can be used.

The holding time of the AlP compound at the molten metal temperature, which is equal to or higher than the crystallization temperature, is preferably 5 to 60 minutes. By setting the holding time to 5 minutes or more, the AlP compound can be sufficiently refined. On the other hand, if the holding time is 60 minutes or less, the miniaturization effect of the AlP compound is not lost, and energy consumption and damage to the melting furnace can be suppressed.

Further, the method for refining the AlP compound of the present invention has an effect of not only refining the AlP compound but also refining the eutectic Si of the aluminum alloy casting finally obtained through casting. The AlP compound that acts as a heterogeneous nucleus of eutectic Si is of a certain size or larger, but in the present invention, the AlP compound is refined, so even if the AlP compound is present, the heterogeneous nucleus of eutectic Si Does not act as a supercooler. This is considered to be the cause of not coarsening the eutectic Si.

Further, it is preferable that aluminum is an Al—Si based alloy. In the Al—Si alloy, scrap such as a hypereutectic Al—Si alloy having a high P content may be used as a raw material, but even when the raw material has a high P content, the AlP compound of the present invention may be used as a raw material. By using the micronization method, good strength and reliability can be imparted to the aluminum alloy casting.

The type of Al—Si alloy is not particularly limited as long as the effect of the present invention is not impaired, and various conventionally known Al—Si alloys can be used, but the Si content is 5 to 30% by mass. It is preferable to do so. By setting the Si content to 5% by mass or more, the fluidity and mold filling property of the molten Al—Si alloy when producing the Al—Si alloy casting can be ensured, and the Al—Si based It is possible to improve the strength and wear resistance of alloy castings. On the other hand, by setting the Si content to 30% by mass or less, it is possible to reduce the mixing of excess P due to the raw material to which Si is added.

Further, the content of P in the molten aluminum is preferably 15 ppm or less. By setting the P content to 15 ppm or less, the eutectic Si can be sufficiently miniaturized, and high strength can be imparted to the aluminum alloy. Here, the more preferable P content in the molten aluminum is 8 ppm or less, and the most preferable P content is 5 ppm or less. By further reducing the P content, the eutectic Si of the aluminum alloy casting can be made more remarkably finer.

2. 2. Aluminum alloy casting The aluminum alloy casting of the present invention is characterized in that the primary crystal α (Al) phase is crystallized, the P content is 15 ppm or less, and the average particle size of AlP particles is 4 μm or less. It is an alloy casting. The average particle size (diameter equivalent to a circle) of eutectic Si is preferably 10 μm or less.

Here, the circle-equivalent diameter is the diameter when the area occupied by the eutectic Si obtained when the metal structure is observed under a microscope is converted into the circle-equivalent area. Specifically, the micrograph can be easily obtained by image processing or the like. Since the contrast between the eutectic Si region and the other regions is clearly different on the micrograph, various image measurement processes are performed after the binarization process. Further, as the average particle size, for example, an average value of the equivalent circle diameter within a constant visual field (measurement area: 1.3 mm ² , number of measurement visual fields: 3) can be used.

The lattice constant of AlP, which is a compound of Al and P, differs from the lattice constant of Si by only about 0.4%, and is considered to be a nucleation substance of polyhedral Si. Utilizing this property, P may be industrially used as a primary crystal micronizing agent for hypereutectic Al—Si alloys, but on the other hand, it is known to inhibit the miniaturization of eutectic Si. ing.

On the other hand, in the aluminum alloy casting of the present invention, the P content is suppressed to 15 ppm or less, and the average particle size (diameter equivalent to a circle) of eutectic Si is 10 μm or less. Here, from the viewpoint of refining the eutectic Si, the P content is preferably 8 ppm or less, and more preferably 5 ppm or less.

Further, it is preferable that the average particle size of the AlP particles does not become 4 μm or more even after the remelting / solidifying heat treatment, and more preferably 4 μm or more even after repeating the remelting / solidifying heat treatment twice or more. Since the AlP particles are not coarsened by the redissolution / solidification heat treatment, they can be used industrially stably.

The method for measuring the diameter of AlP particles is not particularly limited and can be measured by various conventionally known methods. For example, the region of AlP particles is specified by the result of element mapping using EPMA (Electron Probe Micro Analyzer). By doing so, the diameter of AlP particles can be preferably measured. Since the EPMA uses a wavelength dispersive spectroscope, it is possible to perform analysis with higher accuracy than when an energy dispersive spectroscope is used.

Further, in the aluminum alloy casting of the present invention, the Si content is preferably 5 to 30% by mass. By setting the Si content to 5% by mass or more, the fluidity and mold filling property of the molten aluminum alloy when manufacturing the aluminum alloy casting can be ensured, and the strength and abrasion resistance of the aluminum alloy casting can be ensured. Can be improved. On the other hand, by setting the Si content to 30% by mass or less, it is possible to reduce the mixing of P due to the raw material to which Si is added.

Generally, when the Al—Si alloy has a subeutectic composition, the Al—Si alloy casting has a structure composed of primary crystal α (Al) and eutectic, and the Al—Si alloy has a eutectic composition. If the alloy has a eutectic structure, the Al—Si alloy has a hypereutectic composition, and the structure is composed of primary Si and eutectic. However, the Al—Si alloy casting of the present invention preferably has a structure composed of primary crystal α (Al) and eutectic even when it does not have a subeutectic composition.

In the aluminum alloy casting of the present invention, the eutectic temperature is lowered. For example, even when the Al—Si alloy has a substantially eutectic composition, the presence of a coupled zone (cooperative growth region) causes it. , A structure composed of primary crystal α (Al) and eutectic is formed.

In the aluminum alloy casting of the present invention, the layer spacing of eutectic Si is preferably 7 μm or less, and the layer spacing of eutectic Si is 7 μm or less even after the remelting / solidification heat treatment is repeated twice or more. Is more preferable. Since the layer spacing of eutectic Si is not coarsened by the remelting / solidification heat treatment, it can be used industrially stably.

The method for measuring the layer spacing of eutectic Si is not particularly limited and can be measured by various conventionally known methods. For example, in "Casting and Solidification Subcommittee of Japan Institute of Light Metals: Light Metals, 38 (1988) 54-60". It can be measured using the intersection method of the dendrite arm spacing measurement procedure described.

Although the typical embodiments of the present invention have been described above, the present invention is not limited to these, and various design changes are possible, and all of these design changes are included in the technical scope of the present invention. Is done.

<< Example 1 >>
A 99.9 mass% pure aluminum base metal, an Al-25% Si alloy base metal and a rod type Al-19 mass% Cu-1.4 mass% P alloy are blended and inserted into a graphite crucible at 740 ° C. After being dissolved in the air, it was degassed by a rotary degassing device at 740 ° C. Next, the molten metal at 740 ° C. was cast into a boat shape (JIS H 5202) by a gravity casting method. The mold temperature was 150 ° C. Table 1 shows the composition of the obtained non-miniaturized die casting and the crystallization temperature of the AlP compound in the composition. The composition is shown in% by mass.

Next, the residual hot water was heated to 1000 ° C. in the atmosphere and held for 10 minutes (the AlP compound was refined), and then the molten metal at 1000 ° C. was cast into a boat shape at 150 ° C. Next, the obtained mold casting was redissolved, and molten metal at 740 ° C was cast into a boat mold at 150 ° C to obtain an aluminum alloy casting 1.

A 1 cm square cube was cut out from the bottom surface of the obtained aluminum alloy casting 1 at a position of 13 mm, and the cross section was buffed to prepare a sample for microstructure observation. The microstructure observed with an optical microscope is shown in FIG.

<< Example 2 >>
An implemented aluminum alloy casting 2 was obtained in the same manner as in Example 1 except that the composition of the non-miniaturized die casting was set to the value shown in Example 2 in Table 1. FIG. 2 shows a microstructure photograph of the implemented aluminum alloy casting 2 observed in the same manner as in Example 1.

<< Example 3 >>
An implemented aluminum alloy casting 3 was obtained in the same manner as in Example 1 except that the composition of the non-miniaturized die casting was set to the value shown in Example 3 of Table 1. FIG. 3 shows a microstructure photograph of the implemented aluminum alloy casting 3 observed in the same manner as in Example 1.

<< Comparative Example 1 >>
The composition of the non-micronized mold casting was set to the value shown as Comparative Example 1 in Table 1, and the AlP compound was not miniaturized (the residual hot water was raised to 1000 ° C. in the air and held for 10 minutes). A comparative aluminum alloy casting 1 was obtained in the same manner as in Example 1 except for the above. A microstructure photograph of the comparative aluminum alloy casting 1 observed in the same manner as in Example 1 is shown in FIG.

≪Comparative example 2≫
The composition of the non-micronized mold casting was set to the value shown as Comparative Example 2 in Table 1, and the AlP compound was not miniaturized (the residual hot water was raised to 1000 ° C. in the air and held for 10 minutes). A comparative aluminum alloy casting 2 was obtained in the same manner as in Example 1 except for the above. A microstructure photograph of the comparative aluminum alloy casting 2 observed in the same manner as in Example 1 is shown in FIG.

≪Comparative example 3≫
The composition of the non-micronized mold casting was set to the value shown in Comparative Example 3 of Table 1, and the AlP compound was not miniaturized (the residual hot water was raised to 1000 ° C. in the air and held for 10 minutes). A comparative aluminum alloy casting 3 was obtained in the same manner as in Example 1 except for the above. FIG. 6 shows a microstructure photograph of the comparative aluminum alloy casting 3 observed in the same manner as in Example 1.

Regarding the composition of the aluminum alloys of Examples 1 to 3 and Comparative Examples 1 to 3, Example 1 and Comparative Example 1 have a subeutectic composition, Examples 2 and 2 have a eutectic composition, and Examples 3 and 3 have a eutectic composition. Has a hypereutectic composition. Here, comparing the structures shown in FIGS. 1 to 6, no coarse AlP compound was observed in the aluminum alloy castings obtained in the examples regardless of the composition, and the eutectic structure was clearly refined. Can be confirmed.

In order to confirm the particle size distribution of the AlP compound, EPMA (acceleration voltage 15 kV, irradiation current 100 mA, beam diameter φ1 μm using EPMA-1610 manufactured by Shimadzu Corporation) was used for the microstructure observation samples of the aluminum alloy castings 1 to 3. The elemental mapping of P was performed using the above, the region of the AlP compound was specified from the distribution of P, and the particle size of the AlP compound was measured. FIG. 7 shows the results of accumulating the AlP compounds of the aluminum alloy castings 1 to 3. For comparison, FIG. 7 also shows the results of accumulating the AlP compounds of the comparative aluminum alloy castings 1 to 3.

In the comparative aluminum alloy castings 1 to 3 in which the AlP compound has not been refined, a large number of AlP compounds having a particle size of 5 to 6 μm are present, whereas the implemented aluminum alloy casting in which the AlP compound has been refined has been applied. It can be seen that in 1-3, there is no AlP compound having a particle size of 4 μm or more. The average particle size of the AlP compound of the comparative aluminum alloy casting 1 was 6 μm, and the average particle size of the AlP compound of the implemented aluminum alloy casting 1 was 4 μm or less at the maximum.

<< Example 4 >>
The temperature of the molten metal was continuously set to 750 ° C. from the micronization treatment of the AlP compound (the residual hot water was raised to 1000 ° C. in the air and held for 10 minutes), and the molten metal temperature was maintained at 750 ° C. for 10 to 60 minutes. An implementation aluminum alloy casting 4 was obtained in the same manner as in Example 1 except for the above. Microstructure photographs of the aluminum alloy casting 4 carried out when the holding time at 750 ° C. was 10 minutes, 30 minutes, and 60 minutes are shown in FIGS. 8, 9, and 10, respectively. For comparison, FIG. 11 shows a microstructure photograph of an aluminum alloy casting obtained by casting a molten metal at 740 ° C. into a boat shape (JIS H 5202) by a gravity casting method without performing a micronization treatment of an AlP compound. Shown.

From the comparison between FIGS. 8 to 10 and FIG. 11, when the holding temperature is 750 ° C., even if the holding is continued for 60 minutes, more primary α (Al) phases are crystallized than in the case without the holding. The eutectic structure is fine. From the results, it can be seen that if the molten metal is kept at about 750 ° C. after redissolving, the effect of the AlP compound refining treatment can be maintained even after casting after 60 minutes.

<< Example 5 >>
The temperature of the molten metal was continuously set to 620 ° C. from the micronization treatment of the AlP compound (the residual hot water was raised to 1000 ° C. in the atmosphere and held for 10 minutes), and the molten metal temperature was maintained at 620 ° C. for 20 to 180 minutes. An implementation aluminum alloy casting 5 was obtained in the same manner as in Example 2 except for the above. Microstructure photographs of the aluminum alloy casting 5 carried out when the holding time at 620 ° C. was 20 minutes, 60 minutes, 120 minutes and 180 minutes are shown in FIGS. 12, 13, 14 and 15, respectively. For comparison, FIG. 16 shows a microstructure photograph of an aluminum alloy casting obtained by casting the molten metal into a boat shape (JIS H 5202) by a gravity casting method without providing a holding time at 620 ° C.

From the comparison between FIGS. 12 to 15 and FIG. 16, it can be seen that even when the holding temperature is 620 ° C., the effect of the AlP compound miniaturization treatment is maintained regardless of the holding time at the holding temperature.

<< Example 6 >>
In order to confirm the size change of the AlP compound due to repeated remelting and casting, a non-miniaturized die casting having the composition described as Example 2 in Table 1 was examined. Specifically, the implemented aluminum alloy casting 6 was obtained in the same manner as in Example 1 except that the thermal history (conditions 1 to 5) shown in Table 2 was applied.

The microstructure photographs of the aluminum alloy castings obtained under each of the conditions 1 to 5 are shown in FIGS. 17 to 21, respectively. Condition 1 is the case where the AlP compound is not refined, condition 2 is the case where the AlP compound is refined and then remelted and solidified once, and condition 3 is the case where the AlP compound is refined. When the remelting / solidification was performed twice after the treatment, the condition 4 was the micronization treatment of the AlP compound and then the remelting / solidification was performed three times, and the condition 5 was the miniaturization treatment of the AlP compound. This is the case when remelting and solidification are performed four times later. The layer spacing of the eutectic structure of each aluminum alloy casting is shown in FIG. Here, the layer spacing of the eutectic structure was measured by the same method as the intersection method of the dendrite arm spacing measurement procedure.

When the AlP compound is not subjected to the miniaturization treatment (condition 1), the layer spacing of the eutectic structure is 12 μm or more, whereas the layer spacing is reduced to about half by performing the AlP compound miniaturization treatment. There is. Further, even if the number of times of remelting / casting is increased, no change is observed in the layer spacing, and it can be seen that the effect of the AlP compound miniaturization treatment is maintained in at least 4 times of remelting / casting.

Claims (10)

The temperature of the molten aluminum should be higher than the crystallization temperature of the AlP compound in an oxygen-containing atmosphere.
A method for miniaturizing an AlP compound. The holding time at the molten metal temperature shall be 5 to 60 minutes.
The method for miniaturizing an AlP compound according to claim 1. That the aluminum is an Al—Si alloy,
The method for refining an AlP compound according to claim 1 or 2. The primary α (Al) phase crystallizes,
The content of P is 15 ppm or less,
The average particle size of AlP particles is 4 μm or less.
Aluminum alloy castings characterized by. The Si content is 5 to 30% by mass,
The aluminum alloy casting according to claim 4. The average particle size of the AlP particles should not exceed 4 μm even after the remelting / solidification heat treatment.
The aluminum alloy casting according to claim 4 or 5. The average particle size of the AlP particles does not become 4 μm or more even after the redissolving / solidification heat treatment is repeated twice or more.
The aluminum alloy casting according to claim 6. The layer spacing of the eutectic Si is 7 μm or less.
The aluminum alloy casting according to any one of claims 4 to 7. The layer spacing should be 7 μm or less even after the redissolution / solidification heat treatment.
The aluminum alloy casting according to claim 8. The layer spacing should be 7 μm or less even after the redissolution / solidification heat treatment is repeated twice or more.
9. The aluminum alloy casting according to claim 9.