JPH08319523A - Semisolid forming process for metallic material - Google Patents

Abstract

PURPOSE: To apply semisolid processing to a hyper-eutectic Al-Si alloy material and to provide a defect-free product having uniform and superior quality by subjecting a hyper-eutectic Al-Si alloy material to induction heating to a specific solid-phase rate in the slid-liquid coexisting region and then to forming. CONSTITUTION: A hyper-eutectic Al-Si alloy is prepared by regulating Si content to about 11%, a value not lower than the eutectic composition equivalent, in an Al-Si binary alloy. This hyper-eutectic Al-Si alloy material is subjected to induction heating to a solid-liquid coexisting region and then to forming. At this time, heating for the material is stopped at the point of time when the solid-shape rate in the central part reaches 0.65-0.80, and then forming is done. It is preferable to perform this forming by filling the material after the completion of heating into the metal mold of a molding machine in a reduced- pressure state of <=500Torr.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forging a metal material in a solid-liquid coexistence region, working such as die casting, and in particular, using a hypereutectic Al-Si alloy as a material, the solid fraction at the start of processing. The present invention relates to a semi-melt processing method capable of producing a processed component of good quality by appropriately controlling the above and suppressing the entrainment of air when filling a material into a mold.

[0002]

2. Description of the Related Art There are various methods for forming metal materials. Generally, from the viewpoint of strength and reliability, methods such as press forging are generally used for forming parts of structural parts, and the materials are solid phase or below. Molded in the temperature range. On the other hand, for the molding of parts with complicated shapes, methods such as gravity casting and high pressure casting are used even if the characteristics of the molded product are somewhat inferior because the purpose is to give the shape, and the material is liquidus. It is injected into the mold in the above temperature range.

On the other hand, hypereutectic Al-Si as a metal material
Since the alloy has excellent wear resistance, exhibits good high-temperature strength, and has a low coefficient of thermal expansion, it is generally used as a heat resistant and wear resistant component in various industrial machines. A die-casting method, which is one of the casting methods, is generally used for forming the hypereutectic Al-Si alloy material.

However, the hypereutectic Al-Si alloy has a characteristic that the liquidus temperature is higher than that of a general die-cast general purpose alloy. For this reason, the casting temperature is inevitably high, and as a result, the heat load of the mold becomes excessive and the mold is likely to locally melt, resulting in an accident. Further, in the die casting method, since a high temperature molten metal is injected into the mold at a high speed, casting defects such as deviation of primary crystal Si and porosity often occur, which is not satisfactory from the viewpoint of quality.

By the way, in recent years, a method of processing a metal material in a temperature range between a solidus line and a liquidus line, that is, a solid-liquid coexistence region has been noticed and studied in each field. Since the processing method in the solid-liquid coexistence area is generally better than that of the conventional forging method because the material in that area has better fluidity, the processing force is smaller, and it is possible to form difficult-to-process materials and complex shaped parts. This is because it is considered to be advantageous to. Further, even when compared with the conventional casting method, the molding temperature can be lowered to the liquidus or lower. For this reason, it is easy to avoid the adverse effects such as local melting damage of the mold and the generation of porosity, and it is expected that the characteristics of the molded product will be improved.

Therefore, also for Al-Si alloy materials, attempts have been made to apply the semi-melt processing method to eliminate the adverse effects of the conventional method (Japanese Patent Publication No. 58-5748 and Japanese Patent Publication No. 2-51703). Gazette).

[0007]

DISCLOSURE OF THE INVENTION However, considering the contents described in these publications, as the morphology of the alloy material in the coexistence of solid and liquid, the modified dendritic solid particles in a dispersed state are dispersed and suspended in the liquid phase. It is specified that the state or the primary particles are kept separated from each other by the liquid phase matrix so that the interconnected dendritic structure is not formed.

Therefore, the material to be processed is a hypoeutectic alloy. This is because, in the case of a hypereutectic alloy, the primary crystals do not form dendrites during the solidification process. That is, in the case of a hypereutectic Al-Si alloy, first, free Si is used as a primary crystal.
Is deposited, and thereafter, eutectic solidification of Al and Si proceeds, and a clear dendritic structure is not formed. Therefore, hypereutectic A
It is in an unknown situation as a semi-melt processing method for 1-Si alloy materials.

The present invention has been made in view of the above circumstances, and is a semi-melt processing method by which a hypereutectic Al-Si alloy material is smoothly processed in a solid-liquid coexistence region to obtain a good quality product. It is intended to provide.

[0010]

The semi-melt processing method (invention of claim 1) of the present invention, which has achieved the above object, is Al-Si.
When the hypereutectic Al-Si alloy material whose Si content in the binary alloy is equal to or more than the eutectic composition is induction-heated into the solid-liquid coexistence region to perform the forming process, the heating of the material is performed at the central part. The gist is to finish and process when the solid phase ratio reaches 0.65 to 0.80. Further, the semi-melt processing method of the invention of claim 2 is based on the structure of claim 1 and is characterized in that the material after heating is filled into a mold of a molding machine in a depressurized state of 500 Torr or less. Is.

The present invention will be further described in detail. The present invention was made based on the findings obtained as a result of earnest research on how to solve the problems peculiar to the semi-melt processing method. First, the invention of claim 1 will be described. When processing in the solid-liquid coexistence region, the deformation characteristics of the material greatly differ depending on the ratio of the solid phase and liquid phase of the material (hereinafter, this ratio is grasped and displayed as "solid phase ratio"), so processing starts There is a problem that the solid phase ratio at that time must be made appropriate according to the type of material.

That is, if the solid fraction falls outside the proper range and becomes low, inhomogeneous distribution of the liquid phase inevitably occurs in the material in the process of heating to the temperature corresponding to this solid fraction. . When such a non-uniform distribution of the liquid phase locally occurs, the material can no longer maintain the shape of the solid phase region. Therefore, if the material in such a state is filled in the mold, the solid phase and the liquid phase are non-uniformly distributed inside the filled material. Further, the contact surface (boundary surface) between the solid phase and the liquid phase becomes a so-called molten boundary defect. Therefore, a good quality processed product cannot be obtained. On the other hand, if the solid fraction goes out of the proper range and becomes high, the material becomes hard to flow. In this case, a large processing force is required to fill the material into the mold, but this does not make sense to adopt the semi-melt processing method.

Therefore, the present inventor has conducted earnest experiments to find an appropriate range of the solid fraction at the start of processing when a hypereutectic Al-Si alloy is used as a raw material. First, regarding A390, which is one of the typical hypereutectic Al-Si alloys, the already proposed technique, that is, the technique for accurately estimating the solid fraction in the solid-liquid coexistence region (Japanese Patent Application No. 5-269648) is used. Then, the relationship between the temperature and the solid fraction was obtained as shown in FIG.

Next, A39 having a diameter of 58 mm and a length of 36 mm
High frequency heating of 0 material. Specifically, in the ceramic sleeve 2 of the molding machine shown in FIG.
High frequency heating at Hz. At that time, in order to prevent a temperature drop due to heat conduction from the lower surface layer portion of the material 1 to the ceramic sleeve 2, a previously proposed technique (Japanese Patent Application No. Hei 5-273070).
No.) was used, and a pure Al plate having a thickness of about 1.5 mm was laid on a portion corresponding to an area where these two contact each other. As the temperature of the raw material 1 during heating, the temperature of the central portion was measured with a sheath thermocouple.

As a result, the temperature at the center of the material 1 is about 56.
Up to 5 ° C, that is, until the solid fraction is about 0.65, although the material 1 is in a solid-liquid coexisting state, no significant non-uniform distribution of the solid and liquid phases occurs, and the appearance is almost the same. It was confirmed that the shape in the solid-phase region could be maintained and that no significant shape collapse occurred.

The inventor of the present invention has also found that an Al-30% Si-4% Cu alloy having a higher Si content than A390 and A390.
Al-9% Si-3% Cu-1 with lower Si content than
For each of the% Mg, the relationship between the temperature and the solid fraction was examined in the same manner as above. The results are shown in FIGS. 3 and 4, respectively. As is clear from a comparative examination of FIGS. 2, 3 and 4, the solid fraction is 0.6 for all materials.
When it is about 0.8, there is no great difference in the corresponding temperature range, in other words, when the solid phase ratio is in the range of about 0.6 to 0.8, the solid phase and the liquid in these materials are It can be seen that the phase behavior is similar.

Further, in a hypereutectic Al-Si alloy material having a Si content equal to or more than the eutectic composition equivalent (about 11%), the solid phase ratio is up to about 0.65. It was confirmed that there was no significant non-uniform distribution of the liquid phase and the material could maintain its shape in the solid phase region without any significant shape loss. Therefore, if the material in such a state is filled in the mold, the distribution of the solid phase and the liquid phase becomes relatively uniform in the cross section of the molded product, and defects such as a water boundary can be suppressed, which is preferable in terms of quality. Become. On the other hand, if the solid fraction is too high,
Since the fluidity of the raw material decreases and it becomes difficult to fill the material into the mold, it is usually desirable to set it to 0.8 or less.

Based on the above experimental results, as described above, as the semi-melt processing method according to the invention of claim 1, a hypereutectic Al--Si alloy material having a Si content equal to or more than the eutectic composition is solidified. When performing induction heating in the liquid coexistence region for molding,
When the material is heated, the solid fraction in the central portion is 0.65 to 0.
It is possible to adopt a peculiar means for finishing and processing when the range of 80 is reached.

Next, the invention of claim 2 will be described.
Another problem in processing in the solid-liquid coexistence region is a unique problem due to the fact that the heat of the material itself before starting the processing is lower than that of the molten metal in the casting method. That is, in order to smoothly fill the material having a small amount of heat in the mold, at least the filling operation needs to be performed at a relatively high speed. Unless filling at a relatively high speed, the contact time between the material and the mold becomes longer, and as a result, the temperature of the material further decreases, and the material solidifies before filling the entire mold,
This is because a good molded product cannot be obtained. Further, the solid phase and the liquid phase of the material flow nonuniformly when the material is filled in the mold, resulting in a nonuniform distribution of the solid phase and the liquid phase inside the molded article, that is, so-called macro deviation, which is not preferable.

On the other hand, since such a quick filling operation is required, there is a peculiar problem that air is easily trapped inside the material during filling. When such entrainment of air occurs, voids are formed in the surface layer portion or inside of the material after filling, causing defects (blister) after heat treatment and deteriorating mechanical properties, which is not preferable in terms of quality.

[0021] Therefore, the present inventor has conducted extensive research to find out how to suppress the entrainment of air into the material during such rapid filling to the extent that the quality is not adversely affected. It was First, the following experiment was carried out based on the idea that it is possible to prevent the entrainment of air during filling if the interior of the mold is evacuated in advance and the pressure is reduced before the filling operation. FIG. 1 is a schematic view showing a mold part of a molding machine, and a molded product has fin portions Ef and bushes on both sides with a disc portion Ed interposed therebetween, as is apparent from a sectional shape shown by a broken line in an elliptical frame F. It is a component having a portion Eb.

When the heating of the material 1 in the solid-liquid coexisting region is completed, the plunger tip 3 advances rapidly. When this chip 3 passes a predetermined position, suction of air in the mold cavity 5 is started from the exhaust port 4 provided in the mold.
Immediately before the material 1 passes through the exhaust groove 6 and reaches the exhaust port 4, the open / close pin 7 is moved to block the communication between the exhaust groove 6 and the exhaust port 4. In this way, the material 1 can be filled into the mold while the pressure inside the mold is reduced.

When sucking air, specifically, a vacuum pump (not shown) and an exhaust port 4 are connected via a steel tank (not shown), and the inside of the tank is preliminarily set to 1 by the vacuum pump.
Reduce the pressure to about Torr. Then, when the valve of the tank is opened when the plunger tip 3 has passed the predetermined position, the air in the mold cavity 5 passes through the exhaust port 4,
It was designed to be quickly sucked into the tank. Further, if only suction is performed from the exhaust groove 6 provided on the die mating surface, air will enter into the die cavity 5 from the push pin portion 8 or the like on the back surface of the die, causing a problem in the suction effect. Therefore, the chamber 9 is attached to the extruded portion to form a seal structure,
The suction effect can be maintained by preventing the invasion of air. In addition, 10 and 11 are die plates.

When performing a molding experiment in the solid-liquid coexistence region using A390, which is one of the hypereutectic Al-Si alloys, as the material, the evacuation time is changed by changing the opening / closing timing of the valve of the tank for sucking air. It was adjusted so that the degree of vacuum in the mold could be changed. As a result, about 5
It was confirmed that if the pressure was reduced to 00 Torr, entrainment of air during filling could be suppressed, and a molded product of good quality could be obtained. Although A390 was used as the material, the Si content is equivalent to the eutectic composition (about 11%) as in the invention of claim 1.
It is effective for all the hypereutectic Al-Si alloys as described above.

Based on the above experimental results, in the semi-melt processing method according to the invention of claim 2, a hypereutectic Al-Si alloy material having a Si content equal to or more than the eutectic composition is used in the solid-liquid coexistence region. When the induction heating is performed and the forming process is performed, the heating of the material is finished when the solid fraction at the central portion reaches the range of 0.65 to 0.80, and the material is depressurized to 500 Torr or less. It is possible to adopt a unique means of filling the mold of the molding machine in.

As the exhaust means for reducing the pressure, in addition to the experimental example described above, for example, as shown in FIG. 1, air is exhausted only from the fin portion Ef where air is easily trapped, and the die mating surface is molded with a die. A local exhaust means such as a normal air vent section may be used. Further, the above-mentioned pre-depressurizing means in the mold can be applied to the forming process in the solid-liquid coexistence region of Al alloy, Mg alloy, etc. other than the hypereutectic Al—Si alloy.

[0027]

According to the invention of claim 1, when forming a hypereutectic Al-Si alloy material in the solid-liquid coexistence region, the heating is terminated at the stage where the solid phase ratio becomes 0.65 immediately before the start of the processing. Since it is filled in the mold, no significant non-uniform distribution of solid and liquid phases occurs. Further, the material can maintain the shape in the substantially solid phase region, and the shape is not significantly deformed. Therefore, if such a material is molded, the distribution of the solid phase and the liquid phase becomes relatively uniform in the cross section of the molded product, and it is possible to suppress the occurrence of defects such as the molten metal boundary. Further, when the above-mentioned material is molded and processed, the solid fraction immediately before the processing is started is controlled to be 0.8 or less, so that the fluidity of the material can be prevented from decreasing.
Compared to molding in the solid phase, it requires less processing force, and the advantages of semi-melt processing can be fully utilized.

According to the second aspect of the invention, the inside of the mold is depressurized before the mold is filled with the material. Therefore, in the solid-liquid coexistence region, it is possible to completely suppress the entrapment and trapping of air into the material, which is likely to occur because a quick filling operation is required. As a result,
Occurrence of defects (blister) and deterioration of mechanical properties after heat treatment can be prevented.

[0029]

【Example】

(Example 1) A390 material having a diameter of 58 mm and a length of 36 mm was subjected to high-frequency heating at 2000 Hz in a ceramic sleeve having an Al plate of a die casting machine laid on the bottom, and the center temperature was about 565 ° C (solid phase ratio about 0.65). ) Was reached, heating was terminated, and the plunger was rapidly operated (1 m / s) to fill the material into the mold. A photograph of the macrostructure of the cross section of the obtained molded product is shown in FIG. A photograph of the microstructure of the disk portion (corresponding to Ed in FIG. 1) is shown in FIG. It is clear from FIG. 5 that the solid phase and the liquid phase are relatively evenly distributed in the cross section of the molded product, and from FIG. 6 that the microstructure is also sound.

(Comparative Example 1) The same material as in Example 1 was subjected to high frequency heating in a ceramic sleeve of a die casting machine having the same structure, and the center temperature was about 571 ° C (solid phase ratio about 0.5).
When, the heating was terminated and the plunger was quickly operated to fill the material into the mold. A photograph of the macrostructure of the cross section of the obtained molded product is shown in FIG. 7. A photograph of the microstructure of the disc portion is shown in FIG. It can be seen from FIG. 7 that the solid phase and the liquid phase in the cross section of the molded product are non-uniformly distributed, and from FIG.

(Embodiment 2) The same material as that of Embodiment 1 is subjected to high frequency heating in a ceramic sleeve of a die casting machine having the same structure, and the center temperature is about 562 ° C (solid phase ratio about 0.6).
When the temperature reaches 8), the heating is terminated and the plunger is quickly operated (1 m / s), and the material is removed at about 480 Torr.
It was filled in a mold whose pressure was reduced to 1. FIG. 9 is a photograph showing the state of the cross section of the obtained molded product after color check.
As is clear from this figure, no defects such as pores are found in the cross section of the molded product.

(Comparative Example 2) The same material as in Example 1 was subjected to high frequency heating in a ceramic sleeve of a die casting machine having the same structure, and the center temperature was about 562 ° C (solid phase ratio about 0.6).
When 8) was reached, the heating was terminated, the plunger was quickly operated, and the material was filled into the mold that was not depressurized by providing only the air vent portion on the mold mating surface. FIG. 10 is a photograph showing the state of the cross section of the obtained molded product after color check. From this figure, a large void is formed at the tip of the fin portion (corresponding to Ef in FIG. 1), and defects are recognized throughout the cross section.

[0033]

Since the semi-melt processing method of the present invention is constructed as described above, when the hypereutectic Al-Si alloy material is formed in the solid-liquid coexistence region, the solid phase and liquid phase in the cross section are It is possible to manufacture a machined part having a uniform distribution and no defects such as a molten metal boundary with a relatively small machining force. Further, it is possible to manufacture a good-quality processed part by eliminating the risk of occurrence of defects (blister) and deterioration of mechanical properties after heat treatment.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an essential part showing a mold part of a molding machine for carrying out the method of the present invention.

FIG. 2 is a diagram showing a relationship between a temperature and a solid phase ratio in a solid-liquid coexistence region for a hypereutectic Al—Si alloy A390.

FIG. 3 is a diagram showing a relationship between a temperature and a solid phase ratio in a solid-liquid coexistence region for a hypereutectic Al-30% Si-4% Cu alloy.

FIG. 4 is a diagram showing a relationship between a temperature and a solid phase ratio in a solid-liquid coexistence region for a hypereutectic Al-9% Si-3% Cu-1% Mg alloy.

FIG. 5 is a photograph showing a macrostructure of a cross section of a molded product obtained by carrying out the method of the invention of claim 1.

FIG. 6 is a photograph showing a microstructure of a disk portion of the molded product.

FIG. 7 is a photograph showing a macrostructure of a cross section of a molded product obtained in (Comparative Example 1).

FIG. 8 is a photograph showing a microstructure of a disk portion of a molded product obtained in (Comparative Example 1).

FIG. 9 is a photograph showing a state after a color check of a molded product obtained by carrying out the method of the invention as claimed in claim 2.

FIG. 10 is a photograph showing the state of the molded product obtained in (Comparative Example 2) after color check.

[Explanation of symbols]

 1 Material 2 Ceramics Sleeve 3 Plunger Chip 4 Exhaust Port 5 Mold Cavity 6 Exhaust Groove 7 Opening Pin 8 Extruding Pin 9 Chamber 10 and 11 Die Plate

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[Submission date] May 27, 1996

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FIG. 1 is a schematic cross-sectional view of an essential part showing a mold part of a molding machine for carrying out the method of the present invention.

FIG. 2 is a diagram showing a relationship between a temperature and a solid phase ratio in a solid-liquid coexistence region for a hypereutectic Al—Si alloy A390.

FIG. 3 is a diagram showing a relationship between a temperature and a solid phase ratio in a solid-liquid coexistence region for a hypereutectic Al-30% Si-4% Cu alloy.

FIG. 4 is a diagram showing a relationship between a temperature and a solid phase ratio in a solid-liquid coexistence region for a hypereutectic Al-9% Si-3% Cu-1% Mg alloy.

FIG. 5 is a drawing imitating a photograph showing a macrostructure of a cross section of a molded product obtained by carrying out the method of the invention of claim 1.

FIG. 6 is a diagram simulating a photograph showing a microstructure of a disk portion of the molded product.

FIG. 7 is a diagram simulating a photograph showing a macrostructure of a cross section of a molded product obtained in (Comparative example 1).

FIG. 8 is a diagram simulating a photograph showing a microstructure of a disk portion of a molded product obtained in (Comparative Example 1).

FIG. 9 is a drawing imitating a photograph showing a state after a color check of a molded product obtained by carrying out the method of the second aspect of the present invention.

FIG. 10 is a model imitating a photograph showing a state of the molded product obtained in (Comparative Example 2) after color check.

[Explanation of symbols] 1 Material 2 Ceramics sleeve 3 Plunger tip 4 Exhaust port 5 Mold cavity 6 Exhaust groove 7 Opening pin 8 Extruding pin part 9 Chamber 10, 11 Die plate

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Claims (2)

[Claims] 1. A hypereutectic Al-Si alloy material having a Si content in the Al-Si binary alloy equal to or more than the eutectic composition is induction-heated in a solid-liquid coexistence region to perform a forming process. The solid phase rate at the center of the
A semi-melt processing method for a metal material, characterized in that it is finished and processed when the range reaches 0.80. 2. The material which has been heated is heated to 500 Torr.
The semi-melt processing method according to claim 1, wherein the mold is filled in a mold of a molding machine in the following reduced pressure state.