JP2008200692A - Casting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a casting method by which nucleation is promoted, and a solidified crystal structure is easily refined to further improve strength and toughness by applying ultrasonic vibration to a molten metal. <P>SOLUTION: In the casting method, the application of ultrasonic vibration in an extremely short time is started to a supercooled region in the non-applied state of the ultrasonic vibration in a molten metal, so as to promote nucleation at a stretch. The molten metal is composed of an aluminum alloy, and the dendrite of aluminum, Si and an AlSiFe intermetallic compound are crystallized out. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a casting method in which ultrasonic waves are added to a molten metal to refine a solidified crystal structure.

The solidified structure is generally determined by the cooling rate. When the thickness of the product is different, such as in a cast product, the solidified structures are greatly different, and the thin-wall rapidly cooled portion has a fine chill structure. The thick part becomes the final solidified part, and the solidified structure becomes coarse and sink defects occur.
As shown in Patent Document 1 and Non-Patent Document 1 shown below, it is conventionally possible to refine the solidified crystal structure by applying ultrasonic vibration at a temperature sandwiching the liquidus temperature during solidification. It is known.
The inventors have also proposed in Japanese Patent Application No. 2006-036967 that nucleation is promoted and miniaturized even if ultrasonic vibration is applied at a temperature higher than that at which the temperature drops to the liquidus temperature.
Patent Publication 2004-209487 Casting Engineering 78 (2006) 2, 65-70

According to the invention of the previous application, it is necessary to add ultrasonic vibration for about 1 minute to refine the solidification structure. When there is too much molten metal, the casting quality can be stabilized and sufficient ultrasonic vibration can be performed. There was no problem.
In view of such circumstances, the present invention is a casting method in which nucleation occurs at a stretch and the solidified crystal structure can be refined by adding ultrasonic vibration for an extremely short time compared to the conventional case because the molten metal is in a supercooled state. The purpose is to provide.

This supercooling phenomenon is less likely to occur by solidifying while applying ultrasonic vibration.
The present invention is based on the knowledge that, when this supercooling phenomenon occurs, by adding ultrasonic vibration, solidification starts at once in a very short time and easily produces a finely solidified alloy.

  The casting method of the invention 1 is characterized in that the application of ultrasonic vibration is started in a supercooling region in a state where the ultrasonic vibration of the molten metal is not added.

Invention 2 is characterized in that in the casting method of Invention 1, the addition of the ultrasonic vibration is only in the supercooling region.
Invention 3 is characterized in that, in the casting method of Invention 1 or 2, the molten metal is an aluminum alloy, and aluminum dendrite, Si or AlSiFe intermetallic compound is crystallized in the primary crystal.

According to the invention 1, the addition of ultrasonic vibration for about 10 seconds can achieve miniaturization, and the above problems can be largely solved.
By applying the invention 2 when the cooling rate of the alloy or the molten metal having a short supercooling region in the non-addition state is high, the same effect as that of the invention 1 can be exhibited.
According to the invention 2, the effects of the inventions 1 and 2 can be maximized. If the aluminum alloy is supercooled during solidification, the primary crystal does not crystallize at a temperature lower than the liquidus temperature. When ultrasonic vibration is applied during the supercooling of the aluminum alloy, primary dendrites of aluminum, Si and AlSiFe intermetallic compounds are crystallized finely at once. AlSiFe intermetallic compounds are disliked during sand-type solidification because they are coarsely crystallized and brittle compared to mold solidification. This cannot be miniaturized even by electromagnetic stirring, and can be miniaturized by adding ultrasonic vibration. And since supercooling at the time of crystallization is large, it is because it can be made minute at a stretch by adding ultrasonic vibration at the time of this supercooling, and adding for a short time.

  12 to 16 show examples of casting apparatuses used to carry out the present invention.

  The changes in the supercooling degree, the applied temperature of ultrasonic vibration, the loading time, and the structure of the aluminum alloy used in this experiment were summarized. The size in this photograph was expressed as an equivalent circular diameter with a gray coarse plate-like intermetallic compound without vibration addition of the Al-12% Si-4% Fe alloy in FIG.

FIG. 1 is a graph showing the change in the cooling curve of an Al—X% Si-4% Fe alloy due to the addition of ultrasonic vibration.
As a result, in the Al-X% Si-4% Fe alloy, an AlSiFe intermetallic compound crystallizes as the primary crystal. At this time, even if the cooling is as much as sand casting, it is overcooled. However, when ultrasonic vibration is applied to solidify, there is almost no overcooling. It is thought that crystals are crystallized at once with the re-brightening phenomenon by adding ultrasonic vibration during the general cooling of the solidification. In this case, it was found that fine granulation can be expected with addition of ultrasonic vibration for only a few seconds.

  FIG. 2 is a structural photograph of cooling an Al-6% Si-4% Fe alloy in a crucible. It is clear that there is a structure of crucible cooling of an Al-6% Si-4% Fe alloy, a gray coarse plate-like intermetallic compound.

  FIG. 3 is a structural photograph showing the effect of applying ultrasonic vibration in an undercooled state in an Al-6% Si-4% Fe alloy. This shows the structure of the central part of the ingot when the liquidus temperature of the Al-6% Si-4% Fe alloy is 690 ° C, which is supercooled at 690 ° C, and the ultrasonic vibration is performed for a short time of 10 seconds at 680 ° C. It is. It is clear that the primary crystal AlSiFe intermetallic compound is finely granular.

  FIG. 4 is a structural photograph of cooling an Al-12% Si-4% Fe alloy in a crucible. The structure when the Al-12% Si-4% Fe alloy is cooled with a crucible without adding ultrasonic vibrations has a gray coarse plate-like intermetallic compound as shown in FIG.

FIG. 5 is a structural photograph when an ultrasonic vibration is applied to an Al-12% Si-4% Fe alloy at a subcooling degree of 2 ° C. for 10 seconds. It is the photograph of the ingot center part structure | tissue which added the ultrasonic vibration for 10 seconds at 680 degreeC which the liquidus temperature of the Al-12% Si-4% Fe alloy was supercooled 2 degreeC at 681.7 degreeC.
It shows that the primary crystal AlSiFe intermetallic compound is finely granular.

  FIG. 6 is a structure photograph of cooling an Al-18% Si-4% Fe alloy in a crucible. It is the structure | tissue photograph which crucible cooled Al-18% Si-4% Fe alloy, without adding ultrasonic vibration. Gray coarse lump indicates that an intermetallic compound is present, and dark gray is a Si grain, where Al-Si melt and primary intermetallic compound are crystallized later.

  FIG. 7 is a micrograph of an Al-18% Si-4% Fe alloy with a supercooling degree of 10 ° C. and a 10 sec ultrasonic vibration. It is the photograph which shows the ingot center part structure | tissue which added the ultrasonic vibration for 10 seconds at 690 degreeC which the liquidus temperature of Al-18% Si-4% Fe alloy was supercooled at 702.4 degreeC and 12 degreeC. . It can be seen that the primary AlSiFe intermetallic compound is slightly finely granular.

  FIG. 8 is a structural photograph of cooling an Al-6% Si alloy in a crucible. This is a typical Al-Si casting alloy and does not contain impurity iron. Even without adding ultrasonic vibration, there is almost no overcooling, and it is only 3 ° C. The organization is a large dendrite organization that protrudes from this screen, and the size is a reference value.

  FIG. 9 is a structural photograph when an Al-6% Si alloy is subjected to supercooling at 2 ° C. and 10 sec ultrasonic vibration. It is the structure | tissue photograph of the ingot center part which added the ultrasonic vibration for 10 seconds for a short time at 622 degreeC which the liquidus temperature was 624 degreeC and 2 degreeC supercooled. The primary crystal α-Al is not dendritic but granular.

  FIG. 10 is a structural photograph of cooling an Al-18% Si alloy in a crucible. It is made without adding ultrasonic vibration, and the dark gray is the primary hypereutectic Si. It shows that it is a coarse lump.

  FIG. 11 is a structural photograph when an ultrasonic vibration is applied to an Al-18% Si alloy at a subcooling degree of 10 ° C. for 10 seconds. The ingot central part structure | tissue by the addition of a short time that ultrasonic vibration is 10 sec at 650 degreeC which liquid phase temperature was 660 degreeC and 10 degreeC supercooled is shown. The primary hypereutectic Si is finely granular.

  FIG. 12 shows an ultrasonic vibration casting apparatus for batch processing of a supercooled molten metal. A hot molten metal is cast into 18 molds and 15 ultrasonic vibration horns are inserted. When the temperature is measured by the thermocouple of 21 and is in a supercooled state, the power is switched on and the vibration generated by the vibration generator of 10 by the output of the high frequency power supply is transferred to the melt of 12 through the 15 ultrasonic vibration horn. Append. In the supercooled molten metal, nucleation occurs at a stretch by ultrasonic vibration for a very short time, and the crystal grains solidify into fine granules.

  FIG. 13 shows an ultrasonic vibration casting apparatus during casting of a supercooled molten metal near the liquidus. Casting is performed when the molten metal cools in a mold such as 17 sand mold or mold and is in a supercooled state just below the liquidus temperature. At this time, the 15 ultrasonic vibration horn is made to vibrate and causes nucleation at the same time as pouring, so that 18 castings in which the crystal grains are solidified into fine granules can be obtained.

  FIG. 14 shows an ultrasonic vibration casting apparatus in a still supercooled state after mold casting. In advance, 15 ultrasonic vibration horns are inserted into a mold such as 17 sand molds or molds. There, 12 hot melts were cast into 15 molds, and after a predetermined time had passed and the system was overcooled, the power supply was switched on and the vibrations generated by 10 vibration generators by the output of the high frequency power supply exceeded 15 It is added to 12 melts through a sonic vibration horn. The melt of the supercooled state in 15 molds produces 18 castings in which nucleation occurs at once in a very short period of ultrasonic vibration and the crystal grains are solidified into fine granules.

  FIG. 15 shows an ultrasonic vibration casting apparatus during continuous casting to a supercooled molten metal near the liquidus. Casting is performed when the molten metal of 12 in the ladle of 11 is cooled to the gate of 13 and is in a supercooled state just below the liquidus temperature. At this time, the 15 ultrasonic vibration horn is kept in a vibrating state and causes nucleation at the same time as pouring, thereby obtaining 16 continuous ingots in which the crystal grains are solidified into fine granules in the 14 water-cooled mold. it can.

  FIG. 16 shows an ultrasonic vibration casting apparatus during continuous casting to a supercooled molten metal near the liquidus in the tundish. When twelve melts in 11 ladle are cooled in 19 tundishes and are in a supercooled state just below the liquidus temperature, pouring is performed. At this time, 15 ultrasonic vibration horns are kept in a vibrating state to cause nucleation at the same time as pouring, and 16 continuous grains in which crystal grains are solidified into fine granules in 14 water-cooled molds through 13 pouring gates. An ingot can be obtained.

Ultrasonic vibration can suppress the occurrence of supercooling during solidification. This is the case of normal cooling, etc., and with water etc., it solidifies to ice at around -2 ° C. Under ultrasonic vibration, nucleation is promoted during solidification, and solidifies almost without overcooling. Moreover, when supercooling has occurred, solidification occurs at once by the addition of ultrasonic vibration. In this case, the effect of miniaturization is also high, and it can be expected to lead to high productivity.
From this point of view, it can be predicted that a microstructure material can be created efficiently and continuously by performing ultrasonic vibration treatment for a short time in a supercooled state during solidification of the aluminum alloy. In the supercooled state, solidification occurs with a slight impact, but since the vibration can be efficiently transmitted to the nucleation at that time, the micromachining is improved, so the supercooled state is only a little, and the vibration control is directly below the liquidus line. Suitable for.

It is known that the strength of the metal increases as the crystal grains become finer. Further, the toughness is improved as the crystal grains become finer. In recent years, energy saving has been demanded by reducing the weight of transportation equipment due to global warming and the depletion of petroleum resources. It is effective to use a lightweight material such as an aluminum alloy or a magnesium alloy that is highly effective in reducing the weight. However, for frames and undercarriage parts of automobiles, materials having high toughness and strength such as forged products of high-tensile steel plates and steel materials have been used. For aluminum alloys, magnesium alloys, etc., further improvements in toughness and strength are required for adaptation to such parts. For this reason, it is possible to achieve high productivity at a low cost by using a technique for creating a microstructure material very easily by simply applying ultrasonic vibration to the supercooled molten metal shown in this patent for a short time. There is a possibility that high strength aluminum alloys can be produced with toughness. This is an undercarriage casting part of complicated shape such as automobiles. Production of billets of finely solidified structure for producing extruded products such as automobile frames is expected.
In Al-6% Si-4% Fe alloy, Al-12% Si-4% Fe alloy, Al-18% Si-4% Fe alloy, Al-18% Si alloy, AlSiFe intermetallic compound or Si Crystallizes out. These have high hardness, high wear resistance, and high temperature strength. For this reason, if it is finely granulated and uniformly dispersed, it can be used on the inner surface of a cylinder of an automobile engine or the like.

The graph which shows the change of the cooling curve by the ultrasonic vibration addition of an Al-X% Si-4% Fe alloy Structure picture of Al-6% Si-4% Fe alloy cooled in crucible Structure photograph showing the effect of adding ultrasonic vibration in an undercooled state in an Al-6% Si-4% Fe alloy Structure photograph of Al-12% Si-4% Fe alloy cooled in crucible Microstructure photograph when supercooling is applied to Al-12% Si-4% Fe alloy with supercooling degree of 2 ℃ for 10sec Structure picture of Al-18% Si-4% Fe alloy cooled in crucible Structure photograph when adding supersonic vibration to Al-18% Si-4% Fe alloy with supercooling degree 10 ° C, 10sec Microstructure picture of Al-6% Si alloy cooling in crucible Structure photograph when adding supersonic vibration to Al-6% Si alloy with supercooling degree 2 ° C and 10 sec. Structure picture of Al-18% Si alloy cooling in crucible Structure photograph when supersonic vibration is added to Al-18% Si alloy at 10 ° C for 10 sec. Ultrasonic vibration casting equipment for batch processing of supercooled molten metal Ultrasonic vibration casting equipment for casting of supercooled molten metal near liquidus Ultrasonic vibration casting equipment in stationary supercooled state after mold casting Ultrasonic vibration casting equipment for continuous casting to supercooled molten metal near the liquidus Ultrasonic vibration casting equipment during continuous casting to supercooled molten metal near liquidus in tundish

Claims (3)

A casting method in which ultrasonic waves are added to a molten metal to refine a solidified crystal structure, and the addition of ultrasonic vibrations is started in a supercooling region in a non-addition state of the ultrasonic vibrations of the molten metal. Method. The casting method according to claim 1, wherein the ultrasonic vibration is added only in the supercooling region. 3. The casting method according to claim 1, wherein the molten metal is an aluminum alloy, and aluminum dendrite, Si or AlSiFe intermetallic compound is crystallized in the primary crystal.