JP3555485B2 - Rheocasting method and apparatus - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a rheocast method for casting a molten metal in a semi-solid state and a device therefor.
[0002]
[Prior art]
The rheocast method is a method in which a primary crystal (a crystal that solidifies first) is spheroidized in a process of cooling a molten metal, and is cast in a semi-solid state in which a solid phase and a liquid phase coexist. Here, in order to make the primary crystal spheroidized in the process of cooling the molten metal, a method of keeping the molten metal at an isothermal temperature near the temperature at which the molten metal starts to solidify (liquidus temperature), There is a method in which the primary crystal is sheared and rounded by stirring the molten metal. However, in either method, it is necessary to slowly cool the molten metal so as not to cause a temperature difference of the molten metal in the container, so that there is a problem that the grain size of the primary crystal increases and the tensile strength of the cast product decreases. .
[0003]
A technique for solving the above-described problem to some extent is described in Japanese Patent Application Laid-Open No. 8-243707. In this rheocast method, as shown in FIG. 8, a water jacket 2w is provided on a side wall of a container 2 for storing the molten metal so that the molten metal can be rapidly cooled, and the molten metal in the container can be stirred by an ultrasonic horn 4. It was done. This makes it possible to make the primary crystal relatively small.
[0004]
[Problems to be solved by the invention]
However, according to the conventional rheocasting method, since the molten metal in the container is stirred by the ultrasonic horn 4, stirring is relatively well performed when the molten metal is in a liquid state, but solidification proceeds and the viscosity of the molten metal increases. When the height is increased, the effect of the agitation reaches only the vicinity of the ultrasonic horn 4. For this reason, the molten metal at a position away from the ultrasonic horn 4, that is, the molten metal near the wall surface of the container is hardly agitated, so that the molten metal in that portion solidifies in a dendritic state in a state close to nature and spheroidizes the primary crystals. It is difficult. Furthermore, while the vicinity of the wall surface of the container is rapidly cooled by the cooling water, the central portion of the container away from the wall surface is cooled relatively slowly. For this reason, the temperature difference of the molten metal between the vicinity of the wall surface of the container and the central portion becomes large, and the particle size of the primary crystal becomes unstable.
As a result, there is a problem that the semi-molten metal does not form a uniform slurry in the conventional rheocast method.
[0005]
The present invention has been made in order to solve the above problems, and a technical problem of the present invention is to efficiently stir a molten metal in a container and efficiently shear a primary crystal of the molten metal to obtain fine particles. It is to make it spherical.
[0006]
[Means for Solving the Problems]
The above-mentioned problem is solved by the invention of each claim.
The invention according to claim 1 is a rheocasting method for casting a molten metal in a semi-solid state, wherein the tip of a column-shaped ultrasonic horn is immersed from above into the molten metal stored in an open-topped container. Step and while applying vibration to the molten metal by the ultrasonic horn, while stirring the molten metal so that the molten metal flows substantially in the axial direction of the ultrasonic horn, the primary crystal of the molten metal with the ultrasonic horn. And spheroidizing by shearing.
According to the present invention, since the ultrasonic vibration is applied to the molten metal, the primary crystal of the molten metal to which the vibration is applied can be efficiently sheared to be finely spherical. Further, since the molten metal is stirred so as to flow substantially in the axial direction with respect to the ultrasonic horn, ultrasonic vibration can be evenly applied to the molten metal in the container. Further, since the temperature difference of the molten metal is hardly generated in the container due to the stirring, the semi-molten metal becomes a uniform slurry.
[0007]
The invention according to claim 2 is characterized in that the molten metal is stirred by using an electromagnetic force so that the molten metal flows substantially in the axial direction of the ultrasonic horn.
The invention according to claim 3 is characterized in that the ultrasonic horn is reciprocated in the axial direction so that the molten metal flows substantially in the axial direction of the ultrasonic horn, and the molten metal is stirred.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
(First embodiment)
Hereinafter, a rheocast method and an apparatus therefor according to a first embodiment of the present invention will be described with reference to FIGS. This embodiment utilizes the rheocasting method according to the present invention when manufacturing underbody parts of an automobile. FIG. 1 shows a main part of an apparatus (rheocasting apparatus) for performing the rheocasting method. A longitudinal section is shown.
[0009]
The rheocast device 10 includes a heat-resistant container 12 for storing about 3 kg of molten aluminum (hereinafter, referred to as molten metal). The heat-resistant container 12 is an open-top container having a bottomed cylindrical shape, around which an electromagnetic coil 14c of an electromagnetic stirring device 14 for stirring the molten metal in the heat-resistant container 12 is mounted. The inner diameter of the heat-resistant container 12 is set to about 120 mm. That is, the electromagnetic stirring device 14 corresponds to the stirring means of the present invention.
[0010]
An ultrasonic oscillator (not shown) for applying ultrasonic vibration of 18 kHz and 0.6 kW to the molten metal in the heat-resistant container 12 is installed above the heat-resistant container 12. Of the horn 16 is immersed in the molten metal by about 20 mm. The horn 16 is formed in a cylindrical shape by ceramic, and its outer diameter is set to about 40 mm. That is, the horn 16 of the ultrasonic oscillation device corresponds to the vibration applying means of the present invention.
The components of the molten metal stored in the heat-resistant container 12 are 7.34% of Si, 0.01% or less of Cu, 0.33% of Mg, 0.18% of Fe, and 0.19% of Ti, and the rest is Al.
[0011]
Next, the rheocast method according to the present embodiment will be described.
First, about 3 kg of the above-mentioned molten metal is supplied to the heat-resistant container 12. Here, the temperature of the molten metal when supplied to the heat-resistant container 12 is about 620 ° C. When the molten metal is supplied to the heat-resistant container 12, the electromagnetic stirring device 14 is driven to agitate the molten metal, and the horn 16 of the ultrasonic oscillator is immersed in the molten metal, so that ultrasonic vibration of 18 kHz and 0.6 kW is generated. Added.
In this state, the molten metal is cooled at a rate of about 0.6 ° C./sec until the temperature of the molten metal reaches 582 ° C. As a result, the molten metal is semi-solidified into a uniform slurry.
[0012]
The slurry-like semi-solid metal is transferred to a high-pressure caster (not shown) and filled into a mold cavity at an injection speed of 0.2 m / sec.
After the cast product is removed from the mold, the T6 process is performed. Note that the T6 treatment is a heat treatment of aluminum, which means that after performing a solution treatment, an aging treatment is performed at a temperature equal to or higher than room temperature by heating.
The conditions of the T6 treatment according to the present embodiment are as follows: the heating temperature and the heating time in the solution treatment are 530 ° C. for about 5 hours, the cooling is a quenching method using water, and the heating temperature and the heating time in the aging treatment are 140 ° C.・ About 4 hours.
[0013]
FIG. 2 shows a micrograph of the product I that has been cast by the rheocast method according to the present embodiment and then subjected to T6 treatment. FIG. 3 is a photomicrograph of a product II that was cast under the same conditions as the rheocast method according to the present embodiment without applying ultrasonic vibration, and further subjected to T6 treatment.
FIG. 4 is a bar graph showing the size of primary crystals of Product I and Product II, wherein colored bars represent Product I and uncolored bars represent Product II.
As can be seen from FIGS. 2 to 4, the primary crystal is effectively refined by the ultrasonic vibration.
[0014]
FIG. 5 is a graph showing the tensile strength applied to the test piece and the elongation of the test piece. ● indicates data when the product I was used as the test piece, and ○ indicates data when the product II was used as the test piece. . Since the primary crystal of the product I is smaller than that of the product II, it is considered that the tensile strength is improved by that much.
[0015]
Next, in order to investigate the influence of stirring of the molten metal on the primary crystal, the molten metal was semi-solidified (after cooling to 582 ° C.) by the method according to the present embodiment, and the semi-molten metal was solidified as it was. Microstructures of Sample I and Sample II, in which the molten metal was made into a semi-solidified state only by applying ultrasonic vibration without stirring the molten metal, and then the semi-molten metal was directly solidified, were examined with a microscope. FIG. 6 shows the result of the microstructure examination, and shows the primary crystal grain size at each part (position a, position b, position c, and position d) of Samples I and II. Here, ● is the data of sample I, and ○ is the data of sample II.
[0016]
That is, in both samples I and II, the primary crystal is refined in the vicinity of the horn 16 (position a) of the ultrasonic oscillator, but in the sample II, the portion away from the horn 16 (position b, position c, At the position d), the primary crystal has a large particle size. On the other hand, in the sample I, the primary crystal is also refined even at a portion (position b, position c, and position d) apart from the horn 16. Therefore, while the ultrasonic vibration is uniformly applied to the molten metal in the heat-resistant container 12 by stirring the molten metal, the ultrasonic vibration is applied only to the molten metal near the horn 16 unless the molten metal is agitated. I understand.
[0017]
As described above, according to the rheocast method according to the present embodiment, since ultrasonic vibration is applied to the molten metal, the primary crystal of the molten metal to which the vibration is applied is efficiently sheared and finely spheroidized. Can be. Furthermore, since the molten metal is stirred by the electromagnetic stirring device 14 so that the molten metal always comes into contact with the horn 16, ultrasonic vibration can be evenly applied to the molten metal in the container 12. Further, since the temperature difference of the molten metal is hardly generated in the container due to the stirring, the semi-molten metal becomes a uniform slurry. That is, since the primary crystal of the molten metal is finely spheroidized and the semi-molten metal becomes a uniform slurry, the tensile strength (elongation) of a cast product formed by casting the semi-molten metal is improved.
[0018]
(Second embodiment)
Hereinafter, a rheocast method and an apparatus therefor according to the second embodiment of the present invention will be described with reference to FIG.
The rheocast device 20 according to the present embodiment is different from the rheocast device 10 according to the first embodiment in that the molten metal in the heat-resistant container 12 is stirred by the electromagnetic stirrer 14, whereas the horn 26 of the ultrasonic oscillator is used. Is moved up and down to agitate the molten metal in the heat-resistant container 22.
Thereby, the mechanism for stirring the molten metal becomes simple, and the equipment cost can be reduced.
[0019]
In the first embodiment and the second embodiment, after the molten metal is supplied to the heat-resistant container, ultrasonic vibration is immediately applied to the molten metal. Ultrasonic vibration may be applied after the molten metal has cooled to a temperature about 10 ° C. higher than the linear temperature.
The embodiments of the present invention have been described above. It should be noted that the embodiments of the present invention have the following technical matters in addition to the technical matters described in the claims. .
(1) In the reocast device according to claim 2,
The stirrer stirs the molten metal using electromagnetic force.
(2) In the rheocast device according to claim 2,
The stirrer stirs the molten metal by moving the vibration imparting means inside the molten metal.
[0020]
【The invention's effect】
According to the present invention, since the primary crystal of the molten metal is finely spheroidized and the semi-molten metal becomes a uniform slurry, the tensile strength of the cast product formed by casting the semi-molten metal is improved, Product quality can be improved.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a main part of a rheocast device according to a first embodiment of the present invention.
FIG. 2 is a micrograph of a product cast by a rheocast method according to the first embodiment of the present invention.
FIG. 3 is a photomicrograph of a product cast by a rheocast method after cooling a molten metal to a semi-molten state without applying ultrasonic vibration.
FIG. 4 shows primary crystals of a product cast by a rheocast method according to the first embodiment of the present invention and a product cast by a rheocast method by cooling a molten metal to a semi-molten state without applying ultrasonic vibration. 5 is a graph comparing the magnitudes of.
FIG. 5 shows tensile strength between a product cast by a rheocast method according to the first embodiment of the present invention and a product cast by a rheocast method by cooling a molten metal to a semi-molten state without applying ultrasonic vibration. It is the graph which compared this.
FIG. 6 is a graph showing the size of primary crystals in each part of a sample (FIG. A). It is a figure showing each part which measured the size of the primary crystal (Drawing B).
FIG. 7 is a longitudinal sectional view of a main part of a rheocast device according to a second embodiment of the present invention.
FIG. 8 is a longitudinal sectional view of a main part of a conventional rheocast device.
[Explanation of symbols]
12 heat-resistant container 14 electromagnetic stirring device (stirring means)
16 Horn of ultrasonic oscillator (vibration applying means)

Claims (3)

A rheocast method of casting molten metal in a semi-solid state ,
A step of immersing the tip of the columnar ultrasonic horn from above into the molten metal stored in the open top container,
With applying vibration by the ultrasonic horn against the melt, while the melt is stirring the molten metal to flow in a generally axial direction of the ultrasonic horn, and shearing the primary crystal of the molten metal in the ultrasonic horn A step of spheroidizing;
The rheocast method characterized by having .   The rheocast method according to claim 1,
  A rheocast method characterized by agitating the molten metal using electromagnetic force so that the molten metal flows substantially in the axial direction of the ultrasonic horn.   The rheocast method according to claim 1,
A rheocasting method wherein the ultrasonic horn is reciprocated in the axial direction so that the molten metal flows substantially in the axial direction of the ultrasonic horn, and the molten metal is stirred.

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