JP5673157B2 - Ultrasonic horn and method for producing aluminum alloy using the same - Google Patents

Description

  The present invention relates to an ultrasonic horn for generating cavitation in molten aluminum and a method for producing an aluminum alloy using the same.

It is known that, when casting aluminum, acoustic cavitation is generated in the molten metal by irradiating the molten metal with ultrasonic waves, thereby obtaining effects such as molten metal degassing and solidification structure control. The ultrasonic irradiation of the molten metal is performed by inserting the tip of an ultrasonic horn into the molten metal flowing through the transfer tub (slagging process) or in the molten metal in the mold (in-mold / sampling process). It is done by communicating inside.
However, in the ultrasonic treatment of molten aluminum, especially when a metal horn composed of an iron alloy, a titanium alloy or the like is used, the horn tip is eroded with the time of ultrasonic irradiation to the molten aluminum. Therefore, the selection of the horn material becomes an important problem when ultrasonic irradiation is performed in the molten aluminum using an ultrasonic horn.

Therefore, an ultrasonic horn formed of ceramic as a material that does not react with molten aluminum and has excellent high-temperature erosion resistance, and an ultrasonic horn whose surface is coated with ceramic have been used.
For example, Patent Documents 1 and 2 report an ultrasonic horn using a silicon nitride-based ceramic (hereinafter referred to as “silicon nitride-based sintered body”) among ceramics. Ultrasonic horns made of these silicon nitride-based sintered bodies are not susceptible to chemical reactions and are difficult to corrode even when ultrasonically treating high temperature and highly corrosive melts such as aluminum melts. It is known to be adaptable.

JP 2004-209487 A JP-T-2006-522562

However, when a silicon nitride-based sintered body is used, chemical reaction with the molten aluminum is difficult to occur, but wettability with the molten aluminum is not good, so acoustic cavitation occurs at the interface between the molten metal and the tip of the ultrasonic horn. . For this reason, the ultrasonic vibration energy transmission efficiency into the molten metal is insufficient, and as a result, the cavitation strength in the molten metal is reduced and the effect of refining the structure is lowered.
Further, a general silicon nitride-based sintered body has a drawback in durability because of low fracture toughness.

  The present invention has been devised in order to solve such problems, and can improve ultrasonic wave treatment by improving wettability with molten aluminum, and enhance fracture toughness and durability. An object of the present invention is to provide an ultrasonic horn made of a silicon nitride sintered body with improved quality and a method for efficiently miniaturizing an aluminum cast structure using the same.

In order to achieve the object, the ultrasonic horn of the present invention is an ultrasonic horn used when irradiating molten aluminum with ultrasonic waves, and Ti is converted to 1 in terms of metal with respect to 100 parts by mass of Si ₃ N ₄ powder. It consists of a silicon nitride-based sintered body obtained by sintering a raw material composite powder containing 0.0 to 10 parts by mass.
Moreover, it is preferable that content of the said Ti is 1.0-6 mass parts in metal conversion.

Note that the above-mentioned starting composite powder, _Si 3 _{N 4} powder and the Ti, and _Si 3 _{N 4} is used usually powder during sintering _Al 2 _O 3, MgO, and _{SiO 2, Y 2 O 3,} La 2 It means a mixed powder of a sintering aid selected from rare earth oxides of O ₃ and CeO.
As a sintering auxiliary agent, 0.5 to 10 parts by mass with respect to 100 parts by mass of Si ₃ N ₄ powder as a main raw material, at least one compound selected from Al ₂ O ₃ , MgO, and SiO ₂ , Y ₂ 0.5 to 10 parts by mass of at least one compound selected from rare earth oxides of O ₃ , La ₂ O ₃ and CeO is preferable.

The ultrasonic horn of the present invention is made of the above-mentioned silicon nitride-based sintered body, and the length L of the horn is set to L = n × λ / 2 and n = It is designed to be an integer of 2, 3 and 4.
The horn is preferably connected to the vibrator via an insert screw.
And the structure | tissue of an aluminum alloy can be refined | miniaturized by irradiating a molten aluminum with an ultrasonic wave using the above ultrasonic horns.
The vibration amplitude when irradiating with ultrasonic waves is preferably in the range of 16 to 60 μm (pp).

  According to the present invention, the ultrasonic horn is composed of a silicon nitride-based sintered body that hardly causes a chemical reaction with the molten aluminum and has improved strength and fracture toughness. Even when irradiating, the cavitation strength in the molten metal can be increased and the refinement of the metal structure can be efficiently enhanced without generating acoustic cavitation at the interface between the molten metal and the tip of the ultrasonic horn. Furthermore, since it has a long life, it will contribute to cost reduction as a result.

The figure explaining the outline of the ultrasonic treatment equipment using the ultrasonic horn The figure explaining the aspect which ultrasonically processes molten aluminum _{Si 3 N 4 - (TiN)} - graph showing the chemical reactions that proceed in pure Al melt system Graph showing the chemical reaction proceeding in the TiN-pure Al molten metal system Graph showing the chemical reaction proceeding in the TiN- (Al-Si) melt system Diagram explaining the outline of the erosion resistance test equipment Sectional drawing explaining the shape of the ultrasonic horn which consists of a silicon nitride base sintered compact Figure showing a form of connecting a horn to a vibrator Sectional drawing explaining connection part of vibrator and horn Explanatory drawing of the microstructure of the silicon nitride-based sintered body used in the examples and comparative examples of the present invention

1: Ultrasonic generator 2: Vibrator
3: Horn 4: Screw connection
5: Control unit 6: Mold
7: Header 8: Samurai
9: Molten metal 10: Insert connection
11: Crucible 12: Molten aluminum
13: Horn 14: Refractory tube
15: Erosion test piece 16: Sample holder
17: Cut

The inventors of the present invention have made extensive studies on measures for improving wettability and durability of an ultrasonic horn used for refining the structure of molten aluminum.
In the process, when producing a silicon nitride-based sintered body, compounds such as Al ₂ O ₃ , MgO, and SiO ₂ that are usually used as sintering aids, Y ₂ O ₃ , La ₂ O ₃ , CeO, etc. In addition to the rare earth oxides, it has been found effective to use metals of group 4A elements or oxides, nitrides and carbides thereof.
Details will be described below.

First, an example of an ultrasonic processing apparatus generally used for refining the structure of molten aluminum will be described.
As shown in FIG. 1, the ultrasonic processing apparatus includes an ultrasonic generator 1, a vibrator 2, a horn 3 and a control unit 5. However, the vibrator 2 can be selected from magnetostriction or a piezoelectric element. As an example, the operation principle of an ultrasonic generator that constitutes a magnetostrictive vibrator will be described. The AC strong current generated by the ultrasonic generator 1 is applied to the ultrasonic vibrator 2, and the ultrasonic vibration generated by the ultrasonic vibrator 2 is transmitted to the horn tip by the horn 3 via the screw connection 4 and from the tip. It introduce | transduces in the aluminum molten metal which is not shown in figure. In order to maintain the resonance condition, a resonance frequency automatic control unit 5 is provided.
This unit has a function of measuring the current value flowing through the vibrator as a function of frequency and automatically adjusting the frequency so that the current value maintains the maximum value.

As an irradiation position of the ultrasonic wave, an example of irradiation in the molten metal flowing in the cage of the DC casting apparatus is shown in FIG.
The ultrasonic irradiation position is not limited to this, and although not shown, ultrasonic vibration can be applied even in a holding furnace or a mold. Further, not only the DC casting method but also the gravity casting method, the die casting method and other casting methods can obtain the effect of refining the molten aluminum by irradiating ultrasonic waves at a predetermined position.

Next, the material of the ultrasonic horn according to the present invention will be described.
Conventionally, as an ultrasonic horn for molten aluminum, a ceramic material, particularly a silicon nitride-based sintered body, which has high heat resistance and is not easily eroded even when irradiated with ultrasonic waves in the molten aluminum has been used. The ultrasonic horn according to the present invention increases the wettability with the molten aluminum, improves the refinement effect of the metal structure, and further extends the life, in order to sinter the silicon nitride-based raw material composite powder, A sintered body obtained by adding 1.0 to 10 parts by mass of a 4A group element in terms of metal to 100 parts by mass of Si ₃ N ₄ powder is used.

Usually, when producing a silicon nitride-based sintered body, Al ₂ O ₃ , MgO, SiO ₂ , Y ₂ O ₃ , Although rare earth oxides such as La ₂ O ₃ and CeO are added, the above-mentioned sintering aid is similarly used when producing a sintered body for an ultrasonic horn which is the product of the present invention.
In the present invention, a group 4A element or a compound thereof is further used in addition to the usual sintering aid.

Next, a preferable method for producing a silicon nitride-based sintered body for an ultrasonic horn will be described.
At least one compound selected from Al ₂ O ₃ , MgO, and SiO ₂ as a sintering aid for 100 parts by mass of Si ₃ N ₄ powder having an α-Si ₃ N ₄ content of 90% by mass or more and a particle size of 2 μm or less. 0.5-10 parts by mass, preferably 2-5 parts by mass, 0.5-10 parts by mass of at least one compound selected from rare earth oxides such as Y ₂ O ₃ , La ₂ O ₃ , CeO, Preferably, 2 to 5 parts by mass are added to prepare a silicon nitride-based raw material powder.
1.0 to 10 parts by mass, preferably 2 to 5 parts by mass (in terms of a metal in the case of a compound) of 4A group element is added to 100 parts by mass of the Si ₃ N ₄ powder in the silicon nitride-based raw material powder. Prepare raw composite powder.
If necessary, an organic binder is added to the composite powder to form a horn by CIP molding or the like, followed by drying and degreasing and sintering.

As the sintering method, it is preferable to employ the “manufacturing method of silicon nitride sintered body” proposed by the present inventors (see Japanese Patent Publication No. 5-39903), but the sintering method is limited to this. Is not to be done.
Hereinafter, the method according to the manufacturing method of the said silicon nitride sintered compact is demonstrated.
A molded body obtained by a normal molding method such as CIP is embedded in a powder made of silicon nitride, silicon oxynitride and carbon and then sintered. It is preferable to use the embedding powder having a particle size of 100 μm to 10 mm and the composition defined by the following formula.
Si ₂ ON ₂ / (Si ₂ ON ₂ + Si ₃ N ₄ ) = 0.05 to 0.5
C / (C + Si ₂ ON ₂ ) = 0.1 to 0.3

The effect of these embedding powders is effective for lowering the liquidus temperature of the sintering aid and improving toughness.
As the first step of sintering, first, heat treatment is performed at 1100 to 1300 ° C. in an N ₂ gas atmosphere having a CO concentration of 1 to 50 vol% or higher under normal pressure. This lowers the liquidus temperature of the sintering aid and enables sintering from a lower temperature.
As the second step, heating is performed while alternately repeating a reduced pressure of 1 × 10 ^{−3 to} 500 Torr and a pressurized pressure of 5 to 30 kg / cm ² once or more in the temperature range of the maximum temperature of the first step to 1500 ° C. To process. As a result, the effect of suppressing decomposition and volatilization of Si ₃ N ₄ and promoting crystal growth is exhibited.

As a third step, in a pressurized _{N 2} atmosphere 5~30kg / cm ^2, and heat treatment in the range of 1500 to 1850 ° C., cooled after 60~180min held at the maximum temperature. During the main sintering process, gases such as Si, SiO, and N ₂ generated from the embedding powder diffuse into the pores in the molded body and dissolve in the liquid phase, promoting unidirectional growth of β-Si ₃ N ₄ crystals. As a result, long columnar crystals are entangled three-dimensionally to improve fracture toughness. In addition, the 4A group element distributed at the grain boundary reduces the contact angle with the molten Al and contributes to the improvement of wettability.

The 4A group element addition, although long-life effect of fracture toughness improvement with refining effect by improving wettability with molten aluminum is exhibited, 1 part by weight relative to the amount of addition is Si ₃ N ₄ powder 100 parts by weight If it is less than 10 parts by mass, the effect of fracture toughness will be reduced. Moreover, if it is 1.0-6 mass parts especially, since the fall of intensity | strength and the erosion resistance in aluminum molten metal can be suppressed to the minimum, it is more preferable from a viewpoint of lifetime improvement. Within this range, the wettability to the molten Al increases as the amount added increases. The group 4A element is added as a metal of group 4A elements such as Ti, Zr, Hf, and Th, and oxides, nitrides, and carbides thereof.

It is presumed that the mechanism of wettability improvement by adding the 4A group element is as follows.
From previous studies on the interfacial phenomenon between ceramics and molten metal, it is clear that the wettability of ceramics by molten metal is better when the reactivity between the ceramics and molten metal is higher. The reactivity between ceramics and molten metal can be evaluated thermodynamically by comparing the amount of change in free energy with respect to a chemical reaction that can be predicted at the interface between them. Hereinafter, 4A group element-free ceramics (ceramics A: Si ₃ N ₄ —Al ₂ O ₃ —Y ₂ O ₃ ) or 4A group (TiN) -containing ceramics (ceramics B: Si ₃ N ₄ —Al ₂ O _{3), respectively.} -Y ₂ O ₃ -TiN) and the free energy for a proceedable reaction when using pure aluminum or an Al-Si alloy as a melt was calculated using FACT-Sage software as a function of temperature.

As seen in FIG. 3, in the case of pure Al and ceramics A, only the chemical reaction of the formula (1) occurs, and the wettability of AlN, which is a product of the reaction, with respect to the Al melt is extremely poor. On the other hand, in the case of the ceramic B containing TiN, it is considered that the wettability of the ceramic is remarkably improved by forming TiSi ₂ or an intermetallic compound of TiSi as in reactions (2) and (3). Furthermore, reactions (2) and (3) tend to proceed thermodynamically because the Gibbs free energy is much lower than in reaction (1).
Further, as shown in FIG. 4, in the case of ceramics B, TiN directly reacts with the molten Al as shown in reactions (4) and (5) to produce an Al—Ti intermetallic compound that is particularly easily wetted with the molten Al. Therefore, wettability becomes high.

Also, as shown in FIG. 5, when Al—Si molten metal is used, Si in the molten metal reacts with TiN in the ceramics, so that TiSi ₂ or TiSi metal between the reaction equations (6) to (11). The formation of the compound improves the wettability of the ceramic.
From the above results, the reason for improving the wettability of the horn made of Group 4A (TiN) -containing ceramics to the molten aluminum is the reaction that occurs between TiN, Al melting and Si ₃ N ₄ or dissolved Si in the Al melting. This is because a layer of Ti—Si intermetallic compound or Al—Ti intermetallic compound is generated on the surface of the horn tip.

A conventional horn made of a silicon nitride-based sintered body generates stress distribution due to the ultrasonic wave propagating through the horn, and if the fracture toughness value of the silicon nitride-based sintered body is exceeded, cracks in the stress concentration part suddenly There is a problem that the horn life is shortened due to growth.
However, for example, by adding 1.0 to 10 parts by mass of TiO ₂ which is an oxide of Ti, which is a group 4A element, in terms of metal, a conventional silicon nitride-based sintered horn has a K _IC = 6.9 MN / Whereas the ultrasonic horn of the present invention achieves fracture toughness K _IC = 9.0 MN / m ^3/2 , while it was about m ^3/2 , it has a fracture resistance even under large amplitude conditions. It can be increased, and the effect of increasing the life can be expected.
This is because the addition of the 4A group element promotes the growth of the Si ₃ N ₄ crystal in the C-axis direction and forms a microstructure in which long columnar single crystals are entangled three-dimensionally. This is thought to be because fracture toughness was improved as a result of the decrease in structure.

Furthermore, the change of the bending strength by the difference in the addition amount of the 4A group element of the silicon nitride group sintered compact used for the ultrasonic horn of this invention is shown below.
Raw material composite powder in which 0, 1.5, 3, 4.5, 6, and 7.2 parts by mass of TiO ₂ in terms of metal is added to 100 parts by mass of Si ₃ N ₄ powder, respectively, width 60 × length 95 × A square plate was molded by a slip casting method using a gypsum mold having a thickness of 7 mm, and the sample was fired in a nitrogen atmosphere at Max 1770 ° C.

Three specimens each having a width of 4 × thickness of 3 × length of 40 mm were collected from the obtained fired body. The bending strength test measurement was carried out with a three-point bending strength according to JIS R 1601, and the numerical value was shown as an average value of three samples.
Table 1 shows the measurement results of the bending strength at each TiO ₂ addition amount.
From these data, when the TiO ₂ addition amount exceeds 6%, the bending strength starts to decrease. As a result, when using the horn, cracks are likely to occur inside the horn, and the durability against repeated stress and thermal shock is reduced by ultrasonic waves. It was found that 6 parts by mass or less is more preferable.

Then, the test about the change of the erosion resistance in the molten aluminum by the difference in the addition amount of the 4A group element of the silicon nitride base sintered compact used for the ultrasonic horn of this invention was done.
The apparatus used for the erosion test is shown in FIG.
A sandwich type sample holder 16 made of calcium silicate was provided in a crucible 11 made of high-purity alumina, and a sample piece 15 was fixed thereto. Further, a tube 14 made of a refractory is provided on the sample holder 16 to fix the sample holder 16, and the molten aluminum 12 is put into the crucible 11 and is supersonic by an ultrasonic horn 13 made of a silicon nitride-based sintered body. Sonic vibration was applied to confirm erosion of the test piece.
In addition, as shown in FIG.6 (b), the tube 14 made from a refractory is provided with the notch | incision 17 in order to circulate a molten metal easily.

As the sample pieces, the same sintered bodies as those having 0, 3, and 6 parts by mass of TiO ₂ added in the bending strength test were used. Each test piece was immersed in molten aluminum, and an ultrasonic horn was applied for 3 hours, and the surface of the test piece after the test was observed. The size of the average diameter D of the recess formed by ultrasonic cavitation was measured as a standard for the degree of erosion.
The erosion test results of each test piece are as shown in Table 2 below.

As shown above, it can be seen that erosion increases as the amount of TiO ₂ added increases. In addition, when applying the silicon nitride sintered body of the same material to the ultrasonic horn, the cavitation occurring at the tip of the horn is more intense than the cavitation in the test piece, so the absolute value of erosion resistance is likely to change, It is considered that the same tendency as the erosion resistance of each test piece in the molten aluminum is reproduced.
From being predicted is added the test results from 6 parts by mass or more further erosion progresses, more of avoiding TiO ₂ addition, from the viewpoint of long-life due to erosion resistance, 4A group element addition amount in terms of metal 6 parts by mass or less is more preferable.

Note that the ultrasonic horn is generally more effective in diameter from the viewpoint of miniaturization when ultrasonic irradiation is performed with molten aluminum. A conventional horn made of a silicon nitride-based sintered body without addition of a 4A group element does not have a sufficiently high fracture toughness value, and is easily broken when a horn having a large diameter is manufactured and used. For this reason, even when used as a horn, it is expected that the lifetime will be shortened when ultrasonic waves are irradiated using a horn having a large diameter.
However, the silicon nitride-based sintered horn of the present invention can easily produce a horn having a diameter of 40 mm or more, which is considered to have a high effect of refinement of molten aluminum, and compared with a conventional silicon nitride-based sintered horn. Because of its stable structure and high toughness value, it is less likely to break during use. That is, according to the present invention, it is possible to obtain an ultrasonic horn that satisfies both the refinement of the molten aluminum structure and the extension of its own life.

By the way, if the diameter of the ultrasonic horn is 40 mm or more, even in a process with a large molten metal flow rate such as DC casting, the cavitation region is widened, so that the effect of refining the structure can be exhibited. The length of the cavitation region varies depending on various conditions such as the vibration amplitude of the ultrasonic horn, the material of the horn, the chemical composition of the molten metal, the temperature, etc., but is approximately in the range of about 1.5d in width (d is the diameter of the horn tip). To do.
In addition, since the sintered body material has a relatively low thermal conductivity, repeated heating and cooling causes cracks in the horn due to the thermal gradient inside the horn, resulting in thermal shock failure in which the horn breaks. Since the thermal shock temperature gradient becomes more severe as the horn diameter becomes larger, if the horn diameter exceeds the upper limit, the possibility of breakage increases rapidly and the horn life is shortened. The upper limit varies depending on the properties of the sintered body and the conditions of preheating, ultrasonic treatment, and cooling, but it is preferable to produce the upper limit so as not to exceed this diameter. Furthermore, the horn diameter is preferably λ / 4 or less. Here, λ is the wavelength within the horn material.

An ultrasonic horn vibrates in a piston-type manner under normal operating conditions, and the entire surface of the horn tip vibrates with the same amplitude and phase. Therefore, the ultrasonic processing efficiency is deteriorated.
That is, the horn has various vibrations, but when the diameter is within λ / 4, the longitudinal vibration mode is dominant as compared with the other modes, so that the ultrasonic wave can be efficiently irradiated. However, if λ / 4 is exceeded, the influence of other vibration modes increases, and as a result, the longitudinal vibration amplitude that causes cavitation decreases, which is not efficient, and the performance of the horn tends to deteriorate. Note that the wavelength of the material of the present invention is about 0.46 m at an ultrasonic frequency of 20 kHz.
Therefore, it is preferable that the upper limit value of the horn diameter is set to a smaller one of thermal shock destruction and acoustic limitation (λ / 4).

Furthermore, in the ultrasonic horn of the present invention, the shape of the horn is preferably designed so that the vibration amplification factor is 1.6 or more. By designing in this way, vibration obtained by amplifying vibration from the vibrator can be obtained at the tip of the horn.
The procedure for obtaining the vibration amplification factor is as follows. The natural vibration induced in a slender body of a rotating body (cylinder, cone, etc.) that is usually used for a horn and has a variable cross-sectional area is calculated by the following equation.

This equation is derived on the assumption that vibration modes other than longitudinal vibration are ignored, and attenuation of ultrasonic waves in the object is ignored. By solving the equation (1) using the boundary condition Z = 0 and e = e ₀ ; Z = L and e = e _L , the vibration amplification factor of M = e _L / e ₀ ratio can be obtained. However, the vibration amplification factor obtained as described above is an approximate value because it corresponds to the natural vibration condition of only the ultrasonic horn. The actual vibration gain is measured experimentally.

As shown in FIG. 7, there are, for example, (a) a cone type, (b) a dumbbell type, and (c) a step type, as shown in FIG. These measured vibration amplification factors are 1.7 for (a), 2.7 for (b), and 1.8 for (c). Thus, by setting the vibration amplification factor to 1.6 or more, it is possible to reduce the load on the connection portion between the vibrator and the horn.
Furthermore, the length L of the ultrasonic horn of the present invention is based on an ultrasonic half wavelength of λ / 2. For example, in the case of a round bar, L can be calculated by equation (2).

If n is not an integer, the resonance condition cannot be satisfied, and therefore n must be an integer. Even in a horn having a more complicated shape, L can be approximated by equation (2).
In addition, the horn life is governed by the length tolerance DL that satisfies the resonance condition of the ultrasonic generator. An example of obtaining the DL is shown below.

  As can be seen from the equation (5), DL (= horn life) is determined by n. The larger the initial length of the horn and the sound speed in the horn material, the longer. However, n = 2, 3, and 4 are preferable. When n = 1, since the tolerance ΔL of the length that satisfies the resonance condition is small, the life of the horn tends to be shortened. When n> 4, the weight of the horn increases and a load is applied to the vibrator or its connecting portion. Therefore, as the life is shortened or the horn length is increased, the attenuation rate of the ultrasonic vibration in the horn is decreased. This is because the efficiency of ultrasonic wave irradiation is reduced.

The connecting portion between the vibrator and the horn is preferably connected to the vibrator via an insert made of a high strength alloy such as tool steel. Thereby, the impact of a connection part can be relieved, durability of a horn can be strengthened, and damage by abrasion, vibration, etc. can be prevented.
Relatively soft materials such as Fe-Ni-Co alloys and Ti alloys used for vibrators on hard materials such as silicon nitride-based sintered bodies such as horns made of silicon nitride-based sintered bodies of the present invention If the materials are connected directly, the screws will deteriorate quickly and their life will be shortened. Therefore, by inserting a tool steel insert having a hardness between the vibrator and the sintered body, the impact of the connecting portion can be reduced, and the female screw can be strengthened to achieve a durable screw connection. In addition, since the thread is prevented from being damaged due to wear, vibration or the like, the life of the horn can be extended while maintaining a stable screw connection.

By the way, if the horn is left connected to the vibrator, pressure is applied to the screw of the sintered body and the probability of occurrence of cracks is increased. It is necessary to remove the vibrator.
In the case of direct connection without an insert, there is also a problem that the screw collapses when the sintered body is brittle and is repeatedly removed and connected. Therefore, by adding an insert, since the connecting portion is made of metal, it is easy to remove the horn and the vibrator, and there is an effect that such a problem is eliminated.

As a connection aspect of an insert and a vibrator | oscillator, the form as shown to Fig.8 (a)-(c) is mentioned, for example.
(A) is an easily replaceable insert of a type with a washer. The feature is that the connection surface between the vibrator and the horn is not in direct contact. (B) is a non-replaceable insert that provides direct contact between the transducer and the horn, and (c) is a helicate that is a type of insert that provides direct contact between the transducer and the horn.

If there is no direct contact surface between the vibrator and the horn as shown in (a) and there are many contact surfaces between the horn and the insert, an inevitable gap will be created or impurities will easily adhere. A part of the energy disappears and the ultrasonic transmission efficiency deteriorates. Therefore, in general, it is preferable to place the insert as shown in (b), (c) and the like so that the vibrator and the horn are in direct contact with each other.
However, if the vibrator has a direct contact surface between the vibrator and the horn, as in the case of a relatively soft metal such as an Fe alloy, the characteristics such as thermal expansion coefficient, elastic modulus, and hardness are greatly different between the two. Since the contact portion of the vibrator may be plastically deformed, it may be better not to directly contact the vibrator and the horn as shown in (a).

  In the conical horn of FIG. 7 (a), the life when the horn was directly screw connected to the vibrator without the insert connection was 1.5 hours. On the other hand, when connecting with Helisart Fig. 8 (c), it was confirmed up to 73 hours. In the dumbbell horn shown in FIG. 7 (b), the service life was about several minutes when directly screw-connected without insert connection. On the other hand, when it connected by insert figure 8 (a), it was able to confirm to 105 hours.

  Further, it is preferable that the screw in the insert has a pitch number of 10 or more. Thereby, the screw return by the addition of ultrasonic vibration can be prevented. Further, the female screw on the horn side of the insert may be a standard triangular screw at the valley corner, and it is preferable to round the curvature radius in accordance with the shape of the horn connection screw. As a result, unscrewing can be prevented, cracking and breakage due to stress concentration at the valley corners by ultrasonic wave propagation can be prevented, and refinement efficiency can be improved and horn life can be improved. An example is shown in FIG. In this case, the radius of curvature is 1.0. In addition, the connection between the vibrator and the insert side is also connected with a screw in the same manner as the connection between the horn and the insert side.

  In addition, when ultrasonically irradiating using the ultrasonic horn of this invention, it is preferable to manufacture the aluminum alloy which irradiated the ultrasonic wave by 16-60 micrometers (pp), and refine | miniaturized the structure | tissue. Here, pp is a peak-to-peak, and refers to a difference between the maximum value and the minimum value in the case of a sine wave, for example. 16 μm to 60 μm is a suitable value in which the effect of miniaturization proceeds, the burden on the connection portion is reduced, and the horn is not easily damaged.

Example 1:
An aluminum melt having a component composition of Al-17% Si-0.01% P was prepared in a crucible placed in the melting furnace.
Next, the diameter is 40 mm, the vibration amplification factor is 1.7, the length is 425 mm (n = 2), and Y ₂ O ₃ and Al ₂ O ₃ are converted into compounds with respect to 100 parts by mass of the Si ₃ N ₄ powder, respectively. An ultrasonic horn made of a silicon nitride-based sintered body obtained by sintering a compact of a raw material composite powder obtained by adding 5 parts by mass and 5 parts by mass of TiO ₂ in metal conversion is preheated in a preheating furnace, and then DC casting is performed from a melting furnace. A billet of φ97 was cast at a casting speed of 275 mm / min by irradiating ultrasonic waves with a horn immersed in the molten aluminum supplied to the molten metal transfer rod to the mold.

The ultrasonic generator used at this time was an ultrasonic generator manufactured by SONOVITA (Russia), and was set to a frequency of 21.7 kHz and an acoustic output of 0.6 kW. The wavelength λ of the ultrasonic wave in the horn was 430 mm, and the vibration amplitude of the horn was 32 μm (pp).
The connecting portion was connected to the vibrator through an insert made of tool steel. The number of pitches of the insert was 14, and the radius of curvature was 0.5 mm.
The structure of the surface layer portion of the ingot produced in Example 1 was observed with a microscope. The result is shown in FIG.

Example 2:
A molten aluminum having a component composition of Al-17% Si-0.01% P was prepared in a crucible placed in the melting furnace.
Next, the diameter is 42 mm, the vibration amplification factor is 2.7, the length is 460 mm (n = 2), and Y ₂ O ₃ and Al ₂ O ₃ are each 5 in terms of compounds with respect to 100 parts by mass of Si ₃ N _4. An ultrasonic horn made of a silicon nitride-based sintered body obtained by sintering a compact of a raw material composite powder obtained by adding 5 parts by mass of TiO ₂ in terms of metal is preheated in a preheating furnace, and then a DC casting mold from a melting furnace A billet of φ97 was cast at a casting speed of 300 mm / min by irradiating ultrasonic waves with a horn immersed in the molten aluminum supplied to the molten metal transfer bowl.

The ultrasonic generator used at this time was an ultrasonic generator manufactured by TELSONIC (Switzerland), and was set to a frequency of 20 kHz and an acoustic output of 0.5 kW. The wavelength λ of the ultrasonic wave in the horn was 460 mm, and the vibration amplitude of the horn was 48 μm (pp).
The connecting portion was connected to the vibrator through an insert made of tool steel. The number of pitches of the insert was 14, and the radius of curvature was 0.5 mm.
Table 1 shows the average particle diameter of R / 2 part primary silicon of the ingot produced in Example 2.

Example 3:
Except for the horn tip diameter of 24 mm, vibration amplification factor of 1.7, length of 460 mm, and acoustic output of 0.15 kW, casting was performed by irradiating ultrasonic waves in the same manner using the same apparatus as in Example 2. It was.
Table 3 shows the average particle diameter of R / 2 part primary silicon of the ingot produced in Example 3.

Example 4:
A molten aluminum having a component composition of Al-17% Si-0.01% P was prepared in a crucible placed in the melting furnace.
Next, the diameter is 48 mm, the vibration amplification factor is 2.7, and the length is 450 mm. Y ₂ O ₃ and Al ₂ O ₃ are each 5 parts by mass in terms of compounds with respect to 100 parts by mass of the Si ₃ N ₄ powder, TiO 2 _An ultrasonic horn made of a silicon nitride-based sintered body obtained by sintering a compact of a raw material composite powder to which 5 parts by mass of ₂ is added in terms of metal is preheated in a preheating furnace, and then the molten metal is transferred from the melting furnace to a DC casting mold. A billet of φ97 was cast at a casting speed of 200 mm / min by irradiating ultrasonic waves with a horn immersed in the molten aluminum supplied to.

The ultrasonic generator used at this time was an ultrasonic generator manufactured by TELSONIC (Switzerland), and was set to a frequency of 20 kHz and an acoustic output of 0.7 kW. The wavelength λ of the ultrasonic wave in the horn was 0.46 m, and the vibration amplitude of the horn was 32 μm (pp).
The connecting portion was connected to the vibrator through an insert made of tool steel. The number of pitches of the insert was 14, and the radius of curvature was 0.5 mm.
Table 3 shows the average particle diameter of R / 2 part primary silicon of the ingot produced in Example 4.

Example 5:
Except that the vibration amplitude was 24 μm (pp), casting was performed by irradiating ultrasonic waves by the same method using the same apparatus as in Example 1.
Table 3 shows the average particle diameter of R / 2 part primary silicon of the ingot produced in Example 5.

Example 6:
Except that the vibration amplitude was 14 μm (pp), casting was performed by irradiating ultrasonic waves by the same method using the same apparatus as in Example 1.
Table 3 shows the average particle diameter of R / 2 part primary silicon of the ingot produced in Example 6.

Example 7:
Except that the amount of TiO ₂ added to 100 parts by mass of the Si ₃ N ₄ powder is 2.5 parts by mass in terms of metal, the same apparatus and the same apparatus as in Example 1 were irradiated with ultrasonic waves, Went.
Table 3 shows the average particle diameter of R / 2 part primary silicon of the ingot produced in Example 7.

Example 8:
Except that the amount of TiO ₂ added to 100 parts by mass of Si ₃ N ₄ powder was 7.5 parts by mass in terms of metal, ultrasonic irradiation was performed under the same conditions and the same apparatus as in Example 1, and casting Went.
Table 3 shows the average grain size of R / 2 part primary silicon of the ingot produced in Example 8.

Example 9:
Except that the amount of TiO ₂ added to 100 parts by mass of the Si ₃ N ₄ powder was 10.0 parts by mass in terms of metal, the same conditions and the same apparatus as in Example 1 were used to irradiate ultrasonic waves and cast Went.
Table 3 shows the average particle diameter of R / 2 part primary silicon of the ingot produced in Example 9.

As can be seen from Table 3, when the tip of the horn is 40 mm or more, the primary crystal Si is further refined. Also, the larger the amplitude, the easier it is to make it finer.
In Table 3, d ₀ and d _US represent the primary silicon average particle diameter when not treated and the primary silicon average particle diameter when subjected to ultrasonic treatment, respectively.

Comparative Example 1:
Casting was performed by irradiating ultrasonic waves in the same manner using the same apparatus as in Example 1 except that an ultrasonic horn made of a silicon nitride-based sintered body to which TiO ₂ was not added was used.
The structure of the surface layer portion of the ingot produced in Comparative Example 1 was observed with a microscope. The result is shown in FIG.

Comparative Example 2:
For comparison, casting was performed under the same conditions except that ultrasonic irradiation was not performed using the same apparatus as in Example 1.
The structure of the surface layer portion of the ingot produced in Comparative Example 2 was observed with a microscope. The result is shown in FIG.

10A, 10B, and 10C are photomicrographs showing the metal structures of the aluminum alloys produced in Example 1, Comparative Example 1, and Comparative Example 2, respectively.
The black portion is a crystal of primary crystal Si, but it can be seen that the primary crystal Si is finer in Example 1 than in Comparative Example 1 and Comparative Example 2.

Claims (7)

An ultrasonic horn used for irradiating molten aluminum with ultrasonic waves, and sintering raw material composite powder containing 1.0 to 10 parts by mass of Ti in terms of metal with respect to 100 parts by mass of Si ₃ N ₄ powder An ultrasonic horn comprising a silicon nitride-based sintered body. The ultrasonic horn according to claim 1, wherein 1.0 to 6 parts by mass of Ti in terms of metal is included with respect to 100 parts by mass of the Si ₃ N ₄ powder. In addition to the Si ₃ N ₄ powder and the Ti , the Si ₃ N ₄ raw material composite powder is selected from Al ₂ O ₃ , MgO, and SiO _{2 with} respect to 100 parts by mass of the Si ₃ N ₄ powder as a sintering aid. And at least one compound selected from 0.5 to 10 parts by mass and at least one compound selected from rare earth oxides of Y ₂ O ₃ , La ₂ O ₃ , and CeO. Or the ultrasonic horn of 2. A sintered body of the silicon nitride based, the length L of the horn, the ultrasonic half-wavelength of lambda / 2 as the basic unit, an integer of L = n × λ / 2及 beauty n = 2, 3, 4 The ultrasonic horn according to claim 1, wherein the ultrasonic horn is designed as follows. The ultrasonic horn according to any one of claims 1 to 4, wherein the horn is connected to the vibrator via an insert screw. The manufacturing method of the aluminum alloy characterized by irradiating a molten aluminum with an ultrasonic wave using the ultrasonic horn of any one of Claims 1-5 . The manufacturing method of the aluminum alloy of Claim 6 which makes the vibration amplitude at the time of irradiating an ultrasonic wave the range of 16-60 micrometers (pp).