JP2014036964A - Differential pressure casting method, casting thereby and aluminum alloy material used therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a differential pressure casting method for restraining a casting defect such as gas porosity caused by a composition of an aluminum alloy, by using the aluminum alloy for holding high alumite treatment performance for molten metal.SOLUTION: The molten metal is composed of the aluminum alloy including Si: 0.8-2.0 mass%, Mg: 0.3-0.45 mass%, Ti: 0.1-0.2 mass% and Fe: 0.1 mass% or less, and casting is executed by raising a holding container 3 for holding the molten metal and a storage container 5 for storing a casting mold S up to predetermined pressure P of atmospheric pressure or more, by using a differential pressure casting device. When coagulating the molten metal, differential pressure between the inside of the holding container 3 and the inside of the storage container 5 is set to predetermined differential pressure ΔPz, and the molten metal is coagulated while feeding the molten metal.

Description

  The present invention relates to a differential pressure casting method using an aluminum (Al) alloy containing silicon (Si), and more particularly to a differential pressure casting method suitable for use in a cast product such as a vacuum chamber used in a semiconductor manufacturing apparatus, for example. .

  Recently, structural members made of Al and Al alloys are widely used due to the need for weight reduction. Al alloy materials are relatively easy to process, low in cost, and extremely low in metal contamination. Many materials are selected as materials for vacuum parts (for example, vacuum chambers) used in semiconductor manufacturing equipment.

  Conventionally, it has been studied to cast a vacuum part for cost reduction, but it is known that the fluidity of the molten metal required in casting is enhanced by containing a large amount of Si. On the other hand, it is known that when the alumite processability is improved to improve the degree of vacuum of the vacuum part, it is advantageous that the content of Si is less.

  For this reason, Al alloy with low Si content (Si content is 1.2 to 3.0%) is used as the molten metal, and is stored in the holding furnace using a mold having a plurality of gates for filling the molten metal in the cavity. A casting method has been devised in which the molten metal is filled into the mold cavity from the plurality of sprues by a low pressure casting method in which the molten metal is pressurized or sucked, and the molten metal is filled into the cavity without deficiency while improving the alumite processability ( Patent Document 1). In addition, as a result of optimizing the Si content which shows both the effect of increasing the fluidity of the molten metal and the effect of inhibiting the alumite treatment property, casting is performed using an aluminum alloy having a Si content in the range of 4 to 6%. A vacuum vessel has been devised (see Patent Document 2).

JP 2004-174517 A JP 2007-260624 A

  However, in the casting method described in Patent Document 1, casting defects such as gas porosity and shrinkage cavities are likely to occur in the cast product by reducing the amount of Si contained, and it is necessary to maintain a high degree of vacuum with high reliability. It is difficult to apply to certain vacuum parts.

  In addition, the vacuum container described in Patent Document 2 has a Si lower limit so that casting defects are likely to occur when the Si content is less than 4%, and defects such as poor hot water and hot water boundaries do not occur. Is set at 4%, but in order to meet the recent industrial demands for vacuum chambers with higher vacuum and high anodizing ability, the anodizing ability with Si content of about 4% is insufficient. It is.

  Therefore, the present invention uses an Al alloy with a low Si content, while appropriately setting the contents of other magnesium (Mg), titanium (Ti), and iron (Fe) and holding a molten metal, A differential pressure casting method using an aluminum alloy having a specific composition that suppresses casting defects caused by the composition of the aluminum alloy by applying a predetermined pressure to the storage container in which the mold is stored, thereby solving the above-described problems. The purpose is to provide.

The present invention includes a holding container (3) for holding a molten metal, a storage container (5) disposed above the holding container (3) and storing a mold (S), the holding container (3), and the In the differential pressure casting method using the differential pressure casting apparatus (1) including the stalk (6) communicating with the mold (S),
The molten metal contains Si: 0.8 to 2.0 mass%, Mg: 0.3 to 0.45 mass%, Ti: 0.1 to 0.2 mass%, and Fe: 0.1 mass% or less. Made of aluminum alloy containing,
A pressurizing step (S2) for increasing the pressure of the holding container (3) and the storage container (5) to a predetermined pressure (P);
An ascending step (S3) for setting the differential pressure between the holding container (3) and the storage container (5) to a first differential pressure (ΔPx) and raising the molten metal to the upper end position of the stalk (6). S4)
A filling step (S5, S6) in which the pressure difference between the holding container (3) and the storage container (5) is set to a second differential pressure (ΔPy), and the mold (S) is filled with molten metal. When,
Solidification step (S7, S8) for setting the differential pressure between the holding container (3) and the storage container (5) to a third differential pressure (ΔPz) and solidifying the molten metal in the mold (S). When,
A depressurization step (S9) for depressurizing the pressure in the holding container (3) and the storage container (5) to atmospheric pressure,
It is characterized by that.

Cast by the above-described differential pressure casting method and anodized,
It is in the casting characterized by this.

  In particular, the casting is preferably a vacuum chamber (29).

  The aluminum alloy material used for the differential pressure casting method is Si: 0.8 to 2.0 mass%, Mg: 0.3 to 0.45 mass%, Ti: 0.1 to 0.2 mass%, and Fe: 0.1 mass% or less is contained.

  In addition, although the code | symbol in the said parenthesis contrasts with drawing, it does not limit the structure of this invention at all.

According to the first aspect of the present invention, the aluminum alloy of the molten metal is Si: 0.8 to 2.0 mass%, Mg: 0.3 to 0.45 mass%, Ti: 0.1 to 0.2 mass%. , Fe: 0.1% by mass or less, compared with the conventional aluminum alloy having a large Si content, while maintaining a very high alumite processability, and by depositing fine Mg ₂ Si, Strength can be improved. In addition, pressurizing the storage container that holds the mold together with the holding container that holds the molten metal and pushing the molten metal during the solidification process suppresses casting defects such as gas porosity and shrinkage cavities caused by low Si content. Thus, the finish can be improved and a high degree of vacuum can be maintained with high reliability.

  According to the second aspect of the present invention, casting defects can be suppressed and alumite processability can be improved as compared with conventional castings, and thus a casting with a high degree of vacuum can be produced.

  According to the third aspect of the present invention, casting defects can be suppressed and alumite processability can be improved as compared with the conventional vacuum chamber, so that a vacuum chamber with a high degree of vacuum can be manufactured.

  According to the fourth aspect of the present invention, it is possible to improve the alumite processability and strength as compared with the conventional aluminum alloy material.

The schematic diagram which shows the differential pressure casting apparatus which concerns on embodiment of this invention, and its piping structure. The schematic diagram which shows the suitable vacuum chamber manufactured by the differential pressure casting method which concerns on this invention. The flowchart which shows the casting method which concerns on embodiment of this invention. The figure which shows the pressure change of the holding | maintenance container and storage container which concern on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described. First, a differential pressure casting apparatus and a piping configuration thereof will be described with reference to FIG.

  The differential pressure casting apparatus 1 includes a holding container 3 that holds a molten metal, a storage container 5 that is disposed above the holding container 3 and stores a sand mold S, and an upper and lower that communicates the holding container 3 and the sand mold S. Stalk 6 extending in the direction. The molten metal is made of an aluminum alloy having a specific composition to be described later. For example, a distance h1 between the upper end 6a of the stalk 6 and the liquid level M of the molten metal is measured by a distance sensor (not shown) disposed in the storage container 5. It can be done.

  The differential pressure casting apparatus 1 includes a gas supply device 7 that supplies a high-pressure gas suitable for casting, such as air, rare gas, or nitrogen gas. A first air supply pipe 10 connected to the storage container 5 and a second air supply pipe 11 connected to the holding container 3 are connected. The first air supply pipe 10 is provided with a first pressure adjusting valve 12 and a first air supply valve 13 as first pressure adjusting means, and the second air supply pipe 11 includes A second pressure adjusting valve 15 as a second pressure adjusting means and a second air supply valve 16 are provided.

  The secondary side of the first air supply valve 13 in the first air supply pipe 10 and the secondary side of the second air supply valve 16 in the second air supply pipe 11 are connected by a connecting pipe 17. A connecting valve 19 is disposed in the connecting pipe 17. In addition, a first atmosphere release pipe 21 having a first atmosphere release valve 20 connected to the end is connected to the secondary side of the first supply valve 13 in the first supply pipe 10. A second atmosphere release pipe 23 having a second atmosphere release valve 22 connected to the end is connected to the secondary side of the second supply valve 16 in the second supply pipe 11.

  The differential pressure casting apparatus 1 includes a first pressure sensor 25 that detects the pressure in the storage container 5 and a second pressure sensor 26 that detects the pressure in the holding container 3.

  The valves 9, 12, 13, 15, 16, 19, 20, 22 and the first pressure sensor 25 and the second pressure sensor 26 are connected to a control device 27, and the control device 27 performs the above operation. The pressure P1 in the storage container 5 and the pressure P2 in the holding container 3 are controlled.

  Next, the differential pressure casting method according to the present embodiment using the differential pressure casting apparatus 1 is as follows: Si: 0.8 to 2.0 mass%, Mg: 0.3 to 0.45 mass%, Ti: 0 0.1 to 0.2% by mass, and Fe: 0.1% by mass or less (other trace metals) is used, and an aluminum alloy having a special composition is used. The sand mold S of the differential pressure casting apparatus 1 is It is applied to a mold of a vacuum chamber 29 for a semiconductor manufacturing apparatus which is a vacuum component shown in FIG.

  In FIG. 3, first, the control device 27 holds the pressure P <b> 1 in the storage container 5 based on the distance h <b> 1 between the upper end position of the stalk 6 measured by the distance sensor (not shown) and the liquid level M of the molten metal. The first differential pressure ΔPx required for the molten metal to rise up to the upper end 6a of the stalk 6 is filled with the molten metal in the sand mold S (the liquid level M of the molten metal). The second differential pressure ΔPy required for the molten metal to rise to the height h2 of the upper end in the cavity Sc of the sand mold S and the third differential pressure ΔPz larger than the second differential pressure ΔPy is calculated ( Step S1).

  The differential pressure casting method of the present embodiment is performed based on the calculated first, second, and third differential pressures ΔPx, ΔPy, ΔPz, and the pressure P1 in the storage container 5 and the pressure in the holding container 3 A step of boosting P2; a step of raising the molten metal at the upper end position of the stalk 6; a filling step of filling the molten metal in the sand mold S; a solidifying process of solidifying the molten metal in the sand mold S; And a pressure-removing process for depressurizing the pressure P1 in the container 5 and the pressure P2 in the holding container 3 to atmospheric pressure, and these will be described in order for each process.

(Pressure increase process)
The control device 27 performs control to set the pressure P1 in the storage container 5 and the pressure P2 in the holding container 3 to a predetermined pressure P (for example, 650 kPa) higher than the atmospheric pressure (step S2: pressure increase period T1 in FIG. 4). ).

  More specifically, the control device 27 first closes the first and second atmospheric release valves 20 and 22 that are open, and then the pressurization valve 9 and the second air supply valves 13 and 16. Is opened, and the first and second pressure regulating valves 12 and 15 are adjusted so that the pressures of the storage container 5 and the holding container 3 become a predetermined pressure P. At this time, since the connecting valve 19 is in an open state, the storage container 5 and the holding container 3 are increased to a predetermined pressure P at the same speed.

By the way, when the molten metal used in the present embodiment is Si: less than 0.8% by mass, the precipitation amount of Mg ₂ Si during the solution treatment and aging treatment of the solid solution Si and Mg is small and sufficient. There is not enough strength. Further, when Si: 2.0% by mass or more, an alumite processability is insufficient for a vacuum chamber that requires a high anodize processability in order to achieve an ultrahigh vacuum. Therefore, Si: It sets to 0.8-2.0 mass%.

  Due to the pressurizing step, the storage container 5 and the holding container 3 are boosted to a predetermined pressure P higher than the atmospheric pressure, thereby reducing the Si content to a small amount of Si: 0.8 to 2.0 mass%. Thus, the generation of hydrogen gas bubbles during solidification of the molten metal can be prevented, and casting defects such as gas porosity and pinholes can be suppressed.

  As shown in FIG. 2, a vacuum chamber 29 for a semiconductor manufacturing apparatus to which the present invention is applied has a box shape with an open top, and includes a bottom surface portion 31 having a hole 30 and a side surface portion 32. These bottom surface portion 31 and side surface portion 32 do not have a thin-walled portion, and fluidity for filling the sand mold S is ensured even in Si: 0.8 to 2.0 mass%. In addition, better fluidity can be imparted by heating the molten metal.

(Rising process)
The control device 27 detects the pressures P1 and P2 of the storage container 5 and the holding container 3 by the first and second pressure sensors 25 and 26, and when each of the pressures P1 and P2 reaches a predetermined pressure P, a predetermined period of time is detected. After T2 has elapsed and the pressure has settled, the pressures P1 and P2 are set so that the differential pressure between the storage container 5 and the holding container 3 becomes ΔPx (step S3: in FIG. 4). , Rising period T3).

  More specifically, the control device 27 closes the connecting valve 19 when the pressures P1 and P2 reach the predetermined pressure P, so that the first differential pressure ΔPx is reached. The second pressure regulating valve 15 is set so that the pressure P2 is raised above the predetermined pressure P. Then, by adjusting the second pressure regulating valve 15 in this way, the pressure P2 in the holding container 3 is gradually increased, and the differential pressure between the storage container 5 and the holding container 3 becomes the first pressure. 1 differential pressure ΔPx. By setting the differential pressure to the first differential pressure ΔPx in this way, the molten metal is decelerated or temporarily stopped immediately before the sand mold S, and the molten metal is not injected into the sand mold S vigorously.

  Next, the control device 27 determines whether or not the molten metal has reached the upper end 6a of the stalk 6 (step S4). More specifically, since the pressure P2 in the holding container 3 gradually increases, the molten metal in the holding container 3 increases the stalk 6 as the pressure P2 in the holding container 3 increases. When the differential pressure between the storage container 5 and the holding container 3 reaches the first differential pressure ΔPx, the molten metal reaches the upper end 6 a of the stalk 6.

(Filling process)
When the molten metal reaches the upper end 6a of the stalk 6 (step 4: Yes), the control device 27 sets the differential pressure between the storage container 5 and the holding container 3 to be the second differential pressure ΔPy, The molten metal is filled into the cavity Sc of the sand mold S (step S5: filling period T4 in FIG. 4).

  More specifically, the control device 27 sets the first pressure regulating valve 12 so as to reduce the pressure P1 in the storage container 5 from the predetermined pressure P so that the differential pressure becomes the second differential pressure ΔPy. To do. Then, by setting the first pressure regulating valve 12 in this way, the pressure P1 in the storage container 5 is gradually reduced, and the differential pressure between the storage container 5 and the holding container 3 becomes the second pressure. It becomes the differential pressure ΔPy.

  Thus, instead of setting directly to the second differential pressure ΔPy, the first differential pressure ΔPx is set in advance and then set to the second differential pressure ΔPy. It is possible to suppress the molten metal from being ejected vigorously, to suppress the sand mold S from being damaged, and to produce a casting having a good finish.

  In general, the flow length becomes longer as the hot water temperature is higher, and as the molten metal filling time is longer, that is, as the filling speed is slower, the flow length becomes shorter. However, when the filling time is longer than a predetermined time (for example, 10 seconds), It is almost constant without being affected. In addition, the Si content has an influence on the flow length when the Si content is high, such as 7.5% by mass. However, at a low Si content of 2.0% by mass or less, any filling time is required. In addition, it was confirmed by a flow length comparison experiment that the flow length was not affected. Therefore, by setting the second differential pressure ΔPy, the filling period T4 is set to a fine and appropriate value, and in a molten metal made of an aluminum alloy having Si: 2.0% by mass or less, the sand mold S is smoothly filled. In particular, in a vacuum chamber having no thin portion, it is accurately filled with sufficient hot water flow.

  Further, since the pressure P1 in the storage container 5 is reduced, when the molten metal is filled in the sand mold S, the pressure P2 in the holding container 3 on the side of pushing out the molten metal does not fluctuate, so that the flow of the molten metal is smooth. Yes, it is possible to produce castings with good finish.

  Next, the control device 27 determines whether or not the filling of the molten metal into the cavity Sc of the sand mold S is completed (step S6). In the present embodiment, it is determined whether or not the time required for filling has elapsed since the differential pressure between the storage container 5 and the holding container 3 becomes the second differential pressure ΔPy.

(Coagulation process)
When the controller 27 completes filling the cavity Sc of the sand mold S with the molten metal (step S6: Yes), the differential pressure between the storage container 5 and the holding container 3 becomes the third differential pressure ΔPz. (Step S7: Coagulation periods T5, T6, T7 in FIG. 4). More specifically, the control device 27 first sets the pressure P1 in the storage container 5 to the predetermined pressure P in the predetermined period T5 so that the differential pressure becomes the third differential pressure ΔPz, and then the predetermined period. The pressure regulating valves 12 and 15 are set so as to increase the pressure P2 in the holding container 3 at T6.

  In general, when the Si content is small, the quasi-liquid phase range is narrowed and casting defects such as shrinkage are likely to occur. In this way, the pressure P2 in the holding container 3 is finely increased to an appropriate value to increase the sand mold. By applying a follow-up pressure to the molten metal leading to S, the molten metal effect is enhanced and casting defects are reduced, and the Si content of the molten metal is set to Si: 0.8 to 2.0 mass% as in the present embodiment. Even if it is set, it is possible to produce a casting with a good finish. Thereby, the mold shape is accurately transferred without causing a dent in the thickness direction due to solidification shrinkage, and an appropriate cast product, for example, a vacuum chamber is obtained. Depending on the cast product, there is a case where the molten metal is not inserted into the sand mold surface by the third differential pressure ΔPz and the casting surface is not roughened in order to prevent the cast surface from becoming rough. In this case, after setting to the second differential pressure ΔPy in the filling period T4, the pressure P1 in the storage container 5 is increased to the pressure P2 while the pressure P2 in the holding container 3 is maintained, and the storage container 5 And the pressure in the holding container 3 is depressurized to atmospheric pressure (see step S9 described later).

  Next, the control device 27 determines whether or not the molten metal in the sand mold S has solidified (step S8). More specifically, the control device 27 determines whether or not the time required for the molten metal to solidify has elapsed.

(Decompression process)
When the control device 27 determines that the molten metal in the sand mold S has solidified (step S8: Yes), the control device 27 first sets the first pressure regulating valve 12 so that the pressure P2 in the storage container 5 is equal to the pressure P1 in the holding container 3. The first pressure regulating valve 12 is adjusted so as to be the same, and then the pressure in the storage container 5 and the holding container 3 is decompressed to atmospheric pressure (step S9: decompression period T8 in FIG. 4). More specifically, the pressurizing valve 9 and the first and second air supply valves 13 and 16 are closed, and then the first and second atmospheric release valves 20 and 22 are opened.

Next, the contents of Mg, Ti, Fe in the aluminum alloy applied to the present invention will be described in detail. The Mg content is in the range of Mg: 0.3 to 0.45 mass%, and is added to improve the strength by precipitating Mg ₂ Si in a mixture with Si. Mg: If it is less than 0.3% by mass, the amount of Mg ₂ Si deposited decreases, and the strength is impaired. Mg: When it is 0.45 mass% or more, Mg ₂ Si is segregated at the grain boundary, and conversely, strength does not appear. The Ti content is within a range of Ti: 0.1 to 0.2% by mass, and is added for refinement of crystal grains. That is, Mg ₂ Si precipitated by the addition of Ti is refined, resulting in higher strength. When Ti is less than 0.1% by mass, the effect of refining crystal grains is small, and when it is 0.2% by mass or more, a coarse Al—Ti compound is formed, which may be an inhibiting factor for an alumite film. . Fe content is in the range of Fe: ˜0.1 mass%, and since it is an inhibitory factor for an alumite film, the smaller the content, the better. However, a small amount is contained in the refining process.

As described above, according to the present embodiment, the Si content is Si: 0.8 to 2.0% by mass, and by containing a small amount of Si, the alumite processability is improved and an ultra-high vacuum is achieved. By containing Mg: 0.3 to 0.45 mass% and Ti: 0.1 to 0.2 mass%, fine Mg ₂ Si is precipitated to improve the strength.

  In addition, casting defects such as gas porosity and pinholes due to a small Si content and casting defects such as shrinkage cavities that occur when the molten metal in the sand mold S is solidified can be cast at a pressure higher than atmospheric pressure. It is possible to produce a vacuum chamber or other cast product with high accuracy and good finish by suppressing by pushing hot water during solidification.

  In the above embodiment, the present invention has been described based on the casting of the vacuum chamber. However, in the differential pressure casting method, the cast product is not limited to the vacuum chamber. For example, a vacuum shield such as a deposition shield that is used in a vacuum apparatus to prevent the top plate of a vacuum chamber from being eroded by a plasma etching process, and a pipe joint, a flange, etc. may be used. Is possible. Si: 0.8 to 2.0% by mass, Mg: 0.3 to 0.45% by mass, Ti: 0.1 to 0.2% by mass, and Fe: 0.1% by mass or less The aluminum alloy to be refined may be refined to form an ingot (ingot, aluminum alloy material), and this is suitably used as a molten metal for castings by differential pressure casting, particularly for products to be anodized.

  In the present embodiment, in step S5 in FIG. 3, the pressure in the storage container 5 is reduced when the differential pressure between the storage container 5 and the holding container 3 is set to the second differential pressure ΔPy. However, the present invention is not limited to this, and the pressure P2 in the holding container 3 may be increased to set the differential pressure to the second differential pressure ΔPy.

  In the present embodiment, the case where a sand mold is used as a mold has been described. However, the present invention is not limited to this, and the mold may be used as a mold.

DESCRIPTION OF SYMBOLS 1 Differential pressure casting apparatus 3 Holding container 5 Storage container 29 Vacuum chamber P Predetermined pressure (DELTA) Px 1st differential pressure (DELTA) Py 2nd differential pressure (DELTA) Pz 3rd differential pressure S Sand mold (mold)
S2 Boosting step S3, S4 Ascending step S5, S6 Filling step S7, S8 Solidification step S9 Depressurization step

Claims (4)

A difference using a differential pressure casting apparatus comprising a holding container for holding a molten metal, a storage container disposed above the holding container and storing a mold, and a stalk for communicating the holding container and the mold. In the pressure casting method,
The molten metal contains Si: 0.8 to 2.0 mass%, Mg: 0.3 to 0.45 mass%, Ti: 0.1 to 0.2 mass%, and Fe: 0.1 mass% or less. Made of aluminum alloy containing,
A pressurizing step of boosting the holding container and the storage container to a predetermined pressure;
An ascending step of setting the differential pressure between the holding container and the storage container to a first differential pressure, and raising the molten metal to the upper end position of the stalk;
A filling step of setting a differential pressure between the inside of the holding container and the inside of the storage container to a second differential pressure, and filling the mold with molten metal;
A solidification step of setting a differential pressure between the holding container and the storage container to a third differential pressure, and solidifying the molten metal in the mold;
A depressurization step of depressurizing the pressure in the holding container and the storage container to atmospheric pressure,
A differential pressure casting method characterized by that. Cast by the differential pressure casting method according to claim 1 and anodized.
Cast product characterized by that. The casting is a vacuum chamber;
The casting according to claim 2. Si: 0.8 to 2.0% by mass, Mg: 0.3 to 0.45% by mass, Ti: 0.1 to 0.2% by mass, and Fe: 0.1% by mass or less ,
2. An aluminum alloy material used for the differential pressure casting method according to claim 1.

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