JPS59220274A - Casting method of hypereutetic aluminum-silicon alloy - Google Patents

Abstract

PURPOSE:To cast a casting of a hypereutectic Al-Si alloy having less segregation of primary crystal silicon at a good yield by charging a molten metal into a casting mold, acting always a riser at all times and rotating the casting mold. CONSTITUTION:A molten hypereutectic Al-Si alloy is charged into a casting mold and a riser is acted at all times during the time when the molten alloy solidifies in the mold and at the same time the mold is rotated at the speed at which the crystallized primary crystal silicon is dispersed. Then floating direction of the primary crystal silicon changes incessantly and since the primary crystal silicon particles arriving at the upper part are captured by the constantly moving solidification boundary, the structure in which the primary crystal silicon is uniformly dispersed over a wide range of a casting ingot is obtd. after solidification.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention has good dry flow properties and excellent properties as a casting alloy, and also has wear resistance of M and is suitable for use in motors. Regarding casting methods for hypereutectic aluminum-silicon thread alloys used as piston materials, bearing materials, and vane materials for vane-type compressors and pumps, in particular, such hypereutectic aluminum-silicon thread alloys are used as primary silicon thread alloys. The present invention relates to a method for casting a hypereutectic aluminum-silicon thread alloy that can be cast with good yield and with little segregation of elements.

(Background of the invention) Hypereutectic aluminum-silicon thread alloys have the property of good flowability during casting, and also have a solidified structure in which a hard silicon phase crystallizes in the base alloy. Because of this, it also has excellent wear resistance. It also has the characteristic of having a small coefficient of thermal expansion. For this reason, for example, vane materials for vane compressors and pumps, bearing materials, etc. It is used as a material for pistons, etc. However, as shown in the phase diagram in Figure 1, this hypereutectic aluminum-silicon thread alloy has a wide solidification temperature range and the specific gravity of silicon that crystallizes as primary crystals is small compared to the specific gravity of the matrix. Because of this, gravitational segregation is extremely likely to occur during the solidification process, making it a difficult material to cast.

Therefore, when casting a hypereutectic aluminum-silicon thread alloy having such casting characteristics, in order to prevent the occurrence of gravitational segregation and obtain a homogeneous structure with a good yield, (1) primary silicon crystal grains are Method of refining, (2) Coagulation 1l
It is said that it is effective to take measures such as shortening the distance between ji and (3) increasing the specific gravity of primary silicon.

(Prior art) Conventionally, when implementing the measures shown in (+) and (2) above, specifically, Gobe Ohira and Katsuya Iyo Seshin Incorporated Association 1 "
As stated in "Casting Engineering" published by the Japan Institute of Metals, p. 183, P (phosphorus) is added as a phosphorizer to refine primary silicon crystals.''2, in order to shorten the solidification time as much as possible. Generally, it is poured into a mold at as low a temperature as possible.

However, in normal molds, an air cap occurs between the mold and the solidified shell, and the latent heat of solidification of the hypereutectic aluminum-silicon thread alloy itself is large (the latent heat of solidification of silicon is equal to the latent heat of solidification of aluminum). (approximately 4 times as large), the solidification rate does not necessarily increase even when a metal mold is used for the mold. Therefore, in order to prevent the occurrence of gravitational segregation, it is necessary to reduce the size of the casting or make it thinner. Currently, it is necessary to reduce the solidification time by shortening the solidification time to suppress the levitation and segregation of primary silicon during casting, which limits the size and shape of the cast product. was there.

Conventionally, as a measure to solve such problems, there is a method of pressurizing molten metal during solidification, such as in molten metal forging. According to this molten metal forging, the freezing point of the molten metal is increased by 7 years due to the effect of pressurization, which increases the degree of supercooling and refines the crystal grains, and eliminates the air gap between the mold and the solidified shell. Therefore, the cooling rate increases and the solidification time is shortened, which has a great effect of suppressing the occurrence of gravitational segregation. However, in order to expect these effects, pressurization of 1,000 atmospheres or more is required, which makes the equipment extremely large and has the problem of poor productivity. Specifically, when taking the measures shown in (3), as announced in the Abstracts of the Japan Society of Light Metals, Cr (chromium)
By adding a third element such as There is an attempt.

However, there are limits to the elements that can increase the specific gravity of crystallized substances, and the amount added must also take into account the effect on the mechanical properties and wear resistance properties of the aluminum-silicon thread alloy. At present, the method has not been put into practical use industrially.

(Purpose of the Invention) This invention was made by focusing on the two problems of the conventional technology, and it is not necessary to use a metal mold as a casting mold, but the size and shape of the product are subject to significant restrictions. It is possible to produce T4 structures of hypereutectic aluminum-silicon thread alloys with low segregation of primary silicon at a high yield without using large-scale equipment like molten metal forging or adding third elements. The object of the present invention is to provide a method that allows casting.

(Structure of the Invention) This invention provides a hypereutectic aluminum-silicon thread alloy with 14
When manufacturing, a molten hypereutectic aluminum-silicon alloy is injected into a mold, and while the molten alloy solidifies in the mold, a feeder is constantly applied to disperse the primary silicon that crystallizes. The mold is rotated LryC at a speed of 2
(2 rotations, 2 rotations, etc.) is considered as 1.

By the way, in mold casting and sand mold 1J construction for lightning protection, solidification begins from the wall surface of the mold, and the primary silicon that crystallizes there is captured in the solidified part, and the primary silicon that crystallizes in the unsolidified part. Tonto floats to the surface due to the difference in specific gravity and collects in a limited area on the upper part of the casting, causing significant segregation.

On the other hand, in the method according to the present invention, the mold is rotated or turned over while the molten alloy solidifies, so the floating direction of the primary silicon changes constantly, and the upper part Since the primary silicon particles that have arrived are captured by the constantly moving solidification interface, a structure in which primary silicon particles are uniformly dispersed over a wide area of the ingot after solidification is obtained.

Furthermore, the flow of the molten alloy caused by rotating or inverting the mold has the effect of multiplying the crystal grains, so the crystal grains become finer and the grains become finer, promoting the slurry-like solidification. 119. be uniform.

By the way, when the mold is rotated while the molten alloy is solidifying, centrifugal force acts on the molten alloy, and as mentioned above, this centrifugal force pulls the crystallized primary silicon in the centripetal direction due to the difference in specific gravity. At the same time, the effect of the riser will be reduced, so it is more desirable that the speed at the time of turning is not too high. That is, the multiple G of the centrifugal force generated by rotation of the mold relative to gravity is given by: G=1.12rN2xto-5=(1) r: distance from the center (c+n) N: rotational speed (rpm). Here, if we consider r to be the height from the center of the riser, in order for the riser to have this effect, it must be fo pGg d r<p g r = (
2) It is necessary to satisfy the following relationship: g: gravitational acceleration (cm/5ee2) ρ: molten alloy soundness (g/cm3). Therefore, from the above equations (1) and (2).

Therefore, it is desirable to set the upper limit of the rotation speed according to the size of the mold in order to obtain the feeder action during casting.

(Example) FIG. 2 is an explanatory longitudinal cross-sectional view of a casting apparatus used to carry out this invention. In FIG. 2, l is a mold;
This casting! 1 holds the upper mold 2 and the lower mold 3 at both end portions 4,
4, and has a casting space 1a inside, and a feeder part 5 is provided in the center of the casting space 1a over the entire circumference. This feeder part 5 is provided with a breathable heat insulating sleeve 6, and this heat insulating sleeve 6 allows a small feeder to have a large effect.

Further, 7 is a sprue, 8 is a lid made of a heat insulating material that closes the hot water lower, and 9 is a screw for fixing the lid 8. Furthermore, 11 is a total of 4 rolls (the two in front are not shown) on which the mold 1 is placed, 1
2 is a rotating shaft for connecting and fixing the roll 11, 13 is a rotating shaft 1
2 is the fixed pulley, 14 is the rotation of the motor 5 @ 15a
A pulley 16 is fixed to the pulley 13. A bell I is hung on the pulley 13.14. The mold 1 of this device used was one in which the casting space 1a had a diameter of 50 mm and a length of 500 mm, and the feeder portion 5 had a height of 50 mm and a width of 60 mm.

Next, as a hypereutectic aluminum-silicon thread alloy, A
Sen-25% Sf alloy, and AJlcoa A3
90 alloy (A4-18 wt% Si alloy) was selected. Then, 1.5 kg of each of these alloys was melted in a graphite crucible using a metal resistance heating electric furnace, and then poured from the hot water lower of mold I. Next, after installing the lid 8 and fixing it with screws 9, the mold 1 was solidified while rotating or inverting at a speed of 2 to 50 rpm as shown in the table to obtain the cast product 20 shown in FIG. 3. .

In addition, when pouring, in the case of the A-25 wt % Si alloy, it was melted at 900'C, treated as a molten metal at 870°C, and then poured at 870°C. In the case of A390 alloy, it was melted at 850°C, treated at 800°C, and then poured at 780°C. The molten metal was treated using a commercially available degassing agent and a P treatment agent (phosphorizer) for refining primary silicon, and after the treatment was left standing for 10 minutes, the molten metal was poured at the above temperatures. . The temperature of the mold 1 was set at 200° C., and a coating material containing a mixture of calcium carbonate, water glass, silica sand, and kaolin was applied to the inner wall of the mold 1.

(Comparative Example) For comparison, a case was also conducted in which the mold l was not rotated (see table) assuming normal mold casting. In this case, the same conditions as in the previous example were used except for the rotation conditions.

(Evaluation example) Casting product 20 having the shape shown in Fig. 3 obtained by the above process
In order to investigate the degree of segregation of primary silicon particles in the diameter direction in the product part 20a, the product part 20a was sequentially sliced in the longitudinal direction, and the area ratio occupied by the primary silicon particles was measured by a point counting method. This result is ttS
Shown in Figure 4.

As shown in Figure 4, in the case of the comparative example, since it corresponds to normal gravity casting, many primary silicon particles are distributed above the product part, and the primary silicon particles are distributed due to the difference in specific gravity. Typical gravitational segregation occurs, concentrated at the top of the casting.

On the other hand, in the case of Examples 1 to 5, the primary silicon particles were uniformly dispersed over the entire area, resulting in a homogeneous structure, and the distribution of primary silicon particles was different from that in the conventional case. It is clear that this has been significantly improved. And 5i
Even in the case of Example 3 in which ll is considerably large, nk is fairly uniform for the primary silicon particles. In addition,
In Example 5, since the rotational speed was as low as 2 rpm, there was some variation in the dispersion of primary silicon particles. therefore,
Naturally, it was found that the number of revolutions should not be too low, and that it would be better to set it to about 5 rpm or more. On the other hand, in Example 4 where the rotational speed was considerably high, although the primary silicon particles were uniformly dispersed, shrinkage cavities were observed in the central portion of the product portion 20a. This is thought to be due to the riser losing its effectiveness due to the centrifugal force becoming too large, and it was also confirmed that the rotation speed should not be too high. By the way, in the case of this example, the above formula (1)
The upper limit of the rotational speed calculated by (2) was less than 109 rpm, which was actually confirmed by Example 4.

In addition, although the above-mentioned example shows the case where a metal mold is used as the mold l, it is naturally possible to use a sand mold.

However, in the case of a sand mold, the cooling rate is low and there is a risk that the structure will become coarse, so it is thought that it will be necessary to improve the molten metal with sodium.

In addition, in the above embodiment, the feeder section 5 is provided at one location in the central portion, but it is also possible to provide it at multiple locations depending on the size of the product section, as with a normal feeder. . In this case, it goes without saying that it is desirable to select the shape and arrangement, as well as the number of revolutions of the mold, so that the feeder continuously acts during the solidification of the molten alloy. Furthermore, the multi-cast product 20 is simply an alloy ingot, and can be applied not only to cases in which regular-shaped members are cut out from this alloy ingot, but also to cases where the cast product 20 is a product or part itself. Applicable.

(Effects of the Invention) As explained above, according to the present invention, when casting a hypereutectic aluminum-silicon thread alloy, the hypereutectic aluminum-silicon thread alloy is injected into a mold, and the While the molten metal is solidifying in the mold, the feeder is constantly applied and the mold is rotated at a speed that ensures the dispersion of the crystallized primary silicon. Therefore, from the viewpoint of preventing the occurrence of gravitational segregation, the alloy Since there is no need to significantly shorten the solidification rate of molten metal, it is not necessary to use a metal mold as a casting mold, and there are no significant restrictions on the size or shape of the cast product, and large-scale equipment like molten metal casting is used. It is said that it is possible to cast hypereutectic aluminum-silicon thread alloy castings (alloy ingots, 9 product parts, etc.) with a high yield and less segregation of primary silicon without adding any tertiary elements. It can bring about very good effects.

[Brief explanation of the drawing]

Fig. 1 is a state diagram of the aluminum-silicon alloy, Fig. 2 is a vertical cross-sectional explanatory view of the casting device used in the embodiment of this invention, Fig. 3 is an enlarged view of the cast product, and Fig. 4 is the cast product. 2 is a graph showing the distribution of the area ratio of primary silicon depending on the position of . Patent Applicant Kuchisan Jidosha Co., Ltd. Representative Patent Attorney Koshio Standing Pipe 1 Figure S Top (Weight Z) Figure 2 08 4th BQ Procedural Amendment (Voluntary) June 24, 1981 [President of the Patent Office Kazuo Wakasugi 1 , Indication of the case 1981 Patent Application No. 94934-3, Person making the amendment Relationship to the case Patent applicant I1U Address: Mr. 2 Takaracho, Kanayō-ku, Yokohama-shi, Kanagawa Prefecture
Name (399) Nissan Motor Co., Ltd. 7 Sat 6, the number of inventions minus the power increase 1 from the amended number 7, the scope of the claims of the subject of the amendment AAII '+' ai 4 parts 1, specification No. 1 The claims on lines 5 to 12 of the page are amended as follows. 2. Claims (1) When casting a hypereutectic aluminum-silicon thread alloy, a molten hypereutectic aluminum-silicon thread alloy is poured into a mold, and the molten alloy solidifies in the mold. A method for casting a hypereutectic aluminum-silicon thread alloy, characterized in that during the casting process, a riser is constantly applied and the mold is rotated at a speed that ensures the dispersion of primary crystallized silicon.
Agent Patent Attorney Shio Ko Toyote Itomitsu Negative 1j Positive ψ Dimension (Voluntary) November 7, 1981 Japan Patent and Negative Agency Commissioner Kazuo Wakasugi 1, ] 1 yen display 1988 Patent Application No. 94934 2 , Title of defense: Casting method of hypereutectic aluminum-silicon thread 1-7112 3, Relationship with the person making the amendment Patent applicant address (EI: location) Name: 2 Takaracho, Kanayō-ku, Yokohama-shi, Kanagawa Prefecture )(399) 日t)'(l gEI Dogetsuhin Co., Ltd. 2 Representative Shun Ishihara 4, Agent address (registration office) Kobiki IY (Ginza) 2-8-9 Ginza, Chuo-ku, Tokyo 104 Bill Episode 7E (5B?) 2781 #
(Representative) 6, Number of inventions increased by amendment 7, Subject of amendment, , O'+111 'J to JIIf4
"+, "'・Madhi 1 ゛ No. 1, Lines 15 to 16 of page 1 of the specification are amended as follows. [This invention provides wear resistance] 2, page 2, lines 6 to 8 are corrected as follows. [Hypereutectic aluminum-silicon thread platinum is a hard silicon phase crystallized in the base alloy.'' Add phosphorus) to ``. 4. The third line of page 5 is amended as follows. "Specifically, it is described in Japanese Unexamined Patent Publication No. 48-102035." 5. Correct page 6, lines 15 to 16 as described in F. ``Some of the ion is captured in the solidified part, but most of it is due to the difference in specific gravity.'' 6. Correct ``after solidification'' to ``after solidification'' in line 4 of page 7. 7. Correct rAlcaaJ in the first line of page 10 to rAAJ. 8. Delete "(phosphorizer)" from lines 15 to 16 on page 10. 9 The table on page 11 of the same is amended as follows. that's all

Claims (1)

[Claims] (1) When casting a hypereutectic aluminum-silicon thread alloy, the molten hypereutectic aluminum-silicon thread alloy is poured into a mold, and the feeder is constantly turned on while the molten alloy solidifies in the mold. A method for casting a hypereutectic aluminum-silicon thread alloy, characterized in that the mold is rotated at a speed that ensures the dispersion of primary crystalline silicon that crystallizes during the action.