JPH06328225A - Casting method - Google Patents

Abstract

PURPOSE:To provide a casting method, by which a sound cast product without casting defect can be obtd., at the time of applying a thixo-casting method. CONSTITUTION:In the casting method, by which a casting material 9 having solid phase and liquid phase to coexiste is prepared and successively, is passed through a gate 5 in a mold 1 in the pressurizing condition and filled into a cavity 4 in the mold 1, the particles making the viscosity of the liquid phase high, is mingled into the liquid phase in the casting material 9 to set the volume ratio Vf of the particles in the liquid phase to Vf >=20%. By this method, as the solid phase together with the liquid phase are passed through the gate 5, and packed into the cavity 4, the generation of the casting defect in such case of separately packing the solid phase and the liquid phase into the cavity 4 is avoided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting method, and in particular, to preparing a casting material in which a solid phase and a liquid phase coexist, and then passing the casting material through a gate of the mold under pressure to form a cavity in the mold. A casting method for filling.

[0002]

2. Description of the Related Art A thixocasting method is known as a casting method using this type of casting material. According to this method, the degree of freedom regarding the alloy design and shape is large, so that a high quality casting having the required characteristics and the required shape can be obtained.

[0003]

In the thixocasting method, the factors that affect the casting quality include the thixotropy of the casting material, as well as the filling behavior of the casting material, such as the viscosity when passing through the gate. , Shear rate, Reynolds number and the like.

Among them, the shear rate of the casting material when passing through the gate is a particularly important factor in applying a shearing force to the solid phase to achieve its fine spheroidization. This shear rate is increased as the cross-sectional area of the gate becomes smaller.

However, if the cross-sectional area of the gate is reduced to obtain a predetermined shear rate, the following problems will occur in relation to the particle size of the solid phase.

That is, in the process of pressure-filling the casting material into the cavity, a part of the liquid phase having a low viscosity is initially injected into the cavity through the gate, but the solid phase gradually stagnates near the entrance of the gate and solidifies. Because a collection of phases is formed,
The aggregate blocks the entrance of the gate and stops or extremely limits the injection of liquid phase into the cavity.
Since the aggregate of this solid phase has a high viscosity,
It is not immediately injected into the cavity through the gate, but is once pressurized near the gate, then passes through the gate in a laminar flow state and is injected into the cavity. Immediately after that, a low-viscosity liquid phase turbulently flows through the gate. It passes and is ejected to the cavity.

As described above, when the solid phase and the liquid phase are separately filled in the cavity, and when the filling manner in the cavity is different between the solid phase and the liquid phase, the filling pressure of the casting material in the cavity varies. Therefore, segregation is likely to occur in the casting, and air is likely to be entrained in the casting due to ejection of the liquid phase.

For example, in a material equivalent to A357, which is an Al-Si-Mg-based alloy for casting, the phenomenon is explained by using the following mathematical formula.

Reynolds number Re = vdρ / η (v: injection speed, d: pipe diameter, ρ: density, η: viscosity) Loss head h _l = (λl / d) v ² / 2g (λ: pipe friction coefficient, l: pipe length, d: pipe diameter, v: injection speed, g: gravitational acceleration), loss head h ₁ means the mechanical energy lost by a unit weight of fluid.

Here, the pipe friction coefficient λ is λ = 64 / Re in the case of a circular pipe laminar flow, and λ = (64 / Re) 8a ² / (a + b in the case of a rectangular pipe (2a × 2b) laminar flow. ) ² X. X is X = (16/3)-(1024 / π ⁵ ) b /
a {tanh (πa / 2b) + (1/243) tanh
(3πa / 2b) + ...}.

When the aggregate of primary crystals α which is a solid phase closes the gate, the viscosity η of the aggregate increases, so that the Reynolds number Re becomes small. The decrease in Reynolds number Re causes an increase in loss head h _l , so that the aggregate of primary crystals α is pressurized near the gate and then injected into the cavity through the gate.

In view of the above, the present invention increases the viscosity of a liquid phase in a casting material so that the solid phase and the liquid phase are filled in the cavity together, and the solid phase and the liquid phase are separately provided in the cavity. Even if a situation occurs where the liquid phase is filled into the cavity, the filling mode of the liquid phase into the cavity is approximated to that of the solid phase as the viscosity of the liquid phase becomes higher, thereby suppressing the occurrence of casting defects as much as possible. It is an object of the present invention to provide the above-mentioned casting method that can be performed.

[0013]

According to the present invention, a casting material in which a solid phase and a liquid phase coexist is prepared, and then the casting material is passed under pressure through a gate of a mold to fill the cavity of the mold. In the casting method described above, particles for increasing the viscosity of the liquid phase are mixed in the liquid phase of the casting material, and the volume fraction Vf of the particles in the liquid phase is set to Vf ≧ 20%. .

[0014]

When the viscosity of the liquid phase in the casting material is increased as described above, the solid phase and the liquid phase pass through the gate together and are filled in the cavity without being separated. In addition, even when the solid phase and the liquid phase are separately filled in the cavity, the Reynolds number becomes small when the liquid phase passes through the gate next to the solid phase aggregate. The phase passes through the gate in a laminar state, which prevents the liquid phase from jetting into the cavity, and the filling mode of the liquid phase into the cavity approximates that of the solid phase as the viscosity of the liquid phase increases. Can be made.

In order to generate such a phenomenon, it is necessary to increase the viscosity of the liquid phase to about 50 times or more that in the case where no particles are contained. From this viewpoint, the volume fraction Vf of particles in the liquid phase is set to Vf ≧ 20%. This volume fraction V
The upper limit value of f is preferably Vf = 70%. V
When f> 70%, the hot running property deteriorates when casting a casting having a complicated shape.

[0016]

EXAMPLE FIG. 1 shows an outline of a pressure casting apparatus used for carrying out the thixocasting method. The mold 1 of the pressure casting apparatus comprises a fixed mold 2 and a movable mold 3 facing the fixed mold 2.
And forming a molding cavity 4 having a circular cross section and a gate 5 communicating with one end thereof by the two molds 2 and 3.
The gate 5 communicates with the casting material inlet 6 of the fixed mold 2. The fixed mold 2 is provided with a sleeve 7 that communicates with the loading port 6, and a pressure plunger 8 that is inserted into and removed from the loading port 6 is slidably fitted into the sleeve 7.

In carrying out the thixocasting method, the following steps are sequentially carried out. (A) A casting material 9 in which a solid phase and a liquid phase coexist is prepared. (B) The casting material 9 is charged into the charging port 6. (C) The pressurizing plunger 8 is inserted into the charging port 6, and the gate 5 is pressed while pressurizing the casting material 9 by the pressurizing plunger 8.
To sequentially fill the cavity 4 with a high-speed laminar flow. (D) By holding the pressure plunger 8 at the end of the stroke, a pressure is applied to the casting material 9 filled in the cavity 4, and the casting material 9 is solidified under the pressure to obtain a casting.

As the casting material 9, a material in which particles for increasing the viscosity of the liquid phase are mixed is used, and the volume fraction Vf of the particles in the liquid phase is set to Vf ≧ 20%.

When the viscosity of the liquid phase in the casting material 9 is increased as described above, the solid phase and the liquid phase pass through the gate 5 and are filled into the cavity 4 without being separated. Further, even when the solid phase and the liquid phase are separately filled in the cavity 4, the Reynolds number becomes small when the liquid phase passes through the gate 5 next to the solid phase aggregate, so that the Reynolds number becomes small. , The liquid phase passes through the gate 5 in a laminar flow state, thereby preventing the liquid phase from being jetted into the cavity 4, and the filling mode of the liquid phase into the cavity 4 is accompanied by the increase in viscosity of the liquid phase. It can be approximated to that of a solid phase.

In the casting material, when the average particle size of the solid phase is A and the average particle size of the particles is B, the ratio A / B of A and B is set to A / B ≧ 2. By setting in this way, the fluidity of particles between solid phases is improved,
The particles can be evenly dispersed in the liquid phase to increase the viscosity evenly throughout the liquid phase. The ratio A / B
When A / B <2, the average particle diameter B of the particles is too large and the fluidity of the particles between the solid phases deteriorates, resulting in poor dispersibility. Therefore, the viscosity of the liquid phase is made uniform throughout the liquid phase. Cannot be increased.

Such particles include crystallized particles crystallized in the liquid phase and high melting point solid particles added to the casting material.

When the particles are crystallized grains, such crystallized grains exist not only in the liquid phase but also in the solid phase. Therefore, in order to increase the volume fraction Vf of the crystallized grains in the liquid phase and to reduce the average grain size of the crystallized grains, the cooling rate at the time of manufacturing the casting material is increased, and at the time of casting the casting material. A means of setting the volume fraction (solid phase fraction) Vf of the solid phase to be low is adopted.

If the particles are solid particles, the solid particles may be incorporated into the solid material prior to manufacturing the casting material, or
Alternatively, they are added and mixed in the liquid phase at the time when the solid phase crystallizes in the manufacturing process of the casting material. In the liquid phase of the casting material thus obtained, there are cases where only solid particles are mixed, and cases where both solid particles and crystallized particles are mixed due to their chemical components. In addition, some solid particles may be mixed in the solid phase.

A specific example will be described below.

Table 1 shows three Al alloys (a) for casting materials.
The composition of (c) is shown.

[0026]

[Table 1] In Table 1, Al alloy (a) is a Al-Mg ₂ Si alloy, also an Al alloy (b) is a Al-Si-Cu based alloy, further (c) is the Al-Si-Mg based alloy It is a material equivalent to A357.

Table 2 shows examples (1) to (5) of five kinds of casting materials.
The type of Al alloy used when producing (5) and the method for producing the same are shown below.

[0028]

[Table 2] Next, a plurality of castings were cast by applying the thixocasting method using the pressure casting apparatus of Examples (1) to (5) of casting materials and FIG.

In this case, the cross-sectional area of the gate 5 was gradually narrowed as follows to increase the shear rate for the casting material 9.
That is, the cross-sectional area of the gate 5 is 9 mm (length) x 18 mm (width) =
Although it is 162 mm ² , this gate 5 has a diameter of 2 mm (φ
2) The first porous body having a plurality of through holes and the sum of the cross-sectional areas of the through holes being 138 mm ² , and a diameter of 3 mm (φ3)
Has a plurality of through holes, and the sum of the cross-sectional areas of these through holes is 1
A second porous body having a size of 30 mm ² is installed. When the first porous body is installed on the gate 5, the cross-sectional area of the gate 5 becomes about 85% of the initial size, and in the case of the second porous body, the initial cross-sectional area is about 80%.
%.

2 to 6 show examples (1) to (1) of casting materials.
It is a microscope photograph which shows the metal structure when (5) is heated and made into a semi-molten state, and each of FIG. 2, FIG. 3, FIG. 5, and FIG. 6 is 100 times, and FIG. 4 is 400 times. Figure 2 is an example (1)
3 corresponds to the example (2), FIG. 4 corresponds to the example (3), FIG. 5 corresponds to the example (4), and FIG. 6 corresponds to the example (5).

In the example (1) shown in FIG. 2, the dark gray agglomerated particles and in the example (2) shown in FIG. 3, the black spherical particles are intermetallic compounds Mg ₂ Si (specific gravity 1. 99), and this Mg ₂ Si is a solid phase (α-Al).
And mixed in the liquid phase. In the example (3) shown in FIG. 4, the dark gray lump particles are SiC particles that are solid particles, and most of the SiC particles are mixed in the liquid phase, but some of them are in the solid phase (α-Al. ) Mixed in. In the case of the examples (4) and (5) shown in FIGS. 5 and 6, the particles as described above do not exist in the solid phase (α-Al) and the liquid phase.

Table 3 shows the volume fraction Vf of the solid phase (α-Al) in Examples (1) to (5) measured based on FIGS. 2 to 6, its average particle size A and particles (Mg ₂ Si,
The total integration rate Vf of SiC) and the average particle size B of the particles existing in the liquid phase are shown.

[0033]

[Table 3] Table 4 shows the properties of the liquid phase of the casting material regarding various castings, the ratio A / B of the average particle diameter, the structure of the gate, the injection speed of the casting material,
The Reynolds number of the liquid phase and the properties of the casting are shown. Examples (1a) to (5c) of castings and examples (1) to (1) of casting materials
Regarding the relationship with (5), examples (1a) to (1c) are examples (1).
Examples (2a) to (2c) are examples (2), Examples (3a) to
(3c) corresponds to example (3), examples (4a) to (4c) correspond to example (4), and examples (5a) to (5c) correspond to example (5).

In the casting examples (1a) to (3c), the Reynolds number of the liquid phase is a value in a state where particles are mixed in the liquid phase.

In the table, ◯ mark means “absent”, Δ mark means “somewhat”, and X mark means “large amount”.

[0036]

[Table 4] In Table 4, when the opening amount of the gate is as large as 9 mm × 18 mm, it is difficult to separate the solid phase and the liquid phase, so that the casting examples (1a), (2a), (3a) and (4)
Regarding a), its properties are good, but segregation occurs in Example (5a).

When the opening amount of the gate is narrowed by the first porous body (φ2) or the second porous body (φ3), the casting example (1
In b) and (1c), particles (Mg ₂
The volume fraction Vf of Si) is Vf = 17%, therefore Vf
<20%, and A / B is A / B = 1.6, and therefore A / B <2, so that the degree of increase in viscosity of the liquid phase is low and air entrapment occurs.

In the casting examples (2b) and (2c),
As shown in Table 2, the cooling rate when producing the casting material example (2) was set higher than that in the case of the example (1) to obtain particles (Mg ₂ S).
The average particle size B of i) is made small and spherical, and as shown in Table 3, the volume fraction Vf of the solid phase is made lower than that in the case of the example (1) to obtain the volume fraction Vf of the particles in the liquid phase. Measures such as increasing the number are adopted.

As a result, the volume fraction Vf in the liquid phase is V
f = 45%, therefore Vf ≧ 20%, and A /
Due to B being A / B = 2.7 and thus A / B ≧ 2, the viscosity of the liquid phase is as shown in Table 4 for example (1
Since it is increased to 35 times that in the cases of b) and (1c), the properties of the casting become extremely good.

In the casting examples (3b) and (3c),
The volume fraction Vf of particles (SiC) in the liquid phase is Vf = 6
Due to the fact that 0% and A / B are A / B = 10, the properties of the casting become extremely good as described above.

Examples of castings (4b), (4c) and (5)
In b) and (5c), as shown in Table 4, the viscosity of the liquid phase is extremely low, and as a result, a large amount of air entrapment and segregation occur in the casting.

FIG. 7 is a photomicrograph (100 times) showing the metal structure of the casting material in the vicinity of the first porous body when a casting corresponding to the casting example (4b) is obtained. Figure 7
From this, it can be seen that a large number of light gray lumpy solid phases are stagnant in the vicinity of the through holes of the first porous body and aggregates of these solid phases are formed.

Table 5 shows examples (2c) and (3c) of castings.
The properties of the liquid phase of the casting material, the ratio A / B of the average particle diameters, and the properties of the casting are shown for the examples (2c ₁ ) and (3c ₁ ) corresponding to.

[0044]

[Table 5] As is clear from the example (2c ₁ ) of the casting in Table 5, the volume fraction Vf of the particles in the liquid phase is Vf ≧ 20%, and A /
If B is set to A / B ≧ 2, it is possible to obtain a cast product having good properties.

Further, comparing the casting example (2c) in Table 4 and the casting example (3c ₁ ) in Table 5, the V of particles in the liquid phase is compared.
f is Ryorei (2c), if the (3c ₁₎ on the same, also A / B be both Example (2c), but (3c ₁₎ is the same for example for the viscosity of the liquid phase (2c) Is higher than that of the example (3c ₁ ) by 0.2 Pa · sec. This means that the use of crystallized grains as the particles has a higher effect of increasing the viscosity of the liquid phase than the use of solid particles.
Due to this, the cast example (2c) is more cast (3c).
It was found to have a more uniform metallographic structure than that of ₁ ).

In the present invention, metal materials other than Al alloy,
For example, it is also applicable to a casting method using a casting material made of an alloy such as Fe, Cu, Mg, and Ti.

[0047]

EFFECTS OF THE INVENTION According to the present invention, by adopting a relatively simple means such as mixing a specific amount of particles in the liquid phase of the casting material as described above, casting such as air entrainment and segregation can be achieved. It is possible to avoid the occurrence of defects, whereby a casting with good casting quality can be obtained.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a pressure casting device.

FIG. 2 is a micrograph showing a metal structure in an example (1) of a casting material in a semi-molten state.

FIG. 3 is a micrograph showing a metal structure in an example (2) of a semi-molten casting material.

FIG. 4 is a micrograph showing a metal structure in an example (3) of a semi-molten casting material.

FIG. 5 is a micrograph showing a metal structure in an example (4) of a semi-molten casting material.

FIG. 6 is a micrograph showing a metal structure in an example (5) of a semi-molten casting material.

FIG. 7 is a micrograph showing a metal structure of a casting material in a casting process.

[Explanation of symbols]

 1 Mold 4 Cavity 5 Gate 8 Pressure Plunger 9 Casting Material

Claims (5)

[Claims] 1. A casting method in which a casting material in which a solid phase and a liquid phase coexist is prepared, and then the casting material is passed under pressure through a gate of a mold to fill the cavity of the mold. The casting method, wherein particles for increasing the viscosity of the liquid phase are mixed in the liquid phase, and the volume fraction Vf of the particles in the liquid phase is set to Vf ≧ 20%. 2. The ratio A / B of A and B, where A is the average particle size of the solid phase and B is the average particle size of the particles.
The casting method according to claim 1, wherein is A / B ≧ 2. 3. The casting method according to claim 1, wherein the particles are crystallized particles crystallized in the liquid phase. 4. The casting method according to claim 1, wherein the particles are solid particles added to the casting material. 5. The particles are crystallized particles crystallized in the liquid phase and solid particles added to the casting material.
The casting method according to claim 1 or 2.