JP3044519B2 - Cast body and casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cast body, particularly an alloy material having a eutectic structure region having a high hardness and a primary crystal structure region having a low hardness at room temperature, and is subjected to the application of a thixocasting method. And a method for casting the same.

[0002]

2. Description of the Related Art Conventionally, in such a casting, a eutectic structure region and a primary crystal structure region are substantially uniformly dispersed throughout the casting in order to improve mechanical properties.

[0003]

However, in order to further increase the strength and ductility of the cast,
It is necessary to make the hardness of the surface region higher than the hardness of the main region inside.

Therefore, various surface hardening treatment methods have been put to practical use, but it is not desirable to perform the above treatment on the cast body after casting, since the number of production steps and production costs increase accordingly.

[0005] In view of the above, it is an object of the present invention to provide a casting and a method for casting the same, which achieve high strength and high ductility by changing the metal structure of the surface region and the main region.

[0006]

According to the present invention, an alloy material having a eutectic structure region having a high hardness and a primary crystal structure region having a low hardness is cast at room temperature under the application of a thixocasting method. In the cast body, the relationship of A> B is established between the area ratio A of the eutectic structure region in the surface region and the area ratio B of the eutectic structure region in the main region inside the surface region. It is characterized by being established.

The present invention uses an alloy material having a eutectic structure region having a high hardness and a primary crystal structure region having a low hardness at ordinary temperature,
In casting the cast body under the application of the thixocasting method, the shear rate when the semi-solid alloy material in which the solid phase and the liquid phase coexist passes through the gate of the mold is γ, and the viscosity is μ. The shear rate γ is 10 S ⁻¹ ≦ γ ≦ 150
0S ^-1 and between the shear rate γ and the viscosity μ, μ ≦
Characterized in that to establish the relationship 300γ ^-1.2.

[0008]

In the cast body, the surface region has more eutectic structure regions having higher hardness than the main region, so that its hardness is higher than that of the main region, thereby increasing the strength of the cast body. And high ductility is achieved. In this case, since a primary crystal structure region having a low hardness also exists in the surface region, the primary crystal structure region avoids a reduction in toughness due to an increase in hardness of the surface region.

Further, according to the casting method, the cast body can be easily mass-produced.

However, when the shear rate γ is γ <10S ⁻¹ ,
It is difficult to cause a difference in the area ratios A and B of the eutectic structure region between the surface region and the main region, while γ> 15
In the case of 00S- ¹ , the alloy material in a semi-molten state is injected into the cavity, so that pores are easily generated in the casting, and the casting quality is deteriorated.

The relationship between the viscosity μ and the shear rate γ is μ> 3.
In 00Ganma ^-1.2, the same way the surface area and the area rate A of the eutectic zone between the main area, it is difficult to produce a difference in B.

[0012]

FIG. 1 shows a pressure casting apparatus 1, which is an Al alloy as an alloy material by a thixocasting method.
It is used for casting a casting using an alloy material.
The pressure casting apparatus 1 includes a fixed mold 2 and a movable mold 3 having mating surfaces 2a and 3a as molds.
A casting molding cavity 4 is formed between a and 3a.
A chamber 6 in which the Al alloy material 5 is placed is formed in the fixed mold 2, and the chamber 6 communicates with the cavity 4 via a gate 7. A sleeve 8 communicating with the chamber 6 is provided upright on the fixed mold 2, and a pressurizing plunger 9 inserted into and removed from the chamber 6 is slidably fitted to the sleeve 8. The gate 7 is formed by an annular plate 10, which is sandwiched between fixed and movable dies 2, 3.

FIG. 2 shows a phase diagram of the Al-Si alloy.
Table 1 shows the composition of the hypoeutectic Al alloy material. In this case, the solid solubility limit of Si with respect to Al at room temperature is 0.1.
1% by weight. 0.02% by weight of Fe;
0% by weight for Cu, 1.0% by weight for Mg
It is. In FIG. 2, a corresponds to the Al alloy material, and therefore, at room temperature, the Al alloy material has a eutectic structure region having a high hardness, that is, a eutectic Al-Si structure region, a primary crystal structure region having a low hardness, That is, it has a primary crystal α-Al structure region. This Al
The alloy material is cut out from a high-quality long continuous cast material cast under the application of a continuous casting method. Is being done. The dimensions of the Al alloy material are 76 mm in diameter and 85 mm in length.

[0014]

[Table 1] When the differential scanning calorimetry (DSC) was performed on the Al alloy material, the result of FIG. 3 was obtained. In the differential thermal analysis curve b of FIG. 3, the Al alloy material has a first chevron endothermic portion c due to dissolution of the eutectic Al-Si structure region and a second chevron endothermic portion d due to dissolution of the primary crystal α-Al structure region. Have. The peak value E ₁ of the first chevron absorbing portion c is E ₁ = 9.1 mcal / s, and the peak value E ₂ of the second chevron absorbing portion d is E ₂ = 4.5 mca.
1 / s, so that a relationship of E ₁ > E ₂ is established between both peak values E ₁ and E ₂ .

When such a relationship is established, a semi-solid state in which a solid phase (substantially solid phase, the same applies hereinafter) and a liquid phase are prepared by subjecting an Al alloy material to heat treatment. Eutectic Al-Si
The liquid phase generated from the tissue area has a large latent heat. as a result,
In the solidification process of the thixocasting method, the liquid phase is sufficiently supplied around the solid phase in accordance with the solidification contraction of the solid phase, which is the primary crystal α-Al structure region. This is effective in preventing defects such as voids on the order of microns in the casting.

Next, the Al alloy material is placed in the heating coil of the induction heating device, and then the frequency is 1 kHz and the maximum output is
Heating was performed under the condition of 37 kW to prepare a semi-molten Al alloy material in which a solid phase and a liquid phase coexist. In this case, the solid fraction is set to 50% or more and 60% or less.

Thereafter, as shown in FIG. 1, a semi-molten Al alloy material 5 is placed in a chamber 6 and a mold temperature 25
Activating the pressure plunger 9 at 0 ° C.
The alloy material 5 was passed through the gate 7 while being pressurized to fill the cavity 4. Then, by holding the pressurizing plunger 9 at the end of the stroke, a pressing force is applied to the Al alloy material 5 filled in the cavity 4, and the Al alloy material 5 is solidified under the pressure, and the Al alloy material 5 shown in FIG. An alloy casting 11 was obtained.

In this casting operation, the pressure plunger 9
, The shear rate γ and the viscosity μ when the semi-molten Al alloy material 5 passes through the gate 7 were changed.

Table 2 shows the casting conditions of the various castings 11, that is,
The shear rate γ and the viscosity μ, and the area ratios A and B of the eutectic Al—Si structure region in the surface region and the main region inward therefrom are shown, respectively.

[0020]

[Table 2] FIG. 5 is a micrograph showing the metal structure in Example 1 of the cast body 11, (a) corresponding to the surface and its vicinity,
(B) corresponds to the core. FIG. 6 is a schematic drawing of FIG. In the figure, the light gray spherical region is the primary α-Al structure region, and the region filling the primary crystal α-Al structure region is eutectic A.
This is an l-Si tissue area. This is the same in FIGS. 7 and 8 described later.

5 and 6 and Table 2, the area ratio A of the eutectic Al-Si structure region in the surface region is larger than the area ratio B of the eutectic Al-Si structure region in the main region, that is, A> B.
It turns out that it is.

FIG. 7 is a photomicrograph showing the metal structure of Example 3 of the cast body 11. In this case as well, both area ratios A,
The relationship of A> B is established between B.

FIG. 8 is a photomicrograph showing the metal structure of Example 5 of the cast body 11, in which case the area ratios A and B are shown.
The relation of A = B is established between them. Therefore, Example 5 has a substantially uniform metal structure and corresponds to the above-mentioned conventional example.

The area ratios A and B are obtained by performing image analysis based on a micrograph.

FIG. 9 shows the metallographic structure of the surface region in Example 8 of the cast body which was cast using the molten aluminum alloy having the above-mentioned composition (Table 1) under the application of the pressure casting method. is there.

Next, test pieces were prepared from Examples 1 to 8 of the cast body 11 so as to include the surface and the vicinity thereof, and various tests were performed on each test piece. The results shown in Table 3 were obtained. .

In Table 3, the Q value is Q = σ _B + 150 ×
Logderuta (However, sigma _B is the tensile strength, also δ represents elongation, respectively) are represented by one in which the strength and ductility comprehensively determined to determine the quality of the casting 11. In this case, it is regarded as “excellent” if Q ≧ 450, “good” if Q ≧ 400, “acceptable” if Q ≧ 350, and “poor” if Q <350.

[0028]

[Table 3] As is clear from Tables 2 and 3, in Examples 1 to 4 of the casting 11, since the eutectic Al-Si structure region having higher hardness exists in the surface region than in the main region, the hardness is lower. It is higher than the main region, and thereby the cast body has higher strength and higher ductility. In this case, since a primary α-Al microstructure region having low hardness also exists in the surface region, the primary α-Al
The l-textured region avoids toughening associated with an increase in hardness of the surface region.

In the case of Examples 5 to 7, A
> B, the strength and the ductility are lower than those of Examples 1 to 4. In the case of Example 8, since the surface region has a chill structure, the Charpy impact value is particularly low and the toughness is low.

FIG. 10 shows the relationship between the shear rate γ and the viscosity μ when the Al alloy material 5 in the semi-molten state passes through the gate 7. In the figure, points (1) to (7) are examples 1 to 7 of the casting 11.
Respectively.

In FIG. 10, the shear rate γ is 6S ⁻¹ ≦ γ
≦ 1500 S ⁻¹ and the viscosity μ is 0.001 Pa ·
The range where s ≦ μ ≦ 40 Pa · s is the practicable range of the thixocasting method.

However, when the shear rate γ is 6S ⁻¹ ≦ γ <10S
^{In the case of -1} , the liquid phase generated from the eutectic Al-Si structure region cannot be sufficiently leached in the surface region of the alloy material 5 in the semi-molten state to increase the liquid phase concentration. Eutectic Al-Si between the surface region and the main region of
It is difficult to cause a difference between the area ratios A and B of the tissue area.
On the other hand, when γ> 1500S ⁻¹ , since the semi-molten Al alloy material 5 is injected into the cavity 4, pores are easily generated in the casting, and the casting quality is deteriorated.

Therefore, the shear rate γ when the Al alloy material 5 passes through the gate 7 is 10 S ⁻¹ ≦ γ ≦ 1500 S ⁻¹
Is set to Preferably, the Q value of Examples 1, 2 and 4 is 100S ^-1 ≤ γ ≤ 1500S ^-1 .

When the Al alloy material 5 passes through the gate 7, the relationship between Examples 1-4 and Example 5 in FIG. 10 and other plural examples omitted in FIG. result, it is necessary to establish a relationship between μ ≦ 300γ ^-1.2, it was found that. In this case, μ>
In 300γ ^-1.2, the area ratio of the eutectic Al-Si tissue region between Likewise the surface area and the main area A, may give rise to differences in B becomes difficult.

The summary is as follows. In the γ-axis and μ-axis intersecting each other at right angles in FIG. 10, four coordinates, that is, a coordinate f (10, 0.001), a coordinate g (10, 12), a coordinate h (1500, 0.02), and a coordinate j (1500,
0.001), the liquid phase is sufficiently leached into the surface region of the Al alloy material 5 in a semi-molten state by setting the shear rate γ and the viscosity μ so as to fall within the figure drawn (including the outline). As a result, the flow resistance of the Al alloy material 5 to the inner surface of the cavity 4 is reduced, thereby improving the formability of the Al alloy material 5 and achieving high strength and high strength as in Examples 1 to 4.
In addition, a highly ductile cast body 11 can be obtained. From the viewpoint of decreasing the flow resistance, the thickness t of the surface region having a high liquid phase concentration in the Al alloy material 5 is desirably t ≧ 1 μm. In order to further improve the quality of the casting 11 as in Examples 1 and 2, the shear rate γ and the viscosity
That is, the coordinate k (100, 0.001) and the coordinate m (10
0, 1), coordinate h (1500, 0.02) and coordinate j
What is necessary is just to set so that it may be contained in the figure (including the outline) drawn by connecting (1500, 0.001).

The alloy material is not limited to an Al alloy material.

[0037]

According to the present invention, as described above, the area ratio A and B of the eutectic structure region in the surface region and the main region is equal to each other.
By satisfying the relationship of> B, a cast having high strength, high ductility, and excellent toughness can be provided.

Further, according to the present invention, a cast having excellent mechanical properties as described above can be easily mass-produced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a pressure casting apparatus.

FIG. 2 is a phase diagram of an Al—Si alloy.

FIG. 3 is a differential thermal analysis curve of an Al alloy material.

FIG. 4 is a longitudinal sectional view of a casting.

FIGS. 5A and 5B are micrographs showing a metal structure in a first example of a casting, in which FIG. 5A corresponds to the surface and its vicinity, and FIG.

FIG. 6 is a schematic drawing of FIG. 5 (a).

FIG. 7 is a micrograph showing a metal structure of a second example of the casting.

FIG. 8 is a micrograph showing a metal structure of a third example of the casting.

FIG. 9 is a micrograph showing a metal structure of a fourth example of the casting.

FIG. 10 is a graph showing the relationship between shear rate γ and viscosity μ.

[Explanation of symbols]

2, 3 Fixed and movable mold (mold) 5 Al alloy material (alloy material) 7 Gate b Differential thermal analysis curve c, d First and second chevron heat absorbing portions E ₁ , E ₂ peak value

Continued on the front page (72) Inventor Takemi Sugawara 1-4-1 Chuo, Wako-shi, Saitama Pref. Honda Technical Research Institute Co., Ltd. (56) References JP-A-7-316709 (JP, A) JP-A-7- 246453 (JP, A) JP-A-5-261503 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 17/00 B22D 18/02 B22D 27/09 C22C 1/02 503 C22C 21/02

Claims (4)

(57) [Claims] 1. A cast body which is cast at room temperature using an alloy material (5) having a eutectic structure region having a high hardness and a primary crystal structure region having a low hardness under application of a thixocasting method. 1
1) The area ratio A of the eutectic structure region in the surface region
A cast material characterized in that the relationship of A> B is established between the ratio and the area ratio B of the eutectic structure region in the main region inside the surface region. 2. The differential thermal analysis curve (b) of the alloy material (5) shows that the alloy material (5) has a first eutectic structure region due to melting.
It has a chevron heat absorbing portion (c) and a second chevron heat absorbing portion (d) due to dissolution of the primary crystal structure region, and has a peak value E _{1 of} the first chevron heat absorbing portion (c) and the second chevron heat absorbing portion (d). d) Peak value E
_2. The cast body according to claim 1, wherein a relationship of E ₁ > E ₂ is established with the casting. 3. At room temperature, an alloy material (5) having a eutectic structure region having a high hardness and a primary crystal structure region having a low hardness is used, and a cast body (11) is formed under application of a thixocasting method. In casting, the shear rate when the semi-molten alloy material (5) in which the solid phase and the liquid phase coexist passes through the gate (7) of the mold (2, 3) is γ, and the viscosity is μ. Wherein the shear rate γ is set to 10 S ⁻¹ ≦ γ ≦ 1500 S ⁻¹ , and a relationship μ ≦ 300 γ ^−1.2 is established between the shear rate γ and the viscosity μ. 4. The differential thermal analysis curve (b) of the alloy material (5) shows that the alloy material (5) has a first eutectic structure region due to melting.
It has a chevron heat absorbing portion (c) and a second chevron heat absorbing portion (d) due to dissolution of the primary crystal structure region, and has a peak value E _{1 of} the first chevron heat absorbing portion (c) and the second chevron heat absorbing portion (d). d) Peak value E
₂ relation E _1> E ₂ is established between the claim 3 casting methods described.