JP2869889B2 - Thixocasting 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 thixocasting method, and more particularly, to a method having a hypoeutectic composition and a differential thermal analysis curve, wherein a first chevron-shaped heat-absorbing part due to eutectic melting has a melting point higher than the eutectic point. A semi-molten alloy material in which a solid phase (substantially solid phase, the same applies hereinafter) and a liquid phase coexist is prepared by subjecting the alloy material having the second chevron heat-absorbing part due to the dissolution of the components to heat treatment. It then relates to an improved method for filling the mold cavity with semi-solid alloy material under pressure and subsequently solidifying the semi-solid alloy material.

[0002]

2. Description of the Related Art Conventionally, in this type of thixocasting method, when the temperature at the descent end point of the first chevron heat absorbing portion is T ₂ and the peak temperature of the second chevron heat absorbing portion is T ₃ , semi-melting occurs. The casting temperature T of the alloy material is set to T ₂ ≦ T ≦ T ₃ .

The reason why the casting temperature T is set to be relatively high is to lower the solid phase ratio of the semi-molten alloy material to improve its castability.

In this case, the metal structure of the obtained alloy casting is composed of an α phase formed by solidification of a solid phase and an α-β eutectic phase formed by solidification of a matrix and, therefore, a liquid phase. Has appropriate mechanical properties.

[0005]

In order to further improve the mechanical properties of the alloy casting as described above, it is conceivable to finely crystallize the β phase in the matrix.
According to the conventional method, fine crystallization of the β phase cannot be realized.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thixocasting method capable of realizing fine crystallization of a β phase using an alloy material having a hypoeutectic composition.

[0007] To achieve the above object, according to the present invention,
In an alloy material having a hypoeutectic composition and having, in a differential thermal analysis curve, a first chevron-shaped heat absorbing portion due to eutectic melting and a second chevron-shaped heat absorbing portion due to dissolution of a component having a higher melting point than the eutectic point. A heat treatment is performed to prepare a semi-solid alloy material in which a solid phase and a liquid phase coexist, and then, under pressure, filling the mold cavity with the semi-solid alloy material, and then the semi-solid alloy material In the thixocasting method of performing solidification, when the temperature at the rising start point of the first chevron heat absorbing portion is T ₁ and the temperature at the falling end point is T ₂ , the casting temperature T of the semi-molten alloy material is A thixocasting method is provided wherein T ₁ ≦ T ≦ T ₂ .

When the casting temperature T is set as described above, the liquid phase has a eutectic composition in the range of the temperature T, ie, T ₁ ≦ T ≦ T ₂ . Then, in the solidification process, the composition of the liquid phase changes so as to fluctuate from the eutectic point to the hypereutectic side and the hypoeutectic side, so that the β phase is crystallized on the hypereutectic side,
On the hypoeutectic side, an α-β eutectic phase is crystallized.

In this case, since the growth of the β phase is hindered by the α phase, which is a solid phase, miniaturization is achieved.

When the casting temperature T is set as described above, the solid phase ratio of the semi-molten alloy material is increased, but since the β phase exerts an action of inhibiting solid phase mutual aggregation, the semi-molten alloy material is Has good fluidity.

As a result, it is possible to obtain an alloy casting having a hypoeutectic composition with no occurrence of casting defects and improved mechanical properties as compared with the conventional one.

[0012] However, the casting temperature T is T <can not be present liquid phase at T ₁ in the alloy material, whereas, T>
In T ₂ can not achieve crystallization of the β-phase as the conventional method.

[0013]

[Example 1]

Table 1 shows the chemical components of the Al-Si alloy material having a hypoeutectic composition. This Al-Si alloy material is cut out from a high-quality long continuous casting material cast under the application of a continuous casting method, and in the casting, α- Al spheroidizing treatment is performed. Has been done. The dimensions of the Al-Si alloy material are 50 mm in diameter and 65 mm in length.

[0014]

[Table 1]

Differential scanning calorimetry (DSC) was performed on the Al-Si alloy material, and the result shown in FIG. 2 was obtained.
In the differential thermal analysis curve a of FIG.
There is a chevron heat absorbing portion b and a second chevron heat absorbing portion c due to dissolution of a component having a higher melting point than the eutectic point. Temperature T ₁ of the rising start point d in the first angled endothermic section b is T ₁ = 556 ° C., lowering the end point (rising start point of the second angled endothermic section c, hereinafter the same) is the temperature T ₂ of the e T ₂ = 580 ° C and the temperature T _{3 at} the peak f of the second chevron heat absorbing portion c is T ₃ = 598 ° C. The temperature at the peak g of the first chevron heat absorbing portion b is 571 ° C., and the temperature at the descent end point h of the second chevron heat absorbing portion c is 608 ° C.

Next, the Al—Si alloy material is placed in the heating coil of the induction heating device, and then the frequency is set to 1 kHz.
Heating was performed under the condition of a maximum output of 37 kW to prepare a semi-solid Al-Si alloy material in which a solid phase and a liquid phase coexist. In this case, the heating temperature of the semi-solid Al-Si alloy material is 575
° C and its solid fraction was set to 70%.

Thereafter, as shown in FIG.
The Si-based alloy material 5 is placed in the chamber 6 and the semi-solid Al-
Casting temperature T of Si-based alloy material 5 = 575 ° C. (T ₁ ≦ T ≦
T ₂ ), moving speed of the pressure plunger 9 0.2 m / sec
The semi-molten Al-Si alloy material 5 was passed through the gate 7 and pressurized under the condition of a mold temperature of 250 ° C. to fill the cavity 4. Then, by applying pressure to the semi-molten Al-Si alloy material 5 filled in the cavity 4 by holding the pressure plunger 9 at the end of the stroke,
Its under pressure solidifying the semi-molten Al-Si based alloy material 5 was obtained Al alloy casting A _1.

For comparison, the casting temperature T of the semi-solid Al—Si alloy material 5 was set to T = 585 ° C. (T ₂ ≦ T ≦ T ₃ ).
The same casting operation was performed under the same conditions as above, except that the solid phase ratio was set to 45%.
To obtain an alloy castings A _2.

The main part of FIG 3, 4 (a) micrograph showing the metallographic Al alloy castings A ₁ is FIG. 4 (b) FIGS. 4 (a)
It is a map . This metal structure is formed by solidification of α-A
1 phase and a matrix M, thus a primary Si phase and an Al-Si eutectic phase due to solidification of the liquid phase. In this case, the primary crystal Si phase is dispersed around the solid phase, and its volume fraction Vf
Was Vf = 2.8%.

Al-Si having a hypoeutectic composition
Despite the use of the base alloy material, the reason why the metal structure in which the primary crystal Si phase exists can be obtained as described above is as follows. That is, when the casting temperature T is set to T = 575 ° C., the temperature T becomes T ₁ (556 ° C.) ≦ T (57
The liquid phase has a eutectic composition of 11.7% by weight of Si as shown in FIG. 5 because it belongs to the range of 5 ° C. ≦ T ₂ (580 ° C.). In the solidification process, the composition of the liquid phase changes so as to fluctuate from the eutectic point to the hypereutectic side and the hypoeutectic side as shown by the curve i in FIG. , A primary Si phase is crystallized, and an Al-Si eutectic phase is crystallized on the hypoeutectic side.

In this case, the growth of the primary Si phase is hindered by the solid phase α-Al phase, so that the particle diameter D is 5 μm.
m ≦ D ≦ 20 μm. Al-S having hypereutectic composition
In performing gravity casting using an i-based alloy material, the primary crystal Si phase is refined using P or the like. In this case, the particle diameter D of the primary crystal Si phase is 20 μm ≦ D ≦ In comparison with this, it can be seen that according to the method, further refinement of the primary Si phase was achieved.

When the casting temperature T is set as described above, the solid fraction of the semi-molten Al-Si alloy material becomes as high as 70%, but the primary Si phase prevents the solid phase from agglomerating. since cause an effect, the semi-molten Al-Si based alloy material has good flow properties, occurrence of casting defects in the Al alloy castings a ₁ was observed.

The main part of FIG 6, 7 (a) micrograph, FIG. 7 showing a metallographic Al alloy castings A ₂ is (b) the FIGS. 7 (a)
It is a map . The metal structure is α-Al by solidification of the solid phase.
Phase and matrix A and thus A by solidification of the liquid phase
It is composed of an l-Si eutectic phase and has no primary Si phase.

The reason why the primary crystal Si phase is not present is as follows. That is, when the casting temperature T is set to T = 585 ° C., the temperature T becomes T ₂ (580) in FIG.
C) ≦ T (585 ° C.) ≦ T ₃ (598 ° C.), the liquid phase is about 10.4% by weight S as shown in FIG.
i having a hypoeutectic composition. In the solidification process, as shown by the curve j in FIG. 5, the composition changes so as to fluctuate toward the high Si side and the low Si side at about 10.4 wt% Si, but exceeds the eutectic point. Therefore, the primary Si phase does not crystallize.

Next, to produce both Al alloy castings A _1, respectively from A ₂ Test piece A _1, A _2, which A _1, A
₂ was subjected to a T6 treatment, and then subjected to a tensile test and a Charpy impact test. The results shown in Table 2 were obtained.

[0026]

[Table 2]

As is clear from Table 2, the test piece A ₁ having the primary crystal Si phase has improved strength as compared with the test piece A ₂ having no primary crystal Si phase. In the test piece A _1, since the volume fraction Vf with fine primary crystal Si phase is achieved is appropriate, reduction in ductility and toughness is suppressed. Example 2 Table 3 Al-Si with Al-Si based alloy material B ₁ .about.B ₃ and hypereutectic composition having a hypoeutectic composition
The chemical components of the system alloy material B _4. These Al-Si alloy materials B _{1 and the} like are cut out from a high-quality long continuous cast material cast under the application of a continuous casting method. A spheroidizing process has been performed. Al-Si based alloy material B ₁ dimensions, such as diameter 50 mm,
The length is 65 mm.

[0028]

[Table 3]

When differential scanning calorimetry (DSC) was performed on the Al—Si alloy material B _{1 and the} like, the differential thermal analysis curves showed that the first peak-shaped heat absorbing portion due to eutectic melting,
It was found that there was a second chevron endothermic part due to dissolution of components having a higher melting point than the eutectic point.

Table 4 summarizes the temperatures at each point in the differential thermal analysis curves.

[0031]

[Table 4]

Next, the Al—Si alloy material B ₁ is placed in a heating coil of an induction heating device, and then a frequency of 1 kHz is applied.
z, and heated under the conditions of maximum output 37kW, and the solid phase and the liquid phase was prepared semi-molten Al-Si based alloy material B ₁ coexisting.

Thereafter, as shown in FIG.
Si-based alloy material B ₁ (symbol 5) is placed in chamber 6,
Moving speed 0.2 m / sec of the pressurizing plunger 9, in the conditions of a mold temperature of 250 ° C. and passed through a gate 7 while pressing the semi-molten Al-Si based alloy material B ₁ was filled in the cavity 4. Then, the pressure was applied to the semi-molten Al-Si based alloy material B ₁ filled in the cavity 4 by retaining the pressing plunger 9 in the stroke end, the semi-molten Al-Si based alloy material at that pressure Coagulate B ₁ to Al
To obtain an alloy castings B _1. Another Al-Si alloy material B
With ₂ .about.B _4, to obtain an Al alloy castings B ₂ .about.B ₄ performs the same casting operation.

When the metal structure of each of the Al alloy castings B _{1 to} B ₄ was examined, the metal structure was found to be A in Example 1.
Similar to l alloy casting A _1, and alpha-Al phase by solidification of the solid phase was found to consist of a matrix M, thus a primary crystal Si phase and the Al-Si eutectic phase by solidification of a liquid phase. No casting defect was found in each of the Al alloy castings B _{1 to} B ₄ .

Next, a fluidity test was performed on each of the Al—Si alloy materials B _{1 to} B ₄ . As the test movable die 3 _1, its cavity 4 ₁ As shown in FIG. 8, a circular portion 4a which communicates with the gate 7, the bent portion 4b having a substantially concave shape extending from the circular part 4a Was used.

In the fluidity test, first, a semi-solid Al—Si alloy material B ₁ is prepared under the same conditions as in the casting operation, and the material B ₁ is subjected to the cavity 4 _{1 under} the same conditions as described above. And coagulated.

[0037] Mold Opening later by measuring the weight of the clot material B ₁ existing in the bent portion 4b of the cavity 4 _1, the weight of Al
It was flow length -Si alloy material B _1.

Further, other Al-Si alloy materials B _{2 to} B ₄
Were subjected to the same fluidity test as described above, and their flow lengths were measured.

The flow length of the Al—Si alloy material B ₁ is set to “1.0”, and the other Al—Si alloy material B ₂
It was determined flow length ratio of .about.B _4.

Further, test pieces were prepared from the four types of Al alloy castings B _{1 to} B ₄ , respectively, subjected to T6 treatment, and then subjected to a Charpy impact test.

Table 5 shows the casting temperature T, the solid fraction, and various measured values for the Al alloy castings B _{1 to} B ₄ .

[0042]

[Table 5]

From Table 5, it can be seen that the casting temperature T of each of the Al alloy castings B _{1 to} B ₄ was set to T ₁ ≦ T ≦ T ₂ . Also, it can be seen that as the volume fraction Vf of the primary Si phase increases, the fluidity of the semi-molten Al-Si alloy material improves.

FIG. 9 shows the results of the Al alloy castings B ₁ to B ₁ based on Table 5.
In B _4, and the volume fraction Vf of the primary crystal Si phase is a graph showing the relationship between the flow length ratio and the Charpy impact value.

As is clear from Table 5 and FIG. 9, as in the case of the Al alloy castings B _{1 to} B ₃ , the primary crystal Si phase had a particle diameter D of 5 μm.
≦ D ≦ 20 μm and the volume fraction Vf is 1.5%
If ≦ Vf ≦ 4.7%, it is possible to improve the fluidity of the semi-molten Al—Si alloy material, prevent the occurrence of casting defects, and secure the strength and toughness of the Al alloy casting.

[0046] In this connection, flow length ratio for the Al alloy castings A ₁ of Example 1 was 1.1.

The alloy material used in the present invention is Al-
Not only Si based alloy material, Al-CuAl ₂ alloy material, Al-Mg ₂ Si based alloy material, Al-AlFeSi
Intermetallic compound alloy materials are also included.

[0048]

According to the present invention, a high-strength alloy which realizes fine crystallization of β phase using an alloy material having a hypoeutectic composition by employing the means specified as described above. Castings can be obtained.

[Brief description of the drawings]

FIG. 1 is a vertical sectional front view of a pressure casting machine.

FIG. 2 is a differential thermal analysis curve of an Al—Si alloy.

FIG. 3 is a micrograph showing a metal structure of an example of an Al alloy casting.

4A is a partially enlarged photograph of FIG. 3, and FIG.
FIG. 4 is a main part map of FIG.

FIG. 5 shows a main part of a phase diagram of an Al—Si alloy.

FIG. 6 is a micrograph showing a metal structure of another example of the Al alloy casting.

7A is a partially enlarged photograph of FIG. 6, and FIG.
FIG. 4 is a main part map of FIG.

FIG. 8 is a side view of a main part of the movable mold.

FIG. 9 is a graph showing a relationship between a volume fraction Vf of a primary crystal Si phase, a flow length ratio, and a Charpy impact value.

[Explanation of symbols]

 4 Cavity 5 Semi-molten Al alloy material (semi-molten alloy material) a Differential thermal analysis curve b 1st chevron heat absorbing part c 2nd chevron heat absorbing part d Ascending start point e Ascending end point

Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI C22C 21/02 C22C 21/02 (56) References JP-A-9-85409 (JP, A) JP-A 8-192257 (JP, A) JP-A-8-112661 (JP, A) JP-A-7-100570 (JP, A) JP-A-5-200523 (JP, A) JP-A-5-312740 (JP, A) Patent 27947539 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) B22D 17/00 B22D 17/32 B22D 27/04 B22D 46/00 C22C 1/02 501

Claims (1)

(57) [Claims] 1. A heat absorption part (b) having a hypoeutectic composition and having a first angle-shaped endothermic part due to eutectic melting in a differential thermal analysis curve (a).
And an alloy material (5) having a second chevron-shaped heat absorbing portion (c) due to the dissolution of a component having a higher melting point than the eutectic point, so that a semi-solid alloy in which a solid phase and a liquid phase coexist is obtained. A material (5) is prepared and then under pressure the semi-solid alloy material (5)
In the thixocasting method of filling the mold cavity (4) with the following and then solidifying the semi-molten alloy material (5), the temperature of the rising start point (d) of the first chevron heat absorbing portion (b) is and T _1, also characterized by setting its lowered end point temperature of (e) when the T _2, wherein the casting temperature T of the semi-molten alloy material (5) to T ₁ ≦ T ≦ T ₂ thixotropy Casting method.