JPH09122867A - Thixocasting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thixocasting method by which a high-strength Al alloy casting is obtainable. SOLUTION: An Al-Si alloy material which has a hypo-eutectic compsn. and in which the first peak-shaped endothermic part (b) by eutectic dissolution and the second peak-shaped endothermic part (c) by dissolution of the component of the m.p. higher than the m.p. of the eutectic point in a differential thermal analysis curve (a) is subjected to a heat treatment to prepare the half-molten Al-Si alloy material in which a solid phase and a liquid phase coexist in this thixocasting method. The packing of the half-molten Al-Si alloy material into the cavity of a casting mold and the subsequent solidification of the half-melted Al-Si alloy material are then executed under pressurization. The casting temp. T of the half-melted Al-Si alloy material is set at T1 <=T<=T2 when the temp. of the elevation start point (d) of the first peak-shaped endothermic part (b) is defined as T1 and the temp. at the falling end point (e) thereof as T2 . As a result, the fine crystallization of the primary crystal Si phase is embodied and the strength of the Al alloy casting is enhanced.

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, it has a hypoeutectic composition and has a first chevron endotherm due to eutectic melting and a melting point higher than the eutectic point in a differential thermal analysis curve. 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 an alloy material having a second chevron endotherm due to melting of the components to heat treatment. Then, it relates to an improvement in a method of filling a mold cavity with semi-molten alloy material under pressure and then solidifying the semi-molten alloy material under pressure.

[0002]

2. Description of the Related Art Conventionally, in this type of thixocasting method, when the temperature at the end point of the descending end of the first chevron endotherm is T ₂ and the peak temperature of the second chevron endotherm 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 relatively high in this way is to lower the solid phase ratio of the semi-molten alloy material and improve its castability.

In this case, the metal structure of the obtained alloy casting is composed of an α phase due to solidification of a solid phase and an α-β eutectic phase due to solidification of a matrix, that is, a liquid phase. It has suitable 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,
Fine crystallization of the β phase cannot be realized by the conventional method.

[0006]

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

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

When the casting temperature T is set as described above, the liquid phase has a eutectic composition within the range of the temperature T, that is, T ₁ ≤T≤T ₂ . Then, in the solidification process, the composition of the liquid phase changes so as to fluctuate toward the hypereutectic side and the hypoeutectic side with the eutectic point as a boundary, so the β phase crystallizes on the hypereutectic side,
On the hypoeutectic side, the α-β eutectic phase crystallizes out.

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

When the casting temperature T is set as described above, the solid phase ratio of the semi-molten alloy material increases, but the β phase exerts the effect of preventing the mutual solid phase aggregation, so that the semi-molten alloy material is It has good fluidity.

As a result, it is possible to obtain a cast alloy having a hypoeutectic composition, which is free from casting defects and has improved mechanical properties as compared with the conventional ones.

However, when the casting temperature T is T <T ₁ , the liquid phase cannot be present in the alloy material, while T>
In T ₂ can not achieve crystallization of the β-phase as the conventional method.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A pressure casting machine 1 shown in FIG. 1 is used to cast an Al alloy casting using an Al alloy material (alloy material) under the application of a thixocasting method. The pressure casting machine 1 is provided with a mold, which comprises a fixed mold 2 having vertical mating surfaces 2a and 3a and a movable mold 3, and a molding cavity 4 is formed between the mating surfaces 2a and 3a. To be done. A chamber 6 in which a semi-molten Al alloy material (semi-molten alloy material) 5 is installed is formed in the fixed mold 2, and the chamber 6 communicates with the cavity 4 via a gate 7.
Further, a sleeve 8 communicating with the chamber 6 is horizontally attached to the fixed mold 2, and a pressure plunger 9 inserted into and removed from the chamber 6 is slidably fitted to the sleeve 8. The sleeve 8 has a material insertion port 10 in the upper portion of the peripheral wall thereof. [Example 1] Table 1 shows chemical components of an Al-Si alloy material having a hypoeutectic composition. This Al-Si alloy material was cut out from a high-quality long continuous casting material that was cast under the application of the continuous casting method. Is being processed. Al-S
The size of the i-based alloy material is 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 results shown in FIG. 2 were obtained.
In the differential thermal analysis curve a of FIG. 2, the first by eutectic dissolution
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., the temperature T ₃ of the peak f of the second chevron endothermic part c is T ₃ = 598 ° C. The temperature of the peak g of the first chevron endothermic part b is 571 ° C., and the temperature of the end point h of the second chevron endothermic part 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.
A semi-molten Al-Si alloy material in which a solid phase and a liquid phase coexist was prepared by heating under the condition of the maximum output of 37 kW. In this case, the heating temperature of the semi-molten Al-Si alloy material is 575.
C., and its solid fraction was set to 70%.

Thereafter, as shown in FIG. 1, semi-molten Al--
The Si-based alloy material 5 is placed in the chamber 6, and the semi-molten Al-
Casting temperature of Si-based alloy material 5 T = 575 ° C. (T ₁ ≦ T ≦
T ₂ ), moving speed of the pressure plunger 9 0.2 m / sec
While the mold temperature was 250 ° C., the semi-molten Al—Si alloy material 5 was pressurized and passed through the gate 7 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 semi-molten Al—Si alloy material 5 filled in the cavity 4,
The semi-molten Al—Si alloy material 5 was solidified under the pressure to obtain an Al alloy casting A ₁ .

For comparison, the casting temperature T of the semi-molten Al--Si alloy material 5 is set to T = 585 ° C. (T ₂ ≤T≤T ₃ ).
In addition, the same casting operation was performed under the same conditions as described above except that the solid fraction was set to 45%.
An alloy casting A ₂ was obtained.

3 and 4 are micrographs showing the metal structure of the Al alloy casting A ₁ . This metallographic structure is composed of an α-Al phase formed by solidification of a solid phase, and a matrix M, that is, a primary crystal Si phase and an Al—Si eutectic phase formed by solidification of a liquid phase. In this case, the primary crystal Si phase was dispersed around the solid phase, and its volume fraction Vf was Vf = 2.8%.

Thus, Al-Si having a hypoeutectic composition
The reason why the metal structure having the primary crystal Si phase as described above can be obtained despite the use of the base alloy material 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
5 ° C.) ≦ T ₂ (580 ° C.), the liquid phase has a eutectic composition of 11.7 wt% Si as shown in FIG. In the solidification process, the composition of the liquid phase changes so as to fluctuate toward the hypereutectic side and the hypoeutectic side with the eutectic point as a boundary, as shown by the curve i in FIG. , The primary Si phase crystallizes, and the Al-Si eutectic phase crystallizes on the hypoeutectic side.

In this case, since the growth of the primary crystal Si phase is hindered by the solid phase α-Al phase, the grain size D is 5 μm.
m ≦ D ≦ 20 μm. Al-S with hypereutectic composition
When gravity casting is performed using an i-based alloy material, the primary crystal Si phase is refined using P or the like. In this case, the grain size D of the primary crystal Si phase is 20 μm ≦ D ≦ It is 50 μm, and by comparison with this, it can be seen that further miniaturization of the primary crystal Si phase is achieved by the above method.

When the casting temperature T is set as described above, the solid phase ratio of the semi-molten Al-Si alloy material is as high as 70%, but the primary crystal Si phase prevents the mutual solid phase aggregation. 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.

6 and 7 are micrographs showing the metal structure of the Al alloy casting A ₂ . This metallic structure is composed of an α-Al phase obtained by solidification of a solid phase and a matrix M, that is, an Al-Si eutectic phase obtained by solidification of a liquid phase, and there is no primary Si phase.

The reason why the primary Si phase is absent is as follows. That is, when the casting temperature T is set to T = 585 ° C., the temperature T is T ₂ (580
C) ≦ T (585 ° C.) ≦ T ₃ (598 ° C.), the liquid phase is about 10.4 wt% S as shown in FIG.
It has a hypoeutectic composition of i. Then, in the solidification process, the composition changes so as to fluctuate toward the high Si side and the low Si side with about 10.4 wt% Si as a boundary, as shown by the curve j in FIG. 5, 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
_{When the} tensile test and the Charpy impact test were performed after T2 treatment on 2, the results shown in Table 2 were obtained.

[0026]

[Table 2]

As is clear from Table 2, the strength of the test piece A ₁ containing the primary crystal Si phase is higher than that of the test piece A ₂ having no primary crystal Si phase. Further, in the test piece A ₁ , since the primary crystal Si phase is made fine and the volume fraction Vf thereof is appropriate, the decrease in ductility and toughness is suppressed. Example 2 Table 3 shows Al-Si alloy materials B _{1 to} B ₃ having a hypoeutectic composition and Al-Si having a hypereutectic composition.
The chemical composition of the system alloy material B ₄ is shown below. These Al-Si alloy materials B _{1 and the} like are cut out from a high-quality long continuous casting material that is cast under the application of the continuous casting method. The spheroidizing process is being performed. The dimension of the Al-Si alloy material B ₁ etc. is 50 mm in diameter,
The length is 65 mm.

[0028]

[Table 3]

Differential scanning calorimetry (DSC) was carried out on the Al-Si alloy material B _{1 and the} like. As a result, the first chevron endotherm due to eutectic melting in the differential thermal analysis curves,
It was found that there was a second chevron endotherm due to the dissolution of the component 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 the heating coil of the induction heating device, and then the frequency is set to 1 kHz.
By heating under conditions of z and maximum output of 37 kW, a semi-molten Al-Si alloy material B ₁ in which a solid phase and a liquid phase coexist was prepared.

Then, as shown in FIG. 1, semi-molten Al--
Si-based alloy material B ₁ (reference numeral 5) is installed in the chamber 6,
The semi-molten Al—Si alloy material B ₁ was pressed under the conditions of a moving speed of the pressure plunger 9 of 0.2 m / sec and a mold temperature of 250 ° C., while passing through the gate 7 to fill the cavity 4. Then, by holding the pressure plunger 9 at the end of the stroke, a pressure is applied to the semi-molten Al-Si alloy material B ₁ filled in the cavity 4, and under the pressure, the semi-molten Al-Si alloy material B ₁ is applied. B ₁ is solidified to form Al
An alloy casting B ₁ was obtained. Other Al-Si alloy material B
_{Using 2 to} B ₄ , the same casting operation as above was performed to obtain Al alloy castings B _{2 to} B ₄ .

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.
It was found that, like the _1- alloy casting A1, it consisted of an α-Al phase due to solidification of the solid phase, and a primary phase Si phase and an Al-Si eutectic phase due to solidification of the matrix M, and hence the liquid phase. The occurrence of casting defects in the Al alloy castings B ₁ .about.B ₄ was observed.

Next, a fluidity test was conducted on each of the Al--Si alloy materials B _{1 to} B ₄ . As shown in FIG. 8, the movable mold 3 ₁ for testing has a cavity 4 ₁ having a circular portion 4 a communicating with the gate 7 and a bent portion 4 b extending from the circular portion 4 a and having a substantially concave shape. The one consisting of and was used.

[0036] The hitting the fluidity test, first, the prepared semi-molten Al-Si based alloy material B ₁ in casting operations and similar conditions, the cavity 4 ₁ the material B ₁ under the same conditions as the And allowed to solidify.

After the mold was opened, the weight of the solidified material B ₁ existing in the bent portion 4b of the cavity 4 ₁ was measured, and the weight was measured as Al.
It was flow length -Si alloy material B _1.

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

Then, the flow length of the Al-Si alloy material B ₁ is set to "1.0", and another Al-Si alloy material B _{2 is used.}
It was determined flow length ratio of .about.B _4.

Further, test pieces were prepared from four kinds 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 phase ratio and various measured values regarding 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 . Further, it is understood that when the volume fraction Vf of the primary crystal Si phase is increased, the fluidity of the semi-molten Al-Si alloy material is improved.

FIG. 9 shows Al alloy castings B ₁ to
In B ₄ , the relationship between the volume fraction Vf of the primary crystal Si phase, the flow length ratio and the Charpy impact value is graphed.

As is clear from Table 5 and FIG. 9, the grain size D of the primary crystal Si phase is 5 μm as in the Al alloy castings B _{1 to} B _3.
≦ D ≦ 20 μm, and the volume fraction Vf is 1.5%
When ≦ 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.

Incidentally, the flow length ratio of the Al alloy casting 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 and the like are also included.

[0048]

According to the present invention, by adopting the means specified above, a high-strength alloy in which fine crystallization of β phase is realized by using an alloy material having a hypoeutectic composition A casting 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.

FIG. 4 (a) corresponds to a partially enlarged photograph of FIG. 3, and FIG.
[Fig. 3] is a main part map of (a).

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

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

FIG. 7 (a) corresponds to a partially enlarged photograph of FIG. 6, and (b)
[Fig. 3] is a main part map of (a).

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

FIG. 9 is a graph showing the relationship between the volume fraction Vf of the primary crystal Si phase, the flow length ratio and the 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 endothermic part c 2nd chevron endothermic part d Rise start point e Descent end point

[Procedure amendment]

[Submission date] January 31, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction contents]

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A pressure casting machine 1 shown in FIG. 1 is used to cast an Al alloy casting using an Al alloy material (alloy material) under the application of a thixocasting method. The pressure casting machine 1 is provided with a mold, which comprises a fixed mold 2 having vertical mating surfaces 2a and 3a and a movable mold 3, and a molding cavity 4 is formed between the mating surfaces 2a and 3a. To be done. A chamber 6 in which a semi-molten Al alloy material (semi-molten alloy material) 5 is installed is formed in the fixed mold 2, and the chamber 6 communicates with the cavity 4 via a gate 7.
Further, a sleeve 8 communicating with the chamber 6 is horizontally attached to the fixed mold 2, and a pressure plunger 9 inserted into and removed from the chamber 6 is slidably fitted to the sleeve 8. The sleeve 8 has a material insertion port 10 in the upper portion of the peripheral wall thereof. [Example 1] Table 1 shows chemical components of an Al-Si alloy material having a hypoeutectic composition. This Al-Si alloy material was cut from a high-quality long continuous casting material that was cast under the application of the continuous casting method.
Is subjected to spheroidizing treatment of α- Al. The Al-Si alloy material has a diameter of 50 mm and a length of 65 mm.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction contents]

3 and 4 (a) are micrographs showing the metal structure of the Al alloy casting A ₁ , and FIG. 4 (b) is a main part of FIG. 4 (a).
It is a map . This metallic structure is α-A due to solidification of the solid phase.
It consists of the 1 phase and the matrix M, and therefore the primary Si phase and Al—Si eutectic phase due to the solidification of the liquid phase. In this case, the primary Si phase is dispersed around the solid phase, and its volume fraction Vf
Was Vf = 2.8%.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

FIGS. 6 and 7 (a) are micrographs showing the metal structure of the Al alloy casting A ₂ and FIG. 7 (b) is a main part of FIG. 7 (a).
It is a map . This metallic structure is α-Al produced by solidification of the solid phase.
Phase and matrix M, and thus A due to the solidification of the liquid phase
1-Si eutectic phase and no primary Si phase.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C22C 21/02 C22C 21/02

Claims (1)

[Claims] 1. A first chevron endotherm (b) having a hypoeutectic composition and having a differential thermal analysis curve (a) due to eutectic melting.
A semi-molten alloy in which a solid phase and a liquid phase coexist by heat-treating the alloy material (5) having the second chevron endotherm (c) due to melting of a component having a melting point higher than the eutectic point. Preparing a material (5) and then under pressure, said semi-molten alloy material (5)
In the thixocasting method in which the mold cavity (4) is filled with and the semi-molten alloy material (5) is subsequently solidified, the temperature of the rising start point (d) of the first chevron endothermic part (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.