JPH08170134A - Thixocasting and alloy material for thixocasting - Google Patents

Abstract

PURPOSE: To provide a thixocasting method by which a high-toughness casting is obtainable. CONSTITUTION: The following material is used as an alloy material: A first peak type endothermic part (e) by eutectic melting and a second peak type endothermic part (f) by melting of the component of the m.p. higher than the eutectic point exist in a differential thermal analysis curve (d), and an area ratio S1 /S is 0.09<=S1 /S<=0.57 when the area of a two-peak type plane part (j) enclosed by the first peak type endothermic part (e), the second peak type endothermic part (f) and a base line (i) is defined as S and the area of the one peak type plane part (k) as S1 . The alloy material described above is subjected to a heat treatment to prepare a half molten alloy material. A casting operation is then carried out by using this half molten alloy material. In such a case, the casting temp. (t) of the half molten alloy material is set at t1 <=t<=t2 when the temp. at the falling end point (m) of the first peak type endothermic party Q is defined as t1 and the peak temp. of the second peak type endothermic part (f) as t2 . As a result, the casting free from the generation of hole parts is obtd.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a thixocasting method and an alloy material used for carrying out the method.

[0002]

2. Description of the Related Art Conventionally, as a high toughness alloy material, for example, an Al alloy material, an AA standard 6000 series alloy has been known.

[0003]

In carrying out the thixocasting method, the alloy material is subjected to heat treatment so that the solid phase (substantially solid phase, the same applies below) and the liquid phase coexist. A method is used in which an alloy material is prepared, and then the semi-molten alloy material is filled in a cavity of a mold under pressure, and then the semi-molten alloy material is solidified under the pressure.

However, when the conventional 6000 series alloy material is used in the implementation of the thixocasting method, defects such as micron-order holes are easily generated in the grain boundaries of the casting, and its fatigue strength is low. , There was a problem. In the semi-molten state 6000 series alloy material, such a defect has almost no liquid phase due to eutectic melting, and therefore, the liquid phase is not supplied around the solid phase in accordance with solidification shrinkage of the solid phase. caused by.

In view of the above, the present invention improves both the supply of the liquid phase around the solid phase and the compatibility between the solid phase and the liquid phase, which results in sound generation without defects and high fatigue strength. It is an object of the present invention to provide the above thixocasting method capable of obtaining a casting having toughness and strength and an alloy material used for carrying out the method.

[0006]

The thixocasting method according to the present invention is characterized in that in a differential thermal analysis curve, the first chevron endothermic part by eutectic melting and the first chevron endothermic part are connected,
And a second chevron endotherm due to the dissolution of a component having a melting point higher than the eutectic point, the first chevron endotherm, the second chevron endotherm, and the rising start point of the first chevron endotherm and the Second
Let S be the area of the two chevron planes surrounded by the baseline connecting the descent end points of the chevron endotherm, and the temperature scale between the descent end point of the first chevron endotherm and its descent end point on the heating temperature axis. the area of one chevron flat portion by said first angled endothermic section when the bisecting the area S of the bifurcated flat portion when the S ₁ by temperature straight line connecting, the one chevron to an area S of the bifurcated flat portion An alloy material having a ratio S ₁ / S of the flat surface area S ₁ of 0.09 ≦ S ₁ /S≦0.57 is prepared, and the alloy material is subjected to heat treatment to prepare a semi-molten alloy material, Next, when performing a casting operation using the semi-molten alloy material, the temperature at the end point of the lowering of the first chevron endotherm is set to t _1, and the peak temperature of the second chevron endotherm is set to t _2.
And the casting temperature t of the semi-molten alloy material is t ₁ ≦
It is characterized by setting t ≦ t ₂ .

In the differential thermal analysis curve of the alloy material for thixocasting according to the present invention, the first chevron endothermic part due to eutectic melting and the first chevron endothermic part are connected and have a melting point higher than the eutectic point. There is a second chevron endotherm due to the dissolution of components, the first chevron endotherm, the second chevron endotherm, the rising start point of the first chevron endotherm and the descent end point of the second chevron endotherm. Let S be the area of the two chevron plane portion surrounded by the base line connecting the two, and the temperature straight line connecting between the temperature scales at the end point of the first endothermic heat sink and its end point on the heating temperature axis. Area S of the Yamagata plane
When the area of the one chevron plane portion by the first chevron heat absorbing portion when S is divided into two is S ₁ , the area S of the two chevron plane portion is
The ratio S ₁ / S of the area S ₁ of the flat surface of the mountain is 0.09 ≦ S ₁ /S≦0.57.

[0008]

[Operation] By subjecting the alloy material to heat treatment,
A semi-molten alloy material in which a liquid phase and a solid phase coexist is prepared.
In this semi-molten alloy material, the liquid phase has a large latent heat due to the area ratio S ₁ / S being specified as S ₁ /S≧0.09 as described above. As a result, in the solidification process of the semi-molten alloy material, the liquid phase is sufficiently supplied around the solid phase according to the solidification shrinkage of the solid phase, and then the liquid phase is solidified. Further, since the casting temperature t of the semi-molten alloy material (temperature of the material at the time of casting) t is specified as t ₁ ≤t ≤t ₂ as described above, the outer peripheral portion of the solid phase is gelled. . As a result, the compatibility between the gelled peripheral portion of the solid phase and the liquid phase becomes good. As a result, it is possible to prevent the generation of micron-order voids in the casting and improve its strength and fatigue strength.

Further, the area ratio S ₁ / S is S ₁ /S≦0.5
When set to 7, the crystallization amount of the hard and brittle eutectic component in the casting can be suppressed, and thereby the toughness of the casting can be improved.

However, the area ratio S ₁ / S is S ₁ / S <0.
In 09, since the latent heat of the liquid phase becomes small, the supply of the liquid phase around the solid phase becomes insufficient at the time of solidification contraction of the solid phase, and as a result, micron-order voids are likely to occur in the casting.
On the other hand, when S ₁ /S>0.57, the crystallization amount of the eutectic component becomes excessive, so that the generation of the voids can be avoided, but on the other hand, the toughness of the casting decreases. Further, the casting temperature t is t <t
_{In the case of 1} , the outer peripheral portion of the solid phase cannot be gelled, and as a result, the voids are likely to occur in the casting. On the other hand, t> t ₂
However, since the semi-molten alloy material has a low viscosity, the workability of the material deteriorates, and it is not possible to fill the material into the cavity of the mold layer by layer. Is likely to occur.

The area ratio S ₁ / S is S ₁ /S<0.5
When set to, the shape retention of the semi-molten alloy material becomes good,
Also, the temperature control of the material becomes easy.

[0012]

EXAMPLE A pressure casting machine 1 shown in FIG. 1 uses an Al alloy material (alloy material) under the application of the thixocasting method.
l Used for casting alloy castings. The pressure casting machine 1 includes a fixed mold 2 and a movable mold 3 having vertical mating surfaces 2a and 3a, and a casting molding cavity 4 is formed between the mating surfaces 2a and 3a. Semi-molten in fixed mold 2
A chamber 6 in which the 1-alloy material 5 is installed is formed, 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.

Table 1 shows the compositions of Examples A to C and Comparative Examples a to c of the Al alloy material. These Examples A and the like were cut from a high-quality long continuous casting material cast under the application of the continuous casting method, and in the casting, the spheroidizing treatment of the primary crystal α-Al was performed. Is being done. The dimensions of Example A and the like are 50 mm in diameter and 65 mm in length.

[0014]

[Table 1] When the differential scanning calorimetry (DSC) was performed on Example A, the results shown in FIG. 2 were obtained. Differential thermal analysis curve d in FIG.
Has a first chevron-shaped endothermic portion e formed by eutectic melting, and a second chevron-shaped endothermic portion f connected to the first chevron-shaped endothermic portion e and having a melting point higher than the eutectic point. in this case,
A double chevron surrounded by a first chevron endothermic section e, a second chevron endothermic section f, and a base line i connecting the rising start point g of the first chevron endothermic section e and the descending end point h of the second chevron endothermic section f. The area S of the flat surface portion (hatched portion in FIG. 2) j is S = 1500 mm ² . Also, the first chevron shape obtained when the area S of the two chevron plane portion j is bisected by the temperature straight line p connecting the temperature scales of the descent end point m of the first chevron endothermic portion e and the descent end point m on the heating temperature axis n. The area S ₁ of the flat mountain portion (dotted portion in FIG. 2) k formed by the heat absorbing portion e is S ₁ = 135 mm ² . Therefore, the monotonous plane portion k with respect to the area S of the dihedral plane portion j
The ratio S ₁ / S of the area S ₁ of S ₁ is S ₁ /S=0.09.

Next, Example A was installed in the heating coil of the induction heating apparatus, and then the frequency was 1 kHz and the maximum output was 3
It was heated under the condition of 0 kW to prepare Example A in a semi-molten state in which a solid phase and a liquid phase coexist. In this case, the solid fraction is 40
% Or more and 60% or less.

Thereafter, as shown in FIG. 1, the semi-molten embodiment A (reference numeral 5) is installed in the chamber 6, the casting temperature t of the embodiment A is 630 ° C., and the moving speed of the pressure plunger 9 is 0. The pressure was applied to Example A under the conditions of 20 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 example A filled in the cavity 4, and the example A is solidified under the pressure to obtain an Al alloy casting A.

In this case, in FIG. 2, the first chevron-shaped heat absorbing portion e
The temperature t _{1 at the} end point m of d is t ₁ = 598 ° C., and the peak temperature t ₂ of the second chevron endothermic part f is t ₂ = 645 ° C.
Is. Therefore, the casting temperature t of Example A in the semi-molten state is
Since t = 630 ° C., t ₁ ≦ t ≦ t ₂ is set.

Further, DSC was carried out for Examples B and C and Comparative Examples a to c, and using these Examples B and the like, the same casting operation as above was carried out to obtain five kinds of Al alloy castings B, C, and C.
ac was obtained. 3 to 7 show Examples B and C and Comparative Example a.
3 shows the differential thermal analysis curve d for c.

Table 2 shows Al alloy castings A to C and a to c.
Various information, mechanical properties, and the like obtained from the differential thermal analysis curve d regarding are shown.

[0020]

[Table 2] 8 to 13 are micrographs showing the metal structure of the Al alloy casting. 8 corresponds to the Al alloy casting A, FIG. 9 corresponds to the Al alloy casting B, and FIG. 10 corresponds to the Al alloy casting C. FIG. 11 shows an Al alloy casting a, and FIG. 12 shows an Al alloy casting b.
13 corresponds to the Al alloy casting c, respectively.

As is clear from FIGS. 2 to 4, Table 2 and FIGS. 8 to 10, the Al alloy castings A to C have high fatigue strength because they do not generate defects, and have a high Charpy impact value. Therefore, it has high toughness and further high strength.

This is for the following reason. That is, in Examples A to C in the semi-molten state, the liquid phase has a large latent heat due to the area ratio S ₁ / S being specified as S ₁ /S≧0.09 as described above. . As a result, in the solidification process of Examples A to C in the semi-molten state, the liquid phase is sufficiently supplied around the solid phase according to the solidification shrinkage of the solid phase, and then the liquid phase is solidified. Also, the casting temperature t of Examples A to C in the semi-molten state
Due to the fact that is specified as t ₁ ≦ t ≦ t ₂ as described above, the outer peripheral portion 12 of the solid phase 11 is gelled as shown in FIG. As a result, the gelled outer peripheral portion 1 of the solid phase 11
The compatibility between 2 and the liquid phase 13 becomes good. This gives A
It is possible to prevent generation of micron-order voids in the 1-alloy castings A to C and improve the strength and fatigue strength thereof.

Further, the area ratio S ₁ / S is S ₁ /S≦0.5
When set to 7, the crystallization amount of the hard and brittle eutectic component can be suppressed in the Al alloy castings A to C, and thus the toughness of the Al alloy castings A to C can be improved.

As is clear from FIG. 5, the Al alloy casting a of FIG. 11 has a micron-order void portion (black island-like portion) at the grain boundary due to the fact that Comparative Example a has almost no eutectic component. ) Is generated, the fatigue strength is low and the strength is low.

In the case of the Al alloy castings b and c of FIGS. 12 and 13, this is because the area ratio S ₁ / S is S ₁ /S>0.57 and the casting temperature t is t <t _1. In addition, the amount of eutectic component crystallized is relatively large, the outer peripheral portion of the solid phase is not gelled, and in the case of the Al alloy casting c, the α-Al grain size is large, which results in low toughness. And low strength.

The alloy material in the present invention is not limited to the Al alloy material.

[0027]

According to the invention of claim 1, high fatigue strength, toughness and strength can be obtained by using the alloy material specified as described above and by specifying the casting temperature t as described above. It is possible to obtain a casting that has.

According to the second aspect of the present invention, it is possible to provide an alloy material capable of obtaining a casting having the above characteristics under the thixocasting method.

[Brief description of drawings]

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

2 is a differential thermal analysis curve for Example A. FIG.

FIG. 3 is a differential thermal analysis curve for Example B.

FIG. 4 is a differential thermal analysis curve of Example C.

FIG. 5 is a differential thermal analysis curve of Comparative Example a.

FIG. 6 is a differential thermal analysis curve for Comparative Example b.

FIG. 7 is a differential thermal analysis curve of Comparative Example c.

FIG. 8 is a micrograph showing a metal structure of an Al alloy casting A.

9 is a micrograph showing a metal structure of an Al alloy casting B. FIG.

FIG. 10 is a micrograph showing a metal structure of an Al alloy casting C.

FIG. 11 is a micrograph showing a metal structure of an Al alloy casting a.

FIG. 12 is a micrograph showing a metal structure of an Al alloy casting b.

FIG. 13 is a micrograph showing a metal structure of an Al alloy casting c.

FIG. 14 is an explanatory diagram showing semi-molten states of Examples A to C.

[Explanation of symbols]

 5 Semi-molten alloy material d Differential thermal analysis curve e, f 1st and 2nd chevron endothermic part g Rise start point h, m Descent end point i Base line j Diagonal plane part k One chevron plane part n Heating temperature axis p Temperature straight line

Claims (2)

[Claims] 1. In the differential thermal analysis curve (d), a first chevron endotherm (e) due to eutectic melting, and a component which is continuous with the first chevron endotherm (e) and has a melting point higher than the eutectic point. A second chevron endotherm (f) due to melting of the first chevron endotherm (e), the second chevron endotherm (f) and the first chevron endotherm (e) (G) and the base line (i) connecting between the descending end points (h) of the second chevron endothermic part (f) is defined as S, and the area of the two chevron plane part (j) is S, and the first chevron endotherm The dihedral plane portion (j) is defined by the temperature straight line (p) connecting the temperature scales of the descending end point (m) of the part (e) and the descending end point (m) on the heating temperature axis (n).
When the area S of the first chevron endothermic portion (e) when the area S is divided into two is S ₁ , the single chevron plane with respect to the area S of the two chevron flat portion (j). The ratio S ₁ / S of the area S ₁ of the part (k) is 0.09 ≦ S ₁ / S ≦
When an alloy material of 0.57 is prepared, the alloy material is heat-treated to prepare a semi-molten alloy material, and then the semi-molten alloy material is used for casting work, the first chevron-shaped endothermic portion is used. Assuming that the temperature at the end point (m) of (e) is t ₁ ,
When the peak temperature of the second chevron endothermic part (f) is t ₂ , the casting temperature t of the semi-molten alloy material is t ₁ ≦ t ≦
A thixocasting method characterized by setting to t ₂ . 2. In the differential thermal analysis curve (d), a first chevron endotherm (e) due to eutectic melting and a component which is continuous with the first chevron endotherm (e) and has a melting point higher than the eutectic point. A second chevron endotherm (f) due to melting of the first chevron endotherm (e), the second chevron endotherm (f) and the first chevron endotherm (e) (G) and the base line (i) connecting between the descending end points (h) of the second chevron endothermic part (f) is defined as S, and the area of the two chevron plane part (j) is S, and the first chevron endotherm The dihedral plane portion (j) is defined by the temperature straight line (p) connecting the temperature scales of the descending end point (m) of the part (e) and the descending end point (m) on the heating temperature axis (n).
When the area S of the first chevron endothermic portion (e) when the area S is divided into two is S ₁ , the single chevron plane with respect to the area S of the two chevron flat portion (j). The ratio S ₁ / S of the area S ₁ of the part (k) is 0.09 ≦ S ₁ / S ≦
An alloy material for thixocasting, which is 0.57.