JPH08103859A - Formation of half-melting metal - Google Patents

Abstract

PURPOSE: To simply and easily pressurize-form half-melting metal of aluminum alloy, etc., in a low cost. CONSTITUTION: The molten aluminum alloy adding Ti and B or the molten aluminum alloy limiting Si of which degree of superheat just before casting is 30 deg.C or less to the liquidus and the molten aluminum alloy having composition of the max. solid solution limit or higher and which is cast while giving the fine vibration as necessity requires, is cast at 1 deg.C/sec cooling speed in the solidification range. Thereafter, the temp. of a billet is risen at the eutectic temp. or higher and the liquidus ratio is made to be 20-80% by selecting the holding temp. and the holding time, and after spheroidizing the primary crystal, the billet in the half-melting metal state is pressurize-formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a semi-molten metal of an aluminum alloy, and particularly to heating an aluminum alloy billet having fine equiaxed crystals obtained by an improvement of the conventional casting method to a semi-melting temperature range. The present invention relates to a method for molding a semi-molten metal, which is pressure-molded while retaining a spheroidized structure.

[0002]

2. Description of the Related Art The thixocasting method has attracted attention recently because of its advantages such as less casting defects and segregation, uniform metal structure, longer die life and shorter molding cycle than the conventional casting method. Technology. This molding method (A)
The billet used in (1) is obtained by carrying out mechanical stirring or electromagnetic stirring in the semi-melting temperature range, or by utilizing recrystallization after processing. On the other hand, a method of semi-melt molding using a material by a conventional casting method is also known. This is, for example, a method (B) of adding Zr or a method (C) of using a carbon-based refiner in order to generate finer crystals in a Magne alloy which is apt to generate an equiaxed crystal structure. This is a method of heating the material obtained by the method to a semi-melting temperature range to make the primary crystal spherical and molding. In addition, for alloys within the solid solution limit, after heating relatively quickly to a temperature near the solidus line, the temperature of the entire material is made uniform, and in order to prevent local melting, the material is exceeded above the solidus line. There is known a method (D) of gently heating to an appropriate temperature for softening and molding.

[0003]

However, the method (A) described above has a problem that the work is complicated and the manufacturing cost is high in any case of the stirring method and the method utilizing recrystallization. Also, in the case of Magne alloy, (B) and (C)
Although it is possible to obtain a structure of fine crystal grains of about 100 μm by refining with the method described above, it is possible to obtain a structure of 500 μm in an aluminum alloy by simply adding a refining agent.
However, it is not easy to obtain a fine grain structure of 100 μm or less. Further, in the method (D), a thixomolding method has been proposed, which is characterized by heating the material gently beyond the solidus to achieve uniform heating and spheroidization of the material. It does not change to a thixostructure (primary crystal dendrites are spheroidized) even when heated. The present invention focuses on the problems of each of the above-mentioned conventional methods, easily and easily obtain a material having fine equiaxed crystals without employing a complicated method, and after subjecting the material to a predetermined heat treatment,
It is an object of the present invention to provide a method for forming a semi-molten metal.

[0004]

In order to solve such a problem, according to the present invention, a hypoeutectic aluminum alloy having a composition of the maximum solid solution limit or more, and the temperature at the time of hot water supply for a billet die is The aluminum alloy melt is cooled and solidified in the mold at a superheating degree of not less than the liquidus line and in a temperature range not exceeding 30 ° C from the liquidus line, and at a solidification section cooling rate of 1 ° C / sec or more. After the billet is cast by heating, the billet is heated to a temperature higher than the eutectic temperature, and the liquid phase ratio is set to 20 by selecting the holding time and the holding temperature.
After the primary crystal was spheroidized to about 80%, the billet having the liquid phase ratio in a semi-molten state was supplied to a molding die for pressure molding. In the second invention, B is 0.001
.About.0.01% and 0.005 to 0.30% of Ti was added to the aluminum alloy. Further, in the third invention, B is 0.00
1 to 0.01%, 0.005 to 0.30% of Ti, and 4 to 6% of Si were used as an aluminum alloy. Further, in the fourth aspect of the invention, the billet mold is configured to supply hot water while slightly vibrating in a direction substantially perpendicular to the hot water supply direction.

[0005]

[Function] The temperature of the molten aluminum alloy having a composition above the maximum solid solubility limit is set to a superheat degree of less than 30 ° C. with respect to the liquidus temperature, and 1 ° C.
A billet having fine equiaxed crystals can be obtained by casting at a solidification zone cooling rate of not less than 1 sec. The billet is heated to a temperature higher than the eutectic temperature, the liquid phase ratio is set to 20 to 80% by selecting the holding time and the holding temperature to make the primary crystal spherical, and a molded body having a homogeneous structure by pressure molding. Is obtained.

[0006]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1 to 4 relate to an embodiment of the present invention,
FIG. 1 is a process explanatory view showing a method for forming a semi-molten metal, FIG. 2 is a front view of a mold for a serpentine sample, FIG. 3 is a diagram showing a typical equilibrium state of an aluminum alloy, and FIG. 4 is a molded product of the present invention. A micrograph showing a metal structure, and FIG. 5 shows a micrograph showing a metal structure of a comparative example obtained by a conventional molding method. In the present invention, as shown in FIGS. 1 and 3, for an aluminum alloy, first, when an aluminum alloy having a composition higher than the maximum solid solution limit is supplied to a billet mold at a temperature higher than the liquidus line. Moreover, while keeping the temperature within a temperature range not exceeding 30 ° C. from the liquidus, gently inject it into the mold for the hillet. The cooling rate of the molten metal in the billet mold is controlled to 1 ° C / sec or more. In this way, the billet obtained by cooling and solidifying to room temperature is
Next, the temperature is raised from room temperature to a temperature higher than the eutectic temperature, and the holding time and the holding temperature are selected to make the liquid phase ratio 20 to 80% and the primary crystal is made spherical. Next, the billet in the semi-molten state is pressure-molded to form a molded product. As is clear from the figure, the difference between the present invention shown in FIG. 1 and the conventional thixotropic method (one example) shown in FIG. 6 is that in the present invention, a metallic structure characterized by fine crystal grains is obtained in the billet manufacturing process, and After the temperature is raised to the crystal temperature or higher, a predetermined amount of liquid phase is generated by holding the crystal for a predetermined time, the primary crystal is swiftly spheroidized by utilizing the feature of the structure, and the latter half melt molding is performed. On the other hand, in the conventional thixo method, spheroidized primary crystals have already been obtained in the billet manufacturing process, and after the temperature has been raised to the eutectic temperature or higher, the liquid phase is generated by holding for a predetermined time, and the latter half melt molding is performed. That is, the holding at the eutectic temperature or higher in the present invention is performed not only for producing the liquid phase but also for spheroidizing.

Casting conditions, spheroidizing and molding conditions set in each of the above-mentioned processes, ie, the billet manufacturing process, the heating process, and the molding process shown in FIG. 1, the second invention, the third invention, and the fourth invention. The reason for limiting the numerical values shown in the invention will be described below. Casting temperature is 30 ° C against melting point
Or if the solidification zone cooling rate is less than 1 ° C./sec, fine equiaxed crystals cannot be obtained even if the refiner is included. Therefore, the casting temperature is set so that the degree of superheat with respect to the liquidus is less than 30 ° C, and the solidification section cooling rate is set to 1 ° C / sec or more. If the liquid phase ratio is less than 20%, the spheroidization of primary crystals does not easily proceed, and since the deformation resistance is high, pressure molding is not easy and a molding material having a good appearance cannot be obtained. Again 80
If it exceeds%, there is a problem that the billet cannot sufficiently maintain its original shape or a molding material having a uniform structure cannot be obtained. Therefore, the liquid phase ratio in the semi-melting temperature range above the eutectic temperature is set to 20 to 80%. More specifically, in an alloy having a composition having a liquid phase ratio of less than 20% at the eutectic temperature, the alloy is heated to a temperature region higher than the eutectic temperature for a predetermined time, and the liquid phase generation amount at the eutectic temperature is 20 to 80.
% Alloys are heated to a temperature region above the eutectic temperature for a predetermined time, and alloys with a liquid phase ratio at the eutectic temperature of more than 80% and less than 100% are heated at the eutectic temperature for a predetermined time. After making the actual liquid phase rate 20 to 80% and spheroidizing the primary crystal, the billet in a semi-molten state was supplied to a molding die for pressure molding. It is more preferable to set the substantial liquid phase ratio to 30 to 70% because a more homogeneous molding material can be easily molded. The crystals are made finer by suppressing the casting temperature to a low level, but Ti and B are added for further refinement. If Ti is less than 0.005%, the effect of refining is small, and if it exceeds 0.30%, a coarse Ti compound is generated and ductility is deteriorated.
05 to 0.30%. B, together with Ti, promotes the refinement, but if it is less than 0.001%, the crystal grains are not refined, and if it is added in excess of 0.01%, no further effect can be expected. B is 0.001 to 0.01%.
If the Si content is less than 6%, the primary crystal has a petal-like shape,
Sphericalization is easily achieved by maintaining the temperature in the semi-melting temperature range.
If it is less than 4%, the strength is insufficient. Therefore, Si is 4
-6%.

Next, in the fourth aspect of the invention, when the molten metal is supplied to the billet mold, a minute vibration of, for example, 1 to 200 G and an amplitude of 1 μm to 10 mm is applied to the billet mold in a direction substantially perpendicular to the hot water supply direction. give. Any vibration method such as air vibration may be used. It is preferable to give such a minute vibration to the molten metal at the time of hot water supply because a material having finer crystal grains can be obtained. FIG. 2 is a front view of a snake-shaped sample mold 1 for collecting a test piece, in which molten metal is injected through a gate 3 and gas generated inside is degassed through an air vent 2. Table 1 shows a comparative table of various test pieces formed by using the mold 1 for a serpentine sample according to the present invention. Table 1 shows that there is a significant difference in the homogeneity of the molded product and the appearance of the molded product depending on the casting temperature of various alloys, the presence or absence of microvibration, the heating temperature (the spheroidizing temperature in the present invention), and the liquid phase ratio. It is indicated that
The samples (Nos. 1 to 8) of the present invention are comparative examples (Nos. 9 to 9).
It can be seen that, unlike 14), both the homogeneity and the appearance of the molded product are good. As shown in FIG. 4, the sample of the present invention is fine and uniform over the entire area as compared with FIG. 5 of the comparative example. On the other hand, in Comparative Examples 9 and 10, since the liquid phase ratio is low, the spheroidization of the primary crystal does not easily proceed, so that a uniform structure cannot be obtained and a molded product having a good appearance cannot be obtained. Further, in Comparative Examples 11 and 12, the billet cannot maintain its original shape when heated because of the large amount of liquid phase, and the structure of the molded body lacks uniformity. Since the casting temperature is high in Comparative Examples 13 and 14,
Since the crystal grain size of the billet is large, the primary crystal does not easily form a spherical structure even if kept in the semi-melting temperature range. As a result, the texture is not uniform.

[0009]

As is apparent from the above description, in the method for forming a semi-molten metal according to the present invention, the degree of superheat immediately before casting is less than 30 ° C. with respect to the liquidus, and if necessary, a small amount is required. After casting a molten aluminum alloy having a composition higher than the maximum solid solution limit, Ti, B-added aluminum alloy, or Si-limited aluminum alloy at a cooling rate of 1 ° C / sec or more, the billet was co-cast with vibration. Liquid phase ratio of 20-80% depending on the holding temperature and holding time
After spheroidizing the primary crystal, the semi-molten billet was pressure-molded, so that a fine and uniform thixostructure having a thixostructure can be obtained easily and at low cost, regardless of the conventional mechanical stirring method or electromagnetic stirring method. An excellent molded product can be obtained.

[Brief description of drawings]

FIG. 1 is a process explanatory view showing a method of forming a semi-molten metal according to an embodiment of the present invention.

FIG. 2 is a front view of a mold for a serpentine sample according to an example of the present invention.

FIG. 3 is an equilibrium state diagram of a typical aluminum alloy according to an example of the present invention.

FIG. 4 is a micrograph showing a metal structure of a molded product according to an example of the present invention.

FIG. 5 is a micrograph showing a metal structure of a molded product (comparative product) manufactured by a conventional molding method.

FIG. 6 is a process explanatory view showing a conventional molding method.

[Explanation of symbols]

 1 Snake-shaped sample mold 2 Air vent 3 Gate

[Table 1]

Claims (4)

[Claims] 1. A hypoeutectic aluminum alloy having a composition of at least the maximum solid solution limit, and the temperature at the time of supplying hot water to the billet mold is such that the degree of superheat is above the liquidus and exceeds 30 ° C. above the liquidus. In a temperature range that is not present, and after cooling and solidifying the molten aluminum alloy in the mold at a solidification section cooling rate of 1 ° C./second or more to cast a billet, the billet is heated to a eutectic temperature or higher, After selecting the holding time and holding temperature to make the liquid phase ratio 20 to 80% and making the primary crystal spherical, the billet having the liquid phase ratio in the semi-molten state is supplied to a molding die and pressure-molded. A method for forming a semi-molten metal, comprising: 2. An aluminum alloy containing B in an amount of 0.001 to 0.0
The method for forming a semi-molten metal according to claim 1, wherein the aluminum alloy is an aluminum alloy containing 1% and 0.005 to 0.30% Ti. 3. An aluminum alloy containing B in an amount of 0.001 to 0.0
1%, 0.005 to 0.30% of Ti is added, and S
The method for forming a semi-molten metal according to claim 1, wherein the aluminum alloy contains i of 4 to 6%. 4. The method for forming a semi-molten metal according to claim 1, claim 2, or claim 3, wherein the billet mold is supplied with hot water while slightly vibrating in a direction substantially perpendicular to the direction of hot water supply.