JPH0987767A - Method for molding half-molten zinc alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a molding having a fine and spherical thixo structure at a low cost by cooling and holding a liquid zinc ally of a liquidus temp. or above having crystal nuclei under specific conditions to crystallize fine primary crystals and press molding these crystals. SOLUTION: The zinc alloy M which is the perfect liquid in a ladle 10 is cooled to generate the crystal nuclei from the low-temp. melt by using a cooling jig 20 and is poured into a ceramic vessel 30 having a thermal insulating effect to obtain the alloy M right under the liquidus temp. contg. the many crystal nuclei. While the alloy M is cooled in this thermal insulating vessel 30 down to the molding temp. at which the alloy exhibits a prescribed liquid phase ratio. The alloy is then hold in a half molten state for 5 seconds to 60 minutes. The superfine non-dendritic primary crystals are formed from the crystal nuclei during this time. These crystal grow to the spherical primary crystals. The alloy M having the prescribed liquid phase ratio obtd. in such a manner is inserted into an injection sleeve 40 of die casting and is then press-molded within the die cavity 50a of a die casting machine to obtain the molded goods. As a result, the molded goods having the fine and spheroidal structure are easily and simply obtd. at a low cost.

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 zinc alloy, and more particularly to a zinc alloy having a crystal nucleus and in a liquid state above a liquidus temperature, or a crystal state having a crystal nucleus above a forming temperature in a liquid state. In the heat-insulating container having a heat-insulating effect, the above zinc alloy is cooled to a molding temperature exhibiting a predetermined liquid phase ratio and held for 5 seconds to 60 minutes to generate a fine primary crystal in the liquid before adding. The present invention relates to a method for forming a semi-molten metal by pressure forming.

[0002]

2. Description of the Related Art Thixocasting has attracted attention recently because it has fewer casting defects and segregation than conventional casting methods, has a uniform metal structure, has a long mold life, and has a short molding cycle. Technology. This molding method (A)
The billet used in (1) is characterized by a spheroidized structure obtained by carrying out mechanical stirring or electromagnetic stirring in the semi-melting temperature region, or by utilizing recrystallization after processing. On the other hand, a method of semi-solid molding using a material obtained 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 produce finer crystals in a magnesium alloy that is likely to generate an equiaxed crystal structure.
In addition, it is a method (D) of adding Al-5% Ti-1% B mother alloy as a refining agent in an aluminum alloy about 2 to 10 times that of the conventional method, and the material obtained by these methods is semi-melted. This is a method in which the primary crystal is heated to a temperature range so as to be spherical and then molded. Also, for alloys within the solid solubility limit, after heating relatively quickly to a temperature near the solidus, the material exceeds the solidus in order to equalize the temperature of the entire material and prevent local melting. A method (E) of forming by heating gently to an appropriate temperature at which the material is softened is known. On the other hand, unlike the method of heating the billet to the semi-melting temperature range and molding,
A rheocast method (F) is known in which a melt containing spherical primary crystals is continuously produced, and the billet is not solidified once but is shaped as it is.

[0003]

However, the above-mentioned method (A) is complicated in both cases of the stirring method and the method of utilizing recrystallization, and there is a drawback that the manufacturing cost becomes high. Further, in zinc alloys, a method of refining crystals such as (B), (C) and (D) is not generally known. Further, in the method (E), a thixomolding method has been proposed which is characterized by uniformly heating the material and spheroidizing it by gently heating it after passing the solidus line. It does not change to a thixostructure (primary crystal dendrites are spheroidized) even when heated. Moreover, in any of the thixomolding methods (A) to (E), it is necessary to once solidify the liquid phase and raise the billet again to the semi-melting temperature region in order to perform the semi-melt molding, as compared with the conventional casting method. And the cost will increase. Moreover, in the method of (F),
Since it continuously generates and supplies a melt containing spherical primary crystals, it is more cost- and energy-efficient than thixocasting, but it is possible to provide a machine and final product for producing metal raw materials composed of a spherical structure and a liquid phase. It is complicated to interlock with the casting machine to be manufactured. The present invention focuses on the problems of the conventional methods described above,
The purpose of the present invention is to propose a method of obtaining a semi-molten zinc alloy having a fine primary crystal and pressing it easily and easily without using a billet and without taking a complicated method. is there.

[0004]

In order to solve such a problem, in the present invention, in the first invention, a zinc alloy having a crystal nucleus in a liquid state at a liquidus temperature or higher, or a crystal nucleus The solid-liquid coexisting zinc alloy having a temperature above the molding temperature is kept in the liquid for 5 seconds to 60 minutes while being cooled to a molding temperature exhibiting a predetermined liquid phase ratio in a heat insulating container having a heat insulating effect. Then, fine primary crystals were crystallized in the zinc alloy liquid, and the zinc alloy was supplied to a molding die for pressure molding. A second aspect of the present invention is the method of producing crystal nuclei according to the first aspect of the present invention, in which a molten alloy having a superheat degree of less than 300 ° C. with respect to a liquidus temperature is treated at a temperature lower than a melting point of the alloy. It was decided to contact the surface of the ingredient. Further, in the third invention, the jig of the second invention is a metal jig or a non-metal jig, a metal jig whose surface is coated with a non-metal material containing a semiconductor, or a non-metal jig containing a semiconductor. A metal jig that is a composite of metal materials, and
The jig can be cooled from inside or outside. Further, in the fourth aspect of the invention, the crystal nuclei are generated by vibrating the molten zinc alloy in contact with either or both of the jig and the heat insulating container. Fifth
In the invention, the zinc alloy of the first invention or the second invention is a zinc alloy containing aluminum having an amorphous point or lower. In the sixth invention, the degree of superheat with respect to the liquidus temperature is set to 10
The molten zinc alloy held below 0 ° C. was poured directly into a heat insulating container without using a jig.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION A zinc alloy in a liquid state above a liquidus having a crystal nucleus or a zinc alloy in a solid-liquid coexisting state above a molding temperature having a crystal nucleus is molded in a heat insulating container having a heat insulating effect at a molding temperature. By maintaining for 5 seconds to 60 minutes while cooling to, a fine and spherical primary crystal is generated in the liquid,
By supplying the zinc alloy to a molding die and performing pressure molding, a molded body having an excellent uniform structure can be obtained.

[0006]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1 to 5 relate to an embodiment of the present invention,
FIG. 1 is a process explanatory view showing a forming method of a semi-molten metal of a zinc alloy having a hypoeutectic composition, FIG. 2 is a process explanatory view showing a forming method from formation of spherical primary crystals to forming, and FIG. 3 is shown in FIG. Schematic diagram of the metal structure of each process, and FIG. 4 is a typical zinc alloy Zn
-Al binary alloy equilibrium diagram, and Fig. 5 is a copy of a micrograph showing the metal structure of the molded product of the present invention. FIG. 6 is a copy of a micrograph showing the metal structure of the molded product of the comparative example.

In the present invention, as shown in FIGS. 1 and 4, first, (1) a melt of a hypoeutectic zinc alloy whose superheat degree is kept below 300 ° C. with respect to the liquidus temperature is The crystal nuclei are generated in the liquid by contacting the surface of the jig whose temperature is lower than the melting point, or (2) the molten zinc alloy which is maintained at a superheat degree of less than 100 ° C. to the liquidus temperature Pour directly into a heat-insulating container that has a heat-insulating effect without using it, and keep it in the heat-insulating container at a temperature below the liquidus temperature and higher than the eutectic temperature or solidus temperature for 5 seconds to 60 minutes to make it fine. A large number of spherical primary crystals are generated and molded at a predetermined liquid phase rate. The predetermined liquid phase ratio means the amount ratio of the liquid phase suitable for pressure molding, and in high pressure casting such as die casting and squeeze casting, the liquid phase ratio is 20% to 90%, preferably 30% to 70% ( If it is less than 30%, the moldability of the material is poor, and if it is 70% or more, the material is not only difficult to handle because it is soft, but it is difficult to obtain a uniform structure.) In the extrusion method or forging method, 0.1% to 70% , Preferably 0.1
% To 50% (50% or more may cause nonuniformity of the structure). The heat-insulating container in the present invention is a metal container or a non-metal container, or a metal container having a surface coated with a non-metal material containing a semiconductor, or a composite of a non-metal material containing a semiconductor. The container is made of metal, and the container can be heated or cooled from inside or outside.

Specifically, the work is carried out according to the following procedure. The metal M which is a complete liquid contained in the ladle 10 in the step [1] of FIGS. 2 and 3 is processed in the step [2].
In (a), a ceramic container 3 having a heat insulating effect by generating crystal nuclei from a low temperature molten metal by using a cooling jig 20.
0, or (b) directly apply the low temperature melt directly above the melting point,
By pouring into a heat insulating container 30 (ceramic coating metal container 30A) having a heat insulating effect, an alloy immediately below the liquidus line containing a large number of crystal nuclei is obtained. Next, in step [3], the alloy is held in the semi-molten state in the heat insulating container 30 (or 30A). During this period, ultrafine non-dendritic primary crystals are generated from the introduced crystal nuclei ([3] -a), and grow as spherical primary crystals as the solid fraction increases as the temperature of the melt decreases ([3] -a). ] -C). The metal M having a predetermined liquid phase ratio thus obtained is die-casted into the injection sleeve 40 as in [3] -d.
Mold cavity 5 of die casting machine after inserting into
A molded product is obtained by pressure molding in 0a.

The difference between the present invention shown in FIGS. 1, 2 and 3 and the conventional thixocast method and rheocast method is clear from the drawings. That is, in the present invention, unlike conventional methods, the dendrite-like primary crystals crystallized in the semi-melting temperature region are not forcibly crushed into spherical particles by mechanical stirring or electromagnetic stirring, and the crystal nuclei introduced into the liquid A large number of primary crystals that crystallize and grow with a decrease in temperature in the semi-melting temperature region starting from the starting point are continuously spherical due to the amount of heat the alloy itself has (may be externally heated and held if necessary) It is a very simple method because the step of semi-melting by reheating the billet in the thixocasting method is omitted. The casting conditions, the spheroidizing conditions and the molding conditions set in each of the above-mentioned processes, namely, the process of pouring into the cooling jig 20 shown in FIG. The reason for limiting the numerical values shown in the invention and the sixth invention will be described below.

When the casting temperature is higher than the melting point by 300 ° C. or higher, or when the surface temperature of the jig 20 is higher than the melting point, (1) the generation of crystal nuclei is small, and (2) the heat insulation has a heat insulating effect. Since the temperature of the molten metal M when it is poured into the container is higher than the liquidus line, the proportion of remaining crystal nuclei is low and the size of the primary crystal is large. For this reason, the casting temperature is set so that the degree of superheat to the liquidus is less than 300 ° C., and the surface temperature of the jig is lower than the melting point of the alloy. In addition, by setting the degree of superheat to the liquidus line to less than 100 ° C.
By making the temperature of 0 lower than the melting point of the melt M by 50 ° C. or more, a finer primary crystal size can be obtained. There are two methods for bringing the molten metal M into contact with the jig 20: moving the molten metal M on the surface of the jig (flowing the molten metal into the inclined jig 20) and moving the jig 20 in the molten metal. is there. The jig mentioned here refers to a jig that gives a cooling action to the molten metal when the molten metal flows down, but instead of this, for example, a tubular pipe of a water heater may be used. The heat insulating container 30 that holds the molten metal that has fallen just below the liquidus line has a heat insulating effect in order to make the generated primary crystals spherical and achieve a desired liquidus ratio after a predetermined time. The material is not limited, and it is preferable that the material has heat retention and has poor wettability with the molten metal. Further, when a ceramic container having air permeability is used as the heat insulating container 30 and the alloy has a composition that easily oxidizes, it is desirable to set the outside of the container to a predetermined atmosphere (inert atmosphere, reduced pressure atmosphere, etc.). In addition,
The shape of the heat insulating container 30 is not limited to the cylindrical shape,
A shape suitable for the subsequent molding method is possible. Further, instead of the heat insulating container, it may be directly charged into a ceramic injection sleeve. The holding time in the heat insulation container 30 is 5
If it is less than a second, it is not easy to reach a temperature at which a desired liquid phase ratio is exhibited, and it is difficult to form spherical primary crystals. On the other hand, if the holding time exceeds 60 minutes, the generated spherical primary crystals and eutectic structure become coarse and the mechanical properties deteriorate. Therefore, the holding time is 5 seconds to 60 minutes. In the high-pressure casting, if the liquid phase ratio immediately before molding is less than 20%, the deformation resistance during molding is high and it is not easy to obtain a molded product of good quality. If it exceeds 90%, a molded product having a uniform structure cannot be obtained. Therefore, as described above, the liquid phase ratio during molding is preferably 20% to 90%. Furthermore, by setting the substantial liquid phase ratio to 30% to 70%,
Further, a homogeneous and high-quality molding material can be easily pressure-molded. The means for pressure molding is not limited to the high pressure casting method represented by the squeeze casting method and the die casting casting method, and various methods for pressure molding such as extrusion method and forging method are included.

The jig 20 for contacting the molten metal M is not limited in its material as long as it can lower the temperature of the molten metal, but copper, copper alloy, aluminum, aluminum having particularly high thermal conductivity is used. The jig 20 which is made of a metal such as an alloy and which is cooled and controlled so that it can be maintained at a certain temperature or lower is preferable because many crystal nuclei are generated. In addition,
When the molten metal M comes into contact with the jig 20, the metal becomes solid in the jig 2
It is effective to apply a non-metallic material to prevent sticking to zero. The coating method may be mechanical, chemical or physical.

Since a zinc alloy easily forms an equiaxed crystal structure, it is relatively easy to obtain a fine spherical primary crystal without using the jig 20. In this case, the degree of superheat to the liquidus is set to less than 100 ° C. in order to prevent the alloy poured into the heat insulating container 30 having the heat insulating effect from being in a liquid state having crystal nuclei or a solid having a temperature higher than the molding temperature having the crystal nuclei. This is to make the liquid coexist. If the temperature of the poured molten metal in the heat insulating container 30 is high, re-dissolution of crystal nuclei once formed or coarsening of primary crystals occurs, and a desired semi-molten structure cannot be obtained. Further, since the temperature drops to a predetermined liquid phase rate, it takes too much time and the efficiency is poor, and the surface of the poured molten metal M is oxidized, which is inconvenient. Table 1 shows the conditions of the semi-molten metal before forming and the quality of the forming material. The forming was performed by inserting a semi-molten metal into the sleeve as shown in FIG. 2 and then using a squeeze casting machine. Molding conditions are pressing force 950kgf / c
m ² , injection speed 1.0 m / s, mold temperature 200 ° C.,
The product shape was a flat plate having a thickness of 2 mm, 5 mm, and 10 mm, which varied in the longitudinal direction, and had a width of 100 mm and a length of 200 mm.

[0013]

[Table 1]

In Comparative Example 9, the jig 2 for contacting the molten metal M
Since the temperature of 0 is too high, the generation of crystal nuclei is small, and as a result, fine spherical primary crystals cannot be obtained, resulting in coarse amorphous primary crystals. In Comparative Example 10, since the casting temperature is too high,
Almost no crystal nuclei remained in the ceramic container 30, and the same phenomenon as in Comparative Example 9 was exhibited. In Comparative Example 11, since the retention time is long, the liquid phase ratio is small and the appearance is not good. The primary crystal size is also large. In Comparative Example 12, since the holding time in the ceramic container 30 is short and the liquid phase ratio is high, segregation of components inside the molded product as shown in FIG. 6 occurs frequently. In Comparative Example 13, since the metal container having a very small heat insulating effect was used, the dendrite-like solidified layer formed on the inner wall of the heat insulating container 30 was mixed in the spherical primary crystal formed in the center of the container, and segregation occurred. Shows a heterogeneous tissue containing. On the other hand, in Examples 1 to 8 of the present invention, a homogeneous structure having fine spherical primary crystals of 200 μm or less as shown in FIG. 5 can be obtained, and a molded product having a good appearance can be obtained.

[0015]

As is clear from the above description, in the method for forming a semi-molten zinc alloy according to the present invention,
(1) In a heat-insulating container having a heat insulating effect, an alloy in a liquid state having a liquid crystal temperature above the liquidus temperature, or an alloy having a crystal nucleus in a solid-liquid coexisting state above the molding temperature,
5 seconds to 6 while cooling to a molding temperature showing a predetermined liquid phase ratio
Crystallized by holding for 0 minutes, or (2) by bringing the molten alloy whose superheat degree is lower than 300 ° C. with respect to the liquidus temperature into contact with the surface of the jig whose temperature is lower than the melting point of the alloy. Nuclei are generated to generate fine and spheroidized primary crystals in the liquid of the alloy, and the alloy in a semi-molten state having a predetermined liquid phase ratio is supplied to a molding die for pressure molding. Therefore, regardless of the conventional mechanical stirring method and electromagnetic stirring method,
A compact having a fine and spherical structure can be obtained easily and easily at low cost. Further, the degree of superheat with respect to the liquidus temperature was poured directly into a heat-insulating container without using a jig and the molten zinc alloy maintained at less than 100 ° C. was cooled to a molding temperature at which a predetermined liquidus rate was achieved. By maintaining the second to 60 minutes, similarly, fine and spherical primary crystals can be generated.

[Brief description of drawings]

FIG. 1 is a process explanatory view showing a method for forming a semi-molten metal of a hypoeutectic zinc alloy according to the present invention.

FIG. 2 is a process explanatory view showing a molding method from generation of spherical primary crystals to molding according to the present invention.

FIG. 3 is a schematic diagram of a metallographic structure of each step shown in FIG.

FIG. 4 is a typical zinc alloy according to the present invention, Zn-A.
It is a 1-system binary alloy equilibrium diagram.

FIG. 5 is a copy of a micrograph showing the metal structure of a molded article of the present invention.

FIG. 6 is a copy of a micrograph showing a metal structure of a molded product of a comparative example.

[Explanation of symbols]

 10 Laddle 20 Cooling jig 30 Heat insulation container (ceramic container) 30A Ceramic coating metal container 40 Injection sleeve 50 Mold 50a Mold cavity M Metal (molten metal) t Temperature T time

Claims (6)

[Claims] 1. A liquid state zinc alloy having a crystal nucleus at a liquidus temperature or higher, or a solid-liquid coexisting zinc alloy having a crystal nucleus at a forming temperature or higher in a heat insulating container having a heat insulating effect, By holding for 5 seconds to 60 minutes while cooling to a molding temperature exhibiting a predetermined liquid phase rate, fine primary crystals are crystallized in the liquid, and the zinc alloy is used as a molding die. A method for forming a semi-molten zinc alloy, which comprises supplying and pressurizing. 2. The method for producing crystal nuclei comprises contacting a molten alloy having a superheat degree of less than 300 ° C. with respect to a liquidus temperature with a surface of a jig having a temperature lower than a melting point of the alloy. The method for forming a semi-molten zinc alloy according to claim 1. 3. The jig to be brought into contact with the molten metal is a metal jig or a non-metal jig, a metal jig whose surface is coated with a non-metal material containing a semiconductor, or a composite non-metal material containing a semiconductor. The method for forming a semi-molten zinc alloy according to claim 2, wherein the jig is made of a metal, and the jig can be cooled from the inside or the outside of the jig. 4. The semi-molten zinc alloy according to claim 1 or 2, wherein the crystal nuclei are generated by vibrating a molten zinc alloy in contact with either or both of the jig and the heat insulating container. Molding method. 5. The method for forming a semi-molten zinc alloy according to claim 1 or 2, wherein the zinc alloy is a zinc alloy containing aluminum having a eutectic point or lower. 6. The method for forming a semi-molten zinc alloy according to claim 5, wherein the molten zinc alloy having a superheat degree to the liquidus temperature of less than 100 ° C. is poured directly into a heat insulating container without using a jig.