JP3473216B2 - Forming method of semi-molten metal - Google Patents

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, and particularly to an alloy in a liquid state having a crystal nucleus and having a liquidus temperature or higher, or a solid-liquid coexisting state having a crystal nucleus and having a temperature higher than the forming temperature. While cooling the alloy of No. 5 to a forming temperature showing a predetermined liquid phase ratio in an insulating container having an insulating effect.
The present invention relates to a method for forming a semi-molten metal in which a fine primary crystal is crystallized in the alloy liquid by holding for 2 seconds to 60 minutes, and the alloy is inserted into a container of an extruder and pressure-molded. is there.

[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 characterized by a spheroidized structure obtained by performing 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-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. Al-5% as a refiner in aluminum alloys
This is a method (D) in which a Ti-1% B mother alloy is added in an amount of 2 to 10 times that of the conventional method, and the raw material obtained by these methods is heated to a semi-melting temperature range to form primary crystals into spheroids and molded. is there. 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 (E) of gently heating to an appropriate temperature for softening and molding. In addition, the solid fraction is 70-80
It is known to insert% semi-molten metal into a container and extrude (F). On the other hand, unlike the method in which the billet is heated to a semi-melting temperature region and molded, a melt containing spherical primary crystals is continuously generated, and the billet is molded as it is without solidifying it once ( G)
It has been known.

[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 the magnesium alloy, in the case of (B), Zr is high and there is a problem in terms of cost, and in the method of (C), a carbide-based refiner is used to sufficiently exert its refinement effect. For this reason, Be, which is an antioxidant element, needs to be controlled to a low level of, for example, about 7 ppm, which easily causes oxidative combustion during heat treatment immediately before molding, which is inconvenient for work.

On the other hand, in the case of an aluminum alloy, it is about 500 μm by simply adding a refining agent.
It is not easy to obtain a fine grain structure of 00 μm or less. For this reason, there is a method (D) in which a large amount of the finely-dividing agent is added, but the finely-dividing agent is liable to settle on the furnace bottom and is industrially difficult, and the cost is high. Further, in the method (E), a thixomolding method has been proposed, which is characterized by heating the material gently beyond the solidus to achieve uniform heating and spheroidizing of the material. However, it does not change into a thixostructure (primary crystal dendrites are spheroidized). 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. Also,
In the method (F), although semi-melt molding is possible, since the metal is generally a metal having a dendrite structure, the liquid phase and the solid phase are separated at the time of molding and a nonuniform structure is generated. In addition, when a thixovillet having a spherical structure is heated, generally there is no container, so the molding temperature is low, and high pressing force and high extrusion rate are required. In the method (G),
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 above-mentioned conventional methods,
To provide a method for pressure-extruding a semi-molten metal having a uniform structure including spheroidized primary crystals, easily and easily without using a billet and without taking a complicated method. It is intended.

[0005]

In order to solve such a problem, in the present invention, in the first invention, the liquid phase is
Aluminum whose superheat degree is kept below 100 ° C against the wire temperature
Jig the molten magnesium alloy or magnesium alloy
Directly into the insulated container without using
In the heat insulation container that has, below the liquidus temperature, and
Set the temperature higher than the eutectic temperature or solidus temperature,
By holding for 5 seconds to 60 minutes while cooling to a molding temperature showing a liquid phase ratio of 0.1 to 70% , fine primary crystals are crystallized in the alloy liquid, and the alloy is placed in a container of an extruder. Insert into
When doing so, remove the part of the semi-molten metal that is in contact with the bottom of the insulated container.
Extruding by facing the die side of the extruder, or
Extruder with the uppermost part of the semi-molten metal insulated container removed
It was decided to perform extrusion molding so as to face the die side . In addition, in the second invention, the generation of the crystal nuclei in the first invention is performed by vibrating the molten alloy which comes into contact with the heat insulating container. Further, in the third invention, the extruder in the first invention is a horizontal extruder or a vertical extruder, or a horizontal extruder in which the container is tilted from a vertical shape to a horizontal shape before forming and molding. The extrusion method was indirect extrusion or direct extrusion. In the fourth invention, the semi-molten metal to be inserted into the container in the indirect extrusion method according to the third invention is passed through a tube having an inner diameter smaller than that of the semi-molten metal when the semi-molten metal is taken out from the heat insulating container. It was decided to remove the metal surface layer.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION An alloy in a liquid state above the liquidus having crystal nuclei or an alloy in the solid-liquid coexisting state above the molding temperature having crystal nuclei is subjected to a predetermined liquid phase in a heat insulating container having a heat insulating effect. By holding for 5 seconds to 60 minutes while cooling to a molding temperature showing a rate, fine primary crystals are crystallized in the alloy liquid, and the alloy is inserted into a container of an extruder and pressure-molded. By doing so, a molded product having a uniform structure can be obtained.

[0007]

Embodiments of the present invention will now be described 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 method for forming a semi-molten metal of a hypoeutectic aluminum alloy having a composition higher than the maximum solid solution limit, and FIG. 2 is a maximum solid solution limit. 4 is a process explanatory diagram showing a method for forming a semi-molten metal of a magnesium alloy or an aluminum alloy having an internal composition, FIG. 3 is a process explanatory diagram from formation of spherical primary crystals to forming,
Is a schematic diagram of the metal structure of each step shown in FIG. 3, FIG. 5 is an Al-Si alloy equilibrium state diagram which is a typical aluminum alloy, and FIG. 6 is Mg-Al which is a typical magnesium alloy.
System alloy equilibrium diagram, FIG. 7 is a photomicrograph showing the metallographic structure of the comparative example molded product, and FIG. 8 is a photomicrograph showing the metallographic structure of the molded product of the present invention.

In the present invention, as shown in FIG. 1, FIG. 2, FIG. 5 and FIG.
A hypoeutectic aluminum alloy with a composition above the maximum solid solution limit or a magnesium alloy with a composition within the maximum solid solution limit, or a molten aluminum alloy kept below the temperature of the jig is brought into contact with the surface of the jig whose temperature is lower than the melting point of the alloy. Generate crystal nuclei in the liquid and pour it into a heat insulating container having an adiabatic effect, and in the heat insulating container, the temperature is below the liquidus temperature and higher than the eutectic temperature or the solidus temperature for 5 seconds to By holding for 60 minutes, a large number of fine spherical primary crystals are generated, and molding is performed at a predetermined liquid phase ratio. The predetermined liquid phase rate is 0.1% to 70%,
It is preferably 10 to 70%. In addition, the heat insulating container in the present invention is a metal container or a non-metal container,
Alternatively, it is a metal material obtained by coating a composite or non-metal material, and the container can be heated or cooled from inside or outside.

Specifically, the work is carried out according to the following procedure. In the step [1] of FIG. 3 and FIG. 4, the metal M, which is the complete liquid contained in the ladle 10, is processed in the step [2].
In (a), by using the cooling jig 20 to generate crystal nuclei from the low-temperature molten metal (adding an element that promotes crystal nucleation formation as necessary) and pouring the crystal nuclei into the ceramic 30 having a heat insulating effect, An alloy immediately below the liquidus containing crystal nuclei is obtained. Next, in step [3], the alloy is held in a semi-molten state in the heat insulating container 30 (or 30A). During this period, fine granular (non-dendritic) primary crystals are generated from the introduced crystal nuclei (step [3] -a), and grow as spherical primary crystals as the solid fraction increases with the temperature decrease of the melt. (Step [3] -b and Step [3] -c). In this way, the obtained metal M having a predetermined liquid phase ratio is transferred to the container 82 of the extruder 80, for example, as in (step [4]).
After being inserted into, the stem 86 is pressed at a high pressure to pass through the die 84, whereby extrusion molding is performed to obtain an extrusion molded body P. When the semi-molten metal M in the heat-insulating container 30 after crystal nucleus generation is inserted into the container 82 of the extruder 80, the portion of the heat-insulating container 30 facing the bottom of the heat-insulating container 30 with relatively few impurities is placed inside the container 82. When it is housed so as to face the die 84 and extrusion-molded, a high-quality extrusion-molded product containing few impurities can be obtained. Alternatively, before taking out the semi-molten metal M from the heat insulating container 30, the oxide on the surface (upper surface) may be removed and then the semi-molten metal may be stored in the container 82 of the extruder 80.

The difference between the present invention shown in FIGS. 1, 2, 3 and 4 and the conventional thixocast method and rheocast method is clear from the drawings. That is, in the present invention, unlike the conventional method, the dendrite-like primary crystals crystallized in the semi-melting temperature range are not forcibly crushed into spherical particles by mechanical stirring or electromagnetic stirring, and the temperature drop in the semi-melting temperature range is achieved. A large number of primary crystals that crystallize and grow from the crystal nuclei introduced into the liquid as a starting point are continuously spherical due to the amount of heat possessed by the alloy (it may be heated and held from the outside if necessary) It is a very simple method because the step of semi-melting by reheating the billet in the thixocasting method is omitted. Each step described above, that is, FIG.
The casting condition, the spheroidizing condition and the molding condition set in each of the process of pouring into the cooling jig 20, the generation of the primary crystal, the spherical process, and the molding process shown in FIG. The reason for limiting the numerical values shown in the eleventh invention will be described below.

If the casting temperature is higher than the melting point by 300 ° C. or higher, or if the surface temperature of the jig 20 is higher than the melting point,
(1) The generation of crystal nuclei is small, and (2) since the temperature of the molten metal M when poured into a heat insulating container having a heat insulating effect is higher than the liquidus line, the proportion of the remaining crystal nuclei is also small. , The size of the primary crystals increases. 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. By setting the degree of superheat to the liquidus line to be less than 100 ° C., more preferably 50 ° C. or less, and the temperature of the jig 20 lower than the melting point of the alloy M by 50 ° C. or more, A finer primary crystal size can be obtained. Jig 2
There are two methods for bringing the molten metal M into contact with 0: moving the molten metal M on the surface of the jig (flowing the molten metal to the inclined jig 20) and moving the jig 20 in the molten metal.

The jig referred to here is one that gives a cooling action to the molten metal when it flows down, but instead of this, for example, a tubular pipe of a water heater may be used. . Insulation container 30 for holding the molten metal that has fallen directly below the liquidus line
Has an adiabatic effect in order to make the generated primary crystals spherical and to obtain a desired liquid phase 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. When a ceramic container having air permeability is used as the heat insulating container 30, the magnesium alloy easily oxidizes and burns.
It is preferable to make the outside of the container a predetermined atmosphere (inert atmosphere, reduced pressure atmosphere, etc.). Further, in order to prevent oxidation, it is desirable to add Be and Ca to the molten metal in advance. The shape of the heat insulating container 30 is not limited to the cylindrical shape, and may be a shape suitable for the subsequent molding method. If the holding time in the heat insulating container 30 is less than 5 seconds, it is not easy to bring the temperature to a desired liquid phase ratio 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. For this reason,
The holding time is 5 seconds to 60 minutes. The jig 20 for contacting the molten metal is not limited in its material as long as it can lower the temperature of the molten metal, but is made of a metal such as copper, a copper alloy, or an aluminum alloy having a particularly high thermal conductivity. ,
Moreover, the jig 20 controlled to be cooled so as to be maintained at a certain temperature or less is preferable because it produces a large amount of crystal nuclei. Note that it is effective to apply a non-metal material in order to prevent the metal from solidly adhering to the jig 20 when the molten metal M contacts the jig 20. The coating method may be mechanical, chemical or physical.

It is possible to obtain a semi-molten alloy below the liquidus line containing a large number of crystal nuclei by bringing the molten metal M into contact with the jig 20. To obtain the structure, Ti and B are added to the aluminum alloy, and S is added to the magnesium alloy.
r, Si, Ca are added. Ti is 0.005% to 0.
If it exceeds 30%, a coarse Ti compound is generated and the ductility decreases, so Ti is set to 0.005% to 0.30%. B
Together with Ti promotes miniaturization, but if it is less than 0.001%, the miniaturization effect is small, and even if added in excess of 0.01%, no further effect can be expected, so Sr is less than 0.
005% -0.1%. By adding 0.01% to 1.5% of Si to 0.005% to 0.1% of Sr in combination, finer crystal grains can be obtained as compared with the case of adding Sr alone. If Ca is less than 0.05%, the effect of refining is small,
Even if added in excess of 0.30%, no further effect can be expected, so Ca is made 0.05% to 0.30%. Table 1
Shows the condition of the semi-molten metal before forming and the quality of the forming material. Molding was performed by inserting a semi-molten metal into a container as shown in FIG. 3 and then extruding. The molding conditions are as follows. Extruder: 800t, Extrusion speed (product speed): 80m
/ Min. Extrusion billet diameter: 75 mm, extrusion ratio: 20

In Comparative Example 1, 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 therefore fine spherical primary crystals cannot be obtained, and only coarse amorphous primary crystals are obtained as shown in FIG. In Comparative Example 2, since the casting temperature is too high, almost no crystal nuclei remain in the ceramic container 30, and thus the same phenomenon as in Comparative Example 1 is exhibited. In Comparative Example 3, 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 4, since the retention time in the ceramic container 30 is short and the liquid phase ratio is high, only dendrite-like primary crystals are obtained, and since the liquid phase ratio is high, segregation of components inside the molded product is large. . In Comparative Example 5, since a metal container having a small heat insulating effect at room temperature was used, the dendrite-like solidified layer formed on the inner wall of the heat insulating container 30 was mixed with the spherical primary crystal formed in the center of the container, and segregation occurred. Shows a heterogeneous tissue containing. In Comparative Example 7, the jig 20 is not used, but since the alloy does not contain the refiner, the generation of crystal nuclei is small and the same phenomenon as in Comparative Example 1 is exhibited.

On the other hand, in Examples 8 to 18 of the present invention, a homogeneous structure having fine spherical primary crystals of 150 μm or less as shown in FIG. 8 was obtained, and a molded article having a good appearance was obtained (however, Inventive Examples 8 to 11 and 13 to 16 are shown as reference examples).

[0016]

As is apparent from the above description, in the method for forming a semi-molten metal according to the present invention, the liquidus temperature
Aluminium whose superheat degree is kept below 100 ° C
Use a jig to remove molten magnesium alloy or molten magnesium alloy.
It has a heat insulating effect by pouring it directly into an insulated container without using it
Eutectic below the liquidus temperature in an insulated container
Temperature or a temperature higher than the solidus temperature, and 0.
By holding for 5 seconds to 60 minutes while cooling to a molding temperature showing a liquid phase ratio of 1 to 70% , fine primary crystals are crystallized in the alloy liquid, and the alloy is inserted into a container of an extruder. Do
At that time, extruding the part of the semi-molten metal in contact with the bottom of the heat insulating container
Extruded facing the die side of the machine, or
Remove the uppermost part of the molten metal insulation container from the extruder
By extruding while facing the chair side, a compact having a fine and spherical structure can be obtained easily, easily and at low cost, regardless of the conventional mechanical stirring method or electromagnetic stirring method.

[0017]

[Table 1]

[Brief description of drawings]

FIG. 1 is a process explanatory view showing a method for forming a semi-molten metal of a hypoeutectic aluminum alloy having a composition of at least the maximum solid solution limit.

FIG. 2 is a process explanatory view showing a method of forming a semi-molten metal of a magnesium alloy or an aluminum alloy having a maximum solid solution in-limit composition.

FIG. 3 is a process explanatory view from the formation of spherical primary crystals to the molding.

FIG. 4 is a schematic diagram of a metallographic structure in each step shown in FIG.

FIG. 5 is an equilibrium diagram of an Al—Si alloy, which is a typical aluminum alloy.

FIG. 6 is an equilibrium diagram of a Mg—Al alloy, which is a typical magnesium alloy.

FIG. 7 is a copy of a micrograph showing the metal structure of a molded article of the present invention.

FIG. 8 is a copy of a micrograph showing a metal structure of a molded product of a comparative example.

[Explanation of symbols]

10 ladles 20 jigs 30 Thermal insulation container (ceramic container) 30A Ceramic coating metal container 80 extruder 82 container 84 Billet 86 stem 88 shoots M metal (molten metal) P extruded body t temperature T time

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI B22D 17/22 B22D 17/22 Q 18/02 18/02 A (56) Reference JP-A-7-164108 (JP, A) JP-A-7-32113 (JP, A) JP-A-64-96341 (JP, A) Patent 3246273 (JP, B2) European patent 392998 (EP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 1/02 B22D 17/00-17/32 B22D 27/00-27/20

Claims (4)

(57) [Claims] 1. A superheat degree of 100 ° C. with respect to a liquidus temperature.
Aluminum alloy melt or magnesi kept below
Insulate molten um alloy directly without using jigs
Pour it into a container and put it in a heat-insulating container that has a heat-insulating effect.
Below the phase line temperature and from the eutectic temperature or solidus temperature
A high temperature state is maintained for 5 seconds to 60 minutes while being cooled to a forming temperature showing a liquid phase ratio of 0.1 to 70%, whereby fine primary crystals are crystallized in the alloy liquid, and the alloy Extrude
Heat insulation container of the semi-molten metal when it is inserted into the container of the machine
Push the part that touches the bottom of the extruder so that it faces the die side of the extruder.
Or the top of the semi-molten metal insulation container
Extrusion molding with the removed part facing the die side of the extruder
A method for forming a semi-molten metal, comprising: 2. The method for forming a semi-molten metal according to claim 1, wherein the crystal nuclei are generated by vibrating the molten alloy which comes into contact with the heat insulating container. 3. The extruder may be a horizontal extruder or a vertical extruder, or a horizontal extruder in which the container is tilted from a vertical shape to a horizontal shape before forming and molding. The extrusion method may be indirect extrusion or direct extrusion. The method for forming a semi-molten metal according to claim 1, wherein the method is extrusion. 4. The semi-molten metal to be inserted into a container in the indirect extrusion method is removed from the surface layer of the semi-molten metal by passing through a cylinder having an inner diameter smaller than that of the semi-molten metal when taken out from the heat insulating container. The method for forming a semi-molten metal according to claim 3, wherein: