JP2927863B2 - Semi-solid metal production method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a solid in which non-dendritic primary crystals are dispersed in a molten metal.
The present invention relates to a method for stably producing a liquid metal mixture (simply called semi-solid metal for simplicity).

(Prior Art) Methods for producing semi-solid metal include, for example, JP-B-56-20
As disclosed in Japanese Unexamined Patent Publication No. 944, a molten metal (generally an alloy) is vigorously stirred while being cooled by a high-speed rotation of a stirrer in a cylindrical cooling / stirring tank, and the dendrites being formed in the molten metal. The crystal form is changed to a rounded form in which the branches disappear or shrink, and this is dispersed to form a slurry-like semi-solid metal which is mixed in the metal melt,
Discharge continuously from the bottom nozzle of the cooling and stirring tank, or repeatedly discharge and re-inject each time the cooling and stirring device of the semi-solid metal slurry is completed without performing continuous discharging. Etc. are also known.

As a stirring method during the cooling, in addition to the mechanical stirring described above using a stirrer, an electromagnetic stirring method for electromagnetically stirring a molten metal in a cooling stirring tank is also known.

Although semi-solid metal can be produced by these methods, the difference in the rate of increase in the solid fraction per unit time in a solid-liquid coexisting state (simply called the solidification rate for simplicity) in any of the methods. Stable semi-solid metal because the fluidity of the formed semi-solid metal is different, and even if the solid phase ratio is the same, the flow of the semi-solid metal in the tank stops, causing problems such as discharge failure and solidification blockage. Has proven to be difficult to manufacture.

(Problems to be Solved by the Invention) The fluidity of the semi-solid metal generally becomes worse when the solid phase ratio, which is expressed as a ratio of the volume of the solid phase metal to the total volume of the slurry semi-solid metal, increases, Above a certain solid phase ratio, usually above about 0.65, it is not possible to discharge or transfer from the semi-solid metal production device to the next step multi-stage semi-solid metal device, casting device, or holding device, or processing device, The problem of inability to discharge due to stoppage of flow or blockage solidification in the semi-solid metal manufacturing apparatus occurs.

Not only that, even when the solid phase ratio is 0.65 or less, the higher the solidification rate during solidification, the lower the fluidity, and the effect is particularly remarkable. In other words, in order to perform stable production of semi-solid metal or stable discharge and transfer to multi-stage semi-solid metal production equipment, casting equipment, holding equipment and processing equipment in the next process, not only solid phase ratio of semi-solid metal but also solidification It is necessary to clarify the relationship between the solidification rate in the fluid and the fluidity (viscosity), and to properly manage the solid phase ratio and fluidity of the semi-solidified metal.

(Means for Solving the Problems) Production experiments of semi-solid metal in a slurry state under various solidification rates and stirring conditions, and the relationship between the solid fraction and solidification rate that can ensure the fluidity of the semi-solid metal. The above problem can be advantageously solved by changing the solid fraction so as to enable stable discharge to the next step depending on the solidification rate.

That is, the present invention injects the molten metal into the cooling and stirring tank,
When producing a slurry-like semi-solid metal in a solid-liquid coexistence state by providing stirring during the cooling and solidification process, the solid phase ratio f _s of the slurry semi-solid metal is a function of the solidification rate in the solid-liquid coexistence state during stirring and cooling. A method for producing a semi-solid metal, comprising performing a stirring and cooling operation within a range satisfying the following formula (1), and discharging the semi-solid metal from a cooling and stirring tank.

^{_{(SL) f s ≦ 0.65-0.25 × R -1/3}} ---- (1) R = (a / Co) × (0.4 / C) f s; solid fraction of slurry semi-solid metal [-] a = 1 [% / s] Co: Total solute concentration [%] C: Average solidification rate [s ^-1 ] during solidification below the solidification onset temperature (liquidus temperature) of the molten metal.

The present invention also relates to the fact that the stirring and cooling operation of the slurry-like semi-solidified metal is performed by successive repetition in the cooling and stirring tanks provided in multiple stages, wherein the first stage of the cooling and stirring tank is operated at a relatively high solidification rate. It is preferred that the subsequent cooling and stirring tank be operated at a sequentially lower solidification rate, and that the molten metal be an aluminum alloy.

(Operation) The present inventors conducted experiments on the production of slurry-like semi-solid metal using various solidification rates and stirring conditions using molten metals of various compositions, and found that the liquidity limit solidity that can ensure the fluidity of the semi-solid metal. Phase ratio
The relationship between f _scr and the solidification rate C [s ^-1 ] was investigated, and the results shown in FIG. 1 were obtained. That is, the solidification rate C [s ^-1 ] during the solidification below the solidification start temperature (liquidus temperature) of the molten metal.
Is a function (1 / Co) × (0.4 × C) -1/3 liquid limit solid fraction indicating the limit of fluidity depending upon which the value of (simply called critical solid fraction f _ser for simplicity) found that different _{f ser = 0.65-0.25 × {(1} / Co) × (0.4 / C)} is related to ^-1/3, fluidity stably by satisfying the relationship of f _s ≦ f _scr I found that it could be secured.

Here, f _s and f _scr are solid fractions obtained from the equilibrium diagram based on the measured temperature values, and C is the average solidification rate [s ^-1] during solidification at or below the solidification starting temperature (liquidus temperature). And Co is the total volume concentration contained in the molten metal.

According to this result, the solid-phase ratio of the semi-solid metal discharged from the slurry after the cooling and stirring in the production of the semi-solid metal is discharged to the next process
It is preferable that fs is lower than the critical solid fraction f _scr , and desirably (f _scr × 0.85) or less.

However, it is necessary to increase the solidification rate in order to reduce the crystal grain size of the slurry-like semi-solid metal, but if the solidification rate is increased, the critical solid fraction decreases as described above. It is necessary to lower the phase ratio.

Therefore, when producing a semi-solid metal with a high solidification rate in which the solidification rate is increased and the crystal grain size is reduced, the production method using a multi-stage apparatus requires a high solidification rate and a half of the low solid phase rate in the former apparatus. By producing a solidified metal and transferring it to a semi-solidified metal production apparatus having a low solidification rate at a later stage of the next step, and raising the solid phase ratio, a semi-solid metal of fine crystals can be advantageously produced.

Thus, the above-mentioned problems have been solved, and it has become possible to stably produce a target semi-solid metal from a low solid fraction to a high solid fraction discontinuously or continuously.

(Example) Example 1 A molten metal of Al-4.5% Cu alloy was poured into the semi-solid metal apparatus shown in FIG. 2, and the stirrer was set at 600 rpm (shear strain rate = 300 / s).
The average solidification rate during solidification in the cooling tank was 0.06
Cooled at 8 / s, continuously measured the temperature of the semi-solid metal discharged at the bottom nozzle outlet of the device, and discharged a semi-solid metal with a solid phase ratio of 0.20 converted from that temperature based on the equilibrium diagram As a result, semi-solid metal could be produced continuously and stably, and the metal could be discharged to the processing device in the next step without causing stagnation of the flow.

Example 2 A molten metal of an Al-10% Cu alloy was poured into the semi-solid metal production apparatus shown in FIG. 3, and the stirrer was set at 600 rpm (shear strain rate = 280 /
s) The average solidification rate during solidification in the cooling bath was 0.0
The solid was cooled at 047 / s to produce a semi-solid metal having a solid-phase ratio of 0.35 in terms of temperature of the semi-solid metal inside the stirring tank. As a result, a fluid semi-solid metal was produced.

Example 3 In the first stage of the semi-solid metal production apparatus shown in FIG.
The molten metal of the Al-4.5% Cu alloy was poured, and while the stirrer was stirred at 900 rpm (shear strain rate = 450 / s), the average solidification rate during solidification in the cooling bath was cooled at 0.285 / s, and the apparatus was cooled. The semi-solid metal having a solid fraction of 0.12 in terms of the bottom nozzle outlet temperature is discharged and transferred to the subsequent device, and the average solidification rate during solidification in the cooling tank in the subsequent stage is cooled at 0.0017 / s, and the bottom nozzle outlet temperature conversion is performed. As a result of discharging the semi-solid metal having a solid phase ratio of 0.45, it was possible to continuously manufacture and discharge the semi-solid metal stably.

2 to 4, reference numeral 1 denotes a heat retaining tank, 2 denotes a cooling and stirring tank, 3 denotes a stirrer, 4 denotes a drive shaft, 5 denotes a ladle, 6 denotes molten metal supplied, 7 denotes cooling water, 8 denotes a water cooling jacket, 9 Is a slurry-like semi-solid metal, 10 is a thermocouple for temperature measurement, 11 is a discharge nozzle, 12
Is a slide gate, 13 is an induction heating heater, 18 is a tundish, 19 is a heating heater coil, and particularly in FIG.
Reference numeral 16 denotes an apparatus for continuously producing a semi-solid metal in the latter stage, reference numeral 17 denotes a twin roll casting machine, and reference numeral 20 denotes a ceramic coating.

The solidification rate in each of the above-described embodiments was controlled by changing the material of the cooling tank inner wall, the amount of cooling water, and the gap between the cooling tank inner wall and the stirrer.

Table 1 summarizes the results of the other examples in addition to the above examples.

FIG. 5 shows a change in the discharge rate over time during the production of the semi-solid metal of the example according to the present invention, together with a comparative example. In the example of the present invention, the discharging speed is stable, but in the comparative example, the discharging is stopped due to the fluctuation of the discharging speed and the clogging in the tank.

(Effect of the Invention) The method for producing a semi-solid metal according to the present invention exhibits the following effects.

(1) Even a semi-solid metal continuous production apparatus with a high solidification rate at which the semi-solid metal has a poor fluidity and is easily clogged in the apparatus can be stably and continuously produced and discharged.

(2) It is possible to stably and continuously produce a semi-solid metal having a high solid fraction such as 0.6.

(3) It is possible to stably produce a semi-solid metal having good fluidity even with a discontinuous semi-solid metal production apparatus.

(4) Therefore, the semi-solid metal is discharged from the semi-solid metal manufacturing apparatus, and an accident such as blockage in the apparatus due to transfer to a subsequent apparatus or discharge and transfer to a holding apparatus, a casting machine, and a processing apparatus in the next process. And stable operation is possible.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a solidification rate of a semi-solid metal in a slurry state and a liquid limit solid phase ratio, FIG. 2 is an explanatory view showing a semi-solid metal continuous production apparatus used in an embodiment of the present invention, and FIG. FIG. 4 is an explanatory view showing an apparatus for discontinuous production of semi-solid metal similarly used in Examples, FIG. 4 is an explanatory view of a multi-stage semi-solid metal continuous production apparatus for high solid phase ratio, FIG. 5 is a comparison graph of a discharge speed and a discharge solid phase ratio with respect to a discharge elapsed time in Example 1. DESCRIPTION OF SYMBOLS 1 ... Insulated tank, 2 ... Cooling and stirring tank 3 ... Stirrer 4, ... Drive shaft 5 ... Ladle, 6 ... Molten metal supply 7 ... Cooling water, 8 ... Water cooling jacket 9 ... Half Solidified metal, 10 ... Thermocouple for temperature measurement 11 ... Discharge nozzle, 12 ... Slide gate 13 ... Induction heater 14 ... Front-end semi-solidified metal continuous production equipment 15 ... Transfer pipe 16 ... Late-stage semi-solidified metal Continuous production equipment 17: Twin roll casting machine, 18: Tundish 19: Heating heater coil 20: Ceramic coating

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-44428 (JP, A) JP-A-2-89540 (JP, A) JP-A-1-170546 (JP, A) (58) Field (Int. Cl. ⁶ , DB name) B22D 1/00 B22D 21/04 B22D 11/00

Claims (4)

(57) [Claims] When a molten metal is poured into a cooling and stirring tank and stirred during the cooling and solidification process to produce a slurry-like semi-solid metal in a solid-liquid coexistence state, a solid phase ratio f _s of the slurry-like semi-solid metal is produced. Performs a stirring and cooling operation within a range satisfying the following equation (1), which is a function of a solidification rate in a solid-liquid coexisting state during stirring and cooling, and discharges the semi-solid metal from a cooling and stirring tank. , Semi-solid metal production method. ^{_{(SL) f s ≦ 0.65-0.25 × R -1/3}} ---- (1) R = (a / Co) × (0.4 / C) f s; solid fraction of slurry semi-solid metal [-] a = 1 [% / s] Co: Total solute concentration [%] C: Average solidification rate [s ^-1 ] during solidification below the solidification onset temperature (liquidus temperature) of the molten metal 2. The method of claim 1, wherein the stirring and cooling operation of the slurry-like semi-solid metal is performed by successive repetition in a cooling and stirring tank provided in multiple stages. Production method. 3. A high-solids fraction having a high solid fraction according to claim 2, wherein the first cooling-stirring tank operates at a relatively high solidification rate, and the second cooling-stirring tank operates at a successively lower solidification rate. Method for producing solidified metal. 4. A method for producing a semi-solid metal according to claim 1, wherein the molten metal is an aluminum alloy.