Die-casting apparatus, die-casting method, and diecast article

Abstract

A die casting method and apparatus are provided, thereby making it possible to produce a thin diecast product that has hitherto been considered impossible to realize, and a diecast product is also provided. A semi-solidified metallic material is formed having particles in solid phase of a particle size less than 30 m, and is thereupon injected into a die. A die casting machine has a sleeve into which a melt of metallic material is poured, and the semi-solidifying material there when it has a certain proportion of solid phase reached is injected into the die with a plunger to which pressure is applied. The melt of metallic material is poured into the sleeve so that the material occupies inside the sleeve at a proportion in vertical cross-sectional area of 30% or less. The particle size in this semi-solid material is held unvaried in a product as diecast.

Claims

1. A diecast product of an hypo-eutectic aluminum alloy, comprising: non-dendritic spheroidal primary alpha-aluminum crystals that have sizes 10 m-30 m, and microfine spheroidal crystalline (aluminum) particles that have sizes 2 m-4 m situated among said non-dendritic spheroidal primary aluminum crystals.

2. The diecast product according to claim 1, wherein, as cast, the diecast product has a portion having a thickness of 0.5 mm or less.

3. The diecast product according to claim 1, wherein, as cast, the diecast product has a portion having a thickness of 0.1 mm or less.

4. The diecast product according to claim 1, wherein the alloy is an aluminum alloy of AlSi system, AlSiMg system, AlSiCu system, or AlMg system.

5. The diecast product according to claim 1, wherein the diecast product contains an internal gas at a content 1 cc/100 g or less under an environment of ordinary temperature and pressure.

6. The diecast product according to claim 1, wherein said alloy is AC4CH, which is composed of Cu: less than 0.10 Si: 6.5-7.5 Mg: 0.25-0.45 Zn: less than 0.10 Fe: less than 0.20 Mn: less than 0.10 Ni: less than 0.05 Ti: less than 0.20 Pb: less than 0.05 Sn: less than 0.05 Cr: less than 0.05 Al: bal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the Drawings:

(2) FIG. 1 is a flow chart of semi-solid die casting in a sleeve process;

(3) FIG. 2 is a view illustrating a filling factor of a melt poured in a sleeve;

(4) FIG. 3 is a graph illustrating a relation between a sleeve filling factor and a modulus;

(5) FIG. 4 presents photographs showing appearances of diecast products (for a door mirror part) yielded in Embodiment 1 of the invention and Comparative Example 1, respectively;

(6) FIG. 5 presents microphotographs each taken of, and showing, a metallographic structure of each of, various portions of the diecast products yielded in Embodiment 1 of the invention;

(7) FIG. 6 is a graphical representation showing a relation between a proportion of solid phase and a filling behavior;

(8) FIG. 7 is a graphical representation showing an influence of a melt temperature and a sleeve filling factor on a temperature in the sleeve;

(9) FIG. 8 is a graphical representation showing an influence of a melt temperature and a sleeve filling factor on a temperature in the sleeve;

(10) FIG. 9 presents microphotographs showing a relation between a sleeve filling factor and a microfine spheroidal structure;

(11) FIG. 10 is a graph showing results of measurement of a melt temperature in a sleeve;

(12) FIG. 11 is a graph showing a relation between a rate of cooling and a crystalline particle size;

(13) FIG. 12 presents microphotographs showing a relation between an injection time lag and a microfine spheroidal structure; and

(14) FIG. 13 is a graphical representation showing a relation between an injection time lag and a crystalline particle size.

DESCRIPTION OF REFERENCE CHARACTERS

(15) 1a movable platen 1b stationary platen 2 plunger 3 pouring inlet 4 melt 5 sleeve 5a movable stationary die member 5b stationary movable die member

MODES FOR CARRYING OUT THE INVENTION

(16) The present invention utilizes a sleeve into which a melt of metal or metallic material is poured directly, a technique called a sleeve process.

(17) The sleeve process, without using a cup separately, can be practiced with the basic makeup of a conventional die casting machine.

(18) The makeup is illustrated in FIG. 1.

(19) Referring to FIG. 1, a plunger sleeve 5 is shown that communicates with a cavity 10 formed by and between a stationary die member 5a and a movable die member 5b which are mounted in a die casting machine. A melt of metallic material 4 poured into the plunger sleeve 5 is injected by a plunger 2 into and to fill the cavity 10. It may be noted though not shown that the plunger 2 is connected with a coupling to an injection cylinder rod mounted in an injection cylinder so that the rate of flow of hydraulically operating oil stored in an accumulator can be adjusted in accordance with the opening of a flow control valve arranged in a hydraulic circuit system of an injection apparatus to adjust the injection speed in an injection process step.

(20) Process steps of semi-solid die casting in the sleeve process are also shown in FIG. 1. As is seen from FIG. 1, the sleeve process eliminates the need for a separate equipment unit for forming a slurry and requires equipment only of a conventional die casting machine in which in the sleeve to crystallize a large number of crystalline nuclei, making it possible to control growth of crystalline particles properly without ceasing them to exist.

(21) In the sleeve process, the stationary and movable die members 5a and 5b are clamped together (FIG. 1(1)) whereafter the melt 4 is poured through a pouring inlet 3 into the sleeve 5 (FIG. 1(1)). In this step, the pouring temperature, sleeve temperature, sleeve filling factor, etc. are optimally controlled. After pouring, the plunger in an optimum time lag of injection is driven for injection. The state that the injection is completed is shown in FIG. 1(3). After the injection is completed, a product is taken out of the die (FIG. 1(4)). In opening the die to take out the product, the plunger 2 continues to be driven so that its forward end protrudes from the stationary die member 5a (from the latter's left side as shown), leaving the product attached to the movable die member 5b.

(22) Features of the sleeve process are shown infra compared with NRC, nano casting and cup processes.

(23) (1) Optimum control of the temperature of a melt in the sleeve makes it possible to form a slurry without the need to possess a conventional slurry forming unit; It is possible to inject immediately after pouring the melt in a cup (container); Increasing the number of occurrences of nucleation allows micronization; Cup equipment having a particular specification meeting with a particular casting weight is unnecessary; accessory units for cap cooling, cap cleaning and for application of a parting agent are unneeded.

Relation of Sleeve Factor to Modulus and Proportion of Solid Phase

(24) Attaining a semi-solid material formed with finer size particles than in the prior art is considered to require achieving greater supercooling (a higher rate of cooling) and forming a larger number of nuclei. Accordingly, the melt pouring temperature, sleeve size, sleeve temperature, sleeve filling factor and cooling rate are optimized. Of them, the sleeve filling factor is considered markedly influential. The term sleeve filling factor is intended to mean a volume or area proportion: (A/S)100(%) where as shown in FIG. 2, S is a cross-sectional area of the sleeve in a plane perpendicular to a length of the sleeve and A is a cross-sectional area in the plane of the melt poured into the sleeve. In order to further micronize or make the spheroidal structure finer than in the prior art, it is necessary to achieve greater supercooling (a higher rate of cooling) and creating a larger number of sites of nucleation.

(25) The sleeve filling factor can be reduced (increased) to increase the area of contact between the melt and the sleeve. A relation between a sleeve factor and a modulus (V/S) in the sleeve shown in FIG. 3 is as mentioned supra.

(26) The modulus of a melt loaded in the sleeve increases as the sleeve filling factor is increased. The modulus (V/S) is essentially proportional to the distance L from the surface of the melt and the bottom of the sleeve. Thus, as the filling factor is higher, the modulus is greater, extending the time of solidification. To wit, the higher the filling factor, the higher the temperature of the melt immediately after pouring into the sleeve, also reducing the rate of cooling. To achieve a finer spheroidal structure, it is thus important to choose a proper sleeve filling factor.

Embodiment 1

(27) In this embodiment of the invention, a door mirror part shaped as shown in FIG. 1 is produced using a die casting machine of a weight of 125 tons.

(28) The makeup and process steps of the die casting machine are conceptually shown in FIG. 1.

(29) A die casting machine has a stationary platen 1a and a movable platen 1b disposed as opposed to each other. The stationary and movable platens 1a and 1b have a stationary and a movable die members 5a and 5b mounted thereto, respectively. With the stationary and movable die members 5a and 5b clamped together, the space formed between these die members constitutes a product space.

(30) The stationary platen 1a is provided with a sleeve member 4 that is cylindrical. Into the sleeve 4 from its one end is inserted the plunger 2 as a means to press.

(31) On the other hand, the stationary die member 5a is formed with an internal space communicating with that of the sleeve member 4. The internal space in the stationary die member 5a is in communication via a sprue with the product space. The internal spaces of the sleeve member 4 and the stationary die member 5a together constitute a sleeve. In the present invention, a melt poured from a pouring inlet into the sleeve member is designed to flow into the internal space of the stationary die member 5a as well.

(32) The sleeve has a length L that is a distance between a face of the stationary die member at its left hand side and a forward end of the plunger.

(33) After clamping of the stationary and movable die members 5a and 5b is completed, the melt is poured into the sleeve via the pouring inlet 3 (FIG. 1(2)). The filling factor is then controlled.

(34) Upon lapse of a predetermined standby time period after pouring, the plunger is driven, initiating injection under pressure. The state that the injection is completed is shown in FIG. 1(3).

(35) After the injection is completed, a product is taken out of the die. To this end, the die is opened by moving the plunger 2 so that its forward end protrudes slightly from the left face of the stationary die member 5a against the product, leaving the product as attached to the movable die member 5b.

(36) The sleeve in the die casting machine is sized as follows:

(37) Diameter D of the sleeve: 70 mm

(38) Length L of the sleeve: L=5D (=350 mm)

(39) Temperature of the sleeve: 190 C.

(40) On the other hand, the melt is composed of a material that is:

(41) Melt material: AC4CH having: Liquidus temperature T.sub.L: 610 to 612 C. Solidus temperature T.sub.S: 555 C.

(42) Melt pouring temp.: T.sub.L (liquidus temp.)+40 C. (650 C.)

(43) Weight: 450 g

(44) Note further that into the sleeve the melt is poured at a height of 250 mm from the bottom of the sleeve (the height more than 3.5 times of D).

(45) Heat capacity of the sleeve, heat capacity of the melt being poured and latent heat are computed in advance so that when the sleeve and the melt poured therein reach a thermal equilibrium state, a particular proportion of solid phase selected as desired is achieved. The sleeve size or geometry, melt temperature, sleeve temperature, the rate of pouring the melt and the like are designed so that a heat balance is taken at a desired proportion of solid phase.

(46) When temperatures of the melt and sleeve become equal to each other, heat flow is ceased at a temperature not varied any further (referred to herein as equilibrium temperature). This temperature, T.sub.eq, is given by an equation stated below
Equation (1)
T.sub.eq=(T.sub.c+T.sub.m+H.sub.ff.sub.3)/(1+)(1)
where T.sub.c is an initial temperature of the melt, T.sub.m is an initial temperature of the sleeve, H.sub.f is a latent heat of solidification divided by specific heat, and f.sub.s is a proportion of solid phase. Also, and is a heat quantity necessary to raise the temperature of the melt by 1 K, corresponding to a heat quantity necessary to raise the temperature of a cup by 1 K and is given by an equation stated below.
=(.sub.mc.sub.mV.sub.m)/(.sub.cc.sub.cV.sub.c)(2)
where is a density, c is a specific heat and V is a volume whereas subscripts c and m identify the melt and sleeve, respectively.

(47) The filling factor of the melt in the sleeve is assumed to be 30%. It is noted here that a filling factor is a volume or area proportion, namely a cross-sectional area of a poured melt relative to a cross sectional area of a receiving sleeve, the cross-sectional areas being taken in a plane perpendicular to a direction in which a pressing means is driven.

(48) Upon a lapse of 4 seconds after the melt is poured, injection under pressure is initiated, i.e. the injection with a shot time lag of 4 seconds.

(49) In injection under a pressure, the top surface of the melt continues to rise gently and without an occurrence of turbulence. A filling factor of 100% is reached there to finish injection into the die.

(50) It should be noted further that in this form of implementation of the invention, the injection into the die is at a proportion of solid phase that is 50%.

(51) Conditions for casting under pressure are shown in a table below in which those on its right column (semi-solid die casting) are in this form of implementation.

(52) TABLE-US-00001 TABLE 1 Conventional Semi-solid Die Casting Die Casting (Comparative Ex.) (Embodiment 1) Injection Speed 0.2 m/s 0.2 m/s Injection Speed 1.0 m/s 1.0 m/s Casting Pressure 60 MPa 60 MPa Die (fixed) Temp. 250 C. 250 C. Die (moved) Temp. 250 C. 250 C. Pouring Temp. 720 C. 650 C. Sleeve Temp. 190 C.

(53) A diecast product (door mirror part) made according to the present invention is shown in an outline view in FIG. 4.

(54) In FIG. 4, the diecast product indicated by diecast in semi-solid is a door mirror part made according to Embodiment 1. In the door mirror part made according to this embodiment, a cylinder completely has one end filled in the form of a disk. Note that this disk at the one end has a thickness of 0.1 mm. Further, the disk-shaped end portion filled up increases the circularity of the cylindrical portion diecast.

(55) Surface roughness precision and dimensional accuracy of the diecast product are examined, too, yielding results as follows:

(56) Surface roughness precision: 2.1S (acceptance criterion: 6.3S)

(57) Dimensional accuracy: 19/1000 mm (acceptance criterion: 50/1000 mm)

(58) FIG. 5 diagrammatically shows in section a metallographic structure of each of various portions of the door mirror part diecast according to Embodiment 1.

(59) As can be seen from FIG. 5, a structure is shown having particles of a particle size between 10 and 30 m in each of the ten cross sections.

(60) Next, an amount of gas contents in a diecast product as cast is examined.

(61) <Gas Analysis>

(62) The diecast product is disposed in a vacuum melting chamber, whose inside is then purged with a high purity argon gas to remove external gases attached to inner walls of the chamber and surfaces of the product. Thereafter, the inside of the chamber is evacuated whereafter the diecast product is molten to form a melt.

(63) The melt is sufficiently agitated and gases are discharged therefrom.

(64) When pressure inside of the vacuum chamber becomes constant after lapse of a given time period, the pressure that becomes unvaried further is measured.

(65) From the pressure and a volume inside of the chamber, an amount of the gases is computed. The amount of gases contained in an aluminum (Al) melt per 100 g thereof is found to be 0.4 ml at ordinary temperature under normal pressure.

Comparative Example 1

(66) In this comparative example, a material in its liquid state is injected under pressure.

(67) Casting is effected under the conditions shown in the middle column (Conventional Die Casting) of Table 1.

(68) In this comparative example, the melt temperature is higher than in Embodiment 1 and the pressure commences to be applied to the melt immediately after its pouring (i.e. as it is in the liquid state).

(69) During application of the pressure, turbulences (wavy flows leading to splashes) occur in surface regions of the melt.

(70) FIG. 4 shows products in outline views for a door mirror part that result from Embodiment 1 and Comparative Example 1 mentioned above

(71) In FIG. 4, it is seen that the door mirror part product indicated by (as diecast conventionally) and made according to Comparative Example 1 has an end of a cylinder left unfilled, the end that should have been formed with a disk of 0.1 mm thick.

(72) The metallographic structure is in the form of dendrites.

(73) This diecast product fails to achieve an acceptance criterion in both surface roughness accuracy and dimensional precision (circularity).

Embodiment 2

(74) In this embodiment of the invention, die casting is effected under the condition same as in Embodiment 1. In die casting, the plunger as a means to press is measured of a speed or rate at which it is advanced and a pressure which it receives from casting.

(75) Results of the measurement is shown in FIG. 6.

(76) In FIG. 6, a graph shown at the left side is in respect of the comparative example in which the melt at a solid-phase proportion of 0% (in the complete liquid state) is injected under pressure. A graph at the right side is in respect of an embodiment of the invention in which semi-solid one solidified at a proportion of 50% and having a semi-solid structure with particles of a particle size of 30 m or less is injected under pressure. With the solid-phase proportion of 50%, starting to apply pressure after pouring allows injection to proceed at a constant rate and a casting pressure of zero. When the casting enters inside the die, the rate of advance is accelerated while the pressure is increased. When the die is filled up, the rate reaches a peak whereafter it is decelerated. The rate, however, is not decelerated at a time but with a slope until it reaches zero. This means that as material solidifying shrinks in the die, it still flows into shrinking portions, filling them. Such filling occurs because of a particle size selected to be 30 m or less. As can be seen from FIG. 6, this phenomenon proceeds continuously until such portions of shrink vanish away. Thus, if a product to be diecast has a portion having a thickness of 0.5 mm or less, the portion can be filled up completely without causing under-filling. Further, since such a portion of shrink is constantly filled up, there is caused no shrinkage cavity or gas entrapment to develop.

(77) Observation of a cross-section of this sample has revealed no gas entrapment and particles as fine as not more than 30 m in particle size.

(78) On the other hand, with the solid-phase proportion of 0, the rate drops at a time (vertically in the graph). This phenomenon indicates that into a portion of shrink when formed may material not be flowing, leading to the portion of shrink not filled and to a shrinkage cavity.

Embodiment 3

(79) Using a ZDC2 material, a diecast product is made with a particle size of 30 m or less as in Embodiment 1.

(80) In this embodiment of the invention, results in respect of all of filling property, surface roughness and dimensional precision are superior to those of Embodiment 1.

Comparative Example 2

(81) In this comparative example, ZDC2 is used to replace AC4CH in Comparative Example 1.

(82) There ensue a surface roughness of 3.8 S and a dimensional precision (circularity) of 24/1000 mm, each of which reaches an acceptance criterion.

(83) Also, the filling property is better than in Comparative Example 1. However, a diecast has unfilled portions extant in part and, to be acceptable as a commercial product, need to be finished by surfacing or the like.

Embodiment 4

(84) In this embodiment of the invention, an experiment is performed of varying the filling factor of the melt in the sleeve. The filling factor is varied such as by changing the diameter and length of the sleeve. The melt, immediately after it is poured into the sleeve, is rapidly cooled there and its resulting structure is observed. In this embodiment, the sleeve temperature is 200 C. To wit, making the rate of cooling slower than in Embodiment 1, the experiment is conducted in the state that an influence of the filing factor is more likely to develop.

(85) Different values of the filling factor and resultant particle sizes are examined. The results are shown below.

(86) TABLE-US-00002 50% 80-120 m 45% 80-100 m 40% 60-100 m 35% 50-80 m 30% 10-30 m 25% 10-30 m 20% 10-30 m 15% 10-30 m 10% 10-30 m

(87) Between 30 and 35%, it has been found that particle sizes are remarkably reduced.

(88) And, with a particle size of 30% or less, gas contents are markedly reduced than with those more than that.

Embodiment 5

(89) In this embodiment of the invention, a relation is investigated between a filling factor and a distribution of temperature of the melt poured in the sleeve. A. Pouring temperature: T.sub.L+100 C. (710 C.) Filling factor: 35% B. Pouring temperature: T.sub.L+(10-40 C.) (620-650 C.) Filling factor: 35% C. Pouring temperature: T.sub.L+(10-40 C.) (620-650 C.) Filling factor: 10-30% (where T.sub.L is a liquidus temperature)

(90) Measurement is made of the temperature of each of points spaced from a tip of the plunger by distances of 136 mm, 256 mm and 376 mm and spaced from the surface of the sleeve by distances of 1 mm, 5 mm and 11 mm, respectively.

(91) The results are shown in FIGS. 7 and 8. As for C above, a combination of pouring temperature of 64 C. and filling factor of 18% is representative. A filling factor of 30% is also applicable as is the filling factor of 18%.

(92) From FIGS. 7 and 8, it is seen that at a sleeve filling factor of 35% and at a pouring temperature of 710 C. or 640 C., a melt temperature in the sleeve is that which is in excess of a liquidus temperature. In contrast, under conditions of a sleeve filling factor of not more than 30% and a pouring temperature of 10 to 40 C. above the liquidus temperature, it has been found that in the sleeve a melt temperature is that at which solid and liquid phases coexist and further that in both of a longitudinal direction of the sleeve (direction of advance of the plunger) and a direction of height of the sleeve (directed from the sleeve surface) there can be formed a semi-solid slurry that is essentially homogeneous.

Embodiment 6

(93) Using a prism house die, a melt of AC4CH and a die casting machine of 125 ton under the conditions shown in Table 2 below, casting in this embodiment of the invention is effected with a sleeve filling factor of 10%, 30%, 50% and an injection time lag of 5 seconds.

(94) TABLE-US-00003 TABLE 2 Casting conditions: Injection speed (low) 0.2 m/s Injection speed (high) 1.0 m/s Casting pressure 60 MPa Sleeve temperature 190 C. Die (fixed) temperature 130 C. Die (movable) temperature 130 C. Melt temperature 640 C.

(95) FIG. 9 shows results of observation of metallographic structure of products from casting in which the sleeve filling factor is varied as 10%, 30% and 50%.

(96) With a filling factor of 50%, large particles having a particle size of 10 to 30 m are observed entirely over the product.

(97) With a filling factor of 30%, in the product there are observed, together with particles of a particle size of 10 to 30 m, a large number of particles having a particle size of 2 to 3 m.

(98) With a filling factor of 10%, particles having a particle size of 10 m or less are observed entirely over the product. From this structural observation, it has been found that with a filling factor of 30% or less, not only spheroidal crystalline particles of a particle size of 10 to 30 m but also spheroidal crystalline particles as fine as 2 to 4 m which has been believed not to develop normally are created in a large number.

(99) Such a structure has been found to be finer than results achieved by the nano cast process and cap process which the present inventors have strived for and the conventional semi-solid casting process.

(100) FIG. 10 shows results of measurement of melt temperatures in the sleeve.

(101) In Table 3 there are shown comparisons of a rate of cooling and a particle size in a spheroidal structure between the NRC, nano cast and cup processes. Also, FIG. 11 shows a logarithmic graph of a rate of cooling and a particle size in a spheroidal structure.

(102) From these measurement results it is seen that the rate of cooling at nucleation around the liquidus temperature (inclination of tangent shown in FIG. 10) is 20 C./sec which is much faster than a conventional rate of cooling of 0.2 to 2 C./sec at the formation of a semi-solid slurry in the prior art. According to the conventional rheocasting technique, there has been no report of creation of microfine crystalline particles as achieved here.

(103) A rate of cooling and a particle size of spheroidal structure are met on a line of 1:3. It is shown, however, that the value of 20 C./sec deviates from this line, making the particle size micro-finer.

(104) The occurrence of microfine spheroidal crystalline particles in these tests is considered to be due to having such as a low temperature of casting into the sleeve (T.sub.L+50 C. or less where T.sub.L is a liquidus temperature), a limited rate of supply of the melt and a high rate of cooling of the melt in the sleeve (20 C./sec or more), which are considered to create a greater number of crystalline nuclei and in their growth process to cause the adjacent crystallites to restrain each other, forming the microfine spheroidal structure.

(105) TABLE-US-00004 TABLE 3 Comparisons of Cooling Rate and Particle Size in Spheroidal Structure between NRC, Nano Cast and Cup Processes Particle Size Cooling Particle Size Microfine Rate (Normal Structure) Structure NRC Process 0.2 C./sec.sup. 100-150 m (125 m) Nano Cast 2 C./sec 30-70 m (50 m) Process Cup Process 2 C./sec 30-70 m (50 m) Sleeve Process 20 C./sec 10-30 m (20 m) 10 m (mean 4 m)

Embodiment 7

(106) This embodiment of the invention is carried out identically to Embodiment 1 except for a filling factor of 40%, a sleeve width of 0.6 D where D is an inner diameter of the sleeve, a sleeve temperature held at 100 C. and a melt temperature of 640 C.

(107) In this embodiment as well, particles are obtained having a particle size of 30 m or less, making it possible to fill a portion of a thickness of 0.4 mm or less.

Embodiment 8

(108) In this embodiment of the invention, the die in Embodiment 1 is replaced to cast parts each in the form of a plate.

(109) The parts cast are of simply flat plates of thicknesses of 0.6 mm, 0.5 mm, 0.4 mm, 0.3 mm, 0.2 mm and 0.1 mm and of a flat plate having a thickness of 0.4 mm and formed with a diaphragm having a thickness of 0.1 mm. In each casting, a shot time lag of 3 seconds is selected.

(110) Each of these parts has been cast without underfill or leaving any unfilled portion.

Embodiment 9

(111) In this embodiment of the invention, the proportion of solid phase is varied.

(112) It is varied in every 10% between 10 and 80%.

(113) One with a solid-phase proportion of 50% or more is higher in degree of filling up into a thinner portion than with a solid-phase proportion of less than 50%.

Embodiment 10

(114) In this embodiment of the invention, an influence is investigated of a lapse of time up to injection from pouring into the sleeve (shot time lag).

(115) Using a die casting machine of 125 tons and under conditions shown in Table 4, casting is effected with an injection time lag of 0 second, 3 seconds, 5 seconds.

(116) TABLE-US-00005 TABLE 4 Casting Conditions Injection speed (low) 0.2 m/s Injection speed (high) L 0 m/s Casting pressure 60 MPa Die (fixed) temperature 250 C. Die (movable) temperature 250 C. Temperature of melt (AC4CH) 650 C. Sleeve filling factor 25%

(117) FIG. 12 shows a Relation Between an Injection Time Lag and a microfine spheroidal structure with a sleeve filling factor of 25%.

(118) FIG. 13 shows results of measurement, and finding a distribution, of particle sizes of spheroidal crystalline particles by casting with each of these injection time lags.

(119) From such distributions, it has been found here, too, that not only microfine spheroidal crystalline particles having a particle size of 10 to 30 m but also spheroidal crystalline particles as much finer as 3 m in particle size which are not conventionally formed are created in large number.

(120) From results of measurement of melt temperatures in the sleeve, it is seen that the rate of cooling for nucleation around the liquidus temperature is 20 C./sec that is much faster than the rate of cooling of 0.2 to 2 C./sec at which a conventional semi-solid slurry is formed. Using the conventional rheocasting technique, there has been no report of having created spheroidal crystalline particles as microfine as 3 m as achieved here.

(121) As the shot time lag is longer, microfine spheroidal structures that fill up spaces between primary aluminum crystals when it is 0 second are reduced, and when it is 5 seconds, are observed among primary crystals in eutectic structure normally seen of a size of 10 to 30 m. It has not yet been fully clarified what specific history, while a melt of material is poured into the sleeve and the material in the sleeve is injected and molded, is followed in forming and further micronizing such a spheroidal structure. It is noted, however, that incomparably with a time consumed to form, inject and solidify a conventional semi-solid slurry, the rate of cooling after pouring is here fast, as high as 20 C. It. Therefore, the rate of passage immediately above and below the melting point is fast as well. This is presumed to facilitate nucleation to an extent that has not hitherto been confirmed and to permit control extinction and reduction of the crystal nuclei that have occurred for injection while solidification. These are conjectured to explain that post-micronized spheroidal structures are recognized.

(122) While the time lag is extended further, i.e. to exceed 5 seconds, a large number of the crystal nuclei that has been extant become extinct. Thus, in a time period up to immediately before injection, spheroidal crystals appear to have grown in the sleeve. It is deemed that a microfine spheroidal structure is then not formed.

INDUSTRIAL APPLICABILITY

(123) The present invention can widely be utilized in a variety of fields such as electric, electronic, automobile and fuel cell and other industries where thin parts are needed.

(124) Without requiring an exclusive slurry forming equipment unit needed conventionally, an unconventional structure with micro-finer particles is formed in accordance with the invention directly in a sleeve of the conventional die casting machine. Effecting optimum control of a melt temperature and others in the sleeve makes it possible to facilitate nucleation and forming microfine spheroidal crystalline particles in the sleeve whereby a microfine semi-solid slurry can be formed inexpensively, quickly and easily.

(125) Made by the unique sleeve method of the invention, an aluminum semi-solid cast product (AC4CH) yields better results in surface roughness precision and dimensional accuracy than a zinc cast product (ZDC2), making a material substitution possible. The method is henceforth expected to be exploited for weight saving of automobile parts and in production of precision components.