KR20030010643A - Method for manufacturing plastic worked article - Google Patents

Abstract

The method for producing a plastic processed product includes forming a plastic processing product by semi-solid molding in which molten metal including both solid and liquid phases is inserted into a die, and generating bubbles by expanding a gas cavity contained in the plastic processing product. And performing a pre-plastic working heat treatment on the plastic working product to make the plastic working product, and forming the plastic working product by plastic working the plastic working product after the pre-plastic working heat treatment. The plastic working of the plastic working product is performed in the actual use of the plastic working product, in which the tensile stress application direction in the tensile stress application part in which the tensile stress is applied in principle is substantially the same as the plastic processing direction in the part of the plastic working product corresponding to the tensile stress application part. Is executed in a matching way.

Description

METHODS FOR MANUFACTURING PLASTIC WORKED ARTICLE}

Cast-forging, forging a forging product formed into a near-net shape by casting into a forging product, ie a final product, will provide a forging product with mechanical properties equivalent to that obtained by casting at a relatively low cost. It is a process that can. On the other hand, the mechanical properties of forged products are largely improved by T6 heat treatment (solution treatment after ageing precipitation hardening treatment). In this case, T6 heat treatment is applied to the forged product obtained by cast-forging, but bubbles caused by the gas cavity, i.e., internal defects exhibited during forging, are generated on its surface, and these internal defects are caused by mechanical properties and forged products. Reduces the appearance quality.

As an alternative, Japanese Laid-Open Patent Publication No. 2000-197956 discloses the following method. The forging product is formed by filling the cavity in the die with molten light metal, and heat treatment is applied to the forging product obtained above to generate bubbles caused by the expansion of the internal gas, and the resulting forging product is subjected to the heat treatment. Forged. According to Japanese Laid-Open Patent Publication No. 2000-197956, when bubbles are generated at the product stage, the bubbles can be ruptured by forging, so that bubbles can be clearly prevented from occurring in the finally obtained forged product.

However, when heat treatment is performed before forging, as disclosed in Japanese Laid-Open Patent Publication No. 2000-197956, anisotropy in mechanical properties is generated in the finally obtained forged product, and thus the tensile strength is greater in the plastic flow direction than in the forging direction. . This is because the matrix of the liquid phase formed by curing the liquid phase is dotted with a solid phase in a solid state in a semi-solid state, and the forging product is produced by semi-solid molding having a fine structure in which a boundary layer remains between the liquid phase and the solid phase after the heat treatment performed before forging. It is guessed because it becomes. When such a product is forged, the solids are not only compressed in the forging direction but also extend in the plastic flow direction substantially perpendicular to the forging direction. As a result, interfacial flaking between the liquid phase and the solid phase can easily occur in the forging direction rather than the plastic flow direction.

Summary of the Invention

An object of the present invention is to provide a method for producing a plastic processed product in consideration of the anisotropy among the mechanical properties generated in the plastic processed product is produced by plastic processing the product for plastic processing formed by semi-solid molding and subjected to heat treatment before the plastic processing. will be.

In order to achieve this purpose, the plastic working product is plastically processed considering the anisotropy among the mechanical properties generated in the plastic working product, and in such a method, in a tensile stress application part where tensile stress is applied in principle in the actual use of the plastic processed product. The tensile stress application direction of substantially coincides with the plastic flow direction in the part of the plastic working product corresponding to the tensile stress application portion.

In particular, the present invention relates to a method for producing a plastic processed product by plastic working of the plastic processing product, the method for forming a plastic processing product by a semi-solid molding to introduce a molten metal containing both solid and liquid phase into the die Performing a pre-firing heat treatment on the plastic working product to generate bubbles by expanding the gas cavity contained in the plastic working product, and firing the plastic working product by plastic working after the pre-firing heat treatment. Forming a processed product; The plastic working of the plastic working product is carried out in the part of the plastic working product in which the direction of tensile stress application in the tensile stress application part in which tensile stress is applied in principle in actual use of the plastic working product corresponds to the tensile stress application part. It is carried out in a manner substantially coincident with the flow direction.

According to this manufacturing method, the plastic working of the plastic working product is for the plastic working in which the tensile stress application direction in the tensile stress applied part to which the tensile stress is applied in principle in the actual use of the plastic processed product corresponds to the tensile stress applied part. It is carried out in a manner substantially coincident with the plastic flow direction in the part of the product. Therefore, even if the anisotropy in the mechanical properties occurs in the plastic processed product obtained by plastic working of the plastic working product subjected to the pre-plastic working heat treatment, the reinforcing effect of the plastic working can be effectively exhibited in the resulting plastic processed product. In addition, even if the plastically processed product has a smaller thickness, in order to save cost, the required strength can be obtained.

Plastic working is not specifically specified and may be, for example, forged or spun.

The tensile stress application part is a part in which tensile stress is applied in principle in actual use of a plastic processed product, and particularly corresponds to a part where the integral value of the tensile stress is relatively large.

In addition, semi-solid shaping | molding is the shaping | molding method which introduce | transduces the molten metal of the semi-solid state containing both the solid state and liquid phase of a raw material metal into a die, and generally this semi-solid state is obtained by heating a raw material metal below melting | fusing point. In the resulting plastic working product, a fine structure in which a matrix of the liquid portion formed by curing the liquid phase is interspersed in the solid phase that is solid in a semisolid state.

Pre-plastic working heat treatment is carried out to generate bubbles, which are applied to the expansion of internal defects such as gas defects contained on or near the surface of the gas cavity, i.e., the product for plastic working. Is generated, and bubbles are ruptured by plastic working. As a result, the number of gas cavities included in the plastic processed product is reduced, thereby improving the mechanical properties of the plastic processed product. Therefore, in the use of a product for plastic processing formed by a molding method in which a gas cavity is formed more easily, such as semi-solid molding using an injection molding apparatus provided with a cylinder and a screw, an effort to improve the mechanical properties of the plastic processed product This may be particularly notable.

The pre-baking heat treatment is preferably carried out at processing temperatures in the range from 300 ° C to 550 ° C. Thus, bubbles may be generated on and / or in the vicinity of the surface of the product for plastic working while inhibiting oxidation caused by heat treatment. In particular, when the treatment temperature of the pre-baking heat treatment is lower than 300 ° C., bubbles may be insufficiently generated on and / or in the vicinity of the surface of the product for plastic working. In a variant embodiment, when the heat treatment is performed at a temperature above 550 ° C., the surface may be very oxidized or partially eutectic fused. In consideration of this, the treatment temperature is more preferably 350 ° C to 450 ° C.

In addition, the pre-baking heat treatment is preferably performed for 1 hour or more. Thus, bubbles can effectively occur on the surface of the product for plastic working. In addition, the microstructure consisting of the liquid phase and the solid phase is uniform in the solid solution treatment of the T6 heat treatment, so that anisotropy among the mechanical properties generated by the plastic working can be reduced. When the pre-calcination heat treatment is carried out at a treatment temperature in the range of 350 ° C. to 450 ° C., the treatment time is preferably 20 hours or less, more preferably 10 hours to 20 hours.

If the pre-fired heat treatment is carried out for a relatively long time at a relatively high temperature to generate bubbles by expanding the gas cavity contained in the plastic workpiece, the post-fired heat treatment is relatively It can be carried out for a relatively short time at low temperatures. Therefore, the generation of bubbles can be suppressed in post plastic working heat treatment.

The post plastic working heat treatment is preferably performed for a treatment time of 20 minutes to 10 hours at a treatment temperature in the range of 250 ° C to 400 ° C. The post plastic working heat treatment is therefore carried out for a shorter time at a higher temperature than the aging condensation hardening treatment of the T6 heat treatment after plastic working, so that the ductility can be effectively improved, as evident in the experiments detailed below, Strength and strength strength are maintained. The treatment temperature ranges from 250 ° C. to 400 ° C., because the ductility cannot be sufficiently improved when the treatment temperature is lower than 250 ° C., and the strength strength is very low when the treatment temperature is higher than 400 ° C. Further, the treatment time ranges from 20 minutes to 10 hours, which means that when the treatment time is shorter than 20 minutes, the ductility cannot be sufficiently improved, and when the treatment time is longer than 10 hours, the ductility is higher than that obtained without performing heat treatment. Because it can be low. Therefore, the treatment time is preferably 5 hours or less, most preferably 1 hour.

The plastic processed product produced by the above-mentioned method is not specifically specified, but may be, for example, a road wheel or an engine bracket.

When the plastic working product is a road wheel, the plastic working of the plastic working product may be performed in a direction in which an extension of the spoke of the wheel disk corresponding to the tensile stress application portion of the road wheel, that is, a direction substantially along the direction of applying the tensile stress, is performed on the wheel disk. In the part of the plastic working product corresponding to the direction of the plastic flow. Therefore, the strength along the extending direction of the spoke of the wheel disk is effectively improved. In the modified embodiment, the plastic working of the plastic working product may be performed in a direction substantially along the width of the wheel rim of the road wheel, that is, a direction in which the tensile stress application in the tensile stress application part corresponds to the wheel rim. It is carried out in a manner substantially coincident with the plastic flow direction in the part of the workpiece. Therefore, the strength along the width of the wheel rim is effectively improved.

In certain embodiments of plastic working, a thick portion is provided on a portion of the plastic working product corresponding to the tensile stress application, and the plastic working product is adapted to flow in a direction substantially coincident with the direction of tensile stress application. It is shape | molded to a desired shape by the plastic working by carrying out.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a manufacturing method for a plastic processed product, wherein a plastic working product molded by semi-solid molding is subjected to plastic working after generating bubbles by expanding a gas cavity contained in the plastic working product through pre-plastic working heat treatment.

1 is a partial cross-sectional view of an injection molding apparatus according to an embodiment of the present invention,

FIG. 2A is a front view of a wheel disk of a road wheel illustrated as the forging product of this embodiment; FIG.

Figure 2b is a cross-sectional view taken along the line A-A of Figure 2a,

3A is a vertical cross-sectional view of a spoke counterpart of a forging product used to mold a road wheel illustrated as the forging product of this embodiment;

3b is a vertical sectional view of the spoke of a road wheel obtained by forging a forging product;

4A is a vertical cross-sectional view of the spoke counterpart of the forging product of the first embodiment and the resulting spoke obtained by forging;

4B is a vertical cross-sectional view of the spoke counterpart of the forging product of the second embodiment and the resulting spoke obtained by forging;

4C is a vertical cross-sectional view of the spoke counterpart of the forging product of the third embodiment and the resulting spoke obtained by forging;

5 is a vertical sectional view of a road wheel illustrated as a forging product of another embodiment of the present invention;

6A is a vertical cross sectional view of a forging product used to form a road wheel illustrated as a forging product of another embodiment of the present invention;

6b is a vertical sectional view of a road wheel obtained by forging a forging product;

7A and 7B are exemplary diagrams of states achieved before and after forging in Experiment 1,

8 is a graph showing 0.2% yield strength, tensile strength and elongation of a tensile test sample of a forged product prepared under condition A of Experiment 1;

9 is a graph showing 0.2% yield strength, tensile strength and elongation of tensile test samples of forged products made under condition B of Experiment 1;

10a and 10b show the microstructure on the surface of a forged product prepared under conditions A and B of Experiment 1,

FIG. 11 is a graph showing the relationship between the treatment temperature of the post forging heat treatment performed in Experiment 2, the 0.2% bearing strength, the tensile strength and the elongation after fracture, obtained from a forged product manufactured by Alloy B;

12 is a graph showing the relationship between the processing temperature of the post forging heat treatment performed in Experiment 2, the 0.2% bearing strength, the tensile strength and the elongation after fracture, obtained from a forged product made of alloy C.

13A, 13B, 13C and 13D show the microstructure on the surface of a forged product produced by Alloy B subjected to post forging heat treatment under various conditions of Experiment 2,

14A, 14B, 14C and 14D show the microstructure on the surface of a forged product made by alloy C subjected to post forging heat treatment under various conditions of Experiment 2,

15 is a graph showing the relationship between the processing time of the post-forging heat treatment performed in Experiment 3, 0.2% yield strength, tensile strength, and elongation after fracture, obtained from a forged product made of alloy B;

FIG. 16 is a graph showing the relationship between the processing time of the post forging heat treatment performed in Experiment 3 and the 0.2% yield strength, tensile strength, and elongation after break, obtained from a forged product manufactured by Alloy C. FIG.

The method for producing a forged product according to a preferred embodiment of the present invention is described in detail.

(Forging Process-Injection Molding Process)

<Injection molding apparatus>

Fig. 1 shows an injection molding apparatus 1 for molding a forging product (a plastic working product) of a light metal alloy used in this embodiment.

The injection molding apparatus 1 has a main body 2, a screw 3 rotatably supported by the main body 2, and a back of the main body 2 for rotatably driving the screw 3. The rotary drive unit 4 arranged, the cylinder 5 fixed on the main body 2 so as to surround the screw 3, and the circumference of the cylinder 5 at a predetermined pitch along the longitudinal direction of the cylinder 5 Heater 6 disposed around, a hopper 7 for storing the light metal alloy raw material flowing therein, the material stored in the hopper 7 is measured and supplied into the injection molding apparatus 1 Feeder 8, and a die 9 attached on the end of the cylinder 5.

An injection device for propelling the screw 3 along the longitudinal direction in the cylinder 5 is provided on the main body 2. When the injection device detects that the screw 3 has been retracted by a predetermined distance by the force of the molten light metal alloy transferred forward, the rotation and retraction of the screw 3 is stopped and a predetermined amount is required to inject molten metal. The screw 3 is pushed forward for a time. In order to control the rate at which the molten metal enters the cavity 12 in the die 9, the speed at which the screw 3 is pushed forward is controllable.

A nozzle 10 is provided at the end of the cylinder 5 such that the stirred and kneaded molten metal in the cylinder 5 can be injected into the cavity 12 through the nozzle 10. When a predetermined amount of molten metal is collected in the front part of the cylinder 5, the molten metal is injected into the cavity 12, so that molten metal flows out through the nozzle 10 until a sufficient amount for injection is gathered. It needs to be prevented. For this purpose, the temperature of the nozzle 10 is controlled as follows, i.e., while the molten metal collects at the front of the cylinder 5, the nozzle 10 is blocked by a cold plug of solidified molten metal. If this molten metal is to be injected, the cold plug is easily removed and extruded towards the die 9 together with the molten metal being injected.

The heater 6 provided around the circumference of the cylinder 5 is divided into a number of zones, in which temperature is controlled in this zone, so that the temperature increases toward its front along the longitudinal direction of the cylinder 5. Thus, the temperature of the light metal alloy raw material is increased while being transported in the cylinder 5 by the screw 3, so that when the front part of the cylinder 5 is reached, the light metal alloy raw material becomes a molten metal in the semi-solid state below the melting point. Can be.

The hopper 7, the feeder 8, the cylinder 5 and the passages connecting them are filled with an inert gas (such as Ar gas) to prevent oxidation of the light metal alloy.

The die 9 has a runner 11 for guiding molten metal ejected from the nozzle 10. The runner 11 extends linearly from the nozzle 10 of the cylinder 5 and then rises vertically to form an L-shape. A plug receptacle 11a is provided at the L-shaped corner to receive the cold plug removed from the nozzle 10. In addition, the die 9 is housed in the cavity 12 and the cavity 12 which is connected to the runner 11, the gate 13 which acts as a boundary between the cavity 12 and the runner 11, and is melted. An overflow 14 spaced apart from the gate 13 of the cavity 12 to receive the gas displaced by the metal.

<Injection molding method>

The injection molding method used for forging products of light metal alloys is described in detail.

First, a chip of a light metal alloy (such as an Mg-Al alloy) is placed in the hopper 7 of the injection molding apparatus 1 as a raw material. A predetermined amount of light metal alloy chip is measured and supplied to the injection molding apparatus 1 by the feeder 8.

Thereafter, the light metal alloy chip is transferred into the cylinder 5 (this cylinder is heated) by the rotation of the screw 3, sufficiently stirred and kneaded by the rotation of the screw 3, and the predetermined amount in the cylinder 5. Heated to a temperature of As a result, the light metal alloy chip turns into a semi-solid light metal alloy below the melting point.

The molten metal alloy thus obtained is pressed forward by the screw 3 to be collected at the front part of the cylinder 5, and the screw 3 is retracted by the pressure of the collected molten metal alloy. At this point, the temperature of the nozzle 10 provided on the cylinder 5 is lowered so that the nozzle 10 is blocked by a cold plug formed by solidifying a portion of the molten metal. Thus, molten metal is prevented from flowing out of the cylinder 5 through the nozzle 10.

When the screw 3 retreats by a predetermined distance, the injection device of the main body 2 senses this retreat to stop the rotation and retraction of the screw 3. At this point in time, molten metal by one injection amount is collected in the front part of the cylinder 5.

Thereafter, the screw 3 is pressed forward by the injection device to provide pressure to the molten metal. As a result, the molten metal is extruded into the cavity 12 through the nozzle 10 by extruding the cold plug toward the die 9. At this point, the semi-solid light metal alloy enters the cavity in laminar flow or near-laminar flow, whereby air is minimally trapped, forging products with little gas defects such as gas and shrink cavities. It can be molded. The removed cold plug is held by the receptacle 11a of the runner 11.

Finally, after the molten metal is solidified, the die 9 is opened to take out the obtained injection molding material to be used as a forging product.

The forging product thus obtained has a matrix of liquid phase parts formed by curing the liquid phase, interspersed with solid phase parts that are solid in a semisolid state.

(Pre-forged heat treatment)

Forging products injection-molded by the above-described method are subjected to pre-forging heat treatment (pre-plastic working heat treatment) performed at a treatment temperature in the range of 300 ° C to 550 ° C and a treatment time of 1 hour or more (350 ° C to 450 ° C). A treatment temperature and a treatment time of 1 hour to 20 hours are preferred, a treatment temperature of 350 ° C. to 450 ° C. and a treatment time of 10 hours to 20 hours are more preferable). By this pre-forging heat treatment, the microstructure of the forging product is homogenized to the extent that it is difficult (but not complete) to identify the boundary between the liquid phase and the solid phase. In addition, gas defects, ie, internal defects near the surface of the forging product, expand and cause bubbles near the surface of the forging product.

(Forging process)

Forging products subjected to pre-forging heat treatment can be either fully enclosed die forging (fully enclosed die plastic working) or non-completely closed die forging (incompletely closed die firing). Processing) is applied. Fully closed type forging is performed in a forging die in which the forging space is completely closed, while noncompletely closed type forging is performed in a forging die in which at least a part of the product for forging is not pressurized and not plastically deformed. At this point, the forging product has a plastic flow direction in the portion of the forging product in which the tensile stress application direction in the tensile stress application in which the tensile stress is applied in principle in the actual use of the resulting forging product corresponds to the tensile stress application. Forging in a substantially consistent manner.

This will be described in detail by illustrating the road wheels. In practical use of the wheel disc 16 of the road wheel 15, as shown in FIGS. 2A and 2B, the tensile stress is in the direction indicated by the arrow in the figure (i.e. substantially along the extension of the spokes). Is applied to the spoke 16a in principle. In other words, the spokes 16a correspond to tensile stress applications. Thus, as shown in FIG. 3A, the forging product 17 having one or more thick portions on the back surface of the spoke counterpart 17a is formed by casting, and the spoke counterpart as shown in FIG. 3B. The thick portion of 17a is plastically flowed along the direction indicated by the arrow in the drawing, so that the plastic flow direction can substantially coincide with the direction of tensile stress application in actual use of the spoke 16a, i.e., substantially along the extension of the spoke. have. Strictly speaking, tensile stress is applied on the front face of the spoke 16a and compressive stress is applied to the back face of the spoke, so that forging is strongly provided on the front face of the spoke 16a. When forging is strongly applied to the front face of the spoke 16a, the front surface characteristic achieved after the forging is lowered. Therefore, the product material, the dimension of the forging product 17, and the finished dimension of the road wheel 15 are appropriately set so that the reinforcing effect of the forging can be shown in the front even when the forging is performed on the back side. . Specific embodiments are shown in FIGS. 4A-4C. In the first embodiment shown in FIG. 4A, the spoke 16a with uniform thickness is similar to that shown in FIGS. 3A and 3B forging product 17 having a thick portion rising from its radial center on its back side. Is formed by forging. In the second embodiment shown in FIG. 4B, the spokes 16a having uniform thickness are forged by forging a forging product 17 having radially shaped wavy irregularities on its back with protrusions that act like thick portions. Is formed. In the third embodiment shown in FIG. 4C, the spoke 16a having a smaller thickness at the center and a greater thickness at the end is thicker rising from the center in the radial direction on its back similarly to that shown in FIG. 4A. It is formed by forging a forging product 17 having a portion. In these embodiments, the dimensions and shapes of the forging product 17 and the spokes 16a are appropriately set, and forgings are formed as shown by the arrows in each figure, even if the forging is performed on the back side. A reinforcing effect can be exhibited on the front face, applied to the part close to the front face through the center line along the thickness direction of 16a).

During forging, some of the bubbles caused by pre-forging heat treatment near the surface of the forging product burst. As a result, the number of internal defects can be reduced in comparison with forging products obtained after injection molding.

(Post Forging Heat Treatment)

The forged product formed by the forging process is subjected to a post forging heat treatment (post plastic working heat treatment) performed during a treatment temperature of 250 ° C. to 400 ° C. and a treatment time of 20 minutes to 10 hours, and the resultant is cooled to obtain a final forged product. You get Since the pre-forging heat treatment is performed for a relatively long time at a relatively high temperature, the post-forging heat treatment may be performed for a relatively short time at a relatively low temperature. In addition, since the number of internal defect portions is reduced through the forging process, the generation of bubbles can be suppressed in the post forging heat treatment.

According to the above-described method for producing a forged product, the forged product has a stage in which the tensile stress application direction in the tensile stress application portion in which tensile stress is applied in principle in the actual use of the resulting forged product corresponds to the tensile stress application portion. Forging in a manner substantially coincident with the plastic flow direction in the portion of the crude product. Thus, even if the anisotropy in the mechanical properties is generated in the forging product which can be produced by forging the forging product after the pre-forging heat treatment, the reinforcing effect obtained by the forging can be effectively exhibited in the final forging product to be manufactured. In addition, even when the forged product has a smaller thickness, the required strength can be obtained, and the cost can be saved.

Further, the pre-forging heat treatment is performed at a treatment temperature of 300 ° C. to 500 ° C. (preferably 350 ° C. to 450 ° C.) for 1 hour or more (preferably 1 hour to 20 hours, more preferably 10 hours to). Air bubbles can be generated limitedly by expansion of the gas cavity formed near the surface of the forging product. Since these bubbles rupture through forging, the number of gas cavities included in the resulting forged product can be reduced, so that the mechanical properties of the forged product can be improved. In addition, the microstructure consisting of the liquid portion and the solid portion is uniform, thereby reducing the anisotropy in the mechanical properties of the forging product.

In addition, the post forging heat treatment is performed for a higher temperature and a shorter time in the ageing precipitation hardening treatment of the T6 heat treatment after the forging process. Thus, while maintaining the tensile strength and bearing strength of the forged product, the ductility can be effectively improved.

Modification Example

Although the forging product is formed by injection molding in the above-described embodiment, the method for forming the forging product is not limited to this, and other molding methods such as a die-cast method may be used.

Although the forging product may be produced by a light metal (such as an Mg-Al alloy) in this embodiment, the material of the forging product is not limited thereto, and other metal materials may be used.

Although plastic working is performed by forging in this embodiment, plastic working is not limited to this, and spinning and the like can be used.

Further, although the road wheel 15 is described above as a specific embodiment of the forged product in the present embodiment, the forged product is not limited to this, and may be used for an engine bracket or the like.

Although the wheel disc 16 is plastically processed by forging in this embodiment, the wheel rim 18 can be plastically processed by spinning as follows, and as shown in FIG. In practical use of the wheel rim 18, tensile stress is applied in principle to the wheel rim 18 in the direction indicated by the arrow in the figure (ie, substantially along the width of the wheel rim 18). In other words, the wheel rim 18 corresponds to the tensile stress application. Thus, as shown in Fig. 6A, through the spinning of the rim counterpart 19a of the forging product 19, plastic flow is generated in the direction indicated by the arrow in Fig. 6B, and this plastic flow direction is the wheel rim 18 In practical use, the direction of tensile stress can be substantially coincident with the direction substantially along the width of the wheel rim 18. As a result, even if the wheel rim 18 has a smaller thickness, the required strength can be achieved.

(Experiment 1)

Experimental Method

Two forging products, each in the shape of a metal block, were formed by using an injection molding apparatus with alloy A having the compositions listed in Table 1.

One forging product is subjected to the forging process and heat treatment under condition A listed in Table 2. In particular, this forging product is subjected to pre-forging heat treatment for 10 hours at a temperature of 400 ° C. and cooled, followed by incomplete closed type forging to obtain a plate-shaped forging product. Thereafter, the forged product is subjected to a post forging heat treatment at a temperature of 350 ° C. for 1 hour and cooled to obtain a final forged product. In this case, incomplete closed type forging is performed in which a forging rate of 50% is obtained. In particular, as shown in FIG. 7, a non-completely closed type forging was performed to achieve (h ₀ -h ₁ ) / h ₀ × 100 = 50 (forging rate), where h ₀ is the forging direction. and hence the initial thickness, h ₁ is the thickness obtained after the forging.

Other forging products are subjected to the forging process and heat treatment under condition B listed in Table 2. In particular, this forging product is subjected to an incomplete closed type forging to obtain a forging product. The resultant is subjected to a solution treatment and cooled for 10 hours at a temperature of 400 ° C., followed by aging and curing for 16 hours at a temperature of 175 ° C. (ie T6 heat treatment). Load), plate-shaped final forged product is obtained. In this case, incomplete closed type forging is performed in which a forging rate of 50% is obtained.

In each forging product thus obtained, a tensile test sample 21 whose tensile direction coincides with the forging direction, and a tensile test sample 22 whose tensile direction coincides with the plastic flow direction perpendicular to the forging direction are shown in FIG. 7B. As cut.

Tensile tests were carried out on a tensile test sample 21 having a tensile direction coinciding with the forging direction and a tensile test sample 22 having a tensile direction coinciding with the plastic flow direction, obtained by cutting in each forging product.

In addition, the microstructure of the surface of each forged product was observed through a microscope.

Al Zn Mn Si Cu Ni Fe Mg Alloy A 7.1 0.66 0.24 - 0.002 <0.001 0.002 Remainder Alloy B 9.1 0.78 0.24 - 0.001 0.0009 0.003 Remainder Alloy C 6.9 0.60 0.23 0.01 0.002 0.0005 0.002 Remainder

Unit: mass%

Condition A Heat treatment at 400 ℃ for 10 hours → air cooling → hot forging → heat treatment at 350 ℃ for 1 hour → air cooling Condition B Hot forging → heat treatment at 400 ℃ for 10 hours → air cooling → heat treatment at 175 ℃ for 16 hours → air cooling

<Experiment Result>

FIG. 8 shows tensile test results (0.2% bearing strength, tensile strength and elongation after fracture) obtained in each tensile test sample of a forged product made under condition A. FIG. FIG. 9 shows a corresponding relationship with the figure shown in FIG. 8 obtained from each tensile test sample of a forged product made under condition B. FIG. Comparing these graphs, all mechanical properties of 0.2% yield strength, tensile strength and elongation after fracture for the former forged product were found in the tensile test sample having a tensile direction that coincided with the plastic flow direction. It can be seen that it is larger than in the tensile test sample with the corresponding tensile direction. Conversely, for the latter forged product, all the mechanical properties of 0.2% yield strength, tensile strength and elongation after fracture are in the tensile test sample having the tensile direction consistent with the forging direction and in the tensile direction consistent with the plastic flow direction. It can be seen that the tensile test sample having

10A and 10B show the microstructures on the forged product surface prepared under condition A and the forged surface prepared under condition B, respectively. From these figures, the forged product made under condition A has a fine structure, with a matrix of liquid phase interspersed in the solid phase and the solid phase is aligned along the plastic flow direction, while the forged product made under condition B is homogeneous. It can be seen that it has a fine structure of. Anisotropy in the mechanical properties of forged products is probably due to this difference in microstructure. In addition, the forged product produced under condition A has better mechanical properties along the plastic flow direction than along the forging direction, which presumably means that the interfacial flaking between the liquid phase and the solid phase is in the latter direction rather than in the former direction. This can easily be caused by

(Experiment 2)

The metal plate-shaped injection molding material is formed by using an injection molding apparatus with alloy B having the compositions listed in Table 1. In this case, the temperature of the molten metal is controlled to obtain a solid phase proportion of 5% in the resulting injection molding material, which is confirmed through image analysis of the surface of the resulting injection molding material. Alloy B used in the present invention is AZ91D according to ASTM standards. Similarly, the injection molding material in the shape of a metal plate is formed by alloy C having the compositions listed in Table 1. In this case, the temperature of the molten metal is controlled to achieve a 10% solids ratio in the resulting injection molding material.

For each injection molding material that is in the form of a metal plate made by Alloy B and Alloy C, the various forging products are cut into block shapes having a width of 10 mm, a length of 35 mm and a thickness of 21 mm. Forging products cut from the material of Alloy B are cooled after 16 hours of pre-forging heat treatment at a temperature of 410 ° C., and forged products cut from the material of Alloy C are pre-forged for 10 hours at a temperature of 400 ° C. After the heat treatment is performed, it is cooled.

Then, each forging product subjected to the pre-forging heat treatment was forged to shrink in the width direction until the thickness was reduced to 10.5 mm, which is half of 21 mm (that is, having a forging rate of 50%) to obtain a forged product. Lose.

These forged products made by Alloy B and Alloy C are then subjected to post forging heat treatment for 4 hours at a temperature of 170 ° C., 250 ° C., 300 ° C., 350 ° C. or 400 ° C. and then cooled to obtain the final forged product. For comparison, some of the forging products are used directly as the final forging product without post forging heat treatment.

The tensile test is then conducted on forged products subjected to post forging heat treatment and forged products not subjected to post forging heat treatment.

For each forged product made by Alloy B and Alloy C and subjected to post forging heat treatment at 300 ° C., 350 ° C. or 400 ° C., the microstructure on the surface obtained after the tensile test was observed using a microscope. At this point, for the sake of comparison, the surface observation was carried out in forged products subjected to T6 heat treatment rather than pre- and post-heat treatment (where the solidifying treatment was performed at 410 ° C. for forged products made of alloy B). The solidification treatment was carried out at a temperature of 16 hours for 16 hours, the aging condensation curing treatment was carried out for 16 hours at a temperature of 170 ℃, the solid solution treatment for a forged product made by Alloy C was carried out for 10 hours at a temperature of 400 ℃, Aging condensation curing treatment was carried out for 16 hours at a temperature of 175 ℃).

<Experiment Result>

FIG. 11 shows a relationship between the temperature of post forging heat treatment and 0.2% bearing strength, tensile strength and elongation after fracture, obtained in a forged product made of alloy B. FIG. 12 shows a forged product made by alloy C. FIG. It is obtained from, and shows a relationship corresponding to FIG. 11 and 12 show that in forged products manufactured by both alloys B and C, as the treatment temperature is increased, the 0.2% yield strength is lowered, the tensile strength is gradually lowered, and the elongation after fracture is increased. Can be. In addition, when the forging product is subjected to a heat treatment equivalent to the aging condensation hardening treatment (at 170 ° C. to 230 ° C.) of the T6 heat treatment, the elongation after fracture is smaller than when the forging product is not subjected to the above heat treatment. When the temperature is 250 ° C or higher, the elongation after fracture can be greatly improved without significantly lowering the 0.2% yield strength and tensile strength.

13A-13D show the microstructure of a forged product made by alloy B, in particular, FIG. 13A shows the microstructure of a forged product subjected to T6 heat treatment, and FIG. 13B at a temperature of 300 ° C. The microstructure of the forged product subjected to the heat treatment is shown, and FIG. 13C illustrates the microstructure of the forged product subjected to the heat treatment at a temperature of 350 ° C., and FIG. 13D is the forged product subjected to the heat treatment at a temperature of 400 ° C. The fine structure of is shown. 14A-14D are views corresponding to FIGS. 13A-13D, respectively, illustrating the microstructure of a forged product made by alloy C. FIGS. 13A to 13D and 14A to 14D, when the T6 heat treatment (ie, shown in FIGS. 13A and 14A) is performed, the crystal grains are coarse and segregation of the compound (Mg ₁₇ Al ₁₂ ) ( segregation (shown in the black areas in the figure) can be seen in the forged products made by Alloy B. Conversely, in the case where the post-forging heat treatment was performed for a higher temperature and a shorter time than the T6 heat treatment, when the treatment temperature was 300 ° C. (ie, shown in FIGS. 13B and 14B), no clear crystal boundary layer was observed and the compound was uniform. Condenses. If the treatment temperature is 350 ° C. (ie, shown in FIGS. 13C and 14C), the particulate boundary layer is observed and the compound condenses uniformly. If the treatment temperature is 400 DEG C (i.e., shown in Figs. 13D and 14D), the crystal grains are coarse and the compound condenses uniformly.

Judging from the results of tensile test and microstructure observation, the microstructure of the forged product obtained after the post forging heat treatment is related to ductility. In particular, structures that are not recrystallized are difficult to deform, and therefore have high tensile strength while low ductility. As the crystal grains are further deformed through recrystallization, the ductility becomes larger, but if the crystal grains are too large, these crystal grains are difficult to deform, and thus are hardened to lower tensile strength and ductility.

Therefore, in order to obtain a forging product having a high tensile strength, a post-forging heat treatment must be carried out at an appropriately selected processing temperature so as to obtain a microstructure in which crystal grains are not observed. Post forging heat treatment should be performed at appropriately selected processing temperatures to obtain the observed microstructure.

(Experiment 3)

Experimental Method

In the same manner as in Experiment 2, several forging products, in the form of blocks each having a width of 10 mm, a length of 35 mm and a thickness of 21 mm, were prepared by Alloy B and Alloy C. The product made by alloy B is subjected to a pre-forging heat treatment for 16 hours at a temperature of 410 ° C., and the product made by alloy C is subjected to a pre-forging heat treatment at a temperature of 400 ° C. for 10 hours.

Each forging product subjected to the pre-forging heat treatment is forged to shrink in the width direction until the thickness is reduced to 10.5 mm, which is half of 21 mm (that is, having a forging rate of 50%).

Post forging heat treatment is carried out for 1 hour, 4 hours, 10 hours or 15 hours at a temperature of 300 ° C. for forged products made of alloy B and 350 ° C. for forged products made of alloy C. The final forged product is obtained.

Tensile tests are conducted on each forged product thus obtained.

<Experiment Result>

FIG. 15 is obtained from a forged product made of alloy B, which shows the relationship between the processing time of post forging heat treatment and 0.2% bearing strength, tensile strength and elongation after fracture, and FIG. 16 shows forging made by alloy C. FIG. The relationship obtained in the product and corresponding to FIG. 15 is shown. The data corresponding to the zero (treatment time) treatment time correspond to the data obtained from forging products that did not undergo post forging heat treatment in Experiment 2. According to FIGS. 15 and 16, in the forged products made by both alloys B and C, the 0.2% yield strength was relatively very low when the treatment time was shorter than 1 hour, but 0.2% yield strength when the treatment time was longer. It can be seen that the strength gradually decreases. In addition, when the treatment time is 1 hour or less, the tensile strength slightly improves, but when the treatment time becomes longer, the tensile strength gradually decreases. On the other hand, in the forged product manufactured by alloy B, the elongation after breakage is greatly improved when the treatment time is 1 hour or less, while the elongation after breakage is substantially constant when the treatment time is longer, while it is produced by alloy C. In the forged product, the elongation after breakage is maximum when the treatment time is 1 hour, but the elongation after breakage decreases when the treatment time becomes longer. Thus, for forging products made by both alloy B and alloy C, the elongation after fracture can be greatly improved during the first 1 hour after the start of heat treatment, and for forging products made by alloy C, the treatment time is 10 hours. Or less (preferably 5 hours or less), the elongation after fracture can be greatly improved.

As described above, the present invention is useful for the manufacturing method for plastic processed products, wherein the plastic working product formed by semi-solid molding causes bubbles by expanding the gas cavity contained in the plastic working product through pre-plastic working heat treatment. Plastic processing.

Claims (10)

In the method of manufacturing a plastic processed product by plastic-processing a product for plastic working, Molding a product for plastic working by semi-solid molding in which molten metal including both solid and liquid phases is introduced into a die; Subjecting the plastic working product to a pre-plastic working heat treatment to generate bubbles by expanding the gas cavity contained in the plastic working product; Forming a plastic processed product by plastic working the plastic processing product after the pre-plastic working heat treatment, Here, the plastic working of the plastic working product is a part of the plastic working product in which the tensile stress application direction in the tensile stress application part in which tensile stress is applied in principle in the actual use of the plastic working product corresponds to the tensile stress application part. In a manner substantially coincident with the plastic flow direction Method of manufacturing plastic processed products. The method of claim 1, The preplastic working heat treatment is carried out at a treatment temperature in the range of 300 ° C. to 550 ° C. Method of manufacturing plastic processed products. The method of claim 2, The preplastic working heat treatment is carried out for one hour or more of the treatment time. Method of manufacturing plastic processed products. The method of claim 3, wherein The pre-baking heat treatment is carried out for a processing time of 20 hours or less at a processing temperature in the range of 350 ° C to 450 ° C. Method of manufacturing plastic processed products. The method of claim 4, wherein The pre-firing heat treatment is carried out for a treatment time of 10 to 20 hours Method of manufacturing plastic processed products. The method of claim 1, Further comprising performing a post-processing heat treatment on the plastic processed product obtained by the plastic working for a processing time of 20 minutes to 10 hours at a processing temperature of 250 ° C to 400 ° C. Method of manufacturing plastic processed products. The method of claim 1, The plastic processing product is formed by semi-solid molding using an injection molding apparatus provided with a cylinder and a screw Method of manufacturing plastic processed products. The method of claim 1, The thick portion is provided on the portion of the plastic working product corresponding to the tensile stress applying portion, and the plastic working product is caused by the plastic working by causing the thick portion to flow in a direction substantially coincident with the tensile stress application direction. Formed into the desired shape Method of manufacturing plastic processed products. The method of claim 1, The plastic working product is a road wheel, The plastic working of the plastic working product is performed in such a manner that the direction substantially along the extending direction of the spokes of the wheel disk of the road wheel substantially coincides with the plastic flow direction in the portion of the plastic working product corresponding to the wheel disk. felled Method of manufacturing plastic processed products. The method of claim 1, The plastic working product is a road wheel, The plastic working of the plastic working product is performed in such a manner that the direction substantially along the width of the wheel rim of the road wheel substantially coincides with the plastic flow direction in the portion of the plastic working product corresponding to the wheel rim. Method of manufacturing plastic processed products.