CN1296502C - Magnesium alloy sectional stocks, their continuous casting method and device - Google Patents

Abstract

The invention relates to a magnesium alloy cast, as well as a continuously-casting method and apparatus. The magnesium alloy material is melted under state of shutting off from oxygen and the magnesium alloy cast (1), with little casting defect and areas (3) in which mean concentration of at least one composition except magnesium is higher than the ratio of the alloy composition, dispersed in the magnesium alloy crystal grain exists, is obtained by cooling and solidifying the molten-state magnesium alloy.

Description

Magnesium alloy profile blank, its continuous casting method and continuous casting device

technical field

The invention relates to a magnesium alloy profile blank for plastic processing, a continuous casting method and a continuous casting device thereof, which are used to manufacture magnesium alloy parts with magnesium alloy materials.

Background technique

In recent years, as one of countermeasures against mass-produced home appliances, recycling and environmental problems, the use of metal materials instead of conventional resin materials to manufacture exterior members of home appliances has attracted attention. The recycling rate of the resin material is 20%, and 90% recycling of the metal material is possible.

Among metal materials, magnesium alloys in particular are lighter in weight, higher in strength, and excellent in vibration damping properties than other metal alloys. It is being put into practical use in portable electronic devices, automobile parts, etc. Moreover, the melting point of magnesium alloy is relatively low, so it has the characteristics of less energy consumption for recycling.

Fig. 8 is a schematic diagram of the process of manufacturing magnesium alloy parts with magnesium alloy materials. First, in order to obtain magnesium alloy molded products from magnesium alloy materials, casting is generally roughly classified into die casting, investment casting, press working, bending, and plastic working such as forging. On the other hand, the degree of freedom of casting is high, and there are problems on the surface of the casting and the inclusion of air bubbles inside, so there are problems of low yield and high cost. Therefore, for the shell of a household appliance with a relatively simple shape, after pre-casting a profile blank that approximates the final shape of the part, the profile blank is directly plastically processed, or is subjected to primary processing such as extrusion and calendering to form a thin plate, and the thin plate is processed. The method of manufacturing magnesium alloy parts through secondary processing to form magnesium alloy molded products and then coating and drying processes is also being put into practical use. The method of combining casting and plastic working in this way is considered to be advantageous in terms of shortening of the channel during processing, reduction of surface defects, and control of equipment investment, compared with the method of casting alone.

Fig. 7 is a state diagram schematically showing the metallographic structure of a general shape blank for plastic working used in the manufacturing method. The profile blank 4 is an AZ31 magnesium alloy containing aluminum, zinc, and manganese as main alloying elements in addition to magnesium. Compared with other magnesium alloys, AZ series magnesium alloys have high strength and excellent corrosion resistance, and are suitable for housings of household appliances that are easily exposed to sweat and water.

The crystal structure of magnesium alloy is hexagonal crystal, and there are few slip planes in the grain boundary. Compared with other metals, the plastic workability is poor. Therefore, conventionally, in order to improve the plastic workability, it has been proposed to control the cooling rate of the magnesium alloy and add a grain refiner to refine the grain diameter. However, it is possible to control to a certain extent by clarifying the amount of processing deformation and the processing temperature in one processing such as extrusion and rolling to refine the grain diameter.

In the rough profile stage, where there are many casting defects and segregation of inclusions, it is not easy to improve those defects in one processing. That is, the magnesium alloy profile blank shown in Fig. 10 is like that. In the profile blank 4, the compound region 6 is segregated and exists at the grain boundary of the magnesium alloy crystal phase 5, and the internal void 7 generated during casting is precipitated at the grain boundary.

Generally, when the molten AZ series magnesium alloy is solidified, with the growth of magnesium crystal nuclei, the hard-to-dissolve components (metals or oxides) in magnesium gradually segregate at the grain boundaries, and often precipitate in the state of intermetallic compounds near the grain boundaries. . In addition, the hardly solid-soluble gas components in magnesium accumulate at the grain boundaries of magnesium during solidification, forming voids 7 and remaining inside the shape blank 4 .

Casting defects or inclusion segregation parts are likely to become cracks when the profile blank 4 is plastically processed into a thin plate and then plastically processed from the thin plate into a formed product. Such a profile blank 4 lacks workability. In particular, for magnesium alloys with few slip systems and lack of ductility, the quality of the material greatly affects the workability. In order to improve the workability of such magnesium alloys, it is desirable to reduce casting defects and inclusions in the profile blanks used as thin plate raw materials. material, and prevent segregation.

Therefore, in view of the aforementioned practical problems, the object of the present invention is to provide a method for reducing metallographic structure casting defects, inclusions and preventing segregation, which can improve the primary processing of extrusion, rolling, etc. Magnesium alloy profile blanks with plastic workability during secondary processing.

Contents of the invention

The magnesium alloy profile blank of the present invention developed to achieve the aforementioned object is a magnesium alloy profile blank for casting plastic working, and the feature of the profile blank is that the average concentration of components other than magnesium is high in the ratio of the alloy composition, and is dispersed in the magnesium alloy. the interior of the grains.

Components other than magnesium refer to aluminum, zinc, and manganese which are main constituent elements of the alloy. The alloy also contains metals other than these main constituent elements and inclusions such as oxides and carbides of these metals. The region where many inclusions are hardly solid-soluble in Mg is accompanied by or included in the aforementioned "region where the ratio of the average concentration of components other than magnesium to the alloy composition is high".

Hereinafter, the "region where the ratio of the average concentration of components other than magnesium to the alloy composition is high" includes the case where inclusions are contained, and is mainly referred to as the "compound region". The so-called dispersion state of the compound domains in the crystal grains refers to the state in which the dendrite phase of the magnesium alloy undergoes false peaking and grain boundaries are formed, and the components of the compound domains are residually dispersed and inserted into the framework of the dendrite phase.

In this way, since the compound domain is dispersed in the crystal grains, the inclusions also become dispersed, and there is less segregation of large inclusions that become crack cracks, and the profile blank itself is rich in ductility. The profile blank is rich in ductility, and the thin plate obtained by performing primary processing such as extrusion and rolling on the profile blank is also highly ductile, and the plastic workability becomes good.

Practical magnesium alloys should contain the composition ratio of alloy components according to the ASTM standard. The above-mentioned so-called compound region, that is, the region where the average concentration of components other than magnesium is high relative to the alloy composition, can be strictly defined. Among the alloy components other than magnesium specified in the ASTM standard, the concentration exceeds the standard upper limit of the component specified in the ASTM standard. value field.

In the present invention, the compound domain is defined as a domain having an average diameter of 5 μm or more. No matter what kind of magnesium alloy, if the compounds and metals existing inside are observed from the atomic level, there must be a "region where the average concentration of components other than magnesium is high relative to the alloy composition", but the present invention is characterized in that there is no such atomic level compound region , disperse areas with a certain size (5 μm or more).

In addition, the component concentration in the compound region can be measured by SEM-EDS (scanning electron microscope and energy dispersive X-ray spectrometer) or the like.

The overall specific gravity of the aforementioned alloy profile blank (also referred to as profile blank) is 98-100% of the theoretical density calculated based on the alloy element composition. That is, due to the voids and gas involved in the metallographic structure of the profile blank, it is rich in ductility. Therefore, when a thin plate is formed by the primary processing such as extrusion or rolling of the profile blank, and when the secondary processing such as forging is performed on the thin plate, it is possible to prevent the gaps (voids and cavities) from becoming cracks during processing. Cracks can occur, and the problem of surface defects caused by the rupture of internal air cells can be prevented even when the processed molded product is coated and dried.

The profile blank of the present invention is an AZ-based magnesium alloy containing aluminum, zinc and manganese as main components in addition to magnesium, wherein the aluminum contains 2-10 wt%. As mentioned above, AZ-based magnesium alloys are excellent in strength and corrosion resistance, and are widely used as structural materials.

The feature of the present invention is that the compound domains are dispersed in the crystal grains, but if the aluminum content is less than 2%, the compound domains occupying the crystal grains become less, so the compound domains are dispersed, and the effect of dispersion of inclusions is reduced, thereby, It is considered that the plastic workability of the profile blank deteriorates. On the contrary, for a profile blank with an aluminum content higher than 10%, since the compound region itself becomes larger in volume, relatively large-volume inclusions can exist in the compound region, and it is considered that there is a possibility of deterioration in plastic workability. However, the profile blank of the present invention is a magnesium alloy profile blank containing 2 to 10% by weight of aluminum, and the effect of dispersion of inclusions in crystal grains can be expected, resulting in a profile blank excellent in plastic workability.

The cylindrical blank of ordinary casting materials is processed into a plate shape through an extrusion process or a forging process, and then rolled into a magnesium alloy shell plate for plastic processing. On the one hand, if the shape of the above-mentioned profile blank of the present invention is formed into a plate shape, the magnesium alloy shell plate for plastic processing can be obtained by adjusting the thickness of the plate without the extrusion process or the forging process. process to reduce costs.

If the plate thickness of the aforementioned profile blank is less than 10 mm, then the thin plate with the optimum plate thickness of about 0.3-1.5 mm for the housing of household appliances can be obtained by rolling several times without extrusion process or forging process. Reduce costs.

In the X-ray diffraction pattern of the above-mentioned profile blank, the (0002) plane of the crystal on the surface appears preferentially, so it is clear that it is characterized by the crystal growth direction when the material surface is solidified. In general, the (0002) plane becomes prominent on the surface of the magnesium alloy subjected to the pressure, but the product of the present invention shows that the pressure is applied during casting.

In order to achieve the aforementioned object, the feature of the continuous casting method of the magnesium alloy profile blank of the present invention is to include the following two operations, that is, the magnesium alloy material is dropped into the crucible, and the magnesium alloy material in the melting crucible is melted under the oxygen barrier state, and the supply cooling After the casting mold, the molten magnesium alloy is cooled and solidified, and the solidified magnesium alloy is drawn from the cooling mold intermittently or continuously.

When the magnesium alloy in the molten state is solidified in the cooling mold, due to the intermittent or continuous drawing of the solidified magnesium alloy part, the gas components and inclusions existing at the solid-liquid interface that are solidifying are squeezed into the liquid part by inertial force and vibration. It can be seen that the gas components and inclusions contained in the profile blank can be reduced.

The cooling rate of the cooling mold in the continuous casting method is 3-8K/sec. The cooling rate of 3-8K/s is the optimal cooling rate for dendritic phase growth and solidification of the magnesium alloy, and local annealing by heat conduction in the profile blank. The dendrite phase is false peaked. . As mentioned above, the compound domains remain in the framework of the pseudopeaked dendrite phase, and the compound domains exist in the crystal grains in a dispersed state, so that the inclusions are dispersed, and a profile blank with excellent plastic workability can be obtained.

In this continuous casting method, the magnesium alloy material is melted in the state of cutting off oxygen to prevent combustion from contacting oxygen. In order to cut off oxygen, the crucible is placed under an inert gas atmosphere or a degassing agent is put into a molten magnesium alloy. , so that oxygen does not contact the liquid surface method. As the inert gas, argon, helium, air mixed with SF6, etc. are used. As the degassing agent, a flame retardant degassing agent mainly composed of potassium chloride and magnesium chloride can be used. When the degassing agent is added to the material, it also has the effect of preventing metal evaporation from the surface of the molten magnesium alloy.

In the aforementioned method, if the magnesium alloy material put into the crucible is made into solid particles, and the surrounding atmosphere of the crucible is kept in an inert atmosphere, the material is fed, even if the crucible for melting the magnesium alloy does not have a storage furnace, the granular solid material is continuously or intermittently Feeding, continuous casting can be carried out without interruption of feeding. In particular, due to the isolation of oxygen, when a protective atmosphere is generated on the surface of the magnesium alloy in the crucible, the inert atmosphere is released for feeding, and the production cycle is consumed for the establishment of the inert atmosphere again. However, if this method is adopted, even if the inert atmosphere is not released Gas can also be fed, so the production cycle can be shortened.

In order to achieve the aforementioned object, the continuous casting device of the magnesium alloy profile blank of the present invention is equipped with a crucible that is loaded with magnesium alloy material and melted by a heating device; it is connected with the crucible and cooled by a cooling device to solidify the magnesium alloy in the molten state into the desired Cooled molds for shapes; drawing devices for intermittently or continuously drawing solidified magnesium alloys from cooled molds.

In the aforementioned device, the inner wall section of the cooling mold is rectangular, and at least a part of the aforementioned inner wall is tapered so that the lengths of the short sides of the mold on the side of the crucible and the side of the drawing device are different, so that the magnesium alloy is added to the magnesium alloy during drawing. Stress increases and decreases, so the material properties are modified, and the friction between the ingot and the mold is reduced to prevent the ingot from thermal cracking.

Among the aforementioned devices, if graphite is selected as the material of the crucible and/or the cooling mold, it has excellent thermal conductivity and can smoothly implement the heating and cooling of the material. It is better not to contain copper, nickel, and iron materials that are mixed into the profile blank, which will obviously affect the corrosion resistance. In addition, it has also been reported that when graphite is mixed into a magnesium alloy, the crystal grains are refined.

In the aforementioned device, for example, a container is provided outside the crucible, and the structure of the atmosphere in which the crucible is placed can be controlled, so that the surface of the molten magnesium alloy in the crucible or the structure of the peripheral portion of the crucible can be cut off from oxygen, such as vacuuming or being able to Replace inert gas. Furthermore, since it is a magnesium alloy in a molten state, gasification occurs frequently, so it is preferable to install a container in order to prevent the metal vapor from being released into the atmosphere.

In the aforementioned device, if the lid that can be opened to the crucible is provided, the diffusion of the metal vapor to the outside of the crucible can be suppressed, and the diffusion of the metal vapor can be reduced from adhering to the solidified powdered metal on the inner wall of the aforementioned container, etc. The qualified rate of materials is low, and the danger of spontaneous combustion. In addition, as described in the above method, as a device for blocking oxygen from the magnesium alloy material in the crucible, it is also possible to control the evaporation from the surface of the molten magnesium alloy by mixing a degasser into the material, but in this case, there is a degasser The risk of components getting mixed into the profile blank is therefore preferably dealt with by so-called improved devices for capping the crucible.

The aforementioned device is a horizontal continuous casting device in which a cooling mold is connected to the side of a crucible and the magnesium alloy is drawn in a horizontal direction. In this way, impurities floating on the liquid surface of the molten magnesium alloy and impurities accumulated at the bottom of the crucible can be prevented from being involved, and a magnesium alloy profile blank with high ductility and good structure can be produced.

Description of drawings

FIG. 1 is a cross-sectional view schematically showing the metallographic structure of an AZ-based magnesium alloy profile blank according to an embodiment of the present invention.

Fig. 2 is a cross-sectional photograph taken by a scanning electron microscope (SEM) of the AZ series magnesium alloy profile blank of this embodiment.

3A to 3C are cross-sectional photographs taken by an optical microscope of the AZ-based magnesium alloy profile blank in this embodiment.

Fig. 4 is a graph showing the X-ray diffraction pattern of the surface state of the magnesium alloy blank in the embodiment.

FIG. 5 is a longitudinal sectional view schematically showing the continuous casting apparatus of this embodiment.

Fig. 6 is a longitudinal sectional view of main parts of a tapered continuous casting apparatus widened on the pull roll side in this embodiment.

Fig. 7 is a vertical cross-sectional view of main parts of a tapered continuous casting apparatus narrowed on the pull roll side in this embodiment.

Fig. 8 is a general schematic diagram of the process of manufacturing magnesium alloy parts from magnesium alloy materials.

Fig. 9 is a schematic view of a magnesium alloy sheet blank for evaluation of deep drawing of a square container.

Fig. 10 is a cross-sectional view schematically showing the metallographic structure of an AZ-based magnesium alloy profile blank produced by a conventional casting method and casting device.

Detailed ways

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 9 . The embodiment shown below is an example of actualizing the present invention, and by no means limits the technical scope of the present invention.

FIG. 1 is a cross-sectional view schematically showing the state of the metallographic structure of a magnesium alloy shaped material blank 1 according to the present embodiment. The magnesium alloy profile blank 1 adopts the casting method described later, and the magnesium alloy AZ31 with an aluminum content of about 3% and a zinc content of about 1% is formed into a plate shape, and dispersed in the interior of the magnesium alloy crystal phase 2 (inside and outside the crystal grains) . A compound region (a region in which the average concentration of components other than magnesium is high relative to the alloy composition) 3 exists.

This state is the composition of the compound domain 3 divided by the structure of the dendrite phase of magnesium, and even in the state where the dendrite phase false peaks and grain boundaries appear, it is considered that the state remains dispersed in the crystal grains.

Table 1 below lists the ASTM standard of the AZ31 magnesium alloy and the composition ratio of the magnesium alloy profile blank 1 of this embodiment. The unit is % by weight. In addition, in this embodiment, component measurement is performed by ICP emission spectrum analysis.

                                                                                            

Component ratio (weight %) of this embodiment Al Zn mn Fe Si Cu Ni Ca ASTM standard 2.5～3.5 0.5～1.5 ≥0.20 ≤0.03 ≤0.10 ≤0.1 ≤0.005 <0.04 Products of this embodiment 3.0 0.99 0.22 0.0047 0.022 0.0017 0.0012 0.0001

^* The remainder is divided into Mg

FIG. 2 is a cross-sectional photograph of the metallographic structure of the magnesium alloy profile blank 1 of the present embodiment taken with a scanning electron microscope (SEM). 31 to 34 shown in the figure are measurement points measured by a scanning electron microscope-energy dispersive X-ray spectrometer (SEM-EDS), and the following Table 2 lists the element composition ratios (% by weight) of each measurement point.

Table 2 Element composition ratios of the measuring points in Fig. 2 (weight %) Measuring point 31 Measuring point 32 Measuring point 33 Measuring point 34 element weight% element weight% element weight% element weight% Mg 100.00 C 17.76 Mg 55.96 Mg 92.78 o 13.39 al 21.16 al 4.63 Mg 35.91 Zn 22.88 Zn 2.59 al 15.40 mn 17.12 Zn 0.41

As shown in Table 1, the component ratios of the entire shape blank according to the present embodiment are within the ASTM standard. However, the compound region of this embodiment, that is, the region where the ratio of the average concentration of components other than magnesium to the alloy composition is high is the points shown in the measurement points 32 to 34 in FIG. Among the other elements, the ratio of at least one element is greater than the upper limit of the ASTM standard.

In addition, at measurement point 2, the ratio of C and O, which is not specified in the ASTM standard, becomes high, which indicates the possibility that carbides and oxides are contained in the compound region.

The distribution of the above-mentioned precipitate regions corresponding to the grains is shown in Fig. 3A, B and C. Fig. 3A is a partial optical microscope cross-sectional photo of a plate-shaped magnesium alloy profile blank 1a with a thickness of 10 mm in the aforementioned embodiment. Grain boundaries 8 can be observed, the average diameter of the crystal grains is about 200 μm, and compound domains 3 are dispersed inside the crystal grains, and the diameter of a circle corresponding to the internal area of the crystal grains is about several μm to 30 μm. In the cross-sectional structure, the size of such a precipitate region 3 is often equivalent to a circle diameter of 5 μm or more. In the cross-sectional photograph of FIG. 3A , about 30 to 40 precipitate regions 3 corresponding to a circle diameter of 5 μm or more were observed within one crystal grain.

Fig. 3B is a partial optical microscope cross-sectional photo of a plate-shaped magnesium alloy profile blank 1b with a thickness of 5 mm. Grain boundaries 8 were observed, and the average diameter of the grains was about 80 μm. In this cross-sectional structure, about 3 to 20 precipitate domains 3 corresponding to a circle diameter of 5 μm or more were observed within one crystal grain.

Fig. 3C is a partial optical microscope cross-sectional photo of a plate-shaped magnesium alloy profile blank 1c with a thickness of 3 mm. Grain boundaries 8 were observed, and the average grain diameter was about 250 μm. In this cross-sectional structure, about 60 to 120 precipitate domains 3 corresponding to a circle diameter of 5 μm or more were observed within one crystal grain.

In this way, the magnesium alloy shape blank 1 of this embodiment, like the conventional general shape blank 4 shown in FIG. It does not precipitate at the grain boundary. Since the compound domain 3 is relatively small in size and in a dispersed state, the inclusion service is also dispersed. In order to process the magnesium alloy profile blank 1 into a thin plate for extrusion, it is difficult to break during rolling and has good ductility. Moreover, even when it is processed into a thin plate, the thin plate is rich in ductility, and when secondary processing such as press working and forging is performed, it is a material with excellent workability.

Table 3 shows the results of measuring the specific gravity of samples randomly cut out from the magnesium alloy shape blank 1 of the present embodiment. In addition, the volume of this sample is calculated by measuring the dimensions after machining the outer shape.

Table 3 Specific Gravity of Magnesium Alloy Profile Blanks in the Present Embodiment Sample No 1 2 3 Volume (cm ³ ) 1.241 4.526 8.355 Weight (g) 2.177 7.977 14.78 Density (g/cm ³ ) 1.754 1.763 1.769 The ratio corresponding to the theoretical density (1.78g/cm ³ ) 98.6% 99.0% 99.4%

In addition to the aforementioned samples, the specific gravity of the magnesium alloy shape blank 1 according to the present embodiment is in the range of 98 to 100% of the theoretical density calculated from the alloy composition. On the one hand, in the profile blank 4 of the same composition as ^the magnesium alloy profile blank 1 shown in FIG. ³ or less) There are many parts. The magnesium alloy profile blank 1 of the present embodiment has a dense structure and few internal voids. As a result, it is difficult to break in the extrusion or rolling of the subsequent process, and in the subsequent secondary processing, and even the coating and drying process (Fig. 8 ), the problem of surface defects caused by internal bubble rupture can also be avoided.

In the present embodiment, the magnesium alloy shape blank 1 is molded by a casting method described later so that the plate thickness is 3 mm, 5 mm, or 10 mm. No significant difference was found in the above-mentioned cross-sectional structure characteristics and specific gravity due to the difference in plate thickness of the three types.

The present embodiment uses an AZ31 magnesium alloy, but other AZ-based magnesium alloys may also be used. However, in order to realize the cross-sectional structure with the aforementioned characteristics, it is best to use an AZ series magnesium alloy containing 2 to 10 wt% of Al.

The surface of the profile blank 1 of the present embodiment was analyzed by X-ray diffraction, and as shown in FIG. 4 , the crystal orientation of the (0002) plane was preferentially displayed. This phenomenon is considered to be that when the material is solidified, pressure is applied from the vertical direction of the material surface.

FIG. 5 is a configuration diagram of a continuous casting apparatus 21 for manufacturing the magnesium alloy shape blank 1 of the present embodiment.

The continuous casting device 21 is to accommodate the magnesium alloy material 13 and melt the crucible 11 with an electric heater (heating device) 12; it is connected with the crucible 11, and the magnesium alloy 13a in the molten state is cooled by a water-cooled pipe (cooling device) 20 to make it The cooling mold 15 solidified into the required shape; it is composed of the dummy bar 16 and the pulling roller 17 of the drawing device for intermittently or continuously drawing the solidified magnesium alloy 13b in the cooling mold 15 .

In this continuous casting apparatus 21, the magnesium alloy material 13 put into the crucible 11 is heated by the electric heater 12, and becomes the magnesium alloy 13a in a molten state. Since the magnesium alloy is in the molten state-it will burn violently when it comes into contact with oxygen, so it is best to cut off oxygen when melting. In the present embodiment, the crucible 11 is set in the container 14 as the means for shutting off oxygen, and has a structure capable of evacuating and injecting an inert gas (not shown).

The molten magnesium alloy 13a is accumulated in the crucible 11, but it also flows into the cooling mold 15 directly connected to the crucible 11. Therefore, the forming pull roller 17 allows the dummy rod 16 to enter and exit the cooling mold from the lower side of the container 14. 15 Internal structures. In addition, in the middle of the continuous casting process, the previously drawn solidified magnesium alloy 13b is formed instead of the dummy rod 16, and the outflow of the molten magnesium alloy 13a is suppressed.

The cooling mold 15 absorbs the heat released from the molten magnesium alloy 13a and releases it to the peripheral portion. In this embodiment, a cooling device such as a water cooling pipe 20 is arranged around the cooling mold 15 to absorb the released heat. When absorbing heat, it becomes a structure that can adjust the flow rate and temperature of water. As such a cooling device, in addition to water cooling, an air cooling configuration may be employed.

The cross-sectional shape of the inner wall of the cooling mold 15 becomes the solidified magnesium alloy 13b in the inner wall, that is, the cross-sectional shape of the magnesium alloy profile blank 1. The cross-sectional shape of the blank 1 is a rectangle with a width of 50 mm×a thickness of 3 mm, or 5 mm, or 10 mm. In addition, the length of the cooling section of the cooling mold 15 is 170 mm, but another length can be set in consideration of the shape of the magnesium alloy profile blank cast in the cooling mold 15 and the amount of cooling water.

When using the continuous casting device constructed as described above to continuously cast the magnesium alloy profile blank 1, the solidified magnesium alloy 13b (ingot) is likely to break midway, as shown in FIG. , so that the pulling roller 17 side is gradually widened relative to the crucible 11, reducing the friction with the cooling mold 15, and making it difficult for the ingot to break midway. On the contrary, as shown in FIG. 7, a taper 15b is formed at the continuous part of the cooling mold 15 and the crucible 11, so that the side of the pulling roller 17 is narrowed relative to the side of the crucible 11, and the magnesium alloy 13a in the molten state is solidified. Partly, applying moderate stress from the direction perpendicular to the drawing direction can reduce the amount of inclusions and gas involved in the profile blank.

The crucible 11 containing the molten magnesium alloy material 13 has an internal depth of 220 mm, and a cooling mold 15 is connected vertically above the bottom surface by about 10 mm. Impurities 19 on the bottom surface of 11 are less likely to be involved in the composition of the magnesium alloy 13b.

The feeding chute (material supply device) 18 shown in FIG. 5 is arranged on the upper part of the container 14 so that the magnesium alloy material 13 can be continuously fed into the crucible 11 without opening and closing the container 14 . In addition, if the shape of the magnesium alloy material 13 that is initially charged is the size that the crucible 11 holds, then there is no problem, but when feeding through the feeding chute 18, it is preferably in the shape of particles or chips with a diameter of about 1 mm to 10 mm, so as to prevent the crucible 11 from being damaged and The molten magnesium alloy 13 a splashes outside the crucible 11 .

The continuous casting device 21 of this embodiment is a horizontal type in which the cooling mold 15 is connected to the side of the crucible 11, but a vertical type in which the cooling mold 15 is connected to the bottom of the crucible 11 may also be used.

The electric heater 12 used as a heating device is a high-frequency heater capable of achieving a power of about 10KW, and it is not limited to a high-frequency heater as long as it has a heating device capable of heating the alloy material to 780° C. or higher.

The crucible 11 and the cooling mold 15 of the present embodiment are made of graphite, which is a material that has excellent thermal conductivity and hardly reacts with the molten magnesium alloy 13a. Furthermore, materials containing copper, nickel, and iron, which significantly affect the corrosion resistance of the material when mixed with magnesium alloy, are not desired to be used as materials for the crucible 11 and the cooling mold 15 .

The molten magnesium alloy 13 a usually evaporates, and when the metal vapor comes into contact with the inner wall of the container 14 , it solidifies and becomes powder. This phenomenon not only reduces the qualified rate of materials, but also may spontaneously ignite, which is dangerous. It is better to have a lid (not shown) that can be opened and closed for the crucible. And it is preferable to open the lid only when charging, so as to prevent metal vapor from flowing out of the crucible 11.

The dummy bar 16 is preferably made of a material that is resistant to high temperatures (about 650-800° C.) when the magnesium alloy material melts and maintains strength, and the present embodiment uses a stainless steel dummy bar.

Next, the continuous casting method of the magnesium alloy shape blank using the continuous casting apparatus 21 comprised as mentioned above is demonstrated concretely.

First, the magnesium alloy material 13 is put into the crucible 11, and the container 14 is closed to form an airtight state.

Then, after the inside of the container 14 is evacuated, an inert gas, preferably argon, is injected to fill the inside with the inert gas. At this time, the pressure in the container 14 is, for example, 0.1 to 0.2 Torr when evacuated, and 14 to 18 Torr when an inert gas is injected, but it is not limited thereto. If the container 14 is provided with a discharge port for the gas in the container when the inert gas is injected, so that when the inert gas is injected, the air layer that initially enters the interior is discharged from the discharge port, and the vacuuming process can also be omitted.

Next, water is made to flow through the water cooling pipe 20 of the cooling device arranged around the cooling type mold 15 to cool the type casting mold 15 and the dummy bar 16 . At this time, the water volume is controlled at 0.5 to 2.0 liters/minute, and the water temperature is controlled at 20 to 35° C., but they are not limited to these conditions.

Next, the crucible 11 is heated by the electric heater 12 to melt the magnesium alloy material 13 . AZ31 magnesium alloy melts when heated above the melting point of 630°C. However, in this embodiment, considering the fluidity of the molten metal and the temperature gradient inside the metal, it is decided to keep it at 750-780°C. This is due to the experimental results that the ingot (solidified magnesium alloy 13b) tends to break when the temperature of the molten metal is low. This phenomenon is considered to be that when the temperature of the molten metal is low, non-uniformity occurs in the process of cooling the metal, and solid-liquid interfaces occur in multiple locations during continuous casting, which prevents continuous solidification.

Controlling the temperature of the molten metal at the aforementioned temperature increases the fluidity, reduces the surface tension, and forms a state where the gas contained in the inside is easy to escape. As a result, it is considered that casting defects such as voids (voids, cavities) remaining inside the molded product are reduced. On the one hand, when the temperature of the molten metal is raised above the necessary temperature, energy is wasted. In addition, since the vapor pressure of the molten metal increases, the amount of powdered metal adhered to the crucible 11 and the container 14 increases, which is not desirable.

Next, the pulling roller 17 is rotated to pull the dummy bar 16 . In this embodiment, the drawing speed at this time is controlled at 45 to 125 mm/min. In addition, the present embodiment is carried out by intermittent drawing. For example, when the drawing speed is 100 mm/min, 5 mm is drawn at a speed of 10 mm/sec, and continuous casting is carried out under the condition of intermittent drawing for 2.5 sec in this state. , and its comprehensive drawing speed reaches 100mm/min. It is also possible to pull the magnesium alloy 13b while repeatedly drawing and pressing in by controlling the rotation of the pulling roller 17 in combination of forward rotation and reverse rotation.

Compared with the case where the magnesium alloy 13b is continuously drawn at a predetermined speed, the inertial force and vibration exerted on the solid-liquid interface of the molten magnesium alloy 13, inclusions and Air bubbles are discharged from the liquid portion, so it can be expected to form a profile blank with less inclusions and voids (voids) and better plastic workability.

If the dummy bar 16 is sufficiently drawn and the solidified magnesium alloy 13 b reaches the position of the pull roll 17 , the magnesium alloy 13 b in this state takes over the role of the dummy bar 16 .

The temperature of the magnesium alloy 13b just drawn from the cooling mold 15 is about 100° C. or lower, and the cooling mold 15 with a cooling portion of 170 mm is used in the continuous casting apparatus 21 . Thereby, when drawing magnesium alloy 13b with 100mm/min speed, be that the magnesium alloy of 780 ℃ passes through 170mm period in the crucible, promptly 1.7 minutes (102 seconds) are cooled to 100 ℃, therefore, can realize about 6.7K/second cooling rate.

Similarly, when the magnesium alloy 13b is drawn at a speed of 45mm/min, the cooling rate reaches 3.0K/sec, and when the magnesium alloy 13b is drawn at a speed of 125mm/min, the cooling rate reaches 8.3K/sec. In this embodiment, it is confirmed that the metallographic structure with the characteristics shown in Figure 1 is formed, and it is a magnesium alloy profile blank made by continuous casting with a cooling rate of about 3 to 8 K/sec. Therefore, it is predicted that it is possible to obtain the aforementioned metallographic structure at a cooling rate of about 1-20K/sec. When the cooling rate is too fast, the dendrite phase remains and becomes a structure without magnesium grain boundaries. When the cooling rate is too slow, the solid dendrite phase disappears completely, and the compound domain 3 is solid-dissolved in the crystal phase 2 of pure magnesium. Or mobile segregated tissue.

In the embodiment described above, the profile blank that can be produced without solution treatment is characterized in that grain boundaries appear, and components other than magnesium are dispersed and present in the crystal grains in areas where the alloy composition ratio is high.

With continuous casting, as the magnesium alloy material 13a in the crucible 11 decreases, the pressure applied to the solid-liquid interface of material solidification decreases, and the ingot (magnesium alloy 13b) becomes easily interrupted. Therefore, in this embodiment, the material in the crucible 11 is reduced to about half of the initial feeding amount, and then additional feeding is made from the feeding chute 18 . At this time, the atmosphere in the container 14 does not need to leak, and depending on the occasion, it is also possible to supply materials while performing continuous casting. Any of this feeding method, an intermittent feeding method of collectively feeding after a certain amount of material is reduced, and a continuous feeding method of gradually feeding while continuously casting material is reduced is possible.

Next, the superiority of the plastic workability of the magnesium alloy shaped material blank 1 of the present embodiment will be described.

In the magnesium alloy profile blank 1 of the present embodiment, the slabs with a formed plate thickness of 3.0 mm, the slabs with a formed plate thickness of 5.0 mm and the slabs with a formed plate thickness of 10.0 mm are respectively rolled to obtain thin plates with a respective plate thickness of 0.5 mm ( They were designated as test plates 1, 2, and 3 in turn. Cold rolling at a reduction ratio of about 10 to 30% is performed several times so that cracks do not occur in the slab, and annealing at 450° C. for 10 minutes is performed between each rolling process. After reaching a plate thickness of 0.5 mm through the final cold rolling, stress relief annealing is performed at about 200° C. for 1 hour. In addition, the number of times of actual rolling was 6 times for the test panel 1, 7 times for the test panel 2, and 12 times for the test panel 3.

In addition, a magnesium alloy thin plate (test plate 4) with a plate thickness of 0.5 mm (test plate 4), which is not the present embodiment, was prepared, which was produced by extrusion processing and rolling processing on the market. In addition, the average diameter of crystal grains of these 4 test plates was about 7-12 micrometers.

These test panels are cut into the octagonal blank shape shown in Figure 9 (about 40mm×40mm, the corners are cut to 6mm), and the punch shoulder R1.5mm, the punch plane R2.0mm, and the punch shape 25mm×25mm The deep drawing test of the square container has a gap of 0.1mm on one side. Control the descending speed of the metal mold, and test while changing the tensile speed. Strictly speaking, the tensile speed is changed to 100mm/s, 70mm/s, 50mm/s, 20mm/s, 5mm/s, 2mm/s, 1mm/s, 0.75mm/s, 0.5mm/s, 0.1mm/s were tested.

When the stretching speed is fast, cracks will appear in the four corners of the molded product, and if the stretching speed is slow, a molded product without cracks will be obtained. The maximum speed among the stretching speeds without cracks is set as the ultimate stretching speed. The ultimate tensile velocity of each test plate was obtained. In addition, the temperature of the mold was set at 250° C., 200° C., and 150° C., and a molybdenum disulfide-based spray was used as a lubricant. A plurality of blanks 9 were prepared for the test, each condition was implemented more than 3 times, the occurrence of cracks was confirmed visually, and the limit drawing speed was determined based on the average state.

Table 4 below lists the limit drawing speeds of the aforementioned four test pulls.

Table 4 The ultimate drawing speed of each test plate (unit: mm/sec) Metal mold temperature Thin plate made from the profile blank of this embodiment Commercial sheet Test board 1 Breadboard 2 Breadboard 3 Breadboard 4 250°C 100 100 100 10 200℃ 20 10 10 1 150°C 1 1 1 0.1

According to this experiment, it can be said that any one of the test plates 1, 2, and 3 produced by rolling the magnesium alloy profile blank 1 of the present embodiment is compared with the plate (test plate 4) on the market, even if the speed is 10 times faster, it is difficult to Cracks appear, that is, excellent plastic workability.

The above-mentioned experimental results are an example for confirming the excellence of the plastic working of the magnesium alloy shape blank 1 of the present embodiment, and the same effect can be expected not only for stretching but also for other plastic workings such as forging and bending deformation.

As described above, according to the present invention, casting defects such as voids and cavities in the metallographic structure and segregation of inclusions can be prevented, so it is rich in ductility, and the profile blank is subjected to primary processing such as extrusion and rolling to form a thin plate. When the thin plate is subjected to secondary processing such as forging, it can prevent the defective part from becoming a crack cracking point during processing and breakage, and the profile blank is rolled as it is for the thin plate for plastic processing. Simplify the process and seek cost reduction. Furthermore, when coating and drying the molded product after processing, it is also possible to prevent the problem of surface defects caused by the rupture of internal air cells.

Claims (2)

1. the Continuous casting process of magnesium alloy profiles blank, it is characterized in that, comprise following 2 operations, magnesium alloy materials is dropped in the crucible, after under the oxygen barrier state, making magnesium alloy materials fusing in the crucible supply with the cooled mold, make the magnesium alloy cooling of molten state, the operation of solidifying with the speed of cooling of 3～8K/ second; And the operation of the cakey magnesium alloy of drawing.

2. the continuous casing of magnesium alloy profiles blank as claimed in claim 1, its feature are that also the material that drops into melting appartus is a granular solids, keep under the inert state magnesium alloy of molten state being supplied with the cooled mold at peripheral atmosphere gas.

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