KR101392480B1 - Extrusion method of magnesium alloy with zink and ytrium - Google Patents

Abstract

The present invention relates to an extrusion method of a magnesium alloy billet with zinc (Zn) and yttrium (Y) comprising the steps of: adding and mixing 2.5 to 6% by weight of zinc and 0.3 to 1.3% by weight of yttrium relative to 2.8 to 7% by weight of total amount to form a high temperature deposited material and diffusing and annealing a magnesium alloy billet for extrusion which is improved in plastic working at temperature of 250 to 450°C for one minute/mm; removing textured coating of the surface of the billet to which diffusion and annealing are carried out; preheating the billet from which the textured coating is removed at temperature of 250 to 450°C for two to five hours; and extruding and molding the preheated billet into a bar shape in an extrusion container through an extrusion die. The extrusion method of the magnesium alloy according to the present invention can extrude the magnesium alloy, which conventionally has a defect on the surface at the time of extrusion due to a low ductility, without any defect and can process bars even at low extrusion pressure, thereby providing high quality magnesium alloy extrusion materials which are usefully used for portable household electrical appliances, parts for vehicles or aircrafts at low prices.

Description

Extrusion methods of magnesium alloys with zink and yttrium added with zinc and yttrium [

The present invention relates to a method of extruding a magnesium alloy billet to which zinc (Zn) and yttrium (Y) are added. Specifically, zinc and yttrium are mixed and added in an appropriate amount to a magnesium casting structure having good machinability but poor plastic workability By forming the high temperature precipitates, it is possible to improve the plastic workability and to derive the extrusion conditions so as to transform the structure of the alloy having improved plastic workability into microstructure to further improve the plastic workability, The present invention relates to a method of extruding an alloy billet.

As is well known, the magnesium alloy is the lightest metal among the metal materials currently practically used, and has been rapidly used as a material for various parts in place of aluminum in the use of metal materials to achieve further weight reduction. In addition, The demand for electronic products has been rapidly increasing as a substitute for plastic, which has many problems in recycling.

The magnesium alloy has the lightest density of 1.74 g / cc, which is two-thirds of aluminum, among the commonly used structural alloys. Magnesium alloys also have excellent machinability, high vibration damping properties, excellent absorbency against vibration and impact, and excellent electromagnetic wave shielding. In addition, recently, magnesium alloy is rapidly expanded to computers, mobile phones, automobile parts, and the like because it has excellent lightweight and regenerative properties, shields against electromagnetic waves, and can be molded as a thin shape member.

As a result, it can be seen that the magnesium alloy is a good material as a structural material for portable electronic products, which has recently become popular among consumers.

In general, materials such as interior parts for portable electronic products, automobile parts or aircraft parts are required to have light weight, high strength, high toughness and high quality.

However, since magnesium has a dense hexagonal lattice structure with little slip system, which is essential for plastic deformation, extrusion and moldability are poor, and casting is mainly performed.

However, die casting has a lot of restrictions on the shape, and die casting has many problems in the subsequent surface treatment process because the casting structure is porous due to its characteristics. Then, materials such as AZ31 and AM20, which are alloyed with aluminum and zinc or manganese, have been developed and plastic working using the ductility of single phase solid solution has become possible to some extent.

However, they contain process phases with a melting point of 400 ° C or less in a single-phase solid solution, despite the excellent processability and abundant ductility. Therefore, the plate or the shape material which is plastically deformed in one direction is strong in anisotropy and hardly has work hardening ability, and in practical use, there is a problem in plastic workability, and commercialization is progressing slowly.

That is, when extruded at a temperature of 350 ° C or higher, frictional heat of the die caused surface defects such as fine cracks on the surface like fingerprints, making it difficult to obtain a clean and defect-free product. These fine wrinkle-like surface cracks degrade the fatigue strength and should be removed.

In order to solve this problem, a thixo-molding method has been proposed in which magnesium alloy powder is injected in a liquid phase and a solid phase coexistence region. However, this is not widely applied because of the disadvantage that the porous structure is obtained as in the case of die casting and the cost of the raw material powder is high, which increases manufacturing cost.

In addition, there is a lithium-containing alloy which is converted into a body-centered cubic lattice structure capable of being subjected to plastic working to improve plasticity. Lithium has a high solubility for magnesium and is effective. However, it is effective to add a large amount of 5 to 20% by weight because the difference in solubility according to temperature is small and the difference in lattice constant is small. The alloy has to be added with a large amount of expensive lithium and is not actually used for commercial purposes due to its unique battery reaction characteristic.

Many magnesium alloys have been newly devised to overcome the problems of the prior art.

Among them, Korean Patent Application No. 2001-0019353 discloses a magnesium alloy having a composition range of 1 to 10 at% of Zn and 0.1 to 3 at% of Y with the composition of Mg-Zn-Y alloy. In this alloy, the stability at high temperatures of 450 ° C or less is excellent because of the distribution of up to 30% of the stable quasicrystal.

However, when the amount of zinc in the actual dissolution is large, zinc segregation due to the specific gravity and homogeneous uniformity of the mesophase, which is an intermetallic compound during cooling of the billet, are generated. Precipitation is not easy. Therefore, although it is possible in small specimens in the laboratory, in practical size, the ductility of the material is low and the quality is not uniform in each part. In this invention, 30 mm tensile specimens were also tested and were significantly smaller than normal tensile specimen sizes.

A number of other patents have introduced methods of obtaining high strength, lightweight magnesium alloy strips by obtaining amorphous textures by rapid cooling.

Korean Patent Application No. 1993-846 " High Strength Magnesium-Based Alloy ", Japanese Laid-Open Patent Publication No. 05-70880 " High Strength Magnesium Alloy Material and Method for Manufacturing Alloys thereof ", Japanese Unexamined Patent Publication No. Hei 06-41701 'High Strength Amorphous Magnesium Alloy High strength magnesium alloy and its manufacturing method ", and Japanese Patent Laid-Open Publication No. Hei 07-54026," High Strength Magnesium Alloys and Manufacturing Method Thereof, "and U.S. Patent Nos. 4675157, 4765954, 4853035, 4857109, Patents No. 4938809, No. 5071474, No. 5078806, No. 5078807, No. 5087304, No. 5129960, and No. 5316598 all contain amorphous structure by rapid cooling However, the non-amorphized structure has a disadvantage in that it is difficult to perform rolling or press forming by including a brittle intermetallic compound or a process phase.

In addition, U.S. Patent No. 4908181, U.S. Patent No. 5139077, U.S. Pat. No. 5,143,795, U.S. Pat. No. 5,250,124, U.S. Pat. No. 5,647,919, and U.S. Pat. No. 6,139,651 disclose a casting alloy that is not a material for extrusion processing, . These materials are characterized by being able to obtain a high strength in a cast state as a two-phase complex structure containing a large amount of an intermetallic compound by adding an alloying element.

However, when such an alloy is applied in a thin form such as a plate or a shape, a relatively low-strength phase firstly causes plastic deformation at a region where stress concentrates, resulting in cracking. In addition, there are many brittle intermetallic compounds which are not suitable for plastic working or press forming.

In recent years, in order to overcome such problems, there have been developed technologies for developing a magnesium alloy improved in plasticity or for easily plasticizing existing materials.

Patent No. 10-0509648 developed by the present inventors discloses a magnesium alloy excellent in plastic workability. However, although the process for rolling the sheet has been mentioned in this patent, the extrusion method has not been introduced in detail, and commercialization has not been carried out for a long time.

In addition, although the extruding conditions of magnesium added with zinc, yttrium, aluminum, and the like have been introduced in another patent 10-0605741 of the present inventor, it has been found that the extruding pressure is 5 times or more higher than that of a conventional extruder operating at a pressure of 1000 kg / Of the extruder.

In addition to the above-mentioned methods, a technique for machining hardened materials by a method of processing at a high plasticizing ratio through an angle changing channel in a die such as ECAP and ECAE has been developed. However, since the die structure is complicated and high pressing force is required, And productivity is limited, making it generally difficult to commercialize.

1, the die 2 having the cavity 3 is coupled to the extrusion container 1, and the billet 4 is placed in a plane with the die 2, Flows through the cavity 3 due to the pressure of the ram 5 while being in contact therewith, so that flow occurs at an angle of about 60 degrees or less at the die inlet. In this relationship, a dead zone 6 is formed on both sides, The unevenness of the quality of the extruded product occurs and causes deformation. In addition, there is a problem that the extrusion pressure is increased and the size of the extruder is required to be increased.

Korean Unexamined Patent Publication No. 2002-0078936. October 19, 2002.

The present invention has been made in order to eliminate the above problems, and it is an object of the present invention to provide a magnesium alloy billet having a high work hardening ability but low ductility due to the formation of a high-temperature precipitate by adding an appropriate amount of zinc and yttrium to magnesium, The present invention is directed to a method of extruding a magnesium alloy frame member capable of preventing a crack from occurring and allowing extrusion even under a low pressure, and to provide an extrusion die in which a fluidity stress is reduced to minimize a dead zone.

In order to achieve the above object, the present invention provides a magnesium alloy billet for extrusion which is improved in plasticity by mixing zinc and yttrium in a proportion of 7% by weight or less to form a high-temperature precipitate. The magnesium alloy billet is extruded at 250 to 450 ° C for 1 minute / Removing the chill structure of the surface of the billet subjected to the diffusion annealing, holding the chill-removed billet at 250 to 450 DEG C for 2 to 5 hours to preheat and holding the preheated billet, And a step of extruding the molded body from the extruded container into a shape member through an extrusion die.

The extrusion molding step is performed by extruding the extrusion container at an extrusion pressure of 1000 kg / cm 2 or less, an extrusion rate of 100 to 200 mm / min, and an extrusion ratio of 10: 1 to 100: 1 in a state of heating the extrusion container at 250 to 400 캜 In addition,

The extrusion die used in the extrusion step is characterized in that dies of various stages in which the cross-sectional area of the cavity is reduced stepwise are combined.

In addition, the present invention is characterized in that the cavity has a sectional area smaller than the sectional area of the extrusion billet by 50% or more and is connected to the exit side of the extrusion container,

And an output die coupled to the outside of the input die, the shape of which is the same as the cross-sectional area of the final product whose cross-sectional area of the cavity is smaller than the cavity of the input die by 50% or more.

An intermediate die coupled between the outer side of the input die and the inner side of the output die to facilitate smooth plastic deformation, wherein the cavity of the intermediate die comprises one or more cavities and has a cross- And the total reduction rate is formed to be smaller than 50%.

In order to induce a smooth plastic flow, the cavities of the inlet die and the intermediate die are formed to have a cross-sectional area of a cross-section end or an edge larger than an intermediate portion,

The cavities of the inlet die and the intermediate die are characterized in that the material inflow amount is large at a cavity portion where the cross sectional area of the extruded material of the outlet die is large

The inlet of the inlet die is provided with a flow angle of 150 degrees or less or a curvature of 5 mm or more in radius.

 According to the present invention, it is possible to extrude the magnesium alloy, which has a low ductility and defects on the surface during extrusion, without defects, and it is also possible to process the mold with a low-pressure extrusion pressure. It is possible to provide magnesium alloy extruded material, which is useful for weight reduction, to provide excellent quality and low cost.

1 Example of an aluminum extrusion die
Example of the integrated extrusion die of the present invention
3 shows an example of a multi-stage extrusion die according to the present invention.
4 cast billet
Fig. 5-1 Extrusion die (inlet side of two stages)
5-2 Extrusion die (outlet side of two stages)
Figure 6: Cavity shape of the 3-stage extrusion die
Fig. 7 Coiled extruded material

Hereinafter, the present invention will be described in detail.

In the extrusion molding method of the present invention, a magnesium alloy billet containing 2.5 to 6 wt% of zinc and 0.3 to 1.3 wt% of yttrium and 2.8 to 7 wt% of the total amount thereof is added and diffused at a temperature of 250 to 450 DEG C for 1 minute / diffusion annealing; removing the chill structure of the surface of the diffusion-annealed billet; holding the chill-removed billet at 250 to 450 ° C for 2 to 5 hours to preheat; And a step of extruding the preheated billet from the extruded container into a shape material through an extrusion die. The extruded shape of the magnesium alloy shape material,

The reason why the diffusion annealing is performed at a holding time of 1 minute / mm or more depending on the cross-sectional diameter and thickness of the casting material at a temperature range of 250 to 450 ° C. is that the heating temperature is lower than 250 ° C. or the holding time is 1 minute / If it is short, it is not sufficiently heated to the inside, so that it may not be extruded from the die during extrusion processing, and may cause hardening or microcracking of fine wrinkles such as fingerprints on the surface and corners.

When the diffusion annealing is completed, machining is performed to remove the chill texture on the surface, because the chill portion is a composition in which the alloying element is reduced by subcooling and the expected plastic workability is not obtained.

The billet with the chipped structure removed is preheated at 250 to 450 ° C for 2 to 5 hours to maintain the plasticity of the magnesium billet after passing through the extrusion die in the extruded container without preheating, And extrusion becomes impossible.

Wherein the preheated billet is extruded at a temperature of 250 to 400 캜 under an extrusion pressure of 1000 kg / cm 2 or less, an extrusion rate of 100 to 200 mm / 10: 1 to 100: 1,

The reason for limiting the extrusion pressure to 1000 kg / cm 2 or less is that a conventional magnesium alloy billet requires a large extruder having a hydraulic pressure of 6000 ton or more because it is difficult to work with a small extruder because a pressure of 1000 kg / In the case of the present invention, it is possible to manufacture even at a low pressure of 1000 kg / cm 2 or less, and it is possible to work with a small-sized extruder usually used for aluminum extrusion.

Further, when the extrusion rate is in the range of 100 to 200 mm / min and the extrusion ratio is in the range of 10: 1 to 100: 1, there is a marked productivity increase effect. If the extrusion rate is out of the range, fine wrinkles and warpage are generated on the surface, It is restricted because overload can be caused in equipment.

2 and 3, the die 2 is attached to the extrusion container 1, and the die 2 is a die that is designed so that the cross-sectional area of the cavity 3 is stepwise reduced . Particularly, the die is divided into an inlet die A and an outlet die C in the form of a plate, and a plurality of intermediate dies B are added between the inlet A and the outlet C, ) Is reduced stepwise.

In general, materials with high flow stress, such as magnesium alloys, excessively increase the surface temperature of the extruded material due to the friction between the billet and the die when passing through the die. Since the low melting point process phases coexisting in the matrix of the material are dissolved, Fine crack defects occur in the form of fine wrinkles at right angles to the direction through the die.

In order to reduce such defects, the present invention forms a die to provide a flow angle or curvature at the inlet of the die, or to reduce the cross-sectional area of the cavity step by step, thereby reducing the frictional resistance of the billet contacting the die, The plastic flow is facilitated and the dead zone is reduced. As a result, the occurrence of fine surface cracks such as fine wrinkles is remarkably reduced.

In the case of using the multi-step die in the present invention, as shown in FIG. 3, each plate is given an extrusion ratio to gradually decrease the cross-section, thereby reducing the flow stress.

In addition, since the plate-shaped die can be used by replacing only the plate of the most consumable part and can be used in the case of a product of a similar size, the manufacturing cost can be reduced by replacing only the consumable part .

The cross-sectional shape of the cavities of each of the plate-shaped dies is shown below the view of Fig. The die D of the first end die (the inlet die A-A ') is a die whose width is the same as the diameter of the billet and which is a thickness reducing die, and the second stage die (Intermediate die B-B '), the width is increased while the thickness is reduced. And the cavity is formed with a desired width in the third stage die (output die C-C ').

In addition, as shown in Fig. 2, the integrated die inlet may be provided with a flow angle 7 of not more than 150 degrees or a curvature of 5 mm or more. However, when the flow angle is less than 150 degrees or the curvature is less than 5 mm There is a problem that the productivity is lowered because the flow stress is large at the time of working and micro cracks appear on the surface of the extruded material or the extrusion speed is lowered to less than 100 mm / min.

Considering the inlet angle and curvature shape of the die and the cross-sectional area of the cavities in each region, if the extrusion ratios are not largely different for each cavity, the molding can be smoothly performed while the flow stress is small. This principle can also be applied to various shapes other than plate shapes.

The material of the die used in this embodiment is SS400, which is a common steel material. Of course, high alloy steel such as die steel or tool steel can be used. However, wear of the magnesium alloy does not occur at extrusion, and only the consumable part is replaced. Therefore, ordinary carbon steel which is inexpensive and easy to process is sufficient.

FIG. 6 is a photograph of a magnesium material remaining in the wide extrusion die cavity produced in this concept, showing the interior of a cavity of a multi-stage die having three stages. Thus, the cross-sectional shape of the cavity of the present invention can be confirmed.

In the first stage (inlet side), a rounded dumbbell-shaped cavity is formed on both sides of a 200 mm wide rectangle cavity to increase the amount of material flow at both ends. In the second stage (middle) And a plate-like cavity having a width of 250 mm and a thickness of 10 mm was formed in the third stage (outgoing side) to obtain an extruded material having a width larger than the diameter of the billet. In this way, it is possible to reduce the cross-sectional area by 50% or more compared to the cross-sectional area of the billet in the first stage. In the second stage, the cavity is 50% or more smaller than the cavity sectional area of the first stage. Sectional area to form a final extrusion ratio of at least 10: 1 relative to the cross-sectional area of the billet. Here, if the reduction rate of the cross-sectional area of the die cavity is less than 50%, it is difficult to obtain an extrusion ratio of 10: 1 or more because the ratio of the cross-sectional area decreases at the next die, or the flow stress is unevenly increased at a portion inside the die, Defects or deformation may occur. Also, when the flow angle of the cavity of the die exceeds 150 degrees or when the curvature radius of the cavity inlet corner is 5 mm or less, when the extrusion ratio is 10: 1 or higher, the flow stress is large and microcracks appear on the surface of the extruded material, / min. < / RTI >

In the case of adopting the integral die, the flow stress can be reduced by giving a flow angle to the cavity of the die and decreasing the cross-sectional area from the inlet to the outlet as shown in FIG. 2, and even in the multi-stage die of the present invention, Angle and curvature can be given.

Figs. 5-1 and 5-2 are examples of a multi-stage extrusion die composed of two sheets in the present invention.

After extrusion, stretching may be selectively performed to correct twisting or warping during extrusion, or coiling may be performed as shown in Fig. 7 in the case of a plate.

In the case of other magnesium alloys, after the intermediate annealing is separately performed due to the restoration phenomenon after the calibration, stretching is performed. However, since the extruded material of the present invention has excellent plastic workability, stretching correction is possible without intermediate annealing. However, the case of performing the intermediate annealing does not depart from the scope of the present invention.

After extrusion and calibrations are finished, they are loosened if necessary. In the case of a product further subjected to plastic deformation, a uniformly sintered product can be obtained due to the work hardening property while the elongation rate is greatly increased by the annealing process.

After annealing, it is cut to a desired size, and if necessary, the cut magnesium alloy extruded material may be subjected to bending or further plastic working at room temperature.

(Example)

As shown in Table 1, a size billet having a diameter of 177 to 178 mm was produced from the magnesium alloy of the present invention to produce an extruded material. They are all processed to plate shape to confirm process effects such as extrusion ratio, billet heating temperature, extrusion pressure, etc. under the same conditions. However, the shape of frame having different cross-sectional shapes does not fall outside the scope of the present invention.

The billets of Examples 1 to 6 and Comparative Examples 3 to 7 were composed of 2.8% zinc by weight, 0.52% yttrium, and magnesium as the remainder. The billets of Comparative Examples 1 and 2 are AZ31 alloys composed of 3.1% by weight aluminum, 0.98% zinc, 0.18% manganese and the balance magnesium. The billets of Examples 7-12 were composed of 2.8% zinc by weight, 0.47% yttrium, 0.04% manganese and the remainder magnesium.

The billets of Examples 13 to 15 were composed of 5.5% zinc by weight, 0.85% yttrium, 1.4% aluminum and 0.2% manganese, the remainder being magnesium.

The billet of Comparative Example 8 was composed of 6.2% zinc by weight, 1.5% yttrium, 0.4% manganese, 1.1% aluminum and the remainder magnesium.

The production of the billet having such a composition is carried out by putting magnesium in a stainless steel crucible which is shielded with a gas mixed with 2 to 3% of SF ₆ by volume in Ar in an elevator type electric furnace and keeping the temperature of the magnesium melt at 650 to 850 ° C After the zinc and the low-melting point alloying elements are added, when the zinc is completely melted, the temperature of the molten metal is raised to 700 to 850 ° C. and the magnesium-yttrium mother alloy having a concentration of 25% The molten alloy is completely dissolved in the molten metal, and then the crucible is taken out of the elevator and slowly introduced into the water-cooling bath while cooling the mold at a cooling rate of 50 ° C / min or more until the surface temperature of the billet mold is cooled to 300 ° C or less, .

Examples 1 to 6 and Comparative Examples 3 to 8 were worked on a conventional extruder for aluminum having a capacity of 1250 tons, and Examples 7 to 12 and Comparative Examples 1 and 2 were worked in an extruder having a capacity of 1270 tons, .

In Comparative Examples 3 and 4, the billet heating temperature was heated to 240 占 폚 and 204 占 폚 to less than 250 占 폚, so that the plastic working could not be performed with excessive flow stress during extrusion, and the operation was stopped.

The results of the extrusion operations of the examples and the comparative examples are shown in Table 1.

In all of Examples 1 to 15, the billet was heated and maintained at a temperature of 250 to 450 DEG C for 3 hours and extruded at a ratio of 10: 1 or more to obtain a speed of 100 mm / min or more at an extrusion rate. It can be seen that since the higher extrusion rate can be obtained under the same heating conditions as in AZ31 which is the commercial material shown in Comparative Examples 1 and 2, the plastic workability of the alloy of the present invention is excellent.

Even if the material of the present invention is used, as shown in Comparative Examples 3 to 7, when the preheat billet heating temperature is less than 250 ° C, the extrusion rate is low and the productivity deteriorates. When the preheat temperature exceeds 450 ° C, It can be seen that In Comparative Example 8, magnesium alloy billets containing 7.7% or more of zinc and yttrium added in an amount of 7% or more were found to have surface cracks at an extrusion rate of 100 mm / min or more because the high temperature precipitates were excessive and flow stress increased during extrusion Able to know.

The test specimens were taken from the extruded material of Example 7 and subjected to tensile tests of two specimens per each condition. The results are as follows. When the extruded material was subjected to annealing at 300 ° C for 15 minutes, the tensile strength was 303 MPa, the yield strength was 237 MPa, and the elongation was 28%. In the extruded specimen, the tensile strength was 373 MPa, the yield strength was 350 MPa, Was annealed at 300 캜 for 30 minutes to obtain a tensile strength of 299 MPa, a yield strength of 225 MPa and an elongation of 29%. In particular, the curve after annealing shows an upper and lower yield point. This is a phenomenon occurring in materials having excellent work hardening properties and ductility, and it can be seen that the magnesium alloy extruded material of the present invention has excellent plastic workability.

The magnesium alloy extruded material of the present invention can be applied to portable household appliances, automobiles, aircraft parts, and the like to be useful for lightening the weight.

Extrusion test result Extrusion size
(mm) Extrusion ratio Billet heating temperature (캜) container
Temperature (℃) pressure
(kg / cm2) lamb
speed
(m / min) work
time
(min) Extrusion speed
(mm / min) Judgment result Example 1 100X4.5t 55: 1 320 360 230 2.4 18 187 Good Example 2 100X4.5t 55: 1 318 351 235 0.87 29 116 Good Example 3 100X4.5t 55: 1 318 351 190 1.93 29 116 Good Example 4 100X4.5t 55: 1 309 354 220 0.93 18 187 Good Example 5 100X4.5t 55: 1 309 354 200 2.4 18 187 Good Example 6 100X4.5t 55: 1 309 354 180 2.4 18 187 Good Comparative Example 1 100X4.5t 55: 1 350 360 200 One 71 48 Slow down Comparative Example 2 100X4.5t 55: 1 400 360 200 2.4 30 67 Surface microcrack Example 7 150X5t 33: 1 280 360 200 1.56 17 119 Good Example 8 150X5t 33: 1 345 353 210 2.4 12 169 Good Example 9 150X5t 33: 1 345 353 200 2.67 12 169 Good Example 10 150X5t 33: 1 355 350 220 1.3 11 183 Good Example 11 150X5t 33: 1 355 350 200 2.67 11 183 Good Example 12 150X5t 33: 1 355 350 150 4 11 183 Good Comparative Example 3 150X5t 33: 1 240 320 210 1.3 - - Inoperable Comparative Example 4 150X5t 33: 1 204 320 210 One - - Inoperable Comparative Example 5 150X5t 33: 1 460 370 150 0.67 30 67 Surface microcrack Comparative Example 6 150X5t 33: 1 460 370 135 One 30 67 Surface microcrack Comparative Example 7 150X5t 33: 1 460 370 120 1.87 30 67 Surface microcrack Comparative Example 8 150X5t 33: 1 355 350 210 2.67 15 135 Surface crack Example 13 200X5.5t 23: 1 400 380 250 2.38 7.5 184 Good Example 14 200X5.5t 23: 1 440 380 200 2.38 7.5 184 Good Example 15 200X9t 14: 1 400 380 220 1.93 5 169 Good

1: extruded container 2: die 3: cavity 4: billet 5: ram 6: blind spot

Claims (9)

Diffusion-annealing a magnesium alloy billet containing 2.5 to 6 wt% of zinc and 0.3 to 1.3 wt% of zinc in a total amount of 2.8 to 7 wt% at a temperature of 250 to 450 DEG C for 1 min / mm or more; and a step of removing the seven tissues of the billet surface Jin performed, the step of maintaining said fill tissue is removed billet 2-5 hours, preheated at 250 ~ 450 ℃ and extrusion die for the pre-heated billets in the extrusion container And extruding the molten magnesium alloy into a mold. The method of extruding a magnesium alloy to which zinc and yttrium are added . The method according to claim 1,
The extrusion molding is performed by extruding the billet at an extrusion pressure of 1000 kg / cm 2 or less, an extrusion rate of 100 to 200 mm / min, and an extrusion ratio of 10: 1 to 100: 1 under heating the extrusion container at 250 to 450 캜 Wherein the magnesium alloy is added with zinc and yttrium . 3. The method according to claim 1 or 2,
The extrusion die for extrusion used in the shaping method is extrusion of zinc and the yttrium is added to a magnesium alloy, it characterized in that the cross-sectional area of the cavity decreases in a stepwise manner as the multi-stage type. delete delete delete delete delete delete

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