JP4666659B2 - Magnesium alloy forged thin casing and method for manufacturing the same - Google Patents

Description

  The present invention relates to a magnesium alloy, and more particularly to a forged thin-walled casing and a method for manufacturing the same.

Magnesium has the smallest specific gravity among metal materials currently in practical use, and magnesium is 1.8 as compared with 2.7 of aluminum, and is expected as a light weight material and is becoming popular. Most magnesium alloys are used as castings. In addition to the main element magnesium, the alloy elements of the magnesium alloy include the basic elements aluminum and zinc to obtain strength and castability, as well as zirconium to provide strength and toughness, and rare earth elements and silver to provide heat resistance. . Magnesium alloys are widely used in aerospace equipment parts, nuclear coating materials, ground transportation equipment, cargo handling equipment, industrial machinery / tools, electrical / communication equipment, agriculture / forestry / mining machinery, office equipment, optical equipment, sports equipment, etc. It's being used.

As a prior art, for example, Japanese Patent Laid-Open No. 6-172949 (Patent Document 1) discloses a magnesium alloy member in which a member such as a wheel of an automobile is made of a magnesium alloy and a method for manufacturing the same. That is, the disclosed method for producing a magnesium alloy member is as follows: “(1) A magnesium alloy casting material is forged and formed into a member having an average crystal grain size of 100 μm or less, and then subjected to T6 heat treatment (solution treatment and artificial treatment). (2) Set the forging temperature within the range of 300 to 420 ° C. (3) Set the magnesium alloy member to the automobile wheel.
Further, the magnesium alloy member is “a magnesium alloy member formed by performing T6 heat treatment (solution treatment and artificial aging treatment) after casting forging, and at least the surface portion of the member is made of 6-12 aluminum. It contains a weight percentage and has an eutectic structure of an intermetallic compound of magnesium and aluminum and an α phase during the T6 heat treatment (solution treatment and artificial aging treatment), and an average crystal grain size is increased by plastic working during the forging. A magnesium alloy member in which the eutectic composition is 200 μm or less and dispersed in a chain form. ”

As for the magnesium alloy, a technique in which a molded product obtained by high-pressure casting a molten magnesium alloy is subjected to T6 heat treatment (solution treatment and artificial aging treatment), or a so-called cast forging method in which a cast product is forged.
Recently, a new molding method using an injection molding method has attracted attention as a semi-melt molding method performed in a solid-liquid coexistence region. Molded products obtained by this molding method have no dendrites found in general cast products, a fine structure is obtained, and there are fewer pores and higher density than molded products obtained by the die casting method. It is attracting attention because it can be heat-treated, and research and development is underway in various areas.
JP-A-6-172949

However, the technique disclosed in Patent Document 1 is intended for large parts such as automobile wheels, and requires considerable equipment costs for production. Also, T6 heat treatment (solution treatment and artificial aging) is required. (Processing) has a problem that it takes a long time.
Further, a magnesium alloy molded product produced by a semi-melt forming method may have casting defects or oxides inside and on the surface during the manufacturing process. If they are present, even if the surface of the component is plated, the corrosion resistance of the plated surface cannot be improved, and the commercial value as viewed from the outside is also reduced. Therefore, measures are taken to improve the corrosion resistance by surface coating. However, in this case, it is difficult to produce a metallic luster and a problem remains in aesthetics.

The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide a magnesium alloy thin-walled casing that is lightweight and high quality by forging, and a method for manufacturing the same. . The “wall thickness of the main part” in the present invention means a uniform wall thickness that occupies most of the bottom 7 and the side 8 of the housing 6 shown in FIG. However, the protrusion height formed by the predetermined symbol recess 20 is not included, and although there is a local boss or a further locally thin portion not shown, these local bosses and Further local thin wall thickness shall not be taken into account. In addition, the “predetermined symbol” means a symbol such as a character, a number, or a mark formed by protruding from the outer surface by the predetermined symbol recess 20 in FIG.

As a result of various studies on various magnesium alloys in order to solve the above-mentioned problems, the present inventors have found that by weight ratio, Al: 1 to 6%, Zn: 0 to 2%, Mn: 0.5% or less In addition, a magnesium alloy having a composition of trace element 0.2% or less, the balance Mg and inevitable impurities, for example, ASTM standard AM20 alloy and AZ31 alloy has been found to have excellent forgeability, and a plurality of steps of rough forging and finish forging are performed. Invented the magnesium alloy forged thin-walled casing of the present invention and a method for producing the same by forging.

That is, in the magnesium alloy forged thin casing of the present invention, the composition of the magnesium alloy material is, by weight ratio, Al: 1-6%, Zn: 0-2%, Mn: 0.5% or less, trace elements ( Rare earth elements, lithium, zirconium total) A forged thin-walled casing made of a magnesium alloy consisting of 0.2% or less, the balance Mg and inevitable impurities, and having a main part thickness of approximately 1.0 mm or less. The inner corner of the thin housing has a curved surface with a small radius of 0.5 to 1.5 mm, and has a predetermined symbol integrally projected on the outer surface of the forged thin housing, and A special composite anodic oxide film is provided on the entire surface of the forged thin casing.

The method for producing a magnesium alloy forged thin casing of the present invention is, by weight ratio, Al: 1-6%, Zn: 0-2%, Mn: 0.5% or less, trace elements (rare earth elements, lithium, zirconium) Total) Magnesium alloy material consisting of 0.2% or less, balance Mg and inevitable impurities is formed into a rough shape in the rough forging process, and then the corner on the inside of the casing is 0.5 to 1.5 mm in the finish forging process . It is formed into a curved surface having a small radius, the bottom and sides of the casing are formed with a target thickness, and a predetermined symbol is projected from the outer surface on the outer surface of the casing to make the main portion A casing having a thickness of approximately 1.0 mm or less is formed, the casing is trimmed and machined, and then the entire surface of the casing is subjected to a special composite anodized film treatment.

Moreover, the manufacturing method of the magnesium alloy forged thin housing | casing of this invention makes the temperature of the said magnesium alloy raw material 350-550 degreeC, the metal mold | die temperature used for forging is 350-450 degreeC, and 3-30 ton / cm < ² > shaping | molding. Rough forging is performed at a forging speed of 10 to 500 mm / sec while applying a load, then the roughly forged molded casing is 300 to 500 ° C., the mold temperature for forging is 300 to 400 ° C., and 1 to 20 ton / cm ^The forging is performed at a forging rate of 1 to 200 mm / sec while applying a molding load of ² .

The surface of the resulting magnesium alloy forged thin-walled casing is treated with a special composite anodized film to provide excellent anticorrosion properties that cannot be obtained by painting and a metallic luster that makes use of the magnesium alloy substrate. It is a manufacturing method of a thin casing.

Hereinafter, the application and reasons for limitation of various conditions according to the present invention will be described.
1) Magnesium alloy material for forging:
When a magnesium alloy material is forged to form a thin casing, the magnesium alloy must be excellent in forgeability. Therefore, a magnesium alloy material consisting of Al: 1 to 6%, Zn: 0 to 2%, Mn: 0.5% or less, trace elements of 0.2% or less, the balance Mg and unavoidable impurities is selected by weight ratio. . If aluminum is low, the forgeability is good, but the rigidity is poor, so at least 1% of aluminum is necessary. As the aluminum content increases, forgeability and corrosion resistance decrease, so the aluminum content is limited to a maximum of 6%. Zinc also has the same effect, and is limited to 0 to 2% because of forgeability and rigidity. For example, ASTM standard AZ31 alloy and AM20 alloy. The trace elements are rare earth elements, lithium, zirconium and the like.

2) Heating magnesium alloy material for forging:
When heating the magnesium alloy material in the air, the surface will oxidize and adversely affect the forgeability, corrosion resistance, and appearance, so the magnesium alloy material is heated with an inert gas atmosphere such as argon gas. Perform in a furnace. The heating temperature of the magnesium alloy material is uniformly heated at 350 to 550 ° C. (furnace atmosphere temperature), which is slightly higher than the forging temperature. For example, when the size of the material is 30 mmφ × 10 to 30 mm, the heating time is about 10 to 20 minutes. Moreover, the heating temperature of the coarse-shaped housing | casing before finish forging shall be 300-500 degreeC.

3) Forging temperature (temperature of magnesium alloy material during forging):
The temperature of the magnesium alloy material during forging is set to 350 to 550 ° C. If the temperature is lower than 350 ° C., the metal flow of the magnesium alloy during forging (hereinafter referred to as “metal flow”) cannot be obtained smoothly, and it is difficult to reduce the thickness. On the other hand, if the temperature exceeds 550 ° C., the crystal grains become coarse, so 550 ° C. is set as the upper limit temperature. Finish forging is carried out following rough forging, but the temperature of the magnesium alloy material is slightly lower than that during rough forging and is 300 to 500 ° C.

4) Mold temperature:
In order to prevent a temperature drop during forging of the magnesium alloy material, the temperature is kept slightly lower than the magnesium alloy material temperature at 350 to 450 ° C. during rough forging and at 300 to 400 ° C. during finish forging. The mold material preferably has a high temperature strength.

5) Forging speed:
If the forging speed is too fast, the metal flow is not smoothly performed, while if it is too slow, the productivity is lowered. If the forging speed exceeds 500 mm / second, the metal flow cannot smoothly follow the forging speed, and the metal flow is disturbed. Therefore, the upper limit of the forging speed is set to 500 mm / second. If the forging speed is less than 1 mm / second, the productivity is lowered. Therefore, the lower limit of the forging speed is set to 1 mm / second. In particular, in rough forging that emphasizes productivity, the speed is 10 to 500 mm / second, and in finish forging that emphasizes formability, the speed is 1 to 200 mm / second.

6) Molding load:
Particularly in rough forging where importance is placed on productivity, since the load on the product and the mold becomes excessive at a molding load exceeding 30 ton / cm ² , the upper limit of the molding load is set to 30 ton / cm ² . On the other hand, since it becomes difficult to mold at a molding load of less than 1 ton / cm ² , the lower limit of the molding load is set to 1 ton / cm ² . Particularly, rough forging requiring a forming load is 3 to 30 ton / cm ² , and finishing forging which is sufficient even if the forming load is small is set to 1 to ²⁰ ton / cm ² .

7) Surface treatment (formation of special composite anodized film):
The oxide film is formed by a special composite anodizing method based on JIS H8651. The solution is mixed with sodium dichromate, acidic sodium fluoride or acidic potassium fluoride or acidic ammonium fluoride, ammonium nitrate, primary sodium phosphate, aqueous ammonia, etc. according to the magnesium material composition, desired color, etc. Process by temperature, time, current value.
By this special composite anodic oxide film treatment, it is possible to obtain a forged thin-walled casing having excellent corrosion resistance that cannot be obtained by painting and a metallic luster that makes use of the magnesium alloy substrate.

  The magnesium alloy forged thin-walled casing of the present invention is lighter and more rigid than aluminum alloy parts, has a predetermined symbol on its outer surface, and has excellent anticorrosion and special composite anodized film on the entire surface. The metallic luster that makes use of the magnesium alloy base is formed, and its application can be expected as a thin-walled casing for the purpose of reducing the weight of various devices.

Embodiments of the present invention will be described below.
(Embodiment)
FIG. 1 is a diagram showing the forging process of the present invention. FIG. 2 is a schematic longitudinal sectional view of an upper and lower mold for forging with a forging material placed thereon. FIG. 3 is a schematic side view of the forging machine. In the present invention, as shown in FIG. 1, Al is 1 to 6%, Zn is 0 to 2%, Mn is 0.5% or less, trace element is 0.2% or less, remaining Mg and inevitable Magnesium alloy material made of impurities, such as ASTM standard AZ31 alloy (Al 3%, Zn 1%, etc.) and AM20 alloy (Al 2%, Mn 0.5%, etc.) 30-40mmφ × 10 A forging material having a length of ˜30 mm is placed in an electric heating furnace filled with argon gas and heated uniformly at 350 to 550 ° C. Next, the forging material is taken out from the electric heating furnace, placed on the lower mold 2 shown in FIG. 2, rough forging is performed using the forging machine shown in FIG. 3, and then finishing forging is performed. In FIG. 2, 4 indicates a heater and 5 indicates a thermocouple.

As shown in FIG. 3, the forging machine 9 is a mechanical forging machine that applies the rotational force of the flywheel 11, and transmits the force to the connecting rod 12. 3 is detachably connected. The upper die 3 moves in the direction of the arrow L, and a forming load is applied to the forging material 1 placed on the lower die 2 at regular intervals. A rough forging rough forging uses a mechanical forging machine with a fast forging speed, and a final forging for forming final product dimensions uses a hydraulic forging machine with a relatively low forging speed. Reference numeral 10 denotes an eccentric shaft, and 13 denotes a frame.

FIG. 4 (rough forging die) and FIG. 5 (finish forging die) show schematic longitudinal sectional views of the embodiment of the die for use in the present invention. The upper die 3 shown in FIG. 4 subjected to rough forging has a convex lower end corner 14 formed with a radius of 2 to 7 mm. In the rough forging, a portion formed by forging at the lower end corner portion 14 of the convex portion of the upper mold 3 is a corner portion inside the housing 6. In rough forging, the inner corner of the housing 6 is formed to be slightly thick. The thick portions of the bottom portion 7 and the side portion 8 of the casing 6 that are pressed by the two dies 3 and 2 and are forged are formed to have a thickness that is equal to or slightly thicker than the final thickness. Further, as shown in FIG. 4, the lower mold 2 is formed with a concave corner 15 having a radius of 0.5 to 1.5 mm. In rough forging, the forged portion of the concave corner 15 of the lower mold 2 is a corner on the outside of the housing 6, so it is preferable to form the final shape target dimension from the beginning.

Next, as shown in FIG. 5, the upper die 16 used for finish forging is formed with a convex lower end corner 18 having a radius of 0.5 to 1.5 mm. Depending on the shape of the lower end corner 18 of the convex portion, the corner formed into a slightly thick radius of 2 to 7 mm by rough forging is formed to a radius of 0.5 to 1.5 mm, and the two metals shown in FIG. A part of the thick portion of the casing 6 pressed by the dies 3 and 2 and roughly forged to form a metal flow in the recess 20 that is engraved for a predetermined symbol inside the lower die 17 by finish forging. The inner side surface 21 of the bottom 7 of the housing 6 is forged and formed to be flat and have a desired final thickness. The predetermined symbol is formed so as to protrude integrally on the outer surface of the housing 6. A is an example of a case size of 80 mm square. The forging conditions are forging temperature 350 to 550 ° C., mold temperature 350 to 450 ° C., forging speed 10 to 500 mm / second, and molding load 3 to 30 ton / cm ² for rough forging, and forging temperature 300 to The temperature is 500 ° C., the mold temperature is 300 to 400 ° C., the forging speed is 1 to 200 mm / second, and the molding load is 1 to 20 ton / cm ² .

In the present invention, a target main part thickness of 0.5 to 1.0 mm can be obtained by rough forging and finish forging under the forging conditions described above. Representative examples from the experiments will be described as examples below.
Example 1
30 to 40 mmφ × 10 to 40 mm long forging magnesium alloy material (10 pieces) Forging temperature (temperature of magnesium alloy material during forging) 500 ° C., mold temperature 400 ° C., forging speed 200 mm / second, molding load 20 ton When rough forging was performed under forging conditions of / cm ² , a main part having a thickness of 0.8 to 1.0 mm was obtained. Next, as a result of finishing forging under forging conditions of a forging temperature of 400 ° C., a mold temperature of 350 ° C., a forging speed of 50 mm / sec, and a molding load of 10 ton / cm ² , the thickness of the main part is 0.6 to 0 as targeted. It was possible to mold to a thickness in the range of 8 mm.

(Example 2)
When rough forging was performed under the same rough forging conditions as in Example 1 except that the mold temperature was 300 ° C., the thickness of the main part was 1.6 mm or more. Next, as a result of finish forging under the same finish forging conditions as in Example 1, the thickness of the main part was 1.5 mm. As described above, when rough forging is performed at a low mold temperature of 300 ° C., heat is taken away by the low-temperature mold and the material temperature is lowered, so that the plastic flow (metal flow) is difficult to be performed. It turned out that thin wall forming is difficult by finish forging.

(Example 3)
When rough forging was performed under the same rough forging conditions as in Example 1 except that the forging temperature (temperature of the magnesium alloy material during forging) was 340 ° C. and the forming load was 30 ton / cm ² , the thickness of the main part was 1 It became more than 8mm. Next, as a result of finishing forging under the same finishing forging conditions as in Example 1, the thickness of the main part was 1.6 mm or more. This is because the material temperature at the time of forging is low, so even if the molding load is increased to 30 ton / cm ² , it is difficult for plastic flow (metal flow), and it is difficult to perform thin-wall molding by finish forging performed thereafter. I found out that

Example 4
When rough forging was performed under the same rough forging conditions as in Example 1 except that the forging temperature (the temperature of the magnesium alloy material during forging) was 560 ° C. and the mold temperature was 460 ° C., the thickness of the main part was 1. Although it was able to be molded to 0 mm or less, since the material temperature was too high, the plastic flow (metal flow) was intense and wave-like traces of metal flow remained on the surface. Subsequently, finish forging was performed with various finish forging conditions, but the wavy traces of the metal flow could not be made uniform and flat. From this result, it was confirmed that the forging temperature was not good if it was too high.

(Example 5)
When rough forging was performed under the same rough forging conditions as in Example 1 except that the molding load was 0.8 ton / cm ² , the thickness of the main part was 2.0 mm or more. Next, as a result of finishing forging by changing various finishing forging conditions, in particular, by increasing the molding load to 30 ton / cm ² or 40 ton / cm ² , the main part has a thickness of up to 1.0 mm. The thickness was uneven and the moldability was not good.

(Example 6)
When rough forging was performed under the same rough forging conditions as in Example 1 except that the forging speed was 500 mm / second, the plastic flow (metal flow) was disturbed, the filling into the mold was poor, and the shape was accurate. Could not be molded. As for the forging speed, when the rough forging was 10 mm / second or less, the pressing time was slowed and the temperature of the material was lowered, so that the forging speed was 2.5 mm at 5 mm / second.

Since the forged burrs are generated around the upper end of the magnesium alloy forged thin casing obtained in this way, trimming is performed to remove the forged burrs by punching. Next, the necessary part is machined. Magnesium alloy may oxidize and lose metallic luster even after forging, so an oxide film is formed by special composite anodic oxide film treatment, and the metallic luster that makes use of excellent corrosion resistance and magnesium alloy base that cannot be obtained by painting A forged thin-walled housing made of magnesium alloy having

It is process drawing which shows the forge operation process of this invention. It is a schematic longitudinal cross-sectional view of the upper and lower metal mold | die which concerns on this invention and mounts the forging raw material and performs forge molding. 1 is a schematic side view of a forging machine according to the present invention. It is a schematic longitudinal cross-sectional view of the up-and-down metal mold | die used for rough forging in connection with this invention. It is a schematic longitudinal cross-sectional view of the up-and-down metal mold | die used for finish forging in connection with this invention.

Explanation of symbols

1: Forging material
2: Lower mold
3: Upper mold
4: Heater
5: Thermocouple
6: Housing
7: Bottom of the housing
8: Side of housing
9: Forging machine
10: Eccentric shaft
11: Flywheel
12: Linkage
13: Frame
L: Molding load direction
14: Lower end corner of convex portion of upper die for rough forging
15: Concave corner of the lower die for rough forging
16: Upper die for finish forging
17: Lower die for finish forging
18: Lower end corner of convex portion of upper die for finish forging
19: Concave corner of the lower die for finish forging
20: Predetermined symbol recess
21: Inner side surface of the bottom of the housing

Claims (3)

By weight ratio, Al: 1 to 6%, Zn: 0 to 2%, Mn: 0.5% or less, trace elements (total of rare earth elements, lithium and zirconium) 0.2% or less, remaining Mg and inevitable impurities A forged thin-walled casing having a thickness of approximately 1.0 mm or less, wherein the inner corner of the forged thin-walled casing is a curved surface having a small radius of 0.5 to 1.5 mm And has a predetermined symbol integrally projected on the outer surface of the forged thin casing, and further has a special composite anodized film on the entire surface of the forged thin casing. Alloy forged thin housing. By weight ratio, Al: 1 to 6%, Zn: 0 to 2%, Mn: 0.5% or less, trace elements (total of rare earth elements, lithium and zirconium) 0.2% or less, remaining Mg and inevitable impurities Forming a magnesium alloy material into a rough shape in a rough forging process, and then forming a corner inside the casing into a curved surface having a small radius of 0.5 to 1.5 mm in a finish forging process, and the bottom of the casing And the side part is formed to a target thickness, and a predetermined symbol is projected from the outer surface on the outer surface of the casing to form a casing having a main part thickness of approximately 1.0 mm or less, A method for manufacturing a magnesium alloy forged thin casing, wherein the casing is trimmed and machined, and then the entire surface of the casing is subjected to a special composite anodized film treatment. 3. The magnesium alloy forged thin-walled casing according to claim 2, wherein the magnesium alloy forged thin-walled casing according to claim 2 has an excellent anticorrosive property that cannot be obtained by coating and a metallic luster that makes use of the magnesium alloy substrate by applying a special composite anodized film treatment. Production method.

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