JP2001170736A - Method for manufacturing magnesium alloy thin formed body and thin formed body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnesium alloy thin casing having a light weight, high quality, a sufficiently filled boss part and a recessed part at a bottom part. SOLUTION: The method of manufacturing a magnesium alloy forging thin formed body consists of a rough forging process, in which by forging a thin stock at a forging temperature of 200-540 deg.C and at a forging speed of 10-500 mm/sec, the thin stock is forged at a draft of <=75% to be formed to a bottomed rough forged body having a peripheral wall part, and a finish forging process, in which a rough forging formed body obtained in the rough forging process is forged at a forging temperature of 200-540 deg.C and at a draft of <=30% while loading a forming load of 1-20 ton/cm2. In the rough forging process and/or the finish forging process, a projecting part at a center part of a punch and/or a die is arranged so that a thickness near a center of the bottom part of the formed body is thinner than a thickness near a peripheral part, thereby the neighborhood of the bottom center part of the formed body is forged so as to be thinner than a bottom part thickness of the neighborhood of the peripheral part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thin magnesium alloy material by forging, and more particularly to a method of manufacturing a thin magnesium alloy product suitable for use in housings of small and lightweight equipment. It is about.

[0002]

2. Description of the Related Art Magnesium is the material having the lowest specific gravity among the metal materials currently put into practical use. That is, the specific gravity of magnesium is 1.8, which is much smaller than the specific gravity of aluminum, which is currently widely used in various applications as a lightweight material, of 2.7. For this reason,
Magnesium alloys have recently received attention as a lightweight material to replace aluminum alloys, and are being used in a wide range of fields.

However, compared to aluminum alloys,
Magnesium alloys have a problem in plastic workability. For this reason, at present, most magnesium alloys are used as cast materials. In general, a magnesium alloy used as a casting material achieves castability while improving strength by adding aluminum and zinc as basic additive elements to magnesium as a main component element. Also, zirconium may be added to impart strength and toughness, manganese may be added to reduce the size of crystal grains, or rare earth elements or silver may be added to impart heat resistance. . However, compacts obtained by casting a magnesium alloy melt are limited to relatively thick ones due to restrictions on the manufacturing method. Further, during the manufacturing process, there is a great possibility that casting defects and oxides are interposed inside and on the surface. If these defects are present, there is a problem in mechanical strength, and a problem also occurs in corrosion resistance and the like.

As another method for obtaining a thin molded body made of a magnesium alloy, drawing from a magnesium alloy sheet material can be considered. Documents which disclose the drawing of magnesium alloy sheets include, for example, JP-A-6-55230 and JP-A-6-328155. However, these publications state that "when a punch and a flange are formed using a mold heated to a temperature range of 175 ° C. or more and 500 ° C. or less, deep drawing of a magnesium thin plate becomes possible”. Although there is a suggestion about a mold temperature suitable for deep drawing warm working, there is no disclosure or suggestion about forming a boss at a corner or a peripheral wall.

[0005]

In recent years, electronic circuit components and
With high integration and high density of devices, miniaturization and weight reduction of small communication equipment such as mobile phones, small office equipment such as notebook and mobile personal computers, and many other applications are actively pursued. Therefore, miniaturization and weight reduction of housings of these devices are also required. To meet such demands, thin-walled compacts made of aluminum alloys are widely used, but in order to further reduce the weight while maintaining the same or higher mechanical strength, thin-walled compacts made of magnesium alloy The emergence of is desired. However, since the crystal structure of magnesium is dense hexagonal,
Because it is extremely difficult to control the metal flow during forging of the magnesium alloy during forging (hereinafter referred to as “metal flow”),
Ideal plasticity is extremely difficult.

In the above-described drawing from a magnesium alloy sheet material, it is essential to prevent the occurrence of wrinkles.
There is a problem in terms of material yield due to the necessity of a wrinkle holding portion. This is a serious problem particularly when a small molded product is manufactured. Also, when there is a thick boss at the corner or the peripheral wall, the metal flow must be collected at this boss. The present invention has been made in order to solve the problems and the like in the prior art, the thickness of the main portion made of a magnesium alloy lighter than the aluminum alloy is 1.5 mm or less, a thin portion near the bottom center portion It is an object of the present invention to provide a thin-walled molded product having the following. Here, the main portion refers to a portion having a substantially uniform thickness, such as a bottom portion and a peripheral wall portion, and does not include the height of a projection or a boss.

[0007]

Means for Solving the Problems The inventors of the present application have studied various processing methods to achieve the above object, and as a result, forged magnesium alloy sheet material to obtain a desired thin wall. The inventors have found that a molded body made of a magnesium alloy can be produced, and have completed the present invention. That is, the above object can be achieved by a novel means different from drawing, in which a magnesium alloy thin sheet material and a mold are stretched by forging with temperature control to obtain a formed body. Further, a technique is provided in which a thin portion is provided near the center of the bottom portion and the metal is extruded to a boss at a corner or a peripheral wall.

According to the present invention, a thin sheet material made of a magnesium alloy is formed at a forging temperature of 200 to 540 ° C. at a forging temperature of 10 to 500.
By forging at a forging speed of mm / sec, a thin forging material is stretched at a draft of 75% or less to form a rough forged product with a peripheral wall and a bottomed shape. A finishing forging step of performing a forging process at a rolling reduction of 50% or less while applying a forming load of 1 to ²⁰ ton / cm ² at a forging temperature of 200 to 540 ° C. and a rough forging step or / and In the finish forging step, a convex portion is provided at the center of the punch or / and the die so that the thickness near the center of the bottom of the molded body is smaller than the thickness near the peripheral wall. And a method for manufacturing a thin formed body made of a magnesium alloy, wherein the forging is performed so as to be thinner than a bottom wall thickness near a peripheral wall portion. In the invention of the present application, it is preferable to use a magnesium alloy thin plate manufactured to have a shape approximately the same as or slightly larger than the bottom area of the target thin-walled molded product. If the thin sheet material is too large, defects such as wrinkles are likely to occur at the corners of the formed body, and the material yield is also reduced. On the other hand, if it is too small, a good metal flow cannot be obtained at the bosses at the corners and the peripheral wall portion, and insufficient filling or chipping may occur, making it impossible to form a boss having good properties.

In the present invention, the thickness is preferably 3 mm.
The following sheet materials made of magnesium alloy were prepared for 200-5
At a temperature of 40 ° C., it is placed in a rough forging die heated and maintained at 100 to 540 ° C., and 3 to 30 ton / cm ^2.
By forging at a forging speed of 10 to 500 mm / sec while applying a forming load of, a thin material is stretched at a rolling reduction of 75% or less to form a rough forged body having a bottomed shape having a peripheral wall portion. The rough forging step and the rough forging obtained in the rough forging step are performed at a temperature of 200 to 540 ° C. for 100 to 54 ° C.
Placed in a finish forging die heated and held at 0 ° C,
While applying a molding load of 1 to ²⁰ ton / cm ² ,
5 by forging at a forging speed of 200 mm / sec.
In the finish forging step of finish forming at a rolling reduction of 0% or less, and the rough forging step and / or the finish forging step, the punch is formed so that the thickness near the center of the bottom of the formed body is smaller than the thickness near the peripheral wall. And / or providing a convex portion at the center of the die, and forging such that the vicinity of the center of the bottom of the formed body is thinner than the thickness of the bottom near the peripheral wall. Is the way. In the present invention, when a magnesium alloy sheet material having a thickness of more than 3 mm is used, in order to obtain a target thin-walled molded article having a thickness of 1.5 mm or less, the rolling reduction in forging must be increased. In addition, the metal flow of the magnesium alloy during forging becomes remarkable, and recrystallized fine particles may appear along the metal flow or may be segregated. Therefore, in the present invention, the thickness of the thin plate material is preferably set to 3 mm or less. As the thin sheet material, it is preferable to use a rolled material in consideration of the uniformity of the structure, defects, and the like.

[0010] In the present invention, the magnesium alloy sheet material or the rough forged compact is heated and placed in a forging die. The magnesium alloy sheet material is uniformly heated to 200 to 540 ° C. (furnace atmosphere temperature), which is a temperature suitable for the forging temperature. If the temperature is less than 200 ° C., the metal flow during forging cannot be obtained smoothly, and the space formed by the punch and the die is filled with the magnesium alloy and does not expand. In many cases, it is not possible to form a good boss in the portion. On the other hand, if it exceeds 540 ° C., the crystal grains become coarse, and depending on the processing rate, there is a risk of ignition and burning. Preferably, the temperature is 450 ° C. or lower. In the present invention, heating of the sheet material is an indispensable condition. However, in the deep drawing method described in the above-mentioned known literature, there is a difference in the manufacturing method, and there is no suggestion about the necessity of heating the magnesium alloy sheet material itself. It has not been. In the above invention of the present application, when the magnesium alloy sheet material or the rough forged molded body is heated in the air, the surface is oxidized, which may adversely affect forgeability, corrosion resistance, appearance, and the like. For this reason,
It is desirable to carry out in an inert gas atmosphere such as argon gas. In addition, an electric heating furnace whose atmosphere can be easily controlled is usually preferably used for preheating.

In the present invention, forging is desirably performed under the conditions of a forming load of 1 to 30 ton / cm ² and a forging speed of 1 to 500 mm / sec. That is, if the forging speed is as fast as over 500 mm / sec, the metal flow cannot smoothly follow the forging speed, and the metal flow is disturbed and a desired shape cannot be obtained. The upper limit is 500 mm / sec.
On the other hand, if the forging speed is less than 1 mm / sec, the temperature of the thin sheet material is lowered, so that it is difficult to obtain a material having good forging accuracy, and the productivity is lowered. Therefore, the lower limit of the forging speed is set to 1 mm / sec. In the present invention, it is preferable that the rough forging with emphasis on productivity is performed at a forging speed of 10 to 500 mm / sec, and the finish forging with emphasis on formability is performed with a forging speed of 1 to 200 mm / sec.

In the present invention, 30 ton / cm^Two To
If a higher molding load is applied to the product and the mold
The upper limit of the molding load is 30 ton
/ Cm^Two And On the other hand, 1 ton / cm^Two Less than molded load
Heavy weight makes molding difficult, so the lower limit of the molding load is 1 to
n / cm^Two And In the present invention, in particular,
For rough forging that requires a load, 3 to 30 ton / cm^Two Success
1 to 20 tons for finish forging, which is sufficient even with a small form load
on / cm ^Two It is desirable that In the present invention
Therefore, the reduction rate during rough forging was set to 75% or less because
When forging is performed with a draft of more than 5%, heat generated by processing
Is added, and there is a risk of ignition and burning.
Taking safety into account, the rolling reduction during rough forging is 50% or less.
It is preferred that On the other hand, in finish forging,
The radius of the relatively large rising corner during rough forging is
Processing amount, such as forming to the target extremely small radius
Since the moldability is important, the rolling reduction is preferably 50% or less.
Or less than 30%. To do this
Work hardening of the compact can be minimized.
You.

In the present invention, in order to sufficiently flow the metal flow to the bosses at the corners and the peripheral wall, the meat at the center may be caused to flow to the bosses. It is good to form and forcibly direct the metal flow near the center to the boss. As a result, the vicinity of the bottom center of the magnesium thin casing becomes thinner than the vicinity of the peripheral wall. The shape of the thin portion at the bottom may be changed depending on the position of the boss, and the shape of the bottom viewed from the external appearance may be any polygon such as a square, a star or a circle, and may not necessarily be the bottom when viewed in cross section. Is not a straight line, but may be an arc, a sphere, or the like. In addition, the thin portion may be provided on the outer surface side of the housing, may be provided on the inner surface side, or may be provided on both sides. Labels and precautions can be affixed to this thin portion, and a drawing that enhances the aesthetic appearance can be affixed.

The thin molded article according to the present invention is desirably subjected to temporary corrosion protection, painting and anodic oxide film treatment after performing desired trimming, punching and machining. This is because a magnesium alloy forged product has good surface properties and excellent metallic luster, but may be oxidized after forging and lose its metallic luster. In particular, the thin molded body according to the present invention is
Its outer surface is excellent in roughness, and by applying an anodic oxide film treatment to the outer surface of the bottom and / or the side wall, it is possible to realize a molded product utilizing the luster of the metal substrate itself.

When forging a magnesium alloy sheet material to produce a thin-walled compact, it is desirable that the magnesium alloy be excellent in forgeability. Therefore, in the present invention, Al: 1 to 6%, Mn: 0.
It is preferable to select a magnesium alloy material containing 5% or less, a trace element 0.2% or less, the balance being Mg and unavoidable impurities, or a magnesium alloy material further containing Zn: 2% or less in the above composition. If aluminum is low, forgeability is good, but rigidity deteriorates. Therefore, it is preferable that aluminum is at least 1% or more. On the other hand, if the aluminum content increases, the forgeability and corrosion resistance decrease, so the aluminum content is preferably 6% or less. Zinc has a similar effect, and is preferably 2% or less in view of the balance between forgeability and metal flow. Such alloys include, for example, ASTM standard AZ31 alloy, AM20 alloy and the like. The magnesium alloy applicable to the present invention is not limited to the above composition, and a magnesium alloy containing a rare earth element, lithium, zirconium, or the like as a trace element can also be applied to the present invention.

[0016]

Embodiments of the present invention will be described below. (Embodiment) FIG. 2 is a schematic structural perspective view for explaining an example of a thin formed body made of a magnesium alloy to be produced according to the present invention. In FIG. 2, reference numeral 1 denotes a magnesium alloy thin molded body having bosses at corners and peripheral walls, and a cross section having a bottom 2 and a peripheral wall 3 as a basic shape is a cross section taken along the line AA shown in FIG. 3. Thus, it is a substantially concave shaped body. Also, the thickness t of the bottom 2 and the peripheral wall 3 is extremely thin, 1.5 mm or less. Further, as shown in FIG. 3, by setting the thickness w1 at the bottom near the peripheral wall and the thickness w2 near the center of the bottom to be w1> w2, the metal flow of the thin portion 6 shown in FIG. Boss 4,
4 'can be obtained.

FIG. 1 is a schematic structural explanatory view showing an example of a rough forging die for carrying out the manufacturing method of the present invention.
In FIG. 1, reference numeral 11 denotes a thin plate material made of a magnesium alloy, which is placed on a concave portion (hereinafter, also referred to as a “die portion”) 13 provided in a lower mold 12. A central projection 14 of the die 13 is formed. The upper mold 15 has a convex portion called a punch 17, and the punch 17 is provided with depressions 18 and 18 'at positions corresponding to bosses at corners and peripheral walls. In FIG. 1, the thin plate material 11 having a shape slightly larger than the bottom portion size is used and is installed so as to have a slight gap between the bottom surface of the concave portion. However, the present invention is limited to such a mounting method. It is not something to be done. The placement position is determined according to the shape and size of the thin plate material to be used, and may be placed so as to be in contact with the bottom surface of the concave portion, or may be placed at the upper end portion of the concave portion so as to cover the concave portion. The size of the thin plate material used is
An appropriate thickness and size are selected from the target forging conditions such as the thickness of the compact, the height of the peripheral wall, the mold temperature, and the draft. Usually, it is preferable to use a thin plate material slightly larger than the bottom shape of the molded product to be obtained.

The die (not shown) in the finish forging process has substantially the same configuration as the die in the rough forging process. The finish forging process die has dimensions to which a finishing margin, a shaving margin, and the like are added so as to finish to a size that will be a final product. In the present embodiment, an example is shown in which the die has a convex portion corresponding to the thin portion 6 from the rough forging process. However, it is not provided in the rough forging but corresponds to the thin portion 6 at the bottom only in the finish forging process. A projection of the die may be provided.

Since the thin formed body made of the magnesium alloy obtained by the above-mentioned forging usually has forged burrs at the upper end portion of the peripheral wall or the like, it is necessary to perform trimming for removing the forged burrs by a punch or the like. It is. Also, if necessary, a desired portion is appropriately machined. Magnesium alloys may be oxidized even after forging and lose their metallic luster. For this reason, surface treatments such as temporary corrosion protection and painting are performed, especially by forming an oxide film by anodic oxidation film treatment to take advantage of the excellent corrosion protection and alloy base material that cannot be obtained by ordinary painting. It is preferable to use a magnesium alloy thin molded body having a metallic luster.

(Embodiment 1) First, a lower die 12 having a convex portion 14 in the center of a concave portion (die portion) 13 of the lower die, portions corresponding to the peripheral wall bosses 4 and 4 ', and the corner boss 5. Depression 1
A rough forging die having a convex portion (punch portion) 17 of an upper die having 8, 8 'and a thin portion 6 (not shown) at the same position as the rough forging die in a concave portion (die portion) of a lower die. And a convex portion (punch portion) of an upper die having a depression corresponding to each corner boss or peripheral wall boss provided at the same position as the rough forging die. A finish forging die (not shown) was prepared.

Next, a plate thickness of 1.2 mm, 75 × 100 mm
Was placed in an electric heating furnace filled with argon gas and uniformly heated to 450 ° C. Next, the material was taken out of the electric heating furnace, placed on the die of the lower mold, and subjected to rough forging at a mold temperature of 400 ° C., a forging speed of 200 mm / sec, and a molding load of 10 ton / cm ² . As a result, the approximate area of the bottom is 60
× 90mm, effective height of peripheral wall 8mm, wall thickness 0.7m
m, the bottom thin portion was 0.6 mm, and a rough forged product having no corner defects and peripheral wall bosses and having no defects in appearance was obtained.

Next, the obtained rough forged compact was charged into an electric heating furnace and heated to 400 ° C., and the forging conditions were a mold temperature of 350 ° C., a forging speed of 50 mm / sec, and a forming load of 10 ton / cm ² . As a result of finish forging, the area of the bottom was 60 × 9
0mm, effective height of peripheral wall is 8mm, wall thickness is 0.6m
m, a thin-walled molded body made of a magnesium alloy having a corner boss and a peripheral wall boss and having no defect in appearance, having a bottom thin portion of 0.45 mm.

In the embodiments described in the first and second embodiments, the concave portion (die portion) is formed in the lower die, and the convex portion (punch portion) is formed in the upper die. A mold having a configuration may be used. That is, a magnesium alloy thin plate material or a rough forged product may be placed on a punch portion (convex portion) formed in the lower die and molded. In addition, although it has been described that the die portion has a convex portion that forms a thin portion, the punch portion may have a convex portion.

[0024]

The magnesium alloy thin molded article according to the present invention is lighter and more rigid than the aluminum alloy molded article, and has a thin section at the bottom.
The metal flow flows through the bosses at the corners and the peripheral wall, and a good boss shape is obtained. It is possible to attach a label, precautions, etc. to this thin part, and it is also possible to obtain a product with metallic luster utilizing the magnesium alloy base by applying an appropriate coating process, It is widely expected to be suitable for use as a small and thin housing for the purpose of reducing the weight of various devices.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a main part of a rough forging die according to a manufacturing method of the present invention.

FIG. 2 is a schematic structural perspective view showing an example of a thin formed body made of a magnesium alloy according to the present invention.

FIG. 3 is a schematic view showing an AA cross section of FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thin molded body made of magnesium alloy 2 Bottom part 3 Peripheral wall part 4, 4 'boss (peripheral wall part) 5 Boss (corner part) 6 Thin part 11 Magnesium alloy thin plate material 12 Lower mold 13 Lower part of concave part (die) 14 Die Convex part 15 Upper die 17 Convex part (punch) of upper die 18, 18 'Depression of punch corresponding to boss part t Mold thickness w1 Thickness near peripheral wall at bottom w2 Thickness near center of bottom Thickness

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Watanabe 1-2-1 Shibaura, Minato-ku, Tokyo Within Hitachi Metals Co., Ltd. (72) Inventor Babao Hama 11 Kinuigaoka, Moka City, Tochigi Prefecture Hitachi Metals, Ltd. F-term in Shikisha Materials Research Laboratories (reference) 4E087 BA03 BA19 CA11 CB02 CB04 CB11 CB12 DA04 EC11 HA91

Claims (3)

[Claims] 1. A thin sheet material made of a magnesium alloy
By forging at a forging temperature of 00 to 540 ° C. and a forging speed of 10 to 500 mm / sec, the thin material is stretched at a rolling reduction of 75% or less to form a forged bottomed rough molded body having a peripheral wall portion. The rough forging step to be performed and the rough forged body obtained in the rough forging step are forged at a forging temperature of 200 to 540 ° C. for 1 to 2 times.
50% reduction while applying a molding load of 0 ton / cm ²
% In the finish forging process and the rough forging process and / or the finish forging process in which the forging process is performed so that the thickness near the center of the bottom of the molded body is smaller than the thickness near the peripheral wall.
A convex portion is provided at a central portion of a punch or / and a die, and a forging is performed such that a portion near a bottom center portion of the formed body is thinner than a bottom portion thickness near a peripheral wall portion. Production method. 2. A sheet material made of a magnesium alloy having a sheet thickness of 3 mm or less is treated at a temperature of 200 to 540 ° C. for 100 to 5 minutes.
Placed on a rough forging die held at 40 ° C,
While applying a molding load of 3 to 30 ton / cm ² , 10
A rough forging process of expanding a thin material at a reduction rate of 75% or less by forging at a forging speed of up to 500 mm / sec and forming it into a bottomed rough forged product having a peripheral wall portion, and a rough forging process. The obtained rough forged compact was placed at a temperature of 200 to 540 ° C. on a finish forging die heated and maintained at 100 to 540 ° C., and a load of 1 to ²⁰ ton / cm ² was applied thereto while applying a forming load of 1 to ²⁰ ton / cm ^2. In the forging process of performing a forging process at a forging speed of up to 200 mm / sec and a reduction rate of 50% or less, and in the rough forging process and / or the forging process, the thickness near the center of the bottom of the molded body is reduced in the vicinity of the peripheral wall. A protrusion is provided at the center of the punch or / and the die so as to be thinner than the thickness, and forging is performed such that the vicinity of the bottom center of the molded body is thinner than the bottom thickness near the peripheral wall. Magnesium alloy thin-walled Method of manufacturing the body. 3. A compact formed by forging a magnesium alloy sheet material, wherein the thickness of the main part is 1.5 mm or less, and the thickness near the center of the bottom of the compact is peripheral wall. A thin-walled product made of a magnesium alloy, which is thinner than a thickness of a bottom portion in the vicinity.