JP2003277899A - Magnesium alloy member and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a magnesium alloy having stable fine crystal grain structure and excellent formability by solving such problem as coarsening of crystal grains, obstruction to formability and increase of energy consumption and to provide a magnesium alloy member. <P>SOLUTION: After applying a solution-treatment to the magnesium alloy, in a first forging process, a pre-strain of not less than at least 0.4 is given in a temperature range of 250-400°C and thereafter, an ageing treatment is applied and successively, a secondary forging is performed at a necessary temperature of not higher than the forging temperature. In this way, the fine grains of magnesium compound after ageing-treatment are precipitated and the coarsening of the crystal grains is prevented during the heating process in the secondary forging process. Further, the formed product having about ≤10 μm average crystal grain diameter and the stable fine crystal grain structure of ≤5 μm average crystal grain diameter under a suitable condition with a fining action by forging, and the material excellent in formability for the following working process, can be obtained. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnesium alloy member used for automobile parts, railroad car parts, home electric appliance parts and the like.

[0002]

2. Description of the Related Art Magnesium alloy has a small specific gravity and a high specific strength, as well as excellent electromagnetic shielding and recyclability. However, it is being developed for various purposes such as AV equipment and parts of electronic equipment such as notebook computers. On the other hand, since a magnesium alloy is a kind of difficult-to-process material, a casting method such as a die casting method or a thixomolding method is generally used as a method for manufacturing a magnesium alloy member.

The die casting method has disadvantages such as handling a molten magnesium alloy having high chemical activity, and the thixomolding method has a narrow optimum molding temperature range. There are problems that many steps are required for post-processing for such defects and the yield is low.

In order to solve such problems, various plastic working methods such as forging, rolling and extrusion have been studied for magnesium alloys which are difficult to work, and the materials used for these plastic workings have been studied. As a general rule,
A material obtained by extruding a cast material is used.

[0005]

However, when a magnesium alloy member is formed by plastic working, for example, forging, it is difficult to work, so it is necessary to heat it to a required working temperature for each working. Yes, due to repeated heating and cooling, the crystal grains become coarse, and despite the forging process, the strength does not improve, and a large number of processes are required to finish the product into the required shape. Therefore, there is a problem that energy consumption increases. Further, there is a problem that the moldability is hindered by the segregation of the components existing in the material obtained by the above-mentioned extrusion processing.

In order to solve such a problem, Japanese Unexamined Patent Publication (Kokai) No. 6-248402 discloses a method of manufacturing a magnesium alloy member by forging, in which a rough forged material is cast, It is disclosed that a solution treatment is applied to the steel, a finishing work is performed by forging, and an aging treatment is performed after the finishing work. In this method, the solution treatment carried out before the forging process causes the magnesium compound existing in the structure to form a solid solution, so that there is an advantage that the component segregation is improved and the forgeability is improved. Compared to the conventional method of carrying out solution treatment after forging, it is only to the extent that coarsening of crystal grains can be prevented and stably maintains fine crystal grains in the hot or warm working region, thereby forming Properties and mechanical properties such as room temperature strength and ductility have not yet been improved.

Therefore, an object of the present invention is to solve the problems such as coarsening of crystal grains, obstruction of formability, increase of energy consumption, and the like, and a magnesium alloy having a stable fine crystal grain structure and excellent formability. And a magnesium alloy member obtained thereby.

[0008]

In order to solve the above problems, the present invention adopts the following configuration.

That is, a magnesium alloy member is subjected to a solution treatment process of a magnesium alloy material, a first forging process for giving a pre-strain, an aging treatment process after the forging process, and then a fine crystal grain. It was manufactured by a process consisting of a second forging process for making the material.

According to such a process, first, when a commercially available extruded material or the like is used as a material in the solution treatment step, the magnesium compound which is nonuniformly precipitated in the material is sufficiently dispersed in the structure. It is possible to form a solid solution to eliminate segregation of components.

Then, in the first forging step, the material is pre-strained in a required manner, and by the aging treatment of the next step, fine particles of a magnesium compound having a spherical shape or a small aspect ratio are precipitated to homogenize the structure. Can be converted. Then, the precipitated fine particles prevent the growth of crystal grains in the heating process of the material to the processing temperature in the second forging process step, and the crystal grain refining action by the processing stabilizes the fine grain structure. To produce the desired shape of the finished molded article, or 2
It can be formed into a material for subsequent processing.

In the first forging step,
It is desirable that the processing temperature is in the temperature range of 250 ° C. to 400 ° C. and the pre-strain is 0.4 or more in true strain.

In the first forging step, if the processing temperature exceeds 400 ° C., the effect of prestrain is lost, and the structure after solution treatment is likely to become coarse, and the forgeability is poor. And the life of the mold is shortened, and the heating energy consumption is increased, which is not preferable. On the other hand, when the processing temperature is lower than 250 ° C., the deformation resistance of the material to be processed increases and the processing load increases too much, which is not preferable.

If the pre-strain is less than 0.4 in these working temperature regions, the introduction of the working strain into the material to be worked becomes insufficient, and in the subsequent aging treatment step, the spherical shape or the aspect ratio becomes small. It becomes difficult to deposit fine particles of the magnesium compound.

Further, in the aging step, it is desirable to deposit fine particles having an average particle size in the range of 5 nm to 100 nm with an average distribution interval of 5 nm to 200 nm.

By thus precipitating fine particles of the magnesium compound, as described above, the structure of the compact obtained in the second forging step following the preaging step has an average crystal grain size of 10 μm or less. It becomes possible to obtain a stable fine grain structure.

In the second forging step, it is desirable that the processing temperature is equal to or lower than the processing temperature in the first forging step, and the strain rate is 10 ^-1 s ^-1 or less.

As described above, if the working temperature in the second forging step is set not to exceed the working temperature in the first forging step, the fine particles of the magnesium compound precipitated in the aging step will work. , The coarsening of crystal grains is prevented during the heating process to the processing temperature, and the strain rate is 10 ^-1.
If the processing speed is slowed down to s ^-1 or less, dynamic recrystallization occurs in the second forging step, and the average grain size becomes 10
Under suitable conditions, it is possible to realize a fine and stable structure in which the average crystal grain size is 5 μm or less and high-speed superplasticity is also exhibited.

It is also possible to finish-mold the molded body obtained in the second forging step in the third forging step.

As mentioned above, in the second forging step,
Since a material for the next processing step with a stable fine crystal grain structure can be obtained together with the finish molded product, the crystal grains do not coarsen during the heating process in the third forging processing step, and a magnesium alloy that is a difficult-to-process material. Moldability is improved, the processing load is also reduced, a finished molded product with a fine grain structure can be obtained without causing defects during processing, and mechanical properties such as strength and ductility can also be improved. Become. In addition, superplastic forging can be performed at a higher processing speed than in the past, and the workability can be significantly improved.

Further, in such a magnesium alloy having a fine grain structure, the dependency of the strain rate on the formability thereof becomes large, so that when the strain rate is 10 ^-1 s ^-1 or less, forging is performed. While the dynamic recrystallization occurs, the formability is improved, defects during processing can be prevented from occurring, and the processing load is reduced, which is an advantage in processing.

By using such a manufacturing method, the average crystal grain size of the molded body obtained by the second forging step is 0.2.
It is possible to manufacture a magnesium alloy member in the range of μm to 10 μm.

If the average crystal grain size of the molded body obtained in the second forging step is in the range of 0.2 μm to 10 μm, the molded body is used as a raw material in the next processing step. In this case, as described above, the formability of the magnesium alloy, which is a difficult-to-work material, is improved, and the forging load is also reduced. Within this grain size range, as the crystal grains become finer, a superplastic phenomenon appears, so the formability is greatly improved and the forging load is also greatly reduced.

Further, when the molded body is a finished molded product, the mechanical properties of the magnesium alloy largely depend on the crystal grain size. Therefore, such a fine grain structure makes it possible to improve the mechanical properties such as strength and ductility. Physical properties are improved.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying FIGS. 1 to 4.

FIG. 1 shows a flow of the manufacturing method of the present invention. An extruded material such as a commercially available magnesium alloy ZK60 (Mg-Zn-Zr type alloy) of a magnesium alloy member is used as a raw material, and this raw material is used as a material. After raising the temperature to a required temperature range around ℃ and maintaining this temperature range for about 2 hours, solution treatment is performed by water cooling or air cooling to dissolve the magnesium compound into the structure of the material, and then the first In the forging step, this material is reheated to a processing temperature range of 250 ° C. to 400 ° C. and the upset process gives a required prestrain of 0.4 or more. After the pre-strain-introduced molding material is usually heated to a required temperature range of 150 ° C. to 250 ° C. and held for a required time of 10 hours to 500 hours, the aging treatment is performed. , The second forging process step.

The extruded material of ZK60 has a diameter of 32 m.
After subjecting the material with m and height of 30 mm to the solution treatment described above, in the first forging step, the material is heated to 250 ° C., and the reduction rate at which the initial strain rate becomes about 10 ⁻² s ^−1. 0.
At 3 mm / s, the amount of prestrain, that is, the amount of compression is changed variously,
The material to which each pre-strain was given is
The aging treatment was performed by holding for 0 hour. Then, in the second forging step, the same processing temperature 250 as in the first forging step.
At 0 ° C., the initial strain rate is about 2 × 10 ⁻² s ^−1, and the working strain (ε ₂ =
-1.56) is given, and for the purpose of removing distortion, 250
Annealing treatment was performed in the range of 300 to 300 ° C. for 30 minutes. Table 1 shows the results of investigating the stability of crystal grains from the microstructure after the annealing treatment.

[0028]

[Table 1]

Here, the stability of the crystal grains is used as a scale for judging the adequacy of the pre-strain amount in the first forging process, and the second
After the annealing treatment performed after the forging step, is marked with stability when coarse grain is not observed, and is marked with stability when coarse grain is observed, with x, When coarsened crystal grains are observed in a part, each is indicated by a triangle.

From Table 1, the stability of crystal grains is affected by the annealing temperature in addition to the amount of pre-strain when the processing temperature is kept constant at 250 ° C. in the first processing step, and the annealing temperature is 250. When the temperature is as low as 0 ° C., the stability of the crystal grains is good due to the precipitation of the magnesium compound by the above-mentioned aging treatment without prestraining. However, when the annealing temperature rises to 275 ° C., it is necessary to introduce a prestrain in order to stabilize the crystal grains. At this annealing temperature, if the prestrain amount is 0.4 or more, coarsening is surely performed. It is prevented and the crystal grains are stable.
When the pre-strain is in the range of 0.4 or more, as shown in FIG. 2, no coarsening of crystal grains is observed, the stability is good, and a stable fine crystal grain structure having an average crystal grain of 10 μm or less is obtained. It is kept. This is because when the pre-strain introduced into the material becomes larger than 0.4, magnesium compounds such as MgZn are about 10 after the aging treatment as shown in FIG.
Since fine particles of 0 nm or less are deposited, the pinning effect of these fine particles suppresses the growth of crystal grains. On the other hand, if the annealing temperature rises to 300 ° C, the crystal grains will not be stable no matter how much prestrain is applied.

Processing temperature in the first forging step 25
0 ° C. corresponds to a practical lower limit temperature in terms of forging load and die load, and a working temperature higher than 250 ° C. is usually adopted. As for the pre-strain, if the pre-strain is the same, the effect of introducing the pre-strain becomes smaller as the processing temperature becomes higher.
Higher processing temperature is adopted, and accordingly, 250 ℃
If a higher annealing temperature is adopted, the amount of prestrain for stabilizing the crystal grains is at least 0 shown in Table 1 when the annealing temperature is 275 ° C. .4 or more is required. This is because, in a practical heat treatment temperature, if the annealing temperature is set to be higher than 250 ° C., it is necessary to consider a temperature range of about 25 ° C. from the viewpoint of setting accuracy and the like.

Although the annealing temperature differs to some extent among magnesium alloys depending on the alloy system,
Regarding the amount of prestrain, there is no great difference depending on the alloy system in terms of the effect of introduction on the fine precipitation of the magnesium compound.

In the second forging step, the forming material into which the prestrain of 0.4 or more is introduced in the first forging step is the first forging step in the temperature range of 250 ° C to 400 ° C. It is heated to a temperature that does not exceed the processing temperature in the process,
By a molding machine that is loaded into a heated mold and the pressurization speed is set so that the average strain rate in the cross section of the work material is about 10 ^-2 s ^-1 or less. A molded product having a desired shape or a raw material for the next processing step is molded. And, if necessary, these molded products and materials for the next processing step should be heated at 250 to 300 ° C.
Is heated for a required time and annealed.

FIG. 4 shows a cylindrical material of ZK60 alloy,
After holding at 0 ° C for 2 hours, cooling with water and solution treatment,
Processing temperature is 275 ℃, initial strain rate is 0.5 × 10 ^-2 s ^-1
To give a pre-strain ε ₁ = -1.1 by a molding machine with a processing speed set so that the material is held at 180 ° C for 500 hours for aging treatment. In addition, the processing temperature is 275 ℃, the initial strain rate is 1.6 × 10 ^-2 s.
^-1 shows the gear 1 which is closed forged.

As shown in FIG. 4, the action of the fine particles of the magnesium compound deposited in the aging treatment step prevents the coarsening of the crystal grains during the heating process to the processing temperature, and further, the second forging. Since the crystal grains are miniaturized in the processing step, the workability becomes good, and a gear molded product in which the tooth tips 2 are completely filled in the mold without producing defects in the material to be processed can be obtained.

In this second forging step, instead of finishing into a molded product such as the gear, it is possible to form a forming material such as a preform for use in the third forging step. Since the stable fine crystal grain structure as described above is also generated in such a forming material, the formability in the next step is improved, the forging load is reduced, and in addition, it is higher than before. It is also possible to perform superplastic forging at a processing speed and achieve a significant improvement in workability.

The above magnesium alloy member manufacturing method is not limited to Mg-Zn-Zr-based alloys such as ZK60, but Mg-Al-Zn-based alloys such as AZ61A and Mg-.
It can be applied to other alloys such as Mn-based alloys, and in general, Al, Mn, which is a solid solution element necessary for obtaining standard mechanical properties, and stabilization of crystal grains at high temperatures as pinning particles. It is desirable to use an alloy system containing high melting point elements Mn and Zr, which have an effect on the above. In the second forging process step, a stable fine crystal grain structure is generated due to, for example, a refining action due to processing and dynamic recrystallization. In addition, Ce,
It is also applicable to alloy systems containing rare earth elements such as Y and Th that improve heat resistance.

[0038]

As described above, according to the present invention, the magnesium alloy material is subjected to the solution heat treatment, and then subjected to an aging treatment by giving a required pre-strain, and after this aging treatment, a plastic working such as a forging work Since the magnesium alloy member is manufactured, the introduction of this pre-strain makes it possible to obtain a homogenized structure in which fine particles of a magnesium compound of about 100 nm or less are precipitated in the aging treatment step. As a result, in the subsequent forging step, the growth of crystal grains is suppressed, and due to the refining effect due to processing and dynamic recrystallization, the average crystal grain size is 5 μm or less under suitable conditions of about 10 μm or less.
It is possible to obtain a material for secondary processing having a stable fine crystal grain structure that also expresses high-speed superplasticity of m or less and having improved formability, and a finished formed product having improved mechanical properties such as strength and ductility. it can.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a flow of a manufacturing method according to an embodiment of the present invention.

FIG. 2 is a micrograph showing a fine grain structure after a second forging step in the manufacturing method of the embodiment.

FIG. 3 is a TEM photograph showing the precipitation state of fine particles after aging treatment in the manufacturing method of the embodiment.

FIG. 4 is a front view of a gear formed in the second forging step described above.

[Explanation of symbols]

1 gear 2 addendum

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C22F 1/00 673 C22F 1/00 673 683 683 683 691 691B 691C 694 694A 694B (72) Inventor Kitagawa Makoto Osaka 1-12-19 Kitahorie, Nishi-ku, Tokyo, Kurimoto Iron Works Co., Ltd. (72) Inventor Yoshisada Dora 12-1, 19 Kitahorie, Nishi-ku, Osaka (72) Inventor Keiichi Maekawa 1-12-19 Kitahorie, Nishi-ku, Osaka-shi Kurimoto Iron Works Co., Ltd. (72) Inventor Toshihiko Adachi 1-27-6 Taishibashi, Asahi-ku, Osaka-shi Meishin Stock Company (72) Inventor Kenji Higashi Osaka 3-4-9 Teraikedai, Tomitabayashi-shi, F term (reference) 4E087 BA03 CB02 DA02 GA02

Claims (6)

[Claims] 1. A solution treatment step of a magnesium alloy material, a first forging step for giving a prestrain, an aging treatment step after the forging step, and then a first step for refining crystal grains. 2. A method for manufacturing a magnesium alloy member, which comprises the forging step of 2. 2. The magnesium alloy member according to claim 1, wherein in the first forging step, the processing temperature is in the temperature range of 250 ° C. to 400 ° C. and the pre-strain is 0.4 or more in true strain. Production method. 3. The method for producing a magnesium alloy member according to claim 1, wherein in the aging treatment step, fine particles having an average particle size in the range of 5 nm to 100 nm are precipitated with an average distribution interval of 5 nm to 200 nm. . 4. In the second forging step, the processing temperature is equal to or lower than the processing temperature in the first forging step,
The method for producing a magnesium alloy member according to claim ¹ , wherein the strain rate is 10 ^-1 s ^-1 or less. 5. The magnesium alloy member according to claim 1, wherein the formed body obtained in the second forging step after the aging treatment is finish-formed in the third forging step. Production method. 6. A magnesium alloy member having an average crystal grain size of 0.2 μm to 10 μm in a molded body obtained by the second forging step in the manufacturing method according to claim 1.