JP2002371334A - Cold-workable Mg alloy material and method of manufacturing the same - Google Patents

Abstract

(57) [Summary] (with correction) [PROBLEMS] To provide a Mg alloy material capable of being cold worked and a method of manufacturing the same. The present invention provides a cold workable Mg alloy material having a recrystallized grain size of 20 μm or less.
For the alloy material, a solution treatment and an aging treatment are sequentially performed on a base metal of the Mg alloy, and then warm plastic working is performed at a temperature of 150 to 350 ° C., preferably further, nitrogen gas, argon gas,
Produced by quenching with helium gas or oil cooling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Mg alloy material and a method for producing the same, and more particularly, to an Mg alloy material which can be subjected to cold working such as drawing or cold forging at room temperature, and a method for producing the same. On how to do it.

[0002]

2. Description of the Related Art Since Mg alloys are lightweight and have electromagnetic wave shielding properties, their markets have recently been rapidly expanding as housing materials for electronic devices such as notebook computers and mobile phones. At present, as the Mg alloy, ASTM AZ91C, AZ91D, AZ91E, AZ92A, A
Z63A, AZ80, AM100A, ZK51A, ZK
Those having an alloy composition specified by 61A, EZ33A, QE22A, and ZE41A are commercially available. And they are usually manufactured by a casting method.

[0003] By the way, Mg alloy ingots produced by a casting method generally have poor spreadability and extrudability at room temperature, and it is practically impossible to perform plastic working accompanied by large deformation. This is because the grain size of the crystal grains generated in the casting metal is large. That is, since the crystal structure of the Mg alloy is hexagonal, its plastic deformation occurs not on the basis of intragranular slip but on the basis of intergranular slip. It is hard to happen.

In order to solve such a problem, 150 to 35
It is known that, for example, a front extrusion process is once performed on a casting metal in a temperature range of 0 ° C. When such a treatment is performed, coarse crystal grains in the cast structure are refined, thereby improving cold workability such as spreadability at room temperature and at the same time improving mechanical properties. However,
The above treatment has the following problems. That is, immediately after the above-described treatment, the refinement of the crystal grains is realized, but if this is left at room temperature, the grain growth of the fine crystal grains progresses, and the crystal grains become It is a problem that the material becomes coarse again and the cold workability decreases.

On the other hand, in the case of Mg alloy, precipitation strengthened alloy
To ensure its mechanical strength
Alloys have been designed to produce Accordingly
The cast metal is subjected to a solution treatment,
Aging treatment to produce the desired precipitate
After various treatments, they are often sold commercially. example
For example, in the case of AZ31, the above processing is performed after casting,
(Al, Zn) in the tissue _{twenty three}Mg₇Intermetallic compounds such as
Is commercially available.

In the case of such an Mg alloy, although the coarsening of crystal grains is suppressed by the function of the precipitate, in the first place,
Since the crystal grains at the time of casting are coarse, there is a problem that the cold workability is poor. As described above, in the case of an Mg alloy, it is extremely difficult to directly perform cold working on commercially available ingots to achieve large plastic deformation. It is necessary to perform some processing prior to this.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems in commercially available Mg alloys, and
It is an object of the present invention to provide a method of manufacturing an alloy into a Mg alloy material in a state where cold working such as wire drawing is possible, and to provide an Mg alloy material capable of such cold working.

[0008]

Means for Solving the Problems The present inventors paid attention to the following points in the course of research for achieving the above object. (1) Although the cold workability of a Mg alloy having fine crystal grains is improved, the fine crystal grains are coarsened with the passage of time, and as a result, the cold workability is reduced. .

(2) On the other hand, precipitates are formed in the structure of the Mg alloy, and the precipitates improve the alloy strength and exhibit the effect of pinning the grain boundaries in the crystal grains, thereby improving the crystal grain size. Functions as a suppressor of coarsening. (3) Therefore, in the case of the Mg alloy material in which the crystal grains are refined and the precipitates are uniformly dispersed and generated in the structure at the same time, the pinning effect at the grain boundaries of the fine crystal grains causes It is considered that the fine state is maintained, and as a result, the cold workability is improved.

[0010] Based on the above idea, the present inventors performed a process described below on a commercially available Mg alloy and measured the size of recrystallized grains in the obtained Mg alloy material. When the cold workability of the Mg alloy material was examined, it was found that the Mg alloy material described later can be cold worked, and the present invention was developed. That is, first, the Mg alloy material capable of being cold worked according to the present invention has a recrystallized grain of 20 μm.
It is characterized by the following.

Further, in the present invention, a method for producing a Mg alloy material, which comprises sequentially performing a solution treatment and an aging treatment on a Mg alloy base metal, and then performing a warm plastic working, A method for manufacturing a Mg alloy material that is rapidly quenched immediately after completion of the inter-plastic working is provided.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The Mg alloy material of the present invention is a material produced by subjecting a commercially available Mg alloy base metal to the processing described below. And this Mg alloy material
The recrystallized grains have a grain size of 20 μm or less, and have a structure in which precipitates are uniformly dispersed. Particle size 20μm
Larger ones have reduced cold workability, as well as reduced 0.2% proof stress, tensile strength, and mechanical properties such as elongation and draw.

In particular, M having a recrystallized grain size of 1 to 3 μm
The g-alloy material is suitable because it has good elongation and drawability, and therefore has cold workability such that cold wire drawing is possible. In addition, the particle size of the recrystallized grains here is,
It refers to a value defined by a counting method or a judgment method based on a crossed line segment (particle size) in five or more visual fields for the same sample.

Such an Mg alloy material can be manufactured as follows. First, commercially available Mg
Prepare an alloy. As the Mg alloy, for example, a metal immediately after casting may be used.
For example, a treatment such as forward extrusion may be performed in advance at a temperature of up to 350 ° C., and the type thereof is not limited.

This Mg alloy is composed of recrystallized grains having a certain grain size, and has a structure in which a predetermined amount of precipitates exist in the matrix. In the present invention, the Mg alloy is first subjected to a solution treatment. In this process, the entire amount of the precipitate in the starting material is dissolved in the parent phase. The solution temperature at this time is appropriately selected depending on the type of the precipitate, that is, the type of the Mg alloy, but is generally about 300 to 400 ° C. The solution treatment time must be at least the time required for dissolving the entire amount of the precipitate, and it depends on the type of the precipitate, but generally, 8 hours or more is sufficient.

Next, an aging treatment is performed. In this process, precipitates are formed, which are dispersed in the matrix. This precipitate improves the strength characteristics of the Mg alloy material to be produced, and at the same time, exhibits a pinning effect on recrystallized grains to suppress grain growth when left at room temperature after warm plastic working described later. Work. In consideration of the above-mentioned effects of the precipitate, it is preferable that the precipitate is fine and is in a state of being uniformly dispersed in the matrix.

In order to uniformly disperse the fine precipitates in the matrix, in the present invention, although it depends on the type of the Mg alloy, aging treatment is generally performed at a temperature of 150 to 250 ° C. and a treatment time of 1 to 4 hours. Is adopted. Finally, the material after the aging treatment is subjected to warm plastic working to produce a target Mg alloy material. Specifically, warm forging, warm drawing, warm extrusion, or warm rolling is performed.

In this process, the crystal grains in the structure, which had been in the state of aggregation of coarse recrystallized grains during casting, are refined, and the structure is converted into a texture of fine crystal grains as a whole. The fine precipitates precipitated in the previous step remain in a state of being uniformly dispersed in the texture of the fine crystal grains. When a material obtained by processing and refining crystal grains is left, for example, at room temperature, the crystal grains generally grow and the crystal grains become coarse.

However, the Mg obtained by the method of the present invention is
In the case of an alloy material, fine precipitates exhibiting a pinning effect are uniformly dispersed around the fine crystal grains in the texture of the fine crystal grains formed by the warm plastic working. Therefore, the growth of the individual fine crystal grains is suppressed by the function of the precipitate, and the coarsening of the fine crystal grains does not progress, and the entire structure is maintained in the state of the texture of the fine crystal grains. . As a result, this Mg alloy material exhibits cold workability and at the same time improves strength characteristics.

At this time, the particle size of the fine crystal grains is basically determined by the temperature and the working degree during the warm plastic working. In the present invention, it is necessary to set the particle size of the fine crystal grains to 20 μm or less by appropriately selecting the temperature and the workability. If the particle size is larger than 20 μm, the cold workability of the obtained Mg alloy material is reduced. In the case of AZ31, the preferred particle size is 1 to 3 μm.

For this purpose, although the temperature varies depending on the type of the Mg alloy, the temperature during warm plastic working is 150 to 30.
It is set to 0 ° C and the workability is equivalent to plastic strain of 0.3.
It is preferable to set the above. When the temperature is lower than 150 ° C., plastic working becomes difficult and cracks and chips are generated. If the temperature is higher than 300 ° C,
This is because grain growth during heating and after processing becomes remarkable.

Even when the working temperature is 150 to 300 ° C., if the working degree is less than 0.3, the recrystallized grains cannot be reduced to a grain size of 20 μm or less. In this way, the Mg alloy material of the present invention is manufactured.
It is preferable to quench immediately after warm working. This is because by performing the rapid cooling, it is possible to reliably prevent the growth of the formed fine crystal grains.

The means for quenching is not particularly limited, and may be water cooling or air cooling. For example, quenching by blowing an inert gas such as N ₂ gas, Ar gas or helium gas may be used. This is effective from the viewpoint of preventing corrosion of the Mg alloy material. Oil cooling may be applied.

[0024]

EXAMPLES (1) Production of Mg alloy material Various Mg alloys made of AZ31 and subjected to the following pretreatment were prepared as starting materials. Material 1: Cast metal.

Material 2: A material obtained by performing forward extrusion at a temperature of 350 ° C. on a cast metal. These materials were sequentially subjected to a solution treatment, an aging treatment, a warm plastic working, and a cooling under the following conditions in the manner shown in Table 1 to produce a Mg alloy material. The grain size (average value) of the recrystallized grains of the obtained Mg alloy material was measured.

[0026]

[Table 1]

For each of the seven Mg alloy materials, 0.2% proof stress,
Elongation and drawing were measured. The results are shown in Table 2 as average values.

[0028]

[Table 2]

The following is clear from Tables 1 and 2. 1) Material 1 which is a casting metal has a recrystallized grain size of 8
It is as large as 0 μm, and both elongation and drawing are small, and it is not possible to draw cold. 2) When Comparative Example 2 and Example 2 are compared, the starting materials are the same and the conditions of the warm plastic working are the same, but the grain size of the recrystallized grains of Comparative Example 2 is 22 μm, Further, since the drawing and the elongation are small, cold working is difficult. On the other hand, in the case of Example 2 in which the solution treatment and the aging treatment were performed prior to the warm plastic working, the grain size of the recrystallized grains was reduced to 3 μm, and accordingly, the respective characteristics were improved. And ready for cold working.

3) Comparing Example 1 and Example 2, the processing conditions up to cooling are the same for both. However, in the case of Example 1 in which quenching was performed immediately after warm plastic working, the drawing and elongation, particularly the drawing, were good. This shows the usefulness of performing quenching after warm plastic working. 4) Comparing Comparative Example 2, Example 1, Example 2, and Example 3, the elongation and drawing of Comparative Example 2 in which the recrystallized grain size is larger than 20 μm are small, and cold working is difficult.

On the other hand, the elongation and the drawing of each embodiment having a particle size of 20 μm or less are large. And it turns out that as a particle diameter becomes small, elongation and drawing become large, and cold workability improves.

[0032]

As apparent from the above description, the Mg alloy material of the present invention can be recrystallized by subjecting the starting Mg alloy to solution treatment, aging treatment, warm plastic working, and preferably rapid cooling. Since the particle size of the particles is 20 μm or less,
Elongation and drawing are improved, and cold working such as drawing at room temperature can be performed.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22F 1/00 625 C22F 1/00 625 630 630K 685 685A 691 691B 692 692A 694 694B 1/02 1/02

Claims (5)

[Claims] 1. A cold workable Mg alloy material having a recrystallized grain size of 20 μm or less. 2. A method for producing an Mg alloy material, comprising sequentially performing a solution treatment and an aging treatment on a Mg alloy base metal, and then performing warm plastic working. 3. The method for producing an Mg alloy material according to claim 2, wherein the quenching is performed immediately after the completion of the warm plastic working. 4. The warm plastic working is performed at a temperature of 150 to 35.
The method for producing a Mg alloy material according to claim 2, which is performed in a warm range of 0 ° C. 5. The quenching includes nitrogen gas, argon gas,
4. The method for producing a Mg alloy material according to claim 3, wherein the method is performed with helium gas or oil cooling.