JP2011121118A - Method and equipment for multidirectional forging of difficult-to-work metallic material, and metallic material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for multidirectional forging which can introduce a large quantity of strain into a difficult-to-work metallic material in a more appropriate and simple process applicable in an industrial-level, in comparison with the conventional multidirectional forging process under decreasing temperature conditions. <P>SOLUTION: The invented method for multidirectional forging of the difficult-to-work metallic material comprises a step (a) of preparing a workpiece consisting of the difficult-to-work metallic material and a step (b) of sequentially performing one or more cycles of forging the workpiece in three directions which are at right angles to one another. The step (b) is performed so that the quantity of strain introduced in each cycle of forging becomes in a range between 0.01 and 0.2 under the temperature environment of 100°C or lower. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for forging a hard-to-work metal material, and more particularly to a multi-axis forging method for a hard-to-work metal material.

  Until now, it is known that cracks and defects are easily generated when a general processing process such as a rolling process or a forging process is applied to a difficult-to-process metal material such as a magnesium alloy. Therefore, it is difficult to expect a large strength improvement effect by work hardening treatment for difficult-to-work metal materials, and therefore, the application field of difficult-to-work metal materials is limited to specific fields where strength is not considered as important. This is the current situation. For example, although a magnesium alloy has a specific strength exceeding that of an aluminum alloy, its application field is limited to some limited uses such as parts for small electronic devices.

  In order to deal with such a problem, a forging method called a temperature-decreasing multi-axis forging process has recently been proposed (for example, Patent Document 1).

JP 2007-291488 A

  In the above-described temperature-decreasing multi-axis forging method, by changing the forging direction for each pass of forging and lowering the temperature of the workpiece, a large amount of strain can be finally introduced into the workpiece. . Therefore, when the temperature-decreasing multi-axis forging process is applied to a workpiece made of a difficult-to-work metal material, it is expected that the crystal grains can be refined and the strength can be improved.

  However, in such a temperature-decreasing multi-axis forging treatment method, there are various conditions to be controlled during machining, such as the temperature of the workpiece, the amount of strain introduced at each forging pass, and the operation is complicated and difficult. There is. In addition, there is a problem that a high-temperature electric furnace capable of adjusting the temperature of the atmosphere with high accuracy is required during processing. Therefore, the temperature-decreasing multi-axis forging method is not suitable for application at an industrial level, which requires mass production of products and cost reduction.

  The present invention has been made in view of such a background, and in the present invention, compared with the conventional temperature-decreasing multi-axis forging treatment method, it is a difficult-to-work material with a simpler process suitable for application at an industrial level. An object is to provide a processing method capable of introducing a large amount of strain. Moreover, it aims at providing the apparatus for implementing such a method.

In the present invention, a multi-axis forging process of a difficult-to-work metal material,
(A) preparing a workpiece made of a difficult-to-work metal material;
(B) carrying out a process of sequentially forging the workpiece along three forging directions orthogonal to each other for at least one cycle;
Have
The step (b) is performed in a temperature environment of a maximum of 100 ° C. or less so that the amount of strain introduced by each forging is in the range of 0.01 to 0.2. Provided.

  Here, in the method according to the present invention, the step (b) may be performed in a room temperature environment.

  In the method according to the present invention, the step (b) may be performed for 2 to 40 cycles.

In the method according to the present invention, in the step (b), one forging may be performed at a strain rate in the range of 3 × 10 ⁻³ / sec to 10 / sec.

  In the method according to the present invention, the step (b) may be repeated until a total strain amount in a range of 0.5 to 6.4 is introduced into the workpiece.

  In the method according to the present invention, the difficult-to-work metal material may be a material selected from the group consisting of a magnesium alloy, a titanium alloy, and a copper alloy.

Moreover, the method according to the present invention further includes the step (b):
(C) A step of aging treatment of the workpiece may be included.

In this case, the aging process step is:
You may have the step which carries out the aging treatment of the said to-be-processed object in the temperature range of 373K-473K.

Further, in the present invention, an apparatus for multi-axis forging treatment of difficult-to-work metal material,
An apparatus capable of performing any of the foregoing methods is provided.

Furthermore, in the present invention, a multi-axis forging apparatus for difficult-to-work metal material,
A stand for supporting a workpiece made of a difficult-to-work metal material;
Forging means for forging the workpiece along one forging direction;
A workpiece orientation control means capable of adjusting an orientation direction of the workpiece with respect to the forging means;
Have
The forging means introduces a strain amount in the range of 0.01 to 0.2 into the workpiece along the one forging direction by one forging in a temperature environment of 100 ° C. or less at maximum. There is provided an apparatus characterized in that

Here, in the apparatus according to the present invention, the one forging direction of the forging means is a vertical direction,
The workpiece orientation control means may operate such that a forged surface of the workpiece is an upper surface.

  In the apparatus according to the present invention, the workpiece orientation control means may be configured such that, after one forging, a contact surface of the workpiece with the platform becomes one of the side surfaces of the workpiece. The workpiece may be rotated such that one of the side surfaces of the body is a contact surface with the table.

Furthermore, in the present invention,
Within the organization
Including a plurality of first deformation twins extending in at least three different directions and having a width of 5 μm or less,
A metal material is provided in which a finer second deformation twin is formed in at least one of the first deformation twins.

  The present invention provides a processing method capable of introducing a large amount of strain into a difficult-to-work material by a simpler process more suitable for application at an industrial level than a conventional temperature-decreasing multi-axis forging method. Can do. An apparatus for carrying out such a method can also be provided.

It is the figure which showed schematically an example of the multi-axis forge processing method. It is an example of the flowchart of the method of carrying out the multi-axis forge process of the difficultly workable metal material by this invention. It is the figure which showed typically an example of the difficultly workable metal material structure | tissue obtained by the method by this invention. It is a TEM photograph of the structure of a magnesium alloy obtained by the method according to the present invention. It is the figure which showed typically an example of the apparatus for enforcing the method by this invention. It is the figure which showed typically each process at the time of forging a to-be-processed body using the apparatus for implementing the method by this invention. It is the figure which showed typically each process at the time of forging a to-be-processed body using the apparatus for implementing the method by this invention. It is the graph which showed the relationship between the accumulation distortion amount (SIGMA) epsilon and true stress (sigma) (MPa) in a magnesium alloy. It is the figure which showed the optical microscope photograph of the sample after each forge pass. It is the figure which showed the structure | tissue observation result of the magnesium alloy sample after four passes by the crystal orientation dispersion | distribution analyzer. It is the figure which showed the relationship between the number of forging passes, and the hardness of a sample. 4 is a graph showing the relationship between cumulative strain Σε and hardness in each sample. It is the graph which showed the relationship between the stress obtained by the tension test of sample A1 and A2, and distortion. It is the graph which showed the relationship between the stress obtained by the tension test of sample B1 and B2, and distortion. It is the graph which showed the relationship between the stress obtained by the tension test of samples C1 and C2, and distortion. It is the graph which showed the relationship between the stress obtained by the tensile test of samples D0-D3, and distortion.

  Generally, difficult-to-work materials such as magnesium alloys have poor workability, and it is known that cracks and defects are easily generated when general processing such as rolling or forging is performed. Therefore, in the case of a difficult-to-work metal material, there is a problem that it is difficult to introduce a large amount of strain by processing and it is difficult to expect a large strength improvement effect by work hardening treatment.

  For this reason, in recent years, a forging method called a temperature-decreasing multi-axis forging process has been proposed. In this method, the forging direction becomes the longitudinal direction for each pass of forging, that is, the forging direction is changed in the order of three directions orthogonal to each other (for example, the order of X direction → Y direction → Z direction). At the same time, the temperature of the workpiece is lowered. In this method, many strains can be finally introduced into the workpiece by repeating forging in three directions. Therefore, it is considered that when the temperature-decreasing multiaxial forging process is applied to a workpiece made of a difficult-to-work metal material, the crystal grains can be refined and the material strength can be improved.

  However, in such a temperature-decreasing multi-axis forging process, there are a variety of conditions that should be controlled during machining, such as the temperature of the workpiece, the amount of strain introduced at each forging pass, and the operation is complicated and difficult. is there. In addition, there is a problem that a high-temperature electric furnace capable of adjusting the temperature of the atmosphere with high accuracy is required during processing. Therefore, even if the temperature-decreasing multi-axis forging method can be applied at the laboratory level, it is not suitable for application at the industrial level, which requires mass production of products and cost reduction.

  On the other hand, the new method (the method of the present invention) discovered by the inventors of the present application has less processing conditions to be controlled and can be more easily implemented as will be described in detail below. Has characteristics. Further, since the method of the present invention can be carried out at a temperature near room temperature (at most 100 ° C. or less, for example, 50 ° C.), a high-temperature electric furnace is not necessary. Therefore, it is suitable for mass production and can be realized at low cost.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

The present invention is a method for multi-axis forging treatment of difficult-to-work metal material,
(A) preparing a workpiece made of a difficult-to-work metal material;
(B) carrying out a process of sequentially forging the workpiece along three forging directions orthogonal to each other for at least one cycle;
Have
The step (b) is performed in a temperature environment of a maximum of 100 ° C. or less so that the amount of strain introduced by each forging is in the range of 0.01 to 0.2. .

  The method according to the invention is based on a “multi-axis forging process”. Here, the “multi-axis forging process” means a processing method that repeats compression by changing the forging direction of the work material so that the longitudinal direction becomes the compression direction for each forging process in one direction. .

  FIG. 1 is a diagram schematically illustrating a multi-axis forging method. First, a rectangular workpiece (sample) 4 as shown in FIG. 1A is prepared. Next, the workpiece 4 is forged along the first direction (X-axis direction) (first pass).

  Next, as shown in FIG. 1 (2), the workpiece 4 is forged along the second direction (Y-axis direction) (second pass). Further, as shown in FIG. 1 (3), the workpiece 4 is forged along the third direction (Z-axis direction) (third pass). Through the three passes, the workpiece 4 substantially returns to the initial shape in appearance (FIG. 1 (4)).

  Here, the aspect ratio of the workpiece 4 is determined by the compression ratio by forging from the respective compression axis directions (X, Y, and Z directions) shown in FIGS. In other words, the aspect ratio of the workpiece 4 can be changed by the compression rate for each pass to be adopted. For example, in the example of FIG. 1, the aspect ratio of the workpiece 1 is 1.0 (Z direction): 1.49 (Y direction): 2.22 (X direction). This corresponds to the case where the processing strain amount ε introduced into the workpiece 4 is 0.8 in one pass. When the amount of processing strain for each forging is 0.01 to 0.2, this aspect ratio is not necessary, but a workpiece having this aspect ratio is used because it is easy to explain and understand later. Incidentally, when the processing strain for each forging is 0.1, the aspect ratio is 1.11: 1.10: 1.00.

  In such a “multi-axis forging process” method, a large amount of strain can be introduced into the workpiece 4 as a result by sequentially repeating the forging pass from each direction.

  However, as described above, the difficult-to-work material has poor workability. Therefore, when a large strain is introduced into the difficult-to-work material in one pass, cracks and defects are easily generated. Therefore, the present invention is characterized in that forging in each direction is performed with a reduced amount of distortion introduced in each forging (also referred to as one pass). Specifically, the amount of strain introduced in each forging (also referred to as one pass) is in the range of 0.01 to 0.2. Therefore, in the present invention, the amount of processing strain for each forging is small, and the forging direction does not necessarily have to be the longitudinal direction of the workpiece.

  Thereby, even if it is a difficultly workable metal material, it can avoid that a crack and / or a defect arise in a to-be-processed body after a multi-axis forge process. Further, since the processing strain for each forging is small, as a result, formation of texture by processing can be prevented, and deterioration of workability can be prevented.

  FIG. 2 schematically shows an example of the flow of the method according to the present invention. The method according to the present invention includes a step of preparing a workpiece made of a difficult-to-work metal material (S110), and a process of sequentially forging the workpiece along three forging directions orthogonal to each other. A step (S120) of performing more than one cycle. Further, the method according to the present invention may optionally further include a step (S130) of aging the workpiece subjected to the multi-axis forging process. Further, the step of multi-axis forging (S120) and the step of aging treatment (S130) may be repeated. In this case, the strength reduction due to recovery softening after aging can be compensated by work hardening.

  Hereinafter, each step will be described in detail.

(1. Step of preparing a workpiece)
First, a workpiece made of a difficult-to-work metal material is prepared.

  Here, the “difficult-to-work metal material” refers to metals and alloys having a breaking elongation of 40% or less in a tensile test at room temperature. The “difficult-to-work metal material” includes, for example, magnesium alloy, titanium alloy, copper alloy, iron alloy, zirconium alloy, molybdenum alloy, niobium alloy and the like.

  An example of the magnesium alloy is an AZ-based magnesium alloy (a magnesium alloy containing aluminum and zinc), a rare earth element-added magnesium alloy, a Ca-added magnesium alloy, or the like.

  An example of the titanium alloy is an aluminum-added titanium alloy, a tin-added titanium alloy, a vanadium-added titanium alloy, or the like.

  An example of a copper alloy is a copper-titanium alloy and a nickel-silicon-added copper alloy.

  An example of the iron alloy is steel containing a martensite phase.

  The average crystal grain size of the workpiece is not particularly limited. However, in order to obtain a material structure consisting of fine crystal grains after the multi-axis forging process, the larger the average crystal grain size, the more strain is introduced into the work body in the multi-axis forging process step. There is a need to.

(2. Forging process step)
Next, the aforementioned workpiece is sequentially forged along the X direction, the Y direction, and the Z direction (see FIG. 1).

  In the present invention, the multi-axis forging process is performed near room temperature (a temperature of 100 ° C. or less at the maximum). Therefore, equipment such as a high-temperature electric furnace required in the temperature-decreasing multi-axis forging process method is unnecessary, and a low-cost and simple forging method can be provided. Here, “temperature” mainly means the temperature on the environment side where the workpiece is exposed. This is because the temperature of the workpiece rises to some extent as a result of forging, and thus when the “temperature” is defined by the temperature of the workpiece, the value becomes ambiguous.

  Further, as described above, in one pass forging in each direction, the amount of strain introduced into the workpiece is in the range of 0.01 to 0.2. This value is significantly smaller than the typical strain amount introduced into the workpiece in one pass, that is, 0.6 to 0.8 in the temperature-decreasing multi-axis forging method. Thereby, even if it is a difficult-to-work metal material, it can avoid that a crack and / or a defect arise in a to-be-processed body after a multi-axis forge process.

  It should be noted that the amount of strain introduced in one forging pass depends on the material of the workpiece and the like accurately. For example, when the workpiece is a magnesium alloy, the amount of strain introduced in one forging pass is preferably about 0.1 to 0.2. However, in any difficult-to-work metal material, the strain amount is set to 0.2 or less at the maximum. This is because if a strain amount exceeding this is added at once, the possibility of cracking after forging increases.

  Further, the total strain amount (Σε) introduced into the workpiece by the multi-axis forging process is preferably about 1.0 to 40, although it depends on the material constituting the workpiece.

In the present invention, the strain rate in each path is usually in the range of 3 × 10 ⁻³ / sec to 10 / sec. This strain rate may be substantially constant in each pass.

  In addition, when one forging in each forging direction of X, Y and Z is defined as one cycle, the number of cycles is preferably 1 cycle or more, more preferably in the range of 2 to 40 cycles. preferable. Here, it will be clear that the number of cycles is not limited to an integer. That is, the number of cycles may be an integer + 1/3 or an integer + 2/3, and these numbers of cycles are respectively in the X direction forging in the X direction → Y direction → Z direction → ... This means the case where the forging is completed and the case where the forging is completed in the Y direction. Further, the forging direction may be changed in the middle of the X direction → Z direction → Y direction depending on the state and shape of the workpiece.

(3. Aging step)
Next, if necessary, an aging treatment may be further performed on the workpiece. Although the temperature of an aging treatment is not restricted to this, For example, it is the range of 373K-473K. Moreover, the time of an aging treatment is not limited to this, For example, it is the range of several minutes-several hours. The aging treatment may be performed in an oil bath, for example.

  Through the above steps, a workpiece made of a difficult-to-work metal material into which a large amount of strain is introduced can be obtained.

  The structure of the difficult-to-work metal material obtained by such a method has many primary deformation twins extending in at least three different directions and having a width of 5 μm or less when observed with a TEM (transmission electron microscope). In addition, a finer secondary deformation twin is formed in at least one of the primary deformation twins.

  Here, the deformation twin means a region having a different orientation having the same crystal structure as the parent phase formed by shear deformation parallel to a certain surface. The “width” of the primary deformation twin means the shorter length of the longitudinal and horizontal dimensions of the primary deformation twin. This “width” is particularly preferably 1 μm or less. On the other hand, the longer length of the primary deformation twin, that is, the total length is not particularly limited, but is, for example, in the range of 0.1 μm to several hundred μm, which depends on the crystal grain size before deformation. . The total length and width of the secondary deformation twin are not particularly limited, but in the normal case, the total length is in the range of about 0.2 μm to about several hundred μm, and the width is about 0.1 μm to about 50 μm. Range.

  Further, “including many deformation twins” means that at least 5 or more deformation twins are observed in the structure in one field of view (magnification: 5000 to 10,000 times) during TEM observation. To do. In general, at least 10 deformation twins are often observed.

  FIG. 3 schematically shows an example of a hard-to-work metal material structure obtained by the method according to the present invention. This figure was obtained at a magnification of 10,000 times using a TEM apparatus.

  As shown in FIG. 3, a number of primary deformation twins 210 are observed in the structure 200. It can also be seen that at least one of the primary deformation twins 210 has a secondary deformation twin 220 formed therein. For example, in the example of FIG. 3, a plurality of (n + 1) -order higher-order deformation twins 220A are formed inside the n-th order (where n is 1 or more) deformation twins 210A, and the n-th order deformation twins 210B. A plurality of (n + 1) -order high-order deformation twins 220B are formed inside, and a plurality of (n + 1) -order deformation twins 220C are formed inside the n-order deformation twins 210C.

  In FIG. 4, an example of the TEM photograph (magnification 10,000 times) of the actual structure of the magnesium alloy after the multi-axis forging process is shown. This magnesium alloy was obtained after a multi-axis forging process at room temperature for a total of 20 passes (cycle number 6 + 2/3 times). The strain amount ε introduced in one pass is 0.1.

  As is apparent from this structural photograph, the structure of the magnesium alloy prepared by the method according to the present invention has many primary deformation twins, which extend in at least three directions. ing. It is also confirmed that secondary deformation twins are formed in some primary deformation twins. As can be seen from FIG. 10, the primary deformation twins are very large. Therefore, it can be understood that the fine deformation twins in the TEM photograph of FIG. 4 are due to the development of higher-order twin deformations formed in the deformation twins.

  As described above, in the difficult-to-work metal material processed by the method according to the present invention, the crystal grains are refined to form a large number of primary deformation twins and secondary deformation twins. Characteristics can be improved.

(Device according to the invention)
Next, an apparatus for performing the method according to the present invention will be described.

An apparatus for carrying out the method according to the invention comprises at least:
A stand for supporting the workpiece;
Forging means for forging the workpiece along at least one forging direction;
A workpiece orientation control means capable of adjusting an orientation direction of the workpiece with respect to the forging means;
Have

  However, when the forging means can forge the workpiece along each of three mutually perpendicular directions (X direction, Y direction and Z direction), the workpiece orientation control means is not necessary. It is.

  FIG. 5 schematically shows an example of an apparatus for carrying out such a method according to the present invention. The apparatus 100 includes a table 120 that supports the workpiece 110, a forging means 130 that forges the workpiece 110 along one forging direction (Z direction in the example in the figure), and the workpiece 110. It has a workpiece orientation control means 140 capable of adjusting the orientation direction with respect to the forging means 130.

  The forging means 130 operates so as to introduce a strain of 0.01 to 0.2 to the workpiece 110 in one pass in the Z direction of FIG.

  Further, the workpiece orientation control means 140 has a plate-like member having 16 sections 141A to 141P of 4 rows × 4 columns in the X direction and the Y direction in the example of this drawing. The workpiece orientation control means 140 is embedded in the table 120.

  In the normal case, the apparatus 100 further includes a fixing member or the like that prevents displacement of the workpiece 110 when the workpiece 110 is forged. Such a member is unique to the present invention. Since it is not a thing, the description is abbreviate | omitted here.

  Next, the operation of such an apparatus 100 will be described. FIG. 6 and FIG. 7 are diagrams schematically showing each step when the multi-axis forging method according to the present invention is applied to the workpiece 110 using the apparatus 100.

  First, as shown in FIG. 6A, forging (first pass) of the workpiece 110 is performed by the forging means 130 along the Z direction of FIG. At this stage, the bottom surface 110 </ b> A of the workpiece 110 is in contact with the table 120 (more precisely, the workpiece orientation control means 140 embedded in the table 120). Thereby, the to-be-processed object 110 becomes a shape as shown in FIG.6 (b).

  Next, as shown in FIG. 6C, among the sections 141 of the workpiece orientation control means 140 embedded in the table 120, a section 141 that contacts a part of the bottom surface 110 </ b> A of the workpiece 110 (for example, a section). 141F and 141G), and the section 141 (for example, sections 141E and 141H) at the same X coordinate ascend gradually along the Z direction.

  Thereby, as shown in FIG.6 (d), the bottom face 110A of the to-be-processed object 110 is lifted in the state which made the point Q1 the rotation center. Finally, as shown in FIG. 6E, when the workpiece 110 is rotated 90 ° counterclockwise in the XZ plane, the initial bottom surface 110A of the workpiece 110 is a side surface 110A parallel to the YZ plane. It becomes. In addition, this time, the original side surface 110B of the workpiece 110 comes into contact with the table 120 (more precisely, the workpiece orientation control means 140 embedded in the table 120). Here, if necessary, the section 141 may rotate about the Y axis as a rotation axis, thereby rotating the workpiece.

  As shown in FIG. 6 (e), in this state, the forging means 130 forges (second pass) the workpiece 110 along the Z direction.

  Thereby, the to-be-processed object 110 becomes a shape as shown to Fig.7 (a). At this stage, the side surface 110B of the workpiece 110 (appears, the new bottom surface of the workpiece 110) is in contact with the table 120 (more precisely, the workpiece orientation control means 140 embedded in the table 120). Yes.

  Next, as shown in FIG. 7B, among the sections 141 of the workpiece orientation control means 140 embedded in the table 120, a section 141 that contacts a part of the side surface 110 </ b> B of the workpiece 110 (for example, a section). 141F and 141J), and the section 141 (for example, sections 141B and 141N) at the same Y coordinate ascend slowly in the Z direction.

  Thereby, as shown in FIG.7 (c), the side surface 110B of the to-be-processed object 110 is lifted in the state which made the point Q2 the rotation center. Finally, as shown in FIG. 7D, when the workpiece 110 is rotated 90 ° clockwise in the YZ plane, the side surface 110B of the workpiece 110 becomes a new side surface 110B parallel to the XZ plane. Become. Also, this time, the side surface 110C parallel to the XZ plane of the workpiece 110 comes into contact with the table 120 (more precisely, the workpiece orientation control means 140 embedded in the table 120). Here, if necessary, the section 141 may rotate about the X axis as a rotation axis, thereby rotating the workpiece.

  As shown in FIG. 7D, in this state, the forging means 130 forges the workpiece 110 (third pass) along the Z direction.

  By repeating the above steps, the multi-axis forging method according to the present invention can be performed on the workpiece 110 by the apparatus 100.

  Note that the apparatus shown in FIG. 5 and the steps shown in FIGS. 6 and 7 are examples, and the method according to the present invention is applied to the workpiece 110 by another apparatus and another process. It will be clear that this may be implemented.

  Examples of the present invention will be described below.

Example 1
An AZ-based magnesium alloy material (Osaka Fuji Industrial Co., Ltd .: AZ61) having the composition shown in Table 1 was prepared. The dimensions of the alloy material are 20 mm long (X direction) × 20 mm wide (Y direction) × 20 mm high (Z direction). The average crystal grain size was about 62 μm.

Next, the multi-axis forging process was implemented using this alloy material. First, the alloy material was forged at the room temperature (300 K) along the first direction (X direction) of the alloy material (first pass). The strain amount ε introduced by the first pass was set to 0.1. Next, the alloy material was forged along the second direction (Y direction) of the alloy material (second pass). The strain amount ε introduced by the second pass was set to 0.1. Next, the alloy material was forged along the third direction (Z direction) of the alloy material (third pass). The strain amount ε introduced by the third pass was set to 0.1. The above cycle was defined as one cycle, and the alloy material was forged for a maximum of 13 cycles (the total number of passes was 39). Through the above multi-axis forging process, a maximum cumulative strain of 3.9 was introduced into the alloy material. In each pass, the strain rate was 3 × 10 ⁻³ / sec.

  FIG. 8 shows the relationship between the cumulative strain amount Σε and the true stress σ (MPa) up to 38 passes.

  Next, an alloy material sample with 4 passes (cycle number 1 + 1/3) (total strain amount 0.4) and an alloy material sample with 38 passes (cycle number 12 + 2/3) (total strain amount 3) 8) was used to observe the structure after the multi-axis forging process.

  In FIG. 9, the photograph of the optical microscope of each sample is shown. In the figure, (a) shows the structure before forging. Also, (b) and (c) show the tissue in the samples with 4 and 38 passes, respectively.

  In the comparison between (a) and (b) in FIG. 9, no macroscopic difference is observed between the tissues, but in (c) in FIG. 9, the crystal is so fine that it is difficult to discriminate the crystal grain size. I understand that. FIG. 10 shows the result of observing the structure of a sample with four passes using a crystal orientation dispersion analyzer. From this figure, a large number of deformation twins are formed in the structure (gray linear structure extending diagonally in the upper right), and the crystal grains due to the kink band (black linear part in the center) It turns out that the division has occurred. Therefore, microscopically, it can be said that even in the sample with four passes, a large structural change occurs compared to the sample before forging. That is, by applying the present invention to an Mg alloy that is one of difficult-to-process materials, it has become possible to perform a large strain processing at room temperature. As a result, the crystal grains were refined by the action of the grain refinement mechanism such as deformation twins.

  FIG. 11 shows the relationship between the cumulative strain amount Σε and the hardness Hv of the sample. From this result, it is understood that the hardness tends to increase as the cumulative strain amount Σε, that is, the number of forging passes is increased. In particular, when the forging pass number approaches 40 and the cumulative strain amount Σε approaches 4, the hardness of the alloy material is expected to reach an extremely high value of 1200 MPa, which is unusual for a magnesium alloy.

(Example 2)
Next, various samples were prepared by the following method, and the material characteristics of the magnesium alloy material were evaluated.

(Sample A group)
First, a multi-axis forging process was performed on the magnesium alloy material by the same method as in Example 1 described above to prepare a number of samples having different numbers of passes, that is, cumulative strain Σε (hereinafter referred to as Sample A group). ). Through the multi-axis forging process, a maximum cumulative strain Σε of 2.0 was introduced into the magnesium alloy material. In particular, a magnesium alloy material having a cumulative strain Σε of 1.0 is referred to as sample A1, and a magnesium alloy material having a cumulative strain Σε of 2.0 is referred to as sample A2.

(Sample B group)
Sample A2 was subjected to an aging treatment at 403K for 1 hour. Furthermore, after the aging treatment, the multi-axis forging treatment was again performed on this sample. The second multi-axis forging process was performed under the same conditions as the first multi-axis forging process. Thus, a number of samples having different numbers of passes of the second multi-axis forging process, that is, cumulative strain Σε were prepared (hereinafter referred to as sample B group). In particular, a magnesium alloy material having a cumulative strain Σε of 0.2 in the second multi-axis forging process is referred to as sample B2. A magnesium alloy material that has not been subjected to the second multi-axis forging process is referred to as sample B1.

(Sample C group)
First, after performing an aging treatment, a number of samples with different cumulative strains Σε were prepared by performing a multi-axis forging treatment for each number of passes (hereinafter referred to as a sample group C). The condition of the aging treatment is 403K and 1 hour.

  Through the multi-axis forging process, a maximum cumulative strain Σε of 1.7 was introduced into the magnesium alloy material. In particular, a magnesium alloy material having a cumulative strain Σε of 0.5 is referred to as sample C1, a magnesium alloy material having a cumulative strain Σε of 1.0 is referred to as sample C2, and a magnesium alloy material having a cumulative strain Σε of 1.7 is referred to as C3. Called.

(Sample D group)
First, a multi-axis forging process was performed under the same conditions as in Sample A group, and a cumulative strain Σε of 1.0 was introduced. Next, this magnesium alloy material was aged. The condition of the aging treatment is 403K and 1 hour. Furthermore, a second multi-axis forging process was performed on the magnesium alloy material to prepare a number of samples having different cumulative strains Σε (hereinafter referred to as sample D group).

  In particular, a magnesium alloy material having a cumulative strain Σε of 0.4 in the second multi-axis forging process is referred to as sample D1, and a magnesium alloy material having a cumulative strain Σε of 0.8 in the second multi-axis forging process is sampled. A magnesium alloy material having a cumulative strain Σε of 1.0 in the second multi-axis forging process is referred to as sample D3. A magnesium alloy material that has not been subjected to the second multi-axis forging process is referred to as sample D0.

  FIG. 12 shows the relationship between cumulative strain Σε and hardness in each sample group.

  From this figure, it can be seen that the hardness is improved in each of the groups B to D subjected to the aging treatment as compared with the sample A group not subjected to the aging treatment.

  This is because (1) precipitates due to aging hinder the movement of dislocations, thereby improving the deformation resistance, and (2) the deformation resistance is increased and the movement of dislocations becomes more difficult. It is thought that many twins were generated.

Next, a tensile test was performed using each sample. The tensile test was performed at room temperature and a strain rate of 10 ⁻³ / sec.

  FIG. 13 shows the relationship between stress and strain obtained by the tensile test of samples A1 and A2. In the figure, for comparison, the results of the magnesium alloy material sample (A0) as it is annealed are shown at the same time.

  From this figure, it can be seen that the maximum stress and the yield stress are increased in the samples A1 and A2 compared to the sample A0 as it is annealed. This is due to an improvement in deformation resistance.

  FIG. 14 shows the relationship between stress and strain obtained by the tensile test of samples B1 and B2. As is clear from this figure, it can be seen that high maximum stress and yield stress are obtained in any of the samples. It can also be seen that the maximum strength is further improved by the multi-axis forging treatment after the aging treatment.

  FIG. 15 shows the relationship between stress and strain obtained by the tensile test of samples C1 and C2. In the figure, for comparison, the result of the magnesium alloy material sample (C0) as it was subjected to the aging treatment is also shown.

  From this figure, it can be seen that the maximum stress and the yield stress are increased in the samples C1 and C2 as compared with the sample C0 that is still in the aging treatment. It can also be seen that the maximum strength is further improved by increasing the number of passes in the second multi-axis forging process.

  FIG. 16 shows the relationship between stress and strain obtained by the tensile test of samples D0 to D3.

  From this result, it can be seen that high maximum stress and yield stress are obtained in any sample. It can also be seen that the maximum strength is further improved by increasing the number of passes in the second multi-axis forging process.

  Thus, it was confirmed that the material characteristics of the hard-to-work metal material such as magnesium alloy are improved by the method according to the present invention. Further, the total elongation is equal to or about half that of the annealing agent A0, and the elongation is not impaired by the giant strain processing. This is presumably because the amount of processing strain for each forging is small and the texture is difficult to form. In particular, when the aging treatment and the multiaxial forging treatment are combined, the material properties (maximum strength, yield stress, elongation, etc.) can be significantly improved with a small number of passes in the multiaxial forging treatment.

  As described above, it was confirmed that a large amount of strain was introduced into the difficult-to-work metal material by applying the multi-axis forging method according to the present invention. Moreover, it became clear by this that the crystal grain of a difficult-to-work metal material was refined | miniaturized and each characteristic of material improved significantly.

  The present invention can be applied to a method for processing difficult-to-work metal materials such as magnesium alloys.

4 Workpiece 100 Device 110 Workpiece 110A Original bottom 110B Original side 110C Original side 120 120 Forging means 140 Workpiece orientation control means 141 Section 200 Structure 210 (210A to 210C) n-order deformation twins ( N is 1 or more)
220 (220A to 220C) (n + 1) Deformation twin (where n is 1 or more)

Claims (13)

A multi-axis forging method for a difficult-to-work metal material,
(A) preparing a workpiece made of a difficult-to-work metal material;
(B) carrying out a process of sequentially forging the workpiece along three forging directions orthogonal to each other for at least one cycle;
Have
The step (b) is performed in a temperature environment of a maximum of 100 ° C. or less so that the amount of strain introduced in each forging is in the range of 0.01 to 0.2.   The method of claim 1, wherein step (b) is performed in a room temperature environment.   The method according to claim 1 or 2, wherein the step (b) is performed for 2 to 40 cycles. 4. The method according to claim 1, wherein in the step (b), one forging is performed at a strain rate in a range of 3 × 10 ⁻³ / sec to 10 / sec. 5. the method of.   The step (b) is repeated until a total strain amount in a range of 0.5 to 6.4 is introduced into the workpiece. the method of.   The method according to claim 1, wherein the hard-to-work metal material is a material selected from the group consisting of a magnesium alloy, a titanium alloy, and a copper alloy. Furthermore, after the step (b),
The method according to claim 1, further comprising: (c) aging the workpiece. The aging treatment step includes:
The method according to claim 7, further comprising the step of aging the workpiece in a temperature range of 373K to 473K. An apparatus for multi-axis forging of difficult-to-work metal materials,
Apparatus capable of performing the method according to any one of the preceding claims. An apparatus for multi-axis forging of difficult-to-work metal materials,
A stand for supporting a workpiece made of a difficult-to-work metal material;
Forging means for forging the workpiece along one forging direction;
A workpiece orientation control means capable of adjusting an orientation direction of the workpiece with respect to the forging means;
Have
The forging means introduces a strain amount in the range of 0.01 to 0.2 into the workpiece along the one forging direction by one forging in a temperature environment of 100 ° C. or less at maximum. A device characterized by being able to. The one forging direction of the forging means is a vertical direction,
The apparatus according to claim 10, wherein the workpiece orientation control means operates such that a forged surface of the workpiece is an upper surface.   In the workpiece orientation control means, after one forging, the contact surface of the workpiece with the platform becomes one of the side surfaces of the workpiece, and one of the side surfaces of the workpiece is the platform. The apparatus according to claim 11, wherein the workpiece is rotated so as to be a contact surface. Within the organization
Including a plurality of first deformation twins extending in at least three different directions and having a width of 5 μm or less,
A metal material, wherein a finer second deformation twin is formed in at least one of the first deformation twins.