JP2007291488A - Method and device for producing magnesium alloy material, and magnesium alloy material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a magnesium metallic material having high strength and easily subjected to refining. <P>SOLUTION: A metallic material stock made of an AZ61Mg alloy is subjected to temperature dropping multiaxis forging, so as to obtain a worked metallic material having a refined crystal structure. In this way, the magnesium alloy material having high strength, and also having satisfactory workability can be obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method and apparatus for producing a magnesium alloy material and a magnesium alloy material. In particular, an object of the present invention is to obtain a magnesium alloy material having high strength and good workability.

  Magnesium alloys are expected as lightweight and high-strength structural materials, but their practical application is delayed due to poor workability.

  Among them, for AZ31 magnesium alloy (referred to as AZ31Mg alloy), the crystal grains are submicron by performing multi-axis forging (MDF) while lowering the temperature for each pass during processing. A temperature-decreasing multi-axis forging method has been proposed which is controlled as follows and thereby tries to achieve both strength and workability simultaneously (see Patent Document 1).

Here, the AZ31Mg alloy contains magnesium (Mg), aluminum (Al) and zinc (Zn) in a mass ratio of about 3% and about 1%, respectively, and iron (Fe) or manganese as additive elements. A magnesium alloy containing a small amount of (Mn).
International Publication Number WO2004 / 085692A1

  However, when an AZ31Mg alloy is applied as a practical structural material, the specific strength is still low and the corrosion resistance is low, so a magnesium alloy having higher strength and higher corrosion resistance is required.

  There is AZ61 magnesium alloy (this is called AZ61Mg alloy) as a magnesium alloy having higher strength and higher corrosion resistance than AZ31Mg alloy. However, the workability is worse than AZ31Mg alloy, so the workability is improved. There has been little research on.

  Here, the AZ61Mg alloy contains magnesium (Mg) with aluminum (Al) and zinc (Zn) in a mass ratio of about 6% and 1%, respectively, and iron (Fe) or manganese ( Mn) and the like.

  The present invention has been made in consideration of the above points, and is intended to provide an AZ61Mg alloy material with improved workability so that it can be sufficiently applied as a practical structural material.

  In order to solve such a problem, in the present invention, magnesium is made of a magnesium alloy containing aluminum and zinc in a mass ratio of about 6% and 1%, respectively, and at least iron and manganese as additive elements. A processed metal material having a refined crystal structure is obtained by subjecting the material material to a temperature-decreasing multi-axis forging process.

  According to the present invention, a metal material made of a magnesium alloy containing aluminum and zinc in a mass ratio of about 6 [%] and about 1 [%] in magnesium and containing at least iron and manganese as additive elements is cooled. By obtaining a machined metal material having a refined crystal structure by multi-axis forging, a magnesium alloy material having high strength, high corrosion resistance and good workability can be realized.

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

(1) Overall Configuration In FIG. 1, reference numeral 1 denotes a metal material manufacturing system as a whole. In the crystal grain refinement processing apparatus 2, an AZ61Mg alloy bulk material is received as the metal material raw material 3 and The processed metal material 4 obtained by processing is commercialized in the processing unit 6 of the productizing apparatus 5 and then sent out as a practical structure product 7.

  As the metal material 3, for example, one of sample numbers 1 and 2 having components as shown in FIG. 2, for example, AZ61Mg alloy of sample number 1 is used.

  The crystal grain refinement processing apparatus 2 has four stages of refinement processing parts, that is, first to fourth stage refinement process parts 11A to 11D, and the first to fourth stage refinement process parts 11A to 11D. , Multi-axis forging for one pass is performed.

  In the multi-axis forging process, as shown in FIG. 3 (A), the dimensional ratio in the X-axis, Y-axis, and Z-axis directions is 2.22: 1.49: 1.0 for the metal material 8 to be processed. First, by applying a compressive force in the X-axis direction, the dimensional ratio in the X-axis, Y-axis, and Z-axis directions is 1.0: 2.22: 1.49, as shown in FIG. Next, as shown in FIG. 3C, the compression force is applied in the Y-axis direction so that the dimensional ratio in the X-axis, Y-axis, and Z-axis directions is 1.49: 1.0: 2.22. After that, as shown in FIG. 3A, a compressive force is applied in the Z-axis direction so that the dimensional ratio in the X-axis, Y-axis, and Z-axis directions is 2.22: 1.49: 1.0. .

  Thus, the multi-axis forging process for one cycle can be performed while rotating the processing axis of the metal material 8 to be processed, and one forging process in which a compressive force is sequentially applied in the X-axis, Y-axis, and Z-axis directions. This is called “pass”.

  In the case of the embodiment of FIG. 1, one pass for performing the processing shown in FIG. 3A, two passes for performing the processing shown in FIG. 3B, and three passes for performing the processing shown in FIG. 3A is performed in the first stage, the second stage, the third stage, and the fourth stage miniaturization processing unit 11A, 11B, 11C, and 11D in order, and then the four passes for performing the process shown in FIG. By performing the 5-pass compression process in which the process shown in (B) is performed again in the processing unit 6 of the productizing device 5, a strong compression process with a strain amount Δε = 0.8 is performed for each pass.

  The first-stage to fourth-stage refinement processing units 11 </ b> A to 11 </ b> D perform strong compression processing of the metal material 14 to be processed placed in the compression processing chamber 13 formed in the jig 12 with the compression processing tool 15.

  Before being put into the compression processing chamber 13, the metal material 14 to be processed is heated and kept in a heat-retaining furnace 16 so as to have a lowering processing temperature assigned to the first to fourth stage refinement processing portions 11 </ b> A to 11 </ b> D. .

  The heated metal material 14 to be processed is put into the compression processing chamber 13 from the heat insulation furnace 16 as indicated by an arrow a1, and the metal material 14 thus processed is compressed from the compression processing chamber 13 as indicated by an arrow a2. It is taken out and sent to the heat retaining furnace 16 of the next micronization processing section.

  In the case of this embodiment, the first-stage to fourth-stage refinement processing units 11A to 11D perform the true stress indicated by the curves K1, K2, K3, and K4 in FIG. 4 during the compression process from one pass to four passes. The compression processing temperature is set to 623 [K], 573 [K], 523 [K], and 503 [K] so that a cumulative strain curve can be obtained.

  In this way, the compression processing temperature when the metal material 14 to be processed is sequentially compressed from the first pass to the fourth pass from the first stage refinement processing unit 11A to the fourth stage refinement processing unit 11D is gradually lowered. However, by performing multi-axis forging (referred to as a temperature-decreasing multi-axis forging (MDF) method), the crystal of the AZ61Mg alloy which is the metal material 14 to be processed without causing cracks in the metal material 14 to be processed The grain is refined to about 1 [μm], and thereby the processed metal material 4 having high strength and good workability is sent out from the grain refinement processing apparatus 2.

  In the case of this embodiment, the processed metal material 4 obtained from the crystal grain refining processing apparatus 2 is subjected to the compression processing of the fifth pass in the processing unit 6 of the productizing apparatus 5, whereby the crystal grain It has an ultra-fine structure with a diameter of 1 [μm] or less, and is therefore sent out as a practical structural product 7 that is practically high in strength.

(2) Refinement processing result According to the above configuration, the processing temperature is sequentially set to 623 for each pass in the first, second, third, and fourth-stage refinement processing units 11A, 11B, 11C, and 11D. By performing multi-axis forging while lowering to [K], 573 [K], 523 [K], and 503 [K], as shown in FIG. Strain was accumulated in the metal material 14 to be processed, whereby the crystal grains could be easily refined.

  The development state of the fine structure in each pass was as shown in FIG.

  In the photomicrograph of the optical microscope in FIG. 5, when the average crystal grain size was measured by the linear crossing method, the metal material material 3 before multiaxial forging was 38.5 [μm] in a state where the cumulative strain amount was ε = 0. (FIG. 5A), the cumulative strain amount is ε = 1.6 in the second pass (FIG. 5B), and the cumulative strain amount ε = 3 in the fourth pass. 2 (FIG. 5C), it was confirmed that the crystal structure was refined to about 1 [μm].

  Thus, the crystal grain refining apparatus 2 can be made ultrafine from 38.5 [μm] to 1 [μm] with only 4 passes of processing without causing cracks. Thus, a processed metal material 4 having a crystal structure can be obtained, whereby a bulk material suitable for the purpose of commercializing a high-strength practical structural product can be supplied.

  In the commercialization apparatus 5 assuming that the processed metal material 4 as the bulk material is obtained as a practical structure product 7, as the fifth pass, the true strain is obtained at the processing temperature 503 [K] as shown by the curve K5 in FIG. As shown in FIG. 5D, the fine grain structure obtained as a result of the strong processing of 0.8 becomes an ultrafine grain that cannot be confirmed with an optical microscope in a state of cumulative strain ε = 4.0. I understood that.

  The practical structural product 7 having the fine grain structure of the fifth pass can be evaluated as having a much higher strength because the crystal grains are ultrafine.

(3) In the case of metal material materials having different components In the above-described embodiment, as a case where the AZ61Mg alloy of sample number 1 in FIG. As described above, when the temperature-decreasing multi-axis forging process was performed by the same grain refinement processing apparatus 2 using the AZ61Mg alloy of the sample number 2 which is slightly different from the sample number 1 as the metal material 3, the obtained processed metal As shown in FIG. 6, the material 4 was found to have a uniform ultrafine structure having an average crystal grain size of about 1 [μm].

  Thus, it was confirmed that even if the additive element as the metal material 3 is slightly different, the same refined structure can be obtained by the temperature-decreasing multiaxial forging method according to the above-described embodiment.

(4) Change of hardness According to the hardness test, the hardness generated in the metal material 14 to be processed while the crystal grain refining processing device 2 is performing the temperature-decreasing multi-axis forging is represented by a straight line K11 in FIG. As shown, it increases in proportion to the increase in cumulative strain ε.

  As a comparative example with respect to the hardness change curve K11, a change in hardness when the AZ31Mg alloy is subjected to temperature-decreasing multi-axis forging under the same conditions is indicated by a curve K12.

  In the case of the above-described embodiment, the hardness change curve K11 increases in proportion to the increase in the cumulative strain amount ε, increases to 1200 MPa in the fourth pass, and further increases in the fifth pass.

  This hardness change curve K11 has a higher rate of increase in hardness with an increase in the cumulative strain amount (and hence progress of crystal grain refinement) than the hardness change curve K12 of the AZ31Mg alloy as a comparative example. It can be seen that the strength is increased by 30 [%] or more with respect to the increase in the accumulated strain amount.

  Incidentally, conventionally, since AZ31Mg and AZ61Mg alloys have extremely low plastic workability at room temperature, processing and shaping are performed hot and warm. Forging can be expected to improve the strength, but it is only 20% or less (increase from about 500 [MPa] to about 600 [MPa]) in the case of AZ31Mg, for example.

  On the other hand, if the crystal grains are refined by a temperature-decreasing multiaxial forging method, as shown by a change curve K12 in FIG. 7 as a comparative example, the strength of the AZ31Mg alloy increases to about 850 [MPa]. The result 70% increases.

  Compared to the case of this AZ31Mg alloy, in the case of the above-described embodiment, when the crystal grains of the AZ61Mg alloy are ultrafinened by the temperature-decreasing multiaxial forging method, as shown by the change curve K11 in FIG. As a result, the strength is 60% higher than that of the ultrafine-grained AZ31Mg alloy.

  In FIG. 7, the slope of the straight line of the AZ61Mg alloy is larger, which indicates that the strength increase of the AZ61Mg alloy is more remarkable than that of the AZ31Mg alloy. Accordingly, the difference in strength becomes larger as the processing strain increases.

  As described above, the hardness of the processed metal material obtained by subjecting the AZ61Mg alloy to the temperature-lowering multiaxial forging is further increased as compared with the case of the AZ31Mg alloy.

(5) Thermal stability The processed metal material 4 obtained by the crystal grain refining apparatus 2 shown in FIG. 1 has thermal stability as shown in FIG.

  FIG. 8 shows an ultrafine-grained structure after annealing the processed metal material 4 in the fourth pass having a cumulative strain ε = 3.2 at 523 [K] for 15 minutes, Although the crystal grains refined to 1 [μm] are coarsened to 2.0 [μm], the grain coarsening accompanying annealing is extremely small.

  Further, as indicated by reference numeral K13 in FIG. 7, the decrease in hardness caused by this annealing was small, and it was confirmed that the decrease in strength was about 10%.

  These results indicate that the processed metal material 4 obtained as a result of the temperature-decreasing multiaxial forging of the AZ61Mg alloy is extremely excellent in thermal stability.

  On the other hand, the AZ31Mg alloy is easily coarsened even when annealed at a lower temperature, and the ultrafine-grained material obtained by high strain processing is thermally unstable. It has been known.

  From this point of view, the characteristics of the AZ61Mg refined material obtained by the temperature-decreasing multi-axis forging process according to the above-described embodiment are further improved.

(6) Tensile test FIG. 9 shows the result of a tensile test of the AZ61Mg alloy refined material that has been subjected to temperature-decreasing multi-axis forging according to the above-described embodiment, and the tensile axis was perpendicular to the final compression axis.

  This is a method in which the most stretch is not obtained because a (0001) bottom texture is formed on the compression surface.

Nevertheless, extremely high ductility is observed in the 2-pass material with strain rate of 8.3 × 10 ⁻³ [s ⁻¹ ] of 50% or more and the 4-pass material (cumulative strain amount ε = 3.2). (FIG. 9A).

In particular, as shown by symbol K21 in FIG. 9B, when processed at a strain rate of 8.3 × 10 ⁻⁴ [s ⁻¹ ], a tensile test temperature of a 4-pass material (cumulative strain ε = 3.2). At 473 [K], a superplastic elongation of about 300 [%] was obtained.

  It was confirmed that the elongation was about 1.5 [times] and the strength was about 20 [%] higher than the ultrafine-grained AZ31Mg material which was subjected to a tensile test under the same conditions as a comparative material.

  Accordingly, it was found that the ultrafine material obtained by compressing the AZ61Mg alloy by four passes including the result of increasing the cumulative strain in FIG. 4 has high workability and high strength.

  Furthermore, since the plastic workability after the temperature-decreasing multi-axis forging process is extremely high, the processed metal material obtained by the crystal grain refining apparatus 2 is obtained by performing ultra-fine grain processing by the temperature-decreasing multi-axis forging process. 4 shows that when the product 4 is commercialized by the productizing device 5, a rolling device 20 as shown in FIG. 10 as another embodiment can be used.

  The rolling device 20 rolls the workpiece 21 as indicated by an arrow b by passing the workpiece 21 between the two rolling rollers 23A, 23B and 24A, 24B by the guide roller 22.

  In the case of this embodiment, the rotation direction of the rolling rollers 23A, 23B and 24A, 24B is reversed as shown by the arrow c, so that the workpiece 21 is rolled by the rolling rollers 23A, 23B and 24A, as shown by the arrow d. 24B can be passed back and forth, thereby reducing the size of the rolling equipment.

(7) Machining temperature conditions For the temperature-decreasing multi-axis forging process described above with reference to FIG. 4, in order to confirm the proper machining temperature, each process from the machining start temperature (623 [K]) to the machining end temperature (503 [K]) When the processing temperature of the pass was changed by ± 20 [K], it was confirmed that the true stress-cumulative strain curve shown in FIG. 11 was obtained.

  Here, even when the processing temperature in each pass was changed within a range of ± 20 [K], strong processing could be realized without causing any cracks.

  It has been clarified that grain refinement occurs even if the multi-axis forging temperature in each pass is the same as the multi-axis forging temperature in the previous pass. The temperature is set below the multi-axis forging temperature in the pass.

  As shown in FIG. 12, the final refined structure after 4 passes in the result of this experiment is 4 passes (cumulative strain amount of 3 .times.) Even when the processing start temperature and the final processing temperature are different by 20 [K] respectively. The final crystal grain size obtained in 2) is about 1 [μm].

  The refined structure having a higher temperature of +20 [K] has a larger crystal grain size than that of the lower temperature of −20 [K], but the difference is slight.

  In the range of this experiment, it was confirmed that the temperature-falling multi-axis forging process was possible in the whole applied temperature range without cracking at all, and the crystal grains were easily refined.

  At the same time, the temperature-decreasing multi-axis forging process in the above-described embodiment can be confirmed to have a wide temperature range applicable to the AZ61Mg alloy, which is an improvement and practical application of the temperature-decreasing multi-axis forging process. It turned out to be a big advantage.

  Further, the processing temperature from the first pass to the fourth pass may be set between the curves K32 and K33 of ± 50 [K] around the set straight line K31 shown in FIG.

  In practice, an appropriate processing temperature may be set according to the particle size (that is, the initial particle size) of the metal material 3 before processing in the first pass.

(8) Other Embodiments FIG. 14 shows a metal material manufacturing system 31 according to another embodiment, which is the same as the case of the first to fourth stage refinement processing portions 11A to 11D of FIG. Further, the compression processing device 36 is formed so that the metal material 34 to be processed placed in the compression processing chamber 33 of the jig 32 is compressed by the compression processing tool 35 with the compression processing force indicated by the arrow P2.

  The compression processing apparatus 36 is provided with a pre-stage heat-retaining furnace 42 and a post-stage heat-retaining furnace 43, and a metal material processing material 41 made of an AZ61Mg alloy is placed in the pre-stage heat-retaining furnace 42 as a processing target metal material 34, and is kept at a predetermined processing temperature. Is done.

  At the time of processing in the first pass, the metal material 34 to be processed is kept at a predetermined processing temperature 623 [K] in the pre-stage heat-retaining furnace 42, and this is put into the compression processing chamber 33 as shown by an arrow a11 and passes through one pass. After the eye is subjected to compression processing, as shown by an arrow a <b> 12, it is held from the compression processing chamber 33 to the second-stage warming furnace 43.

  The post-stage heat insulation furnace 34 keeps the metal material 34 to be processed at the processing temperature 573 [K] in the second pass.

  Thus, when the first pass compression process is completed for all the work target metal materials 34 put in the pre-stage heat-retaining furnace 42, the work-target metal kept at the second-pass heat treatment furnace 43 at the work temperature 573 [K] in the second pass. The material 34 is put into the compression processing chamber 33 and compressed as shown by an arrow a13, and then taken out from the compression processing chamber 33 to the pre-stage heat-retaining furnace 42 as shown by an arrow a14.

  In the pre-stage insulation furnace 42, the metal material 34 to be processed taken out from the compression processing chamber 33 is kept at the processing temperature 523 [K] in the third pass.

  Thus, when the processing for all the processing target metal materials 34 put in the rear stage heat insulation furnace 43 is completed, the processing target metal material 34 that is subsequently kept at the processing temperature 523 [K] in the third pass in the front stage heat insulation furnace 42 is obtained. Then, as indicated by the arrow a11 again, after being put into the compression processing chamber 33 and subjected to the compression processing, it is taken out to the post-stage insulation furnace 43 as indicated by the arrow a12.

  At this time, the post-stage heat insulation furnace 43 keeps the metal material 34 to be processed at the processing temperature 503 [K] in the fourth pass, and the heat-processed metal material 34 thus held again indicates the compression processing chamber 33 as indicated by an arrow a13. Then, after being compressed, it is taken into the pre-stage warming furnace 42 as indicated by an arrow a14.

  In this way, by using one compression processing device 36, the first pass, the second pass, the third pass, and the fourth pass are subjected to the heat retention temperatures 623 [K], 573 [K], and 523 [K]. And 503 [K], the metal material 34 to be processed having an ultrafine structure whose particle size is refined to 1 [μm] at the end of the fourth pass is held in the pre-stage insulation furnace 42. A state is obtained.

  The metal material 34 to be processed for which the microfabrication processing has been completed is sent out as a processed metal material 44 to a productizing apparatus provided outside.

  According to the above configuration, the temperature reduction multi-axis forging process for four passes can be performed by one compression processing apparatus 36, and thus a metal material production system suitable for the purpose of producing a small amount with a relatively small facility is provided. realizable.

  Accordingly, as in the case described above, the AZ61Mg composite material having excellent hardness characteristics, thermal stability, and elongation characteristics can be realized by being able to be refined without cracking during the processing.

  It can be applied to obtain a magnesium metal material suitable for a practical structural product material.

1 is a schematic system diagram showing a metal material manufacturing system according to an embodiment of the present invention. It is a graph which shows the component added to the metal material raw material. (A), (B), and (C) are the approximate line perspective views used for description of the multi-axis forging process which compresses about an X-axis, a Y-axis, and a Z-axis. It is a characteristic curve figure which shows the true stress-cumulative distortion which arises at the time of the compression process of 1 pass thru | or 5 passes. (A), (B), (C), and (D) show the development state of the refined structure that has been refined by the compression process of the second pass, the fourth pass, and the fifth pass before the compression process. FIG. FIG. 5 is an optical micrograph showing a refined structure refined as a result of temperature-decreasing multiaxial forging in the AZ61Mg alloy of sample number 2. It is a characteristic curve figure which shows the change of the hardness by the strain increase during temperature-fall multi-axis forging process. It is an optical microscope photograph figure which shows the refinement | miniaturization structure | tissue when a metal material is hold | maintained at 523 [K] for 15 [seconds] after temperature-fall multi-axis forging process. (A) And (B) is a characteristic curve figure which shows a tension test result. It is a rough-line system diagram which shows other embodiment of a commercialization apparatus. It is a characteristic curve figure which shows the true stress-cumulative strain curve obtained when changing the temperature range of temperature-fall multi-axis forging process. (A) And (B) is an optical microscope photograph figure which shows the refinement | miniaturization structure | tissue obtained when the temperature range of temperature-fall multi-axis forging process was changed. It is a characteristic curve figure which shows the temperature fall temperature setting range. It is a rough-line system diagram which shows the metal material manufacturing system of other embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 31 ... Metal material manufacturing system, 2 ... Crystal grain refinement processing apparatus, 3 ... Metal material material, 4 ... Processed metal material, 5 ... Commercialization apparatus, 6 ... Processing part, 7 ... ... Practical structure products, 11A to 11D ... 1st stage to 4th stage refinement processing part, 12, 32 ... Jig, 13, 33 ... Compression processing chamber, 14, 34 ... Metal material to be processed, 15 35 ... Compression processing tool 16, 36 ... Incubator, 20 ... Rolling device, 21 ... Work material, 22 ... Guide roller, 23A, 23B, 24A, 24B ... Rolling roller, 41 ... Metal Material material 42... Pre-stage insulation furnace, 43...

Claims (3)

Magnesium contains aluminum and zinc in a mass ratio of about 6% and 1%, respectively, and a metal material made of a magnesium alloy containing at least iron and manganese as additive elements is subjected to a multiaxial forging process. A processed metal material having a crystal structure refined by the method is obtained. Magnesium contains aluminum and zinc in a mass ratio of about 6% and 1%, respectively, and a metal material made of a magnesium alloy containing at least iron and manganese as additive elements is subjected to a multiaxial forging process. A magnesium alloy material manufacturing apparatus comprising compression processing means for obtaining a processed metal material having a crystal structure refined by the process. Magnesium contains aluminum and zinc in a mass ratio of about 6% and 1%, respectively, and a metal material made of a magnesium alloy containing at least iron and manganese as additive elements is subjected to a multiaxial forging process. A magnesium alloy material characterized by having a crystal structure refined by.