JP2006348349A - Magnesium alloy powder raw material, high yield strength magnesium alloy, method for producing magnesium alloy powder raw material, and method for producing high yield strength magnesium alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Mg alloy that achieves both high yield strength and elongation.
An Mg alloy powder raw material is relatively small by subjecting a starting raw material powder having a relatively large crystal grain size to plastic deformation that is compressed or sheared through a pair of rolls. Crystal grain size. The starting raw material powder is an Mg alloy powder in which fine intermetallic compounds 21 are precipitated and dispersed in the substrate 22 by heat treatment. In the Mg alloy powder after plastic working, a working strain 22 exists around the precipitated intermetallic compound 21. The maximum size of the Mg alloy powder after plastic working is 10 mm or less, the minimum size is 0.1 mm or more, and the maximum crystal grain size of Mg particles constituting the substrate 20 is 20 μm or less.
[Selection] Figure 2

Description

  The present invention relates to a magnesium alloy powder raw material, a magnesium alloy produced using the powder raw material, and a production method thereof, and particularly relates to a magnesium alloy that achieves both high yield strength and elongation and a production method thereof.

  The lightest magnesium alloy (hereinafter referred to as Mg) alloy among industrial metal materials is widely used in sports equipment, home appliances, aerospace equipment, other machine parts, etc. by utilizing its light weight effect. Has been. On the other hand, in order to apply the Mg alloy to products / members that require high reliability such as automobile parts, it is necessary to further increase the strength. In particular, an important improvement in proof stress is strongly demanded in component design, and at the same time, it is necessary to realize high elongation (toughness). In other words, by realizing high yield strength and high elongation, it is possible to replace the current lightweight material, aluminum alloy.

  It is already known that refinement of crystal grains and dispersion strengthening of fine intermetallic compounds are effective in improving the strength of Mg alloys. In particular, the manufacturing method that uses Mg alloy powder as a starting material and compacts and solidifies it can form a finer structure than the melting / casting method, making it more effective in increasing strength. It can be called a process.

  For example, although a method for producing a high-strength Mg alloy using a rapid solidification process has been proposed, this method is not practical for the following reasons.

  (A) Although high strength is obtained, the elongation is as low as several percent.

  (B) Since the particle size of the starting raw material powder is as small as several tens to hundreds of microns, there are problems of safety in the handling process and low yield, and the cost is increased by adding more expensive elements. There are economic problems such as inducing

  On the other hand, various methods for producing a Mg alloy by using a cutting powder discharged when cutting an Mg alloy material as a starting material and compacting and solidifying the starting powder have been studied and proposed. For example, JP-A-2-182806 describes a method of extruding an Mg alloy cutting powder after it has been solidified by hot pressing, and JP-A-5-320715 discloses a method of forming an Mg alloy cutting powder. A method of extruding is described.

In the “manufacturing method of magnesium alloy member” described in JP-A-5-306404, the aluminum-containing Mg alloy powder subjected to T6 heat treatment (solution heat treatment + aging heat treatment) is compacted and then extruded. A method of processing has been proposed. In the manufacturing method disclosed here, when solidifying an Mg alloy cutting powder containing an appropriate amount of aluminum (Al), an Mg alloy having excellent mechanical properties by extracting the effects of both T6 heat treatment and extrusion. It is characterized by creating a member. The effect of the T6 heat treatment is to uniformly disperse the fine intermetallic compound Mg ₁₇ Al ₁₂ in the extruded Mg alloy substrate, and the effect of the extrusion process constitutes the extruded Mg alloy substrate. It is to refine crystal grains. As a result, for example, Al: 7.8 to 9.2 wt%, manganese (Mn): 0.12 to 0.35 wt%, zinc (Zn): 0.2 to 0 described in the ASTM standard Mg alloy obtained by forming and extruding with a cutting powder prepared after T6 heat treatment of AZ80 magnesium alloy having a composition of .8 wt%, Mg: balance, has a tensile strength at room temperature Is 382 MPa, and the elongation is 27%. On the other hand, when the T6 heat treatment is not performed, the tensile strength is reported to be 330 MPa and the elongation is 15%, and an effect of improving the tensile strength is seen.
Japanese Patent Laid-Open No. 2-182806 JP-A-5-320715 JP-A-5-306404

  However, in the Mg alloy member manufacturing method described in JP-A-5-306404, the proof stress of the extruded material is 196 MPa when the T6 heat treatment is performed, and 200 MPa when the T6 heat treatment is not performed. It has been reported that there is no improvement in tensile strength. The cause is considered as follows. Compared with Mg alloy crystal grains (50-700 μm) produced by the conventional melting and casting method, recrystallization occurs due to extrusion, and the crystal grains become finer. Considering disclosed data and the like, it is about 10 to 20 μm. In order to improve the tensile strength, it is necessary to further refine the crystal grains. Based on the disclosed data so far, for example, it is effective to improve the proof stress to miniaturize to 1 to 5 μm or less. An Mg alloy having such a fine crystal grain size cannot be realized only by a manufacturing method in which a T6 heat-treated cutting powder is compacted and extruded.

In addition, a method has been proposed to further refine the intermetallic compound Mg ₁₇ Al ₁₂ deposited and dispersed in the substrate by T6 heat treatment by extrusion, but there is a limit to the level at which it can be refined by plastic deformation by extrusion. In order to improve the yield strength, further refinement of intermetallic compounds and fine and uniform dispersion of a plurality of intermetallic compounds are required.

  An object of the present invention is to provide a magnesium alloy that achieves both high yield strength and elongation, and a method for producing the same.

  Another object of the present invention is to provide a magnesium alloy powder raw material used for producing the magnesium alloy and a method for producing the same.

  The magnesium alloy powder raw material according to the present invention is relatively processed by subjecting a starting raw material powder having a relatively large crystal grain size to plastic deformation that is compressed or sheared through a pair of rolls. The crystal grain size is small and is characterized by the following. That is, the starting material powder is a magnesium alloy powder in which fine intermetallic compounds are precipitated and dispersed in the substrate by heat treatment. In the magnesium alloy powder after plastic working, working strain exists around the precipitated intermetallic compound. The maximum size of the magnesium alloy powder after plastic working is 10 mm or less, and the minimum size is 0.1 mm or more. The maximum grain size of the magnesium particles constituting the base of the magnesium alloy powder after plastic working is 20 μm or less.

Preferably, the intermetallic compound is at least selected from the group consisting of Mg ₁₇ Al ₁₂ , Al ₂ Ca, Mg ₂ Si, MgZn ₂ , Al ₃ Re (Re: rare earth element), Al ₁₁ Re ₃ and Al ₆ Mn. One compound. Preferably, the maximum particle size of the intermetallic compound is 5 μm or less, more preferably 2 μm or less.

  Preferably, the maximum grain size of the magnesium particles constituting the base of the magnesium alloy powder is 10 μm or less.

  The high-strength magnesium alloy according to the present invention is obtained by compacting a magnesium alloy powder raw material having the above characteristics and then extruding it, and has the following characteristics. That is, the maximum crystal grain size of magnesium particles constituting the base of the alloy is 10 μm or less, and the tensile strength at room temperature is 250 MPa or more.

  Preferably, the maximum grain size of the magnesium particles constituting the base of the magnesium alloy is 5 μm or less, and the tensile strength at room temperature is 350 MPa or more.

Preferably, the magnesium alloy substrate is selected from the group consisting of Mg ₁₇ Al ₁₂ , Al ₂ Ca, Mg ₂ Si, MgZn ₂ , Al ₃ Re (Re: rare earth element), Al ₁₁ Re ₃ and Al ₆ Mn. At least one intermetallic compound is deposited and dispersed.

  Preferably, the magnesium alloy contains an active metal element selected from the group consisting of strontium (Sr), zirconium (Zr), scandium (Sc), and titanium (Ti) in an amount of 0.5% to 4% by weight. is doing.

  The method for producing a magnesium alloy powder raw material according to the present invention is a method for refining the crystal grain size of magnesium particles constituting the substrate of the starting raw material powder by subjecting the starting raw material powder to plastic working. The following features are provided. That is, a magnesium alloy powder in which a fine intermetallic compound is precipitated and dispersed in a substrate by heat treatment is prepared as a starting material powder. The plastic working is a plastic working in which a starting raw material powder is passed between a pair of rolls and subjected to compression deformation or shear deformation to impart processing strain around the intermetallic compound. The plastic working is repeated until the maximum size of the powder is 10 mm or less, the minimum size is 0.1 mm or more, and the maximum crystal grain size of the magnesium particles constituting the powder base is 20 μm or less.

  In one embodiment, the step of preparing a magnesium alloy powder as a starting raw material powder includes preparing a magnesium alloy ingot by a casting method, solution treatment of the magnesium alloy ingot, and subsequently performing an aging heat treatment. This includes precipitating and dispersing fine intermetallic compounds in the substrate and removing the magnesium alloy powder from the ingot by machining. Preferably, when performing the plastic working, the temperature of the starting raw material powder to be introduced and the surface temperature of the roll in contact with the starting raw material powder are set to be equal to or lower than the temperature of the aging heat treatment.

  A method for producing a high yield strength magnesium alloy according to the present invention includes a step of pressing a magnesium alloy powder raw material having the above-described characteristics in a mold and obtaining a green compact, and a magnesium alloy green compact Are heated at a temperature of 150 ° C. or higher and 450 ° C. or lower, and a magnesium alloy powder compact is immediately extruded after the heating to produce a magnesium alloy.

  Preferably, the maximum grain size of the magnesium particles constituting the base of the magnesium alloy is 10 μm or less, and the tensile strength at room temperature is 250 MPa or more. More preferably, the magnesium alloy powder compact is heated at a temperature of 200 ° C. or higher and 350 ° C. or lower.

  In the following, embodiments and operational effects of the present invention will be described.

  The present invention has been made to solve the above-described conventional problems. A magnesium alloy powder in which fine intermetallic compounds are precipitated and dispersed in a substrate by heat treatment is used as a starting material powder. A coarse Mg alloy powder having a fine structure is produced by plastic deformation that is compressed and / or sheared through a pair of rolls, and this is pressed and extruded to exceed 250 to 350 MPa. An object of the present invention is to provide an Mg alloy having high tensile strength and a method for producing the same.

(1) Starting material powder and method for producing the same Mainly composed of Mg, and other elements that form intermetallic compounds such as Al, Mn, Zn, Re (rare earth elements), Ca, Si, and strontium (Sr) An Mg alloy ingot to which an active metal element selected from the group consisting of zirconium (Zr), scandium (Sc), and titanium (Ti) is added is produced by a casting method. By subjecting this Mg alloy ingot to a known T6 heat treatment (solution heat treatment + aging heat treatment), fine intermetallic compounds produced by each additive element are precipitated and dispersed in the substrate. Examples of the intermetallic compound that precipitates and disperses include Mg ₁₇ Al ₁₂ , Al ₂ Ca, Mg ₂ Si, MgZn ₂ , Al ₃ Re (Re: rare earth element), Al ₁₁ Re ₃ , and Al ₆ Mn. Since these intermetallic compounds are evenly dispersed in the base material of the Mg alloy after the extrusion process, it contributes to the improvement of the proof stress. Further, the strength can be further increased by containing an active metal element such as strontium (Sr), zirconium (Zr), scandium (Sc), and titanium (Ti) in an amount of 0.5% to 4% on a weight basis.

  Since the heat treatment conditions vary depending on the type of element to be added and the amount of the element to be added, it is necessary to set appropriate conditions by observing the structure or measuring the hardness (age hardening curve). Next, a powder having a size of about 0.1 to 10 mm is collected from the Mg alloy ingot by a machine or cutting process such as milling, and this is used as the starting material powder of the present invention. In addition, since it will become easy to ignite if the particle size of powder is less than 0.1 mm, from the viewpoint of safety, a cutting powder having a size of 0.1 mm or more, more preferably 0.5 mm or more is used.

(2) Magnesium alloy powder raw material and manufacturing method thereof The Mg alloy powder subjected to the above-described T6 heat treatment is used as a starting raw material powder, and this is put into a roller compactor apparatus shown in FIG.

  The roller compactor device shown in FIG. 1 includes a case 11, a multistage roll rotating body 12 disposed in the case 11, a crushing device 13, a powder temperature / supply amount control system 14, and a cradle 15. . The multistage roll rotating body 12 constitutes a plastic working part that performs plastic working on the starting raw material powder, and includes three pairs of rolls 12a, 12b, and 12c that perform rolling. The starting material powder undergoes compression deformation and / or shear deformation when passing between the pair of rolls.

  The starting raw material powder is adjusted to a predetermined temperature and a predetermined amount by the powder temperature / supply amount control system 14 and is charged into the case 11. Here, the predetermined temperature is equal to or lower than the temperature of aging heat treatment described later. The inside of the case 11 is maintained in an inert gas atmosphere, a non-oxidizing gas atmosphere, or a vacuum atmosphere from the viewpoint of preventing oxidation of the powder surface. Moreover, the surface temperature of the multistage roll rotating body 12 and the atmospheric temperature in the case 11 are equal to or lower than the temperature of an aging heat treatment described later.

  The powder delivered from the roll pair 12c is subsequently crushed by the crushing device 13 to become granular powder. The granular powder may be returned to the powder temperature / supply amount control system 14 again, and plastic processing by the multistage roll rotating body 12 may be repeated. The processed granular powder is accommodated in the cradle 15.

  The following structure control is performed by performing plastic working in which the powder is passed between a pair of rolls to compress and / or shear.

  (A) As shown in FIG. 2, more work strain 22 is applied to the periphery of the intermetallic compound particles 21 precipitated and dispersed in the base of the magnesium alloy powder 20. The processing strain 22 is twins or dislocations introduced and accumulated around the intermetallic compound particles 21 by plastic processing, and looks like a streak when observed with a transmission electron microscope (TEM).

  (B) The maximum size of the powder after plastic processing is 10 mm or less, and the minimum size of the powder is 0.1 mm or more.

  (C) The starting material powder is relatively smaller than the crystal grain size of magnesium.

  (D) The maximum crystal grain size of the magnesium particles constituting the powder base is 20 μm or less.

  In addition, after performing the crushing, pulverization, and sizing treatment of the Mg alloy powder raw material subjected to the plastic processing by the roll, if necessary, the plastic processing by the roll is repeatedly performed under the same conditions, An Mg alloy powder raw material having a microstructure defined by the present invention is created.

  First, regarding (a), when plastic working is performed by passing the powder between rolls, processing strain is imparted to the entire powder, but intermetallic compound particles are precipitated and dispersed in the base. Compared with the intermetallic compound particles, more processing strain is applied. Therefore, by repeating this plastic working, more work strain accumulates around the intermetallic compound particles. When the processing strain increases, the inventors of the present application generate more nucleation sites for dynamic recrystallization that occurs during the extrusion process, which is a subsequent process, and are finer than the conventional Mg alloy manufacturing method. It was found that crystal grains can be formed.

  Regarding this new knowledge, there is a similar description in JP-A-5-306404. That is, a method of producing an Mg alloy member by extruding a compact after forming a compacted Mg alloy powder collected by cutting from an Al-containing Mg alloy member subjected to T6 treatment. Has proposed. However, in the manufacturing method disclosed here, the T6-treated cutting Mg alloy powder is not compulsorily imparted with the strong plastic processing as proposed by the present invention. Such nucleation sites of dynamic recrystallization are not formed, and fine crystal grains cannot be obtained. For example, the tensile strength of the Mg alloy in the case of using the AZ80 alloy cutting powder subjected to T6 heat treatment shows a low value of about 200 MPa. In addition, as described above, the tensile strength of the extruded material when using AZ80 powder not subjected to T6 heat treatment is 200 MPa, which is not significantly different from that during T6 heat treatment. This is fundamentally different from the manufacturing method in which processing strain is accumulated preferentially and used as a nucleation site for dynamic recrystallization.

  Further, in the present invention, processing strain is imparted in a random (disordered) direction by repeatedly performing plastic processing with a pair of rolls on the powder. As a result, in the Mg alloy after the extrusion process, the crystal orientation is disordered and the elongation is improved. In other words, in a normal extruded material, the (0001) bottom surface, which is the sliding surface of Mg, is arranged along the extrusion direction, so that the elongation is reduced. However, the Mg alloy powder subjected to plastic working by a pair of rolls of the present invention When the body is extruded, in addition to the (0001) bottom surface, non-bottom surfaces such as (10-10) columnar surfaces and (10-11) conical surfaces are also arranged along the extrusion direction. As a result, an Mg alloy having high elongation in addition to high yield strength can be created.

  On the contrary, when the same plastic working is performed on the Mg alloy powder not subjected to the T6 heat treatment by the roller compactor device, although the refinement of the magnesium crystal grains is confirmed, the fineness as in the case where the T6 heat treatment is performed is confirmed. Crystals were not obtained. Therefore, in order to more effectively refine crystal grains by plastic working using a pair of rolls used in the present invention, intermetallic compound particles are precipitated and dispersed in the base material of the Mg alloy powder raw material. It is necessary to keep.

  The size of intermetallic compound particles has a strong correlation with the amount of processing strain accumulated around the particles. As the particle size of the intermetallic compound is smaller, more work strain can be accumulated, and as a result, an Mg alloy having high yield strength can be obtained. Specifically, an Mg alloy having a high yield strength exceeding 250 MPa can be obtained by setting the maximum particle size of the intermetallic compound deposited and dispersed on the raw material powder base to 5 μm or less. When the maximum particle size of the intermetallic compound is 2 μm or less, more processing strain can be accumulated with less plastic processing. As a result, a high yield strength can be obtained, and an economic effect can be obtained in which a fine crystal grain and an Mg alloy having a high yield strength can be produced under a condition in which the number of plastic workings in a pair of rolls is reduced. .

  Therefore, the manufacturing method in which the Mg alloy powder obtained by precipitating and dispersing fine intermetallic compound particles by T6 heat treatment in the substrate in advance is subjected to plastic working through a pair of rolls. This is a feature for realizing an Mg alloy having both high yield strength and high toughness.

  Next, regarding (b), the maximum size of the Mg alloy powder after plastic processing by a pair of rolls is set to 10 mm or less, and the minimum size of the powder is set to 0.1 mm or more. When the maximum size of the powder exceeds 10 mm, the bonding property between the powders is reduced during the compacting of the powder, which is the next process, or the corners of the mold are not filled when put into the mold. For this reason, there arises a problem that an end portion of the green compact after molding is damaged. On the other hand, if the minimum size of the Mg alloy powder is less than 0.1 mm, it tends to ignite, which causes a safety problem in handling.

  Regarding (c) and (d), by performing plastic working with a pair of rolls, an Mg alloy powder having crystal grains relatively smaller than the crystal grain diameter of magnesium of the starting raw material powder is produced. Specifically, in the Mg alloy powder after plastic working with a pair of rolls, the maximum crystal grain size of the magnesium particles constituting the substrate is set to 20 μm or less. An Mg alloy having a yield strength exceeding 250 MPa can be obtained by compacting and extruding such an Mg alloy powder. On the other hand, when the crystal grain size of the magnesium particles of the powder after plastic processing with a roll exceeds 20 μm, a high yield strength exceeding 250 MPa is obtained with an Mg alloy produced using such an Mg alloy powder. Have difficulty. In order to obtain a higher proof stress, for example, characteristics exceeding 350 MPa, in the Mg alloy, the base crystal grain size of the Mg alloy powder after plastic working by a pair of rolls needs to be 10 μm or less.

  In plastic processing using a roll, the temperature of the starting raw material powder to be charged and the surface temperature of the roll in contact with the powder must be equal to or lower than the aging heat treatment temperature in the subsequent step. When plastic working is performed at a temperature higher than the aging heat treatment temperature, the amount of processing strain accumulated around the intermetallic compound particles decreases due to the overaging phenomenon, and dynamic recrystallization during extrusion does not proceed effectively. As a result, it becomes difficult to obtain a high yield strength Mg alloy having fine crystal grains.

(3) Magnesium alloy and manufacturing method thereof Magnesium alloy powder raw material subjected to plastic working by the roll described above is compacted and warm extruded to obtain a high-strength Mg alloy having the following characteristics. It is done.

  (A) The maximum crystal grain size of magnesium particles constituting the base of the obtained Mg alloy is 10 μm or less.

  (B) The tensile strength at room temperature of the alloy is 250 MPa or more.

The inventors of the present application, in particular, when using a raw material having a magnesium alloy crystal grain size of 10 μm or less in the base of the Mg alloy powder, the largest crystal constituting the base of the Mg alloy after extrusion processing It has been found that the particle size is 5 μm or less, and the tensile strength of the alloy at room temperature is 350 MPa or more. Further, Mg ₁₇ Al ₁₂ , Al ₂ Ca, Mg ₂ Si, MgZn ₂ , Al ₃ Re (Re: rare earth element), Al ₁₁ Re ₃ , Al ₆ Mn, etc. dispersed in the base material of the input material subjected to T6 treatment The intermetallic compound also improves the yield strength of the Mg alloy after extrusion.

  The magnesium alloy powder raw material that has been subjected to plastic working by the rolls described above is pressed in a state in which the mold is filled to produce a green compact. The molded body is heated in a temperature range of 150 ° C. or higher and 450 ° C. or lower, and then immediately solidified by extrusion to produce a magnesium alloy material. When the heating temperature is less than 150 ° C., dynamic recrystallization does not proceed, so that fine magnesium crystal grains cannot be obtained. On the other hand, when the heating temperature exceeds 450 ° C., there arises a problem that a fine recrystallization structure grows and becomes coarse. In view of the influence of the heat generated during the extrusion process, it is preferable that the temperature of the compact is 200 ° C. or higher and 350 ° C. or lower. From the viewpoint of densification, the extrusion ratio is 10 or more, more preferably 30 or more.

  AZ91D ingot (composition-Al: 9.1, Zn: 0.85, Mn: 0.23% by weight, Mg: balance) prepared by casting method was solution heat treated (413 ° C. × 16 hours after heating and air cooling) Then, an aging heat treatment (251 ° C. × 4 hours of heating and holding and cooling in a furnace in a nitrogen gas atmosphere) was performed. Powder was produced from this ingot by pulverization (T6 heat-treated AZ91D powder).

  On the other hand, as a comparison, a powder was produced by pulverization under the same conditions in a state where the cast ingot was only subjected to solution heat treatment (solution treatment AZ91D powder). All the powders had a particle size in the range of 0.5 to 4 mm.

  Each AZ91D powder was used as a starting material, and plastic processing was performed using a roller compactor device. Here, the roll diameter was 100 mm, the peripheral speed of the roll was 100 mm / second, the clearance between the rolls was 0.1 mm, and the surface temperature of the roll and the raw material powder temperature were both ordinary temperatures. Predetermined magnesium alloy powder (one-pass product) was produced by pulverizing the plate-like connected powder subjected to plastic working with a roll to a length of about 1 to 5 mm with a cutter mill device. By repeating this process, the crystal grains were refined. Here, N = 20 and 40 are set for the powders that are repeated 20 times and 40 times, respectively, and N = 0 is set when plastic processing by a roll is not performed.

FIG. 3 is a structure photograph of AZ91D ingot, (a) is a structure photograph after casting, (b) is a structure photograph after solution treatment, (c) is a structure photograph after T6 heat treatment (solution treatment + aging heat treatment). Is shown. As is apparent from the structure photograph of FIG. 3, the coarse Mg ₁₇ Al ₁₂ compound precipitated after casting is dissolved in the magnesium substrate by solution treatment, and further subjected to aging heat treatment to obtain a fine metal. It can be seen that the intermetallic compound is uniformly dispersed in the substrate.

  The structure photograph which expanded the structure of AZ91D after T6 heat processing of FIG.3 (c) is shown in FIG. The fine granular compound of 500 to 800 nanometers (nm) is uniformly dispersed, and by performing the T6 heat treatment, the predetermined tissue structure intended by the present invention is formed in the starting material.

  FIG. 5 shows an organization photograph of the AZ91D powder subjected to plastic working with a roll. (a) shows the structure after the T6 treatment according to the present invention, and (b) shows the structure in the case of only the solution treatment of the comparative example. When AZ91D powder that has been subjected to T6 treatment is used, the magnesium substrate shows a homogeneous structure by performing plastic working with a roll 20 and 40 times, and the crystal grain size is about 2 to 5 microns. It is recognized that it is miniaturized. On the other hand, when the AZ91D powder subjected to the solution treatment of (b) is used, the substrate is inhomogeneous even after 40 times of plastic working (a state in which white and black regions are mixed in the photograph) ) And the magnesium base is composed of coarse crystal grains exceeding 20 microns.

  FIG. 6 shows the microhardness (micro Vickers hardness) test results of each powder. In any starting raw material powder, the hardness increases with an increase in the number of plastic workings by rolls, but the hardness of the AZ91D powder subjected to T6 heat treatment shows a higher value. Further, the difference in hardness between the two increases as the number of processing increases. That is, it is recognized that the processing strain due to plastic working using a roll is more effectively accumulated in the substrate in the AZ91D powder subjected to T6 heat treatment.

Each AZ91D powder produced in Example 1 was molded at room temperature using a hydraulic press machine to produce a cylindrical extrusion billet. The billet was heated in a nitrogen gas atmosphere at 400 ° C. for 5 minutes, and then immediately subjected to warm extrusion (extrusion ratio r = 37) to produce a dense bar. Tensile test pieces (parallel portion 20 mm) were collected from each magnesium alloy extruded material and subjected to a tensile test at a strain rate of 10 ⁻⁴ per second at room temperature. Table 1 shows the measurement results of tensile strength (0.2% strain), tensile strength, and elongation at break.

  By using AZ91D powder subjected to T6 treatment which is an example of the present invention, both the tensile strength and 0.2% proof stress of the extruded material via plastic processing by a roll are remarkably increased. Showed a high value exceeding 250 to 300 MPa. Also, the elongation at break is maintained at a high value of about 18%. Thus, by using the production method according to the present invention, it is possible to produce a magnesium alloy having high tensile strength and high toughness.

  On the other hand, when the AZ91D powder subjected to only the solution heat treatment, which is a comparative example, is used, the tensile strength / tensile strength increases as the number of times of plastic working by the roll increases, but the T6 heat treatment of the present invention example. Compared with the results of the powder, these values are low, and it can be seen that the tensile strength has not reached 250 MPa.

  FIG. 7 shows a tissue observation result by an optical microscope for the extruded material when plastic processing by a roll is performed 40 times. As shown in (a), when the T6 heat-treated AZ91D powder of the present invention example was used, the crystal grain size distribution of the magnesium substrate was measured by image analysis. As a result, the maximum crystal grain size was 4.2 μm and the average crystal grain size Was 1.5 μm, and a fine structure was formed by dynamic recrystallization during the extrusion process. On the other hand, when the solution-treated AZ91D powder which is a comparative example of (b) is used, the maximum crystal grain size of the extruded material is 21 μm and the average crystal grain size is 9.6 μm, and the T6 heat treatment shown in (a) Compared to the case of AZ91D powder, the structure is extremely coarse. In other words, when T6 heat-treated Mg alloy powder of the present invention is subjected to plastic working with a roll, more processing strain is accumulated around fine intermetallic compound precipitates that are deposited and dispersed on the substrate. As a result, the dynamic recrystallization promoted more effectively and formed fine crystal grains.

  ZAXE1713 ingot produced by a casting method (composition—Al: 7.1, Zn: 0.95, Ca: 0.93, La: 2.87 wt%, Mg: remainder) solution heat treatment (420 ° C. × 16 hours) Then, after aging and heating, aging heat treatment (180 ° C. × 36 hours after heating and cooling in a furnace in a nitrogen gas atmosphere) was performed. Powder was produced from this ingot by pulverization (T6 heat-treated ZAXE1713 powder). On the other hand, as a comparison, a cast ingot was not subjected to heat treatment, and a powder was produced by pulverization under the same conditions (ZAXE1713 powder without heat treatment). All powders had a particle size in the range of 0.6 to 4 mm. Each ZAXE1713 powder was used as a starting material, and plastic processing was performed using a roller compactor device.

  Here, as in Example 1, the roll diameter was 100 mm, the peripheral speed of the roll was 100 mm / second, the clearance between the rolls was 0.1 mm, and the roll surface temperature and the raw material powder temperature were both room temperature. Predetermined magnesium alloy powder (one-pass product) was produced by pulverizing the plate-like connected powder subjected to plastic working with a roll to a length of about 1 to 5 mm with a cutter mill device. By repeating this, the crystal grains were refined. Here, the number of repetitions of the plastic working by the roll is set to 30 times at maximum, and N = 0 is set when the plastic working by the roll is not performed.

Each ZAXE1713 powder was die-molded at room temperature using a hydraulic press to produce a cylindrical extrusion billet. The billet was heated in a nitrogen gas atmosphere at 400 ° C. for 5 minutes, and then immediately subjected to warm extrusion (extrusion ratio r = 37) to produce a dense bar. A tensile test piece (parallel portion 20 mm) was collected from each extruded material of magnesium alloy, and a tensile test was performed at a strain rate of 5 × 10 ⁻⁴ per second at room temperature. Table 2 shows the measurement results of tensile strength (0.2% strain), tensile strength, and elongation at break.

  By using the ZAXE1713 powder subjected to T6 treatment which is an example of the present invention, both the tensile strength and 0.2% proof stress of the extruded material through plastic processing by rolls are remarkably increased. Showed a high value exceeding 250 to 300 MPa. Also, the elongation at break maintains a high value of 16% or more. Thus, by using the production method according to the present invention, it is possible to produce a magnesium alloy having high tensile strength and high toughness.

  On the other hand, when the ZAXE1713 powder that is not heat-treated is used as a comparative example, the tensile strength / tensile strength increases as the number of times of plastic working by the roll increases, but the result of the T6 heat-treated powder of the present invention As compared with, the values are low, and it can be seen that, in particular, the tensile strength does not reach 250 MPa.

  FIG. 8 shows the observation results of the texture of the ZAXE1713 powder subjected to T6 heat treatment in the extrusion direction of the Mg alloy obtained by extruding and solidifying the powder subjected to plastic processing by a roll 3,10,20,30 times. . As the number of processing increases, the crystal grain size of magnesium constituting the substrate becomes smaller. In particular, the maximum crystal grain size is 9.2 μm at 20 times, the average crystal grain size is 4.8 μm, and the maximum crystal grain at 30 times. The particle size was 4.4 μm, and the average crystal particle size was 1.2 μm.

  AZ80A ingot (composition-Al: 8.2, Zn: 0.51, Mn: 0.18% by weight, Mg: balance) produced by a casting method is solution heat treated (410 ° C. × 6 hours after heating and air cooling) Then, an aging heat treatment (175 ° C. × 26 hours of heating and cooling in a furnace in a nitrogen gas atmosphere) was performed. Powder was produced from this ingot by pulverization (T6 heat-treated AZ80A powder). On the other hand, as a comparison, the cast ingot was not heat-treated, and a powder was produced by pulverization under the same conditions (without heat treatment AZ80A powder). All powders had a particle size in the range of 0.6 to 4 mm.

  Each AZ80A powder was used as a starting material, and plastic processing was performed using a roller compactor device. Here, as in Example 1, the roll diameter was 100 mm, the peripheral speed of the roll was 100 mm / second, the clearance between the rolls was 0.1 mm, and the roll surface temperature and the raw material powder temperature were both room temperature. Predetermined magnesium alloy powder (one-pass product) was produced by pulverizing the plate-like connected powder subjected to plastic working with a roll to a length of about 1 to 5 mm with a cutter mill device. By repeating this, the crystal grains were refined. Here, the maximum number of repetitions of the plastic working by the roll is 50, and N = 0 is set when the plastic working by the roll is not performed.

Each AZ80A powder was molded at room temperature using a hydraulic press machine to produce a cylindrical extrusion billet. The billet was heated in a nitrogen gas atmosphere at 400 ° C. for 5 minutes, and then immediately subjected to warm extrusion (extrusion ratio r = 37) to produce a dense bar. A tensile test piece (parallel portion 20 mm) was collected from each extruded material of magnesium alloy, and a tensile test was performed at a strain rate of 5 × 10 ⁻⁴ per second at room temperature. Table 3 shows the measurement results of tensile strength (0.2% strain), tensile strength, and elongation at break.

  When AZ80A powder subjected to T6 treatment which is an example of the present invention is subjected to plastic working with a roll, the tensile strength is as high as 262 to 317 MPa, and has a high elongation at break of 17.9 to 18.9%. .

  On the other hand, in the comparative example, even when the T6 heat-treated AZ80A powder was used, the tensile proof stress was as low as 208 MPa unless plastic processing was performed using a roll. In the case of AZ80A powder not subjected to heat treatment, even when the plastic working by the roll is performed 20 times, the tensile strength is 218 MPa, which is significantly lower than the example of the present invention.

Using the T6 heat-treated ZAXE1713 powder produced in Example 3 (number of times of plastic working by roll; 30 times), an extrusion billet was produced by die molding. A magnesium alloy extruded material was produced by setting the billet heating temperature at the time of densification and solidification by warm extrusion (extrusion ratio r = 37) as shown in Table 4. A tensile test piece (parallel portion 20 mm) was collected from each extruded material of magnesium alloy, and a tensile test was performed at a strain rate of 5 × 10 ⁻⁴ per second at room temperature. Table 4 shows the measurement results of tensile strength (0.2% strain), tensile strength, and elongation at break.

  When the proper billet temperature specified by the present invention is satisfied, the tensile strength is a high value exceeding 300 MPa. On the other hand, when the billet temperature, which is a comparative example, is 130 ° C., high tensile strength cannot be obtained because recrystallization during the extrusion process does not proceed sufficiently. Further, when the billet temperature, which is a comparative example, is 480 ° C., high tensile strength cannot be obtained because a fine recrystallization structure grows and coarsens during the extrusion process.

Using the T6 heat-treated ZAXE1713 powder produced in Example 3, plastic working with a roll was performed up to 30 times under the same conditions as in Example 1 to refine the powder texture structure. At that time, the temperature of the roll surface and the powder was set to room temperature or 200 ° C. The obtained Mg alloy powder was molded at room temperature by a hydraulic press to produce a cylindrical extrusion billet. The billet was heated in a nitrogen gas atmosphere at 400 ° C. for 5 minutes, and then immediately subjected to warm extrusion (extrusion ratio r = 37) to produce a dense bar. A tensile test piece (parallel portion 20 mm) was collected from each extruded material of magnesium alloy, and a tensile test was performed at a strain rate of 5 × 10 ⁻⁴ per second at room temperature. Table 5 shows the measurement results of tensile strength (0.2% strain), tensile strength, and elongation at break.

  When the temperature of the roll surface and powder, which is an example of the present invention, was normal temperature, the tensile strength, tensile strength, and elongation at break of the obtained Mg alloy extruded material all showed high values.

  On the other hand, when the temperature of the roll surface and the powder, which is a comparative example, is 200 ° C., which is higher than the aging treatment temperature (175 ° C.), both the tensile strength and the tensile strength are significantly higher than those of the examples of the present invention. Declined. In particular, the proof stress was almost constant despite the increase in the number of machining operations. This is because, when plastic working with a roll is performed with the Mg alloy powder heated to an aging temperature or higher, processing strain does not accumulate sufficiently around the precipitate due to overaging phenomenon, and as a result, in the extrusion process This is because it becomes difficult to form a fine structure by dynamic recrystallization, resulting in a decrease in yield strength.

  The pole figure of FIG. 9 shows the results of evaluating the orientation of the bottom surface (0001) of magnesium with respect to the cross section in the extrusion direction of the AZ80A extruded material produced in Example 4. Here, the number of times of plastic working by the roll was set to 5, 10, 30, 50 times. When the number of processing is up to 10, the (0001) plane forms a collective texture indicated by a typical extruded material along the extrusion direction. However, at 30 times and 50 times, the bottom surface orientation is weakened. In other words, non-bottom surfaces such as (10-10) column surfaces and (10-11) cone surfaces other than the (0001) bottom surface are also aligned in the extrusion direction. Are arranged.

  On the other hand, in the Mg alloy powder not subjected to heat treatment, the bottom orientation was not significantly lowered even after 50 times of plastic working.

  From the above results, in the Mg alloy material obtained by extruding after applying T6 heat treated Mg alloy powder to the T6 heat treated Mg alloy powder as defined by the present invention, the fineness of crystal grains by dynamic recrystallization In addition to the increase in tensile strength due to the formation, the elongation at break (toughness) is improved due to the disorder of the assembly structure.

  A cast magnesium ingot having the composition shown in Table 6 was subjected to a solution heat treatment (420 ° C. × 16 hours of heating and air cooling), followed by an aging heat treatment (180 ° C. × 36 hours of heating and holding in a nitrogen gas atmosphere furnace) Cooling).

  Magnesium alloy powder was produced from each ingot by pulverization. All powders had a particle size in the range of 0.6 to 4 mm. Each powder was used as a starting material, and was subjected to plastic working using a roller compactor device. Here, as in Example 1, the roll diameter was 100 mm, the peripheral speed of the roll was 100 mm / second, the clearance between the rolls was 0.1 mm, and the roll surface temperature and the raw material powder temperature were both room temperature.

  Predetermined magnesium alloy powder (one-pass product) was produced by pulverizing the plate-like connected powder subjected to plastic working with a roll to a length of about 1 to 5 mm with a cutter mill device. By repeating this, the crystal grains were refined. Here, the number of repetitions of the plastic working by the roll was 30 times. For comparison, N = 0 is set in the case where plastic working by a roll is not performed.

Subsequently, each processed powder was molded at room temperature using a hydraulic press machine to produce a cylindrical extrusion billet. The billet was heated in a nitrogen gas atmosphere at 400 ° C. for 5 minutes, and then immediately subjected to warm extrusion (extrusion ratio r = 37) to produce a dense bar. A tensile test piece (parallel portion 20 mm) was collected from each extruded material of magnesium alloy, and a tensile test was performed at a strain rate of 5 × 10 ⁻⁴ per second at room temperature. Table 7 shows the measurement results of tensile strength (0.2% strain), tensile strength, and elongation at break.

  Sample No. 1 to 9 are examples of the present invention. 2 to 9 are sample Nos. 1 is an extruded material obtained by using a powder collected from a cast magnesium alloy ingot to which an active metal element such as Zr, Sr, Sc, or Ti is added in an appropriate range. Sample No. Compared with the characteristic 1, the addition of an active metal element such as Zr, Sr, Sc, Ti can improve the tensile strength and the tensile strength without accompanied by a significant decrease in elongation (toughness). .

  On the other hand, sample No. which is a comparative example. In Nos. 10 to 12, when plastic working with a roll was not performed, an increase in tensile strength and tensile strength was not recognized even when an active metal element was added, but a decrease in elongation was caused.

  As mentioned above, although embodiment of this invention was described with reference to drawings, this invention is not limited to the thing of embodiment shown in figure. Various modifications and variations can be made to the illustrated embodiment within the same range or equivalent range as the present invention.

  The present invention can be advantageously used to obtain a magnesium alloy having both high yield strength and elongation.

It is an illustration figure which shows a roller compactor apparatus. It is an illustration figure which shows the state which the process distortion exists in the periphery of an intermetallic compound. It is a structure photograph of AZ91D ingot, (a) is a structure photograph after casting, (b) is a structure photograph after solution heat treatment, (c) is a structure photograph after T6 heat treatment (solution treatment + aging heat treatment) Yes. It is the structure | tissue photograph which expanded the structure | tissue after T6 heat processing. It is the structure | tissue photograph of the AZ91D powder which gave the plastic working by a roll, (a) has shown the structure | tissue of what performed T6 process, (b) has shown the structure | tissue of what has performed solution treatment. It is a figure which shows the test result of the micro hardness (micro Vickers hardness) of powder. It is the structure | tissue photograph by an optical microscope about an extrusion raw material, (a) is a structure | tissue photograph at the time of using T6 heat processing AZ91D powder, (b) has shown the structure | tissue photograph at the time of using solution treatment AZ91D powder. . It is a structure | tissue photograph of the extrusion direction of Mg alloy obtained by extrusion-solidifying the powder which gave plastic processing by a roll 3,10,20,30 times. It is a pole figure of the result of having evaluated the orientation of the bottom face of magnesium.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 Case, 12 Multistage roll rotating body, 13 Crushing device, 14 Powder temperature and supply amount control system, 15 Receiving base, 20 Magnesium alloy base material, 21 Intermetallic compound particle, 22 Processing distortion.

Claims (16)

In a magnesium alloy powder raw material having a relatively small crystal grain size by subjecting a starting raw material powder having a relatively large crystal grain size to plastic deformation by compressing or shearing it through a pair of rolls ,
The starting material powder is a magnesium alloy powder in which fine intermetallic compounds are precipitated and dispersed in the substrate by heat treatment,
In the magnesium alloy powder after the plastic working, there is a working strain around the precipitated intermetallic compound,
The maximum size of the magnesium alloy powder after the plastic working is 10 mm or less, the minimum size is 0.1 mm or more,
A magnesium alloy powder raw material characterized in that the maximum grain size of magnesium particles constituting the substrate of the magnesium alloy powder after plastic working is 20 μm or less. The intermetallic compound is at least one selected from the group consisting of Mg ₁₇ Al ₁₂ , Al ₂ Ca, Mg ₂ Si, MgZn ₂ , Al ₃ Re (Re: rare earth element), Al ₁₁ Re ₃ and Al ₆ Mn. The magnesium alloy powder raw material according to claim 1, which is a compound. The magnesium alloy powder raw material according to claim 1 or 2, wherein a maximum particle size of the intermetallic compound is 5 µm or less. The magnesium alloy powder raw material according to any one of claims 1 to 3, wherein a maximum particle size of the intermetallic compound is 2 µm or less. The magnesium alloy powder raw material in any one of Claims 1-4 whose maximum crystal grain diameter of the magnesium particle which comprises the base of the said magnesium alloy powder is 10 micrometers or less. A metal element selected from the group consisting of strontium (Sr), zirconium (Zr), scandium (Sc), and titanium (Ti) is contained in an amount of 0.5% to 4% by weight, with the balance being substantially magnesium ( The manufacturing method of the magnesium alloy powder raw material in any one of Claims 1-5 which is Mg). A magnesium alloy obtained by compacting and molding the magnesium alloy powder raw material according to any one of claims 1 to 6,
The maximum crystal grain size of the magnesium particles constituting the base of the alloy is 10 μm or less,
A high-strength magnesium alloy having a tensile strength at room temperature of 250 MPa or more. The maximum crystal grain size of magnesium particles constituting the base of the magnesium alloy is 5 μm or less,
The high yield strength magnesium alloy according to claim 7 whose tensile yield strength at normal temperature is 350 MPa or more. At least selected from the group consisting of Mg ₁₇ Al ₁₂ , Al ₂ Ca, Mg ₂ Si, MgZn ₂ , Al ₃ Re (Re: rare earth element), Al ₁₁ Re ₃ and Al ₆ Mn in the base of the magnesium alloy. The high yield strength magnesium alloy according to claim 7 or 8, wherein one intermetallic compound is precipitated and dispersed. It is a method of refining the crystal grain size of the magnesium particles constituting the substrate of the starting material powder by performing plastic working on the starting material powder,
As the starting material powder, preparing a magnesium alloy powder in which fine intermetallic compounds are precipitated and dispersed in the substrate by heat treatment,
The plastic working is a plastic working in which a starting raw material powder is passed between a pair of rolls and compressed or sheared to impart a working strain around the intermetallic compound,
The plastic working is repeatedly performed until the maximum size of the powder is 10 mm or less, the minimum size is 0.1 mm or more, and the maximum crystal grain size of the magnesium particles constituting the powder base is 20 μm or less. A method for producing a magnesium alloy powder raw material. The step of preparing magnesium alloy powder as the starting material powder,
Producing a magnesium alloy ingot by a casting method;
Solution treatment of the magnesium alloy ingot, followed by aging heat treatment to precipitate and disperse fine intermetallic compounds in the base of the ingot;
The method for producing a magnesium alloy powder raw material according to claim 10, comprising taking out the magnesium alloy powder from the ingot by machining. The magnesium alloy powder raw material according to claim 11, wherein the temperature of the starting raw material powder to be charged and the surface temperature of the roll in contact with the starting raw material powder are made equal to or lower than the temperature of the aging heat treatment when performing the plastic working. Manufacturing method. The magnesium alloy ingot contains a metal element selected from the group consisting of strontium (Sr), zirconium (Zr), scandium (Sc), and titanium (Ti) in an amount of 0.5% to 4% on a weight basis, and the balance The manufacturing method of the magnesium alloy powder raw material of Claim 11 or 12 whose is substantially magnesium (Mg). Pressurizing the magnesium alloy powder raw material according to any one of claims 1 to 6 in a mold and obtaining a green compact,
Heating the magnesium alloy compacted body at a temperature of 150 ° C. or higher and 450 ° C. or lower;
A process for producing a magnesium alloy by extruding the magnesium alloy compact immediately after the heating, and producing a magnesium alloy. The manufacturing method of the high yield strength magnesium alloy of Claim 14 whose maximum crystal grain size of the magnesium particle which comprises the base of the said magnesium alloy is 10 micrometers or less, and the tensile yield strength in normal temperature is 250 Mpa or more. The manufacturing method of the high yield strength magnesium alloy of Claim 14 or 15 which heats the said magnesium alloy compacting body at the temperature of 200 to 350 degreeC.