JP4850506B2 - Manufacturing method of superplastic magnesium alloy material - Google Patents

Description

  The present invention relates to refinement of crystal grains of a magnesium alloy using ultrasonic waves, and relates to a method for producing a magnesium alloy material that exhibits superplastic characteristics.

It is known that metal materials generally have higher strength, toughness, vibration damping properties, and corrosion resistance as crystal grains become smaller. When the crystal grains are made several μm or less, a superplastic phenomenon appears, and the ductility is dramatically improved under specific heating conditions while realizing high strength at room temperature.
In general, the definition of superplasticity is “a phenomenon in which deformation stress shows high strain dependency in tensile deformation of a polycrystalline material and exhibits a huge elongation of several hundred percent or more without causing local shrinkage”. Specifically, an equiaxed material having a small crystal grain of 10 μm or less is deformed at a strain rate of about 10 ⁻⁴ / s under the condition that the material is heated to a temperature of 1/2 or more of the melting point expressed in absolute temperature. Then, it is said that a huge elongation is expressed with a low deformation stress of 10 MPa or less. However, the strain rate required in industrial production is about 10 ⁻² / s, and this condition is referred to as high-speed superplasticity when the conditions indicating an elongation of 300% or more are satisfied.

Methods for refining crystal grains of ferrous materials and non-ferrous metal materials include methods of adding crystal growth inhibiting elements, methods of using transformation, precipitation, and recrystallization in a combination of rolling and heat treatment, and methods of applying strong shearing Are known (see, for example, Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4).
In many cases, the method of applying strong shearing is to heat treatment after processing to form a recrystallized structure. In this case, a combination of rolling and heat treatment is used to transform, precipitate, and recrystallize and to refine the grains. The principle is approximate and can be regarded as a similar method. When a strong shearing process is applied under heating, a recrystallized structure can be obtained without performing a heat treatment after the process. Such a phenomenon is called dynamic recrystallization.

For steel materials, a method that uses transformation, precipitation, and recrystallization by combining rolling and heat treatment is effective, and a fine grain structure of less than 1 μm has been obtained on a laboratory scale. The problem is how to simplify the process.
On the other hand, for non-ferrous metal materials, especially aluminum, it has been difficult to make a fine grain structure of 10 μm or less uniformly. In Japan, the New Energy and Industrial Technology Development Organization is used to create a fine grain structure of 3 μm or less. Technology development was carried out in a five-year plan from 1997 as a project by (NEDO), but the basic technology is a method of applying strong shearing to the material.

  Recently, magnesium alloys have been widely used as casings for notebook personal computers and mobile phones, taking advantage of the characteristics of being lightweight, tough and having high vibration absorption. Magnesium alloys have a hexagonal close-packed crystal structure, and therefore have low ductility at room temperature, making high-speed press molding difficult. Therefore, die casting and thixo molding are used as the main molding methods, but die casting and thixo molding have the disadvantages of high production cost due to poor yield and a large number of finishing processes. Realization of high-speed press forming is desired.

  In order to solve this problem, technical development for obtaining a fine grain structure of 1 μm or less has been performed. The main method is a method of applying a strong shearing process like aluminum. In general, heat treatment is performed after extrusion and special roll rolling to form a recrystallized structure. Recently, an ECAP method (Equal Channel Angular Pressing method) and the like have been developed.

  Extrusion is literally a method of extruding a billet or slab from a die having a hole of a predetermined shape, and generally a direct method of extruding through a die orifice. For example, pure magnesium heats and extrudes billets or slabs at 350-400 ° C, but the balance between billet temperature and extrusion speed is difficult compared to aluminum. There is a fault that it oxidizes. Mg-Al-Zn alloys (AZ alloys) and the like need more precise control.

Roll rolling is a method of manufacturing a thin plate by feeding a magnesium alloy in one direction while pressing it with upper and lower rolls. As special roll rolling, repeated roll rolling (Accumulative Roll Bonding), different peripheral speed rolling, molten metal rolling, warm rolling and the like have been studied.
Repeated joint rolling is a method in which a rolled plate is divided in half in the length direction, subjected to a surface treatment such as degreasing, and then the two plates are overlapped and rolled again. This method has a feature that it can be subjected to a strong shearing process without changing the plate thickness. However, the internal structure of the plate is wrinkled in the plate thickness direction, and the manufacturing cost is increased because there are many steps.

Different peripheral speed rolling is a method of changing the peripheral speed of the upper and lower rolls and applying a strong shearing process to the material. However, since rolling is performed without lubrication, it is susceptible to non-uniform shearing force and the surface condition becomes rough. .
Molten metal rolling is a method of rapid cooling by pouring a molten metal in which the additive element is supersaturated into a water-cooled roll. The additive element has the effect of promoting recrystallization nucleation and at the same time suppressing large grain growth. Magnesium alloys are easy to oxidize, so a sufficient atmosphere adjustment is required, making them unsuitable for mass production.

  Warm rolling is a method of rolling at a temperature equivalent to the intermediate between hot rolling that rolls above the recrystallization temperature and cold rolling that rolls at room temperature. For example, an Al-Zn-Mg-Cu alloy that is a kind of aluminum alloy In an alloy in which an appropriate amount of Zr is added, an effect other than a magnesium alloy has been confirmed, such as obtaining a fine grain structure. However, it is very difficult to control the intermediate temperature with a magnesium alloy having a small specific heat capacity, and no clear effect has been confirmed.

  The ECAP method is a method for obtaining a fine grain structure by placing a billet or slab in a die having a hole with a certain angle and applying a strong shearing force to the billet or slab by pressing and extruding. It is an effective method and attracts attention from an academic point of view. However, since the billet or slab undergoes work hardening, applying a strong shear force repeatedly requires a very large extrusion force, and application to a large billet or slab handled on an industrial production scale is impractical.

In addition, as a method for compensating for the drawbacks of the ECAP method, a continuous shear deformation method (Conshearing method) in which the ECAP method is continued has been proposed (see Non-Patent Document 1).
Each method is a method of strong shearing a melted billet or the like, and requires a very large stress for the shearing processing, or the magnesium alloy is deformed thinner and longer than necessary by the strong shearing processing. Therefore, there is a drawback that applicable products are limited.

JP 2003-043331 A JP 2002-194472 A JP 2002-105568 A JP 2000-271893 A Two outside Saitou, “PROPOSAL OF NOVEL CONTINUOUS HIGH STRATINGPROCESS-DEVELOPMENT OF CONSHEARING PROCESS”, Advanced Technology of Plasticity, Vol.III, Proceedings of the 6th International Conference on Technology of Plasticity, Sept, 19-24, 1999, p.2459 ~ 2464

  The present invention solves the above-mentioned problems of the prior art, and provides a method for producing a superplastic magnesium alloy material that can easily obtain a magnesium alloy material having a fine grain structure and exhibiting superplastic properties. The purpose is to provide.

  In the method for producing a superplastic magnesium alloy material according to the present invention, the magnesium alloy is immersed in water having a dissolved gas concentration of 0.004 ml / ml or less, and the ultrasonic horn irradiation surface is within a range of 2 to 40 mm from the water surface or the water tank wall surface. The above-mentioned problem is solved by applying ultrasonic waves oscillated from the ultrasonic horn irradiation surface to the magnesium alloy through water as a transmission medium in a state of protruding into the water.

  The vibration transmitted to the metal material is attenuated with the passage of time and finally stops. There are two mechanisms for damping vibration. One is called external friction, in which vibration energy is released from a vibrating metal material to the outside via air or the like. The other is internal friction, which is a mechanism in which vibration energy is converted into heat or strain inside a metal material. Internal friction is also called dampingcapacity.

Magnesium exhibits the maximum damping capacity among metals, and the damping capacity is quantified as specific damping capacity (SDC).
The intrinsic damping capacity is represented by the vibration energy loss rate per cycle of the vibrating object as shown in the following equation.
SDC (%) = (ΔW / W) × 100
Here, W is vibration energy, and ΔW is energy lost in one cycle.

Magnesium has an intrinsic damping capacity of 60% or more and accumulates much vibration energy as strain. Further, it is known that a magnesium alloy having improved strength and corrosion resistance, although not as pure magnesium, exhibits a large intrinsic damping capacity.
Damping capacity is classified into the following four types according to the difference in vibration energy conversion mechanism.
(1) By causing viscous flow or plastic flow at the interface between the parent phase and the second phase.
(2) By irreversible movement of the magnetic domain wall.
(3) Dislocations trapped by impurity atoms are separated and moved.
(4) By deformation twin formation.

The ultrasonic vibration energy transmitted to the magnesium alloy is consumed as the dislocations trapped by the impurity atoms of the vibration energy conversion mechanism (3) dissociate and move, or the formation of deformation twins of (4) It is considered to be consumed.
At this time, since a large strain similar to mechanically applying a shear stress is introduced into the magnesium alloy, a temperature obtained by multiplying the melting point of the magnesium alloy by an absolute temperature by 0.35 to 0.6. When heated at, the dislocations and deformed twins rearrange or change into a recrystallized structure composed of equiaxed fine grains in the process of releasing energy by mutual coalescence.

  Furthermore, when a magnesium alloy is immersed in a liquid having a dissolved gas concentration of 0.004 ml / ml or less and ultrasonic waves are applied to the magnesium alloy using the liquid as a transmission medium, the same as when a mechanical shear stress is applied to the magnesium alloy. In addition, dislocations and rearrangement of deformation twins or mutual annihilation occur, resulting in a change to a fine grain structure. That is, a change corresponding to the conventional recrystallized structure occurs only by applying an ultrasonic wave, and the crystal grain refining process can be greatly shortened.

  As a result of further earnest studies on the above method, the inventors of the present invention immersed the magnesium alloy in water having a dissolved gas concentration of 0.004 ml / ml or less, and the ultrasonic horn irradiation surface was 2 to 40 mm from the water surface or the tank wall surface. When ultrasonic waves oscillated from the ultrasonic horn irradiation surface are applied to the magnesium alloy through the water, which is the transmission medium, in a state of protruding into the water in a range, ultrasonic vibration energy larger than before is transmitted to the magnesium alloy. It was found that the crystal grain size was changed to a more advanced crystal structure.

The first factor that causes this phenomenon is that the threshold for cavitation generation (ultrasonic power per unit area, W / cm ² ) is high in water having a dissolved gas concentration of 0.004 ml / ml or less. Therefore, cavitation is suppressed as the dissolved gas concentration decreases. By suppressing the cavitation, the scattering of ultrasonic waves is reduced, and it becomes possible to transmit large ultrasonic vibration energy with high efficiency by the magnesium alloy. In addition, the effect becomes more remarkable as the dissolved gas concentration approaches 0 ml / ml.

  Water is used as a transmission medium for achieving a dissolved gas concentration of 0.004 ml / ml or less. Comparing saturated dissolved air concentrations in various liquids used for ultrasonic cleaning, water is 0.017 ml / ml (25 ° C), whereas ethyl alcohol is 0.169 ml / ml (25 ° C), and acetone is Like 0.203 ml / ml (25 ° C.), the organic liquid exhibits a high saturated dissolved gas concentration, so it is difficult to make the dissolved gas concentration lower than 0.004 ml / ml.

In the case of water, there is a problem that the surface of the magnesium alloy is easily eroded (erosion), but erosion is reduced because the cavitation is suppressed when the dissolved gas concentration is 0.004 ml / ml or less.
As a second factor, an ultrasonic wave is oscillated from an ultrasonic horn irradiation surface inserted in the range of 2 to 40 mm into the water from the water surface or the water tank wall surface, and the ultrasonic wave is applied to the magnesium alloy through water as a transmission medium. Thus, the present inventors have found that cavitation is further suppressed and a stronger ultrasonic wave can be applied.

  In Table 1, a titanium alloy step type horn having a diameter of 22 mm is inserted into the surface of a liquid tank filled with pure water having a dissolved air concentration of 0.004 ml / ml, and an ultrasonic wave having a frequency of 19 KHz, an output of 300 W, and a vibration amplitude of 42 μm. The relationship of the cavitation length with respect to the distance of a horn irradiation surface when it irradiates and a water surface is shown. When the distance between the horn irradiation surface and the water surface exceeds 40 mm, the cavitation length increases rapidly.

  This phenomenon is thought to be affected by changes in the water flow around the ultrasonic horn. Irradiation of ultrasonic waves in water causes a pressure difference between the area directly below the ultrasonic horn irradiation surface and its surroundings, causing water convection. When the ultrasonic horn irradiation surface is inserted deeply below the water surface, the convection draws a larger circle and becomes strong. Under the horn irradiation surface, a large negative pressure that is pulled from the surroundings acts, so that cavitation is likely to occur. However, when the ultrasonic horn irradiation surface is brought close to the water surface, the convection draws a small circle and becomes weak, and the negative pressure pulled from the surroundings just below the horn irradiation surface becomes small, so cavitation is considered to be suppressed.

This phenomenon is the same even if the ultrasonic horn is arranged on the wall surface of the water tank. An explanatory view of the arrangement of the ultrasonic horn is shown in FIG. FIG. 1A shows a state in which an ultrasonic horn 1 is inserted into water in a water tank 4 from above, in which 2 is a cone, 3 is an ultrasonic transducer, 6 is a magnesium alloy, and L1 is an ultrasonic horn. 1 represents the distance from the ultrasonic irradiation surface (tip surface) 1 to the water surface 5. The state of the ultrasonic horn 1 is protruded in the range of 2~40mm from the wall surface of the water tub 4 in the water tank 4, it refers to the state shown in FIG. 1 (b), the ultrasonic horn from the wall surface in the figure L2 is water tank 4 This represents the distance to the irradiation surface (tip surface).

  When the distances L1 and L2 in FIG. 1 are less than 2 mm, the vibration of the ultrasonic horn irradiation surface is used to vibrate the water surface or the wall surface of the water tank 4, so that the ultrasonic vibration transmitted to the magnesium alloy below the water surface is weak. Become. If the insertion length of the ultrasonic horn from the water surface or the wall surface of the water tank exceeds 40 mm, cavitation increases rapidly, so that the ultrasonic waves are scattered and the ultrasonic intensity transmitted to the magnesium alloy is weakened.

An ultrasonic horn is used for ultrasonic application.
It is known that the ultrasonic intensity is given by equation (1).
I = 2π ² ρc (fa) (1)
Here, I is the ultrasonic intensity (W / cm ² ), ρ is the medium density, c is the velocity of the sound wave in the medium (cm / s), f is the ultrasonic frequency (1 / s), and a is the vibration amplitude. To express.

From formula (1), it can be understood that the higher the frequency and the larger the vibration amplitude, the better for obtaining a large ultrasonic intensity. However, since the damping ability of the magnesium alloy is considered to be small with respect to vibrations at high frequencies, for the purpose of the present invention, in order to effectively apply ultrasonic waves to the magnesium alloy, a large vibration amplitude at low frequencies. It is necessary to use ultrasonic waves.
As a means for applying ultrasonic waves to the magnesium alloy, (a) a method in which the magnesium alloy is placed in a liquid tank to which an ultrasonic vibrator is bonded, and ultrasonic waves are applied to the magnesium alloy via a transmission medium in the liquid tank; (B) There is a method in which a magnesium alloy is placed in a liquid tank filled with a liquid serving as a transmission medium, an ultrasonic horn is inserted from the water surface or the wall surface of the water tank, and an ultrasonic wave is applied to the magnesium alloy.

  The method (a) is suitable for applying an ultrasonic wave to a large-area magnesium alloy, but it is difficult to vibrate the liquid tank to which the ultrasonic vibrator is bonded with a large vibration amplitude. On the other hand, in the method (b), the amplitude of the ultrasonic wave oscillated from the ultrasonic vibrator can be applied to the magnesium alloy, and a large ultrasonic vibration energy can be transmitted to the magnesium alloy. The ultrasonic horn has a function as a vibration amplitude expander.

The amplitude enlargement ratio is related to the area ratio of both end faces of the ultrasonic horn. For example, if the cross section is circular simple step horn, the area S ₁ of the amplitude magnification factor M is large end _face, when the area S ₂ of the small end face, given by equation (2).
M = S ₁ / S ₂ (2)
If the large end surface is an ultrasonic transducer surface or an ultrasonic transmission body (cone) end surface with a certain area, and the small end surface is an ultrasonic radiation surface, the amplitude of the ultrasonic radiation surface is reduced by the area of the ultrasonic irradiation surface. Enlarging in proportion to The relationship between the area ratio and the amplitude magnification ratio varies depending on the ultrasonic horn shape, but the amplitude magnification ratio increases in all horn shapes when the ultrasonic radiation surface is reduced.

In addition, as a method for transmitting ultrasonic vibration energy with high efficiency, there is a method in which an ultrasonic transmission body (cone) is directly connected to a magnesium alloy without using a liquid as a transmission medium. In this method, a standing wave is formed inside the magnesium alloy, so that the crystal grains are refined at the vibration nodes, but not at the vibration antinodes. This problem is slightly improved by means such as application of ultrasonic waves of a plurality of frequencies or frequency sweep. However, when an ultrasonic wave having a large vibration amplitude is applied, a very large tensile stress and compressive stress are repeatedly received at the vibration node, so that there is a risk that the magnesium alloy is damaged.
Therefore, as in the present invention, as the ultrasonic wave application means, a method of applying ultrasonic waves oscillated from the ultrasonic horn irradiation surface to the magnesium alloy through water as a transmission medium is suitable.

  According to the method for producing a superplastic magnesium alloy material according to the present invention, it becomes possible to introduce a large strain inside without changing the shape of the magnesium alloy, thereby promoting the formation of fine crystal grains, A magnesium alloy material having plasticity can be easily obtained.

Below, the manufacturing method of a typical superplastic magnesium alloy material is demonstrated in detail.
There are no special restrictions on the external shape and dimensions of the magnesium alloy material. For example, it is possible to use a powder solidified molded body or a plate material, a bar material, a pipe, or a molded body that is press-molded into a desired shape. The powder solidified molded body is a powder sintered body or a solidified molded body produced by compressive shearing of the powder, and the melted material is a cast or extruded or extruded magnesium alloy solidified after melting into a target shape. It is a processed one.

  In the present invention, the magnesium alloy is immersed in water having a dissolved gas concentration of 0.004 ml / ml or less. General means for reducing the dissolved gas concentration in water to 0.004 ml / ml or less include a vacuum degassing method, a method using a gas separation membrane, and a heat degassing method by heating and boiling. Among them, the water circulation type vacuum degassing method is suitable because it can maintain a low dissolved gas concentration.

  Water is passed through a gas-liquid separation membrane tube installed in a vacuum system, and then supplied to a liquid tank on which a magnesium alloy is placed. The water flowing out of the liquid tank is circulated again into the gas-liquid separation membrane tube. With this circulation system, the dissolved gas concentration of water in the liquid tank can be maintained at 0.004 ml / ml or less. The water is optimally pure water. Groundwater and tap water containing impurity ions cause corrosion deterioration of the magnesium alloy.

  In the present invention, it is desirable to make the dissolved gas concentration as low as possible, but it is difficult to completely remove it. This dissolved gas is air in a normal working environment, but in order to prevent the surface oxidation of the magnesium alloy, it is desirable to use an inert gas such as argon or nitrogen rather than air (oxygen). Therefore, it is possible to replace the air in water with these gases in advance. In addition to argon and nitrogen, magnesium alloys are not significantly corroded or oxidized, there is no risk of ignition, and a gas with a low saturated dissolved gas concentration may be used. Examples of such gases include helium, neon, krypton, and xenon. There is.

Examples of the magnesium alloy include Mg—Al alloy, Mg—Al—Zn alloy, Mg—Zr alloy, Mg—Zn—Zr alloy, Mg—Mg ₂ Ni alloy, Mg—RE—Zn alloy (RE is rare earth), Mg— Ag-RE alloys, Mg-Y-RE alloys, Mg-Al-Ca alloys, Mg-Al-Ca-RE, and the like are known as practical alloys. However, among Mg—Al alloys, Mg—Al—Zn alloys, Mg—Al—Ca alloys, or Mg—Al—Ca—RE, magnesium alloys with a large amount of Al added have a low intrinsic damping capacity. For example, Mg-10% Al alloy (AM100), Mg-9% Al-1% Zn alloy (AZ91), Mg-6% Al-3% Zn alloy (AZ63), etc. have an intrinsic damping capacity of less than 10%. .

  When the intrinsic damping capacity is less than 10%, most of the ultrasonic vibration energy is released to the outside of the magnesium alloy as external friction, so that the energy efficiency for introducing strain into the magnesium alloy is significantly reduced. Therefore, a magnesium alloy having an intrinsic damping capacity of 10% or more is optimal. However, it should be noted that the intrinsic damping capacity varies depending on the crystal orientation and grain size in addition to the alloy type. If the same alloy is used, the angle between the (0001) plane of the crystal and the ultrasonic irradiation direction is 90 °. The crystal grain size is larger as it is smaller. In the case of a texture, care must be taken because secondary recrystallization occurs when ultrasonic waves are applied for a long time.

As the material of the ultrasonic horn, a titanium alloy with high fatigue strength, low specific acoustic impedance (product of density and sound velocity), and high resonance sharpness (high resonance characteristics) is suitable for obtaining a large vibration amplitude. ing.
For example, a dissolved air concentration of 0.004 ml / obtained by passing a water circulation type vacuum degassing device with respect to a rolled material (50 mm × 50 mm × 1.25 mm) of an Mg—3% Al—1% Zn alloy (AZ31) Place a AZ31 rolled material test piece in a polypropylene water tank filled with ml of pure water and immerse it in pure water, and make an ultrasonic homogenizer titanium alloy horn (diameter 22 mm) so that the distance from the AZ31 rolled material is 19 mm. ) Is inserted from the water surface, and the water level is adjusted so that the horn irradiation surface is 2 mm to 40 mm below the water surface. Then, an ultrasonic wave having a frequency of 19 KHz, an output of 300 W, and a horn vibration amplitude of 42 μm is applied to the underwater AZ31 rolled material for 1 minute. To do.

  The magnesium alloy after the application of ultrasonic waves has a crystal grain size of about 26% or less before the application of ultrasonic waves while maintaining the initial shape. In the case of AZ31 rolled material (50 mm × 50 mm × 1.25 mm), the size of the material does not change, and the crystal structure having an average crystal grain size of 9.8 μm becomes an equiaxed crystal structure of 2.5 μm or less. It is possible to modify the AZ31 rolled material that exhibits superplasticity.

According to the method for producing a superplastic magnesium alloy material according to the present invention as described above, a superplastic magnesium alloy material having a uniform fine grain structure can be obtained in a short time without changing the shape of the magnesium alloy material. be able to.
In addition, the manufacturing method of the superplastic magnesium alloy material by this invention is applicable also to pure magnesium. Furthermore, if the magnesium alloy billet is performed before rolling or before extrusion, the flow stress is reduced due to the refinement of crystal grains, so that the time required for the rolling or extrusion process can be shortened.

[Example 1]
As a magnesium alloy, a 50 mm × 50 mm × 1.25 mm test piece was cut from an AZ31 rolled material with an outer cutter, and the surface of the cut AZ31 rolled material test piece was quickly washed with ethanol, and then a polypropylene liquid tank (inside An AZ31 rolled material test piece was placed on a pedestal in the 8 liter solution. Next, after the titanium alloy step type horn (diameter 22 mm) of the ultrasonic homogenizer is brought close to the AZ31 rolled material test piece so that the distance from the AZ31 rolled material test piece is 19 mm, the liquid tank is filled with pure water. Using a water circulation type vacuum degassing device that passes through the gas-liquid separation membrane tube, the pure water in the liquid tank is circulated between the vacuum degassing device and the polypropylene liquid tank, and dissolved in the pure water. The air concentration was reduced to 0.003 ml / ml. And after adjusting the water level of a liquid tank so that the distance from a horn irradiation surface to a water surface may be set to 2 mm, an ultrasonic wave with a frequency of 19 KHz and an output of 300 W is applied to an AZ31 rolled material test piece for 15 minutes. Applied. The vibration amplitude of the horn at this time was 42 μm.

Almost no deformation or dimensional change of the AZ31 rolled material test piece was observed by the above treatment. The elongation at break of the AZ31 rolled material test piece after application of ultrasonic waves was examined at an absolute temperature of 573 K and a strain rate of 10 ⁻² / s using an S18 test piece in accordance with JIS H7501. Further, a 10 mm × 10 mm × 1.25 mm microstructure observation test piece was cut out from the AZ31 rolled material test piece, etched with a 5% picric acid ethanol solution, and then observed with an optical microscope, and a magnesium alloy structure according to JIS G0551. The average crystal grain size was determined.
As shown in Table 2, the average crystal grain size at this time was reduced to about 26% before application of ultrasonic waves to 2.5 μm. It was confirmed that the elongation at break was 209% and superplasticity was exhibited. A small amount of surface oxidation occurred on the test piece.

[Example 2]
Except that the water level of the liquid tank was adjusted so that the distance from the horn irradiation surface to the water surface was 5 mm, the ultrasonic application operation similar to that in Example 1 was performed to measure the elongation at break of the AZ31 rolled material test piece. The average crystal grain size of the alloy structure was determined.
As shown in Table 2, the average crystal grain size at this time decreased to about 23% before application of ultrasonic waves and became 2.3 μm. It was confirmed that the elongation at break was 213% and superplasticity was exhibited. A small amount of surface oxidation occurred on the test piece.

[Example 3]
Except that the water level of the liquid tank was adjusted so that the distance from the horn irradiation surface to the water surface was 10 mm, the ultrasonic application operation similar to that in Example 1 was performed to measure the elongation at break of the AZ31 rolled material test piece. The average crystal grain size of the alloy structure was determined.
As shown in Table 2, the average crystal grain size at this time was as small as about 22% before application of ultrasonic waves, to 2.2 μm. It was confirmed that the elongation at break was 220% and superplasticity was exhibited. A small amount of surface oxidation occurred on the test piece.

[Example 4]
Except that the water level of the liquid tank was adjusted so that the distance from the horn irradiation surface to the water surface was 15 mm, the ultrasonic application operation similar to that of Example 1 was performed to measure the elongation at break of the AZ31 rolled material test piece. The average crystal grain size of the alloy structure was determined.
As shown in Table 2, the average crystal grain size at this time was as small as about 22% before application of ultrasonic waves, to 2.2 μm. It was confirmed that the elongation at break was 216% and superplasticity was exhibited. A small amount of surface oxidation occurred on the test piece.

[Example 5]
Except that the water level of the liquid tank was adjusted so that the distance from the horn irradiation surface to the water surface was 20 mm, the ultrasonic application operation similar to that of Example 1 was performed to measure the elongation at break of the AZ31 rolled material test piece. The average crystal grain size of the alloy structure was determined.
As shown in Table 2, the average crystal grain size at this time was as small as about 22% before application of ultrasonic waves, to 2.2 μm. It was confirmed that the elongation at break was 218% and superplasticity was exhibited. A small amount of surface oxidation occurred on the test piece.

[Example 6]
Except that the water level of the liquid tank was adjusted so that the distance from the horn irradiation surface to the water surface was 25 mm, the ultrasonic application operation similar to that of Example 1 was performed to measure the elongation at break of the AZ31 rolled material test piece. The average crystal grain size of the alloy structure was determined.
As shown in Table 2, the average crystal grain size at this time was as small as about 22% before application of ultrasonic waves, to 2.2 μm. It was confirmed that the elongation at break was 220% and superplasticity was exhibited. A small amount of surface oxidation occurred on the test piece.

[Example 7]
Except that the water level of the liquid tank was adjusted so that the distance from the horn irradiation surface to the water surface was 30 mm, the ultrasonic application operation was performed in the same manner as in Example 1 to measure the elongation at break of the AZ31 rolled material test piece. The average crystal grain size of the alloy structure was determined.
As shown in Table 2, the average crystal grain size at this time was as small as about 22% before application of ultrasonic waves, to 2.2 μm. It was confirmed that the elongation at break was 218% and superplasticity was exhibited. A small amount of surface oxidation occurred on the test piece.

[Example 8]
Except for adjusting the water level of the liquid bath so that the distance from the horn irradiation surface to the water surface is 35 mm, the ultrasonic application operation similar to that of Example 1 was performed to measure the elongation at break of the AZ31 rolled material test piece. The average crystal grain size of the alloy structure was determined.
As shown in Table 2, the average crystal grain size at this time decreased to about 23% before application of ultrasonic waves and became 2.3 μm. It was confirmed that the elongation at break was 210% and superplasticity was exhibited. A small amount of surface oxidation occurred on the test piece.

[Example 9]
Except that the water level of the liquid tank was adjusted so that the distance from the horn irradiation surface to the water surface was 40 mm, the ultrasonic application operation similar to that in Example 1 was performed to measure the elongation at break of the AZ31 rolled material test piece. The average crystal grain size of the alloy structure was determined.
As shown in Table 2, the average crystal grain size at this time was reduced to about 26% before application of ultrasonic waves to 2.5 μm. It was confirmed that the elongation at break was 200% and superplasticity was exhibited. A small amount of surface oxidation occurred on the test piece.

[Comparative Example 1]
Except that the water level of the liquid tank was adjusted so that the distance from the horn irradiation surface to the water surface was 45 mm, the ultrasonic application operation similar to that of Example 1 was performed to measure the elongation at break of the AZ31 rolled material test piece. The average crystal grain size of the alloy structure was determined.
As shown in Table 2, the average crystal grain size at this time was as small as about 58% before application of ultrasonic waves, and became 5.7 μm. It was confirmed that the elongation at break was 98% and superplasticity was exhibited. A small amount of surface oxidation occurred on the test piece.

[Example 10]
Using a water circulation type vacuum degassing device that fills the liquid tank with pure water and passes through the gas-liquid separation membrane tube, the pure water in the liquid tank is circulated between the vacuum degassing device and the polypropylene liquid tank. The dissolved air concentration in pure water was reduced to 0.004 ml / ml. Next, except that the water level of the liquid tank was adjusted so that the distance from the horn irradiation surface to the water surface was 25 mm, the breaking application of the AZ31 rolled material test piece was measured by performing the same ultrasonic application operation as in Example 1. Further, the average crystal grain size of the alloy structure was obtained.
As shown in Table 3, the average crystal grain size at this time was reduced to about 28% before application of ultrasonic waves and became 2.7 μm. It was confirmed that the elongation at break was 205% and superplasticity was exhibited. A small amount of surface oxidation occurred on the test piece.

[Example 11]
As a magnesium alloy, a 50 mm × 50 mm × 1.25 mm test piece was cut from an AZ31 rolled material with an outer cutter, and the surface of the cut AZ31 rolled material test piece was quickly washed with ethanol, and then a polypropylene liquid tank (inside An AZ31 rolled material test piece was placed on a pedestal in the 8 liter solution. Next, an ultrasonic homogenizer titanium alloy step type horn (diameter 22 mm) was brought close to the AZ31 rolled material test piece so that the distance from the AZ31 rolled material test piece was 19 mm, and the liquid tank was filled with pure water. Thereafter, 500 liters of nitrogen per minute was blown into the liquid tank for 30 minutes to replace the dissolved air in pure water with nitrogen. Then, using a water circulation type vacuum degassing device that passes through the gas-liquid separation membrane tube, the pure water in the liquid tank is circulated between the vacuum degassing apparatus and the polypropylene liquid tank, The dissolved nitrogen concentration was reduced to 0.004 ml / ml. Thereafter, the same operation as in Example 10 was performed to measure the elongation at break of the AZ31 rolled material specimen, and the average crystal grain size of the alloy structure was obtained.
As shown in Table 3, the average crystal grain size at this time was reduced to about 28% before application of ultrasonic waves and became 2.7 μm. It was confirmed that the elongation at break was 206% and superplasticity was exhibited. Further, no surface oxidation occurred on the test piece.

[Example 12]
Using a water circulation type vacuum deaeration device that passes through the gas-liquid separation membrane tube, the pure water in the liquid tank is circulated between the vacuum deaeration device and the polypropylene liquid tank, and dissolved air in the pure water. Except that the concentration was reduced to 0.002 ml / ml, the same operation as in Example 11 was performed to measure the elongation at break of the AZ31 rolled material test piece, and the average crystal grain size of the alloy structure was obtained.
As shown in Table 3, the average crystal grain size at this time was as small as about 21% before application of ultrasonic waves, to 2.1 μm. It was confirmed that the elongation at break was 222% and superplasticity was exhibited. Further, no surface oxidation occurred on the test piece.

[Example 13]
As a magnesium alloy, a 50 mm × 50 mm × 1.25 mm test piece was cut from an AZ31 rolled material with an outer cutter, and the surface of the cut AZ31 rolled material test piece was quickly washed with ethanol, and then a polypropylene liquid tank (inside An AZ31 rolled material test piece was placed on a pedestal in the 8 liter solution. Next, an ultrasonic homogenizer titanium alloy step type horn (diameter 22 mm) was brought close to the AZ31 rolled material test piece so that the distance from the AZ31 rolled material test piece was 19 mm, and the liquid tank was filled with pure water. Thereafter, 500 liters of argon per minute was blown into the liquid tank for 30 minutes, and the dissolved air in the pure water was replaced with argon. Then, using a water circulation type vacuum degassing device that passes through the gas-liquid separation membrane tube, the pure water in the liquid tank is circulated between the vacuum degassing apparatus and the polypropylene liquid tank, The dissolved argon concentration was reduced to 0.004 ml / ml. Thereafter, the same operation as in Example 10 was performed to measure the elongation at break of the AZ31 rolled material specimen, and the average crystal grain size of the alloy structure was obtained.
As shown in Table 3, the average crystal grain size at this time was reduced to about 29% before application of ultrasonic waves, and was 2.8 μm. It was confirmed that the elongation at break was 201% and superplasticity was exhibited. Further, no surface oxidation occurred on the test piece.

It is explanatory drawing for demonstrating arrangement | positioning of an ultrasonic horn.

Explanation of symbols

1 Horn 2 Cone 3 Ultrasonic Vibrator 4 Water Tank 5 Water Surface 6 Magnesium Alloy

Claims (1)

  The magnesium alloy is immersed in water having a dissolved gas concentration of 0.004 ml / ml or less, and the ultrasonic horn irradiation surface is projected into the water within a range of 2 to 40 mm from the water surface or the water tank wall surface. A method for producing a superplastic magnesium alloy material, characterized in that oscillated ultrasonic waves are applied to the magnesium alloy via water as a transmission medium.

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