JP2014152354A - Thin plate and foil material of magnesium-based alloy, and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin plate material and a foil material of a magnesium alloy having an addition amount of solute elements reduced and excellent in strength and attenuation characteristics, the magnesium alloy being suitable for a member of acoustic devices such as a speaker and a headphone.SOLUTION: A magnesium alloy of the present invention is a Mg-X alloy, wherein the additive element X is one or a plurality of kinds among Ag, Al, Li, Sn, and Zn. The content of the X element meets the expression: 0.001≤Xmol%<0.3, and the balance of the chemical composition is magnesium and inevitable impurities. The additive element is uniformly solid-soluble in a Mg host phase without forming a deposit. The average crystal grain size of a magnesium alloy ranges from 10 μm to 500 μm. A magnesium alloy of an average crystal grain size of 50 μm or less is rolled to 1 mm or less at a temperature between 200 and 400°C and a rolling reduction of 10 to 20% per one roll to manufacture a thin plate material and a foil material of the magnesium alloy.

Description

  The present invention relates to a magnesium-based alloy to which a small amount of a solute element such as silver or aluminum is added, and relates to a magnesium-based alloy thin plate and a foil material in which the thickness of the alloy material is 1 mm or less.

  Magnesium alloy is the lightest weight among practical metal materials and has excellent specific strength and rigidity, so it can be used as a weight reduction material for mobile devices such as electronic devices such as laptop computers and automobiles and motorcycles. It is used. Magnesium has excellent attenuation characteristics, so it is used as a member for reducing vibration and noise from vibration sources such as coils and machinery, such as acoustic parts such as speakers and headphones, and reactor storage cases. Yes.

  Pure magnesium exhibits excellent damping properties, but its strength is very low compared to other metal materials. Therefore, as shown in Patent Documents 1 and 2, a solute element is added to increase the strength of the material while maintaining high attenuation characteristics. For example, as listed in Patent Document 1, Mg- (0.5-9) mass% Ni- (0.2-3) mass% Ca alloy, Mg- (0.2-10) mass% Cu- ( 0.1-3) mass% Ca alloy, Mg- (0.05-0.6) mass% Mn- (0.2-3) mass% Ca- (0.01-0.1) mass% Be alloy Mg- (0.05-0.6) mass% Mn- (0.2-3) mass% Ca- (0.001-0.1) mass% Be alloy has been developed. In addition, as shown in Patent Document 2, one or more elements selected from Y, Nd, and Sr are added (0.01 to 6) mass% per element, and Al, Ca, Zr, Sn, and Mn are added. By not containing substantially, it has both high strength and high damping characteristics. However, since the alloys of these documents are intended to reduce vibration and noise, the shape of the alloy material is a bulk material having a plate thickness including a cast material, and is not intended for a thin plate or a foil material.

  In order to adapt to acoustic components, it is necessary to reduce the thickness of the material. Magnesium thinning and foil slicing are generally produced by warm rolling as shown in Patent Documents 3-5. Patent Document 3 discloses a plate thickness (0.2-2) containing Al (1-3.5) mass%, Zn (1-6) mass%, and Mn (0.1-2) mass%. ) Mm magnesium alloy sheet is disclosed. Patent Document 4 discloses a plate thickness (0) containing Al (1-11) mass%, Zn (0.1-2) mass%, and Mn (0.15-0.5) mass%. A 0.02-0.2) mm magnesium alloy sheet is disclosed. In Patent Document 5, at least one kind selected from Al, Zn, Mn, Si, Ca, Sr, Y, Cu, Ag, Ce, Sn, Li, Zr, Be and rare earth elements (excluding Y and Ce) is used. A magnesium alloy plate containing a total of 7.3 mass% of elements and having a thickness of 5 mm or less is disclosed.

  By the way, the main mechanism of material strengthening mechanism and damping behavior is dislocation motion (interaction between dislocation and solute element), but it is impossible to improve the strength and damping ability at the same time. That is, inhibiting the dislocation movement by adding a solute element leads to an increase in strength of the material, but conversely reduces the damping characteristics. Therefore, adding a large amount of a solute element does not improve the damping characteristics.

  Patent Documents 6 and 7 disclose magnesium binary alloys to which a small amount of solute element is added. Patent Document 6 discloses a high-strength and high-strength structure in which one solute atom having a larger atomic radius than magnesium is 0.03 to 0.54 mol% and the balance is magnesium, and the average crystal grain size of the magnesium matrix is 1.5 μm or less. A highly ductile magnesium alloy is disclosed. However, when the crystal grain size is fine like this magnesium alloy, the crystal grain boundary inhibits the dislocation motion, so that there is a problem that the damping characteristic is lowered. Patent Document 7 discloses a magnesium alloy to which Ce, La, and Y are added in an amount of 0.01 to 0.5 mol%. However, this magnesium alloy is intended to improve high strength and deep drawability, and no description is given about the damping characteristics.

JP 2003-113436 A JP 2012-087379 A JP 2003-328063 A JP 2009-12083A JP2012-21182A JP 2006-16658 A JP 2008-214668 A

  As described in Patent Documents 1 and 2, although high damping capacity magnesium alloys have been developed, all of these alloys are limited to bulk materials and relate to magnesium alloy thin plates and foils having high strength and high damping characteristics. It is not a thing. This is due to the hard plastic workability of magnesium. As disclosed in Patent Documents 3 and 4, the magnesium alloy is thinned and made into a foil only by a commercial magnesium alloy (AZ-based alloy) added with Al and Zn, which are relatively easy to plastically process. . On the other hand, addition of a large amount of solute element is not preferable from the viewpoint of improving the damping capacity as described above. For this reason, the present condition is that the magnesium alloy sheet material and foil material which have both high strength and a high damping characteristic have not been developed yet.

  As a result of detailed test studies, the inventors have found that by adding a small amount of a specific solute element, it is possible to improve the damping characteristic while maintaining a high hardness (strength) characteristic. The dislocation movement of magnesium near room temperature is only on the bottom surface. However, it was found that the damping characteristics can be improved while maintaining the high hardness characteristics by using the few sliding systems. In other words, the hardness characteristics are improved by solid solution strengthening with solute elements, and measures to prevent degradation of the attenuation characteristics by controlling the orientation of the bottom surface, which is the main slip system of magnesium crystals, and the temperature conditions of plastic processing during deformation. Adopted.

  The first aspect of the present invention is that the Ag content is 0.001 mol% ≦ Ag mol% <0.3 mol%, the balance is Mg and inevitable impurities, and Ag forms precipitates in the Mg matrix. There is provided a magnesium alloy thin plate material or foil material that is uniformly solid-solved and has an average crystal grain size ranging from 10 μm to 500 μm and excellent in strength and damping ability.

  A second aspect of the present invention is the magnesium alloy thin plate material or foil material according to the first aspect of the present invention, wherein a part or all of the solid solution Ag is substituted with one or more of Al, Li, Sn, and Zn. The present invention provides a magnesium alloy sheet material or foil material excellent in strength and damping capacity.

  A third aspect of the present invention provides a magnesium alloy thin plate material or foil material according to the first or second aspect of the present invention, wherein the final thickness of the raw material is 1 mm or less and excellent in strength and damping capacity. .

4th of this invention is a manufacturing method of the magnesium alloy thin plate material or foil material in any one of invention 1 thru | or 3, Comprising: In the said magnesium alloy cast piece after casting,
In a temperature range of 450 to 525 ° C., after holding for 1 to 12 hours, solution heat treatment is performed with water cooling,
In a temperature range of 200 to 450 ° C., a plastic deformation process with an equivalent plastic strain of 2 or less is performed on the magnesium alloy slab until an average grain size becomes 50 μm or less,
In a temperature range of 200 to 400 ° C., a magnesium alloy thin film excellent in strength and damping capacity is obtained by rolling the plastic deformation magnesium alloy material to 1 mm or less under the condition that the rolling reduction rate is 10 to 20%. A method for producing a plate material or a foil material is provided.

  In order to obtain the present invention, the addition amount a of the solute element is 0.001 mol% ≦ a <0.3 mol%, preferably 0.02 mol% ≦ a ≦ 0.2 mol%. When the addition amount is 0.3 mol% or more, it is desirable from the viewpoint of improving the strength, but since the addition amount of the solute element is large, it is not preferable from the viewpoint of improving the damping characteristics. On the contrary, if it is less than 0.001 mol%, the improvement in strength is low, and it is difficult to achieve both high hardness and high damping ability. Further, the average crystal grain size of the magnesium matrix of the magnesium alloy thin plate or foil is 10 μm or more, more preferably 20 μm or more. As the grain size becomes finer, the ratio of grain boundaries increases and contributes to the improvement of hardness, but the grain boundaries inhibit dislocation motion, so the crystal grain size may be coarse from the standpoint of improving damping capacity. desirable. The average crystal grain size before and after thin plate and foil processing is compared, and the crystal grain size becomes fine when processed under conditions of low temperature and large rolling reduction that promotes dynamic recrystallization. During the rolling process, the crystal grains may be coarsened under the processing conditions where the processing temperature is high and the rolling reduction is small, but the limit value is 500 μm in order to maintain the strength and damping capacity of the present invention.

  In the present invention, Ag (atomic radius 0.144 nm, maximum solid solution amount 3.8 mol% with respect to magnesium) was treated as an additive element, but Li (0.157 nm, 17 mol%), Al (0.144 nm, 11.5 mol) %), Zn (0.137 nm, 2.4 mol%), and Sn (0.158 nm, 3.4 mol%). The reason is that the atomic radius of Ag is smaller than the atomic radius of magnesium of 0.160 nm and acts as a substitutional element. The above alternative solute elements also exhibit the same behavior because they are smaller than the atomic radius of magnesium and close to the atomic radius of Ag. Moreover, the addition amount of 0.3 mol% of the present invention is extremely small as compared with the maximum solid solution amount of Ag with respect to magnesium. Therefore, solute elements exist in a solid solution state in the magnesium matrix, and the main factor affecting the strength and damping ability is considered to be the interaction between individual solid solute elements and dislocations. Since the above-mentioned alternative elements also have a wide solid solubility limit with respect to magnesium, it is obvious that they exist in the same state as Ag in the magnesium matrix and can be substituted because they behave in the same manner.

  In order to obtain the thin plate material and foil material of the present invention (the foil material in the present invention is defined as a thin plate material having a thickness of 0.20 mm or less), the following processing methods and procedures are exemplified. First, an ingot material (processed material) to be processed into a thin plate or foil is produced using gravity casting, continuous casting, die casting, or the like. If the initial average grain size of the processed material is coarse, deformation twins are generated during processing into a thin plate or foil, and wrinkles, burrs or cracks are generated, making it difficult to create a sound material. Therefore, before processing into a thin plate or foil, it is desirable to set the average crystal grain size of the processed material to 50 μm or less using extrusion, rolling, or forging. Generation | occurrence | production of the deformation | transformation twin which becomes a starting point of a wrinkle, a burr | flash, a crack, etc. can be suppressed as a crystal grain diameter is 50 micrometers or less. At that time, since it is not the purpose to perform high strain processing, the equivalent plastic strain is 2 or less and the processing temperature may be 200 to 450 ° C. Of course, if the average grain size of the processed material is 50 μm or less, it may be processed directly into a thin plate or foil. Moreover, in order to reduce the casting (dendritic) structure | tissue of a processed material and to make a solute element form a solid solution before performing strong strain processing, solution treatment may be performed at a temperature range of 450 to 525 ° C. for 2 to 12 hours. desirable. The solution treatment temperature may be within the temperature range in which the added amount of the solute element is 0.3 mol%. Further, when the holding time is 12 hours or longer, the additive element can be sufficiently dissolved, so that it is not necessary to perform the solution treatment for a long time. On the other hand, when the holding time is 2 hours or less, it is considered that the cast structure remains because the diffusion of the solute element is insufficient.

  Next, thinning or foiling of the processed material is desirably performed by rolling in order to thin the material and to control the texture of the bottom surface. The temperature and rolling reduction during rolling may be 200 to 400 ° C. and 10 to 20%. When the processing temperature is low (temperature lower than 200 ° C.) or the rolling reduction is large (rolling ratio larger than 20%), as shown in FIG. 7, cracks occur at the edge of the sample, and it is difficult to manufacture a sound material. On the other hand, when the processing temperature is high (400 ° C. or higher), the sample may be burned during processing, which is dangerous in operation. Moreover, when the processing rate is small (10% or less), it is difficult to wind the sample, the surface roughness becomes large (the gloss is lost), and the surface state is not preferable.

  By the said invention, compared with the hardness and damping capability of pure magnesium, it came to show the outstanding intensity | strength and damping characteristic. This is presumed to be the formation of a bottom texture by solid solution strengthening by adding solute elements and warm rolling. Although the alloy of the present invention has excellent material properties, the amount of the solute element added is extremely small, so that it does not cause a significant increase in cost.

The external appearance photograph of the sound Mg-0.03 mol% Ag alloy foil of a present Example. The microstructure example of Mg-0.05 mol% Ag alloy before foil processing. The example of the fine structure of a Mg-0.05 mol% Ag alloy using EBSD observation. An example of observation of an optical microscope structure of an Mg-0.1 mol% Ag alloy. An example of forming a bottom texture of an Mg-0.05 mol% Ag alloy. Relationship between added amount of Ag and internal friction ratio. An appearance photograph of Mg-0.1 mol% Ag alloy foil having cracks at the ends because the processing temperature is low and the rolling reduction is large.

<Example>
Six types of Mg—Ag alloy castings having a target Ag content of 0.02 mol%, 0.03 mol%, 0.05 mol%, 0.1 mol%, 0.2 mol%, and 0.3 mol% were melted. Ag target content 0.02 mol%, 0.03 mol%, 0.05 mol%, 0.1 mol%, 0.2 mol% are examples within the scope of the present invention, Ag target content 0.3 mol% is It is a comparative example outside the scope of the invention. After adding 800 g of silver (Ag) and pure magnesium (Mg) (purity 99.94 mass%) of the target content and placing in a melting furnace that can be replaced with an argon atmosphere, completely melting at 750 ° C. The cast material was produced by casting in an iron mold. The content of Ag was evaluated by ICP emission spectroscopic analysis after solution treatment of the cast material at 500 ° C. for 2 hours. The results of the composition analysis are shown in Table 1. All six types of alloys were prepared according to the following procedures and conditions.

  The obtained cast material was subjected to a solution heat treatment in which water was cooled after being held in a furnace at a temperature of 500 ° C. for 2 hours, and then a cylindrical billet for extrusion having a diameter of 40 mm and a height of 50 mm was produced by machining. The billet is put into an iron container having a diameter of 190 mm and a height of 170 mm that can be heated up to 450 ° C., held at a temperature of 275 ° C. for 30 minutes, and then given a warm strain by extrusion at an extrusion ratio of 42: 1. Processing was performed to produce an extruded material having a thickness of 3 mm and a width of 10 mm. Then, using the rolling machine which heated and maintained the roll atmosphere at 300 degreeC with respect to the said extrusion material, rolling process was repeated on the conditions of the rolling reduction rate of 10% for every time, and the magnesium alloy foil whose final thickness is 23 micrometers is obtained. Produced. A typical appearance photograph produced in this example is shown in FIG.

  FIG. 2 shows an example of microstructure observation of a sample immediately before foil piece processing, that is, an Mg-0.1 mol% Ag alloy sample subjected to extrusion processing after solution treatment. In the fine structure observation using an optical microscope, the average crystal grain size of the magnesium matrix was 10 μm. Other Mg—Ag alloys also had an average crystal grain size of 50 μm or less within a range of 25 to 10 μm. The average crystal grain size was calculated using the intercept method.

  The microstructure of the Mg-Ag alloy separated into foil pieces was observed using a scanning electron microscope / electron beam backscatter diffraction (EBSD) and an optical microscope. Examples of observation are shown in FIGS. All microstructures were observed on the rolling surface. From FIG. 3, the crystal grain boundaries are composed of large-angle grain boundaries with an orientation difference of 15 ° or more, and the average of crystal grains surrounded by the large-angle grain boundaries (denoted as G in the figure) was 80 μm. Table 1 shows the average crystal grain size after processing the foil pieces of each alloy. From the observation of the structure using the optical microscope of FIG. 4, the presence of precipitates and inclusions could not be confirmed. Further, FIG. 5 shows an example of texture formation of an Mg-0.05 mol% Ag alloy. In a magnesium alloy wrought material using rolling or extrusion, each crystal grain is oriented parallel to the processing direction due to the hexagonal crystal structure. The alloy of the present invention can also confirm the formation of the bottom texture accumulated on the bottom surface (0001). The other Mg—Ag alloys were the same as the microstructures shown in FIGS.

  Generally, the hardness of a material is evaluated using a Vickers hardness tester. However, since the thickness of the sample produced by the present invention is as thin as 23 μm, the hardness of each sample was evaluated using nanoindentation in which the indentation depth can be controlled in the nanometer order. A nanoindentation test was performed under the conditions of an indentation load of 1 mN and an indentation speed of 1 mN / s, and the hardness was determined for each indent using the Oliver-Pharr equation. Each sample was measured 50 times or more in order to reduce variation. Table 1 shows the average values. Here, the average value was obtained from the measurement results of the remaining 80% by deleting the hardness values of 10% above and below the total number of measurements. For example, in the case of 50 measurement points, the measurement results were removed from the maximum value by 5 points and from the minimum value by 5 points, and the average value was obtained from the remaining 40 points. As shown in Table 1, as the solute element was added and the amount added was increased, the hardness was improved. Further, since the hardness of the Mg—Ag alloy showed a larger value than that of pure magnesium, an increase in strength has been achieved.

  The internal friction (damping) characteristic was evaluated by vibrating the tip of the indenter at an arbitrary frequency (within 1 to 300 Hz) during the nanoindentation test to obtain Tan δ. Each sample was measured 50 times or more at a constant indentation load of 1 mN under three conditions of frequencies of 2, 20, and 200 Hz. The average value is obtained by the same method as the hardness, and the results are shown in Table 1. FIG. 7 shows the relationship between the solute element addition amount and the internal friction ratio. Here, the internal friction ratio is defined as the ratio of Tan δ of each alloy to Tan δ of pure magnesium, and a value larger than 1 indicates that it is superior to the internal friction characteristics of pure magnesium. Moreover, although the broken line in the figure shows a value of 80% with respect to Tanδ of pure magnesium, it was determined that the attenuation characteristic as a magnesium alloy material is inferior below this value. With the addition of solute elements, a large internal friction ratio, that is, an improvement in internal friction characteristics was observed. However, the Mg-0.3 mol% Ag alloy showed 80% or less of the internal friction characteristics of pure magnesium in all three conditions. From the above, it can be said that the addition amount of the solute element is appropriate to be less than 0.3 mol% from the viewpoint of improving both the strength and damping ability.

<Comparative Example 1>
A pure magnesium foil having a thickness of 23 μm under the same conditions as in the Examples except that pure magnesium (purity: 99.94 mass%) was processed into an extruded billet having a diameter of 40 mm and a height of 40 mm, and the extrusion temperature was 225 ° C. Was made. The average of the crystal grains surrounded by the large-angle grain boundaries of the sample was 100 μm. Table 1 shows the results of hardness and internal friction characteristics obtained from the nanoindentation test.

<Comparative example 2>
A commercial magnesium alloy (Mg-3 mass% Al-1 mass% Zn: AZ31) rolled plate was used, and a pure magnesium foil having a thickness of 23 μm was produced under the same conditions as in the examples. The average of the crystal grains surrounded by the large-angle grain boundaries of the sample was 27 μm. Table 1 shows the results of hardness and internal friction characteristics obtained from the nanoindentation test.

G: Crystal grains surrounded by large-angle grain boundaries LAG: Small-angle grain boundaries: Crystal grain boundaries in which the orientation difference between adjacent crystal grains is less than 15 ° I: The degree of accumulation of crystal orientation (the larger the value, the higher the degree of accumulation) )

  If the magnesium alloy foil material of the present invention is used, it can be applied as an insert material for structural parts where vibration and noise are problematic as well as acoustic related members. In addition, taking advantage of the thinness of the material, it is expected to be applied to miniaturization of devices such as medical equipment.

Claims (4)

Mg-Ag binary magnesium alloy, Ag content is 0.001 mol% ≦ Agmol% <0.3 mol%, the balance is Mg and inevitable impurities, and Ag is in the Mg matrix A magnesium alloy thin plate material or foil material excellent in strength and damping capacity, characterized in that it uniformly dissolves without producing precipitates and has an average crystal grain size range of 10 μm to 500 μm. It is a magnesium alloy thin plate material or foil material of Claim 1, Comprising: Part or all of the said solid solution Ag is substituted by 1 or more types in Al, Li, Sn, Zn. A magnesium alloy sheet or foil material excellent in strength and damping capacity. The magnesium alloy sheet material or foil material according to claim 1 or 2, wherein the material has a final thickness of 1 mm or less, and is excellent in strength and damping capacity. A method for producing a magnesium alloy sheet or foil material according to any one of claims 1 to 3,
To the magnesium alloy slab after casting,
In a temperature range of 450 to 525 ° C., a solution heat treatment that is held for 1 to 12 hours and then water-cooled is performed,
In a temperature range of 200 to 450 ° C., a plastic deformation process with an equivalent plastic strain of 2 or less is performed on the magnesium alloy slab until an average grain size becomes 50 μm or less,
In the temperature range of 200-400 ° C., the plastic deformation magnesium alloy material is excellent in strength and damping capacity, characterized by rolling to 1 mm or less under the condition that the rolling reduction rate is 10-20%. A method for producing a magnesium alloy sheet or foil material.