Magnesium-based alloy wrought material

Abstract

To provide a Mg group alloy extension material which can reduce yield anisotropy while maintaining excellent tensile yield strength characteristics.SOLUTION: An Mg group alloy extension material contains at least one or more elements of three kinds of elements of In, Ge and Ga, and the balance Mg with inevitable impurities, wherein a content of the contained element among In, Ge and Ga is 0.03 mol% or more and 1 mol% or less, and room temperature strength is excellent. There is provided an Mg group alloy extension material which contains any one element of two kinds of elements of Mn and Bi in addition to at least one element of three kinds of elements of In, Ge and Ga, wherein contents of the five kinds of elements are 0.03 mol% or more, contents of In, Ge and Ga are 1.0 mol% or less, and room temperature strength is excellent. The extension material has yield stress obtained by tensile test of 200 Mpa or more, and a ratio of the yield stress to yield stress obtained by compression test of 0.6 or more.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] This invention relates to a magnesium (Mg)-based alloy wrought material exhibiting excellent room-temperature strength and reduced yield anisotropy. [Background technology]

[0002] Mg alloys are attracting attention as next-generation lightweight metallic materials. When used as structural components, the development of materials and components with superior strength properties is desired to ensure safety and reliability. In metallurgy, grain refinement has long been used as an effective method for improving strength. In particular, Mg has a large Hall-Petch coefficient compared to other metals due to its crystal structure (hexagonal structure) (Non-Patent Literature 1), making grain refinement highly effective for increasing strength. Another well-known and experimental method for improving strength is to add one or more elements other than Mg to create alloys. In particular, the greater the difference in atomic radius from the base metal of the element, the greater the improvement effect, and in Mg alloys, adding rare earth metals is the most effective. However, the use of rare earth elements is undesirable from an economic standpoint because it increases the cost of the material.

[0003] Looking at common elements, Mg-Al-Zn:AZ alloys containing aluminum and zinc, and Mg-Zn-Zr:ZK alloys containing zinc and zirconium are commercially available. These Mg alloys are subjected to drawing processes with heat treatment to refine the grain size and improve their strength. During this drawing process, the basal planes are oriented parallel to the processing direction, forming a basal texture. As a result, although the tensile strength improves due to the refinement of the grain size, the compressive strength is only about half of the tensile strength, exhibiting a problem of yield anisotropy where the yield stress changes depending on the direction of stress application. Normally, plastic deformation of metallic materials is driven by dislocations, but in the case of Mg, when compressive stress is applied along the c-axis, deformation twins are formed with a stress smaller than that of dislocation movement. This difference in the plastic deformation mechanism causes yield anisotropy and is a factor that limits the handling of Mg drawing materials.

[0004] Against this backdrop, the inventors focused on adding only one type of solute element and investigated and researched how to increase the strength of Mg-based alloys. Based on the results of this research, Patent Document 1 discloses a fine-grained Mg alloy with excellent strength properties, in which the crystal grains are refined by containing a trace amount of one element from among rare earth elements or common elements such as Ca, Sr, Ba, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Dr, Tm, Yb, and Lu. The main reason for the increased strength of this alloy is that the added solute element segregates at the grain boundaries.

[0005] Furthermore, Patent Document 2 discloses an Mg-based alloy with excellent room-temperature strength properties, containing 14.5 mass% or less of Sn, with an average grain size of 10 μm or less of the Mg matrix, and where sub-grain boundaries (small-angle grain boundaries) with an average grain size of 2 μm or less constitute a large proportion of the grain boundaries surrounding the Mg matrix. It was discovered that the above-mentioned finding of introducing sub-grain boundaries at high density can also be applied to Mg-based alloys containing 3.5 to 11 mass% of Al, and this is disclosed in Patent Document 3. The Mg-based alloys disclosed in Patent Documents 2 and 3 are characterized not only by their excellent strength, but also by a reduction in yield anisotropy between compressive yield stress and tensile yield stress, due to the presence of sub-grain boundaries.

[0006] Furthermore, Patent Document 4 discloses a high-strength Mg-based alloy in which two or more solute elements are added, characterized in that Ca and Zn are contained within the solid solution amount, and Ca and Zn are segregated parallel to the c-axis direction of Mg.

[0007] The inventors also diligently investigated and researched Mg-based alloys containing Mn. Based on the results of this research, Patent Document 5 discloses an Mg alloy with excellent fracture toughness containing 1 mol% or less of Mn and deformation twins present in the Mg matrix. Patent Document 6 discloses an Mg-based alloy with excellent room-temperature ductility, containing 0.07 to 2 mass% of Mn with a Mg matrix size of 5 μm or less. These alloys are characterized by a fracture elongation of approximately 100% and an m-value of 0.1 or higher, which is an indicator of the contribution rate of grain boundary slip to deformation. Furthermore, the stress reduction degree is used as an indicator of formability, and the value is characterized by being 0.3 or higher. Furthermore, Patent Document 7 discloses a Mg-based alloy consisting of Mg-Amol%Mn-Bmol%X, where A is 0.03 to 1 mol%, B is less than 1 times A, and it contains Bi, Sn, and Zr, and exhibits excellent room-temperature ductility without fracture even when subjected to a nominal strain of 0.2 or more. However, these Patent Documents 5 to 7 concern improvements in fracture toughness and room-temperature ductility, and do not describe or disclose improvements in strength properties.

[0008] The element Mn added to Mg is mostly used as an impurity removal element, bonding with iron (Fe) or silicon (Si) during melting. It is known that Mg alloys containing Mn as the principal element (first element) are given ductility (Patent Documents 6, 7, Non-Patent Documents 2, 3). This is because the addition of Mn activates grain boundary sliding. Furthermore, regarding the strength and ductility of Mg-Mn alloys, there are reported examples in Non-Patent Documents 4, 5 as Mg-Mn-X ternary alloys. X can be Al, Bi, Li, Sn, Y, Zn, or Zr. The addition of Bi, Li, and Zr has little effect on increasing strength but has a great effect on improving ductility. On the other hand, Al, Sn, Y, and Zn show the opposite effect, excelling in improving strength but degrading ductility. From these reported examples, it can be concluded that the added element X is effective in improving either strength or ductility, but it is difficult to achieve both strength and ductility. Furthermore, in alloys with ternary or greater systems, intermetallic compounds can form, making the elemental functions on strength and ductility unclear, and thus difficult to apply conventional solid solution strengthening theories. Of course, in alloys with Mn as the main element, where research history is short and there are no research reports, it is unknown whether the addition of a third element has any effect on strength or ductility.

[0009] On the other hand, focusing on other elements that can be dissolved in Mg at a solid solution level of 0.03 mol% or more, indium (In), gallium (Ga), and germanium (Ge) are available. Mg-based alloys containing In are disclosed in Patent Documents 8-10, Mg-based alloys containing Ge are disclosed in Patent Document 10, and Mg-based alloys containing Ga are disclosed in Patent Documents 11 and 12.

[0010] Patent document 8 discloses a Mg-based alloy characterized by containing less than 12 mol% In, and patent document 9 discloses one characterized by containing 40 mol% In. However, since the main focus is on improving recyclability and damping properties, the effects of drawing on strength and ductility are not described. Patent document 10 discloses a corrosion-resistant ternary Mg-based alloy containing 0.5 mass% to 2 mass% Ge and 0.5 mass% to 2 mass% In, and a method for manufacturing it. Similar to patent documents 8 and 9, there is no description of drawing, and the effects on strength, ductility, and anisotropy reduction are unknown. Patent document 11, which contains Ga, discloses a Mg-based alloy for stents containing 1.26 to 2.6 mass% Mn and 2 to 4.2 mass% Ga. It requires extrusion at 435 to 835°C, but considering the melting point of Mg, the drawing temperature is high and dangerous from the standpoint of work safety. On the other hand, Patent Document 12 discloses an Mg-based alloy containing Li and 3-8.5 mass% Ga, exhibiting excellent strength properties. In this patent document, drawing is considered optional, but since the main factor in exhibiting strength properties is age hardening of the Mg-Ga-Li ternary precipitate phase, the contribution of strengthening by drawing and Ga addition is not disclosed. From these prior patent documents, the effects of adding In, Ge, and Ga elements on strength, ductility, and anisotropy reduction remain unclear. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2006-16658 [Patent Document 2] Patent No. 6080067 [Patent Document 3] Patent No. 5561592 [Patent Document 4] Patent No. 5787380 [Patent Document 5] Patent No. 6587174 [Patent Document 6] Patent No. 6648894 [Patent Document 7] Japanese Patent No. 6860235 [Patent Document 8] CN101967590 [Patent Document 9] Japanese Unexamined Patent Publication No. 63-270441 [Patent Document 10] CN111394631 [Patent Document 11] CN113718145 [Patent Document 12] CN110983135 [Non-Patent Literature]

[0012] [Non-Patent Literature 1] K. Kubota et al., J. Mater. Sci., 34 (1999) pp.2255-2265. [Non-Patent Literature 2] H. Somekawa et al., Philo. Mag. 96 (2016) pp.2671-2685. [Non-Patent Literature 3] H. Somekawa et al., Mater. Sci. Eng., A730 (2018) pp.355-362. [Non-Patent Literature 4] H. Somekawa et al., Mater. Sci. Eng., A766 (2019) 138384. [Non-Patent Literature 5] H. Somekawa et al., Metal. Mater. Trans., 53A (2022) pp.1110-1118. [Summary of the Invention] [Problem to be Solved by the Invention]

[0013] An object of the present invention is to provide a Mg-based alloy worked product having excellent room-temperature strength and reduced yield anisotropy, to which at least one or more of three elements selected from In, Ge, and Ga are added. [Means for Solving the Problem]

[0014] The first aspect of the present invention provides a wrought Mg-based alloy material comprising Mg-Amol%X, with the remainder being Mg and unavoidable impurities, wherein X is one or more elements from In, Ge, and Ga, and the value of A is 0.03 mol% or more and 1 mol% or less.

[0015] The second aspect of the present invention provides a wrought Mg-based alloy material comprising Mg-Amol%X-Bmol%Z, with the remainder being Mg and unavoidable impurities, where X is one or more elements from In, Ge, and Ga, Z is either Mn or Bi, the value of A is 0.03 mol% or more and 1 mol% or less, the relationship between A and B is B ≥ A, the upper limit of A is 1.0 times or less than the upper limit of B, and the lower limit of B is 0.03 mol% or more.

[0016] The third aspect of the present invention provides a Mg-based alloy wrought material according to invention 1 or 2, wherein elements other than Mg are segregated at the grain boundaries of the Mg-based alloy wrought material. The fourth aspect of the present invention provides a Mg-based alloy wrought material according to inventions 1 to 3, wherein the average crystal grain size of the Mg matrix of the Mg-based alloy wrought material is 20 μm or less.

[0017] Invention 5 is a wrought Mg-based alloy material according to Inventions 1 to 4, wherein the initial strain rate of the wrought Mg-based alloy material is 1x10⁻¹⁰. -3 s -1 The present invention provides a wrought Mg-based alloy material having a yield stress of 200 MPa or more and a fracture elongation of 15% or more in the stress-strain curve obtained by the above-described room-temperature tensile test. The present invention 6 is a wrought Mg-based alloy according to inventions 1 to 5, wherein the initial strain rate of the wrought Mg-based alloy is 1x10⁻¹⁰. -3 s -1The above provides a wrought Mg-based alloy material in which the ratio of yield stresses obtained by room-temperature tensile and compression tests at the same initial strain rate (=compressive yield stress ÷ tensile yield stress), i.e., the yield anisotropy, is 0.6 or higher. Invention 7 is a wrought Mg-based alloy according to Inventions 1 to 5, wherein the initial strain rate of the wrought Mg-based alloy is 1x10⁻¹⁰. -5 s -1 The present invention provides a wrought Mg-based alloy that can be subjected to a compressive strain of 0.5 or more in the following room-temperature compression test. [Effects of the Invention]

[0018] According to the present invention described above, it is possible to provide a wrought Mg-based alloy material with high room-temperature strength (yield stress) and reduced yield anisotropy. [Brief explanation of the drawing]

[0019] [Figure 1] This is the nominal stress-nominal strain curve obtained by room temperature tensile and compression tests of Mg-3mass%Al-1mass%Zn alloy extruded material. [Figure 2A] The image shows the microstructure of an example obtained by electron beam backscatter diffraction, revealing a Mg-0.3mol%Ge alloy extruded material. [Figure 2B] The image shows the microstructure of an example obtained by electron beam backscatter diffraction, revealing a Mg-0.3mol%Ga alloy extruded material. [Figure 3A] Examples obtained by transmission electron microscopy: Microstructural observation images of Mg-0.3mol%In alloy extruded material, showing STEM-BF images. [Figure 3B] Example obtained by transmission electron microscopy: Microstructural observation image of Mg-0.3mol%In alloy extruded material, showing In-L lines. [Figure 4A] Examples obtained by transmission electron microscopy: Microstructural observation images of Mg-0.3mol%Mn-0.1mol%Ga alloy extruded material, showing STEM-BF images. [Figure 4B]Example obtained by transmission electron microscopy: Microstructural observation image of Mg-0.3mol%Mn-0.1mol%Ga alloy extruded material, showing Ga-L lines. [Figure 4C] Example obtained by transmission electron microscopy: Microstructural observation image of Mg-0.3mol%Mn-0.1mol%Ga alloy extruded material, showing Mn-K lines. [Figure 5] This is the nominal stress-nominal strain curve obtained by a room-temperature tensile test on the extruded material of the example. [Figure 6] This is the nominal stress-nominal strain curve obtained by a room-temperature compression test on the extruded material of the example. [Modes for carrying out the invention]

[0020] The Mg-based alloy material for obtaining the effects of the present invention consists of Mg-Amol%X or Mg-Amol%X-Bmol%Z, where X = one or more elements selected from the group of three elements: In, Ga, and Ge. Z may be either Mn or Bi, or both. The relationship between A and B is B ≥ A, and the value of B is preferably 2 mol% or less, more preferably 1.5 mol% or less, and even more preferably 1.0 mol% or less. If the value of B exceeds 2 mol%, high-density α-Mn particles or α-Bi particles precipitate in the matrix, causing premature fracture during deformation. The lower limit of A is 0.03 mol%, preferably 0.1 mol%, and more preferably 0.3 mol%. The upper limit of A is preferably 1.0 times or less, more preferably 0.9 times or less, and even more preferably 0.8 times or less than the upper limit of B. The lower limit of B is 0.03 mol%. Here, 0.03 mol% is the value that defines the boundary between unavoidable impurities and added elements. When recycled Mg-based alloys are used as raw materials for Mg-based alloys, various alloying elements may already be present. This value is used to exclude the content that would normally be present when using recycled Mg-based alloys as raw materials. Examples of elements included in unavoidable impurities are Fe, Si, Cu (copper), and Ni (nickel).

[0021] The Mg-based alloy wrought material, after drawing, preferably has an average grain size of 20 μm or less in the Mg matrix. More preferably, it is 15 μm or less, and even more preferably 10 μm or less. Grain size measurement is preferably performed using the section method based on the G0551 JIS standard. If the grain size is fine or the grain boundaries are unclear, the section method is difficult to use; therefore, measurement may be performed using bright-field images or electron beam backscatter diffraction images obtained by a transmission electron microscope. Here, if the grain size is coarser than 20 μm, the volume of grain boundaries within the bulk decreases, reducing the barriers (=grain boundaries) that inhibit dislocations during plastic deformation, and the strength tends to decrease. Of course, if the average grain size can be maintained at 20 μm or less, heat treatment such as strain-relieving annealing may be performed after hot working.

[0022] To determine whether or not solute elements are segregated at grain boundaries, it is desirable to utilize an elemental analyzer attached to a transmission electron microscope or to use Z-contrast analysis with a high-resolution electron microscope. These observations reveal that one or more of In, Ge, or Ga, or Mn, or Mn and one or more of the three aforementioned elements, are segregated at the grain boundaries. Here, grain boundary segregation is defined as when the concentration of the element at the grain boundary is 10% or more higher than the concentration in the matrix phase.

[0023] Furthermore, α-Mn particles, α-Bi particles, and intermetallic compound particles bonded to Mn or Bi are dispersed within the Mg matrix and at the grain boundaries of drawable materials doped with Mn or Bi. These dispersed particles contribute to improving the yield stress under compression and reduce yield anisotropy. The size of the dispersed particles is preferably 0.5 μm or less, more preferably 0.25 μm or less, and even more preferably 0.1 μm or less. The proportion (volume fraction) of particles dispersed in the Mg matrix and at the grain boundaries is preferably 10%, more preferably 7.5%, and even more preferably 5% or less. If coarse particles exceeding 0.5 μm are dispersed, these coarse particles are prone to delamination at the matrix interface, which can become the initiation point for microcracks and potentially cause premature fracture. Even fine particles, if dispersed at high density with a volume fraction exceeding 10%, can act as a barrier to dislocation movement and contribute to a decrease in ductility. Furthermore, when α-Mn particles are dispersed at high density, the added Mn element is used to precipitate α-Mn particles and intermetallic compound particles bonded to Mn, which can lead to the problem of Mn not segregating at grain boundaries. In addition to metal compound particles bonded to Mg and Mn or Bi, and intermetallic compound particles bonded to Mn or Bi and the aforementioned X (In, Ge, Ga), intermetallic compound particles also include those bonded to Mg and the aforementioned X, and intermetallic compound particles bonded to X itself. In this specification, these are all referred to as "intermetallic compound particles." The presence of α-Mn particles, α-Bi particles, and intermetallic compound particles can be confirmed using XRD, and particle size and volume fraction can be measured from microstructural observation using an optical microscope or scanning electron microscope.

[0024] The strength of a wrought Mg-based alloy at room temperature is calculated from the nominal stress and nominal strain curves obtained by a room-temperature tensile test. Since mechanical properties, including strength, are easily affected by the test speed, 1 x 10 -3 s -1 The nominal stress and nominal strain curve obtained for the initial strain rate are as follows. Note that if the strength is affected by the test speed, the strength tends to increase with increasing test speed. Therefore, the above initial strain rate was set assuming a general-purpose test speed, within the quasi-static test speed range, and the minimum test speed.

[0025] FIG. 1 shows nominal stress-nominal strain curves obtained from a room-temperature tensile test of a comparative extruded material of Mg-3mass%Al-1mass%Zn, commonly known as AZ31. In the stress-strain curve obtained during the tensile test shown in FIG. 1, after yielding, a slight work hardening is exhibited, and fracture occurs when the nominal strain reaches approximately 0.2. The yield stress is calculated based on JIS Z2241, using the value of the slope of a straight line obtained in the elastic region at a 0.2% offset of nominal strain. In the present invention, the calculated yield stress in tension preferably exceeds 200 MPa, more preferably 250 MPa or higher, and still more preferably 300 MPa or higher. When the yield stress is 200 MPa or lower, it is equivalent to that of a general-purpose stretched Mg-based alloy material. Further, the elongation at break is also calculated using the slope of the straight line obtained in the elastic region, and preferably exceeds 15%, more preferably 20% or higher, and still more preferably 25% or higher. When the elongation at break is 15% or lower, it is equivalent to that of a general-purpose stretched Mg-based alloy material. Note that the elongation at break may be measured by a butt joint method using a sample after the tensile test.

[0026] Yield anisotropy is calculated using yield stresses obtained from tensile and compression tests at an initial strain rate of 1x10 -3 s -1 . That is, the value obtained by dividing the compressive yield stress by the tensile yield stress is defined as yield anisotropy, which is preferably more than 0.6, more preferably 0.7 or more, and still more preferably 0.75 or more. When the yield anisotropy is 0.6 or less, it is equivalent to that of a general-purpose stretched Mg alloy material.

[0027] Further, in a compression test, the deformation of a stretched Mg alloy material is often dominated by deformation twinning. In this case, the yield stress and elongation at break are hardly affected by the deformation rate, making it difficult to obtain excellent compressive deformability. Therefore, even if the initial strain rate in the compression test is reduced to from 1x10 -3 s -1 to 1x10 -5 s -1 , the improvement effect on elongation at break is poor.

Examples

[0028] (Example 1) Using commercially available pure in (99.9 mass%) and commercially available pure magnesium (99.98 mass%), the target content was adjusted to 0.3 mol% in, and a Mg-In alloy casting was produced using an iron crucible. The melting conditions were under an Ar atmosphere, with a melting temperature of 700°C and a holding time of 5 minutes. Casting was performed using an iron mold with a diameter of 50 mm and a height of 200 mm. Subsequently, the casting was solution-treated at 500°C for 24 hours.

[0029] The cast material after solution treatment was machined into a cylindrical extruded billet with a diameter of 40 mm and a length of 40 mm. The processed billet was held in a container set to 120°C for 30 minutes, and then subjected to hot strain application by extrusion at an extrusion ratio of 25:1 to produce a Mg-based alloy wrought material of the Mg-0.3In alloy according to Example 1 (hereinafter, the Mg-based alloy wrought material will be referred to as the extruded material) with a diameter of 8 mm and a length of 500 mm or more. In Example 1, when the extrusion temperature T was set to 120°C, the average crystal grain size d was 2.3 μm.

[0030] The various extruded materials described in Examples 2 to 8 and Comparative Example 2 were prepared as described below. When Mn was used as an additive element, a Mg-Mn master alloy was prepared using commercially available pure Mn (99.9 mass%) and commercially available pure Mg. When Ge and Ga were used as additive elements, a master alloy was not prepared, and commercially available pure metals were used. Each additive element was adjusted to achieve the desired composition, and various casting materials were melted in an iron crucible. Subsequently, the various extruded materials were prepared under the same conditions as described above, including solution treatment conditions (temperature and time), cylindrical extruded billet dimensions, extrusion ratio during extrusion, and holding time. The extrusion temperature T is shown in Table 1.

[0031] (Example 2) The target content of In was changed from 0.3 mol% to 0.1 mol%, and the target content of Mn was adjusted to 0.3 mol%, and a Mg-0.3Mn-0.1In alloy casting was melted using an iron crucible. In Example 2, when the extrusion temperature T was set to 189°C, the average grain size d was 1.9 μm.

[0032] (Examples 3-4) The target Ge content was adjusted to 0.3 mol%, and the Mg-Ge alloy casting was melted using an iron crucible. In Example 3, when the extrusion temperature T was 144°C, the average grain size d was 3.1 μm. In Example 4, when the extrusion temperature T was 168°C, the average grain size d was 4.7 μm.

[0033] (Example 5) The target content of Ge was changed from 0.3 mol% to 0.1 mol%, and the target content of Mn was adjusted to 0.3 mol%, and a Mg-0.3Mn-0.1Ge alloy casting was melted using an iron crucible. In Example 5, when the extrusion temperature T was set to 196°C, the average grain size d was 1.7 μm.

[0034] (Example 6) The target Ga content was adjusted to 0.3 mol%, and the Mg-Ga alloy casting was melted using an iron crucible. In Example 6, when the extrusion temperature T was set to 188°C, the average grain size d was 4.3 μm.

[0035] (Examples 7-8) The target content of Ga was changed from 0.3 mol% to 0.1 mol%, and the target content of Mn was adjusted to 0.3 mol% and 0.6 mol%, respectively. Using an iron crucible, Mg-0.3Mn-0.1Ga alloy castings were melted in Example 7. In Example 7, when the extrusion temperature T was 196°C, the average grain size d was 1.7 μm. In Example 8, a Mg-0.6Mn-0.1Ga alloy casting was produced. In Example 8, when the extrusion temperature T was 237°C, the average grain size d was 2.0 μm.

[0036] The microstructure of various extruded materials was observed using an optical microscope and electron backscatter diffraction, and the average grain size of the base material was determined by sectioning, as summarized in Table 1. Figure 2 shows microstructure observation images of the examples obtained by electron backscatter diffraction; Figure 2A shows a Mg-0.3mol%Ge alloy extruded material, and Figure 2B shows a Mg-0.3mol%Ga alloy extruded material. The black lines represent large-angle grain boundaries where the orientation difference angle between adjacent crystals is 15 degrees or more. The region enclosed by the black lines represents a single grain, and the average grain size is determined to be 4.3 μm and 3.1 μm, respectively. Furthermore, the average grain size for all extruded materials in the examples is 10 μm or less.

[0037] For some of the extruded materials, we used EDS analysis, which is an attachment to transmission electron microscopy (TEM), to observe grain boundary segregation other than Mg. Figure 3 shows microstructural observation images of an example: Mg-0.3mol%In alloy extruded material acquired by transmission electron microscopy. Figure 3A is a STEM-BF (Bright-Field Scanning Transmission Electron Microscopy) image, and Figure 3B shows the In-L line. In the mapping image for the In element in Figure 3B, the grain boundaries are clearly visible, confirming that the In element is segregated at the grain boundaries. The characteristic X-ray energy (keV) of the In-L line is, for example, 3.286 keV for Lα and 3.487 keV for Lβ1.

[0038] Figure 4 shows examples of microstructural observations of Mg-0.3mol%In alloy extruded material and Mg-0.3mol%Mn-0.1mol%Ga alloy extruded material. Figure 4A shows the STEM-BF image, Figure 4B shows the Ga-L line, and Figure 4C shows the Mn-K line. In Figure 4, the grain boundaries in the mapping images for Ga and Mn elements are clear, confirming that Ga and Mn elements are segregated at the grain boundaries. The characteristic X-ray energy (keV) of the Ga-L line is, for example, 1.098 keV for Lα and 1.303 keV for LIab. The characteristic X-ray energy (keV) of the Mn-K line is, for example, 3.312 keV for Kα and 3.589 keV for Kβ.

[0039] For test specimens taken from Mg-based alloy extruded material, the initial strain rate was 1 x 10⁻¹⁰. -3 s -1 Tensile and compressive tests were performed at room temperature. For the tensile tests, a round bar specimen with a parallel section length of 10 mm and a parallel section diameter of 2.5 mm was used, and for the compressive tests, a cylindrical specimen with a diameter of 4 mm and a height of 8 mm was used. All specimens were taken from a direction parallel to the extrusion direction. Typical tensile nominal stress and nominal strain curves are shown in Figure 5 and summarized in Table 1. The tensile yield stress of all extruded materials exceeded 200 MPa, and the elongation at break exceeded 25%, indicating excellent strength and ductility. Figure 6 shows typical compressive nominal stress and nominal strain curves. The compressive yield stress also exceeded 200 MPa, and the yield anisotropy, calculated by dividing the tensile yield stress by the compressive yield stress, was found to be 0.93 and 0.83, respectively, confirming that it exceeds 0.6.

[0040] Furthermore, for Mg-0.3mol%In alloy extruded material and Mg-0.3mol%Ge alloy extruded material, 1 x 10 -5 s -1 In room-temperature compression tests with initial strain rates, the elongation at fracture was 50% or more in all cases.

[0041] [Table 1]

[0042] (Comparative Example 1) Using extruded materials of a commercial magnesium alloy (Mg-3mass%Al-1mass%Zn: commonly known as AZ31), tensile and compressive tests were conducted at room temperature, and the resulting nominal stress and strain curves are shown in Figure 1. In all cases, the specimen dimensions and test conditions were the same as in the above-mentioned examples. The yield stress in tension was 200 MPa, the elongation at break was 15%, the yield stress in compression was 120 MPa, and the yield anisotropy was 0.6. (Comparative Example 2) Extruded material was prepared using the same procedure as in the example, with the only difference being the extrusion temperature. The average grain size, measured by sectioning based on optical microscope images, is listed in Table 1. It can be seen that the grain size is larger compared to the extruded material in the example, due to the extrusion temperature. In addition, tensile and compression tests were performed at room temperature, and the results are summarized in Table 1. The yield stress in tensile conditions was 144 MPa, the elongation at break was 19.5%, and the yield stress in compression was 93 MPa. The yield anisotropy is 0.65, but it cannot be said that the yield strength is excellent. The specimen dimensions and test conditions were the same as in the example described above. [Industrial applicability]

[0043] The Mg-based alloy of the present invention exhibits excellent room-temperature strength properties and low yield anisotropy, thus possessing three-dimensional isotropic deformability. Therefore, it is suitable for applications in moving parts, including automobiles. Furthermore, because it uses only trace amounts of common elements and does not contain rare earth elements, it is possible to reduce the cost of the material compared to conventional rare earth-added Mg alloys.

Claims

1. A wrought Mg-based alloy consisting of Mg-Amol%X, with the remainder being Mg and unavoidable impurities. Here, X is an element of In or Ga, The value of A is between 0.03 mol% and 1 mol%, The average grain size is 10 μm or less. A wrought Mg-based alloy in which elements other than Mg are segregated at the grain boundaries.

2. A wrought Mg-based alloy consisting of Mg-Amol%X-Bmol%Z, with the remainder being Mg and unavoidable impurities. Here, X is an element of In or Ga, and Z is an element of Mn, The relationship between A and B is B ≥ A, where the value of B is 0.3 mol%, and the lower limit of A is 0.03 mol%. The average grain size is 10 μm or less. A wrought Mg-based alloy in which elements other than Mg are segregated at the grain boundaries.

3. Initial strain rate of the Mg-based alloy wrought material: 1 x 10⁻¹⁰ －３ s －１ The Mg-based alloy wrought material according to claim 1 or 2, wherein the stress-strain curve obtained by the above room-temperature tensile test has a yield stress of 200 MPa or more and an elongation at break of 15% or more.

4. Initial strain rate of the Mg-based alloy wrought material: 1 x 10⁻¹⁰ －３ s －１ The above describes the Mg-based alloy wrought material according to claim 1 or 2, wherein the ratio of yield stresses obtained by room temperature tensile and compression tests at the same initial strain rate (= compressive yield stress ÷ tensile yield stress), i.e., the yield anisotropy, is 0.6 or more.

5. Initial strain rate of the Mg-based alloy wrought material: 1 x 10⁻¹⁰ －５ s －１ The Mg-based alloy wrought material according to claim 1 or 2, which can impart a compressive strain of 0.5 or more in the following room-temperature compression test.

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