Magnesium group alloy extension 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] The present invention relates to a wrought magnesium (Mg)-based alloy material that has excellent room temperature strength and reduced yield anisotropy. [Background technology]

[0002] Magnesium alloys are attracting attention as next-generation lightweight metal materials. To ensure safety and reliability when used as structural components, the development of materials and components with excellent strength characteristics is desired. In metallurgy, grain size refinement has long been used as an effective method for improving strength. In particular, magnesium has a larger Hall-Petch coefficient than other metals due to its hexagonal crystal structure (Non-Patent Document 1), which makes grain size refinement a significant strength enhancer. Another well-known and experimental approach to improving strength is alloying with one or more elements other than magnesium. The greater the difference in atomic radius between the element and the base metal, the greater the improvement effect. For magnesium alloys, the addition of rare earth metals is the most effective. However, the use of rare earth elements increases the material price, making them undesirable from an economic standpoint.

[0003] Turning to commodity elements, Mg-Al-Zn:AZ alloys containing aluminum and zinc and Mg-Zn-Zr:ZK alloys containing zinc and zirconium are currently available. These Mg alloys undergo elongation processing, involving heat treatment, to refine the grain size and improve their strength. During this elongation processing, the basal planes orient parallel to the processing direction, forming a basal texture. As a result, while the tensile strength improves due to the refined grain size, the compressive strength is only about half of the tensile strength, and these alloys suffer from yield anisotropy, where the yield stress varies depending on the stress direction. While dislocations typically drive plastic deformation in metallic materials, in the case of Mg, when compressive stress is applied along the c-axis, deformation twins form at stresses smaller than the dislocation motion. This difference in plastic deformation mechanism causes yield anisotropy, limiting the use of wrought Mg materials.

[0004] In light of this background, the inventors have investigated and studied ways to increase the strength of Mg-based alloys, focusing on the addition of only one solute element. Based on the results of this research, Patent Document 1 discloses a fine-grained Mg alloy with excellent strength properties, which contains a trace amount of one element selected from the group consisting of rare earth elements or general-purpose elements Ca, Sr, Ba, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Dr, Tm, Yb, and Lu, and has fine grains. The high strength of this alloy is mainly due to the segregation of the added solute element at the grain boundaries.

[0005] Furthermore, Patent Document 2 discloses an Mg-based alloy that contains 14.5 mass% or less Sn, has an Mg matrix with an average grain size of 10 μm or less, and has a majority of subgrain boundaries (low-angle grain boundaries) with an average grain size of 2 μm or less among the grain boundaries surrounding the Mg matrix, resulting in excellent room-temperature strength characteristics. The above-mentioned knowledge of introducing subgrain boundaries at high density has been found to be applicable to Mg-based alloys containing 3.5 to 11 mass% 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 excellent strength but also by reduced yield anisotropy between compressive yield stress and tensile yield stress due to the presence of subgrain boundaries.

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

[0007] The inventors also conducted extensive research on Mg-based alloys containing Mn. Based on the results of this research, Patent Document 5 discloses an Mg alloy containing 1 mol% or less of Mn and having excellent fracture toughness due to the presence of deformation twins in the Mg matrix. Patent Document 6 discloses an Mg-based alloy with excellent room-temperature ductility, in which the size of the Mg matrix is ​​5 μm or less and the Mg content is 0.07 to 2 mass%. These alloys are characterized by having a fracture elongation of approximately 100% and an m-value, which is an index of the contribution of grain boundary sliding to deformation, of 0.1 or more. Furthermore, the stress reduction is used as an index of formability, and the value is 0.3 or more. Furthermore, Patent Document 7 discloses a Mg-based alloy consisting of Mg-A mol % Mn-B mol % X, where A is 0.03 to 1 mol %, B is 1 or less times A, and containing Bi, Sn, and Zr, and having excellent room temperature ductility that does not fracture even when a nominal strain of 0.2 or more is applied. However, Patent Documents 5 to 7 relate to improvements in fracture toughness and room temperature ductility, and do not describe or disclose improvements in strength properties.

[0008] Mn, which is added to Mg, is usually used to remove impurities by bonding with iron (Fe) or silicon (Si) during melting. It is known that Mg alloys containing Mn as the primary (leading) element are endowed with ductility (Patent Documents 6 and 7, Non-Patent Documents 2 and 3). This is due to the activation of grain boundary sliding by the addition of Mn. Regarding the strength and ductility of Mg-Mn alloys, Non-Patent Documents 4 and 5 report examples of Mg-Mn-X ternary alloys, where X represents Al, Bi, Li, Sn, Y, Zn, or Zr. The addition of Bi, Li, or Zr has little effect on increasing strength but is highly effective in improving ductility. On the other hand, Al, Sn, Y, and Zn exhibit the opposite behavior, improving strength but deteriorating ductility. These reports suggest that the additive element X is effective in improving either strength or ductility, but it is difficult to achieve both. Furthermore, when alloys are ternary or higher, they can form intermetallic compounds, so the elemental functions related to strength and ductility are unclear, making it difficult to apply conventional solid-solution strengthening theories.Of course, when a third element is added to an alloy whose main element is Mn, for which there is a short history of research and no reported examples, it is unclear whether these elements have an effect on strength and ductility.

[0009] On the other hand, focusing on other elements that can form a solid solution with Mg at 0.03 mol % or more, there are indium (In), gallium (Ga), and germanium (Ge). Mg-based alloys containing In are disclosed in Patent Documents 8 to 10, Mg-based alloys containing Ge in Patent Document 10, and Mg-based alloys containing Ga 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 a 40 mol% In content. However, because each document focuses on improving recyclability and damping properties, the effects of stretching on strength and ductility are not described. Patent Document 10 discloses a ternary Mg-based alloy with excellent corrosion resistance containing 0.5 mass% to 2 mass% Ge and 0.5 mass% to 2 mass% In, and a method for manufacturing the alloy. As with Patent Documents 8 and 9, there is no description of stretching, and the effects on strength, ductility, and anisotropy reduction are unclear. Patent Document 11, which also contains Ga, discloses a Mg-based alloy for stents containing 1.26 to 2.6 mass% Mn and 2 to 4.2 mass% Ga. Extrusion processing is required at 435 to 835°C, but considering the melting point of Mg, the stretching temperature is high and hazardous from the viewpoint of work safety. On the other hand, Patent Document 12 discloses a Mg-based alloy containing Li and 3 to 8.5 mass% Ga and exhibiting excellent strength characteristics. Although this patent document states that stretching is optional, the main factor in exhibiting the strength characteristics is the age hardening of the Mg-Ga-Li ternary precipitate phase, and therefore does not disclose the contribution of strengthening due to stretching or the addition of Ga. From these prior patent documents, the effects of adding In, Ge, and Ga on strength, ductility, and reduction of anisotropy are unclear. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open 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] Patent No. 6860235 [Patent Document 8] CN101967590 [Patent Document 9] Japanese Patent Application Laid-Open No. 63-270441 [Patent Document 10] CN111394631 [Patent Document 11] CN113718145 [Patent Document 12] CN110983135 [Non-patent literature]

[0012] [Non-Patent Document 1] K. Kubota et al., J. Mater. Sci., 34 (1999) pp.2255-2265. [Non-patent document 2] H. Somekawa et al., Philo. Mag. 96 (2016) pp.2671-2685. [Non-patent document 3] H. Somekawa et al., Mater. Sci. Eng., A730 (2018) pp.355-362. [Non-patent document 4] H. Somekawa et al., Mater. Sci. Eng., A766 (2019) 138384. [Non-patent document 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] The present invention aims to provide an Mg-based alloy wrought material that has excellent room temperature strength and reduced yield anisotropy, to which at least one of the three elements In, Ge, and Ga has been added. [Means for solving the problem]

[0014] The first aspect of the present invention provides an Mg-based alloy wrought material consisting of Mg-A mol% X, with the remainder consisting of Mg and unavoidable impurities, where X is one or more elements selected from the group consisting of 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 an Mg-based alloy wrought material consisting of Mg-A mol%X-B mol%Z, with the remainder consisting of Mg and unavoidable impurities, where X is one or more elements of 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 the upper limit of B, and the lower limit of B is 0.03 mol% or more.

[0016] A third aspect of the present invention provides an extruded Mg-based alloy according to the first or second aspect, in which elements other than Mg are segregated at the grain boundaries of the extruded Mg-based alloy. A fourth aspect of the present invention provides an extruded Mg-based alloy according to any one of the first to third aspects, wherein the average crystal grain size of the Mg matrix of the extruded Mg-based alloy is 20 μm or less.

[0017] Invention 5 is the Mg-based alloy wrought material according to Inventions 1 to 4, wherein the initial strain rate of the Mg-based alloy wrought material is 1x10 -3 s -1 In the stress-strain curve obtained by the above room temperature tensile test, a wrought Mg-based alloy material is provided that has a yield stress of 200 MPa or more and a fracture elongation of 15% or more. Invention 6 is the Mg-based alloy wrought material according to Inventions 1 to 5, wherein the initial strain rate of the Mg-based alloy wrought material is 1x10 -3 s -1As a result, a wrought Mg-based alloy is provided in which the ratio of yield stresses obtained by room temperature tensile and compressive tests at the same initial strain rate (= compressive yield stress ÷ tensile yield stress), i.e., yield anisotropy, is 0.6 or more. Invention 7 is the Mg-based alloy wrought material according to Inventions 1 to 5, wherein the initial strain rate of the Mg-based alloy wrought material is 1x10 -5 s -1 The present invention provides a magnesium-based alloy wrought material that can be given 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 having high room temperature strength (yield stress) and reduced yield anisotropy. [Brief explanation of the drawings]

[0019] [Figure 1] 1 shows nominal stress-nominal strain curves obtained by room temperature tensile and compression tests of an extruded Mg-3 mass% Al-1 mass% Zn alloy. [Figure 2A] 1 shows a microstructure observation image of an example obtained by electron backscatter diffraction, showing an extruded Mg-0.3 mol % Ge alloy. [Figure 2B] 1 is a microstructure observation image of an example obtained by electron backscatter diffraction, showing an extruded Mg-0.3 mol % Ga alloy material. [Figure 3A] Example: A microstructure observation image of an extruded Mg-0.3 mol% In alloy obtained by a transmission electron microscope, showing a STEM-BF image. [Figure 3B] Example: A microstructure observation image of an extruded Mg-0.3 mol% In alloy obtained by a transmission electron microscope, showing the In-L line. [Figure 4A] 1 shows a STEM-BF image of the microstructure of an extruded Mg-0.3 mol % Mn-0.1 mol % Ga alloy obtained by a transmission electron microscope. [Figure 4B]This is an observation image of the microstructure of an example Mg-0.3 mol % Mn-0.1 mol % Ga alloy extrusion obtained by a transmission electron microscope, showing the Ga-L line. [Figure 4C] This is an image of the microstructure of an extruded Mg-0.3 mol % Mn-0.1 mol % Ga alloy obtained by a transmission electron microscope, showing the Mn-K line. [Figure 5] 1 is a nominal stress-nominal strain curve obtained by a room temperature tensile test on an extruded material of an example. [Figure 6] 1 is a nominal stress-nominal strain curve obtained by a room temperature compression test on an extruded material of an example. DETAILED DESCRIPTION OF THE INVENTION

[0020] The Mg-based alloy material for achieving the effects of the present invention is composed of Mg-Amol%X or Mg-Amol%X-Bmol%Z, where X is one or more elements selected from the group consisting of In, Ga, and Ge. Furthermore, 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 and 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, of 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 inevitable impurities and added elements. When recycled Mg-based alloys are used as raw materials for Mg-based alloys, there is a possibility that various alloy elements may already be contained in them. Therefore, when used as raw materials for Mg-based alloys, the amount of elements that would normally be contained is to be excluded. Elements contained in inevitable impurities include, for example, Fe, Si, Cu (copper), and Ni (nickel).

[0021] The average grain size of the Mg matrix in the Mg-based alloy wrought material after stretching is preferably 20 μm or less. More preferably, it is 15 μm or less, and even more preferably, it is 10 μm or less. The grain size is preferably measured using the sectioning method based on the JIS standard G0551. When the grain size is small or the grain boundaries are unclear, it is difficult to use the sectioning method. Therefore, measurement may be performed using bright-field images or electron backscatter diffraction images obtained by a transmission electron microscope. Here, when the grain size is coarser than 20 μm, the volume of the grain boundaries within the bulk is reduced, and the barriers (=grain boundaries) that inhibit dislocations generated during plastic deformation are reduced, which tends to lower the strength. Of course, as long as the average grain size can be maintained at 20 μm or less, heat treatment such as stress relief annealing may be performed after hot working.

[0022] The presence or absence of segregation of solute elements at grain boundaries is preferably determined using an elemental analyzer attached to a transmission electron microscope or Z-contrast using a high-resolution electron microscope. These observations reveal that one or more of In, Ge, and Ga, or Mn, or Mn and one or more of the above three 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.

[0023] Furthermore, in wrought steels containing Mn, Bi, or both, 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. These dispersed particles contribute to improving the yield stress under compression and reducing the 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. When coarse particles exceeding 0.5 μm are dispersed, these coarse particles are prone to peeling at the matrix interface, which can serve as the initiation point for microcracks and lead to premature fracture. Even fine particles dispersed at a high density, such as a volume fraction exceeding 10%, can act as a barrier to dislocation motion and reduce ductility. Furthermore, when α-Mn particles are dispersed at high density, the added Mn element is consumed in the precipitation of α-Mn particles and intermetallic compound particles bonded to Mn, which makes it difficult for Mn to segregate at the grain boundaries. In addition to intermetallic compound particles in which Mg is bonded to Mn or Bi, and intermetallic compound particles in which Mn or Bi is bonded to the X (In, Ge, Ga), intermetallic compound particles also include intermetallic compound particles in which Mg is bonded to the X, and intermetallic compound particles in which X atoms are bonded to each other, and these are collectively referred to as "intermetallic compound particles" in this specification. The presence of α-Mn particles, α-Bi particles, and intermetallic compound particles can be confirmed using XRD, and the particle size and volume fraction can be measured by microstructural observation using an optical microscope or scanning electron microscope.

[0024] The strength of Mg-based alloy wrought materials at room temperature is calculated from the nominal stress and nominal strain curve obtained by room temperature tensile testing. Since mechanical properties such as strength are easily affected by the test speed, -3 s -1 The nominal stress and nominal strain curves are obtained at an initial strain rate of 100 MPa. Note that when strength is affected by the test speed, strength tends to increase as the test speed increases. 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] Figure 1 shows the nominal stress and nominal strain curves obtained from a room-temperature tensile test using a comparative example, an extruded Mg-3% by mass Al-1% by mass Zn (commonly known as AZ31). The stress-strain curve from the tensile test shown in Figure 1 shows slight work hardening after yielding, followed by fracture when the nominal strain reached approximately 0.2. The yield stress was calculated based on JIS Z2241, using the slope of the line obtained in the elastic region as the value at a nominal strain offset of 0.2%. In the present invention, the calculated yield stress during tension preferably exceeds 200 MPa, more preferably 250 MPa or more, and even more preferably 300 MPa or more. A yield stress of 200 MPa or less is equivalent to that of a general-purpose Mg-based alloy wrought material. The fracture elongation was also calculated using the slope of the line obtained in the elastic region, and is preferably greater than 15%, more preferably 20% or more, and even more preferably 25% or more. If the elongation at break is 15% or less, it is equivalent to that of a general-purpose Mg-based alloy wrought material. Note that the elongation at break may also be measured by the butting method using a sample after tensile testing.

[0026] The yield anisotropy is 1x10 -3 s -1 The yield anisotropy is calculated using the yield stress obtained by tension and compression tests at an initial strain rate of 100 MPa. That is, the yield anisotropy is the value obtained by dividing the compressive yield stress by the tensile yield stress, and is preferably greater than 0.6, more preferably 0.7 or greater, and even more preferably 0.75 or greater. A yield anisotropy of 0.6 or less is equivalent to that of a general-purpose wrought magnesium alloy.

[0027] In addition, in compression tests, deformation of Mg alloys is often dominated by deformation twins. In this case, the yield stress and fracture elongation are not easily affected by the deformation rate, making it difficult to obtain excellent compressive deformability. Therefore, the initial strain rate of the compression test is set to 1x10 -3 s -1 From 1x10 -5 s -1 Even if the elongation is slowed down, the effect of improving the elongation at break is small. [Example]

[0028] Example 1 Commercially available pure In (99.9 mass%) and commercially available pure Mg (99.98 mass%) were used, and the target In content was adjusted to 0.3 mol%. Cast Mg-In alloys were melted in an iron crucible. The melting conditions were an Ar atmosphere, a melting temperature of 700°C, and a melt holding time of 5 minutes. Casting was performed in an iron mold with a diameter of 50 mm and a height of 200 mm. The cast material was then solution-treated at 500°C for 24 hours.

[0029] The solution-treated cast material was machined to form a cylindrical extrusion billet with a diameter of 40 mm and a length of 40 mm. The processed billet was then held in a container set at 120°C for 30 minutes, and then subjected to hot straining by extrusion at an extrusion ratio of 25:1 to produce an Mg-based alloy extruded material of the Mg-0.3In alloy according to Example 1 (hereinafter, the Mg-based alloy extruded 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, the extrusion temperature T was set to 120°C, and 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 produced as described below. When Mn was used as an additive element, an Mg-Mn master alloy was produced using commercially available pure Mn (99.9 mass%) and commercially available pure Mg. When Ge and Ga were used as additive elements, no master alloy was produced, and commercially available pure metals were used. The additive elements were adjusted to achieve the target composition, and various cast materials were melted in an iron crucible. Thereafter, various extruded materials were produced under the same solution treatment conditions (temperature and time), cylindrical extrusion billet dimensions, extrusion ratio and holding time during extrusion as described above. The extrusion temperature T is as shown in Table 1.

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

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

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

[0034] Example 6 The target Ga content was adjusted to 0.3 mol%, and an Mg—Ga alloy cast material was extruded using an iron crucible. In Example 6, the extrusion temperature T was set to 188° C., and the average crystal grain size d was 4.3 μm.

[0035] (Examples 7 to 8) The target Ga content was changed from 0.3 mol% to 0.1 mol%, and the target Mn content was adjusted to 0.3 mol% and 0.6 mol%, respectively, and an Mg-0.3Mn-0.1Ga alloy cast material was produced using an iron crucible in Example 7. In Example 7, the extrusion temperature T was set to 196°C, and the average crystal grain size d was 1.7 μm. A cast Mg-0.6Mn-0.1Ga alloy material was produced in Example 8. In Example 8, the extrusion temperature T was set to 237°C, and the average crystal grain size d was 2.0 µm.

[0036] The microstructures of the various extruded materials were observed using an optical microscope and electron backscatter diffraction. The average grain size of the base material was determined using the intercept method and is summarized in Table 1. Figure 2 shows microstructure images of examples obtained using electron backscatter diffraction. Figure 2A shows an extruded Mg-0.3 mol% Ge alloy, and Figure 2B shows an extruded Mg-0.3 mol% Ga alloy. The black lines indicate high-angle grain boundaries, where the misorientation angle between adjacent crystals is 15 degrees or greater. The area surrounded by the black lines represents a single grain, and the average grain sizes were determined to be 4.3 μm and 3.1 μm, respectively. Furthermore, the average grain size of all the extruded materials in the examples was 10 μm or less.

[0037] For some of the extruded materials, EDS analysis attached to a transmission electron microscope (TEM) was used to observe grain boundary segregation of elements other than Mg. Figure 3 shows microstructure images of an example Mg-0.3 mol% In alloy extrusion obtained using a transmission electron microscope. Figure 3A shows a STEM-BF (bright-field scanning transmission electron microscopy) image, and Figure 3B shows the In-L line. The mapping image of In in Figure 3B clearly shows the grain boundaries, confirming that In elements are segregated at the grain boundaries. The energy (keV) of the characteristic X-rays 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 microstructure observations of extruded Mg-0.3mol%In alloy and Mg-0.3mol%Mn-0.1mol%Ga alloy. Figure 4A shows a 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 clearly visible, confirming that Ga and Mn elements are segregated at the grain boundaries. The energy (keV) of the characteristic X-rays of the Ga-L line is, for example, 1.098 keV for Lα and 1.303 keV for L1ab. The energy (keV) of the characteristic X-rays of the Mn-K line is, for example, 3.312 keV for Kα and 3.589 keV for Kβ.

[0039] The specimens were taken from the extruded Mg-based alloys, and the initial strain rate was 1x10 -3 s -1 Tension and compression tests were conducted at room temperature using round bar specimens with a parallel section length of 10 mm and a parallel section diameter of 2.5 mm for the tensile tests, and cylindrical specimens with a diameter of 4 mm and a height of 8 mm for the compression tests. All specimens were taken parallel to the extrusion direction. Typical tensile nominal stress-nominal strain curves are shown in Figure 5 and summarized in Table 1. The tensile yield stress of each extruded material exceeded 200 MPa and the fracture elongation exceeded 25%, demonstrating excellent strength and ductility properties. Figure 6 shows typical compressive nominal stress-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] In addition, the Mg-0.3mol%In alloy extrusion material and the Mg-0.3mol%Ge alloy extrusion material were subjected to 1x10 -5 s -1 In room temperature compression tests with an initial strain rate of 100%, the elongation at break is 50% or more.

[0041] [Table 1]

[0042] (Comparative Example 1) Room-temperature tensile and compression tests were performed using a commercial magnesium alloy (Mg-3 mass% Al-1 mass% Zn, commonly known as AZ31) extrusion, and the resulting nominal stress-strain curves are shown in Figure 1. The test specimen dimensions and test conditions were the same as those in the previous 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 materials were produced using the same casting material as in the examples, except for the extrusion temperature, under the same conditions. The average grain size measured by the sectioning method based on optical microscope images is listed in Table 1. It can be seen that the larger grain size is due to the extrusion temperature compared to the extruded materials in the examples. Room-temperature tensile and compression tests were also conducted, and the results are summarized in Table 1. The yield stress in tension was 144 MPa, the elongation at break was 19.5%, and the yield stress in compression was 93 MPa. Although the yield anisotropy was 0.65, it is difficult to say that the yield strength was excellent. The test specimen dimensions and test conditions were the same as in the examples. [Industrial Applicability]

[0043] The Mg-based alloy of the present invention exhibits excellent room-temperature strength characteristics and, due to its small yield anisotropy, possesses three-dimensional isotropic deformability. Therefore, it is considered suitable for use in automobiles and other mobile components. Furthermore, because it does not contain trace amounts of general-purpose elements or rare earth elements, the cost of the material can be reduced compared to conventional rare-earth-added Mg alloys.

Claims

1. A wrought Mg-based alloy consisting of Mg-Amol%X, with the remainder consisting of Mg and unavoidable impurities, Here, X is at least one element selected from the group consisting of In, Ge, and Ga, A magnesium-based alloy wrought material in which the value of A is 0.03 mol % or more and 1 mol % or less.

2. A wrought Mg-based alloy consisting of Mg-A mol% X-B mol% Z, with the remainder consisting of Mg and unavoidable impurities, Here, X is one or more elements selected from the group consisting of In, Ge, and Ga, and Z is one of the elements Mn and Bi, The value of A is 0.03 mol% or more and 1 mol% or less, A magnesium-based alloy wrought material in which the relationship between A and B is B≧A, the upper limit of A is 1.0 times or less the upper limit of B, and the lower limit of B is 0.03 mol% or more.

3. An Mg-based alloy extended material as described in claim 1 or 2, in which elements other than Mg are segregated at the grain boundaries of the Mg-based alloy extended material.

4. An Mg-based alloy extensible material as described in claim 1 or 2, wherein the average crystal grain size of the Mg parent phase of the Mg-based alloy extensible material is 20 μm or less.

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

6. Initial strain rate of the Mg-based alloy wrought material: 1 x 10 －３ s －１ The Mg-based alloy wrought material according to claim 1 or 2, wherein the ratio of the 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.

7. Initial strain rate of the Mg-based alloy wrought material: 1 x 10 －5 s －１ 3. The Mg-based alloy wrought material according to claim 1 or 2, which can be given a compressive strain of 0.5 or more in the following room temperature compression test.

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