Magnesium-lithium alloy, optical device, imaging device, electronic device, and mobile body

Abstract

To provide a magnesium-lithium-based alloy that has excellent anticorrosion properties even if the alloy is exposed to a high-temperature and high-humidity environment for a long period of time.SOLUTION: A magnesium-lithium-based alloy contains Mg, Li, Al and Ge, and further contains at least one kind selected from Si, P, Zn and As, where the sum of the content of the Mg and the content of the Li is 90 mass% or more, the content of Li for the sum of the content of the Mg and the content of the Li is 0.5 mass% or more and 15 mass% or less, the sum of the content of the Al and the content of the Ge is 3 mass% or more and 7 mass% or less, the content of the Ge is 0.1 mass% or more and less than 1 mass%, Vickers hardness after leaving the allay to stand under the environment of temperature 70°C and humidity 80 RH% for 1000 hours is 75 (Hv) or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a magnesium-lithium alloy.

Background Art

[0002] Magnesium alloys are used as metal materials for reducing the weight of articles. In recent years, further weight reduction of articles has been required, and for example, magnesium-lithium alloys such as those described in Patent Document 1 have been proposed. However, since lithium is a very active (easily ionized, easily dissolved) metal element, it has, for example, a property of being easily corroded in a wet state. Therefore, the corrosion resistance of magnesium-lithium alloys has become more important than that of magnesium alloys. Patent Document 1 describes that the strength is improved by containing aluminum.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, even when an article is formed of a conventional magnesium-lithium alloy, if the article is exposed to a high-temperature and high-humidity environment for a long period of time, there has been a problem that the alloy corrodes. Therefore, an alloy having more excellent corrosion resistance than the conventional one has been demanded.

[0005] Therefore, an object of the present invention is to provide a magnesium-lithium alloy having excellent corrosion resistance even when exposed to a high-temperature and high-humidity environment for a long period of time.

Means for Solving the Problems

[0006] The inventors investigated the cause of corrosion in magnesium-lithium alloys produced by conventional methods and hypothesized that the corrosion was caused by the formation of a precipitated phase in the matrix phase, which consists of magnesium and lithium, through the compounding of aluminum and magnesium. They also hypothesized that segregation of lithium-rich grain boundaries (lithium-rich phase) in the matrix phase might be the cause. Furthermore, the inventors hypothesized that when water adheres to the surface of the alloy, localized electrolytic corrosion occurs between the precipitated phase or lithium-rich phase and the matrix phase, causing lithium to dissolve and corrode the alloy. Therefore, the inventors discovered that precipitation and segregation can be suppressed by incorporating germanium into the alloy.

[0007] One aspect of the present disclosure is a magnesium-lithium alloy containing Mg, Li, Al, and Ge, and further containing at least one selected from Si, P, Zn, and As, characterized in that the sum of the Mg content and the Li content is 90% by mass or more, the Li content is 0.5% by mass or more and 15% by mass or less with respect to the sum of the Mg content and the Li content, the sum of the Al content and the Ge content is 3% by mass or more and 7% by mass or less, the Ge content is 0.1% by mass or more and less than 1% by mass, and the Vickers hardness after being left for 1000 hours in an environment of 70°C and 80RH is 75(Hv) or more. [Effects of the Invention]

[0008] According to the present invention, corrosion of the alloy can be suppressed even when exposed to a high-temperature, high-humidity environment for a long period of time. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram showing an imaging device according to an embodiment. [Figure 2] This is a partial cross-sectional view of the housing of a lens barrel according to an embodiment and the film formed on its surface. [Figure 3] This is an SEM image of the surface of the Mg-Li alloy of Example 1. [Figure 4]This graph shows the results of the component analysis on the surface of the Mg-Li alloy in Example 1. [Figure 5] This is an SEM image of the surface of the Mg-Li alloy of Comparative Example 1. [Figure 6] This graph shows the results of the component analysis on the surface of the Mg-Li alloy in Comparative Example 1. [Figure 7] This is a schematic diagram showing an electronic device according to an embodiment. [Figure 8] This is a schematic diagram showing a mobile body according to an embodiment. [Modes for carrying out the invention]

[0010] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. Figure 1 shows the configuration of a single-lens reflex digital camera 600, which is an example of a preferred embodiment of the imaging device of the present invention. In Figure 1, the camera body 602 and the lens barrel 601, which is an optical device, are coupled together, and the lens barrel 601 is a so-called interchangeable lens that can be attached to and detached from the camera body 602.

[0011] Light from the subject passes through an optical system 630 consisting of multiple lenses 603, 605, etc., arranged on the optical axis of the imaging optical system within the housing 620 of the lens barrel 601, and is received by the image sensor 610 to capture the image. Here, lens 605 is supported by an inner barrel 604 and is movably supported relative to the outer barrel of the lens barrel 601 for focusing and zooming.

[0012] During the observation period before shooting, light from the subject is reflected by the main mirror 607 inside the housing 621 of the camera body 602, passes through the prism 611, and the image is projected onto the photographer through the viewfinder lens 612. The main mirror 607 is, for example, a half-mirror, and the light that passes through the main mirror is reflected by the sub-mirror 608 towards the AF (autofocus) unit 613, and this reflected light is used, for example, for distance measurement. The main mirror 607 is also attached and supported to the main mirror holder 640 by adhesive or the like. During shooting, the main mirror 607 and sub-mirror 608 are moved out of the optical path via a drive mechanism (not shown), the shutter 609 is opened, and the image of the shooting light incident from the lens barrel 601 is projected onto the image sensor 610. The aperture 606 is configured to change the brightness and depth of field during shooting by changing the aperture area. Although the imaging device of the present invention has been described using a single-lens reflex digital camera 600 as an example, the present invention is not limited to this, and may also be used with smartphones or compact digital cameras.

[0013] Figure 2 is a partial cross-sectional view of the housing 620 of the lens barrel 601 according to this embodiment and the film formed on its surface. As shown in Figure 2, a chemical conversion coating 110, a primer 120, and a paint film 130 are formed on the surface 620A of the housing 620. The chemical conversion coating 110 is a coating for improving the corrosion resistance of the housing 620, and is preferably a phosphate-based coating such as magnesium phosphate. The paint film 130 is a paint film formed from a heat-shielding paint containing a heat-shielding material. The housing 620 is a component (molded product) made of a magnesium-lithium alloy (Mg-Li alloy). The Mg-Li alloy that constitutes the housing 620 in this embodiment has Mg (magnesium) as its main component.

[0014] Mg-Li alloys are lightweight metal materials, which can reduce the weight of the housing 620 and improve its rigidity and vibration absorption (damping). However, since Li (lithium) is a base metal and easily corroded, it is necessary to improve the corrosion resistance of the Mg-Li alloy. Therefore, in this embodiment, a chemical conversion coating 110 that improves corrosion resistance is applied to the surface of the housing 620 as a base for the paint film 130.

[0015] On the one hand, conventionally, a Mg-Li-based alloy containing Al (aluminum) has been known. A member made of this Mg-Li-based alloy was fabricated, and after a chemical conversion film was coated on the surface of the member, a sample coated with a coating film was fabricated. When this sample was subjected to a durability test for 1000 hours in a high-temperature and high-humidity environment, specifically, in an environment of a temperature of 70°C and a humidity of 80%RH, the coating film peeled off and corrosion progressed on the surface of the member.

[0016] In this Mg-Li-based alloy, Al is added for the purpose of improving strength, and it is considered that a precipitated phase in which Al and Mg are combined is formed. Also, it is considered that a lithium-rich grain boundary (lithium-rich phase) segregates in the matrix phase. When water adheres to the surface of the alloy, local corrosion occurs between the precipitated phase or the lithium-rich phase and the matrix phase, and it is presumed that lithium elutes to the surface and reacts with the surface water, generating hydrogen gas and causing swelling and peeling of the coating film.

[0017] The present inventor has found that in a Mg-Li-based alloy, in order to obtain a homogeneous composition in which segregation and precipitation growth are suppressed, it is only necessary to inhibit the movement of atoms when the alloy is mixed and melted and solidified. Specifically, it was considered that when the atomic radii between the main elements of the alloy differ by 1.2 times or more, segregation and precipitation can be suppressed within the solidification time. Also, since the mixing entropy between the main elements is negative, the state of mixing and dispersion of atoms becomes energetically stable, and it was considered that segregation and precipitation can also be suppressed by selecting elements in such a combination.

[0018] In a Mg-Li-based alloy containing Al, as described above, the atomic radius (160 pm) of the main component Mg element is 1.1 times smaller than the atomic radius (143 pm) of Al. Therefore, it was found that elements of Group 2 and Groups 11 to 15 in the periodic table having a smaller atomic radius than the Al element satisfying the above conditions may be partially substituted for the Al element.

[0019] The metal element that partially replaces the Al element is preferably one or both of the Ge (germanium) element and the Be (beryllium) element. That is, in the Mg-Li-based alloy, by containing at least one of Al, Ge, and Be, segregation and precipitation that serve as the starting points of corrosion are prevented, and the alloy is likely to have a homogeneous composition. That is, the alloy is likely to be amorphous or the crystal grains contained in the alloy are likely to be refined. Due to the refinement of the alloy crystals or the amorphization of the alloy, precipitation and segregation are prevented, so the corrosion resistance of the alloy is improved. Here, the atomic radii of Ge and Be are both 122 pm. The content of Ge in the alloy is preferably 0.1% by mass or more and less than 1% by mass, and more preferably 0.1% by mass or more and 0.8% by mass or less in terms of increasing the strength of the alloy. The content of Be in the alloy is preferably 0.04% by mass or more and less than 3% by mass, and more preferably 0.04% by mass or more and 0.11% by mass or less in terms of increasing the strength of the alloy. Also, the contents of Be and Ge are less than the content of Al.

[0020] In addition to Ge and Be, as the metal element that partially replaces the Al element, it is preferable to further contain at least one metal element among Si (silicon), P (phosphorus), Zn (zinc), and As (arsenic). Here, the atomic radii of Si, P, Zn, and As are 117 pm, 110 pm, 137 pm, and 121 pm, respectively. These metal elements also have smaller atomic radii than the Al element, and further prevent precipitation and segregation, so the corrosion resistance of the alloy is improved. Note that although the atomic radius of Cu is 128 pm, which is smaller than that of Al, if the Mg-Li-based alloy contains Cu, there is a risk of being easily oxidized. Therefore, it is not preferable to contain Cu. Also, the contents of Si, P, Zn, and As are less than the content of Al.

[0021] In the Mg-Li-based alloy of this embodiment, in order to prevent precipitation and segregation, it is necessary to make the sum of the content of Mg and the content of Li 90% by mass or more. If it is less than 90% by mass, refinement of crystal grains or amorphization cannot be expected, the workability decreases, the manufacturing cost increases, and it is not practical.

[0022] In the Mg-Li alloy of this embodiment, it is preferable that the sum of the Al content and the Ge and Be content is 3% by mass or more and 7% by mass or less. This makes it possible to synergistically enhance the effect of Al in increasing the alloy strength and the effect of Ge and Be in increasing the alloy strength in the Mg-Li alloy.

[0023] Furthermore, in the Mg-Li alloy of this embodiment, it is preferable that the Li content is 0.5% by mass or more and 15% by mass or less relative to the sum of the Mg content and Li content. This allows for effective weight reduction of the alloy in the Mg-Li alloy. If the Li content is less than 0.5% by mass, it is not possible to make the alloy lighter than the Mg alloy, which is undesirable from the viewpoint of weight reduction. If the Li content is more than 15% by mass, the vibration damping properties may not be sufficient.

[0024] Furthermore, in the Mg-Li alloy of this embodiment, it is preferable that the sum of the Ge and Be content, the Al content, and the content of one or more metal elements selected from Si, P, Zn, and As is 3% by mass or more and 10% by mass or less. This makes it easier to further refine or amorphize the crystal grains. As a result, the corrosion resistance of the alloy is further improved. When the Mg-Li alloy contains multiple metal elements selected from Si, P, Zn, and As, the sum of the total content of the selected multiple metal elements, the Ge and Be content, and the Al content is 3% by mass or more and 7% by mass or less. For example, when the Mg-Li alloy contains Si and Zn, the sum of the Ge and Be content, the Al content, the Si content, and the Zn content is 3% by mass or more and 7% by mass or less.

[0025] Furthermore, in the Mg-Li alloy of this embodiment, it is preferable that the Ca content is 0.1% by mass or more and 1.6% by mass or less. This further improves the corrosion resistance of the alloy in the Mg-Li alloy.

[0026] Furthermore, the Mg-Li alloy of this embodiment may contain metal elements other than those listed above, as long as they do not alter the properties. These metal elements include unavoidable impurities that cannot be avoided during manufacturing. Examples of unavoidable impurities include Fe, Ni, Cu, and Mn. For Fe, Ni, and Cu, the properties will not change if their respective content in the Mg-Li alloy is less than 0.1 mass%. Similarly, for Mn, the properties will not change if their respective content is less than 1 mass%.

[0027] The above describes the case where an Mg-Li alloy is used for the metal constituting the housing 620 of the lens barrel 601, but it is not limited to this. The metal constituting the housing 621 of the camera body 602 may also be an Mg-Li alloy with the same configuration as that used for housing 620.

[0028] The manufacturing method for the Mg-Li alloy in this embodiment is not particularly limited. Examples of manufacturing methods include casting, extrusion, and forging. Methods for adjusting the composition include mixing and melting metal pieces or alloy pieces made of the desired metal elements.

[0029] Furthermore, it is preferable to perform heat treatment (post-annealing) on ​​the Mg-Li alloy of this embodiment after it has solidified from a molten state. This is because, near the recrystallization temperature, metallic elements such as Mg, Li, Al, and Ge contained in the Mg-Li alloy diffuse and form new compounds, thereby increasing its hardness.

[0030] <Electronic equipment> Figure 7 shows the configuration of a personal computer, which is an example of a preferred embodiment of the electronic device of the present invention. In Figure 7, the personal computer 800 comprises a display unit 801 and a main unit 802. Electronic components 830 are provided inside the housing 820 of the main unit 802. The magnesium-lithium alloy of the present invention can be used for the housing 820 of the main unit 802. The housing 820 may be made solely of the magnesium-lithium alloy of the present invention, or a coating film may be applied to the magnesium-lithium alloy of the present invention. Because the magnesium-lithium alloy of the present invention is lightweight and has excellent corrosion resistance, it is possible to provide a personal computer that is lighter and has better corrosion resistance than conventional personal computers.

[0031] Although the electronic device of the present invention was described using the personal computer 800 as an example, the present invention is not limited to this, and may also be a smartphone or a tablet.

[0032] <Mobile> Figure 8 shows an embodiment of a drone, which is an example of a mobile device of the present invention. The drone 700 comprises a plurality of drive units 701 and a main body 702 connected to the drive units 701. The drive units 701 have, for example, propellers. As shown in Figure 8, the main body 702 may be connected to legs 703 or to a camera 704. The magnesium-lithium alloy of the present invention can be used for the housing 710 of the main body 702 and legs 703. The housing 710 may be made solely of the magnesium-lithium alloy of the present invention, or a coating film may be applied to the magnesium-lithium alloy of the present invention. Because the magnesium-lithium alloy of the present invention has excellent vibration damping and corrosion resistance, it is possible to provide a drone with better vibration damping and corrosion resistance than conventional drones.

[0033] [Examples] First, Mg ingots were heated to 700-800°C in an argon atmosphere and melted. Then, metal pieces or alloy pieces of each element (Al, Ge, etc.) were added in the required amounts according to the composition ratios shown in Table 1, and the mixture was cast into a mold and cooled to produce Mg alloy ingots.

[0034] Next, the Mg alloy ingot was cut into small pieces, and these pieces were mixed with Li alloy pieces in a ceramic crucible. The mixture was then remelted at 850°C in an argon atmosphere by high-frequency induction heating, and thoroughly stirred electromagnetically within the crucible. The amount of Li alloy pieces added was varied to change the Li concentration, and alloys with the compositions shown in Table 1 were prepared. Hereafter, "mass%" may be expressed by omitting the letters "%" and "mass". [Table 1]

[0035] A molten alloy material was blown onto a copper roll using argon gas pressure in a ceramic or carbon crucible to obtain a ribbon approximately 0.2 mm thick and 7 mm wide. The elemental composition was measured using X-ray fluorescence and corrected for concentration.

[0036] As part of the environmental testing, the surface of the obtained ribbons was left untreated and left for 1000 hours in a high-temperature, high-humidity environment of 70°C and 80 RH%. After the period, surface changes were observed using an optical microscope and SEM-EDX (ZEISS, product name: FE-SEM). Hardness was also measured using a Vickers hardness tester (Mitutoyo, product name: Micro Vickers Hardness Tester HM-200). The results of the surface condition evaluation and hardness measurement from the environmental testing are shown in Table 2. In Table 2, samples with good surface condition from the environmental testing are indicated as "A", and those with poor surface condition are indicated as "B". The crystalline state was also measured by 2θ-θ measurement using an X-ray diffractometer (Rigaku, product name: Multipurpose X-ray Diffractometer Ultima IV). [Table 2]

[0037] <Examples 1, 2, and 7> As Example 1, an Mg-Li alloy of Mg-1.67%Li-1.6%Ca-4.8%Al-0.8%Ge-0.2%Zn-0.02%Mn was prepared. As Example 2, an Mg-Li alloy of Mg-3.35%Li-1.2%Ca-4.6%Al-0.6%Ge-0.4%Zn-0.04%Mn was prepared. As Example 7, an Mg-Li alloy of Mg-8.6%Li-1.2%Ca-5.7%Al-0.1%Ge-0.11%Mn-0.05%Si was prepared.

[0038] In all of the Mg-Li alloys in Examples 1, 2, and 7, the sum of the Mg content and Li content was 90% by mass or more. Furthermore, all of the Mg-Li alloys in Examples 1, 2, and 7 contained Al, Ca, and Ge.

[0039] Furthermore, in all of the Mg-Li alloys of Examples 1, 2, and 7, the sum of the Al content and the Ge content was within the range of 3% by mass or more and 7% by mass or less. Furthermore, in all of the Mg-Li alloys of Examples 1, 2, and 7, the Ca content was within the range of 0.1% by mass or more and 1.6% by mass or less. Also, in all of the Mg-Li alloys of Examples 1, 2, and 7, the Li content relative to the sum of the Mg content and the Li content was within the range of 0.5% by mass or more and 15% by mass or less. In addition, in all of the Mg-Li alloys of Examples 1 and 2, Zn was included as at least one metallic element from Si, P, Zn, and As. Also, in all of the Mg-Li alloys of Examples 1 and 2, the sum of the Ge content, Al content, and Zn content was within the range of 3% by mass or more and 7% by mass or less.

[0040] <Examples 3 and 4> As Example 3, an Mg-Li alloy of Mg-5.9%Li-1.2%Ca-4.4%Al-0.11%Be was prepared. As Example 4, an Mg-Li alloy of Mg-8.8%Li-0.9%Ca-3.9%Al-0.07%Be was prepared.

[0041] In both Examples 3 and 4, the sum of the Mg content and Li content was 90% by mass or more. Furthermore, both Examples 3 and 4 contained Al, Ca, and Be.

[0042] Furthermore, in both Mg-Li alloys of Examples 3 and 4, the sum of the Al content and the Be content was kept within the range of 3% by mass or more and 10% by mass or less. Furthermore, in both Mg-Li alloys of Examples 3 and 4, the Ca content was kept within the range of 0.1% by mass or more and 4% by mass or less. In addition, in both Mg-Li alloys of Examples 3 and 4, the Li content relative to the sum of the Mg content and Li content was kept within the range of 0.5% by mass or more and 15% by mass or less.

[0043] <Examples 5 and 6> As Example 5, an Mg-Li alloy of Mg-10.3%Li-1.4%Ca-3.6%Al-0.6%Ge-0.05%Be-0.3%Si was prepared. As Example 6, an Mg-Li alloy of Mg-11%Li-1.0%Ca-3.4%Al-0.4%Ge-0.04%Be-0.2%Si was prepared.

[0044] In both Examples 5 and 6, the sum of the Mg content and Li content was 90% by mass or more. Furthermore, both Examples 5 and 6 contained Al, Ca, Ge, and Be.

[0045] Furthermore, in both Mg-Li alloys of Examples 5 and 6, the sum of the Al content and the Ge and Be content was within the range of 3% by mass to 10% by mass. Furthermore, in both Mg-Li alloys of Examples 5 and 6, the Ca content was within the range of 0.1% by mass to 4% by mass. Also, in both Mg-Li alloys of Examples 5 and 6, the Li content relative to the sum of the Mg content and Li content was within the range of 0.5% by mass to 15% by mass. In addition, in both Mg-Li alloys of Examples 5 and 6, Si was included as at least one metallic element from Si, P, Zn, and As. Furthermore, in both Mg-Li alloys of Examples 5 and 6, the sum of the Ge and Be content, the Al content, and the Si content was within the range of 3% by mass to 10% by mass.

[0046] The Mg-Li alloys of Examples 1 to 7 retained their metallic luster when subjected to the aforementioned environmental tests. After the environmental tests, the Mg-Li alloy of Example 1 was observed using SEM. Figure 3 is an SEM image of the surface of the Mg-Li alloy of Example 2. As shown in Figure 3, most of the surface was smooth.

[0047] Figure 4 is a graph showing the results of the component analysis on the surface of the Mg-Li alloy of Example 1. EDX observation of the smooth surface of the Mg-Li alloy of Example 1 revealed that, as shown in Figure 4, the elements Mg, Li, and O were almost the same as in the initial state, indicating that oxidation, i.e., corrosion, on the surface was suppressed.

[0048] In particular, in the Mg-Li alloys of Examples 1, 2, and 5-7, where the Ge element content was less than 1 mass%, and in the Mg-Li alloys of Examples 3 and 4, where the Be element content was less than 0.1 mass%, oxidative corrosion of the alloy surface was effectively suppressed. XRD results showed that the alloys of Examples 1-7 were polycrystalline, and a shift to the high-angle side due to compression was observed in the Mg matrix. The presence or absence of peak shift was determined by the peak around 2θ = 63°. From this peak shift, it can be inferred that constituent elements other than Mg are substituted and dissolved in the matrix. Also, as shown in Table 1, the hardness increased by approximately Hv10 when Ge was added, reaching a maximum of Hv80.

[0049] Next, Example 7 underwent further heat treatment. Specifically, the Mg-Li alloy sample was heated on a hot plate for 30 minutes until its temperature reached 250°C. After heating, the hardness of the Mg-Li alloy of Example 7 increased to Hv94. This is thought to be because, near the recrystallization temperature, metallic elements such as Mg, Li, Al, and Ge contained in the Mg-Li alloy diffused and formed new compounds, resulting in an increase in hardness.

[0050] <Comparative Example 1> As Comparative Example 1, an Mg-Li alloy of Mg-0.28%Li-2%Ca-6%Al was prepared. When the aforementioned environmental test was performed on the Mg-Li alloy of Comparative Example 1, a large portion of the surface turned black.

[0051] After the environmental testing, SEM observation was performed on the Mg-Li alloy of Comparative Example 1.

[0052] Figure 6 is a graph showing the results of the component analysis on the surface of the Mg-Li alloy of Comparative Example 1. EDX observation of the surface of the Mg-Li alloy of Comparative Example 1 revealed that the elements of Li and O had increased significantly from the initial state, as shown in Figure 6, indicating that oxidation had progressed on the surface. XRD results showed that the Mg-Li alloy of Comparative Example 1 was polycrystalline and contained compound phases, while the peak shift observed in the examples was not observed. Even the alloy of Comparative Example 1, which had Al and Ca elements added to improve the corrosion resistance of Mg alloys, could not stop corrosion under these conditions.

[0053] <Comparative Example 2 and Comparative Example 3> As Comparative Example 2, an Mg-Li alloy of Mg-1.67%Li-1.6%Ca-5.6%Al-0.2%Zn-0.02%Mn was prepared. As Comparative Example 3, an Mg-Li alloy of Mg-3.35%Li-1.2%Ca-5.2%Al-0.4%Zn-0.04%Mn was prepared. When the aforementioned environmental tests were performed on the Mg-Li alloys of Comparative Example 2 and Comparative Example 3, a large portion of the surface turned black. Figure 5 is an SEM image of the surface of the Mg-Li alloy of Comparative Example 2. As shown in Figure 5, most of the surface was significantly uneven.

[0054] After environmental testing, SEM observation of the Mg-Li alloys of Comparative Examples 2 and 3 revealed that, similar to Comparative Example 1, a large portion of the surface was significantly uneven. EDX observation of the surfaces of the Mg-Li alloys of Comparative Examples 2 and 3 showed a significant increase in Li and O elements compared to the initial state, indicating that oxidation had progressed on the surface. Even the alloys of Comparative Examples 2 and 3, which were modified with Al, Zn, and Mn elements commonly used to improve the corrosion resistance of Mg alloys, could not stop corrosion under these environmental conditions.

[0055] <Comparative Example 4> As Comparative Example 4, an Mg-Li alloy of Mg-14.48%Li-0.3%Ca-3%Al-0.15%Mn was prepared. When the aforementioned environmental test was performed on the Mg-Li alloy of Comparative Example 4, the entire surface turned white and the surface became brittle and crumbled.

[0056] <Comparative Example 5> As Comparative Example 5, an Mg-Li alloy of Mg-9.5%Li-4.2%Al-1.0%Zn was prepared. When the aforementioned environmental test was performed on the Mg-Li alloy of Comparative Example 5, the entire surface turned white and the surface became brittle and crumbled, similar to Comparative Example 4.

[0057] Here, the Mg-Li alloy of Example 1 is obtained by substituting some of the Al with Ge compared to the Mg-Li alloy of Comparative Example 2. The Mg-Li alloy of Example 2 is obtained by substituting some of the Al with Ge compared to the Mg-Li alloy of Comparative Example 3. The Mg-Li alloys of Examples 3 and 4 are obtained by substituting some of the Al with Be compared to the Mg-Li alloy of Comparative Example 1. The Mg-Li alloys of Examples 5 to 7 are obtained by substituting some of the Al with Ge, or Ge, Be, and Si, compared to the Mg-Li alloy of Comparative Example 4. As a result of environmental tests, it was found that the alloys of Examples 1 to 7 showed improved corrosion resistance compared to the alloys of Comparative Examples 1 to 4, even when exposed to high temperature and high humidity environments for extended periods.

[0058] After environmental testing, SEM observation of the Mg-Li alloys of Comparative Examples 4 and 5 revealed that most of the surface was severely uneven. EDX observation of the surfaces of the Mg-Li alloys of Comparative Examples 4 and 5 showed a significant increase in Li and O elements compared to the initial state, indicating that oxidation had progressed on the surface. It was observed that alloys with a large amount of Li element in solid solution corroded severely.

[0059] It should be noted that the present invention is not limited to the embodiments described above, and many modifications are possible within the technical concept of the present invention. Furthermore, the effects described in the embodiments are merely a list of the most preferred effects resulting from the present invention, and the effects of the present invention are not limited to those described in the embodiments. [Explanation of Symbols]

[0060] 600 Single-lens reflex digital camera (imaging device) 601 Lens barrel (optical instrument) 700 Drones (Mobile Devices) 800 Personal computers (electronic devices)

Claims

1. A magnesium-lithium alloy containing Mg, Li, Al, and Ge, and further containing at least one element selected from Si, P, Zn, and As, The sum of the Mg content and the Li content is 90 mass% or more, The Li content is 0.5% by mass or more and 15% by mass or less with respect to the sum of the Mg content and the Li content, the sum of the Al content and the Ge content is 3 mass% or more and 7 mass% or less, The Ge content is 0.1 mass % or more and less than 1 mass %, A magnesium-lithium alloy characterized in that it has a Vickers hardness of 75 (Hv) or more after being left in an environment of a temperature of 70°C and a humidity of 80% RH for 1000 hours.

2. 2. The magnesium-lithium alloy according to claim 1, wherein the sum of the contents of Si, P, Zn and As is less than the content of Al.

3. 3. The magnesium-lithium alloy according to claim 1, wherein the sum of the Ge content, the Al content, and the Si, P, Zn, and As contents is 3% by mass or more and 10% by mass or less.

4. Further containing Be, 4. The magnesium-lithium alloy according to claim 1, wherein the Be content is 0.04% by mass or more and less than 3% by mass.

5. 5. The magnesium-lithium alloy according to claim 4, wherein the sum of the content of Al and the contents of Ge and Be is 3% by mass or more and 7% by mass or less.

6. The magnesium-lithium alloy according to claim 4 or 5, characterized in that the sum of the contents of Ge and Be, the content of Al, and the contents of Si, P, Zn, and As is 3 mass% or more and 10 mass% or less.

7. 7. The magnesium-lithium alloy according to claim 4, wherein the sum of the contents of Ge, Be, Si, P, Zn and As is less than the content of Al.

8. Further containing Ca, 8. The magnesium-lithium alloy according to claim 1, wherein the Ca content is 0.1% by mass or more and 1.6% by mass or less.

9. 9. The magnesium-lithium alloy according to claim 1, wherein at least one element selected from the group consisting of Si, P, Zn, and As is an element that partially replaces the Al.

10. An optical device comprising a housing and an optical system consisting of a plurality of lenses arranged in the housing, An optical device, characterized in that the housing comprises the magnesium-lithium alloy according to any one of claims 1 to 9.

11. An imaging device comprising a housing and an imaging element disposed within the housing, 10. An imaging device, wherein the housing comprises the magnesium-lithium alloy according to claim 1.

12. 12. The imaging device according to claim 11, wherein the imaging device is a camera.

13. An electronic device comprising a housing and an electronic component disposed within the housing, 10. An electronic device, wherein the housing comprises the magnesium-lithium alloy according to claim 1.

14. A moving body including a main body and a drive unit, A moving body, wherein the housing of the main body comprises the magnesium-lithium alloy according to any one of claims 1 to 9.

Images