Highly corrosion-resistant magnesium-lithium alloy

Abstract

The objective of the present invention is to provide an ultralightweight and highly corrosion-resistant magnesium-lithium alloy capable of solving the problem of being highly corrosive compared to commercial magnesium alloys. According to an embodiment of the present invention, provided is a magnesium-lithium alloy comprising aluminum (Al), manganese (Mn), calcium (Ca), yttrium (Y), and lithium (Li), and having a mixed phase including a phase having an HCP crystal structure and a phase having a BCC crystal structure.

Description

High corrosion resistance magnesium-lithium alloy

[0001] The present invention relates to a magnesium-lithium alloy, and more particularly, to a magnesium-lithium alloy having ultra-lightweight, high corrosion resistance properties.

[0002] This invention refers to the research project of Material Components Technology Development (Project Unique Number: 2410004169, Project Number: 20024843) carried out with support from the Korea Institute of Industrial Technology Planning and Evaluation with funds from the Ministry of Trade, Industry and Energy.

[0003] Magnesium alloy is a representative lightweight alloy used as a structural material. The specific gravity of magnesium is 1.73 g / cm 3 It corresponds to a lightweight metal. Research is being conducted on magnesium-lithium alloy as an ultra-light structural metal. Magnesium-lithium alloy is CFRP (carbon fiber reinforced plastic, specific gravity 1.5 to 1.6 g / cm) depending on the content of lithium (Li) added. 3 ) and has the advantage of being able to produce a metal alloy that can float on water. In addition, depending on the composition range of lithium added to magnesium, it can exhibit a single-phase structure of the HCP (hexagonal close packed) crystal structure, a mixed-phase structure of the HCP and BCC (body centered cubic) crystal structures, and a single-phase structure of the BCC crystal structure. When the magnesium-lithium alloy includes the BCC crystal structure, it is also developed as a high-formability alloy that can improve the low formability caused by the HCP crystal structure of the magnesium alloy. Such magnesium-lithium alloys are being applied to some electronic products such as laptop cases.

[0004] However, the addition of lithium to magnesium alloys, which are inherently fast-corroding, further accelerates their corrosion rate. This rapid corrosion rate poses a challenge to the durability of the product and poses a significant obstacle to the commercialization of alloy products.

[0005] The present invention was conceived to address the aforementioned issues, and its purpose is to provide an ultra-lightweight, highly corrosion-resistant magnesium-lithium alloy capable of significantly reducing corrosion resistance compared to commercial magnesium alloys. However, these tasks are exemplary and are not intended to limit the scope of the present invention.

[0006] According to one embodiment of the present invention, a magnesium-lithium alloy is provided, which includes aluminum (Al), manganese (Mn), calcium (Ca), yttrium (Y), and lithium (Li), and has a mixed phase including a phase having an HCP crystal structure and a phase having a BCC crystal structure.

[0007] According to one embodiment of the present invention, the aluminum (Al) may be in a range of 3 to 9 wt%, the manganese (Mn) may be in a range of 0.1 to 0.5 wt%, the calcium (Ca) may be in a range of 0.1 to 1 wt%, the yttrium (Y) may be in a range of 0.1 to 1 wt%, and the lithium (Li) may be in a range of 6 to 10 wt%.

[0008] According to one embodiment of the present invention, the magnesium-lithium alloy is Mg 17 Al 12 May include awards.

[0009] According to one embodiment of the present invention, the magnesium-lithium alloy has a density of 1.5 g / cm 3 1.6 g / cm 3 can have a certain proportion.

[0010] According to one embodiment of the present invention, the magnesium-lithium alloy may have a corrosion rate of 2 mm / year to 4 mm / year.

[0011] According to one embodiment of the present invention, a magnesium-lithium alloy is provided, which comprises, in wt%, aluminum (Al): 3 to 9%, manganese (Mn): 0.1 to 0.5%, calcium (Ca): 0.1 to 1%, yttrium (Y): 0.1 to 1%, lithium (Li): 6 to 10%, the remainder being magnesium (Mg) and inevitable impurities, and has a mixed phase structure including a phase having an HCP crystal structure and a phase having a BCC crystal structure.

[0012] According to one embodiment of the present invention, as described above, an ultra-lightweight, highly corrosion-resistant magnesium-lithium alloy can be provided that overcomes corrosion resistance that is significantly inferior to that of commercial magnesium alloys. Of course, the scope of the present invention is not limited by these effects.

[0013] Figure 1 shows the X-ray diffraction analysis results of the SEN6 series alloy.

[0014] Figure 2 shows the X-ray diffraction analysis results of the AM60 series alloy.

[0015] Figure 3 is a graph showing the results of measuring the specific gravity of the manufactured magnesium-lithium alloy.

[0016] Figure 4 is a graph showing the results of measuring the corrosion rate of the manufactured magnesium-lithium alloy.

[0017] Figure 5 shows the results of observing the microstructure of the SEN6 series alloy using an electron microscope.

[0018] Figure 6 shows the results of EDS mapping performed for component analysis of the SEN6L13 alloy.

[0019] Hereinafter, various preferred embodiments of the present invention will be described in detail with reference to the attached drawings. These embodiments are provided to more fully explain the present invention to those skilled in the art. The following embodiments may be modified in various ways, and the scope of the present invention is not limited to the following embodiments. Rather, these embodiments are provided to further faithfully and completely convey the spirit of the present invention to those skilled in the art.

[0020] According to the technical idea of ​​the present invention, in order to solve the problem of low corrosion resistance of magnesium-lithium containing aluminum, calcium (Ca) and yttrium (Y) are added to the magnesium-lithium alloy to secure high corrosion resistance.

[0021] A magnesium-lithium alloy according to one embodiment of the present invention includes aluminum (Al), manganese (Mn), calcium (Ca), yttrium (Y), and lithium (Li). In addition, the magnesium-lithium alloy has a mixed phase structure including a phase having an HCP crystal structure and a phase having a BCC crystal structure.

[0022] Lithium may be contained to the extent that the magnesium-lithium alloy has a mixed phase of an HCP crystal structure and a BCC crystal structure. Magnesium has an HCP crystal structure. When lithium having a BCC crystal structure is added to the magnesium, an alpha (α) phase of an HCP crystal structure is formed at a low lithium content, but when the lithium content increases, a beta (β) phase having a BCC crystal structure is generated, thereby exhibiting a mixed phase structure in which the alpha and beta phases coexist. When the lithium content is further increased, the magnesium-lithium alloy transitions to a beta phase having a BCC crystal structure.

[0023] According to the technical idea of ​​the present invention, when a magnesium-lithium alloy has a mixed phase structure of HCP crystal structure and BCC crystal structure, it exhibits superior corrosion resistance compared to when it has a single phase structure of HCP crystal structure or BCC crystal structure. Therefore, the lithium content must be appropriately controlled so that the magnesium-lithium alloy has the above mixed phase.

[0024] In the magnesium-lithium alloy according to one embodiment of the present invention, the composition of lithium for having the mixed phase may be in the range of 6 to 10 wt%. When the composition of lithium is less than 6 wt%, all of the added lithium is dissolved in the magnesium matrix, so that the magnesium-lithium alloy has a single-phase structure of an HCP crystal structure, and the potential of the magnesium matrix is ​​lowered, so that the corrosion resistance may be lowered. When the composition of lithium exceeds 10 wt%, the magnesium-lithium alloy forms a single-phase structure of a BCC crystal structure, and the calcium and yttrium added for high corrosion resistance properties are formed as a new secondary phase of a completely different form from the phase formed in the region having the single-phase structure of the HCP crystal structure, so that the effect of improving corrosion resistance is lost, so that the corrosion resistance may be lowered.

[0025] Aluminum is known as an element added to magnesium to improve strength and corrosion resistance in wet environments or salt water. Aluminum is Mg in magnesium alloys. 17 Al 12 It can form an award. Mg 17 Al 12 The magnesium alloy can have various tissue forms depending on the solidification rate during the manufacturing process. For example, the above Mg 17 Al 12When the phase solidifies at a low rate, it may exhibit a eutectic structure with a lamellar structure in which layers are stacked. Alternatively, when it solidifies at a relatively fast rate, it may have various tissue forms other than a lamellar structure. In the magnesium-lithium alloy according to one embodiment of the present invention, the composition of aluminum may range from 3 to 9 wt%. When the composition of aluminum is less than 3 wt%, Mg formed at the grain boundaries of the magnesium-lithium alloy 17 Al 12 The problem of greatly reducing the fraction of the phase can occur by exposing the grain boundaries to corrosion, which can significantly reduce the corrosion resistance, and the added yttrium can create a secondary phase with a compound with a low aluminum content rather than a compound with a high aluminum content (secondary phase) that can lower the potential difference, which can reduce the corrosion resistance. When the composition of aluminum exceeds 9 wt%, Mg 17 Al 12 The problem of the magnesium-lithium alloy being formed at an excessively high fraction may occur, which significantly reduces the elongation of the magnesium-lithium alloy.

[0026] Manganese can be added to control impurities. Furthermore, when added to magnesium, it can refine the grain size of the magnesium alloy and prevent magnesium from oxidizing, thereby contributing to maintaining the alloy's surface quality. Manganese, when added together with aluminum, can enhance the corrosion resistance of the magnesium alloy and improve its workability and castability. In a magnesium-lithium alloy according to one embodiment of the present invention, the manganese content may range from 0.1 to 0.5 wt%.

[0027] According to the technical idea of ​​the present invention, calcium and yttrium are added to improve the corrosion resistance of a magnesium-lithium alloy containing aluminum. The added aluminum, manganese, and yttrium can form an Al8Mn4Y phase. In the magnesium-lithium alloy containing aluminum, calcium and yttrium are Mg 17Al 12 or, Mg 17 Al 12 and It can act in a complex manner with the Al8Mn4Y phase to reduce the corrosion rate of the alloy. The corrosion resistance improvement effect due to the complex action of calcium and yttrium and the formed phases can be realized within the lithium addition range where the HCP crystal structure remains in the magnesium-lithium alloy and the HCP crystal structure and the BCC crystal structure are mixed. In the magnesium-lithium alloy according to one embodiment of the present invention, the composition of calcium can be in the range of 0.1 to 1 wt%, and the composition of yttrium can be in the range of 0.1 to 1 wt%.

[0028] Regarding the corrosion resistance of magnesium-lithium alloys, in the case of magnesium-lithium alloys with HCP single-phase structure, lithium, which has a lower standard potential than magnesium, is dissolved in magnesium, which significantly reduces the overall corrosion resistance and Mg 17 Al 12 The fraction of is not sufficient to suppress corrosion propagation, so the corrosion rate increases significantly. On the other hand, in the case of a magnesium-lithium alloy with a beta-phase single-phase structure of a BCC crystal structure, the added aluminum, calcium, and yttrium elements form a secondary phase of a different form from that of a magnesium-lithium alloy with an HCP structure, which causes a different corrosion mechanism and reduces corrosion resistance.

[0029] A magnesium-lithium alloy according to one embodiment of the present invention comprises 1.5 g / cm 3 1.6 g / cm 3 It can have a specific gravity of . In addition, the magnesium-lithium alloy can have a corrosion rate of 2 mm / year to 4 mm / year.

[0030] Hereinafter, experimental examples are provided to aid in understanding the present invention. However, the following experimental examples are provided solely to aid in understanding the present invention, and the present invention is not limited to the following experimental examples.

[0031] Table 1 shows the names of the specimens and the corresponding alloy compositions of the experimental examples. All alloys in Table 1 were manufactured by melting in a furnace and then casting into a mold.

[0032]

[0033] Specimen name Base alloy Li (wt%) Phase SEN6Mg-6Al-Mn-0.3Ca-0.2Y0HCP Single phase SEN6L1Mg-6Al-Mn-0.3Ca-0.2Y1HCP Single phase SEN6L3Mg-6Al-Mn-0.3Ca-0.2Y3HCP Single phase SEN6L7Mg-6Al-Mn-0.3Ca-0.2Y7HCP + BCC mixed phase SEN6L13Mg-6Al-Mn-0.3Ca-0.2Y13BCC Single phase AM60AM60 alloy0HCP Single phase AM60L1AM60 alloy1HCP Single phase AM60L3AM60 alloy3HCP Single phase AM60L7AM60 alloy7HCP + BCC mixed phase AM60L13AM60 alloy13BCC Single phase

[0034]

[0035] Referring to Table 1, the SEN6 alloy with the sample name is Mg-6Al-Mn-0.3Ca-0.2Y (an alloy containing 6%, 0.2%, 0.3%, and 0.2% of Al, Mn, Ca, and Y in wt%, respectively, and the remainder containing Mg and inevitable impurities), and the SEN6L1, SEN6L3, SEN6L7, and SEN6L13 alloys with the sample names are alloys manufactured by adding 1%, 3%, 7%, and 13% of lithium in wt% to the SEN6 alloy, respectively. The AM60 alloy is a commercial magnesium alloy, AM60 alloy (an alloy containing 6% and 0.2% by weight of Al and Mn, respectively, and the remainder containing Mg and inevitable impurities), and the AM60L1, AM60L3, AM60L7, and AM60L13 are alloys manufactured by adding 1%, 3%, 7%, and 13% by weight of lithium to AM60, respectively.

[0036] SEN6 alloy and AM60 alloy without lithium addition can be referred to as base alloy.

[0037] The SEN6 alloy differs from the AM60 alloy in that it contains the same aluminum and manganese contents, but contains 0.3 wt% and 0.2 wt% more calcium and yttrium, respectively. Therefore, the SEN6 alloy can be expressed as AM60 alloy-0.3Ca-0.2Y.

[0038] SEN6 alloy and alloys to which lithium is added (SEN6L1, SEN6L3, SEN6L7, SEN6L13) may be referred to as SEN6 series alloys. AM60 alloy and alloys to which lithium is added (AM60L1, AM60L3, AM60L7, AM60L13) may be referred to as AM60 series alloys.

[0039] Table 1 shows the phase analysis results of the manufactured specimens. The phase analysis of the specimens was performed using X-ray diffraction analysis. Figure 1 shows the X-ray diffraction analysis results of the SEN6 series alloy, and Figure 2 shows the X-ray diffraction analysis results of the AM60 series alloy.

[0040] Referring to Table 1 and Fig. 1, among the SEN6 series alloys, the SEN6, SEN6L1, and SEN6L3 alloys exhibited a single-phase structure of the HCP crystal structure, the SEN6L7 alloy exhibited a mixed-phase structure of the HCP crystal structure and the BCC crystal structure, and SEN6L13 exhibited a single-phase structure of the BCC crystal structure. That is, as the lithium content added to the SEN6 alloy increased, the crystal structure exhibited a single-phase structure of the HCP crystal structure, then transitioned to a mixed-phase structure of the HCP crystal structure and the BCC crystal structure, and finally exhibited a single-phase structure of the BCC crystal structure.

[0041] This trend of change in crystal structure with increasing lithium was also observed in the AM60 series alloys in Fig. 2. Referring to Table 1 and Fig. 2, AM60, AM60L1, and AM60L3 showed a single phase of HCP crystal structure, AM60L7 showed a mixed phase of HCP crystal structure and BCC crystal structure, and AM60L13 showed a single phase of BCC crystal structure.

[0042] Figure 3 is a graph showing the results of measuring the specific gravity of the manufactured magnesium-lithium alloy. Referring to Figure 3, the specific gravity of the base alloys, SEN6 alloy and AM60 alloy, is 1.777 g / cm, respectively. 3 and 1.778g / cm 3 As a result, they showed practically the same specific gravity. In the case of the SEN6 series alloy, it can be confirmed that the specific gravity of the magnesium alloy decreases as the content of lithium, which has a lower specific gravity than magnesium, increases.

[0043] Fig. 4 is a graph showing the results of measuring the corrosion rate (mm / y) of the manufactured magnesium-lithium alloy. The corrosion evaluation was performed by immersion in 3.5% salt water for 72 hours according to ASTM G31-72, and the corrosion rate was measured by removing corrosion products according to ASTM G1-90. Ref. in Fig. 4 represents the SEN6 alloy and AM60 alloy without lithium addition, and L1, L3, L7, and L13 on the x-axis represent the contents of added lithium in wt%, which are 1%, 3%, 7%, and 13%, respectively.

[0044] Referring to Fig. 4, in the case of the base alloy, the SEN6 alloy showed a lower corrosion rate than the AM60 alloy. The same trend was observed when lithium was added to each of the SEN6 and AM60 alloys. That is, in the case of the AM60 series, when lithium was added in an amount of 1 wt% or more, the corrosion rates all showed a high value exceeding 12 mm / y. In contrast, in the case of the SEN6 series alloy, although the corrosion rate increased when lithium was added in an amount of 1 wt% or more, it was less than 7 mm / y in all cases, showing a relatively significantly lower corrosion rate than the AM60 series alloy. In particular, in the case of SEN6L7, the corrosion rate was 3.10 mm / y, which was lower than the corrosion rate of 3.54 mm / y of the AM60 alloy that did not contain lithium.

[0045] The SEN6 series alloys contain more calcium and yttrium than the AM60 series alloys, which is believed to contribute to their lower corrosion rates. Although the corrosion rate of the SEN6 series alloys containing calcium and yttrium increases with the addition of lithium, the increase in corrosion rate is relatively less pronounced compared to the AM60 series alloys, confirming that the addition of calcium and yttrium enhances the corrosion resistance of the magnesium-lithium alloy.

[0046] In the case of the SEN6L7 alloy with 7 wt% lithium added, it has a mixed phase structure of HCP crystal structure and BCC crystal structure, and exhibits better corrosion resistance than SEN6, SEN6L1, and SEN6L3 which have a single phase structure of HCP crystal structure, and SEN6L13 which has a single phase structure of BCC crystal structure.

[0047] Figure 5 shows the results of observing the microstructure of the SEN6 series alloys using an electron microscope. Referring to Figure 5, no significant change in the microstructure is observed up to 3 wt% of lithium addition, and all exhibit the alpha (α) phase of the HCP crystal structure. In the case of the SEN6L7 alloy with a lithium content of 7 wt%, the beta (β) phase with the BCC crystal structure is formed in some parts, and the Mg in the form of a lamellar 17 Al 12 (E) is observed. This network-like dense lamellar-shaped Mg 17 Al 12 The award is known to play a role in inhibiting the spread of corrosion.

[0048] In the case of a magnesium-lithium alloy in which a mixed phase of HCP crystal structure and BCC crystal structure exists, the fraction of the above-mentioned eutectic structure appears to have increased due to a change in the solubility limit of aluminum in the existing alpha phase region as a beta phase with a BCC phase is formed. It is believed that this increase in the fraction of the above-mentioned eutectic structure has led to an improvement in corrosion resistance.

[0049] The SEN6L13 alloy, which contains 13 wt% lithium, exhibited a higher corrosion rate compared to the SEN6L7 alloy, resulting in a decrease in corrosion resistance. Referring to Fig. 5, in the case of SEN6L13, as the lithium content increased to 13 wt%, the crystal structure took on a single-phase structure of the BCC crystal structure, and secondary phases (P) in the form of precipitates not observed in other alloys were present.

[0050] Figure 6 shows the results of EDS (energy dispersive spectroscopy) mapping performed to analyze the distribution of alloy elements in the SEN6L13 alloy, and the mapping results for magnesium (Mg), aluminum (Al), manganese (Mn), calcium (Ca), and yttrium (Y) are shown. The relatively bright areas in each photograph of Figure 6 are areas where the corresponding elements were detected. Referring to Figure 6, it can be confirmed that the secondary phase (P) contains aluminum as its main component.

[0051] In the case of SEN6L13, the cause of the increased corrosion rate compared to the SEN6L7 alloy is the presence of calcium and yttrium added to the alloy in the tissue where the HCP crystal structure exists, and Mg 17 Al 12 and Al8Mn4Y phases play a role in reducing the corrosion rate of the alloy in a complex manner, but in the case of having a single phase with a completely BCC crystal structure, the elements added to the alloy (e.g., aluminum) are Mg 17 Al 12 It is believed that this is because the corrosion mechanism is completely different by forming a secondary phase (P) of a different form from the original phase.

[0052] While the present invention has been described with reference to the embodiments illustrated in the drawings, these are merely exemplary, and those skilled in the art will appreciate that various modifications and equivalent alternative embodiments are possible. Therefore, the true scope of technical protection of the present invention should be determined by the technical spirit of the appended claims.

[0053] According to the technical idea of ​​the present invention, magnesium alloy is the lightest alloy with excellent corrosion resistance, and can be applied to various casting and processing processes. It can be applied to almost all fields requiring corrosion resistance and lightweight, such as automobile, railway, aviation parts, and electromagnetic parts, and has a wide range of applications.

Claims

1. A mixed phase structure containing aluminum (Al), manganese (Mn), calcium (Ca), yttrium (Y), and lithium (Li), and including a phase with an HCP crystal structure and a phase with a BCC crystal structure. High corrosion resistance magnesium-lithium alloy.

2. In paragraph 1, The aluminum (Al) has a range of 3 to 9 wt%, the manganese (Mn) has a range of 0.1 to 0.5 wt%, the calcium (Ca) has a range of 0.1 to 1 wt%, the yttrium (Y) has a range of 0.1 to 1 wt%, and the lithium (Li) has a range of 6 to 10 wt%. High corrosion resistance magnesium-lithium alloy.

3. In paragraph 1, Mg 17 Al 12 including awards, High corrosion resistance magnesium-lithium alloy.

4. In paragraph 1, 1.5 g / cm 3 1.6 g / cm 3 has a specific gravity of, High corrosion resistance magnesium-lithium alloy.

5. In paragraph 1, Having a corrosion rate of 2 mm / year to 4 mm / year, High corrosion resistance magnesium-lithium alloy.

6. Consists of aluminum (Al): 3 to 9%, manganese (Mn): 0.1 to 0.5%, calcium (Ca): 0.1 to 1%, yttrium (Y): 0.1 to 1%, lithium (Li): 6 to 10%, the remainder being magnesium (Mg) and inevitable impurities, Having a mixed phase structure including a phase with an HCP crystal structure and a phase with a BCC crystal structure, High corrosion resistance magnesium-lithium alloy.

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