Mg ALLOY, METHOD FOR MANUFACTURING Mg ALLOY, AND CONSTRUCTION MATERIAL AND BIOMATERIAL USING Mg ALLOY

Abstract

To provide a Mg alloy in which Ni is dispersed in a magnesium alloy and which can accelerate decomposition.SOLUTION: In a magnesium alloy containing Mg, Al, Mn, and Ni, an Al-Mn-Ni-based intermetallic compound containing Ni is formed and crystallized.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an Mg alloy, a method for producing the Mg alloy, and civil engineering and biomaterials using the Mg alloy, and more particularly to an Mg alloy that can promote decomposition. [Background technology]

[0002] Magnesium alloys have a low density among metal materials used in structures and equipment, and therefore, by replacing iron and other materials with magnesium alloys in various fields, the weight of these materials has been reduced. Furthermore, because magnesium alloys are electrically less noble than other metals, they are also used as sacrificial electrode materials for corrosion protection of structures and as excavation materials. Furthermore, because magnesium alloys are degradable or biodegradable, they are also used in materials that do not require recovery, and development of their applications in underground structures, underwater structures, biomaterials, and medical materials is also underway.

[0003] Patent Document 1 relates to MgZn alloys and MgZnCa alloys with improved decomposition properties, and discloses implants having three-dimensional structures based on these alloys. As these are materials for medical applications, including surgical implants, specifically, ultra-high purity magnesium contains 2.0 to 6% by weight of high purity Zn (paragraphs 0002, 0004, 0045, etc. of Patent Document 1).

[0004] Furthermore, Patent Document 2 relates to a magnesium alloy material having excellent mechanical properties and surface quality, and discloses that when performing continuous casting, the material forming the portion that comes into contact with the molten magnesium alloy is formed from a low-oxygen material with an oxygen content of 20 mass % or less (paragraphs 0008, 0009, etc. of Patent Document 2).

[0005] As described above, magnesium alloy materials have been developed that are lightweight and have excellent mechanical properties and decomposition properties depending on the intended use. On the other hand, commercially available magnesium contains impurities, and it is believed that the presence of such impurities increases the decomposition rate due to the formation of microgalvanic elements including Fe, Cu, and Ni (see, for example, paragraph 0004 of Patent Document 1). In other words, Ni has the property of increasing the decomposition rate, and it is thought that the decomposition rate can be adjusted depending on its state in the magnesium alloy. However, Ni has a higher melting point and density than Mg or magnesium alloys (the melting point of Mg is 650°C, and the density of Mg is 1.738 g / cm). 3 , the melting point of Ni is 1455℃, and the density of Ni is 8.908g / cm 3 ), it was difficult to add Ni to magnesium alloys and dissolve it in the temperature range where magnesium alloys melt, or to completely disperse it in the alloy. Furthermore, as mentioned above, it is difficult to add Ni to a magnesium alloy and dissolve it or to completely disperse it in the alloy. Therefore, simply adding Ni, which has the property of increasing the decomposition rate, to a magnesium alloy is unlikely to result in an Mg alloy that can promote decomposition as intended. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2015-532685 [Patent Document 2] International Publication No. 2006 / 003899 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a magnesium alloy in which Ni is dispersed in the magnesium alloy together with the metals contained in the magnesium alloy. [Means for solving the problem]

[0008] In order to solve the above problems, the Mg alloy of the present invention contains Mg, Al, Mn, and Ni, and has crystallized Al-Mn-Ni intermetallic compounds.

[0009] The Mg alloy may further contain Zn.

[0010] The Mg alloy may further contain Ca.

[0011] The Mg alloy containing Ca may contain one or more compounds selected from the group consisting of Al2Ca, (Mg, Al)2Ca, and Mg2Ca.

[0012] In the Mg alloy, the Al content is preferably 0.1 mass % or more and the Mn content is preferably 0.05 mass % or more relative to the total amount of the Mg alloy.

[0013] In the above-mentioned Mg alloy containing Zn, the Zn content is preferably 0.05 mass % or more and 1.5 mass % or less relative to the total amount of the Mg alloy.

[0014] In the above-mentioned Mg alloy containing Ca, the Ca content is preferably 0.1 mass % or more and 2.0 mass % or less relative to the total amount of the Mg alloy.

[0015] The Al-Mn-Ni intermetallic compound preferably contains 0.1 mass % or more of Ni.

[0016] In the above Mg alloy, the Al-Mn-Ni intermetallic compound has a density of 1 particle / cm per unit cross-sectional area. 2 It is preferable that the particle size is 1 nm or more and / or that the particle size is 1 nm or more and 25 μm or less.

[0017] The Al-Mn-Ni intermetallic compound may form clusters.

[0018] The method for producing a Mg alloy having crystallized Al-Mn-Ni-based intermetallic compounds of the present invention includes a casting step, which includes the steps of blending Mg, Al, Mn, and Ni to prepare a mixture, heating the prepared mixture to 720°C or higher to prepare a molten metal, stirring the prepared molten metal to prepare a complete melt, and casting the complete melt prepared by stirring.

[0019] In the step of preparing the mixture, Zn and / or Ca may be further added.

[0020] The civil engineering material or biomaterial of the present invention uses the above-mentioned Mg alloy, and due to the decomposability of the Mg alloy, recovery after use is not required. [Effects of the Invention]

[0021] In the Mg alloy containing Mg, Al, Mn, and Ni according to the present invention, by having crystallized Al-Mn-Ni based intermetallic compounds, it is possible to provide an Mg alloy capable of promoting decomposition. Furthermore, according to the method for producing an Mg alloy of the present invention, an Al-Mn-Ni intermetallic compound containing Ni as well as the metals Al and Mn contained in the magnesium alloy can be formed and crystallized, and Ni can be dispersed in the magnesium alloy, thereby producing an Mg alloy whose decomposition can be promoted. [Brief explanation of the drawings]

[0022] [Figure 1] An example of the manufacturing process of the present invention will be described below. [Figure 2] An example of the relationship between the content ratio relative to the amount of Ni added in the present invention and the molten metal temperature is shown below. [Figure 3] Figure 3(a) shows an example of the types of crystals that can be produced with or without stirring during the casting process, while Figure 3(b) shows an example of the types of crystals that can be produced with or without stirring during the casting process. [Figure 4]An example of the casting process of the present invention is shown in Figure 4. Figure 4(a) shows an example of the relationship between the elapsed time and temperature in the casting process, Figure 4(b) is a metallurgical microscope photograph of the billet cast in Figure 4(a), and Figure 4(c) is an enlarged metallurgical microscope photograph of Figure 4(b). [Figure 5] Examples of metallurgical microscope photographs of Mg alloys with different amounts of Ni added are shown in Figure 5(a) where the Ni content is 0.4 mass%, and Figure 5(b) where the Ni content is 5 mass%. [Figure 6] Metallurgical microscope photographs of Al-Mn-Ni intermetallic compounds in a homogenized billet are shown in Figure 6(a) for field 1, Figure 6(b) for field 2, and Figure 6(c) for field 3. [Figure 7] Metallurgical microscope photographs of the Al-Mn-Ni intermetallic compound of the extruded material are shown in Figure 7(a) and Figure 7(b) respectively. [Figure 8] An example of the relationship between Ni concentration and decomposition rate in the Mg alloy of the present invention is shown below, depending on whether or not Ca is added. [Figure 9] 9(a) and 9(b) show examples of SEM-EDS analysis results when Ca is added to the Mg alloy of the present invention. [Figure 10] The following shows an example of the relationship between the Ca addition concentration and the tensile breaking strength, 0.2% yield strength, and elongation properties. [Figure 11] An example of a decomposition mechanism investigation is shown in Figure 11(a) which shows the extrusion direction and observation direction of the sample, Figure 11(b) shows an example of a metallurgical microscope photograph of the extruded material before the immersion test, and Figure 11(c) shows an example of a metallurgical microscope photograph of the extruded material after the immersion test. [Figure 12] Figure 12(a) shows an example of a cluster formed sample in which Al-Mn-Ni intermetallic compounds are clustered in the Mg alloy of the present invention, and Figure 12(b) shows another example of a cluster formed sample. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, an embodiment of the present invention will be described.

[0024] The Mg alloy of the present invention contains Mg, Al, Mn, and Ni, and has crystallized Al-Mn-Ni intermetallic compounds.

[0025] (Mg alloy) As the name suggests, Mg alloys are alloys whose main component is Mg. As long as the main component Mg and the added elements Al, Mn, and Ni can be dissolved (dispersed) by heating or by heating and stirring, each alloy may be blended, or Ni may be added to an Mg-Al-Mn alloy, Mg-Al-Zn-Mn alloy, Mg-Al-Mn-Ca alloy, or Mg-Al-Zn-Mn alloy.

[0026] Mg alloys contain crystallized Al-Mn-Ni intermetallic compounds. As mentioned above, Ni has a high melting point and density, so it is difficult for it to disperse in Mg alloys by itself. However, when Ni forms Al-Mn-Ni intermetallic compounds with Al and Mn added to the Mg alloy and crystallizes, the Al-Mn-Ni intermetallic compounds disperse in the Mg alloy and promote the decomposition of the Mg alloy. The presence of Al-Mn-Ni intermetallic compounds crystallized in the Mg alloy has the effect of increasing the decomposition rate of the Mg alloy, and the effect of allowing the Mg alloy to be decomposed uniformly or locally depending on the location of crystallization. In terms of increasing the decomposition rate, it is "easily decomposable." Details of Al-Mn-Ni intermetallic compounds will be discussed later.

[0027] The amount of Al added to the Mg alloy is preferably 0.1% by mass or more, more preferably 0.1% by mass to 16% by mass, even more preferably 0.1% by mass to 11% by mass, and even more preferably 0.3% by mass to 11% by mass. If the Al content is less than 0.1% by mass, the formation of Al-Mn-Ni intermetallic compounds becomes difficult. On the other hand, if the Al content increases, the internal stress during casting increases, which tends to make continuous casting more difficult, but the concentration should be within a range that allows the formation and crystallization of Al-Mn-Ni intermetallic compounds.

[0028] The amount of Mn added to the Mg alloy is preferably 0.05% by mass or more, more preferably 0.05% by mass to 1.0% by mass, and even more preferably 0.1% by mass to 1.0% by mass, based on the total amount of the Mg alloy. If the Mn content is less than 0.1% by mass, the formation of Al-Mn-Ni intermetallic compounds becomes difficult. On the other hand, as the Mn content increases, it tends to become more difficult for Mg alloys, especially Mg alloys containing Al, to contain Mn. However, the concentration should be within a range that allows the formation and crystallization of Al-Mn-Ni intermetallic compounds.

[0029] The amount of Ni added to the Mg alloy is preferably 0.1% by mass or more relative to the amount of the crystallized Al-Mn-Ni intermetallic compound. If the Ni content is less than 0.1% by mass, it becomes difficult to generate a potential difference that promotes decomposition between the Al-Mn-Ni intermetallic compound and α-Mg. On the other hand, as the Ni content increases, the crystallization temperature of the Al-Mn-Ni intermetallic compound increases, and therefore it tends to precipitate and separate easily once crystallization begins in the molten Mg. However, the Ni content should be within a range that allows for the appropriate formation and crystallization of the Al-Mn-Ni intermetallic compound. The Ni content of the Mg alloy is preferably 0.01% by mass or more, more preferably 0.01% by mass to 0.6% by mass, and even more preferably 0.01% by mass to 0.5% by mass. This is because, even if 0.6% by mass or more of Ni is added, it is thought that a large amount of Ni will settle and separate at the bottom of the furnace without being sufficiently dispersed and diffused within the Mg alloy (see the results of Evaluation Test 5 described below). Intermetallic compounds are compounds made up of two or more metals, and some of them exhibit unique physical and chemical properties that differ from those of the constituent elements.

[0030] The Mg alloy may further contain Zn. The Zn added to the Mg alloy is preferably 0.05% by mass or more and 1.5% by mass or less, more preferably 0.1% by mass or more and 1.5% by mass or less, based on the total amount of the Mg alloy. When Zn is added to the Mg alloy, solid solution strengthening can improve the 0.2% proof stress and elongation and promote age precipitation. On the other hand, when more than 1.5% by mass of Zn is added, the decomposition rate tends to decrease.

[0031] The Mg alloy may further contain Ca. The Ca added to the Mg alloy is preferably 0.1% by mass or more and 2.0% by mass or less, more preferably 0.2% by mass or more and 2.0% by mass or less. When Ca is added to the Mg alloy to which Al has been added, one or more compounds selected from the group consisting of Al2Ca, (Mg,Al)2Ca, or Mg2Ca are crystallized, and these compounds contribute as the driving force for decomposition, so the decomposition rate increases. Further, by crystallizing these compounds, a Mg alloy with improved flame retardant properties and heat resistance can be obtained. Here, the ratio of these Ca-containing compounds is generally determined by the addition ratios of Al and Ca. When the addition ratio is Al>Ca, Al2Ca is the main component; when the addition ratio is Al≒Ca, (Mg,Al)2Ca is the main component; and when the addition ratio is Al<Ca, Mg2Ca is the main component. On the other hand, when the Ca addition amount exceeds 2.0% by mass, the tensile properties such as the 0.2% proof stress and elongation may decrease.

[0032] The number density of the crystallized Al-Mn-Ni intermetallic compound present in the Mg alloy is preferably 1 piece / cm 2 or more per unit cross-sectional area in SEM or a metallurgical microscope. This is because it is desirable to crystallize the Al-Mn-Ni intermetallic compound, which becomes nobler electrochemically, at 1 piece / cm 2 or more per unit cross-sectional area to ensure the decomposition rate. Furthermore, the size of the crystallized Al-Mn-Ni intermetallic compounds is preferably 1 nm or more and 25 μm or less. This is because if the Al-Mn-Ni intermetallic compounds crystallize with a particle size of 25 μm or more, they can become the starting point for fractures such as fatigue (see the results of Evaluation Test 5 described later). As described above, by adjusting the size of the Al-Mn-Ni intermetallic compounds that are potentially noble, the degree of decomposition promotion can be adjusted depending on the intended use.

[0033] It is preferable that the number of crystallized Al-Mn-Ni intermetallic compounds present at the grain boundaries in the extruded material after the extrusion process shown in Fig. 1 is greater than the number present within the grains. That is, it is preferable that more than 50% but not more than 100% of all Al-Mn-Ni intermetallic compounds are present at the grain boundaries. The Al-Mn-Ni intermetallic compounds present at the grain boundaries are stable in high temperature regions, and therefore have the effect of preventing the coarsening and growth of the fine crystal grains of the Mg alloy formed by strain induced in the extrusion process (plastic processing), thereby making the crystalline structure of the Mg alloy in the extruded material fine and uniform, and also making the decomposition uniform. In the homogenized billet before the extrusion step (plastic working), the proportion of the number of intermetallic compounds present within the crystal grains may be higher than that of the extruded material. Specifically, 30% to 100% of all the Al-Mn-Ni-based intermetallic compounds may be present within the crystal grains.

[0034] Furthermore, when Ni is added to an Al-containing Mg alloy, the Al-Mn-Ni intermetallic compounds can form clusters, such as when inclusions act as heterogeneous nuclei. When Al-Mn-Ni intermetallic compounds form clusters on the decomposition surface, which is the surface that comes into contact with the solution, the area of ​​the potentially noble portion increases, which can locally increase the decomposition rate.

[0035] The Mg alloy may contain other elements in addition to the essential elements Mg, Al, Mn, Ni, and optional Zn and Ca, or the other elements may be only unavoidable impurities. Examples of unavoidable impurities include, but are not limited to, Si, Fe, and Cu. In other words, the balance of the essential elements Al, Mn, Ni, optional Zn, and Ca in the Mg alloy may be Mg and unavoidable impurities. The effects of each element are generally as follows: Al promotes solid solution strengthening and precipitation strengthening, improving castability and corrosion resistance. Mn suppresses the coarsening of recrystallized grains during plastic processing. Zn improves castability and strength. Ca improves creep strength and heat resistance, and provides flame retardancy.

[0036] (Method of manufacturing Mg alloy) The method for producing the Mg alloy of the present invention includes a casting step, a homogenization step, an extrusion step, or a forging step. Figure 1 shows a simplified flow chart of a manufacturing method for Mg alloys. A billet is produced in a casting process, and then a homogenized billet is produced from the billet in a homogenization process. The homogenized billet is then extruded to produce an extruded material in an extrusion process, or forged to produce a forged material in a forging process. Note that extruded and forged materials are also called plastically processed materials.

[0037] (Casting process) The casting process includes a step of preparing a mixture, a step of heating the mixture to prepare a molten metal, a step of stirring the mixture to prepare a completely melted material, and a step of casting the completely melted material.

[0038] In the casting process, the step of blending Mg, Al, Mn, and Ni to prepare a mixture is a step of preparing metals or metal ingots according to the alloy composition, mixing them, and preparing a mixture. In addition to the essential elements Mg, Al, Mn, and Ni, optional elements Zn and Ca can also be added.

[0039] In one example of the subsequent step of heating the prepared mixture to prepare a molten metal, the mixture is heated to 720° C. or higher, preferably 730° C. or 740° C., and more preferably 750° C. or lower. At temperatures higher than 750° C., the molten metal becomes active, which may result in the generation of many void defects.

[0040] The process of stirring the prepared molten metal to produce a completely melted material involves stirring the heated mixture and further dissolving it evenly and almost completely to produce a completely melted material. A completely melted material refers to a liquid state in which the blended metals, metal ingots, and crystallized compounds are mixed evenly without precipitating or separating from the Mg alloy. Examples of stirring methods include mechanical stirring, manual stirring, ultrasonic molten metal stirring, and electromagnetic stirring. The stirring time varies depending on the amount and temperature of the heated molten metal, the stirring method, the size and power of the stirring device, and other factors, but is typically between 10 and 60 minutes. Stirring Mg alloys at high temperatures for long periods of time can result in large amounts of coatings and oxides on the surface of the molten metal being entrained, making it impossible to maintain the quality of the ingot. In such cases, the quality of the billet, homogenized billet, extrusion material, and forged material (plastically processed material) can be maintained by adjusting the stirring time or by performing molten metal treatment after stirring so that the coatings and oxides on the surface of the molten metal are not at least contained in the billet.

[0041] The produced completely melted material is poured into a die having, for example, a diameter of 70 mm (inner diameter of 70 mm) to produce a billet.

[0042] The term "casting" in the casting process refers to raising the temperature of a metal above its melting point, pouring it into a mold, and cooling and solidifying it. The casting method in the casting process of the present invention is not limited as long as it performs such casting, and examples include sand casting (green (sand) mold casting, dry mold casting, self-hardening mold casting, thermosetting mold casting, gas-hardening mold casting, lost foam casting, V-process casting, freeze-molding, etc.), plaster casting, precision casting, metal mold casting (gravity casting, die-casting, low-pressure casting, high-pressure casting), continuous casting, etc.

[0043] (Homogenization process) The homogenization process is a process in which intermetallic compounds, etc., that crystallize during the casting process are dissolved in α-Mg, suppressing segregation of the components and forming an ingot with minimal fluctuation in component concentration. For example, in the case of an Mg-Al-Zn-Ni alloy, the low-melting-point Mg-Al-Zn intermetallic compounds that crystallize during the casting process are dissolved in α-Mg and homogenized. If the low-melting-point compounds remain in the extrusion process, cracking is likely to occur, and remaining Mg-Al-Zn intermetallic compounds pose a risk of fire. Therefore, the homogenization process is one of the processes that not only forms an alloy with minimal fluctuation in component concentration, but also maintains mechanical strength to prevent cracking and other issues, and is also performed for safety reasons such as preventing fire. As an example, a φ70 billet is cut to φ60 (outer diameter 60 mm) and homogenized at 400°C to 420°C, preferably about 410°C, to produce a homogenized billet.

[0044] (Extrusion process) In the extrusion process, extrusion is a method in which a material (such as a homogenized billet) is placed in a pressure-resistant container, and pressure is applied to the material, forcing it out of a mold (die) that has been drilled to the desired cross-sectional shape, thereby forming it into the desired cross-sectional shape. In the extrusion process of the present invention, for example, the homogenized billet is extruded to a diameter of φ10 (outer diameter of 10 mm) in an atmosphere of 300°C to 410°C, preferably about 400°C, to form an extruded material (plastically worked material). The extruded material is further processed into parts or components using the Mg alloy.

[0045] (Forging process) Forging in the forging process is a method in which material is placed between a pair of upper and lower dies and crushed with a press to form the desired shape. In the forging process of the present invention, for example, a homogenized billet is pressed between upper and lower dies in an atmosphere of 300°C to 410°C, preferably about 400°C, to form a forged material (plastically worked material). Alternatively, the billet is forged to form a round casting of an appropriate size, such as φ10 (outer diameter 10 mm) and a length of 200 mm to 300 mm, to form a forged material (plastically worked material). The forged material is further machined into parts or components using an Mg alloy.

[0046] (Application of Mg alloys) Mg alloys are used in civil engineering materials such as structural members, vibration-damping members, sacrificial electrode materials, excavation members, underground structures, underwater structures, biomaterials, medical materials, etc. In particular, the degradability of Mg alloys may eliminate the need for recovery after use of civil engineering materials used underground or underwater, and biomaterials used inside the body. [Example]

[0047] The results of the evaluation tests including examples of the present invention will be specifically explained below, but the present invention is not limited to these examples in any way.

[0048] -Evaluation test 1 (preparation of evaluation samples and measurement of decomposition rate)- Metals were added (blended) to the contents shown in Tables 1A, 1B, and 1C, and extruded materials were formed using the casting, homogenization, and extrusion processes described above to create evaluation samples 1 to 51. The mass percentages of metals in Tables 1A, 1B, and 1C represent the proportions of the metals contained in the evaluation samples. The alloy types are listed using names specified by ASTM or names based on the ASTM naming rules. For example, A is aluminum, Z is zinc, M is manganese, N is nickel, and X is calcium, and the numbers following each represent the mass percentages rounded to one digit and arranged in order. Furthermore, the decomposition rate was measured for Samples 1 to 51. The decomposition rate was measured by immersing a sample piece whose weight (mg) had been measured in a 2% KCl aqueous solution at 93°C for a certain period of time, then removing it, drying it, and measuring the weight (mg) to confirm the weight change. The mass loss was calculated as the surface area (1 cm) per day. 2 ) is the decomposition rate (mg / cm2 / day).

[0049] [Table 1A]

[0050] [Table 1B]

[0051] [Table 1C]

[0052] -Evaluation test 2 (Regarding the ratio of Ni content to the amount of Ni added)- In the present invention, it is important that the added Ni forms an Al-Mn-Ni intermetallic compound in the Mg alloy and crystallizes. However, if the added Ni cannot sufficiently form an Al-Mn-Ni intermetallic compound in the Mg alloy, or if Ni cannot disperse in the Mg alloy due to its high melting point or high density and is instead precipitated and removed, the Ni content in the billet or plastically worked material (extruded material, forged material) will be lower than the amount added. Therefore, the ratio of the Ni content in the billet to the amount of Ni added was measured depending on the heating temperature (molten metal temperature) in the casting process and whether or not stirring was performed. The results are shown in Figure 2 and Table 2.

[0053] [Table 2]

[0054] As shown in Figure 2 and Table 2, when the heating temperature was 720°C or higher, the proportion of Ni content was higher with stirring than without stirring, and when the heating temperature was 740°C or higher, with stirring, more than 90% of the added Ni was blended into the billet or plastically processed material (extruded material, forged material). Therefore, under the conditions of Evaluation Test 2, it was found that Ni was dissolved (dispersed) in the Mg alloy if stirring was carried out at a heating temperature of 720°C or higher.

[0055] -Evaluation test 3 (SEM-EDS analysis by Ni content)- The molten metal temperature in the casting process in Table 2 was 750°C, and SEM-EDS analysis was carried out on the extruded material without stirring and the extruded material with stirring. SEM (scanning electron microscope) analyzes the surface structure of a sample by irradiating it with an electron beam and detecting secondary electrons emitted from the sample. EDS (energy dispersive X-ray spectroscopy) analyzes the elements and concentrations that make up a sample by detecting fluorescent X-rays that are generated when the sample is irradiated with an electron beam or X-rays.

[0056] The surface structure of the extruded material, with or without stirring during the casting process, was confirmed using SEM, and the elements and concentrations in the crystalline portion were analyzed using EDS. Figure 3(a) shows the field of view of the extruded material without stirring at a heating temperature (molten metal temperature) of 750°C, and Table 3 shows the results of the point analysis. Figure 3(b) shows the field of view of the extruded material with stirring at a heating temperature (molten metal temperature) of 750°C, and Table 4 shows the results of the point analysis.

[0057] [Table 3]

[0058] [Table 4]

[0059] From the analysis results of positions 001 and 002 in FIG. 3(a) and Table 3, it was confirmed that no Al-Mn-Ni intermetallic compounds were formed in the extruded material without stirring at 750°C. On the other hand, the analysis results of positions 001 and 002 in Figure 3(b) and Table 4 confirmed the formation of Al-Mn-Ni intermetallic compounds in the extruded material with stirring at 750°C. Therefore, it was found that stirring can dissolve and disperse Ni more reliably, resulting in the formation and crystallization of Al-Mn-Ni intermetallic compounds.

[0060] -Evaluation test 4 (billet production and evaluation)- Regarding the production of billets in the casting process, Figure 4(a) shows an example of the elapsed time, temperature, and steps of the casting process, Figure 4(b) shows a metallurgical microscope photograph of the billet cast in Figure 4(a), and Figure 4(c) shows an enlarged metallurgical microscope photograph of Figure 4(b).

[0061] In the casting process, the heating and stirring step shown in Fig. 4(a) is a step for dissolving Ni evenly and completely or almost completely in the Mg alloy to produce a completely melted product. A molten metal treatment step can be performed before or after this stirring step. The molten metal treatment step is a step for maintaining the quality of the ingot, which is easily deteriorated by heating and stirring. After the billet underwent the heating and stirring process shown in Figure 4(a) and the molten metal treatment process, metallurgical microscope images such as those shown in Figure 4(b) and Figure 4(c) were obtained, and EDS analysis confirmed the formation and crystallization of Al-Mn-Ni intermetallic compounds. Therefore, the results of Evaluation Test 4, as with Evaluation Test 3, also revealed that heating and stirring can more reliably dissolve and disperse Ni completely, resulting in the formation and crystallization of Al-Mn-Ni intermetallic compounds.

[0062] -Evaluation test 5 (regarding the amount of Ni added)- Evaluation test 2 showed that the ratio of the Ni content in the billet to the amount of Ni added in the casting process can be increased by stirring during the casting process. However, as the amount of Ni added increases, the crystallization temperature of Al-Mn-Ni intermetallic compounds tends to increase, so even if stirring is performed, it may not be possible to sufficiently form Al-Mn-Ni intermetallic compounds. Therefore, billets with different amounts of Ni added were evaluated.

[0063] When the Ni content was 0.4 mass%, the Ni content of the billet was 0.4 mass%. Figure 5(a) shows the results of SEM-EDS analysis of the billet. This billet contained 100% of the added Ni (content / addition amount = 0.4 / 0.4 = 100%), and it was confirmed that Al-Mn-Ni intermetallic compounds had formed and were present in needle-like or granular shapes at the grain boundaries. The formation of needle-like or granular intermetallic compounds at the grain boundaries is thought to be due to the Al-Mn-Ni metallic compounds exerting a pinning effect on the recrystallized grains during plastic working, thereby suppressing the coarsening of the recrystallized grains.

[0064] On the other hand, when the amount of Ni added was 5 mass%, the Ni content of the billet was 0.4 mass%. Figure 5(b) shows the results of SEM-EDS analysis of the billet. This billet contained only 8% added Ni (content / addition amount = 0.4 / 5 = 8%), and it was confirmed that Al-Mn-Ni intermetallic compounds were crystallized in a dendritic (branch-like) state in this billet. The dendritic intermetallic compounds are formed because their crystallization temperature is higher than that of α-Mg, and they are thought to form as primary crystals. Furthermore, the results of this evaluation test suggest that even if 0.6 mass% or more of Ni is added to an Mg-Al-Zn-Mn alloy, it will settle and separate at the bottom of the furnace without being sufficiently dispersed or diffused within the Mg alloy.

[0065] Therefore, it was found that if the ratio of Ni content to the amount of Ni added becomes too low, Al-Mn-Ni intermetallic compounds cannot be sufficiently dispersed in the Mg alloy, and coarse Al-Mn-Ni intermetallic compounds with a particle size of 25 μm or more are crystallized. Furthermore, if Al-Mn-Ni intermetallic compounds crystallize with a particle size of 25 μm or more, they can become the starting point for fractures such as fatigue.

[0066] -Evaluation test 6 (crystallization location of Al-Mn-Ni intermetallic compounds in homogenized billets)- After the homogenization process and before the extrusion process, the homogenized billet was evaluated for the crystallization positions of Al-Mn-Ni intermetallic compounds. A homogenized billet of AZ80 (a magnesium alloy with an expected Al content of 8 mass% and a Zn content of 0% rounded off) with an expected Ni content of 0.4 mass% was prepared and observed under a metallurgical microscope.

[0067] Figure 6(a) shows metallurgical microscope photographs of field 1, Figure 6(b) shows field 2, and Figure 6(c) shows field 3. Table 5 shows the results of counting the number of Al-Mn-Ni intermetallic compounds present within crystal grains and at the crystal grain boundaries.

[0068] [Table 5]

[0069] From Figures 6(a), 6(b), 6(c) and Table 5, it was found that approximately 65% ​​to 90% of the Al-Mn-Ni intermetallic compounds in the homogenized billet before the extrusion process in this evaluation test were present within the crystal grains.

[0070] -Evaluation test 7 (crystallization location of Al-Mn-Ni intermetallic compounds in extruded material)- The crystallization positions of Al-Mn-Ni intermetallic compounds in the extruded material after the extrusion process were evaluated. A homogenized billet of AZ80 (a magnesium alloy with an expected Al content of 8 mass% and a Zn content of 0% rounded off) with an expected Ni content of 0.4 mass% was prepared and observed under a metallurgical microscope.

[0071] Figure 7(a) shows a metallurgical microscope photograph of field 1, and Figure 7(b) shows field 2. The results of counting the number of Al-Mn-Ni intermetallic compounds present within crystal grains and at crystal grain boundaries are also shown in Figures 7(a) and 7(b).

[0072] From Figures 7(a) and 7(b), it was found that approximately 80% to 85% of the Al-Mn-Ni intermetallic compounds in the extruded material after the extrusion process in this evaluation test were present at the grain boundaries.

[0073] The ratio of the crystallization sites of the Al-Mn-Ni intermetallic compounds changes before and after the extrusion process as follows: When an Mg alloy is subjected to an extrusion process (plastic processing), strain is generated within the alloy, resulting in the formation of fine crystal grains. The grains then coarsen to recover from the strain, but the presence of compounds such as Al-Mn-Ni intermetallic compounds, which are stable at high temperatures, acts as a pinning effect to prevent the crystals from coarsening (growth). This pinning occurs at the grain boundaries, so Al-Mn-Ni intermetallic compounds are present at the grain boundaries. Furthermore, by pinning the crystals from coarsening, the crystals within the extruded material become fine, uniform, and stable. Therefore, it can be seen that the Al-Mn-Ni intermetallic compounds present at the grain boundaries of fine, uniform crystals are finely dispersed within the Mg alloy, which can promote the decomposition of the Mg alloy and also makes it easier to control the decomposition rate uniformly overall.

[0074] -Evaluation test 8 (relationship between Ni concentration and decomposition rate, and whether or not Ca was added)- The relationship between the Ni concentration and decomposition rate of the extruded materials was evaluated for the evaluation samples in Tables 1A, 1B, and 1C, divided into those with and without Ca addition. Figure 8 shows the evaluation results.

[0075] From Figure 8, it can be seen that the decomposition rate increases as the Ni content increases. Furthermore, when Ca is added, the decomposition rate increases compared to when no Ca is added, reaching approximately 2.0 times when Ni is 0.2 mass%, approximately 2.2 times when Ni is 0.4 mass%, and approximately 2.4 times when Ni is 0.6 mass%. Therefore, from the viewpoint of the decomposition rate of Mg alloys, it was found that the addition of Ca can increase the decomposition rate.

[0076] -Evaluation test 9 (SEM-EDS analysis of Ca-added Mg alloy)- In the Mg alloy added with Al (AZ series alloy, sample 28 in Table 1B), when Ca is added, if Al > Ca, mainly Al2Ca is formed; if Al ≒ Ca, mainly (Mg, Al)2Ca is formed; if Al < Ca, mainly Mg2Ca is formed. Examples of SEM-EDS analysis results when Ca is added to the Mg alloy added with Al (sample 43 in Table 1C) are shown in Fig. 9(a), Fig. 9(b), Table 6, and Table 7. Fig. 9(a) and Table 6 show field 1, and Fig. 9(b) and Table 7 show field 2.

[0077]

Table 6

[0078]

Table 7

[0079] Also, the decomposition rate of the Mg alloy added with Ca (sample 43 in Table 1C) is about 3000 mg / cm 2 / day, which is about twice that of the Mg alloy without Ca addition (see Fig. 8) at about 1500 mg / cm 2 / day. Therefore, from the results of this evaluation test, it was also found that adding Ca can increase the decomposition rate from the perspective of the decomposition rate.

[0080] - Evaluation Test 10 (Relationship between Ca addition concentration and tensile fracture strength, 0.2% proof stress, and elongation characteristics) - As shown in Evaluation Tests 8 and 9, it was found that adding Ca can increase the decomposition rate. Here, other characteristics were also evaluated.

[0081] Metals were added (blended) to achieve the contents described in Table 8, and extruded materials were formed through the above-mentioned casting process, homogenization treatment process, and extrusion process, and used as samples 52 to 55 for evaluation (AM90 + Ni mass%).

[0082]

Table 8

[0083] For Samples 52 to 55 in Table 8, tensile tests were carried out based on JIS Z 2241 (Method of tensile testing for metallic materials) to measure the tensile breaking strength, 0.2% yield strength, and elongation. The tensile test specimen shape used was a JIS No. 14A test specimen. The measurement results are shown in Table 9 and FIG.

[0084] [Table 9]

[0085] From FIG. 10, it is clear that as the Ca content increases, the 0.2% proof stress and elongation decrease significantly. Therefore, increasing the Ca content increases the decomposition rate of the Mg alloy, as seen in evaluation test 8. However, taking into consideration that the properties may be reduced in terms of at least 0.2 proof stress and elongation, it was found that the amount of addition must be adjusted depending on the intended use.

[0086] -Evaluation test 11 (Consideration of decomposition mechanism)- An extruded AZ80+0.1Ni alloy (sample 44 in Table 1C) was embedded in resin and subjected to microstructural observation. It was then immersed in a 2% KCl solution at 93°C for 8 minutes, and the microstructural observation was performed at the same position. Figure 11(a) shows the extrusion direction and observation direction of the sample, Figure 11(b) shows a metallurgical microscope photograph of the extruded material before the immersion test, and Figure 11(c) shows a metallurgical microscope photograph of the extruded material after the immersion test.

[0087] The white area in Figure 11(b) is α-Mg, where the concentrations of Al and Ca that make up the alloy are relatively low. The black bands in Figure 11(b) are β-phase and Al2Ca compounds, where the concentrations of Al and Ca are high. Furthermore, the granular areas in Figure 11(b) are Al-Mn-Ni intermetallic compounds. The order of potential of these is Al-Mn-Ni intermetallic compounds > Al2Ca > β-phase > α-Mg, with α-Mg being the most noble part. On the other hand, as shown in Figure 11(c), it was found that the white area, i.e., the α-Mg, had decomposed. In other words, the decomposition occurred not around the Al-Mn-Ni intermetallic compound, which is the noble area, but in the α-Mg, which is the less noble area. From these results, it was considered that the decomposition mechanism is not one in which a galvanic reaction occurs locally, centered on the Al-Mn-Ni intermetallic compound, but rather a macroscopic galvanic reaction occurs within the surface, with decomposition preferentially proceeding from the α-Mg, which is the most noble part in terms of potential.

[0088] -Evaluation Test 12 (Cluster formation of Al-Mn-Ni intermetallic compounds)- When Ni is added to AZ alloys, Al-Mn-Ni intermetallic compounds are crystallized in clusters due to the inclusions acting as heterogeneous nuclei. Metallurgical microscope photographs of cluster formation are shown in Figure 12(a) and Figure 12(b).

[0089] When clusters of Al-Mn-Ni intermetallic compounds are present on the surface in contact with the solution, the area of ​​the potentially noble part increases, resulting in a locally high decomposition rate. [Industrial Applicability]

[0090] As described above, the Mg alloy can maintain the desired mechanical properties for a certain period of time, and the overall decomposition rate can be controlled so that the alloy dissolves or decomposes after that period. The Mg alloy of the present invention is expected to be applied to Mg alloys that promote decomposition under various environments, from the perspective of crystallization of Al-Mn-Ni intermetallic compounds.

Claims

1. A magnesium alloy containing magnesium, aluminum, manganese, and nickel and having crystallized Al--Mn--Ni intermetallic compounds.

2. 10. The Mg alloy of claim 1, further comprising Zn.

3. The Mg alloy according to claim 1 or 2, further containing Ca.

4. Al 2 Ca, (Mg, Al) 2 Ca or Mg 2 4. The Mg alloy of claim 3, comprising one or more compounds selected from the group consisting of: Ca.

5. The Mg alloy according to any one of claims 1 to 4, wherein the Al is 0.1 mass% or more and 16 mass% or less, and the Mn is 0.05 mass% or more, based on the total amount of the Mg alloy.

6. The Mg alloy according to claim 2, wherein the Zn content is 0.05 mass % or more and 1.5 mass % or less relative to the total amount of the Mg alloy.

7. The Mg alloy according to claim 3, wherein the Ca content is 0.1 mass % or more and 2.0 mass % or less relative to the total amount of the Mg alloy.

8. The Mg alloy according to any one of claims 1 to 6, wherein the Al-Mn-Ni-based intermetallic compound contains 0.1 mass% or more of Ni.

9. The Al-Mn-Ni intermetallic compound has a density of 1 particle / cm per unit cross-sectional area. 2 The Mg alloy according to any one of claims 1 to 8, wherein the Mg alloy has a particle size of 1 nm or more and a size of 1 nm or more and 25 μm or less.

10. A method for producing an Mg alloy, comprising: The method for producing the Mg alloy includes a casting step, The casting process includes: blending Mg, Al, Mn, and Ni to form a mixture; a step of heating the prepared mixture to 720°C or higher to prepare a molten metal; a step of stirring the prepared molten metal to prepare a completely melted material; casting the completely melted product produced by stirring; A method for producing an Mg alloy having crystallized Al-Mn-Ni intermetallic compounds, comprising:

11. The method for producing an Mg alloy according to claim 10, wherein Zn and / or Ca is further added in the step of preparing the mixture.

12. A civil engineering material or a biomaterial using the Mg alloy according to any one of claims 1 to 9, wherein the Mg alloy is degradable and does not require recovery after use.

13. A civil engineering material or a biomaterial manufactured by the method for manufacturing an Mg alloy according to claim 10 or 11, wherein the decomposability of the Mg alloy makes recovery after use unnecessary.

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