WO2022113323A1 - Mg合金、Mg合金の製造方法、及び、Mg合金を用いた土木材料及び生体材料 - Google Patents
Mg合金、Mg合金の製造方法、及び、Mg合金を用いた土木材料及び生体材料 Download PDFInfo
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- WO2022113323A1 WO2022113323A1 PCT/JP2020/044435 JP2020044435W WO2022113323A1 WO 2022113323 A1 WO2022113323 A1 WO 2022113323A1 JP 2020044435 W JP2020044435 W JP 2020044435W WO 2022113323 A1 WO2022113323 A1 WO 2022113323A1
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Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C23/00—Alloys based on magnesium
- C22C23/02—Alloys based on magnesium with aluminium as the next major constituent
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/02—Making non-ferrous alloys by melting
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/02—Making non-ferrous alloys by melting
- C22C1/03—Making non-ferrous alloys by melting using master alloys
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C23/00—Alloys based on magnesium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C23/00—Alloys based on magnesium
- C22C23/04—Alloys based on magnesium with zinc or cadmium as the next major constituent
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C23/00—Alloys based on magnesium
- C22C23/06—Alloys based on magnesium with a rare earth metal as the next major constituent
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/06—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of magnesium or alloys based thereon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
Definitions
- the present invention relates to Mg alloys, methods for producing Mg alloys, and civil engineering materials and biomaterials using Mg alloys.
- it relates to an Mg alloy that can promote decomposition.
- Magnesium alloy has a low density among the metal materials used for structures and equipment, so the weight of the members has been reduced by replacing the members in various fields with magnesium alloys from iron and the like. Further, since the magnesium alloy is potentially lower than other metals, it is also applied to sacrificial electrode materials and excavation members for corrosion protection of structures. Further, since magnesium alloys have degradability or biodegradability, they are also used for members that do not need to be recovered, and application development to underground structures, underwater structures, biomaterials, and medical materials is being promoted.
- Patent Document 1 relates to MgZn alloys and MgZnCa alloys having improved decomposition characteristics, and discloses implants having a three-dimensional structure based on these alloys. Since it is a material for medical use including surgical implants, specifically, ultra-high-purity magnesium contains 2.0% by weight to 6% by weight of high-purity Zn (Patent Document 1, paragraphs 0002, 0004, 0045). etc).
- Patent Document 2 relates to a magnesium alloy material having excellent mechanical properties and surface quality, and in continuous casting, the material for forming the portion of the magnesium alloy in contact with the molten metal has a low oxygen content of 20% by mass or less. It discloses that it is formed of an oxygen material (Patent Document 2, paragraph 0008, 0009, etc.).
- magnesium alloy materials having excellent weight reduction, mechanical properties, and decomposition properties have been developed according to the purpose of use.
- commercially available magnesium contains impurities, and it is considered that the presence of such impurities increases the decomposition rate due to the formation of microgalvanic elements including Fe, Cu, and Ni (Patent Document 1, paragraph 0004). etc). That is, Ni has a property of increasing the decomposition rate, and it is considered that the decomposition rate can be adjusted depending on the state of existence in the magnesium alloy.
- Ni is higher than the melting point and density of Mg or magnesium alloy (Mg has a melting point of 650 ° C, Mg has a density of 1.738 g / cm 3 , Ni has a melting point of 1455 ° C, and Ni has a density of 8.908 g / cm. From 3 ), there was a problem that it was difficult to add Ni to the magnesium alloy and dissolve it in the temperature range where the magnesium alloy melts, or to completely disperse it in the alloy. Further, as described above, it is difficult to add Ni to a magnesium alloy to dissolve it or to completely disperse it in the alloy. Therefore, it is intended to simply add Ni having a property of increasing the decomposition rate to the magnesium alloy. There is also a problem that it is difficult to form an Mg alloy that can promote decomposition along the above.
- the present invention has been made in view of the above circumstances, and an object of the present invention is to provide an Mg alloy in which Ni is dispersed in a magnesium alloy together with a metal contained in the magnesium alloy.
- the Mg alloy of the present invention contains Mg, Al, Mn and Ni and has a crystallized Al—Mn—Ni intermetallic compound.
- the above Mg alloy may further contain Zn.
- the above Mg alloy may further contain Ca.
- the Mg alloy containing Ca may contain one or more compounds selected from the group consisting of Al 2 Ca, (Mg, Al) 2 Ca, or Mg 2 Ca.
- the Al is preferably 0.1% by mass or more and the Mn is preferably 0.05% by mass or more with respect to the total amount of the Mg alloy.
- the Zn is preferably 0.05% by mass or more and 1.5% by mass or less with respect to the total amount of the Mg alloy.
- the Mg alloy containing Ca is preferably 0.1% by mass or more and 2.0% by mass or less with respect to the total amount of Mg alloy.
- Ni is 0.1% by mass or more with respect to the above-mentioned Al—Mn—Ni-based intermetallic compound.
- the Al—Mn—Ni-based intermetallic compound preferably has a size of 1 piece / cm 2 or more per unit cross-sectional area and / or a size of 1 nm or more and 25 ⁇ m or less.
- the above-mentioned Al—Mn—Ni-based intermetallic compound may form a cluster.
- the method for producing an Mg alloy having a crystallized Al—Mn—Ni-based metal compound of the present invention includes a casting step, and the casting step is a step of blending Mg, Al, Mn and Ni to prepare a mixture.
- Zn and / or Ca may be further added in the step of producing the above mixture.
- the civil engineering material or biomaterial of the present invention uses the above-mentioned Mg alloy, and recovery after use is unnecessary due to the degradability of the above-mentioned Mg alloy.
- Mg alloy containing Mg, Al, Mn, and Ni of the present invention it is possible to provide an Mg alloy capable of accelerating decomposition by having a crystallized Al—Mn—Ni-based intermetallic compound. Further, according to the method for producing an Mg alloy of the present invention, an Al—Mn—Ni-based intermetallic compound containing Ni is formed and crystallized together with the metals Al and Mn contained in the magnesium alloy, and Ni is converted into a magnesium alloy. It is possible to produce an Mg alloy that can be dispersed therein and can accelerate decomposition.
- FIG. 3A is an example without stirring
- FIG. 3B is an example with stirring
- An example of the casting process of the present invention is shown.
- 4 (a) is an example of the relationship between the elapsed time of the casting process and the temperature
- FIG. 4 (b) is a metal micrograph of the billet cast in FIG. 4 (a)
- FIG. 4 (c) is FIG. (B) is an enlarged metal micrograph.
- An example of a metal micrograph of an Mg alloy depending on the amount of Ni added is shown.
- FIG. 5A is an example when the Ni addition amount is 0.4% by mass
- FIG. 5B is an example when the Ni addition amount is 5% by mass.
- the metal micrograph of the Al—Mn—Ni intermetallic compound of the homogenized billet is shown.
- 6 (a) shows an example of the field of view 1
- FIG. 6 (b) shows an example of the field of view 2
- FIG. 6 (c) shows an example of the field of view 3.
- the metal micrograph of the Al—Mn—Ni-based intermetallic compound of the extruded material is shown.
- 7 (a) shows an example of the field of view 1
- FIG. 7 (b) shows an example of the field of view 2.
- FIG. 9 (a) shows an example of the field of view 1
- FIG. 9 (b) shows an example of the field of view 2.
- An example of the relationship between the Ca addition concentration and the tensile fracture strength, 0.2% proof stress, and elongation characteristics is shown.
- An example of the decomposition mechanism investigation is shown.
- 11 (a) shows the extrusion direction and the observation direction of the sample
- FIG. 11 (b) is a metal micrograph of the extruded material before the immersion test
- FIG. 11 (c) is a metal micrograph of the extruded material after the immersion test. An example is shown. In the Mg alloy of the present invention, an example in which Al—Mn—Ni-based intermetallic compounds are clustered is shown.
- FIG. 12 (a) shows an example of a cluster-forming sample
- FIG. 12 (b) shows another example of a cluster-forming sample.
- the Mg alloy of the present invention contains Mg, Al, Mn, and Ni, and has a crystallized Al—Mn—Ni-based intermetallic compound.
- Mg alloy As the word implies, an Mg alloy is an alloy containing Mg as a main component.
- the main components Mg and added Al, Mn, and Ni may be mixed with gold in various places as long as they are dissolved (dispersed) by heating or heating and stirring, or Mg-Al-Mn alloy, Mg-.
- Ni may be added to the Al—Zn—Mn alloy, the Mg—Al—Mn—Ca alloy, and the Mg—Al—Zn—Mn alloy.
- the Mg alloy contains crystallized Al—Mn—Ni-based intermetallic compounds. As described above, since Ni has a high melting point and density, it is difficult to disperse it in the Mg alloy by itself, but it forms an Al—Mn—Ni intermetallic compound together with Al and Mn added in the Mg alloy and crystallizes. By doing so, it is possible to disperse in the Mg alloy and promote the decomposition of the Mg alloy.
- the inclusion of the crystallized Al-Mn-Ni intermetallic compound in the Mg alloy has the effect of increasing the decomposition rate of the Mg alloy, the effect of uniformly decomposing the Mg alloy depending on the crystallizing location, or the local decomposition. Has the effect that can be done. In terms of increasing the decomposition rate, it is "easy to decompose". Details of the Al—Mn—Ni intermetallic compound will be described later.
- the Al added to the Mg alloy is preferably 0.1% by mass or more, more preferably 0.1% by mass or more and 16% by mass or less, and more preferably 0.1% by mass or more and 11 by mass with respect to the total amount of the Mg alloy. It is more preferably mass% or less, 0.3 mass% or more and 11 mass% or less.
- Al is less than 0.1% by mass, it becomes difficult to form an Al—Mn—Ni-based intermetallic compound.
- the concentration may be within the range in which the Al—Mn—Ni intermetallic compound is formed and crystallized. ..
- the Mn added to the Mg alloy is preferably 0.05% by mass or more, more preferably 0.05% by mass or more and 1.0% by mass or less, and 0.1% by mass, based on the total amount of the Mg alloy. It is more preferably 1.0% by mass or less.
- Mn is less than 0.1% by mass, it becomes difficult to form an Al—Mn—Ni-based intermetallic compound.
- Mn increases, it tends to be difficult for Mn to be contained in Mg alloys, especially Mg alloys containing Al, but the concentration is within the range where Al—Mn—Ni intermetallic compounds are formed and crystallized. good.
- the amount of Ni added to the Mg alloy is preferably 0.1% by mass or more with respect to the crystallized Al—Mn—Ni intermetallic compound.
- Ni is less than 0.1% by mass, a potential difference that promotes decomposition between the Al—Mn—Ni-based intermetallic compound and ⁇ —Mg is less likely to occur.
- Ni increases, the crystallization temperature of the Al—Mn—Ni intermetallic compound rises, so when crystallization starts in the molten Mg, it tends to precipitate and separate easily, but Al—Mn—Ni. Any concentration may be used as long as the concentration is such that the formation and crystallization of the intermetallic compound are appropriately performed.
- the amount of Ni contained in the Mg alloy is preferably 0.01% by mass or more, more preferably 0.01% by mass or more and 0.6% by mass or less, more preferably 0.01% by mass, based on the total amount of the Mg alloy. More preferably 0.5% by mass or less. This is because even if Ni is added in an amount of 0.6% by mass or more, it is considered that many of them are settled and separated on the bottom of the furnace without being sufficiently dispersed and diffused in the Mg alloy (in the evaluation test 5 described later). See results). Further, the intermetallic compound is a compound composed of two or more kinds of metals, and some of them exhibit peculiar physical and chemical properties different from the constituent elements.
- 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, and more preferably 0.1% by mass or more and 1.5% by mass or less with respect to the total amount of the Mg alloy. ..
- Zn is added to the Mg alloy, the solid solution strengthening can improve the yield strength and elongation by 0.2% and promote aging precipitation.
- Zn is added in an amount of more than 1.5% by mass, the decomposition rate tends to decrease.
- Ca may be further contained in the Mg alloy.
- the Ca added to the Mg alloy is preferably 0.1% by mass or more and 2.0% by mass or less, and more preferably 0.2% by mass or more and 2.0% by mass or less.
- one or more compounds selected from the group consisting of Al 2 Ca, (Mg, Al) 2 Ca, or Mg 2 Ca are crystallized, and these compounds are crystallization. Since it contributes as a driving force for decomposition, the decomposition speed increases. Further, by crystallizing these compounds, it is possible to obtain an Mg alloy having improved flame retardant properties and heat resistance.
- the ratio of these Ca-containing compounds is generally determined by the addition ratio of Al and Ca.
- the number density of the crystallized Al—Mn—Ni-based intermetallic compound present in the Mg alloy is preferably 1 piece / cm 2 or more per unit cross-sectional area in an SEM or a metallurgical microscope. This is because it is desirable to crystallize 1 piece / cm 2 or more of the potentially noble Al—Mn—Ni-based intermetallic compound per unit cross-sectional area in order to secure the decomposition rate.
- the size of the crystallized Al—Mn—Ni intermetallic compound is preferably 1 nm or more and 25 ⁇ m or less.
- the Al—Mn—Ni-based intermetallic compound crystallizes with a particle size of 25 ⁇ m or more, it can be a starting point of fracture such as fatigue (see the result of evaluation test 5 described later).
- the size of the potentially noble Al—Mn—Ni intermetallic compound as described above the degree of decomposition promotion can be adjusted depending on the purpose of use.
- the number of crystallized Al—Mn—Ni intermetallic compounds present in the Mg alloy in the extruded material after the extrusion step shown in FIG. 1 is larger at the grain boundaries than at the grain boundaries. It is preferable that there are many. That is, among all Al—Mn—Ni-based intermetallic compounds, it is preferable that more than 50% and 100% or less of the intermetallic compounds are present at the grain boundaries. Since the Al-Mn-Ni intermetallic compound existing in the crystal grain boundary is stable in the high temperature region, the fine crystal grains of the Mg alloy formed by the strain generated by the extrusion processing (plastic processing) are coarsened.
- the crystal structure of the Mg alloy of the extruded material can be made finely uniform, and the decomposition can also be made uniform.
- the proportion of the number present in the crystal grains may be larger than that of the extruded material. Specifically, among all Al—Mn—Ni-based intermetallic compounds, 30% or more and 100% or less of the intermetallic compounds may be present in the crystal grains.
- the Al—Mn—Ni intermetallic compound may form a cluster.
- the Al—Mn—Ni intermetallic compound is formed in a cluster shape on the decomposition surface which is the contact surface with the solution, the area of the potentially noble portion becomes large, and the decomposition rate can be locally increased. ..
- the Mg alloy in addition to essential Mg, Al, Mn, Ni, arbitrary Zn, and Ca, other elements may be contained, and the other elements may be only unavoidable impurities.
- examples of the unavoidable impurities include, but are not limited to, Si, Fe, Cu, and the like.
- the balance of essential Al, Mn, Ni, arbitrary Zn, and Ca may be Mg and unavoidable impurities.
- Al promotes solid solution strengthening and precipitation strengthening, and improves castability and corrosion resistance.
- Mn suppresses the coarsening of recrystallized grains in plastic working.
- Zn improves castability and strength.
- Ca improves creep strength and heat resistance, and imparts flame retardancy.
- the method for producing an Mg alloy of the present invention includes a casting step, a homogenization treatment step, an extrusion step or a forging step.
- FIG. 1 shows a simplified flow of a method for manufacturing an Mg alloy. Billets are produced in the casting process, and the billets are homogenized in the homogenization process. For the homogenized billet, an extruded material is produced in an extrusion process, or a forged material is produced in a forging process. The extruded material and the forged material are also called plastic working materials.
- the casting step includes a step of preparing a mixture, a step of heating to prepare a molten metal, a step of stirring to prepare a complete melt, and a step of casting the complete melt.
- the step of blending Mg, Al, Mn and Ni to prepare a mixture is a step of preparing a base metal or a metal ingot according to the alloy composition and mixing them to prepare a mixture.
- any Zn and Ca can be blended.
- the step is to heat the mixture to 720 ° C. or higher, preferably 730 ° C., 740 ° C., more preferably 750 ° C. or higher. If the temperature is higher than 750 ° C., the molten metal may become active and many pore defects may easily occur.
- the step of stirring the prepared molten metal to prepare a complete melt is a step of stirring the heated mixture and further melting it almost completely evenly to prepare a complete melt.
- the complete solution refers to a liquid state in which the blended bullion, metal lumps, and crystallized compounds are evenly mixed without precipitating or separating from the Mg alloy.
- mechanical stirring, manual stirring, ultrasonic molten metal stirring, electromagnetic stirring and the like are exemplified.
- the stirring time depends on the amount and temperature of the heated molten metal, the stirring method, the size and power of the stirring device, and the like, and is exemplified by 10 minutes or more and 60 minutes or less.
- the quality of extruded materials and forged materials (plastically processed materials) can be maintained.
- the prepared complete melt is poured into a mold having a diameter of 70 (inner diameter of 70 mm) as an example, and a billet is prepared.
- Casting in the casting process means raising the temperature of the metal to above the melting point, pouring it into a mold, and cooling it to harden it.
- the casting method of the casting process of the present invention is not limited as long as it performs such casting, and is a sand casting method (raw (sand) casting method, dry casting method, self-hardening mold casting method, thermosetting mold casting). Method, gas hardening type casting method, vanishing model casting method, V process casting method, freeze mold manufacturing method, etc.) Gypsum casting method, precision casting method, mold casting method (gravity casting method, die casting method, low pressure casting method, high pressure) Casting method), continuous casting method and the like are exemplified.
- the homogenization treatment step is a step of dissolving an intermetallic compound or the like crystallized in a casting step in ⁇ -Mg, suppressing segregation of components, and forming an ingot with little fluctuation in component concentration.
- a low melting point Mg—Al—Zn intermetallic compound crystallized in the casting step is solidified in ⁇ —Mg and homogenized. If the compound is subjected to the extrusion step in a state where the compound having a low melting point remains, cracking is likely to occur, and if the Mg—Al—Zn-based intermetallic compound remains, there is a risk of ignition.
- the homogenization treatment step is a step that not only forms an alloy with less fluctuation in the component concentration, but also maintains mechanical strength so that cracks and the like are less likely to occur, and is also carried out from the viewpoint of safety such as ignition.
- a billet of ⁇ 70 is cut to ⁇ 60 (outer diameter 60 mm) and homogenized at 400 ° C. to 420 ° C., preferably about 410 ° C. to prepare a homogenized billet.
- Extrusion in the extrusion process is to put a material (homogenized billet, etc.) in a pressure-resistant container and apply pressure to the material to extrude it from a die that has been drilled into a predetermined cross-sectional shape. It is a method of molding into the cross-sectional shape of.
- the homogenized billet is extruded in an atmosphere of 300 ° C. to 410 ° C., preferably about 400 ° C. so as to have a diameter of 10 (outer diameter 10 mm), and the extruded material (plastic working) is extruded. Material) is formed.
- the extruded material is further processed into parts and members using Mg alloy.
- Forging in the forging process is a method in which a material is put between a pair of upper and lower dies and crushed by a press to process it into a desired shape.
- a homogenized billet is pressed with an upper die and a lower die in an atmosphere of 300 ° C. to 410 ° C., preferably about 400 ° C. to form a forged material (plastic work material).
- forging is performed so as to form a round cast having an appropriate size such as ⁇ 10 (outer diameter 10 mm) and a length of 200 mm to 300 mm to form a forged material (plastically processed material).
- the forged material is further cut into parts and members using Mg alloy.
- Mg alloys are applied to members such as structures, vibration damping members, sacrificial electrode materials, excavation members, underground structures, civil engineering materials such as underwater structures, biomaterials, medical materials and the like.
- civil engineering materials used in the ground or underwater and biomaterials used in the body may not need to be recovered after use due to the degradability of Mg alloys.
- -Evaluation test 1 (Preparation of evaluation sample and measurement of decomposition rate)- Metals are added (blended) so as to have the contents shown in Tables 1A, 1B, and 1C, an extruded material is formed by the above-mentioned casting step, homogenization treatment step, and extrusion step, and samples 1 to 1 for evaluation are formed. It was used as sample 51.
- the mass% of the metal in Table 1A, Table 1B, and Table 1C is the ratio of the metal contained in the sample for evaluation.
- the alloy type is a name defined by ASTM, or a name based on the rules of ASTM's name.
- A is aluminum
- Z is zinc
- M is manganese
- N is nickel
- X is calcium, and the numbers after that are rounded to the nearest digit and arranged in order.
- the decomposition rates of Samples 1 to 51 were measured. To measure the decomposition rate, immerse the sample piece whose weight (mg) has been measured in a 2% -KCl aqueous solution at 93 ° C. for a certain period of time, take it out, dry it, and measure the weight (mg) to confirm the weight change. Was done by.
- the decomposition rate (mg / cm 2 / day) is the value obtained by converting the reduced mass per day surface area (1 cm 2 ).
- FIG. 3A shows the field of view of the extruded material having a heating temperature (melting temperature) of 750 ° C. and no stirring, and Table 3 shows the results of point analysis.
- FIG. 3B shows a field of view of the extruded material having a heating temperature (melting temperature) of 750 ° C. and stirring, and Table 4 shows the results of point analysis.
- FIG. 4A shows an example of the elapsed time and temperature of the casting process and the implementation process
- FIG. 4B shows a metal micrograph of the billet cast in FIG. 4A
- FIG. 4 (c) shows an enlarged metal micrograph of FIG. 4 (b).
- the step of heating and stirring in FIG. 4A is a step of uniformly or almost completely dissolving Ni in the Mg alloy to prepare a completely dissolved product. It is also possible to carry out the molten metal treatment step before and after the step of performing this stirring.
- the molten metal treatment step is a step for maintaining the ingot quality that tends to deteriorate by heating and stirring.
- metallurgical microscopic images as shown in FIGS. 4B and 4C are obtained, and Al is analyzed by EDS. -Formation and crystallization of Mn-Ni intermetallic compounds were confirmed. Therefore, from the results of the evaluation test 4, as in the evaluation test 3, the Al—Mn—Ni-based intermetallic compound is formed by more reliably and completely dissolving and dispersing Ni by heating and stirring. It turned out to crystallize.
- FIG. 5A shows the SEM-EDS analysis result of the billet.
- FIG. 5B shows the SEM-EDS analysis results of the billet.
- the dendrite-like intermetallic compound is formed because the crystallization temperature is higher than that of ⁇ -Mg, and it is considered that the dendrite-like intermetallic compound is formed as a primary crystal compound.
- the Al—Mn—Ni-based intermetallic compound cannot be sufficiently dispersed in the Mg alloy, and the coarse Al—Mn—Ni having a particle size of 25 ⁇ m or more cannot be sufficiently dispersed. It was found that the intermetallic compound crystallized. When the Al—Mn—Ni-based intermetallic compound crystallizes with a particle size of 25 ⁇ m or more, it can be a starting point of fracture such as fatigue.
- FIG. 6 (a) shows the field of view 1
- FIG. 6 (b) shows the field of view 2
- FIG. 6 (c) shows the metal micrograph of the field of view 3.
- Table 5 shows the results of counting the number of Al—Mn—Ni-based intermetallic compounds existing in the crystal grains and the number existing in the crystal grain boundaries.
- FIG. 7 (a) shows a metal micrograph of the field of view 1
- FIG. 7 (b) shows a metal micrograph of the field of view 2.
- the results of counting the number of Al—Mn—Ni-based intermetallic compounds existing in the crystal grains and the number existing in the crystal grain boundaries are also shown along with FIGS. 7 (a) and 7 (b).
- the ratio of the crystallization position of the Al—Mn—Ni intermetallic compound changes before and after the extrusion step as follows.
- strain is formed in the Mg alloy and fine crystal grains are formed.
- the crystal grains become coarse in order to recover the strain, but if there is a compound such as an Al—Mn—Ni intermetallic compound that is stable in a high temperature region, the pinning effect of suppressing the coarsening (growth) of the crystal is obtained. work. Since this pinning occurs at the grain boundaries of the crystal grains, the Al—Mn—Ni-based intermetallic compound becomes present at the grain boundaries.
- the Al—Mn—Ni-based intermetallic compound existing in the grain boundaries of the finely uniform crystal can be finely dispersed in the Mg alloy to accelerate the decomposition of the Mg alloy and reduce the decomposition rate as a whole. It can be seen that it is easy to control evenly.
- the decomposition rate increases as the Ni content increases. Further, when Ca is added, the decomposition rate is increased as compared with the case where Ca is not added, and when Ni is 0.2% by mass, it is about 2.0 times, and when Ni is 0.4% by mass, it is about 2.2 times. When Ni was 0.6% by mass, it was about 2.4 times. Therefore, from the viewpoint of the decomposition rate of the Mg alloy, it was found that the decomposition rate can be increased by adding Ca.
- the decomposition rate of the Mg alloy to which Ca was added was about 3000 mg / cm 2 / day, and the decomposition rate of the Mg alloy to which Ca was not added (see FIG. 8) was about 1500 mg / cm 2 / day. It was about twice as much as. Therefore, from the results of this evaluation test, it was found that the decomposition rate can be increased by adding Ca from the viewpoint of the decomposition rate.
- FIG. 11A shows the extrusion direction and the observation direction of the sample
- FIG. 11B shows a metallurgical photograph of the extruded material before the immersion test
- FIG. 11C shows the metallurgical microscope after the immersion test of the extruded material. Shown in the photo.
- the white part in FIG. 11B is ⁇ -Mg, and the concentrations of Al and Ca constituting the alloy were relatively low. Further, the black band portion in FIG. 11B was a ⁇ phase or an Al 2 Ca compound, and the concentration of Al or Ca was high. Further, what appears to be granular in FIG. 11 (b) is an Al—Mn—Ni-based intermetallic compound. The order of these potentials is Al—Mn—Ni-based intermetallic compound> Al 2 Ca> ⁇ phase> ⁇ -Mg, and ⁇ -Mg is the most base part. On the other hand, as shown in FIG. 11 (c), it was found that the white portion, that is, ⁇ -Mg was decomposed.
- ⁇ -Mg which is a potentially low part
- the decomposition reaction is not a locally galvanic reaction centered on the Al—Mn—Ni intermetallic compound, but a macroscopic galvanic reaction occurs in the plane, which is the most potentially lowly. It was considered that the decomposition mechanism is such that the decomposition proceeds preferentially from the partial ⁇ -Mg.
- the Mg alloy can secure the desired mechanical properties for a certain period of time, but after that period, the overall decomposition rate can be controlled so as to dissolve or decompose.
- the Mg alloy of the present invention is expected to be applied to the Mg alloy that promotes decomposition in various environments from the viewpoint of crystallization of Al—Mn—Ni-based intermetallic compounds.
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Abstract
Description
一方で、市販のマグネシウムには不純物が存在し、かかる不純物の存在が、Fe、Cu、Niを含むマイクロガルバニ元素の形成に起因して分解速度を高めると考えられている(特許文献1段落0004等)。つまり、Niは分解速度を高める性質を有するものであり、マグネシウム合金中での存在状態によっては分解速度を調整することが可能と考えられる。しかしながら、Niは、Mgあるいはマグネシウム合金の融点や密度より高いこと(Mgの融点は650℃、Mgの密度は1.738g/cm3、Niの融点は1455℃、Ni密度は8.908g/cm3)から、マグネシウム合金が溶融する温度領域でマグネシウム合金にNiを添加して溶解させたり、合金中に完全に分散させることは難しいという課題があった。
また、上記のようにマグネシウム合金にNiを添加して溶解させたり、合金中に完全に分散させることは難しいため、分解速度を高める性質を有するNiを単にマグネシウム合金中に添加しても、意図に沿った分解の促進が可能なMg合金になりにくいという課題もあった。
さらに、本発明のMg合金の製造方法によれば、マグネシウム合金中に含まれる金属のAl、MnとともにNiを含むAl-Mn-Ni系金属間化合物を形成させて晶出させ、Niをマグネシウム合金中に分散させることができ、分解の促進が可能なMg合金を製造することができる。
Mg合金は、その言葉のとおりMgを主成分とする合金である。主たる成分のMg、添加されるAl、Mn、Niは、加熱、又は、加熱及び攪拌により溶解(分散)させられれば、各地金を配合してもよいし、Mg-Al-Mn合金、Mg-Al-Zn-Mn合金、Mg-Al-Mn-Ca合金、Mg-Al-Zn-Mn合金にNiを添加してもよい。
Mg合金に晶出したAl-Mn-Ni系金属間化合物が含まれることにより、Mg合金の分解速度が高まる効果や、晶出する場所によりMg合金を均質に分解できる効果、あるいは局所的に分解できる効果を有する。分解速度が高まる点においては、「易分解性」である。Al-Mn-Ni系金属間化合物について、詳細は後述する。
なお、Mg合金に含有するNiは、Mg合金全量に対しては0.01質量%以上であることが好ましく、0.01質量%以上0.6質量%以下がより好ましく、0.01質量%以上0.5質量%以下がさらに好ましい。Niを0.6質量%以上添加しても、Mg合金内に十分に分散・拡散することなく炉底に沈降分離されものが多くなってくると考えられるからである(後述する評価試験5の結果参照)。
また、金属間化合物とは、2種類以上の金属によって構成される化合物であり、構成する元素とは異なる特有の物理的、化学的性質を示すものもある。
一方、Ca添加量が2.0質量%を超えると、0.2%耐力や伸びといった引張特性が低下する場合がある。
また、晶出したAl-Mn-Ni系金属間化合物のサイズは、1nm以上25μm以下の大きさを有することが好ましい。Al-Mn-Ni系金属間化合物が粒径25μm以上の粒径で晶出すると、疲労をはじめとした破壊の起点になり得るからである(後述する評価試験5の結果参照)。上述したように電位的に貴となるAl-Mn-Ni系金属間化合物のサイズを調整すれば、用途目的により分解促進の程度を調整することができる。
なお、押出工程(塑性加工)前の均質化処理済みビレットにおいては、上記押出材に比べ、結晶粒内で存在する数の割合が多くてもよい。具体的には、全Al-Mn-Ni系金属間化合物のうち、30%以上100%以下の金属間化合物が結晶粒内に存在してもよい。
なお、各元素の効果は概ね以下のとおりである。Alは固溶強化や析出強化を促進し、鋳造性と耐食性を改善する。Mnは塑性加工における再結晶粒の粗大化を抑制する。Znは鋳造性と強度を改善する。Caはクリープ強度、耐熱強度を改善し、難燃性を付与する。
本発明のMg合金の製造方法には、鋳造工程、均質化処理工程、押出工程又は鍛造工程が含まれる。
図1に、Mg合金の製造方法の簡略フローを示す。鋳造工程でビレットが作製され、該ビレットは均質化処理工程で均質化処理済みビレットが作製される。該均質化処理済みビレットは、押出工程で押出材が作製される、又は、鍛造工程で鍛造材が作製される。なお、押出材と鍛造材は塑性加工材とも呼ばれる。
鋳造工程は、混合物を作製する工程、加熱して溶湯を作製する工程、攪拌して完全溶解物を作製する工程、完全溶解物を鋳造する工程を含む。
必須のMg、Al、Mn、Niの他、任意のZn、Caを配合することもできる。
撹拌時間は、加熱された溶湯の量や温度と、攪拌方法や撹拌装置の大きさやパワー等にもよるが、10分以上60分以下が例示される。Mg合金に対し、高温での撹拌を長時間行うと、溶湯表面の被膜や酸化物を大量に巻き込み、鋳塊品質を維持することができない場合がある。このような場合、撹拌時間を調整するか、撹拌後に溶湯処理を実施し、上記溶湯表面の被膜や酸化物が少なくともビレット中に含まれないよう調整することで、ビレット、均質化処理済みビレット、押出材や鍛造材(塑性加工材)の品質を維持することができる。
均質化処理工程は、鋳造工程で晶出する金属間化合物等をα-Mg中に固溶させ、成分の偏析を抑制し、成分濃度の揺らぎの少ない鋳塊を形成する工程である。たとえば、Mg-Al-Zn-Ni系合金においては、鋳造工程で晶出する低融点のMg-Al-Zn系金属間化合物をα-Mg中に固溶させ、均質化処理を行う。なお、低融点の化合物が残っている状態で押出工程に供すると、割れが生じやすく、また、Mg-Al-Zn系金属間化合物が残っていると発火の危険がある。よって、均質化処理工程は、成分濃度の揺らぎの少ない合金を形成するのみならず、割れ等が生じにくいように機械的な強度を維持したり、発火等の安全面からも実施される工程の1つである。
一例としてφ70のビレットをφ60(外径60mm)まで切削加工を行い、400℃~420℃、好ましくは約410℃で均質化処理を行い、均質化処理済みビレットを作製する。
押出工程における押出とは、耐圧性のコンテナ内に素材(均質化処理済みビレット等)を入れ、素材に圧力を加えることで、所定の断面形状に穴あけ加工した金型(ダイス)から押出し、所望の断面形状に成形する方法である。
本発明の押出工程では、一例として均質化処理済みビレットを300℃~410℃、好ましくは約400℃の雰囲気中でφ10(外径10mm)となるように押出加工を行い、押出材(塑性加工材)を形成する。押出材はMg合金を用いた部品や部材にさらに加工される。
鍛造工程における鍛造とは、上下一組の金型の間に材料を入れ、プレスで押しつぶして所望の形状に加工する方法である。
本発明の鍛造工程では、一例として均質化処理済みビレットを300℃~410℃、好ましくは約400℃の雰囲気中で上型と下型でプレスして鍛造材(塑性加工材)を形成する。あるいは、φ10(外径10mm)、200mm~300mmの長さ等、適宜のサイズの丸鋳となるように鍛造を行い、鍛造材(塑性加工材)を形成する。鍛造材はMg合金を用いた部品や部材にさらに切削加工される。
Mg合金は、構造物等の部材、制振部材、犠牲電極材、掘削部材、地中構造物、水中構造物等の土木材料、生体材料、医療材料等に応用される。特に、地中や水中で使用される土木材料や、体内で使用される生体材料は、Mg合金の分解性により使用後の回収が不要となり得る。
表1A、表1B、表1Cに記載の含有量となるように金属を添加(配合)し、上述した鋳造工程、均質化処理工程、押出工程で押出材を形成し、評価用の試料1~試料51とした。表1A、表1B、表1Cの金属の質量%は、評価用の試料に含有する金属の割合である。合金種はASTMで定められた呼称、又は、ASTMの呼称のルールを参考にした名前を記載したものである。たとえば、Aはアルミニウム、Zは亜鉛、Mはマンガン、Nはニッケル、Xはカルシウムであり、その後ろの数字は、質量%を1桁に四捨五入して順に並べたものである。
さらに、試料1~試料51について分解速度を測定した。分解速度の測定は、重量(mg)を測定した試料片を93℃の2%-KCl水溶液に一定時間浸漬し、取り出した後に乾燥させて重量(mg)を測定し、重量変化を確認することにより行った。減少した質量を1日あたり表面積(1cm2)あたりに換算したのが分解速度(mg/cm2/day)である。
本発明は、添加されたNiがMg合金中でAl-Mn-Ni系金属間化合物を形成し晶出することが重要である。しかしながら、添加したNiがMg合金中でAl-Mn-Ni系金属間化合物を十分に形成することができない場合や、Niの高い融点や高い密度に起因してMg合金に分散できずに沈殿し取り除かれた場合、添加量に対してビレットや塑性加工材(押出材、鍛造材)のNi含有量が低くなる。
そこで、鋳造工程のおける加熱温度(溶湯温度)と、撹拌の有無により、Ni添加量に対するビレット中のNi含有量の割合について測定した。
結果は、図2、表2に示す。
よって、本評価試験2の条件では、加熱温度を720℃以上で撹拌を行えば、NiはMg合金に溶解(分散)されることが分かった。
表2の鋳造工程における溶湯温度が750℃であって、撹拌なしの押出材と撹拌ありの押出材について、SEM-EDS分析を行った。
SEM(走査型電子顕微鏡)は、対象試料に電子ビームを照射し、対象試料から放出される二次電子等を検出することで、対象試料の表面の構造を解析するものである。EDS(エネルギー分散型X線分析)は、対象試料に電子線やX線を照射した際に発生する蛍光X線を検出することで、対象試料を構成する元素と濃度を解析するものである。
図3(a)に加熱温度(溶湯温度)750℃、撹拌なしの押出材の視野を示し、表3に点分析結果を示した。また、図3(b)に加熱温度(溶湯温度)750℃、撹拌ありの押出材の視野を示し、表4に点分析結果を示した。
一方、図3(b)及び表4の位置001、002の分析結果より、750℃撹拌ありの押出材では、Al-Mn-Ni系金属間化合物の形成が確認された。
よって、撹拌を行うことにより、Niをより確実に溶解分散させることで、Al-Mn-Ni系金属間化合物が形成し晶出することが分かった。
鋳造工程におけるビレットの作製について、図4(a)に、鋳造工程の経過時間と温度及び実施工程の一例を示し、図4(b)に図4(a)で鋳造したビレットの金属顕微鏡写真を示し、図4(c)に図4(b)を拡大した金属顕微鏡写真を示す。
図4(a)のような加熱及び撹拌を行う工程、及び、溶湯処理工程を経たビレットは、図4(b)、図4(c)のような金属顕微鏡画像が得られ、EDS分析によりAl-Mn-Ni系金属間化合物の形成及び晶出が確認された。
よって、評価試験4の結果からも、評価試験3と同様に、加熱及び撹拌を行うことにより、Niをより確実に完全に溶解分散させることで、Al-Mn-Ni系金属間化合物が形成し晶出することが分かった。
評価試験2において、鋳造工程におけるNiの添加量に対するビレット中のNi含有量の割合は、鋳造工程における撹拌により大きくすることができることを示した。一方でNiの添加量の増加に伴い、Al-Mn-Ni系金属間化合物の晶出温度が高くなる傾向があるため、撹拌を行ってもAl-Mn-Ni系金属間化合物を十分に形成させることができない場合がある。そこで、Niの添加量の違いよるビレットの評価を行った。
このビレットには、添加したNiの量が100%(含有量/添加量=0.4/0.4=100%)含有されており、かつ、Al-Mn-Ni系金属間化合物が形成し、結晶粒界に針状や粒状の形状で存在していることが確認できた。結晶粒界に針状や粒状の形状の金属間化合物が形成されるのは、塑性加工の際にAl-Mn-Ni系金属化合物が再結晶粒の粗大化に対してピン止め効果を発揮することで再結晶粒の粗大化を抑制しているためと考えられる。
このビレットには、添加したNiの量が8%(含有量/添加量=0.4/5=8%)しか含有されておらず、このビレット中にはAl-Mn-Ni系金属間化合物がデンドライト状(樹枝状)に晶出していることが確認できた。デンドライト状の金属間化合物が形成されるのは、α-Mgより晶出温度が高いためであり、初晶化合物として形成されることが考えられる。また、本評価試験結果からも、Mg-Al-Zn-Mn系合金中にNiを0.6質量%以上添加しても、Mg合金内に十分に分散・拡散することなく炉底に沈降分離されると考えられる。
均質化処理工程後、押出工程前の均質化処理済みビレットにおける、Al-Mn-Ni系金属間化合物の晶出位置について評価した。
AZ80(Alが8質量%、Znが四捨五入して0%の含有を予定した、Mg合金)に、Niが0.4質量%の含有を予定した均質化処理済みビレットを作製し、金属顕微鏡観察を行った。
押出工程後の押出材における、Al-Mn-Ni系金属間化合物の晶出位置について評価した。
AZ80(Alが8質量%、Znが四捨五入して0%の含有を予定した、Mg合金)に、Niが0.4質量%の含有を予定した均質化処理済みビレットを作製し、金属顕微鏡観察を行った。
押出工程(塑性加工)を施すと、Mg合金内に歪ができ、微細な結晶粒が形成される。歪の回復のため、該結晶粒は粗大化するが、高温領域で安定なAl-Mn-Ni系金属間化合物のような化合物があると、結晶の粗大化(成長)を抑えるピン止め効果が働く。このピン止めは結晶粒の粒界で起こるため、Al-Mn-Ni系金属間化合物は結晶粒界に存在するようになる。また、結晶の粗大化をピン止めすることにより、押出材内部の結晶は微細均一になって安定する。
よって、微細均一な結晶の粒界に存在するAl-Mn-Ni系金属間化合物は、Mg合金内に微細に分散し、Mg合金の分解を促進させることができるとともに、分解速度を全体的にむらなく制御しやすいことが分かる。
表1A、表1B、表1Cの評価用試料の中から、押出材のNi濃度と分解速度の関係を、Ca添加の有無で分けて評価した。
図8に、評価結果を示す。
よって、Mg合金の分解速度の観点からは、Caを添加すると分解速度を増大させることができることが分かった。
Alを添加されたMg合金(AZ系合金、表1Bの試料28)において、Caを添加すると、Al>Caの場合主にAl2Caが形成され、Al≒Caの場合主に(Mg、Al)2Caが形成され、Al<Caの場合主にMg2Caが形成される。
図9(a)、図9(b)、表6、表7に、Alが添加されたMg合金において、Caを添加した場合(表1Cの試料43)のSEM-EDS分析結果の例を示す。図9(a)及び表6は視野1、図9(b)及び表7は視野2を示す。
よって、本評価試験結果からも、分解速度の観点からは、Caを添加すると分解速度を増大させることができることが分かった。
評価試験8や9に示したように、Caを添加すると、分解速度を増大させることができることが分かった。ここで、他の特性についても評価を行った。
測定結果を表9及び図10に示す。
よって、Ca含有量を増やすと、評価試験8等からMg合金の分解速度は増大する。しかしながら、少なくとも0.2耐力、伸びの観点においては特性が低下する場合があることも考慮して、目的用途により添加量を調整する必要があることが分かった。
AZ80+0.1Ni合金(表1Cの試料44)の押出材を樹脂に埋め込み、組織観察を行った。次に、93℃の2%KCl溶液に浸漬し、8分後同一位置で組織観察を行った。
図11(a)にサンプルの押出方向と観察方向を示し、図11(b)に押出材の浸漬試験前の金属顕微鏡写真を示し、図11(c)に押出材の浸漬試験後の金属顕微鏡写真を示す。
一方、図11(c)に示すように、白い部分すなわちα-Mgが分解していることが分かった。つまり、電位的に貴な部分であるAl-Mn-Ni系金属間化合物の周辺ではなく、電位的に卑な部分であるα-Mgが分解をしていたことになる。
以上の結果から、分解反応はAl-Mn-Ni系金属間化合物を中心として局所的にガルバニック反応が起こっているのではなく、面内でマクロ的にガルバニック反応が起こり、電位的に最も卑な部分であるα-Mgから優先的に分解が進む、という分解メカニズムであることが考察された。
AZ系合金にNiを添加した際に、介在物を異種核とする等を原因としてAl-Mn-Ni系金属間化合物がクラスター状に晶出される。
図12(a)及び図12(b)にクラスター形成の金属顕微鏡写真を示す。
Claims (14)
- Mg、Al、Mn、Niを含有し、晶出したAl-Mn-Ni系金属間化合物を有する、Mg合金。
- Znをさらに含有する、請求項1に記載のMg合金。
- Caをさらに含有する、請求項1又は2に記載のMg合金。
- Al2Ca、(Mg、Al)2Ca、又は、Mg2Caからなる群から選択される1以上の化合物を含む、請求項3に記載のMg合金。
- Mg合金全量に対し、前記Alは0.1質量%以上であり、前記Mnは0.05質量%以上である、請求項1~4いずれか一項に記載のMg合金。
- Mg合金全量に対し、前記Znは0.05質量%以上1.5質量%以下である、請求項2に記載のMg合金。
- Mg合金全量に対し、前記Caは0.1質量%以上2.0質量%以下である、請求項3に記載のMg合金。
- 前記Al-Mn-Ni系金属間化合物に対し、Niが0.1質量%以上である、請求項1~6いずれか一項に記載のMg合金。
- 前記Al-Mn-Ni系金属間化合物は、単位断面積あたり1個/cm2以上である、及び、1nm以上25μm以下の大きさを有する、請求項1~8いずれか一項に記載のMg合金。
- 前記Al-Mn-Ni系金属間化合物は、クラスターを形成している、請求項1~9いずれか一項に記載のMg合金。
- Mg合金の製造方法であって、
該Mg合金の製造方法は鋳造工程を含み、
前記鋳造工程は、
Mg、Al、Mn及びNiを配合して混合物を作製する工程と、
前記作製された混合物を720℃以上に加熱し溶湯を作製する工程と、
前記作製された溶湯を攪拌して完全溶解物を作製する工程と、
前記攪拌して作製された完全溶解物を鋳造する工程と、
を含む、晶出したAl-Mn-Ni系金属間化合物を有するMg合金の製造方法。 - 前記混合物を作製する工程において、さらにZn及び/又はCaを配合する、請求項11に記載のMg合金の製造方法。
- 請求項1~10いずれか一項に記載のMg合金を用いた土木材料又は生体材料であって、前記Mg合金の分解性により使用後の回収が不要である、土木材料及び生体材料。
- 請求項11又は12に記載のMg合金の製造方法で製造された土木材料又は生体材料であって、前記Mg合金の分解性により使用後の回収が不要である、土木材料及び生体材料。
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