JP2021195605A - Al-Mn BASED ALUMINUM ALLOY CASTING AND METHOD FOR MANUFACTURING THE SAME - Google Patents

Abstract

To provide an Al-Mn based aluminum alloy casting having a fine and homogeneous metallographic structure, and a method for manufacturing the same, more concretely, to provide an Al-Mn based aluminum alloy casting capable of improving ductility while maintaining a strength, a Young's modulus and a sufficiently low conductivity equal to or more than those of the conventional Al-Mn based aluminum alloy casting, and a method for simply and efficiently manufacturing the same.SOLUTION: An Al-Mn based aluminum alloy casting consists of aluminium alloy including Mn of 2.0-12.0 mass%. A metallographic structure mainly consists of an Al-Mn eutectic structure and an Al6Mn based crystallized product; an average Ferre size of the Al6Mn based crystallized product is 30 μm or less; and an area ratio occupied by the crystallized product of less than 10 μm2 is 40% or less to the total area of the crystallized product.SELECTED DRAWING: None

Description

The present invention relates to an Al—Mn-based aluminum alloy casting having a fine and homogeneous metal structure and a method for producing the same.

Since Al-Mn-based aluminum alloy has both high strength and excellent corrosion resistance, it is used in a wide range of applications such as beverage cans and building materials. In addition to the relatively low cost of _{Mn, Al 6} Mn-based crystallized products are electrochemically stable with respect to the aluminum base material and do not impair corrosion resistance. Further, it is known that the Al—Mn-based aluminum alloy improves mechanical properties such as Young's modulus by increasing the amount of Mn added.

However, in a hypereutectic structure in which the amount of Mn added is eutectic composition (Mn: 1.95% by mass) or more, the ductility tends to decrease, and this tendency becomes remarkable as the amount of Mn increases. More specifically, in the hypereutectic composition, the Al—Mn-based compound crystallizes as primary crystals during casting, and the crystallized material becomes coarse, which serves as a starting point of fracture when stress is applied to the cast material. Become.

On the other hand, for example, in Patent Document 1 (Japanese Unexamined Patent Publication No. 2018-70899), Mn is contained in an amount of 3.0 to 12% by weight, and the main metal structure is an Al—Mn eutectic structure, which is an Al—Mn system. A hypercolonic Al—Mn-based aluminum alloy casting material, characterized in that the maximum major axis of the crystal grains of the compound is less than 100 μm, is disclosed.

In the hypereutectic Al-Mn-based aluminum alloy cast material described in Patent Document 1, solidification occurs in the super-cooled state when cast at a cooling rate of 500 ° C./s or higher, and even in the hypereutectic Al-Mn-based aluminum alloy. Since a fine eutectic structure is formed with almost no crystallization of the primary Al-Mn-based compound, crystallization and coarsening of the primary-crystal Al-Mn-based compound are suppressed without adding a transition metal element. It is said that it can be done.

Japanese Unexamined Patent Publication No. 2018-70899

In the hypereutectic Al-Mn-based aluminum alloy casting material described in Patent Document 1, the coarsening of the Al-Mn-based compound, which lowers ductility and toughness, is effectively suppressed by increasing the cooling rate during casting. is doing. On the other hand, the homogeneity of the metal structure has a large effect on the mechanical properties of the aluminum alloy material, and the structure is not controlled from this point of view.

That is, at present, it cannot be said that the metal structure is sufficiently optimized so that various properties including the strength and ductility of the Al—Mn-based aluminum alloy casting are exhibited to the maximum, and in addition to the miniaturization of the structure. If homogenization can be achieved, for example, further improvement in mechanical properties of Al—Mn-based aluminum alloy castings can be expected.

In view of the above problems in the prior art, an object of the present invention is to provide an Al—Mn-based aluminum alloy casting having a fine and homogeneous metal structure and a method for producing the same. More specifically, Al-Mn-based aluminum alloy castings with improved ductility while maintaining strength equal to or higher than that of conventional Al-Mn-based aluminum alloy castings, Young's ratio, and sufficiently low conductivity, and their convenience and efficiency. The purpose is to provide a conventional manufacturing method.

In order to achieve the above object, the present inventors are keen on the relationship between the manufacturing conditions of the Al-Mn-based aluminum alloy casting, the metal structure of the Al-Mn-based aluminum alloy casting, and various physical properties of the Al-Mn-based aluminum alloy casting. As a result of repeated studies, it was found that it is extremely effective to simultaneously achieve microstructural fineness and microstructural homogenization of Al—Mn-based aluminum alloy castings by using molten metal overheat treatment, and reached the present invention.

That is, the present invention
Mn: made of an aluminum alloy containing 2.0 to 12.0% by mass.
The metallographic structure mainly consists of an Al-Mn eutectic structure and an Al ₆ Mn-based crystallized product.
The average ferret diameter of the Al ₆ Mn-based crystallized product is 30 μm or less.
^{The area ratio of crystallization of less than 10 μm 2} to the total area of crystallization is 40% or less.
Provided is an Al—Mn-based aluminum alloy casting, which is characterized by the above.

In the Al—Mn-based aluminum alloy casting of the present invention, _{in addition to being miniaturized so that the average ferret diameter of the Al 6} Mn-based crystallized product is 30 μm or less, the total area of the crystallized product is relative to the total area of the crystallized product. The biggest feature is that the area ratio occupied by crystallization of less than 10 μm ^{2 is 40% or less.}

In general, the inhomogeneous microstructure distribution reduces the strength and ductility of metal materials, but the relationship between the microstructure distribution of Al-Mn-based aluminum alloy castings and the tensile properties of Al-Mn-based aluminum alloy castings is detailed. As a result of the investigation ^{, it was clarified that the area ratio of the crystallization of less than 10 μm 2} is large and small with respect to the total area of the crystallization, but it is the main factor that lowers the homogeneity of the microstructure. In general, it is often said that finer compounds are better. However, as a result of diligent research by the inventor of the present application, it has become clear that even if there are too many fine crystals, it is not preferable for the mechanical properties. It is best if all the crystallization can be miniaturized, but when the casting is actually manufactured, crystallization having a size of about ^{100 μm 2 is formed to some extent.} In such a state, if there are too many crystallizations of less than ^{10 μm 2, the homogenization of the structure will be poor.} In the Al—Mn-based aluminum alloy casting of the present invention, the structure of the fine Al ₆ Mn-based crystallized material is controlled so that the area ratio occupied by the crystallized material of less than ^{10 μm 2 is 40% or less, which is excellent.} Both strength and ductility are achieved.

Further, in the Al—Mn-based aluminum alloy casting of the present invention, it is preferable that the average ferret diameter of the _{Al 6 Mn-based crystallized product present at the grain boundary of the eutectic α (Al) is 5 μm or less. When coarse Al 6} Mn-based crystals are present at the crystal grain boundaries of the eutectic α (Al), the ductility and toughness of the Al—Mn-based aluminum alloy casting are significantly reduced, but the Al ₆ Mn-based crystals are crystallized. When the average ferret diameter of the object is 5 μm or less, excellent durability and toughness can be imparted to the Al—Mn-based aluminum alloy casting.

Further, in the Al—Mn-based aluminum alloy casting of the present invention, it is preferable that the Mn content is 3.0 to 5.0% by mass. By setting the Mn content to 3.0% by mass or more, the strength and Young's modulus of the Al—Mn-based aluminum alloy casting can be sufficiently improved. On the other hand, by setting the Mn content to 5.0% by mass or less, _{only Al 6} Mn-based crystals can be crystallized as Al-Mn-based compounds in the solidification process, resulting in finer structure and homogeneity. The effect of chemical conversion can be surely expressed. When the Mn content is larger than 5.0% by mass, there is _{a region where Al 4} Mn-based crystals are crystallized in the cooling process of the molten metal.

Further, in the Al—Mn-based aluminum alloy casting of the present invention, it is preferable that the Young's modulus is 75 GPa or more and the breaking elongation is 15% or more. Since the Al—Mn-based aluminum alloy casting has these mechanical properties, the applicable range of the Al—Mn-based aluminum alloy casting can be expanded. Further, when the Al—Mn-based aluminum alloy casting is formed into various member shapes, good plastic workability and the like can be imparted.

Further, in the Al—Mn-based aluminum alloy casting of the present invention, it is preferable that the conductivity is 20% IACS or less. By setting the conductivity of the Al—Mn-based aluminum alloy casting to 20% IACS or less, it can also be suitably used for members requiring high resistivity such as motor cases and motor housings.

Further, the present invention is characterized in that a molten aluminum alloy containing Mn: 2.0 to 12.0% by mass is cast after being subjected to a molten metal superheat treatment for holding the molten metal at 1020 ° C. or higher. Also provided is a method for manufacturing aluminum alloy castings.

In the method for producing an Al-Mn-based aluminum alloy casting of the present invention, a molten aluminum alloy containing Mn: 2.0 to 12.0% by mass is cast after being subjected to a molten metal overheat treatment of holding it at 1020 ° C. or higher. This makes it possible to form a fine and homogeneous metal structure in the finally obtained Al—Mn-based aluminum alloy casting. It is considered that the cause is that the coagulation time is shortened by the molten metal superheat treatment in which the molten metal temperature is 1020 ° C. or higher, and _{the growth and its variation of Al 6 Mn-based crystals are suppressed extremely effectively.} Even if the molten metal temperature is higher than 1200 ° C., the effect is not significantly improved. When the molten metal temperature is heated to a temperature higher than 1200 ° C., not only the energy consumption increases but also the damage to the melting furnace increases. Therefore, the heating temperature of the molten metal is preferably 1200 ° C. or lower.

The Al-Mn based aluminum alloy casting obtained by the production method of Al-Mn series aluminum alloy casting of the present invention consists mainly Al-Mn eutectic structure and _Al 6 Mn system crystallized substance, the _Al 6 Mn KeiAkira The metal structure is characterized in that the average ferret diameter of the product is 30 μm or less, and the area ratio of the crystal having a size of less than ^{10 μm 2 is 40% or less with respect to the total area of the crystal.} Is formed.

Further, in the method for producing an Al—Mn-based aluminum alloy casting of the present invention, it is preferable that the holding time at 1020 ° C. or higher is 5 to 60 minutes. By setting the time of the molten metal superheat treatment for keeping the molten aluminum alloy at a high temperature of 1020 ° C. or higher to 5 minutes or longer, the Al ₆ Mn-based crystallized material can be sufficiently melted and can be reliably refined. On the other hand, if the holding time is 60 minutes or less, the _{effect of miniaturizing Al 6} Mn-based crystals is not lost, and the increase in energy consumption and deterioration of equipment such as a melting furnace are suppressed. can do.

According to the present invention, it is possible to provide an Al—Mn-based aluminum alloy casting having a fine and homogeneous metal structure and a method for producing the same. More specifically, Al-Mn-based aluminum alloy castings with improved ductility while maintaining strength equal to or higher than that of conventional Al-Mn-based aluminum alloy castings, Young's ratio, and sufficiently low conductivity, and their convenience and efficiency. Manufacturing method can be provided.

Further, in the Al—Mn-based aluminum alloy casting obtained by melting and recasting the Al—Mn-based aluminum alloy casting of the present invention, the same effect can be obtained without performing the molten metal overheat treatment again.

It is an optical micrograph of the Al-Mn-based aluminum alloy casting obtained in the Example. It is an optical micrograph of the Al-Mn-based aluminum alloy casting obtained in the comparative example. FIG. 2 is _{an enlarged photograph of a fine Al 6} Mn-based crystallized material accumulation region in FIG. 2. It is a graph which shows the area ratio which the crystallization having each area range occupies with respect to the total area of crystallization. It is a graph which shows the relationship between the eutectic solidification supercooling temperature and the molten metal superheating temperature.

Hereinafter, the Al—Mn-based aluminum alloy casting of the present invention and a method for producing the same will be described in detail, but the present invention is not limited to these.

1. 1. Al-Mn-based aluminum alloy casting (1) Composition The Al-Mn-based aluminum alloy casting of the present invention contains Mn: 2.0 to 12.0% by mass. Hereinafter, the components of the Al—Mn-based aluminum alloy casting of the present invention will be described in detail.

(1-1) Additive element Mn: 2.0 to 12.0% by mass
By adding Mn to the Al—Mn-based aluminum alloy, it contributes to the improvement of mechanical properties and the increase of electrical resistance. Further, even if the Mn content is increased, the corrosion resistance and the anodic oxide film property of the Al—Mn-based aluminum alloy are not lowered. When the Mn content is close to the eutectic composition (near 1.95% by mass in the Al-Mn binary system), the primary crystal Al-Mn system compound is crystallized. Eventually, Al ₆ Mn-based crystals are formed, and usually, the Al ₆ Mn-based crystals become coarser as the amount of Mn added increases. However, the Al—Mn-based aluminum alloy casting of the present invention is used. _{In, the average ferret diameter of the Al 6} Mn-based crystallized product is 30 μm or less even when 12.0% by mass of Mn is contained, and the crystal size is less than ^{10 μm 2 with respect to the total area of the crystallized product.} The area ratio of the products is 40% or less.

Since the Al—Mn-based aluminum alloy casting of the present invention targets a hypereutectic composition, the Mn content is 2.0% by mass or more. Further, even if the Mn content exceeds 12.0% by mass, the mechanical properties of the Al—Mn-based aluminum alloy casting are not improved, so that the Mn content is 12.0% by mass or less.

The Mn content is preferably 3.0 to 5.0% by mass. By setting the Mn content to 3.0% by mass or more, the strength and Young's modulus of the Al—Mn-based aluminum alloy casting can be sufficiently improved, and the electric resistance value can be increased. On the other hand, by setting the Mn content to 5.0% by mass or less, _{only Al 6} Mn-based crystals can be crystallized as Al-Mn-based compounds in the solidification process, resulting in finer structure and homogeneity. The effect of chemical conversion can be surely expressed.

(1-2) Arbitrary additive element Fe: More than 0% by mass and 0.1% by mass or less When an Al-Mn-based aluminum alloy casting is obtained by die casting such as a die casting method, it has an effect of preventing seizure on the die. , Fe is preferably contained. In the Al—Mn-based aluminum alloy, the larger the Fe content, the easier it is to form coarse Al—Fe—Mn-based crystals, and the lower the elongation. Therefore, from the viewpoint of suppressing the decrease in ductility, the content of Fe in the Al—Mn-based aluminum alloy is preferably 0.1% by mass or less.

(1-3) Inevitable Impurities In the Al—Mn-based aluminum alloy casting of the present invention, elements such as Cr, V, Ni, Co, Zr, Ti, Si, and B may be contained as unavoidable impurities. The content of unavoidable impurities is preferably 0.05% by weight or less.

(2) Metal structure In the Al—Mn-based aluminum alloy casting of the present invention, the metal structure mainly consists of an Al—Mn eutectic structure and an Al ₆ Mn system crystallized product, and the average ferret diameter of the _{Al 6 Mn system crystallized product.} Is 30 μm or less, and the area ratio of the crystallization of less than ^{10 μm 2 is 40% or less with respect to the total area of the crystallization.} Hereinafter, the characteristics of the metallographic structure will be described in detail.

The ^{method for measuring the area ratio occupied by the crystallization of less than 10 μm 2 with} respect to the average ferret diameter of the _{Al 6} Mn-based crystallization and the total area of the crystallization is particularly limited as long as the effect of the present invention is not impaired. However, various conventionally known measuring methods can be used. For example, it can be easily obtained by performing image processing or the like on a micrograph or an SEM observation image of an Al—Mn-based aluminum alloy casting. Since the _{contrast between the Al 6} Mn-based crystallized region and the other regions is clearly different in the micrograph and the SEM observation image, it may be binarized and then various image measurement processes are performed. Further, the measurement area can be, for example, within a constant field of view of an optical microscope at a magnification of about 200 times or within a constant field of view of SEM observation.

The average ferret diameter of the Al ₆ Mn-based crystallized product is 30 μm or less, but _{the maximum ferret diameter of the Al 6} Mn-based crystallized product is preferably 100 μm or less, preferably 50 μm or less. More preferred. In addition to the average Feret's diameter of Al 6 _Mn-based crystallized matter is small, by refining the Al 6 _Mn-based crystallized matter having a maximum Feret's diameter, more effectively Al-Mn series aluminum alloys The ductility and toughness of the casting can be improved.

In a conventional general Al-Mn-based aluminum alloy casting that has not been subjected to molten metal overheat treatment, a "layer of network structure" → from the surface in contact with the casting wall toward the center of the Al-Mn-based aluminum alloy casting. The microstructure changes from " _{a layer in which a large amount of fine Al 6} Mn-based crystals are present" to "a layer in which Al ₆ Mn-based crystals are present". In contrast, in the Al-Mn series aluminum alloy casting of the present invention, a "layer of reticulated tissue" → "layer Al 6 _Mn-based crystallized matter exists" and "fine Al 6 _Mn KeiAkirade There is no clear "layer with many things". Here, corresponding to the "fine Al 6 _Mn system crystallizate abundant layer" generally "less than 10 [mu] m ² of fine Al 6 _Mn system crystallized substances are present area", to the total area of the precipitated crystalline The area ratio of the fine Al ₆ Mn-based crystallized product is 40% or less. Further, _{the preferable area ratio of the fine Al 6} Mn-based crystallized product having a size of less than ^{10 μm 2 is 30% or less.}

Further, in the Al—Mn-based aluminum alloy casting of the present invention, it is preferable that the average ferret diameter of _{the Al 6 Mn-based crystals present at the grain boundaries of the eutectic α (Al) is 5 μm or less. When coarse Al 6} Mn-based crystals are present at the crystal grain boundaries of the eutectic α (Al), the ductility and toughness of the Al—Mn-based aluminum alloy casting are significantly reduced, but the Al ₆ Mn-based crystals are formed. When the average ferret diameter of the object is 5 μm or less, excellent durability and toughness can be imparted to the Al—Mn-based aluminum alloy casting.

(3) Various Physical Properties The Al—Mn-based aluminum alloy casting of the present invention has various excellent mechanical and electrical properties due to the addition of Mn, miniaturization and homogenization of the metal structure. ..

The Al—Mn-based aluminum alloy casting of the present invention preferably has a Young's modulus of 75 GPa or more and a breaking elongation of 15% or more. In addition to having a high Young's modulus due to the addition of Mn, the Al—Mn-based aluminum alloy casting of the present invention is controlled by controlling the size and dispersion state of the _{Al 6 Mn-based crystallized product formed by the addition of Mn.} Has excellent breaking elongation. Further, it is preferable that the Al—Mn-based aluminum alloy casting has a tensile strength of 120 MPa or more and a 0.2% proof stress of 50 MPa or more.

Further, the conductivity of the Al—Mn-based aluminum alloy casting of the present invention is preferably 20% IACS or less. A more preferred conductivity is 18% IACS or less, and the most preferred conductivity is 16% IACS or less. The conductivity of the Al—Mn-based aluminum alloy casting can be reduced by increasing the amount of Mn added.

The Al—Mn-based aluminum alloy casting of the present invention can be suitably obtained by the method for producing an Al—Mn-based aluminum alloy casting of the present invention. Further, the Al—Mn-based aluminum alloy casting of the present invention maintains the above-mentioned various properties even if it is melted and recast.

2. 2. Method for manufacturing Al-Mn-based aluminum alloy casting The method for manufacturing Al-Mn-based aluminum alloy casting of the present invention holds a molten aluminum alloy containing Mn: 2.0 to 12.0% by mass at 1020 ° C. or higher. It is characterized by casting after molten metal overheat treatment.

By superheating the molten metal at 1020 ° C. or higher, the colloidal particles that become solidified nuclei of the Al—Mn-based compound are decomposed, and fine Al ₆ Mn-based crystals can be formed. As a result, in addition to the average ferret diameter of _{Al 6} Mn-based crystals being 30 μm or less, the area ratio of crystals less than ^{10 μm 2 to the total area of crystals is 40% or less.} be able to. _{In addition, the average ferret diameter of Al 6} Mn-based crystals present at the grain boundaries of eutectic α (Al) can be 5 μm or less.

The holding time in the molten metal superheat treatment is preferably 5 to 60 minutes. By setting the time of the molten metal superheat treatment for keeping the molten aluminum alloy at a high temperature of 1020 ° C. or higher to 5 minutes or longer, the Al ₆ Mn-based crystallized material can be sufficiently melted and can be reliably refined. On the other hand, if the holding time is 60 minutes or less, the _{effect of miniaturizing Al 6} Mn-based crystals is not lost, and the increase in energy consumption and deterioration of equipment such as a melting furnace are suppressed. can do.

The atmosphere of the molten metal superheat treatment is not particularly limited as long as the effect of the present invention is not impaired, and for example, a vacuum, an inert gas atmosphere and an atmosphere containing oxygen can be used. Further, the heating means for the molten aluminum is not particularly limited as long as the effect of the present invention is not impaired, and various conventionally known heating methods can be used.

The casting method other than the molten metal superheat treatment is not particularly limited as long as the effect of the present invention is not impaired, and various conventionally known casting methods can be used. For example, an aluminum alloy ingot, a scrap ingot, a mother alloy, etc. are heated and melted in a melting furnace or the like, the components are adjusted to a predetermined alloy composition range, and then the obtained molten aluminum alloy is heated to 1020 ° C. or higher for 5 to 5 After holding for 60 minutes (hot metal overheat treatment), the product may be cooled to an appropriate temperature, subjected to a hot metal cleaning treatment such as flux treatment, degassing and filtration, and then cast into a predetermined shape.

Further, when it is necessary to make the metal structure finer, the cooling rate at the time of casting may be increased. The obtained cast material may be used as it is, or may be formed into a predetermined shape by subjecting it to hot, warm feeling, cold plastic working, cutting, etc. such as forging, extrusion, and rolling.

Although the typical embodiments of the present invention have been described above, the present invention is not limited to these, and various design changes are possible, and all of these design changes are included in the technical scope of the present invention. Will be.

<< Example >>
Using an aluminum alloy material with a purity of 99.9% and an aluminum alloy material containing 3.5% by mass of Mn and the balance being aluminum as raw materials, 8 kg of these are blended and the temperature is raised to 792 ° C in a graphite crucible. Dissolved in the air. After melting, the molten metal was degassed by a rotary degassing device at 792 ° C., and then the molten metal was cast into a boat shape (JIS H5202) by a gravity casting method. The mold temperature was 150 ° C. When measured using a luminescence analysis method according to JIS H1305 (equipment used: QSG750II manufactured by OBLF), the composition of the Al—Mn-based aluminum alloy casting was Mn: 3.5% by mass and Fe: 0.05% by mass. , Al: Bal. Met.

Next, the residual hot water was heated to 1050 ° C. in an ultrasonic furnace and held for 10 minutes (molten superheat), and then the molten metal at 1050 ° C. was cast into a boat shape at 150 ° C. Next, the obtained mold casting was redissolved, and the molten metal degassed by a rotary degassing device at 792 ° C was cast into a boat mold at 150 ° C to carry out an Al—Mn-based aluminum alloy casting. Obtained.

≪Comparison example≫
In the examples, the Al—Mn-based aluminum alloy casting before the molten metal overheat treatment was used as a comparative Al—Mn-based aluminum alloy casting.

A cross-sectional sample was cut out from the Al—Mn-based aluminum alloy castings obtained in Examples and Comparative Examples, and buffed and subjected to hydrofluoric acid etching to prepare a sample for microstructure observation. An optical micrograph of the Al—Mn-based aluminum alloy casting obtained in the examples is shown in FIG. 1, and an optical micrograph of the Al—Mn-based aluminum alloy casting obtained in the comparative example is shown in FIG. 2, respectively.

In the Al—Mn-based aluminum alloy casting obtained in the comparative example, _{there is a remarkable region where very fine Al 6} Mn-based crystals are densely present (representative regions are circled in FIG. 2). Surrounding). An enlarged photograph of this region is shown in FIG. 3, and it can be seen that _{Al 6 Mn-based crystals having an average ferret diameter of 5 μm or less are formed.} Further, when the area ratio of the crystallization of less than ^{10 μm 2} was calculated by image analysis with respect to the total area of the crystallization of the fine Al _{6 Mn-based crystallization in FIG. 2, it was 58 to 65%.} ..

On the other hand, in the Al—Mn-based aluminum alloy casting obtained in the examples, the fine Al ₆ Mn-based crystallized material accumulation region is not clearly formed. ^{The area ratio of the crystallization of less than 10 μm 2 to} the total area of the crystallization obtained from FIG. 1 by image analysis was 28%, which was 40% or less. The average ferret diameter of the _Al-6 Mn-based crystallized product of the Al—Mn-based aluminum alloy casting obtained in the examples was 27.5 μm.

With respect to the Al—Mn-based aluminum alloy castings obtained in Examples and Comparative Examples, the area ratio occupied by the crystallization having each area range with respect to the total area of the crystallization is shown in FIG. The Al—Mn-based aluminum alloy castings obtained in Examples and Comparative Examples are measured twice with different observation fields. It can be seen that ^{the area ratio of the crystallized product having an area of 0 to 10 μm 2} clearly changes depending on the presence or absence of the molten metal superheat treatment, and becomes 40% or less by the molten metal superheat treatment.

When the conductivity of the Al—Mn-based aluminum alloy castings obtained in Examples and Comparative Examples was measured, the Al—Mn-based aluminum alloy castings of Examples were 19.6% IACS, and the Al—Mn-based aluminum of Comparative Example was used. The alloy casting was 19.4% IACS, and it was confirmed that the low conductivity was maintained even in the Al—Mn-based aluminum alloy casting of the example. A digital conductivity meter (Auto Sigma 3000 / DL) manufactured by Hocking was used for measuring the conductivity.

The tensile properties of the Al—Mn-based aluminum alloy castings obtained in Examples and Comparative Examples were evaluated. A 14B tensile test piece of JIS Z 2241 was cut out from each Al-Mn-based aluminum alloy casting, and a tensile test was conducted under the condition of a tensile speed of 5 mm / min. As a result of the tensile test, the tensile strength of the Al—Mn-based aluminum alloy casting obtained in the examples was 128 MPa, the 0.2% proof stress was 56 MPa, the breaking elongation was 14.3%, and the Young's modulus was 75.5 GPa. The tensile strength of the Al—Mn-based aluminum alloy casting obtained in Comparative Example was 125 MPa, the 0.2% proof stress was 57 MPa, the breaking elongation was 10.9%, and the Young's modulus was 75.3 GPa. From these results, it can be seen that the Al—Mn-based aluminum alloy casting of the present invention has improved fracture elongation while maintaining high tensile strength, 0.2% proof stress and Young's modulus.

In order to clarify the effect of molten metal superheat on the degree of supercooling, the diameter and height are 4 mm centered at the position 13 mm from the bottom surface of the Al—Mn-based aluminum alloy casting before the molten metal superheat obtained in the examples. A 4 mm cylinder was cut out and subjected to thermal analysis by DTA.

Using a TG-DTA device (Rigaku, Thermo plus EVO2), the sample for thermal analysis was heated from room temperature to 800 to 1200 ° C. at 10 ° C./min under an air atmosphere, and held at that temperature for 10 minutes (heated molten metal). process). Then, the temperature was lowered to 400 ° C. at 10 ° C./min, and then quenching was performed with an air cooling fan to room temperature. Alumina was used as a reference for DTA analysis.

FIG. 5 shows the relationship between the start temperature of eutectic solidification obtained by thermal analysis by DTA and the temperature of the molten metal overheat. It can be seen that the eutectic solidification supercooling temperature is influenced by the temperature of the molten metal superheating, and that there is a region where the supercooling degree is maximum at the molten metal superheating temperature of 1020 ° C. or higher.

Claims (7)

Mn: made of an aluminum alloy containing 2.0 to 12.0% by mass.
The metallographic structure mainly consists of an Al-Mn eutectic structure and an Al ₆ Mn-based crystallized product.
The average ferret diameter of the Al ₆ Mn-based crystallized product is 30 μm or less.
^{The area ratio of crystallization of less than 10 μm 2} to the total area of crystallization is 40% or less.
An Al—Mn-based aluminum alloy casting characterized by. The average ferret diameter of the _{Al 6} Mn-based crystals present at the grain boundaries of the eutectic α (Al) is 5 μm or less.
The Al—Mn-based aluminum alloy casting according to claim 1. The Mn content is 3.0 to 5.0% by mass.
The Al—Mn-based aluminum alloy casting according to claim 1 or 2. Young's modulus is 75 GPa or more, breaking elongation is 15% or more,
The Al—Mn-based aluminum alloy casting according to any one of claims 1 to 3. Conductivity is 20% IACS or less,
The Al—Mn-based aluminum alloy casting according to any one of claims 1 to 4. Casting of a molten aluminum alloy containing Mn: 2.0 to 12.0% by mass after being superheated to keep it at 1020 ° C or higher.
A method for manufacturing an Al—Mn-based aluminum alloy casting. The holding time at 1020 ° C. or higher in the molten metal superheat treatment shall be 5 to 60 minutes.
The method for producing an Al—Mn-based aluminum alloy casting according to claim 6.

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