JP7775607B2 - Fe-Al alloy, Fe-Al alloy member, and method for producing the Fe-Al alloy. - Google Patents

Description

The present invention relates to Fe-Al alloys used as vibration-damping alloys, Fe-Al alloy members, Fe-Al alloy powders, and methods for producing Fe-Al alloys.

As a vibration countermeasure to improve the quietness of automobiles and other vehicles, there is a demand for metal materials with excellent vibration-damping properties. Examples of vibration-damping alloys include Fe-Al alloys, Fe-Cr-Al alloys, and Fe-Co-V alloys, which are known as ferromagnetic vibration-damping alloys. All of these materials have high magnetostriction, and the magnetic domain walls within the material move due to the magnitude of the distortion caused by vibration, absorbing the elastic energy of vibration. Another vibration-damping alloy is Mn-Cu alloy, but this utilizes twin deformation in thermoelastic martensitic transformation and loses its vibration-damping effect above the transformation temperature. Ferromagnetic types maintain vibration-damping effects up to relatively high temperatures, and Fe-Al alloys, in particular, are known as vibration-damping alloys with excellent vibration-damping properties due to their low raw material costs.

This Fe—Al alloy is often used as a plate after being subjected to plastic working such as rolling. For example, Patent Document 1 (JP 2014-80676 A) discloses a manufacturing process for a cold-rolled material having a thickness of 1.4 mm or less, and Patent Document 2 (JP 2014-114468 A) discloses a cold working process in which plastic working by hot working and cold rolling are performed.
In these plastically processed materials, the grain boundaries hinder the movement of domain walls, so the larger the grains, the greater the magnetostriction, which has the effect of increasing internal friction. Patent Document 3 (JP 2001-59139 A) specifies the average grain size to be within the range of 300 to 700 μm. If the grain size is too large, cold workability will decrease and there is a concern that the strength required for a structural material will decrease, so an upper limit has been set.

Patent Document 4 also discloses an Fe-Al alloy vibration-damping member obtained by locally melting and solidifying Fe-Al alloy powder using a laser or other method on these rolled materials to form a structure of any shape. This manufacturing method is characterized by a shaping process that obtains a shaped body, and an annealing process that reduces the crystal grain size to within the range of 700 to 2000 μm. This method makes it possible to obtain vibration-damping members of any shape that cannot be produced by plastic processing such as rolling.

JP 2014-80676 A JP 2014-114468 A JP 2001-59139 A WO2020/241530

However, when a large number of vibration-damping members are manufactured using the additive manufacturing method described above, some of the members may have poor vibration-damping properties. Patent Documents 1 to 4 do not mention the above-mentioned problem, and there is still room for further investigation.
An object of the present invention is to provide an Fe-Al alloy, an Fe-Al alloy member, an Fe-Al alloy powder, and a method for producing an Fe-Al alloy, all of which have improved vibration-damping properties.

The present invention is an Fe-Al alloy consisting of, by mass, 4.0 to 12.0% Al, the remainder being Fe and unavoidable impurities, with an average crystal grain size of more than 700 μm and no more than 2000 μm, and with an area ratio of fine crystal grains with a crystal grain size of less than 100 μm being less than 20%.

It is also preferable that the alloy further contains Ga, and that the total of Al and Ga, by mass%, is greater than 4.0% and less than or equal to 12.0%.

The present invention also provides an Fe-Al alloy member containing 4.0 to 12.0% Al, the remainder being Fe and unavoidable impurities, with an average crystal grain size of more than 700 μm and no more than 2000 μm, an area ratio of fine crystal grains with a crystal grain size of less than 100 μm being less than 20%, and an internal friction of 0.0020 or greater at 22°C measured using the central vibration method.

It is also preferable that there are areas with a thickness of 5 mm or more.

The present invention also provides an Fe-Al alloy powder characterized by containing, by mass%, Al: 4.0% or more and less than 12.0%, Ga: more than 0%, and the balance being Fe and unavoidable impurities, with the total of Al and Ga being more than 4.0% and less than 12.0%.

It is also preferable that the average particle size be 10 μm or more and 200 μm or less.

Atomized powder is also preferred.

The present invention also provides a method for producing an Fe-Al alloy, comprising: a shaping step in ^which a powder containing, in mass %, 4.0 to 12.0% Al, with the remainder being Fe and unavoidable impurities, is melted and solidified using a heat source with a surface energy density of 2.6 to 4.8 J/mm2 to obtain a shaped body; and an annealing step in which the shaped body is held at a temperature exceeding 1050°C and not exceeding 1250°C for one hour or more.

Furthermore, it is preferable that the powder further contains Ga, and that the total of Al and Ga, by mass%, is greater than 4.0% and less than or equal to 12.0%.

The present invention provides Fe-Al alloys, Fe-Al alloy members, Fe-Al alloy powders, and methods for producing Fe-Al alloys with improved vibration-damping properties.

1A and 1B are cross-sectional photographs of an example of the present invention before annealing, where (a) is a low-magnification image and (b) is a high-magnification image. 1 is a cross-sectional photograph of an example of the present invention after annealing. 3A and 3B are cross-sectional photographs of a comparative example before annealing, where (a) shows a low-magnification image and (b) shows a high-magnification image. 1 is a cross-sectional photograph of a comparative example after annealing. 10 is a cross-sectional photograph of another comparative example before annealing. 10 is a cross-sectional photograph of another comparative example after annealing.

Hereinafter, embodiments of the present invention will be described in detail.
The Fe-Al alloy of the present invention contains, in mass %, 4.0 to 12.0% Al, with the remainder being Fe and unavoidable impurities, and is characterized in that the area ratio of fine crystal grains having an average crystal grain size of more than 700 μm and not more than 2000 μm, and having a crystal grain size of less than 100 μm, is less than 20%.

<Fe-Al alloy>
(Al)
Al dissolves in Fe and increases magnetostriction, contributing to vibration damping. As the Al content increases, magnetostriction increases, reaching a maximum at around 10%. On the other hand, as the Al content increases, the magnetic permeability decreases, making it difficult for the domain walls to move. For these reasons, the Al content is set to 4.0 to 12.0%. The preferred lower limit is 6.0%, and the preferred upper limit is 10.0%.

(Ga)
In addition to Al, Ga, an element of the same group as Al, may be added. Like Al, Ga dissolves in Fe and contributes to vibration damping through the effect of increasing magnetostriction. Ga (atomic radius: 0.141 nm) has a smaller atomic radius than Al (atomic radius: 0.143 nm) and is closer to Fe (atomic radius: 0.126 nm), which is thought to have the effect of reducing lattice strain and facilitating the movement of grain boundaries during annealing. Like Al, the more Ga added, the greater the magnetostriction, but if the amount added is increased, it will not dissolve but will form a compound (such as Ga ₃ Fe) and become embrittled. For this reason, the amount of Ga added, in total with Al, is set to more than 4.0% and not more than 12.0%. The preferred lower limit of the total amount with Al is 6.0%, and the preferred upper limit is 12.0% or less. Furthermore, to exhibit the effect of adding Ga, it is sufficient to add more than 0%, and more preferably 0.1% or more.

The damping member of this embodiment is also characterized by an average crystal grain size in the range of more than 700 μm and no more than 2000 μm. The damping member of this embodiment is characterized by the remaining amount of fine crystal grains (also called residual fine crystal grains) with a crystal grain size of less than 100 μm, which are generated during the rapid melting, quenching, and solidification process in additive manufacturing, being less than 20% (including 0) in terms of area ratio. If the damping member contains 20% or more fine crystal grains, the domain wall movement will be hindered, resulting in a deterioration of damping characteristics.

By controlling the average crystal grain size to exceed 700 μm, the movement of the domain walls is less likely to be hindered, making it possible to demonstrate vibration-damping properties.

On the other hand, if the average crystal grain size becomes too large, the ductility of the vibration-damping member tends to decrease, so the upper limit is set to 2000 μm. The lower limit of the average crystal grain size is preferably 800 μm, and more preferably 900 μm. The upper limit of the average crystal grain size is preferably 1800 μm, more preferably 1600 μm, even more preferably 1400 μm, and particularly preferably 1200 μm.
The average grain size in this specification can be determined by a cutting method from the distance between the intersection of a line segment parallel to the lamination direction and the grain boundary when observing a cross section of a sample.

If there are too many defects, such as voids, introduced during molding, sufficient vibration-damping properties will not be obtained even if the average crystal grain size is as described above, so it is preferable that the cross-sectional defect rate be less than 0.1%. This cross-sectional defect rate can be measured, for example, by mirror-polishing a cross section parallel to the thickness direction of the component, observing it with an optical microscope, and analyzing the resulting image to determine the area rate.

Furthermore, an embodiment of an Fe-Al alloy member using an Fe-Al alloy has the characteristics of the above-mentioned Fe-Al alloy, specifically, it contains, by mass, 4.0 to 12.0% Al, with the remainder being Fe and unavoidable impurities, has an average crystal grain size of more than 700 μm and less than 2000 μm, an area ratio of fine crystal grains with a crystal grain size of less than 100 μm is less than 20%, and has an internal friction of 0.0020 or greater at 22°C measured using the central vibration method. Furthermore, for example, it is preferable that the plate-shaped Fe-Al alloy member has a portion with a thickness of 5 mm or greater.

(Fe-Al alloy powder)
One embodiment of the Fe-Al alloy powder contains, by mass%, 4.0 to 12.0% Al, with the balance being Fe and unavoidable impurities. Another embodiment of the Fe-Al alloy powder is characterized in that it contains, by mass%, 4.0% or more but less than 12.0% Al, more than 0% Ga, with the balance being Fe and unavoidable impurities, and the sum of Al and Ga is more than 4.0% but not more than 12.0%.

The average particle size of the Fe-Al alloy powder (hereinafter referred to as alloy powder 20) is preferably 10 μm or more and 200 μm or less from the viewpoint of handling and filling. The preferred average particle size varies depending on the additive manufacturing method used, with 10 μm or more and 50 μm or less being preferred for selective laser melting (SLM), and 45 μm or more and 105 μm or less being more preferred for electron beam additive manufacturing (EBM). Furthermore, for laser beam powder deposition (LAM), it is preferable to use a particle size of 50 μm or more and 150 μm or less. If the average particle size is 10 μm or more, the alloy powder 20 is less likely to fly up in the subsequent additive manufacturing process, which makes it easier to prevent a decrease in the shape accuracy of the alloy additive manufacturing body. On the other hand, by setting the average particle size to 200 μm or less, it becomes easier to prevent the surface roughness of the layered product from increasing in the subsequent layered manufacturing process, and to prevent the alloy powder 20 from being insufficiently melted.
The average particle size in this specification refers to the median diameter (D50) measured by laser diffraction.

<Method for producing Fe—Al alloy>
Next, a method for producing the Fe—Al alloy of this embodiment will be described. First, an alloy powder having the desired composition of the vibration-damping member is prepared. The alloy powder used can be obtained, for example, by atomization. There are no particular limitations on the atomization method, and conventional methods can be used. For example, gas atomization (vacuum gas atomization, electrode induction melting gas atomization, etc.), centrifugal atomization (disk atomization, plasma rotating electrode atomization, etc.), plasma atomization, etc. can be preferably used.

One of the features of an embodiment of a method for producing an Fe-Al alloy is that it includes a shaping step in which a powder containing, in mass %, 4.0 to 12.0% Al, with the remainder being Fe and unavoidable impurities, is melted and solidified using a heat source with a surface energy density of 2.6 to 4.8 J/mm to obtain a shaped body, and an annealing step in which the shaped body is held at a temperature above 1050°C and not higher than 1250°C for one hour or longer.
(modeling process)
In the shaping process of this embodiment, the alloy powder is melted and solidified using a heat source to obtain a shaped body. The heat source may have a surface energy density of 2.6 to 4.8 J/mm. This surface energy density is calculated as P/(v·p), where P is the output of the scanning heat source, v is the scanning speed, and p is the scanning interval. By melting and solidifying the metal powder within the above-mentioned surface energy density range, it is possible to prevent the occurrence of bubbles and unmelted voids as described above and to stably obtain coarse crystal grains after annealing.

The above-mentioned surface energy density of 2.6 to 4.8 J/mm2 can be achieved, for example, by setting the scanning speed of the heat source to 50 mm/sec to 3000 mm/sec. The lower limit of the scanning speed is more preferably 100 mm/sec, and even more preferably 700 mm/sec. The upper limit is more preferably 2000 mm/sec, and even more preferably 1700 mm/sec. The scanning interval should be adjusted to match the scanning speed, between 0.01 mm and 0.4 mm, and more preferably between 0.02 mm and 0.2 mm, to achieve the above-mentioned surface energy density. When observing the molded body after this molding process, the structure obtained by the rapid solidification process contains fine crystal grains, with an average crystal grain size of, for example, 5 μm to 300 μm.

By setting the heat source scanning speed to 50 mm/sec or higher, a stable melt pool is more easily formed and the incorporation of air bubbles into the molded body can be suppressed. Furthermore, by setting the heat source scanning speed to 3000 mm/sec or less, the raw material powder can be prevented from remaining unmelted and the formation of voids in the molded body can be suppressed. Preventing the formation of these bubbles and voids is also important for coarsening the crystal grains.

In this embodiment, the commonly known powder additive manufacturing method can be used as the means for melting and solidifying the powder. Examples of powder additive manufacturing methods include the powder bed method and the direct metal deposition method. The heat source can also be selected appropriately from laser, electron beam, arc, plasma, etc. In this embodiment, the powder bed method using a laser as the heat source is selected.

In order to anneal the molded body after the molding process to produce coarse crystal grains exceeding 700 μm in size, it is necessary to leave a moderate amount of internal strain in the molded body. Internal strain is introduced by thermal stress due to rapid heating and cooling and transformation stress associated with phase transformation, and the magnitude of this strain acts as the driving force for recrystallization during the annealing process. Through studies of the additive manufacturing process and annealing process by the inventors, it was confirmed that recrystallization occurs over a wide range of additive manufacturing conditions by increasing the temperature in the annealing process, as described below, or by adding Ga.

The shaped body of this embodiment has a metal structure consisting of a collection of rapidly solidified structures after the additive manufacturing process. The microstructure has a columnar structure aligned in the stacking direction.

(Annealing process)
In the annealing step of this embodiment, the obtained shaped body is annealed. This is because, since the shaped body as is only capable of obtaining crystal grains of approximately 100 μm at most, it is necessary to coarsen the crystal grains by annealing and recrystallizing them. In order to recrystallize the additive manufacturing body containing fine crystal grains obtained in the additive manufacturing step described above, the lower limit of the annealing temperature is preferably above 1050°C, more preferably 1100°C or higher.
Furthermore, if the temperature exceeds 1250°C, the growth of crystal grains becomes slow and the heat treatment deformation becomes large, so the upper limit can be set to 1250°C. Furthermore, adding Ga is preferable because it promotes the coarsening of crystal grains during the annealing process. An annealing time of 1 hr or more is preferable because it stabilizes the properties. Although a longer annealing time can be set, considering the possibility of surface changes occurring during heat treatment, it is recommended to set it to 12 hours or less. The annealing atmosphere is selected from air, vacuum, hydrogen flow, and inert gas atmospheres such as nitrogen, argon, and helium. A hydrogen flow or inert gas atmosphere is preferable to prevent surface oxidation during heat treatment. After annealing, cooling can be performed at a rate of approximately 100°C/min by methods such as forced cooling with hydrogen gas or inert gas, opening the furnace to the atmosphere, or rapid cooling by liquid immersion.

The manufacturing method of this embodiment does not require the introduction of strain through plastic processing during the manufacturing process, and can reduce the fine crystal grains that are an issue with additive manufacturing, making it possible to manufacture Fe-Al alloy components of any shape. This effect is particularly suitable for manufacturing plate-shaped Fe-Al alloy components with sections that are 5 mm or thick, for which plastic processing has been difficult to apply.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention as set forth in the claims.

The Fe-Al alloy and its manufacturing method of the present invention can provide Fe-Al alloy components with improved vibration-damping properties by reducing the fine grain size. This makes it possible to apply the alloy to vibration-damping components of any desired shape, such as thicknesses exceeding 5 mm, for automotive and other vehicle components that require greater quietness and vibration control.

Gas-atomized powder (hereafter referred to as "raw material A") containing 8.4% Al, the remainder being Fe and unavoidable impurities, and gas-atomized powder (hereafter referred to as "raw material B") containing 7.0% Al and 2.0% Ga (total of Al and Ga: 9.0%), the remainder being Fe and unavoidable impurities, were prepared and classified to achieve an average particle size D50 of 30-35 μm. Gas atomization was performed by high-frequency melting in a vacuum, dropping the molten alloy from a 5 mm diameter nozzle below the crucible, and atomizing it with high-pressure argon. Using this as raw material powder, a 3D additive manufacturing machine (EOS Corporation, EOS-M290) was used to fabricate a 2.5 mm wide, 60 mm long, and 11 mm high-rise model using a powder bed method with an S45C base plate and high-speed laser irradiation for rapid melting and rapid solidification. The layer thickness per layer was 40 μm, and the irradiation direction was rotated 67° for each layer. The laser beam diameter was approximately 0.1 mm and the laser output was 300 W. The molding conditions are shown in Table 1. Annealing was performed by heating and holding the material in a hydrogen gas flow at the annealing temperature shown in Table 1 for 0.25 hours (15 minutes), 0.5 hours (30 minutes), or 1 hour (60 minutes), followed by cooling at approximately 100°C/min.

Next, structural observation and measurement of various properties were carried out. Two types of microstructures were observed, one before annealing and one after annealing, on cross sections perpendicular to the thickness direction (stacking direction). Specifically, the cross sections perpendicular to the thickness direction were mirror-polished and then observed with a scanning electron microscope (magnification: 200x, measurement range: 10 ^mm2 ). Ten horizontal and ten vertical lines were drawn at equal intervals on the obtained images, and the number of intersections where fine crystal grains (residual fine grains) existed was taken as the area ratio of fine crystal grains (fine crystal part ratio). Ten images were extracted per cross section, and the average value of the area ratio of fine crystal grains measured was calculated.

The crystal grain size was calculated by observing the sample under an optical microscope (magnification: 100x), drawing a 3 mm line perpendicular to the thickness direction, and counting the number of intersections with the crystal grain boundaries in the area excluding the fine crystal portion mentioned above. Ten lines were drawn at random so as not to intersect with the same crystal grain, and the average value was taken as the average crystal grain size. The results are also shown in Table 1. Hardness was also determined by averaging five points on the sample surface using a micro Vickers hardness tester (Future Tech) at a load of 0.5 kgf for a loading time of 10 seconds.

The vibration-damping properties were measured by cutting the above-mentioned shaped body into strip-shaped test specimens measuring 1.5 mm wide, 60 mm long, and 10 mm high, and then annealing them.The internal friction was then measured at room temperature (22°C) using a free resonance central excitation method.

The results in Table 1 show that in Examples 1 to 5 of Raw Material A and Examples 6 to 14 of Raw Material B, which were annealed (heat treated) at a temperature of 1100°C, the microcrystalline portion ratio (area ratio of fine crystal grains) after annealing was less than 10%. The average crystal grain size exceeded 700 μm, and the defect rate was less than 0.1%. All of Examples 1 to 14 achieved good internal friction values of 0.0020 or greater. In particular, Examples 6 to 14, in which the microcrystalline portion ratio was 0, achieved even better values of 0.0030 or greater. All of Examples 1 to 14 exhibited stable Vickers hardness characteristics of 170 HV to 210 HV, confirming that they have sufficient strength for practical use.

Figures 1 and 2 show the microstructures of Example 6 before and after annealing as a representative example of the microstructure before and after annealing. Before annealing, fine columnar crystal grains growing in the stacking direction were observed, with a width of approximately 10 μm. However, after annealing, these fine columnar crystal grains disappeared, and coarse recrystallized grains with an average crystal grain size of approximately 1,360 μm were formed. It was also confirmed that recrystallization occurred during annealing, with the majority of the fine crystal grains disappearing, and the area ratio (area ratio) of fine crystal grains becoming less than 20%.

In contrast, Comparative Examples 1 to 4 were cases in which the annealing (heat treatment) temperature was 1050°C or lower, and the fine crystal grains were not sufficiently eliminated during annealing, resulting in an area ratio of 20% or more. As an example, Figure 3 shows the microstructure of Comparative Example 4 before annealing, and Figure 4 shows the microstructure after annealing. As shown in Figure 3, before annealing, fine columnar crystal grains that had grown in the stacking direction were observed, with a width of approximately 10 μm. The internal friction was less than 0.0020 in all cases.

In addition, in Comparative Example 5, the areal energy density was 5 J/ ^mm2 or more, and there were many defects before annealing, with the defect rate exceeding 0.1%. It was confirmed that recrystallization occurred after annealing, but the crystal grain size was small. For Comparative Example 5, Figure 5 shows the microstructure before annealing, and Figure 6 shows the microstructure after annealing. As shown in Figure 5, before annealing, fine columnar crystal grains that grew in the stacking direction were observed, with a width of approximately 10 μm. Furthermore, as shown in Figure 6, recrystallization was observed after annealing, but the disappearance of the fine crystal grains was insufficient. From the above, it is believed that the internal friction value of the damping alloy of Comparative Example 5 was less than 0.0020, which was lower than the values of Examples 1 to 14.

Claims (4)

In mass%,
Al: 4.0% to 12.0%;
Ga: 0.1% or more and 2.0% or less,
The balance consists of Fe and unavoidable impurities,
The average crystal grain size is more than 700 μm and less than 2000 μm,
An Fe-Al alloy characterized in that the area ratio of fine crystal grains having a crystal grain size of less than 100 μm is less than 20%. In mass%,
Al: 4.0% or more and 12.0% or less;
Ga: 0.1% or more and 2.0% or less,
The balance consists of Fe and unavoidable impurities,
The average crystal grain size is more than 700 μm and less than 2000 μm,
The area ratio of fine crystal grains having a crystal grain size of less than 100 μm is less than 20%,
An Fe-Al alloy member characterized in that the internal friction at 22°C measured by the central vibration method is 0.0020 or more. The Fe-Al alloy member according to claim 2 , having a portion having a thickness of 5 mm or more. In mass%,
Al: 4.0% to 12.0% ;
Ga: 0.1% or more and 2.0% or less,
a shaping step in which the powder, the balance of which is Fe and unavoidable impurities, is melted and solidified using a heat source with a surface energy density of 2.6 to 4.8 J/mm to obtain a shaped body;
and an annealing step in which the shaped body is held at a temperature higher than 1050°C and not higher than 1250°C for one hour or longer , so that the area ratio of fine crystal grains having an average crystal grain size of more than 700 μm and not more than 2000 μm and a crystal grain size of less than 100 μm becomes less than 20% .