Method for producing aluminum alloy powder for additive manufacturing

Abstract

Provided is a method for producing aluminum alloy powder for additive manufacturing with sufficient fluidity. The present invention utilizes the method for producing aluminum alloy powder for additive manufacturing, the method including, in this order: a first step for filling a chamber equipped with a rotatable disk with nitrogen so that the oxygen amount in the chamber is 1,000 ppm or less; a second step for pouring molten aluminum alloy onto the rotating disk and centrifuging the molten aluminum alloy to obtain the aluminum alloy powder; and a third step for sieving the aluminum alloy powder so that the aluminum alloy powder having a particle size of 45-212 μm accounts for 50% or more by weight.

Description

Method for Producing Aluminum Alloy Powder for Additive Manufacturing

[0001] The present invention relates to a method for producing an aluminum alloy powder for additive manufacturing.

[0002] As the aluminum alloy powder used in the additive manufacturing method, it is preferable that the fluidity is high in order to form a desired shape during the shaping. For this reason, as the aluminum alloy powder used in the additive manufacturing method, it has been considered to use an aluminum alloy powder having a particle shape close to spherical. For example, it has been considered to use an aluminum alloy powder having an average circularity of 0.75 or more (Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2017-66432

[0004] However, regarding the fluidity of the aluminum alloy powder shown in Patent Document 1, when the fluidity is measured using a Carney flowmeter having an orifice diameter of 5.0 mm, it is called ASTM B964 Standard Test Methods for Flow Rate of Metal Powders Using the Carney Funnel (hereinafter simply referred to as "ASTM 964 method"). When the test was conducted by a standard test method for evaluating the fluidity of metal powders, it was found that sufficient fluidity could not be obtained. Therefore, an object of the present invention is to provide a method for producing an aluminum alloy powder for additive manufacturing having sufficient fluidity.

[0005] To solve the above problems, it was found that sufficient fluidity can be obtained in the ASTM 964 method by implementing specific conditions when manufacturing aluminum alloy powder for additive manufacturing. Specifically, the present invention provides a method for manufacturing aluminum alloy powder for additive manufacturing, comprising, in order: a first step of filling a chamber equipped with a rotatable disk with nitrogen so that the amount of oxygen in the chamber is 1000 ppm or less; a second step of obtaining the aluminum alloy powder by pouring molten aluminum alloy onto the rotating disk and centrifuging it; and a third step of sieving the aluminum alloy powder so that 50% or more by weight consists of particles with a particle size of 45 μm or more and 212 μm or less. Furthermore, it is more preferable to set the rotation speed of the disk to 10,000 rpm or more and 300,000 rpm or less.

[0006] The aluminum alloy powder for additive manufacturing obtained by the above method exhibits sufficient fluidity in the ASTM964 process.

[0007] Embodiments of the present invention will be described in detail below. The present invention provides a method for producing aluminum alloy powder for additive manufacturing, comprising, in order: a first step of filling a chamber equipped with a rotatable disk with nitrogen so that the amount of oxygen in the chamber is within a predetermined range; a second step of pouring molten aluminum alloy onto the rotating disk and centrifuging it to obtain the aluminum alloy powder; and a third step of sieving the aluminum alloy powder so that the amount of aluminum alloy powder having a predetermined particle size is within a predetermined range. These will be described in detail below.

[0008] <First Step> The first step is to fill a chamber equipped with a rotatable disc with nitrogen so that the oxygen level in the chamber is 1000 ppm or less. The disc here refers to a rotatable disc-shaped body. A nozzle for dropping molten aluminum alloy is provided on the top of the disc. This disc can spray the molten aluminum alloy dropped from the nozzle in all directions by centrifugal force. The chamber here refers to a container that contains a space for filling the area to be centrifuged with an inert gas.

[0009] The method of reducing the oxygen level in the chamber to 1000 ppm or less involves using a vacuum pump to efficiently replace the air in the chamber with an inert gas; that is, removing the air from the chamber with a vacuum pump and then injecting an inert gas. In addition to nitrogen, noble gases such as argon and helium can be used as the inert gas.

[0010] The aforementioned aluminum alloy is an alloy mainly composed of aluminum (Al) and containing at least one of the following: iron (Fe), manganese (Mn), chromium (Cr), nickel (Ni), zirconium (Zr), magnesium (Mg), silicon (Si), etc. In addition to these metals, it may also contain impurity elements. These impurity elements may be elements that are inevitably mixed in during the production of aluminum alloy powder (unavoidable impurities), or they may be modifying elements that are intentionally added.

[0011] Specific examples of the aforementioned impurity elements include magnesium (Mg), copper (Cu), zinc (Zn), lithium (Li), silicon (Si), iron (Fe), manganese (Mn), chromium (Cr), nickel (Ni), titanium (Ti), calcium (Ca), sodium (Na), strontium (Sr), yttrium (Y), niobium (Nb), molybdenum (Mo), tungsten (W), antimony (Sb), beryllium (Be), phosphorus (P), vanadium (V), tin (Sn), lead (Pb), bismuth (Bi), cobalt (Co), silver (Ag), gallium (Ga), scandium (Sc), and cerium (Ce). The composition of such aluminum alloys is not particularly limited, but examples of industrially used alloy compositions include Al-10 wt% Si-0.4 wt% Mg.

[0012] <Second Step> The second step is to obtain the aluminum alloy powder by pouring droplets of molten aluminum alloy supplied from a nozzle located at the center of rotation on the rotating disk onto the disk and centrifuging it. The molten aluminum alloy referred to here is an aluminum alloy in the region where the liquid phase is approximately 100%, with a temperature of 660°C to 2520°C.

[0013] The rate at which the molten aluminum alloy is poured is not particularly limited, but generally, a method of pouring it by gravity from a nozzle at a rate of 60 kg per hour is used. The rotation speed of the disc is also not particularly limited, but for example, 10,000 rpm to 300,000 rpm is preferred. More preferably, 15,000 rpm to 150,000 rpm is preferred, and 20,000 rpm to 100,000 rpm is even more preferred. By rotating at this rotation speed and spraying droplets, aluminum alloy powder according to the present invention having a predetermined particle size can be obtained. The diameter of the disc is 15 to 60 mm, the thickness is 1.5 to 6 mm, and the distance between the molten metal dropping position and the disc surface can be appropriately adjusted within the range of 15 to 60 mm.

[0014] <Third Step> The third step is to sieve the aluminum alloy powder so that particles with a diameter of 45 μm or more and 212 μm or less make up 50% or more by weight. The sieving method is not particularly limited, but for example, a sieve with a mesh size in the range of approximately 50 μm (about 45 μm) to approximately 200 μm (about 212 μm) can be used. Particularly preferably, a sieve with a mesh size in the range of 60 μm to 150 μm is used. As for the sieving machine mechanism, a circular vibrating sieve with an ultrasonic or vibration motor, or an in-plane sieve such as a gyroshifter or a rotex screener can be used.

[0015] [ASTM 964 Method] The resulting aluminum alloy powder for additive manufacturing is tested using a Carney flowmeter with an orifice diameter of 5.0 mm. The measured flow rate of this test method, called ASTM B964 Standard Test Methods for Flow Rate of Metal Powders Using the Carney Funnel, is preferably 33 seconds or less. According to Beverloo's law, which calculates flow rate using the apparent density of the powder, the flow rate of aluminum alloy powder in a Carney flowmeter is calculated to be 33 seconds. Therefore, a flow rate of 33 seconds or less indicates superior flow rate compared to the theoretical value.

[0016] It is preferable that the product of the aeration ratio (AR) of the aluminum alloy powder and its circularity is 40 or higher. Here, the AR value is an index that evaluates the effect of the aeration rate on the energy during powder flow, and the AR value of aluminum alloy powder can be measured, for example, using a powder rheometer. The circularity of the aluminum alloy powder is a numerical representation of how close the aluminum alloy powder is to a circle, with a value closer to 1 indicating a perfect circle, and a value less than 1 indicating a more complex shape. The circularity of aluminum powder can be measured, for example, using a particle image analyzer. When the product of the AR value and circularity of the aluminum alloy powder is 40 or higher, it has excellent fluidity, and if it is less than 40, there is a risk of reduced fluidity.

[0017] The present invention will be described below using examples. First, the test method and raw materials used in this example are shown below.

[0018] (Test Method) [Measurement of Flowability] The flowability (sec) of the powder was measured according to ASTM B964 Standard Test Methods for Flow Rate of Metal Powders Using the Carney Funnel. Specifically, 50 g of powder was placed in a funnel of a Carney flow meter (manufactured by Tsutsui Chemical Instruments Co., Ltd.: powder flowability meter) with an orifice diameter of 5.0 mm, and the flowability was measured by measuring the time it took for the obtained powder to pass through the funnel.

[0019] [Apparent Density] The apparent density of the powder is determined according to ASTM B417 Standard Test Method for Apparent Density of Non-Free-Flowing Metal Powders Using the Carney Funnel, and the apparent density (g / cm³) is calculated accordingly. ３ ) was measured. Specifically, the Kearney flowmeter and a 25 cm³ volume were used to measure the fluidity. ３Measurements were performed using a cylindrical cup. By placing the cup under a funnel, the powder that passed through the funnel was filled into the cup, and the mass of powder required for filling was measured. From the cup's volume and the mass of the powder, the apparent density was calculated.

[0020] [AR Value (Aeration Ratio)] To evaluate the adhesion and cohesiveness between powder particles through aeration, the aeration index (Aeration Ratio, AR value) was measured using a powder rheometer FT4 (manufactured by Freeman Technology). The measurement conditions were as follows: a 25 ml container was filled with powder, and a 23.5 mm diameter blade was moved while rotating. The AR value was calculated as the ratio of the total energy when no air was aerated vertically downwards to the total energy at the lowest value when air was aerated up to 15 mm / sec.

[0021] [Circularity] For measuring circularity, a particle image analyzer (Malvern Corporation: product name "Mofologi G3") conforming to ISO 13322-1 Particle size analysis - Image analysis methods - was used. After dispersing additive manufacturing aluminum alloy powder using a pressurized pulsed sample dispersion unit, image analysis was performed to measure the circularity. The circularity measured by Mofologi is calculated from the ratio of the circumference of a circle with the same area as the projected object to the perimeter of the object. Measurements were performed on approximately 10,000 randomly selected additive manufacturing aluminum alloy powders, and the average value was taken as the circularity.

[0022] [Example 1] The raw materials were mixed to prepare a powder composition of 10% silicon, 0.35% magnesium, and the remainder being aluminum, and were thoroughly melted at 850°C. Next, a 50 mm diameter, 2 mm thick disc, with a nozzle having a hole of 1 to 10 mm in diameter at its tip and a supply unit at its center of rotation, was placed in a chamber filled with nitrogen and adjusted to have an oxygen content of 1000 ppm or less and rotated at 80000 rpm. The molten metal was then poured from a height of 50 mm into the supply unit of the nozzle located in the center of the disc, and the molten metal was ejected from the tip of the disc by centrifugal force to pulverize it. Next, the obtained powder was collected and sieved so that aluminum alloy powder with a particle size of 45 μm to 212 μm accounted for 50% or more by weight. Specifically, a sieve with a mesh size of 150 μm was set on a round vibrating sieve with a vibration motor, and the powder that passed through the sieve was collected. Furthermore, when using a sieve with a mesh size of 150 μm, some particles slightly larger than 150 μm (up to about 212 μm) will pass through. Therefore, the particles that pass through a 150 μm sieve will contain not only particles between 45 μm and 150 μm, but also some particles between 150 μm and 212 μm. In addition, the obtained powder was sieved, and the proportion (by weight) of particles with a particle size between 45 μm and 212 μm was calculated. Specifically, the obtained powder was placed on a metal mesh with a mesh size of 212 μm, which was placed on top of a metal mesh with a mesh size of 45 μm, installed in a rotap-type sieve shaker (manufactured by Iida Seisakusho Co., Ltd.). The shaker was operated at 50 Hz for 10 minutes, and the weight of the powder remaining on the 45 μm metal mesh was measured 10 minutes after the start of shaking. Next, the sieved powder was subjected to a fluidity test according to the method described above. As a result, all the powder passed through in 20 seconds. The circularity was 0.935, the AR value was 43.8, and the product of the AR value and circularity was 41.0.

[0023] [Example 2] Using a 50 mm diameter, 2 mm thick disc rotated at 65,000 rpm, pulverization and sieving were carried out in the same manner as in Example 1 to obtain powder. The percentage (by weight) of particles with a particle size of 45 μm or more and 212 μm or less was calculated from the obtained powder in the same manner as in Example 1, and was found to be 64.0%. Furthermore, the fluidity of the sieved powder was measured according to the method described above. As a result, all the powder passed through in 18 seconds. In addition, the circularity was 0.941 and the AR value was 50.0, and the value obtained by multiplying the AR value and circularity was 47.0.

[0024] [Example 3] Using a 50 mm diameter, 2 mm thick disc rotated at 55,000 rpm, pulverization and sieving were carried out in the same manner as in Example 1 to obtain powder. The percentage (by weight) of particles with a particle size of 45 μm or more and 212 μm or less was calculated from the obtained powder in the same manner as in Example 1, and was found to be 68.2%. The fluidity of the sieved powder was measured according to the method described above. As a result, all the powder passed through in 17 seconds. Furthermore, the circularity was 0.938 and the AR value was 63.0, and the value obtained by multiplying the AR value and circularity was 59.1.

[0025] [Example 4] Using a 50 mm diameter, 2 mm thick disc rotated at 45,000 rpm, pulverization and sieving were carried out in the same manner as in Example 1 to obtain powder. The percentage (by weight) of particles with a particle size of 45 μm or more and 212 μm or less was calculated from the obtained powder in the same manner as in Example 1, and was found to be 93.3%. Furthermore, the fluidity of the sieved powder was measured according to the method described above. As a result, all the powder passed through in 16 seconds. In addition, the circularity was 0.941 and the AR value was 75.9, and the value obtained by multiplying the AR value and circularity was 71.5.

[0026] [Comparative Example 1] Using a 50 mm diameter, 2 mm thick disk rotated at 100,000 rpm, pulverization and sieving were carried out in the same manner as in Example 1 to obtain powder. The percentage (by weight) of particles with a particle size of 45 μm or more and 212 μm or less was calculated from the obtained powder in the same manner as in Example 1, and was found to be 19.1%. Furthermore, the fluidity of the sieved powder was measured according to the method described above. As a result, all the powder passed through in 38 seconds. In addition, the circularity was 0.932, the AR value was 27.9, and the value obtained by multiplying the AR value and circularity was 26.0.

[0027] [Comparative Example 2] Using a 50 mm diameter, 2 mm thickness disc rotated at 120,000 rpm, pulverization and sieving were carried out in the same manner as in Example 1 to obtain powder. The percentage (by weight) of particles with a particle size of 45 μm or more and 212 μm or less was calculated from the obtained powder in the same manner as in Example 1, and was found to be 0.6%. Furthermore, the fluidity of the sieved powder was measured according to the method described above. As a result, the powder did not pass through. In addition, the circularity was 0.931 and the AR value was 15.6, and the value obtained by multiplying the AR value and circularity was 14.5.

[0028] [Comparative Example 3] Using a 50 mm diameter, 2 mm thick disk rotated at 90,000 rpm, pulverization and sieving were carried out in the same manner as in Example 1 to obtain powder. The percentage (by weight) of particles with a particle size of 45 μm or more and 212 μm or less was calculated from the obtained powder in the same manner as in Example 1, and was found to be 46.2%. The fluidity of the sieved powder was measured according to the method described above. As a result, all the powder passed through in 35 seconds. The circularity was 0.842, the AR value was 34.2, and the value obtained by multiplying the AR value and circularity was 28.8.

[0029] [Comparative Example 4] Using a 50 mm diameter, 2 mm thick disk rotated at 75,000 rpm, the oxygen concentration in the chamber was set to 2000 ppm, and pulverization and sieving were performed to obtain powder. The percentage (by weight) of particles with a particle size of 45 μm or more and 212 μm or less was calculated from the obtained powder in the same manner as in Example 1, and was found to be 58.2%. The fluidity of the sieved powder was measured according to the method described above. As a result, all the powder passed through in 36 seconds. The circularity was 0.715, the AR value was 54.9, and the value obtained by multiplying the AR value by the circularity was 39.2.

[0030]

[0031] As is clear from Examples 1 to 4, powders in which the proportion of powder with a particle size of 45 μm to 212 μm is 50% or more, and the product of the AR value and circularity is 40 or more, exhibited excellent fluidity, with a flow rate of 33 seconds or less. On the other hand, as is clear from Comparative Examples 1 to 3, powders in which the proportion of powder with a particle size of 45 μm to 212 μm is less than 50%, and the product of the AR value and circularity is 40 or less, exhibited a flow rate exceeding 33 seconds or did not flow at all, indicating that they did not possess sufficient fluidity.

Claims

1. A method for producing aluminum alloy powder for additive manufacturing, comprising: a first step of filling a chamber equipped with a rotatable disk with nitrogen so that the oxygen content in the chamber is 1000 ppm or less; a second step of obtaining aluminum alloy powder by pouring molten aluminum alloy onto the rotating disk and centrifuging it; and a third step of sieving the aluminum alloy powder so that 50% or more by weight consists of particles with a particle size of 45 μm or more and 212 μm or less.

2. The method for producing aluminum alloy powder for additive manufacturing according to claim 1, wherein the rotational speed of the disk is 10,000 rpm or more and 300,000 rpm or less.

3. The method for producing aluminum alloy powder for additive manufacturing according to claim 1, characterized in that the value obtained by multiplying the air permeability index AR value of the aluminum alloy powder by its circularity is 40 or more.

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