JP6048217B2 - Magnesium-based alloy powder and magnesium-based alloy compact - Google Patents

Description

  The present invention relates to a magnesium-based alloy powder and a magnesium-based alloy molded body.

  Magnesium has a Clark number (ratio of elements present near the ground surface) that is more than 100 times that of nickel and copper, and is abundant in terms of resources. Moreover, since the specific gravity of magnesium is about two-thirds that of aluminum and about one-fourth that of iron, when various structures are manufactured using magnesium, the structure can be significantly reduced in weight. Against this background, parts made of magnesium alloys are beginning to be used in product fields such as automobiles, aircraft, mobile phones, and notebook computers.

Magnesium also has properties such as electromagnetic shielding properties, vibration damping capability, machinability, and biosafety.
When manufacturing a magnesium structure, casting methods such as gravity casting and die casting, plastic processing methods such as hot extrusion of billets, cold extrusion, rolling and forging, molding by powder hot pressing and hot extrusion, etc. Powder metallurgy is used. Among these, according to the powder metallurgy method, since a local composition fluctuation | variation is suppressed, a more homogeneous structure can be manufactured.

On the other hand, magnesium has a problem that it easily burns in the atmosphere. In particular, magnesium powder has a risk of causing a so-called dust explosion by floating in the air. For this reason, it is impossible to simply replace a general metal material or metal powder with magnesium, which has prevented the spread of magnesium as a structural material.
In view of such a problem, research on the flame retardancy of magnesium is underway. And it was discovered that flame retardancy is imparted to magnesium by adding calcium. For example, Patent Document 1 discloses an Mg alloy extruded material containing 4 to 8% by mass of calcium. In such flame-retardant magnesium, the ignition temperature is higher by 200 ° C. or more than conventional, so that not only the flame retardance of the structure itself is improved, but also the safety when producing the structure is improved. For this reason, it seems that the use of this flame-retardant magnesium will promote the spread of magnesium-made structures.
However, flame retardant magnesium has a problem of low mechanical strength. For this reason, there is an increasing need to develop a material capable of producing a flame-retardant magnesium-based metal molded body having more excellent mechanical properties.

JP 2010-82693 A

  An object of the present invention is to provide a magnesium-based alloy powder that is excellent in compaction at the time of molding and can produce a compact having high mechanical properties, and a magnesium-based alloy with high mechanical properties that is manufactured using this magnesium-based alloy powder. The object is to provide a molded body.

The above object is achieved by the present invention described below.
The magnesium-based alloy powder of the present invention is composed of a magnesium-based alloy containing 0.2 mass% or more and 5 mass% or less calcium,
The average particle size is 100 μm or more and 1500 μm or less,
The average value of the hardness variation index, which is a value obtained by dividing the difference between the maximum value and the minimum value of the micro Vickers hardness measured at 10 points of the particle cross section by the maximum value, is 0.3 or less,
The particle surface is covered with a coating layer containing calcium oxide.
Thereby, since it becomes the powder excellent in the compactness at the time of shaping | molding, maintaining the outstanding flame retardance, the magnesium base alloy powder which can manufacture a molded object with a high mechanical characteristic is obtained.

In the magnesium-based alloy powder of the present invention, in the X-ray diffraction spectrum, the intensity of the strongest peak derived from an intermetallic compound composed of calcium and aluminum is not less than 3% of the intensity of the strongest peak derived from magnesium. % Or less is preferable.
As a result, a magnesium-based alloy powder that can further enhance the mechanical properties during molding while maintaining flame retardancy is obtained.

In the magnesium-based alloy powder of the present invention, it is preferable that the coating layer is mainly composed of a mixture of calcium oxide and magnesium oxide.
As a result, not only the effect of coexistence of the flame retardancy due to calcium oxide and the mechanical properties at the time of molding, but also the effect of shielding oxygen by magnesium oxide, inside the particles of the magnesium-based alloy powder, Magnesium becomes more difficult to oxidize. Therefore, an increase in oxygen content in the entire particle can be suppressed, and a decrease in mechanical properties of the finally obtained molded body can be suppressed.

In the magnesium-based alloy powder of the present invention, the magnesium-based alloy preferably further contains 2.5% by mass or more and 12% by mass or less of aluminum.
Thereby, since the intermetallic compound of calcium and aluminum precipitates, the flame retardance of magnesium-based alloy powder can be improved and the heat resistance of a molded object can be improved.
In the magnesium-based alloy powder of the present invention, the dendritic arm spacing (DAS) of the crystal structure is preferably 0.05 μm or more and 5 μm or less.
As a result, the balance between the size of the crystal structure and the volume ratio occupied by the magnesium-based alloy is optimized, so that the dislocation movement in the crystal structure can be suppressed and the deformation due to the sliding of the grain boundary can be suppressed. The original mechanical properties can be obtained.

The magnesium-based alloy powder of the present invention is preferably produced by a high-speed rotating water stream atomization method.
As a result, a magnesium-based alloy powder having a relatively large particle size and a uniform particle size can be obtained.
The magnesium-based alloy compact of the present invention is characterized by being manufactured using the magnesium-based alloy powder of the present invention.
Thereby, a magnesium-based alloy molded body having excellent flame retardancy and excellent mechanical properties can be obtained.
The magnesium-based alloy molded body of the present invention is preferably manufactured through a process of subjecting the magnesium-based alloy powder to hot extrusion.
Thereby, a magnesium-based alloy compact with a uniform and fine crystal structure as a whole is obtained.

It is a longitudinal cross-sectional view which shows an example of the apparatus which manufactures a magnesium base alloy powder by the high-speed rotation water flow atomization method.

Hereinafter, the magnesium base alloy powder and the magnesium base alloy compact of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
[Magnesium-based alloy powder]
The magnesium-based alloy powder of the present invention is composed of a magnesium-based alloy containing 0.2 mass% or more and 5 mass% or less of calcium, and the particle surface is covered with a coating layer containing calcium oxide. The magnesium-based alloy powder of the present invention has an average particle size of 100 μm or more and 1500 μm or less, and the difference between the maximum value and the minimum value of micro Vickers hardness measured at 10 locations on the particle cross section is the maximum value. Is a powder that satisfies the condition that the average value of the hardness variation index, which is a value divided by 1, is 0.3 or less.
Such a magnesium-based alloy powder has excellent flame retardancy, is less segregated by intermetallic compounds, and is excellent in compaction during molding. Thereby, the molded object (magnesium base alloy molded object) excellent in the mechanical characteristic is obtained.

Hereinafter, the magnesium-based alloy powder will be further described in detail.
The magnesium-based alloy constituting the magnesium-based alloy powder contains magnesium as a main component and contains 0.2 mass% or more and 5 mass% or less calcium. A magnesium-based alloy containing calcium at such a ratio has sufficient flame retardancy without greatly degrading mechanical properties. Calcium may be present in any state, for example, in the state of a simple substance, an oxide, an intermetallic compound, or the like. These may be uniformly dispersed (solid solution) in the alloy or segregated at the grain boundaries.

In addition, when the content rate of calcium is less than the said lower limit, sufficient flame retardance is not provided to a magnesium base alloy, and the flame retardance of the molded object manufactured will be inferior. On the other hand, when the content rate of calcium exceeds the said upper limit, the ratio of calcium with respect to magnesium will become large, and the mechanical characteristic of the molded object manufactured will fall.
The calcium content is preferably about 0.5% by mass to 4% by mass, and more preferably about 0.8% by mass to 3.5% by mass.

  The magnesium-based alloy may contain other components in addition to magnesium and calcium. Examples of other components include lithium, beryllium, aluminum, silicon, manganese, iron, nickel, copper, zinc, strontium, yttrium, zirconium, silver, tin, gold, rare earth elements (for example, cerium), and the like. 1 type (s) or 2 or more types may be added.

Among these, as the other component, at least one selected from the group consisting of aluminum, manganese, yttrium, strontium, and rare earth elements is particularly preferably used.
The content of other components is preferably about 0.01% by mass to 10% by mass, and more preferably about 0.1% by mass to 5% by mass.
Magnesium is basically present in a single state, but may be partially present in the form of an oxide or an intermetallic compound.

  The average particle size of the magnesium-based alloy powder is 100 μm or more and 1500 μm or less, preferably 300 μm or more and 1300 μm or less, more preferably 500 μm or more and 1100 μm or less. By setting the average particle size within the above range, agglomeration often observed in fine powder (aggregation due to powder shape) can be suppressed, and the filling property during molding can be improved. In addition, the crystal grain size formed in the compact can be reduced. This is because when the average particle size is within the above range, the temperature rise of the particles during heating becomes relatively uniform, and as a result, enlargement of the local crystal particle size is prevented and the crystal particle size is reduced. This is because it is considered that the particle size distribution of the material becomes narrow. By the above, the compactness at the time of shaping | molding can be improved and the molded object excellent in the mechanical characteristic is obtained.

  Further, calcium can be dispersed relatively uniformly, and a molded article having high flame retardancy can be obtained. This is because by setting the average particle size within the above range, even when an intermetallic compound containing calcium is precipitated, the distribution of the intermetallic compound in the molded body is likely to be uniform. This is because uniformity is also achieved. By making the flame retardance uniform, the number of parts having low flame retardancy is locally reduced, so that the overall flame retardancy is improved. In addition, since the distribution of the intermetallic compound is uniform, the local mechanical strength is prevented from being lowered due to the segregation of the intermetallic compound, and thus a molded article having excellent mechanical characteristics can be obtained. .

In addition, since the surface area of the particles can be kept relatively small, the precipitation of oxides in the molded body can be kept relatively small. As a result, a molded body having particularly excellent mechanical properties can be obtained.
In addition, the average particle diameter of the magnesium-based alloy powder is an average value of the diameters of circles having the same area as the area (projected area of the particles) of the particle image captured using an optical microscope or an electron microscope, For the calculation of the average value, 100 or more randomly selected particles are used.

Moreover, when an average particle diameter is less than the said lower limit, the cohesiveness of magnesium base alloy powder becomes high, and the compaction property at the time of shaping | molding becomes low. On the other hand, when the average particle size exceeds the upper limit, the powder filling property is lowered, and the compaction property at the time of molding is lowered.
Further, the maximum particle size of the magnesium-based alloy powder is preferably 4000 μm or less, and more preferably 3000 μm or less. By setting the maximum particle size within the above range, the particle size distribution can be optimized and the filling property during molding can be improved. That is, by setting the maximum particle size within the above range, the temperature rise of the particles during heating becomes more uniform, and as a result, local crystal particle size enlargement is prevented and the crystal particle size is increased. The particle size distribution can be further narrowed.

In addition, the said largest particle size means the largest particle size among the particle sizes of 100 or more particles selected at random.
Further, the average particle size is preferably 0.1 to 0.7 times the maximum particle size, more preferably 0.15 to 0.6 times, and more preferably 0.2 to 0 times. More preferably, it is 5 times or less. By satisfying such a relationship between the average particle size and the maximum particle size, the compactness at the time of molding can be particularly improved, and a molded product having particularly excellent mechanical properties can be obtained.

The average circularity of the magnesium-based alloy powder is preferably 0.5 or more and 1 or less, and more preferably 0.6 or more and 1 or less. The magnesium-based alloy powder having such an average circularity is excellent in fluidity and high in filling property at the time of molding. As a result, the compactness at the time of molding can be improved, and a molded body having excellent mechanical properties can be obtained.
In addition, the average circularity of the magnesium-based alloy powder is determined by (circumference of a circle having the same area as the projected area of the particle) / (contour of the particle image) in a particle image captured using an optical microscope or an electron microscope. The average value of circularity calculated by (length), and 100 or more particles selected at random are used for calculating the average value.

  The average aspect ratio of the magnesium-based alloy powder is preferably 0.5 or more and 1 or less, and more preferably 0.6 or more and 0.9 or less. The magnesium-based alloy powder having such an average aspect ratio is also excellent in fluidity and high in filling property at the time of molding. As a result, the compactness at the time of molding can be improved, and a molded body having excellent mechanical properties can be obtained.

  The average aspect ratio of the magnesium-based alloy powder is an average value of the aspect ratio calculated by the minor axis / major axis in a particle image captured using an optical microscope, an electron microscope, or the like. More than 100 randomly selected particles are used. The major axis is the maximum length that can be taken in the particle image, and the minor axis is the maximum length in the direction orthogonal to the maximum length.

Further, when the average aspect ratio exceeds the upper limit, the powder filling property is lowered, and the compaction property at the time of molding is lowered. On the other hand, when the average aspect ratio is lower than the lower limit, the shape retention at the time of molding is lowered, and the dimensional accuracy of the molded body is lowered.
Further, the apparent density of the magnesium-based alloy powder is preferably 0.2 g / cm ³ or more and 1.2 g / cm ³ or less, more preferably 0.3 g / cm ³ or more and 0.8 g / cm ³ or less. preferable. By setting the apparent density within the above range, a magnesium-based alloy powder with particularly high compaction during molding can be obtained.

The apparent density is also called bulk specific gravity. Desired. For example, JIS Z 2504 is used as a standard for the measurement method.
Moreover, when an apparent density is less than the said lower limit, powder filling property will fall and the compaction property at the time of shaping | molding will become low. On the other hand, when the apparent density exceeds the upper limit, the powder filling property is increased while the fluidity is decreased. For this reason, the compactness is lowered at the time of molding.

  In addition, the magnesium-based alloy powder of the present invention measures micro Vickers hardness at 10 points evenly distributed in the cross section of the particle, and determines the difference between the maximum value and the minimum value in 10 measured values. One of the characteristics is that when the “hardness variation index”, which is a value divided by ## EQU2 ## is calculated, the average value of the hardness variation index is 0.3 or less. Such a magnesium-based alloy powder has a sufficiently uniform crystal structure in one particle. For this reason, even if it becomes a molded object, the molded object which hardly contains the enlarged crystal structure etc. will be obtained, and such a molded object becomes a thing with especially high mechanical characteristics. In other words, a powder containing a part with a low hardness partially may cause a reduction in mechanical properties of the whole molded article by causing breakage starting from the part when it becomes a molded article. The inventor has found that by suppressing the variation in the micro Vickers hardness in the cross section of the particles within the above range, even if there is a site that can be a starting point of the fracture, the progress of the fracture can be reliably suppressed.

  The micro Vickers hardness is a measurement value obtained by measuring the hardness of 10 uniformly dispersed portions with a micro Vickers hardness meter with respect to the cross section of one particle. Then, a hardness variation index is obtained from the ten measured values obtained. Such a hardness variation index is calculated for 50 or more particles, and the average value may be 0.3 or less. At the time of measurement, the load applied to the indenter is 25 gf (0.245 N). In order to obtain the hardness variation index, first, the maximum length L of the cross section of the particle is measured. The 50 or more particles for obtaining the hardness variation index include 50 or more particles randomly extracted from particles whose maximum length L is included in the range of the average particle size ± 20% described above. To do. Further, when determining 10 measurement points in the cross section of one particle, after measuring the hardness of a first point randomly selected in the cross section of the particle, the maximum length is measured from the first measurement point. The second measurement point is selected from a position separated by 5% or more of the length L. Thereafter, by repeating this, 10 measurement points are determined. For example, in the case of particles having a maximum length L of 100 μm, the separation distance between the first measurement point and the second measurement point is 5 μm or more, and the third and subsequent points are separated by 5 μm or more from the previous measurement point. What is necessary is just to select the point.

In addition, the average value of the hardness variation index is preferably 0.2 or less, and more preferably 0.15 or less.
In the magnesium-based alloy powder of the present invention, the particle surface is covered with a coating layer containing calcium oxide. Thereby, oxidation of magnesium is relaxed in each particle, and it is possible to avoid deterioration of the mechanical properties of the finally obtained molded body. That is, a molded article having excellent mechanical properties can be obtained by covering the particle surface with calcium oxide. In addition, when the surface of the particles is covered with calcium oxide, when the magnesium-based alloy powder is molded into a molded body, the distribution of calcium tends to be relatively uniform throughout the molded body, so that the flame retardancy is made uniform. Will be illustrated. As a result, the flame retardancy is raised.

  Whether or not the particle surface is covered with the coating layer can be evaluated by analyzing the density in an observation image obtained by an electron microscope and the distribution state of calcium. As the latter, for example, if the calcium concentration on the surface is higher than the inside of the particle, it can be evaluated that a coating layer containing calcium oxide is formed on the particle surface. For the measurement of calcium concentration, for example, spark discharge emission analysis (OES), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), electron beam microanalysis (EPMA), Auger electron spectroscopy (AES) Rutherford backscatter analysis (RBS) or the like is used.

Specifically, the calcium concentration on the particle surface is preferably at least 2 times the calcium concentration inside the particle by mass ratio, more preferably about 3 to 1000 times, and more preferably 5 to 800 times. More preferably, it is about. When the difference in calcium concentration is within the above range, excellent flame retardancy and excellent mechanical properties after molding can be achieved at a high level.
The particle surface refers to a region from the particle surface to a depth of 100 nm.

  From the above, it is a magnesium-based alloy powder composed of a magnesium-based alloy containing 0.2% by mass or more and 5% by mass or less of calcium, the particle surface being covered with a coating layer containing calcium oxide, The magnesium-based alloy powder of the present invention that satisfies the condition that the average particle size is 100 μm or more and 1500 μm or less and the average value of hardness variation index is 0.3 or less is formed while maintaining excellent flame retardancy. It has a hardness distribution suitable for. For this reason, by using the magnesium-based alloy powder of the present invention, it is possible to obtain a molded body (magnesium-based alloy molded body) that is excellent in compaction during molding and excellent in mechanical properties.

  Moreover, it is preferable that a coating layer uses a mixture of calcium oxide and magnesium oxide as a main material. By providing such a coating layer, not only the effect of achieving both the flame retardance due to calcium oxide and the mechanical properties during molding, but also the effect of shielding oxygen by magnesium oxide is imparted. As a result, magnesium is less likely to be oxidized inside the particles of the magnesium-based alloy powder. Therefore, an increase in oxygen content in the entire particle can be suppressed, and a decrease in mechanical properties of the finally obtained molded body can be suppressed.

Further, when magnesium oxide is contained in the coating layer, a common element exists between the coating layer and the inside of the particle, so that the adhesion between the inside of the particle and the coating layer is improved. As a result, the coating layer becomes difficult to peel off, and the effect of suppressing the oxidation inside the particles is more stably maintained.
The average thickness of the coating layer is not particularly limited, but is preferably about 1% to 20% of the average particle diameter of the magnesium-based alloy powder, more preferably about 2% to 15%. It is more preferable that the ratio is about 12% or more and 12% or less. If the average thickness of the coating layer is within the above range, the coating layer can provide flame retardancy and oxygen shielding properties, while ensuring the compactness during molding inside the particles, and finally obtained. The mechanical properties of the molded product can be improved.

  Further, when the magnesium-based alloy powder is subjected to crystal structure analysis by X-ray diffraction, in the obtained X-ray diffraction spectrum, the strongest peak intensity derived from magnesium oxide is the strongest peak intensity derived from magnesium alone. It is preferably 5% or more and 45% or less, and more preferably 7% or more and 40% or less. Thus, by containing a certain amount of magnesium oxide with respect to the magnesium simple substance, the magnesium-based alloy powder can further improve the mechanical properties during molding while maintaining flame retardancy. The reason why such an effect is obtained is considered to be that the above-described effect of suppressing the oxidation inside the particles becomes more remarkable by optimizing the content of magnesium oxide. In addition, the mechanical properties of the finally obtained molded body are further enhanced from the viewpoint that the compactness during molding inside the particles can be further enhanced.

  Further, as described above, the magnesium-based alloy may contain other components in addition to magnesium and calcium, but preferably contains 2.5% by mass or more and 12% by mass or less of aluminum. By adding this amount of aluminum, calcium and aluminum precipitate an intermetallic compound. Since this intermetallic compound has a high melting point, the flame retardancy of the magnesium-based alloy powder can be particularly enhanced, and the heat resistance of the compact can be enhanced. In addition, since the intermetallic compound has a low solid solubility in the parent phase, there is a possibility that mechanical properties such as ductility of the molded body are deteriorated. Therefore, when adding aluminum, by setting the amount of addition within the above range, the flame retardancy of the magnesium-based alloy powder and the heat resistance of the compact are sufficiently reduced while minimizing the deterioration of the mechanical properties. Can be secured.

The aluminum content is more preferably 3% by mass or more and 11% by mass or less, and further preferably 4% by mass or more and 10% by mass or less.
Further, when the magnesium-based alloy powder is subjected to crystal structure analysis by X-ray diffraction, the intensity of the strongest peak derived from an intermetallic compound composed of calcium and aluminum in the obtained X-ray diffraction spectrum is magnesium alone. It is preferably 3% to 40%, more preferably 4% to 35%, and still more preferably 5% to 30% of the intensity of the strongest peak derived from. As described above, when the intermetallic compound is contained in a certain amount with respect to the magnesium simple substance, the magnesium-based alloy powder can further improve the mechanical characteristics at the time of molding while maintaining the flame retardancy. The reason why such an effect can be obtained is not clear, but one is that the intermetallic compound has a pinning effect (an effect of suppressing the movement of dislocation caused by deformation), thereby improving the mechanical properties. Can be mentioned.
Incidentally, as an intermetallic compound, for example, AlCa, _Al 2 Ca, and the like.

  The presence of the intermetallic compound can also be confirmed, for example, by observing the particle cross section of the magnesium-based alloy powder with a scanning electron microscope or the like. Specifically, it is observed that particles composed of intermetallic compounds are dispersed in a magnesium matrix, and the average particle size of the particles is preferably about 50 nm to 500 nm, preferably about 100 nm to 300 nm. More preferably.

  In the X-ray diffraction spectrum obtained for the magnesium-based alloy powder, the intensity of the strongest peak derived from magnesium oxide is smaller than the intensity of the strongest peak derived from an intermetallic compound composed of calcium and aluminum. preferable. Specifically, when the intensity of the former peak is 1, the intensity of the latter peak is preferably 0.01 or more and 0.5 or less, and more preferably 0.02 or more and 0.4 or less. . Thereby, the mechanical characteristics at the time of shaping | molding become especially high with the effect of the oxidation suppression inside a particle | grains by magnesium oxide, and the improvement of compaction, and the pinning effect by an intermetallic compound.

  The average dendrite arm spacing (DAS) of the crystal structure in the magnesium-based alloy powder particles is preferably 0.05 μm or more and 5 μm or less, more preferably 0.3 μm or more and 4 μm or less, and even more preferably 0.5 μm. The thickness is 3.5 μm or less. When the average DAS of the crystal structure is within the above range, a molded article having particularly excellent mechanical properties can be obtained.

  That is, when the average DAS of the crystal structure is below the lower limit, the volume occupied by the grain boundary is too large, so the volume occupied by the magnesium-based alloy is relatively small, and depending on the composition of the magnesium-based alloy, The original mechanical properties of the alloy may be impaired. On the other hand, when the average DAS of the crystal structure exceeds the upper limit, dislocation movement (slip deformation) or the like is likely to occur in the crystal structure, and depending on the composition of the magnesium base alloy, the mechanical properties inherent to the magnesium base alloy may still be present. There is a risk of damage.

  The DAS can be measured according to the procedure described in, for example, “Dendrite Arm Spacing Measurement Procedure” (Casting and Solidification Committee of the Light Metal Society), and 100 or more randomly selected values can be calculated for the average value. Particles are used. And arm spacing is calculated | required about the dendrite observed in the center part of a particle | grain cross section, and what averaged this is made into average DAS.

Similarly, when the DAS is measured at 10 points on the cross section of the particle, the difference between the maximum value and the minimum value is preferably 30% or less of this maximum value, and is 20% or less. Is more preferable, and it is further more preferable that it is 15% or less. Thereby, a molded body having a uniform crystal structure and particularly high mechanical properties can be obtained.
Such a magnesium-based alloy powder of the present invention may be produced by any method, and as a production method, an atomizing method (for example, a water atomizing method, a gas atomizing method, a high-speed rotating water stream atomizing method, etc.), reduction Various pulverization methods such as a method, a carbonyl method and a pulverization method can be mentioned. Among these, what was manufactured by the atomizing method is preferable, and what was manufactured by the high-speed rotation water stream atomizing method is more preferable. Such a magnesium-based alloy powder has a relatively large particle size and easily has a uniform particle size as compared with those produced by other powdering methods. For this reason, the fluidity | liquidity of powder becomes high and it becomes the thing excellent also in the fillability at the time of shaping | molding. Furthermore, the amount of magnesium oxide in the entire powder can be kept small. Further, since the raw material in a molten state can be rapidly cooled in a very short time, the refinement of the crystal structure in each particle becomes remarkable. As a result, a powder capable of producing a molded body having excellent mechanical properties can be obtained.

  Among these, in the high-speed rotating water flow atomization method, the coolant is jetted and supplied along the inner peripheral surface of the cooling cylinder and swirled along the inner peripheral surface of the cooling cylinder, so that the cooling liquid layer is formed on the inner peripheral surface. Form. On the other hand, the raw material of the magnesium-based alloy is melted, and the obtained molten metal (molten metal) is naturally dropped, and a liquid or gas jet is sprayed on the molten metal. As a result, the molten metal is scattered and taken into the coolant layer. As a result, the molten metal that has been dispersed and pulverized is rapidly cooled and solidified to obtain a magnesium-based alloy powder.

FIG. 1 is a longitudinal sectional view showing an example of an apparatus for producing a magnesium-based alloy powder by a high-speed rotating water stream atomization method.
A powder production apparatus 100 shown in FIG. 1 is used to supply a molten metal 25 to a cooling cylinder 1 for forming a cooling liquid layer 9 on an inner peripheral surface and a space 23 inside the cooling liquid layer 9. The crucible 15 which is a supply container, the pump 7 which is a means for supplying the cooling liquid to the cooling cylinder 1, the trickling molten metal 25 which has flowed down is divided into droplets and supplied to the cooling liquid layer 9. And a jet nozzle 24 for ejecting a liquid jet 26 for the purpose.

  The cooling cylinder 1 has a cylindrical shape, and is installed such that the cylinder axis is inclined along the vertical direction or inclined at an angle of 30 ° C. or less with respect to the vertical direction. In addition, FIG. 1 has shown the state inclined with respect to the perpendicular direction. The upper end opening of the cooling cylinder 1 is closed by the lid 2, and an opening 3 for supplying the molten metal 25 flowing down to the space 23 of the cooling cylinder 1 is formed in the lid 2. Yes.

  In addition, a cooling liquid jet pipe 4 configured so that the cooling liquid can be jetted and supplied in a tangential direction of the inner peripheral surface of the cooling cylinder 1 is provided on the upper portion of the cooling cylinder 1. A plurality of discharge ports 5 of the coolant jet pipe 4 are provided at equal intervals along the circumferential direction of the cooling cylinder 1. Further, the pipe axis direction of the coolant jet pipe 4 is set to be inclined downward by about 0 ° or more and 20 ° or less with respect to a plane orthogonal to the axis of the cooling cylinder 1.

  The coolant jet pipe 4 is connected to a tank 8 via a pump 7, and the coolant in the tank 8 sucked up by the pump 7 is jetted into the cooling cylinder 1 via the coolant jet pipe 4. Supplied. Thereby, the cooling liquid gradually flows down while rotating along the inner peripheral surface of the cooling cylinder 1, and accordingly, a cooling liquid layer (cooling liquid layer 9) along the inner peripheral surface is formed. In addition, you may make it interpose a cooler in the tank 8 or the middle of a circulation flow path as needed. As the cooling liquid, oil (silicone oil or the like) is used in addition to water, and various additives may be further added. Moreover, the oxidation accompanying cooling of the powder to be manufactured can be suppressed by removing the dissolved oxygen in the coolant in advance.

In addition, a layer thickness adjusting ring 10 that adjusts the thickness of the coolant layer 9 is detachably provided at the lower portion of the inner peripheral surface of the cooling cylinder 1. By providing the layer thickness adjusting ring 10, the flow rate of the cooling liquid can be suppressed, the thickness of the cooling liquid layer 9 can be secured, and the layer thickness can be made uniform.
A cylindrical liquid draining net 11 is connected to the lower portion of the cooling cylinder 1, and a funnel-shaped powder recovery container 12 is provided below the liquid draining net 11. ing. A cooling liquid recovery cover 13 is provided around the liquid cutting net body 11 so as to cover the liquid cutting net body 11, and a drain port 14 formed at the bottom of the cooling liquid recovery cover 13 is connected via a pipe. Connected to the tank 8.

The space 23 is provided with a jet nozzle 24 for ejecting air, inert gas, or the like. The jet nozzle 24 is attached to the tip of a gas supply pipe 27 inserted through the opening 3 of the lid body 2, and has a jet outlet formed of a trickle-shaped molten metal 25, a coolant layer 9, and the like. It is arranged to be oriented.
In order to manufacture the magnesium-based alloy powder in such a powder manufacturing apparatus 100, first, the pump 7 is operated to form the cooling liquid layer 9 on the inner peripheral surface of the cooling cylinder 1, and then in the crucible 15 Molten metal 25 is caused to flow down into space 23. When the liquid jet 26 is sprayed on the molten metal 25, the molten metal 25 is scattered and the pulverized molten metal 25 is entrained in the coolant layer 9. As a result, the pulverized molten metal 25 is cooled and solidified to obtain a magnesium-based alloy powder.

In the high-speed rotating water atomization method, the coolant layer 9 under certain conditions can be stably maintained by continuously supplying the coolant, so the particle size, aspect ratio, crystal structure, etc. of the manufactured magnesium-based alloy powder Is also stable. As a result, the above-described magnesium-based alloy powder of the present invention can be produced particularly efficiently.
The particle size, aspect ratio, apparent density, DAS of crystal structure, micro Vickers hardness, circularity, etc. of the magnesium-based alloy powder can be controlled by adjusting the production conditions. For example, by increasing the cooling rate, the DAS of the crystal structure can be reduced or the micro Vickers hardness can be increased even with a larger particle size, and the dispersion of DAS in one particle or the micro Vickers hardness can be increased. The variation of can also be reduced. Moreover, the particle size of the magnesium-based alloy powder can be further reduced by increasing the pressure at the time of jetting the coolant.

  More specifically, it is preferable to set the pressure at the time of ejection of the coolant supplied to the cooling cylinder 1 to about 50 MPa to 200 MPa and the liquid temperature to about −10 ° C. to 40 ° C. Thereby, the flow velocity of the coolant layer 9 is optimized, and the finely divided molten metal 25 can be cooled appropriately and evenly. That is, when the pressure of the cooling liquid is lower than the lower limit value or the liquid temperature is higher than the upper limit value, the cooling capacity is insufficient, and the crystal structure may be enlarged in particles having a large particle size. On the other hand, when the pressure of the cooling liquid exceeds the upper limit, the finely divided molten metal 25 is stretched by the flow of the cooling liquid, and the particle shape may be deformed. In addition, when the liquid temperature is lower than the lower limit, it is difficult to maintain the liquid temperature, and the liquid temperature may increase with time, so the characteristics of the manufactured magnesium-based alloy powder may vary. There is.

Further, when melting the raw material of the magnesium-based alloy, the melting temperature is preferably set to about Tm + 20 ° C. or more and Tm + 200 ° C. or less, and set to about Tm + 50 ° C. or more and Tm + 150 ° C. or less with respect to the melting point Tm of the magnesium-based alloy. It is preferable. Thereby, when the molten metal 25 is pulverized with the liquid jet 26, variation in characteristics among the particles is suppressed to be particularly small, and particles whose particle size, aspect ratio, apparent density, hardness, and the like are in the above-described range are reduced. can get.
In addition, the particle size of the magnesium-based alloy powder can be controlled by adjusting the ejection pressure of the liquid jet 26 ejected from the jet nozzle 24. For example, by increasing the jet pressure of the liquid jet 26, the particle size of the magnesium-based alloy powder can be further reduced.

  The jet nozzle 24 may be provided if necessary and may be omitted. In this case, the cooling cylinder 1 is installed so that the axis is inclined with respect to the vertical direction, and the trickle molten metal 25 is caused to flow directly to the cooling liquid layer 9. As a result, the molten metal 25 is pulverized and cooled and solidified by the flow of the coolant layer 9, and a magnesium-based alloy powder having a relatively large particle size is obtained. In addition, this method is particularly useful in terms of making the crystal structure finer and uniform because the cooling width per unit time becomes very large.

[Magnesium-based alloy compact]
The magnesium-based alloy molded body of the present invention is obtained by subjecting the magnesium-based alloy powder of the present invention to a hot press sintering method, a hot isostatic sintering method (HIP method), a pulsed current pressure sintering method, an electric furnace or a gas furnace. It is manufactured by molding and firing by various sintering methods such as atmospheric pressure sintering method or the like, or hot extrusion.

  In hot pressing, a magnesium-based alloy powder is filled in a mold and heated while being pressurized. Thereby, a magnesium-based alloy molded body (sintered body) is obtained. At this time, pressurization and heating in a reduced-pressure atmosphere and an inert gas atmosphere suppress the oxidation of the magnesium-based alloy, and a material having a low magnesium oxide content can be obtained. The pressure during decompression is not particularly limited, but is about 95 kPa or less, preferably about 0.1 kPa or more and 90 kPa or less.

The molding temperature in the hot press is appropriately set according to the composition and particle size of the magnesium-based alloy powder, the shape of the molded body, etc., but is preferably set to, for example, 100 ° C. or higher and 800 ° C. or lower, and 200 ° C. or higher and 700 ° C. or lower. It is more preferable that the temperature is set to be equal to or lower.
Also, the molding pressure in the hot press is appropriately set according to the composition and particle size of the magnesium-based alloy powder, the shape of the molded body, etc., but is preferably set to 300 MPa to 1500 MPa, for example, 400 MPa to 1100 MPa. More preferably, it is set to.

  On the other hand, in hot extrusion, a powder or a green compact (billet) is extruded while being heated. Thereby, a magnesium base alloy compact is obtained. Since the magnesium-based alloy molded body manufactured by such a method is easy to achieve uniformity during manufacturing, a crystal structure having a uniform size is distributed as a whole. This is because a shear stress is applied to the powder along with the hot extrusion process, so that even if a relatively large crystal structure is included, the crystal structure can be further refined. As a result, the entire crystal structure can be made uniform in size. Further, it is useful in that it can be efficiently produced even if it is a complex shape or a hollow shaped body only by appropriately selecting the shape of the die.

The extrusion temperature in the hot extrusion is appropriately set according to the composition and particle size of the magnesium-based alloy powder, the shape of the molded body, etc., but is preferably set to, for example, 250 ° C. or more and 500 ° C. or less, and 300 ° C. or more. More preferably, it is set to 450 ° C. or lower.
Further, the extrusion pressure in the hot extrusion is appropriately set according to the composition and particle size of the magnesium-based alloy powder, the shape of the molded body, etc., but is preferably set to 300 MPa to 1000 MPa, for example, 400 MPa to 800 MPa. More preferably, it is set as follows.

Such a magnesium-based alloy molded body may be used for any purpose. For example, in addition to parts for transport equipment such as automobile parts, railway vehicle parts, marine parts, aircraft parts, etc. It is used for various structures such as parts for electronic devices such as parts for personal computers and parts for mobile phone terminals, ornaments, artificial bones, and artificial tooth roots.
As described above, the magnesium-based alloy powder and the magnesium-based alloy compact of the present invention have been described based on preferred embodiments, but the present invention is not limited to this. For example, an arbitrary film may be formed on the particle surface of the powder according to the above-described embodiment.

Next, specific examples of the present invention will be described.
1. Manufacture of magnesium-based alloy compact (Sample No. 1)
[1] First, the raw material was melted in a high-frequency induction furnace and pulverized by a high-speed rotating water stream atomization method to obtain a magnesium-based alloy powder. The alloy composition of the obtained magnesium-based alloy powder is shown below.
Al: 5.699 mass%, Zn: 0.057 mass%, Mn: 0.271 mass%, Fe: 0.002 mass%, Si: 0.025 mass%, Cu: 0.005 mass%, Ni: 0.002 mass%, Ca: 1.880 mass%, Mg: remainder The setting conditions of a high-speed rotation water flow atomizer (powder production apparatus) are shown below.
・ Coolant jet pressure: 100 MPa
Coolant temperature: 30 ° C
-Molten metal temperature: Tm + 20 ° C

[2] Next, a portion of the obtained magnesium-based alloy powder was pressure-formed (hot pressed) into a cylindrical shape to obtain a green compact (billet). At this time, the molding temperature was 300 ° C., the molding pressure was 350 MPa, and the molding atmosphere was a reduced pressure atmosphere.
[3] Next, hot extrusion was performed using the obtained green compact to obtain a magnesium-based alloy compact. At this time, the extrusion temperature was 300 ° C. and the extrusion pressure was 700 MPa.

  [4] Here, the obtained magnesium-based alloy powder was imaged with a scanning electron microscope. Then, the diameter of a circle having the same area as that of the captured particle image was calculated. Thus, the diameter of the circle was calculated for 100 particles, and this was averaged to obtain the average particle size of the magnesium-based alloy powder. In addition, the maximum value among the 100 particle size data was defined as the maximum particle size.

[5] Further, the aspect ratio calculated by the minor axis / major axis was obtained for the captured particle image. Then, the aspect ratio was calculated for 100 particles, and this was averaged to obtain the average aspect ratio of the magnesium-based alloy powder.
[6] Further, the apparent density of the obtained magnesium-based alloy powder was measured according to the method defined in JIS Z 2504.

  [7] Further, the particles of the obtained magnesium-based alloy powder were cut, and the hardness was measured with a micro Vickers hardness meter at 10 points on the cut surface. Then, the maximum value and the minimum value of the ten measured values were obtained, the difference was calculated, and the ratio of the difference to the maximum value (hardness variation index) was calculated. This was performed for 100 particles, and the average value was obtained. During the measurement, the load applied to the indenter was 25 gf (0.245 N).

[8] Further, with respect to the obtained magnesium-based alloy powder, the cross section of the particle was observed with an electron microscope, and the arm spacing (DAS) of the dendrite observed in the central portion was obtained. Then, arm spacing was calculated for 100 particles, and this was averaged to obtain the average DAS of the magnesium-based alloy powder. For the measurement of DAS, the procedure described in “Dendrite Arm Spacing Measurement Procedure” (Casting and Solidification Committee of the Light Metal Society) was applied mutatis mutandis.
Table 1 shows the average particle diameter, average aspect ratio, apparent density, average value of hardness variation index, and average DAS measured and calculated as described above.

(Sample Nos. 2-4, 9-11)
Except for changing the characteristics of the magnesium-based alloy powder as shown in Table 1, sample No. In the same manner as in No. 1, a magnesium-based alloy compact was obtained.
In addition, the setting conditions of the high-speed rotating water stream atomizer were changed as follows. And the powder from which an average particle diameter differs was manufactured by changing the ejection pressure of the liquid jet ejected from a jet nozzle for every sample.
・ Coolant jet pressure: 150 MPa
・ Cooling liquid temperature: 10 ℃
-Temperature of molten metal: Tm + 100 ° C

(Sample No. 5-8)
Except for changing the characteristics of the magnesium-based alloy powder as shown in Table 1, sample No. In the same manner as in No. 1, a magnesium-based alloy compact was obtained.
In addition, the setting conditions of the high-speed rotating water stream atomizer were changed as follows. And the powder from which an average particle diameter differs was manufactured by changing the jet pressure of a cooling fluid within the following range for every sample. Moreover, the jet nozzle was omitted in the high-speed rotating water stream atomizer.
・ Cooling liquid jet pressure: 120 MPa to 200 MPa ・ Cooling liquid temperature: 20 ° C.
-Molten metal temperature: Tm + 150 ° C

(Sample Nos. 12, 13, 14, 15)
Sample No. was changed except that the composition of the magnesium-based alloy was changed as shown below. Magnesium-based alloy compacts were obtained in the same manner as in 1, 4, 5, and 8.
Al: 6.161 mass%, Zn: 0.074 mass%, Mn: 0.228 mass%, Fe: 0.006 mass%, Si: 0.003 mass%, Cu: 0.001 mass%, Ni: 0.002 mass%, Ca: 2.020 mass%, Mg: balance

(Sample No. 16, 17)
Sample No. was changed except that the composition of the magnesium-based alloy was changed as shown below. Magnesium-based alloy compacts were obtained in the same manner as in Examples 4 and 5.
Al: 6.810 mass%, Zn: 0.964 mass%, Mn: 0.011 mass%, Fe: 0.008 mass%, Ca: 1.031 mass%, La: 2.961 mass%, Mg: The rest

(Sample No. 18)
Instead of hot pressing and hot working, sample no. In the same manner as in No. 1, a magnesium-based alloy compact was obtained.
In Table 1, each sample No. Among the magnesium-based alloy powder and the magnesium-based alloy molded body, those corresponding to the present invention are shown as “Examples” and those not corresponding to the present invention are shown as “Comparative Examples”.

2. 2. Evaluation of magnesium-based alloy powder 2.1 Element distribution of magnesium-based alloy powder Elemental analysis was performed on the cross section of the magnesium-based alloy powder by electron microanalysis. As a result, segregation of calcium was observed on the surface of each particle. Therefore, chemical bonding state analysis was performed on the surface of each particle by X-ray photoelectron spectroscopy. As a result, it was recognized that most of the calcium on the surface was present in the form of calcium oxide. It was also observed that magnesium oxide was accumulated on the surface in addition to calcium oxide.

Moreover, the magnification of the calcium concentration on the particle surface with respect to the calcium concentration inside the particle measured by electron beam microanalysis was calculated. The calculation results are shown in Table 1.
Furthermore, the average thickness of the coating layer was calculated based on the observation image of the cross section of the magnesium-based alloy powder by an electron microscope and the distribution state of calcium. And the ratio of the average thickness of the coating layer with respect to an average particle diameter was computed. The calculation results are shown in Table 1.

2.2 Crystal structure analysis of magnesium-based alloy powder The magnesium-based alloy powder was analyzed for crystal structure by X-ray diffraction (XRD). In the obtained X-ray diffraction spectrum, the ratio of the intensity of the strongest peak derived from magnesium oxide (MgO) to the intensity of the strongest peak derived from magnesium alone was calculated. Similarly, in the obtained X-ray diffraction spectrum, the ratio of the intensity of the strongest peak derived from the intermetallic compound of aluminum and calcium to the intensity of the strongest peak derived from magnesium alone was calculated. Each calculation result is shown in Table 1.

3. 3. Evaluation of Magnesium-Based Alloy Molded Body 3.1 Tensile strength of magnesium-based alloy molded body With respect to the magnesium-based alloy molded body, the tensile strength was measured according to the method specified in JIS Z 2241. And sample no. The relative values when the tensile strength measured for 18 magnesium-based alloy compacts is taken as 1 are shown in Table 1.

3.2 0.2% yield strength of magnesium-based alloy compact The 0.2% proof stress was measured in accordance with the method prescribed in JIS Z 2241. And sample no. Table 1 shows the relative values when the 0.2% proof stress measured for 18 magnesium-based alloy compacts is taken as 1.

3.3 Elongation of magnesium-based alloy compact With respect to the magnesium-based alloy molded body, the elongation (%) was measured according to the method specified in JIS Z 2241. And sample no. The relative values when the elongation (%) measured for 18 magnesium-based alloy compacts is set to 1 are shown in Table 1.
The evaluation results are shown in Table 1.

As is apparent from Table 1, the magnesium-based alloy molded body corresponding to the examples is excellent in the balance of mechanical properties such as tensile strength, 0.2% proof stress, and elongation, and is useful as a structure. It was recognized that
On the other hand, it was confirmed that the magnesium-based alloy molded body corresponding to the comparative example has particularly low mechanical properties as compared with the one corresponding to the example.
Moreover, when the flame retardance was evaluated about the magnesium-based alloy molded body corresponding to each Example, the ignition temperature in air was as high as 600 ° C. or more, and the flame retardancy was sufficient.

  DESCRIPTION OF SYMBOLS 1 ... Cooling cylinder 2 ... Lid 3 ... Opening 4 ... Coolant jet pipe 5 ... Discharge port 7 ... Pump 8 ... Tank 9 ... Coolant layer 10 ... Layer thickness adjustment Ring 11 ... Network for draining 12 ... Powder recovery container 13 ... Coolant recovery cover 14 ... Drain port 15 ... Crucible 23 ... Space 24 ... Jet nozzle 25 ... Molten metal 26 ... Liquid jet 27 …… Gas supply pipe 100 …… Powder production equipment

Claims (8)

It is composed of a magnesium-based alloy containing 0.2 mass% or more and 5 mass% or less calcium,
The average particle size is 100 μm or more and 1500 μm or less,
The average value of the hardness variation index, which is a value obtained by dividing the difference between the maximum value and the minimum value of the micro Vickers hardness measured at 10 points of the particle cross section by the maximum value, is 0.3 or less,
A magnesium-based alloy powder characterized in that the particle surface is covered with a coating layer containing calcium oxide.   In the X-ray diffraction spectrum of the magnesium-based alloy powder, the intensity of the strongest peak derived from an intermetallic compound composed of calcium and aluminum is 3% to 40% of the intensity of the strongest peak derived from magnesium. The magnesium-based alloy powder according to claim 1.   The magnesium-based alloy powder according to claim 1, wherein the coating layer is mainly composed of a mixture of calcium oxide and magnesium oxide.   The magnesium-based alloy powder according to any one of claims 1 to 3, wherein the magnesium-based alloy further contains 2.5 mass% or more and 12 mass% or less of aluminum.   The magnesium-based alloy powder according to any one of claims 1 to 4, wherein an average dendrite arm spacing (DAS) of the crystal structure is 0.05 µm or more and 5 µm or less.   The magnesium-based alloy powder according to any one of claims 1 to 5, wherein the magnesium-based alloy powder is produced by a high-speed rotating water atomization method.   A magnesium-based alloy formed article manufactured using the magnesium-based alloy powder according to any one of claims 1 to 6.   The magnesium-based alloy molded body according to claim 7, wherein the magnesium-based alloy powder is manufactured through a process of subjecting the magnesium-based alloy powder to hot extrusion.

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