JP7266269B2 - Mg-based sintered composite material, manufacturing method thereof, and sliding member - Google Patents

Description

Application of Article 30, paragraph 2 of the Patent Act ▲1 ▼ Announced on page 199 of the Japan Institute of Metals and Materials 2017 (161st) Fall Conference Summary ▲2 ▼ The Japan Institute of Metals and Materials 2017 (161st) Autumn Conference ▲3 ▼Presented on pages 297-298 of the 133rd Fall Meeting of the Japan Institute of Light Metal ▲4▼ Presented at the 133rd Fall Meeting of the Japan Institute of Light Metal

TECHNICAL FIELD The present invention relates to a Mg-based sintered composite material, a method for producing the same, and a sliding member.

Magnesium (Mg) has abundant underground reserves and is the lightest metal material in practical use. On the other hand, when used as a member, contact with other parts is inevitable, and development of Mg and Mg alloys with excellent strength and friction and wear properties is required. In general, increasing the strength of a metal material is an effective means of refining the grain size, and the same effect is exhibited for Mg and Mg alloys. However, it is known that grain refinement of Mg and Mg alloys is not effective as means for improving friction and wear characteristics (Non-Patent Document 1). Due to the large grain boundary diffusion coefficient of Mg, grain boundary sliding occurs easily, so as the grain size becomes smaller, the grain boundary volume ratio increases, grain boundary sliding is promoted, and work softening occurs during friction wear. break out. Therefore, in order to further improve the friction and wear properties of Mg and Mg alloys, it is preferable to coarsen the crystal grains of the parent phase, but this poses a problem of deterioration in strength properties.

In addition to refining the crystal grain size, particle dispersion in the matrix phase is often used to increase the strength of the material. Above all, in the case of metal materials, it is effective to increase the strength by dispersing intermetallic compounds precipitated or crystallized from the matrix phase. Particle dispersion also has the effect of suppressing grain boundary sliding. The inventors of the present invention have disclosed in Patent Document 1 an Mg alloy in which intermetallic compounds that are spherical or do not have sharp angles are dispersed in the Mg matrix phase and that have excellent frictional properties. Dispersing the intermetallic compound in the Mg matrix is an effective means for improving the strength. The phase size is coarse, and further enhancement of strength is desired.

In the case of metallic materials, in addition to dispersing precipitated or crystallized intermetallic compounds, particles made of substances or materials that do not solidly dissolve in metals (e.g., graphite, ceramics, etc.) are dispersed in the matrix. This is an effective technique for improving strength. However, since Mg has extremely poor wettability with additive particles for the purpose of forming a composite, a composite material cannot be created by the casting method. Therefore, as disclosed in Patent Documents 2 and 3, the Mg powder and the additive powder are solidified using a mechanical alloying method, a cyclic shear strain imparting method that requires several tens of strain imparting processes, or the like. , Mg-based sintered composite materials are created, but both methods are complicated and require a large number of work processes, which inevitably increases the material cost.

On the other hand, it is known to modify the surface layer of the Mg alloy in order to maintain the strength characteristics of the material itself and improve the friction and wear characteristics. In Patent Document 4, a surface modification structure is formed on the surface of an Mg alloy by anodizing treatment, and the surface modification structure is impregnated with molybdenum disulfide, which is a solid lubricant, to improve the friction and wear characteristics of Mg. It is disclosed as an effective method for It is possible to maintain the strength characteristics because only the surface layer is modified without depending on the crystal grain size of the Mg matrix. However, since it is necessary to perform an anodizing treatment as an additional process when using the material, there is a concern that the cost will rise.

The present inventors focused on a simpler production method, mixed SiC powder and Mg powder, and produced a Mg-based sintered composite material by warm and hot working. In these composite materials, the SiC particles are dispersed in the Mg matrix, and when subjected to frictional wear while maintaining excellent strength characteristics, the SiC particles reaggregate in the portion that has received this frictional wear and self-reaggregate. It has been confirmed to exhibit film-forming ability. On the other hand, when aiming for further property modification and versatility of Mg- based sintered composite materials, not only carbides such as SiC but also other compounds should be used as particles to be dispersed in the Mg matrix. should also be considered.

In the creation of metal matrix composites, the wettability between the metal matrix and the additive powder is extremely important. Regarding Mg- based sintered composite materials, when nitrides and oxides with different wettability from Mg in the matrix are used as additive powders, there are no cracks or cracks, and the additive powder is homogeneously formed without segregation in the Mg matrix. It has not been clear until now whether it is possible to create dispersed and sound Mg- based sintered composites. Of course, it goes without saying about its friction and wear characteristics.

JP 2008-240032 A JP 2008-75127 A WO 2003/27342 JP-A-2002-363679

Takashi Matsuoka et al. Materials 51 (2002) p1154.

The present invention has been made in view of the above circumstances. An object is to provide a moving member.

In order to solve the above problems, the Mg- based sintered composite material of the present invention is a particle-dispersed Mg- based sintered composite material, and has an average diameter of 0.05 μm or more in the metal structure of the Mg-based sintered composite material. When the oxide or nitride particles of are dispersed in the Mg matrix and are subjected to frictional wear, the friction coefficient of the portion subjected to this frictional wear is reduced in a short time, and the frictional wear is the ball-on-disk A dry friction wear test using a wear tester, wherein the short time is a test time from the start of the test to 180 seconds to 40 seconds, and the friction coefficient of the portion of the sliding surface that has undergone friction wear is The coefficient of friction at the start is reduced to less than 0.20 in the short time, the crystal grain size of the Mg matrix is 200 μm or less, and the oxide or nitride is MnO ₂ , Si ₃ N ₄ or It is characterized by being _SiO2 .
Further, the Mg- based sintered composite material of the present invention is a particle-dispersed Mg- based sintered composite material, and the metal structure of the Mg- based sintered composite material contains oxides or nitrides having an average diameter of 0.05 μm or more. When the particles are dispersed in the Mg matrix and are subjected to friction wear, the friction coefficient of the portion subjected to this friction wear decreases in a short time, and the friction wear is measured by dry friction using a ball-on-disk wear tester. In the wear test, the short time is a test time from the start of the test between 180 seconds and 400 seconds, and the friction coefficient of the portion of the sliding surface that has received frictional wear is reduced from the friction coefficient at the start. decreases to less than 0.20 in a short period of time, and the ratio of the average diameter of the oxide or nitride particles to the grain size of the Mg matrix is in the range of 1:4 to 1:10; The oxide or nitride is MnO ₂ , Si ₃ N ₄ or SiO ₂ .
Here, in the dry friction wear test using the ball-on-disk wear tester, the disk surface obtained by cutting the Mg-based extruded composite material of the Mg-based sintered composite material in the direction perpendicular to the extrusion direction was used as a measurement surface. Using a ball made of carbon chromium bearing steel (SUJ2) with a diameter of 4.7 mm, the distance from the disk center, that is, the radius of rotation of 1 mm, the additional load of 0.49 N, the rotation speed of 9.5 rpm, and the test time of 5000 seconds. , to carry out a dry friction wear test.
In this Mg- based sintered composite material, the ratio of the oxide or nitride particles to the crystal grain size of the Mg matrix is preferably in the range of 1:4 to 1:10.
The Mg- based sintered composite preferably has an oxide or nitride particle content of less than 65% by mass.

The sliding member of the present invention is a sliding member containing the Mg- based sintered composite material, has a sliding surface made of the Mg- based sintered composite material, and when the sliding surface is subjected to friction wear , the friction coefficient of the part subjected to this frictional wear is reduced in a short time, and the frictional wear is a dry frictional wear test using a ball-on-disk type wear tester, and the short time is the test from the start of the test. The time is between 180 seconds and 400 seconds, and the friction coefficient of the portion of the sliding surface that has received frictional wear is characterized by decreasing from the friction coefficient at the start to less than 0.20 during the short time. .

The method for producing a Mg- based sintered composite material of the present invention includes the steps of filling and enclosing a mixed powder containing Mg powder and oxide or nitride powder having an average diameter of 0.05 μm or more in a billet, and The billet filled and enclosed with the mixed powder is subjected to warm or hot strain imparting processing at a temperature of 50 ° C. or higher and 550 ° C. or lower with a cross-sectional reduction rate of 50% or more, and the oxide or nitride is MnO ₂ , _{Si3N4 or SiO2} .
In this method for producing a Mg- based sintered composite material, the content of the oxide or nitride powder in the mixed powder is less than 65% by mass with respect to the total amount of the Mg powder and the oxide or nitride powder. is preferred.
In the method for producing the Mg- based sintered composite material, the warm or hot strain imparting processing is preferably extrusion processing, forging processing, rolling processing, or drawing processing.

INDUSTRIAL APPLICABILITY According to the present invention, a Mg-based sintered composite material having excellent strength properties due to particle dispersion in a matrix phase and high friction and wear properties, a method for producing the same, and a sliding member are provided.

The figure which showed typically the example of the shape of the typical billet used for warm or hot strain imparting processing. (a) Appearance photograph and (b) cross-sectional photograph of the Mg-based extruded composite material in the example. 1 is a photograph of microstructures of Mg-based extruded composite materials of Examples 1 to 3 observed with an optical microscope. (a) Mg—Si ₃ N ₄ (Sample No. 1), (b) Mg—SiO ₂ (Sample No. 3), (c) Mg—MnO ₂ (Sample No. 5). 4 is a photograph of the microstructure of the Mg- based sintered composite material (Sample No. 6) of Comparative Example 1 observed with an optical microscope. Sample No. 1, No. 3, No. 5 and No. 6 is a diagram showing the relationship between the coefficient of friction obtained by Ball-on-Disk test (dry friction wear test) of No. 6 and the sliding distance/test time. A two-dimensional cross-sectional image of the measurement surface after the friction wear test measured with a laser microscope.

Regarding the Mg-based sintered composite material of the present invention, its manufacturing method and sliding member, 1. Preparation of raw material powder;2. 2. billet preparation and mixed powder filling; 4. warm or hot strain imparting processing; The microstructure of the Mg-based sintered composite material and the sliding member will be described in order.

In the present invention, the average diameter of the raw material Mg powder, the average diameter of the oxide or nitride powder (hereinafter also referred to as the additive powder), and the additive powder particles in the metal structure of the Mg-based Mg- based sintered composite material and the crystal grain size (crystal grain size) of the Mg parent phase of the Mg- based sintered composite material can be measured by the following method.
<Average diameter of Mg powder and additive powder>
Using a laser diffraction/scattering particle size distribution analyzer, the median diameter (d ₅₀ , volume basis) based on the cumulative distribution is taken as the average diameter from the particle size distribution measured by the laser diffraction/scattering method.
<Average diameter of added powder particles>
The particle size of each particle of the additive powder is D = (L1 + L2) / 2 (where D is the particle size, L1 is the major diameter of the particle, and L2 is the minor diameter of the particle) from the image observed with an SEM or an optical microscope. ) is obtained using the formula
The average diameter is obtained by extracting 100 or more particles from an image observed with an SEM or an optical microscope, obtaining the particle diameter of each particle from the above formula, and calculating the average value.
<Crystal grain size of Mg matrix>
It is measured and calculated by the intercept method described in JIS H 0542:2008 "Method for testing grain size of rolled magnesium alloy sheet".

1. Preparation of Raw Material Powder The raw material powder used to manufacture the Mg- based sintered composite material of the present invention includes Mg powder and one or more oxide or nitride powders (additive powders).
The Mg powder consists of pure magnesium and has a powder particle density of 1.74. The average diameter of the Mg powder is preferably 1 μm or more. Since Mg is highly reactive with oxygen, when the Mg powder has an average diameter of 1 μm or more, heat is generated during mixing of the Mg powder and the additive powder, the risk of ignition can be reduced, and the safety of the work process can be improved. can be enhanced. The Mg powder may be ordinary powder or cutting powder generated from Mg bulk material by machining such as milling and lathe processing, and these are also broadly expressed as Mg powder in this specification. The upper limit of the average diameter of the Mg powder is not particularly limited, but considering the bonding and sintering of the Mg powders, it is preferably 1000 μm or less.

The oxide or nitride of the additive powder is not particularly limited, but examples thereof include Al ₂ O ₃ , CuO, MnO ₂ , Si ₃ N ₄ , SiO ₂ and Y ₂ O ₃ .
The average diameter of the additive powder is 0.05 μm or more, preferably 0.1 μm or more. When the average diameter is less than 0.05 μm, the surface area of the powder per unit volume increases, thereby increasing the proportion of oxygen that contacts the surface of the added powder particles. Therefore, the formation of an oxide made of Mg and incorporation of the oxide at the interface or boundary between the Mg powder and the additive powder suppresses a decrease in the coefficient of friction. The upper limit of the average diameter of the additive powder is not particularly limited, but is preferably 1000 μm or less, more preferably 100 μm or less, in consideration of increasing the strength of the base composite material.

The mass of the additive powder used, that is, the content of the additive powder in the Mg-based sintered composite material is preferably less than 65% by mass, more preferably less than 60% by mass, with respect to the total mass of the powder mixed with the Mg powder. More preferably less than 50% by mass. When the mass of the additive powder is 65% by mass or more with respect to the total mass of the mixed powder, the Mg matrix of the Mg- based sintered composite material after warm or hot strain imparting processing has an area ratio of 50 mass % or more of the added powder particles are dispersed, and it is difficult to call it a Mg base material.

A method of mixing the Mg powder and the additive powder and the state of the mixed powder will be described. The mixed powder is preferably in a state in which the Mg powder and the additive powder are not segregated with each other. In the mixed powder state, if any powder is segregated, when the Mg-based sintered composite material is subjected to abrasion friction, the part subjected to friction abrasion becomes a site of stress concentration, and the desired abrasion friction Properties can be difficult to obtain. In order to prevent the Mg powder and the additive powder from segregating with each other, it is preferable to mix the additive powder little by little, that is, so that the mass of the additive powder added at one time is 50 g or less. If it exceeds 50 g, mixing becomes difficult, and there is a concern that powder segregation will occur.

The container used for mixing is not particularly limited as long as it is a container that can mix the powder, such as a mortar. It is preferable that the Mg powder and the additive powder are mixed in the atmosphere using a mortar within 10 minutes from the viewpoint of simplification of the working process. Since the Mg powder easily reacts with oxygen, if the mixture is mixed for more than 10 minutes, oxides and the like are incorporated into the mixed powder, making it difficult to obtain a sound mixed powder. Of course, considering work safety, the mixed powder may be mixed in an argon atmosphere or in a vacuum using a stirrer as in the mechanical alloying method.

2. Billet Preparation and Mixed Powder Filling The mixed powder is filled into billets for warm or hot straining. An example of a typical billet shape is schematically shown in FIG. The material (raw material) used for the billet is preferably a metallic material such as Mg or Mg alloy that can be subjected to warm or hot strain imparting processing. Of course, metal materials other than Mg and Mg alloys, such as Al and Al alloys, may be used.

In FIG. 1, the billet size: S varies depending on the total cross-sectional reduction rate used during strain imparting processing, but the total cross-sectional reduction rate is preferably 50% or more, more preferably 60% or more, and still more preferably 70% or more. The size is such that it is possible to

The size of the void for filling the mixed powder: V is preferably 50% or more and 95% or less, preferably 50% or more, with respect to the billet total volume (corresponding to S × L in FIG. 1). It is more preferably 90% or less, and even more preferably 55% or more and 85% or less. Void size: When V is less than 50%, since the amount of mixed powder that can be filled is small, most of the processed material obtained after strain imparting processing becomes the material used for billets, and Mg-based sintering In some cases, it can no longer be called a composite material. Void size: If V exceeds 95%, the billet may crack during warm or hot strain imparting processing, and powder may leak to the outside.

As a method of putting the mixed powder into the billet, a green compact may be produced by a hand press and put into the billet. Of course, a container that can scoop the powder, such as a spoon, may be used to put the powder in the billet. At that time, all the operations are preferably carried out in an argon atmosphere or in a vacuum in order to suppress the reaction between the mixed powder and oxygen, but they may be carried out in the air for convenience in operation. In order to control and improve the filling rate of the mixed powder, it is preferable to apply pressure using a hand press after filling the billet with the mixed powder. However, in order to prevent mutual segregation of the Mg powder and the additive powder, it is undesirable to excessively tap the billet or apply vibration. After the mixed powder is filled in the billet, a lid made of the same material as the billet is used to seal the billet so that the mixed powder does not spill out.

The filling rate of the mixed powder is preferably 60% or more, more preferably 70% or more, and still more preferably 80% or more with respect to the void size: V. The lower the filling factor, the shorter the time required to fabricate the Mg-based sintered composites of the present invention. However, when the filling rate is less than 60%, the percentage of defects present in the composite material increases, making it difficult to use it as a structure or member.

3. Warm or hot strain imparting processing The purpose of warm or hot strain imparting processing is to bond and sinter the Mg powder into a sound Mg matrix, and to segregate the particles of the additive powder in the Mg matrix. It is to disperse evenly without The temperature of the warm or hot working is preferably 50°C or higher and 550°C or lower. If the processing temperature is less than 50° C., the Mg powders may not be bonded or sintered due to the low processing temperature. In addition, the metal material used for the billet may crack during processing, making it impossible to produce a sound composite material. If the processing temperature exceeds 550° C., the Mg powder is exposed to high temperatures, and there is concern about the danger of ignition due to local melting. In addition, it may cause a reduction in the life of the mold used in extrusion processing.

Strain imparting during warm or hot working is such that the total reduction in area is preferably 50% or more, more preferably 60% or more, and still more preferably 70% or more. If the total cross-sectional reduction rate is less than 50%, the strain is not sufficiently imparted, so the bonding between the powders is not promoted, and a sound composite material may not be produced. Typical warm or hot working methods include extrusion, forging, rolling, and drawing, but any plastic working method that can impart strain may be used.

4. Microstructure of Mg- Based Sintered Composite Material and Sliding Member The microstructure of the Mg- based sintered composite material of the present invention will be described. Mg powder is bonded and sintered during warm or hot strain imparting processing to form a Mg parent phase, but in order to maintain the strength characteristics of the Mg-based sintered composite material and obtain excellent friction and wear characteristics In addition, the size of the Mg parent phase, that is, the crystal grain size, is preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. When the crystal grain size of the Mg matrix is larger than 200 μm, the proportion of crystal grain boundaries in the composite material is small, so dislocation motion is not hindered by crystal grain boundaries, making it difficult to maintain strength characteristics.

Further, it is preferable that the additive powder of oxide or nitride is homogeneously dispersed in the Mg mother phase without segregating as particles of the oxide or nitride. The average diameter of the added powder particles in the metallographic structure of the Mg-based sintered composite material is 0.05 μm or more, preferably 0.1 μm or more. When the average particle size of the added powder particles is 0.05 μm or more, the Mg-based sintered composite material has high strength properties and excellent friction and wear properties.

Also, the ratio of the oxide or nitride particles to the crystal grain size of the Mg matrix is preferably in the range of 1:4 to 1:10, more preferably in the range of 1:4 to 1:9. is more preferable. When the ratio of the oxide or nitride particles to the crystal grain size of the Mg matrix is within the above range, the Mg- based sintered composite material has high strength properties and excellent friction and wear properties. .

Also, the oxide or nitride particles are preferably considered to have poor wettability with the Mg matrix. The wettability can be expressed as a function of the contact angle and the surface energy difference between the two substances, and the larger the surface energy difference, the larger the contact angle and the wettability tends to be poor. That is, the greater the difference in surface energy between the magnesium and the particles, the poorer the wettability. Therefore, during the friction and wear test, separation between the particles and the mother phase is likely to occur, and the effects of the present invention are likely to be obtained. For example, the surface energies of Si ₃ N ₄ and SiC are 2500 and 2300 dyn/cm, which are larger than magnesium (=560 dyn/cm). On the other hand, the surface energy of Al ₂ O ₃ is 1000 dyn/cm, which is close to that of magnesium (for example, Tsujiro Kohara, Interface of Composite Material and Wettability of Metal, Bulletin of Japan Institute of Metals, Vol. 14, No. 8). (1975), pp. 581-587; see Osami Kamigaito, Critical Dimension of Nanometer Composite Material Structure Seen from Surface Energy, Society of Powder and Powder Metallurgy, Vol.37, No.7 (1990)).

According to the present invention, a Mg- based sintered composite material can be produced in which oxide or nitride particles are homogeneously dispersed without segregating in the Mg matrix in the metallographic structure of the Mg-based sintered composite material . When the Mg- based sintered composite material of the present invention is subjected to frictional wear, the coefficient of friction of the portion subjected to this frictional wear decreases in a short period of time. That is, the Mg- based sintered composite material of the present invention shows a sudden decrease in friction coefficient after a certain period of time from the start of the test in a dry friction and wear test as described later, and after that, shows a constant friction coefficient. , exhibits excellent wear friction properties. The degree of decrease in the coefficient of friction may vary depending on the test conditions. The coefficient stabilizes at values less than 0.20. For example, in one embodiment of the present invention, when the oxide or nitride particles are Si ₃ N ₄ , the coefficient of friction at the start of the dry friction wear test is 0.4, and from 250 seconds after the start of the test, the friction rapidly increases. The coefficient begins to drop, and after 50 seconds (that is, after a test time of 300 seconds), the coefficient of friction shows 0.15.

Thus, according to the present invention, it is possible to provide a material having excellent friction and wear properties, and the Mg-based sintered composite material of the present invention can be suitably used as a sliding member. This sliding member contains the Mg- based sintered composite material of the present invention, has a sliding surface made of the Mg- based sintered composite material, and receives frictional wear when the sliding surface receives frictional wear. The coefficient of friction of the part where the As described above, the sliding member of the present invention can improve the properties of the sliding surface which is constantly subjected to frictional wear. Therefore, the sliding member of the present invention is suitable for mechanical parts, such as automobile parts and space equipment, in which the portion subjected to sliding is made of magnesium. It can be expected to be applied in various fields such as parts and aircraft parts.

In addition, Mg and Mg alloy wrought materials such as extruded materials originate from the crystal structure (hexagonal crystal) of Mg, and the bottom faces are aligned in the working direction. Therefore, there is a large difference in yield stress between tensile deformation and compressive deformation, and it is known that three-dimensional isotropic deformation is difficult. This yield anisotropy is caused by deformation stress occurring at low deformation stress. On the other hand, dispersing fine particles in the Mg matrix suppresses the formation of deformation twins, or increases the stress generated by deformation twins. Therefore, according to the present invention, it is possible to provide Mg and Mg alloys with reduced yield anisotropy and capable of three-dimensional isotropic deformation.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples.
<Example 1>
Commercially available pure Mg powder (powder diameter 180 μm) and commercially available Si ₃ N ₄ powder (powder diameter 2 to 3 μm) were used. The content of Si ₃ N ₄ particles dispersed in the Mg mother phase of the Mg-based sintered composite material was weighed to 10%, and the Mg powder and the Si ₃ N ₄ powder were dry-mixed in a mortar.

A commercially available Mg alloy (Mg-3Al-1Zn; AZ31) material having an outer diameter of 40 mm and a length of 70 mm was used to fill the mixed powder of Mg and Si ₃ N ₄ , and was machined to have an inner diameter of 20 mm and a depth of 20 mm. A hole with a depth of 55 mm was made to prepare an extruded billet having a cup shape as shown in FIG. After filling the mixed powder into an extruded billet, the billet was sealed with a Mg alloy (AZ31) material having a diameter of 20 mm and a thickness of 5 mm. At that time, in order to control the filling rate, the volume of the mixed powder was filled to 95% or 85% of the void; V (=volume of inner diameter 20 mm x depth 55 mm) in Fig. 1 . After that, it is held in a container set at 250 ° C. for 30 minutes or more, and then subjected to hot strain imparting processing by extrusion at an extrusion ratio of 16: 1, and an extruded material having a diameter of 10 mm and a length of 500 mm or more (hereinafter , referred to as Mg-based extruded composites).

<Example 2>
A _mixed powder was prepared by exactly the same procedure as in Example 1 except that the _Si3N4 powder was replaced with a commercially available _SiO2 powder, and the volume of the mixed powder was 95% or 85%. After filling the mixture, extrusion was performed in the same manner as in Example 1 to prepare a Mg-based extruded composite material.

<Example 3>
A _mixed powder was prepared by exactly the same procedure as in Example 1 except that the _Si3N4 powder was replaced with a commercially available _MnO2 powder, and the mixed powder was filled in an extruded billet so that the volume of the mixed powder was 95%. Thereafter, extrusion processing was performed in the same manner as in Example 1 to prepare an Mg-based extruded composite material.

<Comparative Example 1>
After filling the extruded billet so that the volume of the Mg powder becomes 90%, the extruded billet was extruded in the same manner as in Example 1 by exactly the same procedure as in Example 1 except that the additive powder was not used. An extruded material was produced.

Table 1 summarizes the conditions for creating each Mg-based extruded composite. FIG. 2 shows the external appearance (a) and cross-sectional photograph (b) of a typical Mg-based extruded composite material produced with a mixed powder filling rate of 95% in the extruded billet. From the photograph of the external appearance of FIG. 2(a), it can be confirmed that the surface of the Mg-based extruded composite material has no cracks or defects, and that a sound elongated material has been produced. Also, from the cross-sectional observation of FIG. 2(b), the outer peripheral portion of the Mg-based extruded composite material is made of Mg alloy (AZ31), and the inside is made of a composite material made of mixed powder of Mg powder and additive powder. I know there is.

Table 1 shows the filling factor of the Mg-based extruded composite measured by Archimedes' law. Sample No. 1 to No. The filling rates of the mixed powders of No. 5 were 95%, 86%, 96%, 85% and 93%, respectively. It is possible to adjust the filling rate of the mixed powder by controlling the filling of the extruded billet.

In order to determine the average crystal grain size (crystal grain size) of the Mg parent phase, microstructure observation of the produced Mg-based extruded composite material was performed using an optical microscope. FIG. 3 shows a typical microstructure example of each Mg-based extruded composite material. In FIGS. 3(a) to 3(c), the bright regions are Mg matrix and the dark regions are Si ₃ N ₄ grains, SiO ₂ grains, or MnO ₂ grains. Table 1 summarizes the average crystal grain size of the Mg parent phase of each Mg-based extruded composite material determined by the intercept method. The average crystal grain size of the Mg mother phase was about 13.0 μm to about 18.0 μm, regardless of the added powder size when mixed with the Mg powder and the filling rate of the mixed powder into the extruded billet. Also, the ratio of the added powder diameter to the average crystal grain diameter of the Mg matrix was in the range of 1:4.37 to 1:8.95.

FIG. 4 is an example of a typical microstructure of the Mg-based extruded material of Comparative Example 1 (Sample No. 6) observed using an optical microscope. The average crystal grain size of the Mg matrix obtained by the intercept method was 14.7 μm.

Using a Vickers hardness tester, the hardness of the cut surface of the Mg-based extruded composite material (Fig. 2(b)) was measured. The results obtained are summarized in Table 1. The hardness was about 48.0 to 53.0 (Hv) regardless of the filling rate of the mixed powder. The hardness of composite materials can generally be expressed by the rule of composition. That is, it is the sum of the hardness and content of the base metal and the additive. Sample No. 1 to No. The average crystal grain size of the Mg mother phase of No. 5 was about 13.0 μm to about 18.0 μm, and the content of the additive powder was 10%. I understand. The hardness of the Mg-based extruded material of Comparative Example 1 was 35.2 (Hv), which was lower than the Mg-based extruded composite materials of Examples 1-3.

The dry friction and wear properties of the Mg-based extruded composite material were investigated using a Ball-on-Disk type friction and wear tester. The surface of the Mg-based extruded composite material cut perpendicular to the extrusion direction (Fig. 2(b)) is used as the measurement surface, and a disk A dry friction wear test was performed under the conditions of a distance from the center, that is, a radius of rotation of 1 mm, an applied load of 0.49 N, a rotation speed of 9.5 rpm, and a test time of 5000 seconds. Friction coefficient and sliding distance and test of Example 1 (Sample No. 1), Example 2 (Sample No. 3), and Example 3 (Sample No. 5) obtained by dry friction and wear test FIG. 5 shows the relationship with time. Since the coefficient of friction was a constant value during the test time of 1000 to 5000 seconds, FIG. 5 shows the results up to the test time of 1000 seconds.

From FIG. 5, sample number No. 1, sample number no. 3, sample number no. 5, the friction coefficient from the start of the test to the test time: about 150 seconds shows a value of about 0.25 to 0.40, but the test time: about 180 seconds to about 400 seconds. It can be confirmed that a sudden drop occurs to less than 0.20 (about 0.03 to about 0.18), and then a constant value is shown (FIGS. 5(c), (e), and (d)). In particular, sample no. 3 (Mg—SiO ₂ ), sample number no. 5 (Mg—MnO ₂ ), the friction coefficient dropped very sharply to less than 0.07 (about 0.03 to about 0.06) in a short test time of about 180 seconds to about 230 seconds. It can be confirmed that it occurs and then stably exhibits a constant value (FIGS. 5(e) and 5(d)). On the other hand, in the Mg-based extruded material (Sample No. 6) containing no additive powder, no decrease in the coefficient of friction was observed from the start of the test, and the decrease in the coefficient of friction was confirmed even after the test time of 1000 seconds. (Fig. 5(a)). From these results, it can be seen that the presence or absence of the additive powder has a great effect on the reduction of the friction coefficient of the Mg-based sintered composite material. As a reference example, FIG. 5 also shows test results of a Mg-based extruded composite material produced using a mixed powder of pure Mg powder and Al ₂ O ₃ powder. It can be confirmed that the coefficient of friction abruptly decreased to about 0.1 at the test time of about 600 seconds, and thereafter showed a constant value as in the samples of Examples 1 to 3 (FIG. 5(b)).

After the friction wear test, the surface roughness of the measurement surface was measured with a laser microscope, and the amount of wear was determined by the following formula (1). However, since the amount of wear varies depending on the applied load P, the slip distance D, etc., the specific wear amount K was used to evaluate the wear characteristics in this example.

(Number 1)
K=A·b/P/D (1)

A in the formula (1) is a cross-sectional area measured with a laser microscope or the like, and b is the rotation circumference of the ball during the Ball-on-Disk test (6.2 mm in this example). FIG. 6 shows a typical two-dimensional cross-sectional image of the measurement surface after the friction wear test measured with a laser microscope. A portion indicated by an arrow in the center of the drawing is formed by the friction wear test and corresponds to A in Formula (1). Table 1 summarizes the specific wear amount of each Mg-based extruded composite material. All the specific wear amounts of the Mg-based extruded composite material show smaller values than the Mg-based extruded material containing no additive powder (Comparative Example 1), indicating excellent wear characteristics. The superior wear properties of such Mg-based extruded composites can be related to the hardness of the extruded material. That is, it can be seen that the higher the hardness of the extruded material, the smaller the specific wear amount and the more excellent the friction characteristics. This is due to the wear mechanism, and the higher the hardness of the material, the more aggressively it attacks the mating material (the ball in this example). This is because under such circumstances, an abrasive wear mechanism that forms a smooth surface condition is likely to be induced, making it possible to suppress wear.

Claims (8)

A particle-dispersed Mg-based sintered composite material,
In the metal structure of the Mg- based sintered composite material, oxide or nitride particles having an average diameter of 0.05 μm or more are dispersed in the Mg matrix,
When subjected to frictional wear, the coefficient of friction of the portion subjected to this frictional wear decreases in a short time, and the frictional wear is a dry friction wear test using a ball-on-disk type wear tester. , The test time from the start of the test is between 180 seconds and 400 seconds, and the friction coefficient of the portion of the sliding surface that has received frictional wear has decreased from the friction coefficient at the start to less than 0.20 in the short period of time. declining,
In the dry friction wear test using the ball-on-disk wear tester, the disk surface obtained by cutting the Mg-based extruded composite material of the Mg-based sintered composite material in the direction perpendicular to the extrusion direction is used as the measurement surface, and the high-carbon chromium bearing Using a steel (SUJ2) ball with a diameter of 4.7 mm, a dry friction wear test was performed under the conditions of a rotation radius of 1 mm from the disk center, an additional load of 0.49 N, a rotation speed of 9.5 rpm, and a test time of 5000 seconds. to implement
The crystal grain size of the Mg parent phase is 200 μm or less,
A Mg- based sintered composite, wherein said oxide or nitride is MnO ₂ , Si ₃ N ₄ or SiO ₂ . A particle-dispersed Mg-based sintered composite material,
In the metal structure of the Mg- based sintered composite material, oxide or nitride particles having an average diameter of 0.05 μm or more are dispersed in the Mg matrix,
When subjected to frictional wear, the coefficient of friction of the portion subjected to this frictional wear decreases in a short time, and the frictional wear is a dry friction wear test using a ball-on-disk type wear tester. , The test time from the start of the test is between 180 seconds and 400 seconds, and the friction coefficient of the portion of the sliding surface that has received frictional wear has decreased from the friction coefficient at the start to less than 0.20 in the short period of time. declining,
In the dry friction wear test using the ball-on-disk wear tester, the disk surface obtained by cutting the Mg-based extruded composite material of the Mg-based sintered composite material in the direction perpendicular to the extrusion direction is used as the measurement surface, and the high-carbon chromium bearing Using a steel (SUJ2) ball with a diameter of 4.7 mm, a dry friction wear test was performed under the conditions of a rotation radius of 1 mm from the disk center, an additional load of 0.49 N, a rotation speed of 9.5 rpm, and a test time of 5000 seconds. to implement
the ratio of the average diameter of the oxide or nitride particles to the crystal grain size of the Mg matrix is in the range of 1:4 to 1:10;
A Mg- based sintered composite, wherein said oxide or nitride is MnO ₂ , Si ₃ N ₄ or SiO ₂ . 3. The Mg-based sintered composite material according to claim 2, wherein the Mg matrix has a crystal grain size of 200 μm or less. The Mg- based sintered composite material according to any one of claims 1 to 3, wherein the content of said oxide or nitride particles is less than 65% by mass. A sliding member comprising the Mg- based sintered composite material according to any one of claims 1 to 4,
Having a sliding surface made of the Mg-based sintered composite material,
When the sliding surface receives frictional wear, the friction coefficient of the portion that has received this frictional wear decreases in a short time, and the frictional wear is a dry friction wear test using a ball-on-disk type wear tester. , the short time is a test time from the start of the test between 180 seconds and 400 seconds, and the friction coefficient of the portion of the sliding surface that has received frictional wear is within the short time from the friction coefficient at the start falls below 0.20 and
In the dry friction wear test using the ball-on-disk wear tester, the disk surface obtained by cutting the Mg-based extruded composite material of the Mg-based sintered composite material in the direction perpendicular to the extrusion direction is used as the measurement surface, and the high-carbon chromium bearing Using a steel (SUJ2) ball with a diameter of 4.7 mm, a dry friction wear test was performed under the conditions of a rotation radius of 1 mm from the disk center, an additional load of 0.49 N, a rotation speed of 9.5 rpm, and a test time of 5000 seconds. Sliding member to implement. A method for producing a Mg- based sintered composite material according to any one of claims 1 to 4,
A step of filling and enclosing a mixed powder containing Mg powder and an oxide or nitride powder having an average diameter of 0.05 μm or more in a billet; The above includes the step of applying warm or hot straining at a temperature of 550 ° C. or less with a cross-sectional reduction rate of 50% or more, and the oxide or nitride is MnO ₂ , Si ₃ N ₄ or SiO ₂ A method of making a Mg-based sintered composite. 7. The Mg-base according to claim 6, wherein the content of the oxide or nitride powder in the mixed powder is less than 65% by mass with respect to the total amount of the Mg powder and the oxide or nitride powder. A method for producing a sintered composite . 8. The method for producing a Mg- based sintered composite material according to claim 6 or 7, wherein the warm or hot strain imparting processing is extrusion processing, forging processing, rolling processing, or drawing processing.

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