JP2019131857A - Mg-BASED COMPOSITE MATERIAL, MANUFACTURING METHOD THEREFOR, AND SLIDE MEMBER - Google Patents

Abstract

To provide a Mg-based composite material having excellent strength property by particle dispersion to a base phase, and having high frictional wear property, a manufacturing method therefor, and a slide member.SOLUTION: The Mg-based composite material is a particle dispersion type Mg-based composite material, a particle of an addition powder of oxide or nitride with average diameter of 0.05 μm or more is dispersed in a Mg base phase in a metal structure of the Mg-based composite material, and exhibiting superior frictional wear property to pure magnesium because friction coefficient of a part which receives friction wear is reduced in short time when the friction wear is added to the Mg-based composite material.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an Mg-based composite material, a manufacturing method thereof, and a sliding member.

  Magnesium (Mg) has abundant underground reserves and is the lightest practical metal material. Therefore, application to moving structural members such as automobiles has been actively studied. On the other hand, when used as a member, contact with other parts is inevitable, and development of Mg and Mg alloy having excellent strength and frictional wear characteristics is required. In general, increasing the strength of a metal material is an effective means of reducing the crystal grain size, and the same effect is exhibited for Mg and Mg alloys. However, it is known that crystal grain refinement of Mg and Mg alloys is not effective as a means for improving frictional wear characteristics (Non-patent Document 1). Due to the large grain boundary diffusion coefficient of Mg, grain boundary sliding easily occurs, and as the crystal grain size becomes finer, the grain boundary volume ratio increases, grain boundary sliding is promoted, and work softening occurs during frictional wear. Occur. Therefore, in order to further improve the friction and wear characteristics of Mg and Mg alloy, it is preferable to increase the crystal grains of the parent phase, but this causes a problem of deterioration of strength characteristics.

  In addition to refinement of the crystal grain size, particle dispersion in the parent phase is often used to increase the strength of the material. In particular, in the case of a metal material, it is effective for increasing the strength to disperse the intermetallic compound precipitated or crystallized from the matrix phase. Particle dispersion also has the effect of suppressing grain boundary sliding. The inventors have disclosed an Mg alloy in which an intermetallic compound having no spherical or acute angle is dispersed in an Mg matrix and is excellent in friction characteristics. Dispersing the intermetallic compound in the Mg matrix is an effective means for improving the strength, but in Patent Document 1, since the intermetallic compound is precipitated and crystallized from the cast material, The phase size is coarse, and further enhancement of strength is desired.

  In the case of metal materials, not only the dispersion of precipitated and crystallized intermetallic compounds, but also particles (eg, graphite, ceramics, etc.) made of substances and materials that do not dissolve in metal are dispersed in the matrix, that is, composites are also formed. This is an effective technique for improving strength. However, since Mg has very poor wettability with additive particles for the purpose of compounding, it is not possible to create a compound material by a 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 or a repeated shear strain applying method that requires a strain applying process of several tens of times or more. Although Mg-based composite materials have been created, since all the methods are complicated and require a large number of work steps, a rise in material costs is inevitable.

  On the other hand, modification of the surface layer of Mg alloy is known in order to maintain the strength characteristics of the material itself and improve the friction and wear characteristics. In Patent Document 4, it is possible to improve the frictional wear characteristics of Mg by forming a surface modified structure on the surface of the Mg alloy by anodizing and impregnating the surface modified structure with molybdenum disulfide, which is a solid lubricant. Is disclosed as an effective technique. Since it is a modification of only the surface layer without depending on the crystal grain size of the Mg matrix, it is possible to maintain strength characteristics. However, since it is necessary to perform an anodizing process as an additional step when using the material, there is a concern about an increase in cost.

  The present inventors pay attention to a simpler creation method, mix SiC powder and Mg powder, and create an Mg-based composite material by warm and hot working. In these composite materials, SiC particles are dispersed in the Mg matrix and maintain excellent strength characteristics. It has been confirmed that it exhibits a film-forming ability. On the other hand, when aiming at further property modification and versatility of Mg-based composite materials, not only attention is given to carbides such as SiC as particles to be dispersed in the Mg matrix, but also to using other compounds. It is necessary to consider.

  In the creation of a metal matrix composite, the wettability between the metal matrix and the additive powder is extremely important. As for Mg-based composite materials, when nitrides or oxides having different wettability from Mg of the matrix phase are used as additive powders, there is no cracking or cracking, and the additive powder is uniformly dispersed without segregating in the Mg matrix phase. It has not been clarified so far whether a sound Mg-based composite material can be created. Of course, it goes without saying about the friction and wear characteristics.

JP 2008-240032 A JP 2008-75127 A International Publication No. 2003/27342 JP 2002-363679 A

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

  The present invention has been made in view of the above circumstances, and has an excellent strength characteristic due to particle dispersion in a matrix phase, and has a high frictional wear characteristic, a Mg-based composite material, a manufacturing method thereof, and a sliding member It is an issue to provide.

In order to solve the above problems, the Mg-based composite of the present invention is a particle-dispersed Mg-based composite, and an oxide or nitride having an average diameter of 0.05 μm or more in the metal structure of the Mg-based composite When the particles are dispersed in the Mg matrix and subjected to frictional wear, the friction coefficient of the portion subjected to this frictional wear is reduced in a short time.
In this Mg-based composite material, the crystal grain size of the Mg matrix is preferably 200 μm or less.
In this Mg-based 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 composite material preferably has an oxide or nitride particle content of less than 65% by mass.
This Mg-based composite material preferably has a friction coefficient of less than 0.20 in a portion subjected to frictional wear after a test time of 800 seconds obtained by a dry frictional wear test.
In this Mg-based composite material, the oxide or nitride is preferably MnO ₂ , Si ₃ N ₄ or SiO ₂ .

The sliding member of the present invention is a sliding member containing the Mg-based composite material, and has a sliding surface made of the Mg-based composite material. This is characterized in that the coefficient of friction of the portion subjected to the reduction decreases in a short time.
This sliding member preferably has a friction coefficient of less than 0.20 at a portion subjected to frictional wear on the sliding surface after a test time of 800 seconds obtained by a dry friction wear test.

The method for producing an Mg-based composite material according to the present invention includes 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, and a mixed powder The billet is filled and sealed with a process of applying a warm or hot strain imparting process with a cross-sectional reduction rate of 50% or more at a temperature of 50 ° C. or more and 550 ° C. or less.
In this method for producing an Mg-based 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. preferable.
In this Mg-based composite material production method, the oxide or nitride is preferably MnO ₂ , Si ₃ N ₄ or SiO ₂ .
In this Mg-based composite material manufacturing method, the warm or hot strain imparting process is preferably an extrusion process, a forging process, a rolling process, or a drawing process.

  According to the present invention, there are provided an Mg-based composite material having excellent strength characteristics due to particle dispersion in a matrix and high friction and wear characteristics, a manufacturing method thereof, and a sliding member.

The figure which showed typically the example of the shape of the typical billet used for a warm or hot strain imparting process. The (a) external appearance photograph and (b) cross-sectional photograph of Mg group extrusion composite material in an Example. The photograph which observed the fine structure of Mg group extrusion composite material of Examples 1-3 with the 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). The photograph which observed the fine structure of Mg group composite material (sample number No. 6) of comparative example 1 with the optical microscope. Sample No. 1, no. 3, no. 5 and No. The figure which shows the relationship between the friction coefficient obtained by the Ball-on-Disk test (dry friction wear test) of 6, and a sliding distance and test time. A two-dimensional cross-sectional image of the measurement surface after a frictional wear test measured by a laser microscope.

  Regarding the Mg-based composite material of the present invention, its production method and sliding member: 1. Preparation of raw material powder 2. Billet preparation and mixed powder filling 3. Warm or hot straining process The microstructure of the Mg-based composite material and the sliding member will be described in this 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 additive powder), the average diameter of the additive powder particles in the metal structure of the Mg-based composite material, the Mg group The crystal grain size (crystal grain size) of the Mg matrix of the composite can be measured by the following method.
<Average diameter of Mg powder and additive powder>
Using a laser diffraction / scattering particle size distribution measuring apparatus, the median diameter (d50, volume basis) based on the cumulative distribution is taken as the average diameter from the measured value of the particle size distribution by the laser diffraction / scattering method.
<Average diameter of added powder particles>
The particle size of the individual particles of the additive powder is D = (L1 + L2) / 2 (where D is the particle size, L1 is the major axis of the particle, and L2 is the minor axis of the particle, based on an image observed with an SEM or an optical microscope. )).
For the average diameter, 100 or more particles are extracted from an image observed with an SEM or an optical microscope, the particle diameter of each particle is obtained from the above formula, and the average value is calculated.
<Grain size of Mg matrix>
Measured and calculated by the intercept method described in JIS H 0542: 2008 “Method for testing grain size of magnesium alloy rolled sheet”.

1. Preparation of Raw Material Powder The raw material powder used in the production of the Mg-based composite material of the present invention includes Mg powder and one or more oxide or nitride powders (additive powder).
Mg powder consists of pure magnesium, and the density of the powder particles is 1.74. The average diameter of the Mg powder is preferably 1 μm or more. Since Mg has a high reactivity with oxygen, if the average diameter of the Mg powder is 1 μm or more, the heat generated during mixing of the Mg powder and the additive powder can reduce the risk of ignition and reduce the safety of the work process. Can be increased. The Mg powder may be a cutting powder generated from an Mg bulk material by machining represented by milling or lathe processing, in addition to normal powder, 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 is preferably 1000 μm or less in consideration of bonding / sintering between Mg powders.

The oxide or nitride of the addition powder is not particularly limited, for _example, Al ₂ O _{3, CuO,} and the like _{MnO 2, Si 3 N 4,} SiO 2, 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, so that the proportion of oxygen in contact with the surface of the added powder particles increases. Therefore, the decrease in the friction coefficient is suppressed by the formation of the oxide made of Mg and the incorporation of the oxide at the interface or boundary between the Mg powder and the additive powder. The upper limit of the average diameter of the additive powder is not particularly limited, but is preferably 1000 μm or less and more preferably 100 μm or less in view of increasing the strength of the Mg-based composite material.

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

  The mixing method of Mg powder and additive powder and the state of the mixed powder will be described. The mixed powder is preferably in a state where the Mg powder and the additive powder do not segregate with each other. When any powder is segregated in the mixed powder state, when the Mg-based composite material is subjected to wear friction, the portion subjected to friction wear becomes a site of stress concentration, and the desired wear friction characteristics are obtained. It may be difficult to obtain. In order to prevent the Mg powder and the additive powder from segregating from each other, it is preferable to mix the additive powder in small amounts, that is, so that the mass of the additive powder added at a time is 50 g or less. If it exceeds 50 g, mixing is difficult and there is a concern that segregation of the powder occurs.

  The container used at the time of mixing will not be specifically limited if it is a container which can mix powder, represented by the mortar. The mixing of the Mg powder and the additive powder is preferably performed within 10 minutes using a mortar in the air in order to simplify the work process. Since Mg powder easily reacts with oxygen, when mixed for more than 10 minutes, it is difficult to obtain a sound mixed powder because oxides and the like are taken into the mixed powder. Of course, in consideration of the safety of work, the mixed powder may be mixed in an argon atmosphere or in a vacuum using a stirrer as in the mechanical alloying method.

2. Preparation of billet and filling of mixed powder The mixed powder is filled into a billet for warm or hot strain application. An example of a typical billet shape is schematically shown in FIG. The material (raw material) used for the billet is preferably a metal material that can be warmed or hot-strained, such as Mg or Mg alloy. Of course, metal materials other than Mg and Mg alloys, for example, Al and Al alloys may be used.

  In FIG. 1, the billet size S varies depending on the total cross-section reduction rate used during the straining process, but the total cross-section reduction rate is preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more. And a size that can be

  The size of the void for filling the mixed powder: V is preferably 50% or more and 95% or less, and preferably 50% or more, relative to the total volume of the billet (corresponding to S × L in FIG. 1). It is more preferably 90% or less, and further preferably 55% or more and 85% or less. Void size: When V is less than 50%, the amount of mixed powder that can be filled is small, so after the straining process, the majority of the processed material obtained is the material used for the billet, and the Mg-based composite material It may not be said. Void size: When V exceeds 95%, the billet may break during warm or hot strain imparting processing and the powder may leak to the outside.

  As a method of putting the mixed powder in the billet, a green compact may be produced by a hand press and placed in the billet. Of course, it may be put in the billet using a container represented by a spoon and capable of scooping powder. At that time, all the operations are preferably performed in an argon atmosphere or in a vacuum in order to suppress the reaction between the mixed powder and oxygen, but may be performed in the atmosphere for the convenience of the operation. Moreover, in order to control and improve the filling rate of mixed powder, it is preferable to apply pressure using a hand press after filling the billet with mixed powder. However, in order not to segregate the Mg powder and the additive powder from each other, it is not desirable that the billet is tapped excessively or vibration is applied. After the mixed powder is filled in the billet, it is sealed using an upper lid made of the same material as 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 size of the gap: V. The lower the filling rate, the shorter the time required to produce the Mg-based composite of the present invention. However, when the filling rate is less than 60%, the ratio of defects existing in the composite material is increased, so that it is difficult to use as a structure or member.

3. Warm or hot strain imparting process The purpose of warm or hot strain imparting process is to combine and sinter Mg powder into a healthy Mg matrix and segregate the particles of the added powder into the Mg matrix. It is to disperse | distribute uniformly, without doing. The temperature of warm or hot working is preferably 50 ° C. or higher and 550 ° C. or lower. When the processing temperature is less than 50 ° C., the processing temperature is low, and thus the Mg powders may not be bonded and sintered. In addition, the metal material used for the billet may be broken during processing, making it impossible to produce a sound composite material. When processing temperature exceeds 550 degreeC, Mg powder will be exposed to high temperature and there exists a concern about the danger of the ignition by local melting. Moreover, it may cause a decrease in the life of the mold used in the case of extrusion.

  For the application of strain during warm or hot working, the total area reduction rate is preferably 50% or more, more preferably 60% or more, and still more preferably 70% or more. When the total cross-section reduction rate is less than 50%, the strain application is insufficient, and thus the bonding between the powders is not promoted and a healthy composite material may not be produced. The warm or hot working method is typically extrusion, forging, rolling, or drawing, but any working method may be used as long as it is a plastic working method capable of imparting strain.

4). Microstructure of Mg-based composite material and sliding member The microstructure of the Mg-based composite material of the present invention will be described. Mg powder is bonded and sintered during warm or hot straining to form a Mg matrix, but to maintain the strength characteristics of the Mg-based composite and to obtain excellent friction and wear characteristics, The size of the Mg matrix, 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 parent phase is larger than 200 μm, the proportion of crystal grain boundaries in the composite material is small, so that the dislocation motion is not hindered by the crystal grain boundaries and it is difficult to maintain strength characteristics.

  In addition, it is preferable that the oxide or nitride additive powder is uniformly dispersed without segregation in the Mg matrix as particles of the oxide or nitride. The average diameter of the added powder particles in the metal structure of the Mg-based composite material is 0.05 μm or more, preferably 0.1 μm or more. When the average diameter of the additive powder particles is 0.05 μm or more, an Mg-based composite material having excellent frictional wear characteristics while having high strength characteristics is obtained.

  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, and preferably in the range of 1: 4 to 1: 9. It is more preferable. When the ratio between the oxide or nitride particles and the crystal grain size of the Mg matrix is within the above range, an Mg-based composite material having excellent frictional wear characteristics while having high strength characteristics is obtained.

It is also preferably considered that the oxide or nitride particles 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. The larger the surface energy difference, the larger the contact angle and the worse the wettability. That is, the greater the surface energy difference between magnesium and particles, the worse the wettability, so that during the frictional wear test, separation between the parent phase and the particles is likely to occur, and the effects of the present invention are easily obtained. For example, the surface energy of Si ₃ N ₄ or SiC is 2500, 2300 dyn / cm, which is a large value with respect to 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, Goro Ohara, Wetability of composite interface and metal, Japan Institute of Metals, Vol. 14, No. 8 (1975), pp.581-587; see Ueaki Ogai, critical dimension of nanometer composite structure as seen from surface energy, Japan Society for Powder Metallurgy, Vol. 37, No. 7 (1990)).

According to the present invention, it is possible to produce an Mg-based composite material in which oxide or nitride particles are uniformly dispersed in the metal structure of the Mg-based composite material without segregating in the Mg matrix. And when the Mg-based composite material of the present invention is subjected to frictional wear, the friction coefficient of the portion subjected to this frictional wear decreases in a short time. That is, the Mg-based composite material of the present invention is excellent in a dry friction and wear test as described later, after a certain period of time has elapsed since the start of the test, a sharp decrease in the coefficient of friction occurs, and thereafter a constant coefficient of friction is exhibited. Demonstrate wear friction characteristics. The degree of reduction in the friction coefficient may vary depending on the test conditions. For example, the friction coefficient decreases by more than half in 60 seconds between 150 seconds and 1000 seconds after the start of the test, and the friction after the test time of 1000 seconds elapses. The coefficient is stable at a value of 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 friction coefficient at the start of the dry friction wear test is 0.4, and the friction is rapidly increased from 250 seconds after the test starts. The coefficient starts to decrease, and after 50 seconds (that is, after a test time of 300 seconds), the coefficient of friction is 0.15.

  Thus, according to the present invention, a material excellent in friction and wear characteristics can be provided, and the Mg-based composite material of the present invention can be suitably used as a sliding member. This sliding member includes the Mg-based composite material of the present invention, and has a sliding surface made of the Mg-based composite material. When the sliding surface is subjected to frictional wear, the friction of the portion subjected to this frictional wear The coefficient decreases in a short time. As described above, since the characteristics of the sliding surface that is constantly subjected to frictional wear can be improved, the sliding member of the present invention is suitable for a mechanical part made of magnesium, such as an automobile part or a space device. Applications in various fields such as parts and aircraft parts can be expected.

  In addition, Mg and Mg alloy wrought materials including extrusion have a bottom surface aligned in the processing direction due to the Mg crystal structure (hexagonal crystal). Therefore, it is known that there is a great difference in yield stress between tensile deformation and compression deformation, and three-dimensional isotropic deformation is difficult. This yield anisotropy is caused by deformation stress generated at low deformation stress. On the other hand, by dispersing fine particles in the Mg matrix, the formation of deformation twins is suppressed, or the stress formed by twin deformation increases. Therefore, according to the present invention, it is possible to provide Mg and an Mg alloy that have a reduced yield anisotropy and are capable of three-dimensional isotropic deformation.

EXAMPLES Hereinafter, the present invention will be described in more detail 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 Si ₃ N ₄ particles dispersed in the Mg matrix of the Mg-based composite material were weighed so that the content was 10%, and the Mg powder and the Si ₃ N ₄ powder were dry mixed in a mortar.

In order to fill the mixed powder of Mg and Si ₃ N _4, a commercially available Mg alloy (Mg-3Al-1Zn; AZ31) material having an outer diameter of 40 mm and a length of 70 mm is used. A hole having a length of 55 mm was formed, and an extruded billet having a cup shape shown in FIG. 1 was produced. After the mixed powder was filled into the extruded billet, it was sealed using an 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 mixed powder was filled such that the volume of the mixed powder became 95% or 85% with respect to the void in FIG. 1; V (= volume of inner diameter 20 mm × depth 55 mm). Thereafter, after being held in a container set at 250 ° C. for 30 minutes or more, hot straining by extrusion is performed 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 “extruded material”) , Referred to as an Mg-based extruded composite).

<Example 2>
A mixed powder was prepared in exactly the same procedure as in Example 1 except that the Si ₃ N ₄ powder was replaced with a commercially available SiO ₂ powder, and the volume of the mixed powder was 95% or 85% in the extruded billet. Then, extrusion was performed in the same manner as in Example 1 to produce an Mg-based extruded composite material.

<Example 3>
A mixed powder was prepared in exactly the same procedure as in Example 1 except that the Si ₃ N ₄ powder was replaced with a commercially available MnO ₂ powder, and filled in an extruded billet so that the volume of the mixed powder was 95%. Thereafter, extrusion was performed in the same manner as in Example 1 to produce an Mg-based extruded composite material.

<Comparative Example 1>
Except that the additive powder was not used, the same procedure as in Example 1 was used, and after filling the extruded billet so that the volume of the Mg powder was 90%, the extrusion process was performed in the same manner as in Example 1 to obtain an Mg group. An extruded material was produced.

  Table 1 summarizes the creation conditions of each Mg-based extruded composite material. FIG. 2 shows an external appearance (a) and a cross-sectional photograph (b) of a typical Mg-based extruded composite material prepared with a filling rate of the mixed powder in the extruded billet of 95%. From the appearance photograph of FIG. 2A, there is no crack or defect on the surface of the Mg-based extruded composite material, and the creation of a healthy long material can be confirmed. Further, from the cross-sectional observation of FIG. 2B, 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 understand that.

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

In order to obtain the average crystal grain size (crystal grain size) of the Mg matrix, the microstructure of the produced Mg-based extruded composite material was observed using an optical microscope. FIG. 3 shows a typical microstructure of each Mg-based extruded composite material. In FIG. 3A to FIG. 3C, the bright region is Mg matrix and the dark region is Si ₃ N ₄ particles, SiO ₂ particles, or MnO ₂ particles. Table 1 summarizes the average crystal grain size of the Mg matrix of each Mg-based extruded composite obtained by the intercept method. The average crystal grain size of the Mg parent phase was about 13.0 μm to about 18.0 μm, regardless of the added powder size at the time of mixing with the Mg powder and the filling rate of the mixed powder into the extruded billet. 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.

  4 is a typical microstructure example of the Mg-based extruded material of Comparative Example 1 (Sample No. 6), which was 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 Mg-based extruded composite material with respect to the cut surface (FIG. 2B) was measured. The results obtained are summarized in Table 1. Regardless of the filling rate of the mixed powder, the hardness was about 48.0 to 53.0 (Hv). In general, the hardness of a composite material can be expressed by a composite rule. That is, it is the sum of the hardness and content of the base metal and additive. Sample No. 1-No. 5 has an average crystal grain size of about 13.0 μm to about 18.0 μm, and the content of the additive powder was 10%, the filling rate may hardly affect the hardness. 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 to 3.

  Using a Ball-on-Disk type friction and wear tester, the dry friction and wear characteristics of the Mg-based extruded composite were investigated. The surface of the Mg-based extruded composite material cut in the direction perpendicular to the extrusion direction (FIG. 2 (b)) was used as the measurement surface, and a disk having a diameter of 4.7 mm made of high carbon chrome bearing steel (SUJ2) was used. A dry friction and wear test was performed under the conditions of a distance from the center, that is, a rotation radius of 1 mm, an additional load of 0.49 N, a rotation speed of 9.5 rpm, and a test time of 5000 seconds. Friction coefficient and sliding distance / test of Example 1 (Sample No. 1), Example 2 (Sample No. 3), and Example 3 (Sample No. 5) obtained by the dry friction wear test The relationship with time is shown in FIG. In addition, since the friction coefficient was a fixed value in test time; 1000 second-5000 second, in FIG. 5, the result to test time; 1000 second is shown.

From FIG. 1, sample number no. 3. Sample 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 in the test time: about 180 seconds to about 400 seconds, the friction coefficient is It can be confirmed that a rapid drop occurs to less than 0.20 (about 0.03 to about 0.18), and thereafter a constant value is shown (FIGS. 5C, 5E, and 5D). In particular, sample no. 3 (Mg—SiO ₂ ), Sample No. 5 (Mg—MnO ₂ ), the test time; in a short time of about 180 seconds to about 230 seconds, the coefficient of friction decreases very rapidly to less than 0.07 (about 0.03 to about 0.06). After that, it can be confirmed that it shows a stable and constant value (FIGS. 5E and 5D). On the other hand, in the Mg-based extruded material (sample No. 6) containing no additive powder, no decrease in the friction coefficient was observed from the start of the test, and a decrease in the friction coefficient was confirmed after the test time of 1000 seconds. (FIG. 5 (a)). From these results, it can be seen that the presence or absence of the added powder greatly affects the reduction of the friction coefficient of the Mg-based composite material. In FIG. 5, as a reference example also shows test results of the Mg based extruded composite material produced using a mixed powder of pure Mg powder and the Al ₂ O ₃ powder. Test time: It can be confirmed that the friction coefficient rapidly decreases to about 0.1 at about 600 seconds, and then shows a constant value as in the samples of Examples 1 to 3 (FIG. 5B).

  After the frictional 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 equation (1). However, since the wear amount varies depending on the applied load P, the sliding distance D, and the like, in this example, the wear characteristics were evaluated using the specific wear amount K.

(Equation 1)
K = A ・ b / P / D (1)

  A in the formula (1) is a cross-sectional area measured from a laser microscope or the like, and b is a rotation circumference (6.2 mm in this embodiment) of the ball at the Ball-on-Disk test. FIG. 6 shows a typical two-dimensional cross-sectional image of the measurement surface after the frictional wear test measured by a laser microscope. A portion indicated by an arrow in the center of the figure is formed by a frictional wear test and corresponds to A in formula (1). Table 1 summarizes the specific wear amount of each Mg-based extruded composite material. It can be seen that the specific wear amount of the Mg-based extruded composite material is smaller than that of the Mg-based extruded material containing no additive powder (Comparative Example 1) and is excellent in wear characteristics. The excellent wear characteristics of such Mg-based extruded composites can be related to the hardness of the extruded material. That is, it can be seen that the greater the hardness of the extruded material, the smaller the specific wear amount and the better the friction characteristics. This is due to the mechanism at the time of wear. The higher the hardness of the material, the more aggressive the opponent material (in this example, the ball). This is because, under such a situation, it is easy to induce an abrasive wear mechanism that forms a smooth surface state, and wear can be suppressed.

Claims (12)

A particle-dispersed Mg-based composite material,
In the metal structure of the Mg-based composite material, when the oxide or nitride particles having an average diameter of 0.05 μm or more are dispersed in the Mg matrix and subjected to frictional wear, the friction coefficient of the portion subjected to this frictional wear Mg-based composite material that decreases in a short time.   The Mg-based composite material according to claim 1, wherein a crystal grain size of the Mg matrix is 200 μm or less.   3. The Mg-based composite material according to claim 1, wherein a ratio between the oxide or nitride particles and the crystal grain size of the Mg matrix is in the range of 1: 4 to 1:10.   The Mg-based composite material according to any one of claims 1 to 3, wherein a content ratio of the oxide or nitride particles is less than 65 mass%.   The Mg-based composite material according to any one of claims 1 to 4, wherein a friction coefficient of a portion subjected to the friction wear after a test time of 800 seconds obtained by a dry friction wear test is less than 0.20. The oxide or _nitride, MnO _{2, Si} 3 _{N 4} or Mg based composite material according to any one of claims 1 to 5 is SiO _2. A sliding member comprising the Mg-based composite material according to any one of claims 1 to 6,
Having a sliding surface made of the Mg-based composite material;
A sliding member in which, when the sliding surface is subjected to frictional wear, the friction coefficient of the portion subjected to the frictional wear decreases in a short time.   The sliding member according to claim 7, wherein a friction coefficient of a portion subjected to frictional wear on the sliding surface after a test time of 800 seconds obtained by a dry frictional wear test is less than 0.20. A method for producing an Mg-based composite material according to any one of claims 1 to 6,
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, and filling and enclosing the mixed powder in the billet at 50 ° C. or higher A method for producing an Mg-based composite material, comprising a step of performing a warm or hot strain imparting process with a cross-section reduction rate of 50% or more at a temperature of 550 ° C or lower.   10. The Mg group according to claim 9, wherein a content of the oxide or nitride powder in the mixed powder is less than 65 mass% with respect to a total amount of the Mg powder and the oxide or nitride powder. A method of manufacturing a composite material. The oxide or _nitride, MnO _{2, Si} 3 _{N 4} or the method of manufacturing the Mg based composite material according to claim 9 or 10 is a SiO _2.   The method for producing an Mg-based composite material according to any one of claims 9 to 11, wherein the warm or hot strain imparting process is an extrusion process, a forging process, a rolling process, or a drawing process.