JP2002292461A - Surface hardening method for half molten forming member and surface hardening member by the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface hardening method for a member formed with a half molten forming material of a light metal without applying heat treatment and capable of enhancing its surface hardness, and a hardened member of the half molten forming material hardened with the surface by such a method. SOLUTION: Against the surface 1f of the member 1 formed by the half molten forming material of the light metal with 10% or more of a solid rate, a rotating body 10 is made to enter the surface part of the member while making contact with the surface to stir the surface part 1a of the member by the rotating body in a nonmolten state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for hardening a surface of a member formed of a semi-solid molding material of light metal, and a surface-hardened member of a semi-solid molding material hardened by such a method.

[0002]

2. Description of the Related Art Conventionally, light metals such as, for example, magnesium (hereinafter appropriately denoted by its element symbol Mg) and its alloy or aluminum (hereinafter, appropriately denoted by its element symbol Al) and its alloy are used as materials. As a method of manufacturing a molding material, a molten metal of a light metal is semi-molten (hereinafter referred to as a “molten metal” even if it is not a completely molten state but a semi-molten state). BACKGROUND ART A semi-solid molding method in which a molding material is obtained by filling is known. In this semi-solid molding method, since the temperature of the molten metal is lower than that of the conventional molding method in which the raw material is heated to a predetermined temperature equal to or higher than the melting point and molded in a completely molten state, so-called "burrs" are less likely to appear and high speed and / or Alternatively, it can be applied to molding at high pressure, which is advantageous in improving productivity, and is also attracting attention as a process capable of obtaining a highly accurate and homogeneous light metal molding in terms of quality.

[0003] In the case of manufacturing machine parts and structural members using a light metal molding material as a material, the use of a light metal can achieve a significant reduction in weight as compared with an iron or steel material, but on the other hand, fatigue strength. , The durability may be insufficient for portions that are subjected to repeated loads.
Regarding such a problem, for example, Japanese Patent Application Laid-Open No. 10-183316
In the publication, for the purpose of improving the durability by increasing the fatigue strength of a specific portion of the Al casting material,
"A surface modification method of an Al casting material characterized by applying a friction stir welding process of bringing a probe rotating at a high speed into contact with the surface of the Al casting material to soften by friction heat" is disclosed.

In this surface modification method according to the prior art, the rotating member is caused to proceed while being brought into contact with the abutting contact portion of the metal member. A so-called friction stir welding method that joins both metal members by causing a plastic state in the metal part in contact with and in the vicinity thereof and solidifying the material part (plastic part) in the plastic state. The purpose is to improve the durability of the Al casting by increasing the fatigue strength of the Al casting. That is, according to the method for modifying the surface of an Al casting material, the metal structure on the surface of the Al casting material becomes denser, the elongation and toughness are improved, and the fatigue strength is higher than when the surface is modified by melting. Is said to improve. Further, unlike the case where the surface is melted and reformed, there is no problem that the internal gas of the casting material forms a blow hole.

[0005]

Problems to be Solved by the Invention By the way, Mg or A
When a light metal molding such as l-system is manufactured by the above-mentioned semi-solid molding method, as described above, a high-quality (high-precision, uniform without burrs) light metal molding can be obtained. In the case of the semi-solid molding method, the molten metal is filled in the cavity of the mold in a semi-molten state in which a liquid phase and a solid phase coexist to obtain a molding material, so that the metal structure of the obtained molding material is
Usually, it has a tissue state in which a solid phase is mixed in a matrix (liquid phase). In the semi-solid formed material of a light metal alloy having such a metal structure, the liquid phase portion has considerable hardness because the intermetallic compound is crystallized, but the solid phase portion has a chemical composition of pure light metal. Since the composition is close to the composition, the hardness is low.

Accordingly, in the case of a semi-solid molded material having a solid fraction of a certain degree or more, the surface hardness of the member is low because a solid part having a low hardness is contained in a certain amount or more. However, there is a problem that the method cannot be applied to a mechanical part or a structural member having a portion requiring a certain degree of surface hardness. In particular, in the case of Mg and its alloy,
Since the hardness of pure Mg is particularly low (compared to, for example, Al), the problem of insufficient surface hardness of the semi-solid formed material was particularly remarkable. In the case of Mg and its alloy, since its ignition point is low, it is not possible to perform a remelt treatment using, for example, a laser beam as in the case of an Al-based alloy.

For this reason, it is conceivable to increase the hardness by heat treatment. In the case of an Al-based or Mg-based light metal or an alloy thereof, in order to increase the hardness, an artificial aging treatment is performed after the solution treatment, so-called T6. Processing is required. However, when the T6 treatment is applied to these light metal semi-solid molded materials, there are the following disadvantages. That is, during the solution treatment, so-called blisters are likely to be generated due to the gas inevitably contained in the material. At the time of solution treatment, the members are likely to be deformed, and the deformation is particularly large for large members. In order to partially improve the hardness, it is necessary to perform T6 treatment on the entire member, which is uneconomical particularly for a large member. Therefore, in the case of a semi-solid formed material of an Al-based or Mg-based light metal or an alloy thereof, it is generally not preferable to perform T6 treatment to improve the surface hardness.

Accordingly, the present invention provides a surface hardening method capable of increasing the surface hardness of a member formed of a semi-solid molding material of light metal without performing heat treatment.
A basic object of the present invention is to provide a cured member of a semi-solid molded material whose surface is cured by such a method.

In the present specification, the “semi-molten state” of a molten metal as a raw material of a member is basically defined as
A state in which a solid-state raw material (solid phase) and a molten raw material (liquid phase) coexist, and are usually obtained by heating a raw material below its melting point. is there. However, a case where the temperature of the molten metal is substantially at or just above the melting point and the solid phase ratio is substantially equal to 0 (zero)% is also included in the “semi-molten state”. Even when the molten metal itself has such a substantially solid phase ratio of 0%,
Considering the actual process of forming a semi-molten member, one time (one shot) is filled into the mold and the next time (the next shot)
Until the filling is performed, the molten metal remaining in the molten metal supply path is cooled, and a solidified portion (a so-called cold plug) or a high solid phase portion having a high solid fraction is generated at the end of the supply path. Therefore, the molten metal actually filled in the mold inevitably contains a solid phase portion.

[0010] In this specification, the term "solid phase" refers to "a portion of a molten metal that is not melted and remains in a solid state when it is in a semi-molten state". Refers to “a part that is completely melted and is in a liquid state”. By observing the solidified structure of the obtained semi-solid molded member, the “solid phase” is referred to as a “part that has been maintained in a solid state without being molten in a semi-molten molten metal state”, The liquid phase portion, which was completely melted in the molten metal state to be in the liquid state, can be easily identified. The term “solid phase” for a semi-solid molded member refers to a “portion that has been maintained in a solid state without being melted in a semi-molten molten metal (solid phase)”.
Further, in the present specification, the “solid fraction” refers to “the ratio of the solid phase to the entire molten metal (solid phase + liquid phase) in the metal melt in a semi-molten state”. By observing the tissue, the ratio (area ratio) of the portion that was the “solid phase” to the entire observation region can be obtained numerically.

In view of the above technical problems, the inventors of the present application have conducted intensive studies to develop a practical surface hardening method for a semi-solid molded member made of a light alloy. By solidifying the surface of the member by friction stirring with a rotating body, it is possible to effectively increase the hardness of the surface of the member without performing a heat treatment such as # 6 treatment.
It has been found that the effect of improving the surface hardness is particularly large when the solid fraction is equal to or higher than a certain value or when a Mg-based light metal material is used.

[0012]

SUMMARY OF THE INVENTION Therefore, claim 1 of the present application is provided.
The method for hardening a surface of a semi-molten molded member according to the invention (hereinafter referred to as the first invention) comprises contacting a rotating body with a surface of a member formed of a semi-solid molded material of a light metal having a solid phase ratio of 10% or more. The member is caused to enter the surface of the member while being stirred, and the surface of the member is agitated in a non-molten state by the rotating body.

The reason why the lower limit of the solid phase ratio of the semi-solid molding material of light metal is set to 10% is that when the solid phase ratio is less than this value, the hardness difference between the base of the metallic structure of the member and the solid phase. Is relatively small, and the effect of the mixture of solid phase in the matrix on the hardness of the member is relatively small (that is, the degree of insufficient hardness is small). Is small.

Further, the invention according to claim 2 of the present application (hereinafter referred to as “the invention”)
The second invention) is characterized in that, in the first invention, the light metal is an Mg alloy.

Further, the invention according to claim 3 of the present application (hereinafter referred to as “the invention”)
A third invention) is characterized in that, in the second invention, the semi-solid molding member is formed using a semi-solid molding material having a solid fraction of 25% or more.

Here, the solid fraction of the semi-solid molding material is set to 2
The reason that the solid phase ratio is 5% or more is that when the solid phase ratio exceeds this value, the hardness difference between the base of the metal structure of the member and the solid phase is large, and the hardness of the member due to the mixture of the solid phase in the base is reduced. This is because the effect is particularly large (that is, the degree of insufficient hardness is particularly large), so that a particularly large effect of improving the hardness can be obtained by surface hardening.

Further, the invention according to claim 4 of the present application.
(Hereinafter, referred to as a fourth invention) according to the second or third invention, wherein the semi-solid molding member is formed by injection molding and die casting using a semi-solid molding material having a solid fraction of 60% or less. It is characterized by being formed by one of the casting methods.

The reason why the upper limit of the solid phase ratio of the semi-solid molding material is set to 60% is that when the solid phase ratio exceeds this value, the fluidity of the material is reduced (in other words, the flowability of the molten metal is reduced). This makes it difficult to produce members by injection molding or die casting, and the practicality of producing semi-solid molded members is reduced.

Further, the invention according to claim 5 of the present application.
(Hereinafter, referred to as a fifth invention) is characterized in that, in any one of the second to fourth inventions, the semi-solid molding material contains Mg by 90%.
It is characterized in that it is a Mg-Al alloy containing at least% by weight. Here, the reason why the Mg content of the semi-solid molding material is set to 90% by weight or more is that, when the Mg content is large, the hardness is reduced, so that the Mg content is less than 90% by weight. This is because the degree of the effect of surface hardening increases.

Further, the invention according to claim 6 of the present application (hereinafter referred to as “the invention”)
A sixth aspect of the invention) uses a member formed of a semi-solid molding material of a light metal having a solid phase ratio of 10% or more as a base material, and applies a rotating body to the surface of the base material while applying a rotating body to the surface of the base material. The semi-solid molded member is formed in such a manner that a hardened layer is formed on the surface portion of the semi-molten molded member by entering the substrate and stirring the substrate surface portion in a non-molten state by the rotating body. Here, the lower limit of the solid phase ratio of the semi-solid molding material of light metal is set to 10% for the same reason as in the first invention.

[0021]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. 1 and 2 are a perspective view and a cross-sectional explanatory view illustrating a surface hardening target member and a main part of a friction stir processing apparatus for explaining a surface hardening method of a semi-solid molded member according to the present embodiment.
As shown in these drawings, in the surface hardening method according to the present embodiment, the semi-solid molded member 1 of light metal to be subjected to the surface hardening treatment is placed and fixed on a base (not shown). This is performed by causing the rotating body 10 to enter the member surface portion 1f while contacting the rotating body 10 with the surface 1f of the light metal member 1.

The rotating body 10 has a rotating base 11 composed of a rotatable cylindrical body having a predetermined diameter, and a relatively fixed length (the rotating base 1) integrally fixed to the center of the tip of the rotating base.
And a probe section 12 formed of a small-diameter cylindrical body. The rotating base portion 11 is rotatably supported around an axis by a holder (not shown), and is driven by driving the holder (not shown) or the base (not shown) to rotate the rotating body. 10 enters the semi-solid molded member 1 in a direction perpendicular to the surface 1f thereof (that is, in the depth direction of the member 1).
It can be relatively moved along f. Since a mechanism for relatively moving the rotating body 10 along the member surface 1f is conventionally known, a detailed description and illustration thereof will be omitted.

As shown in FIGS. 1 and 2, the rotating body 10 is not limited to a rotating body 11 provided with a small-diameter probe 12 at the tip (lower end) of a rotating base 11. Instead, a flat (flat) lower surface on which the probe section 12 is not provided may be used. When the surface hardening depth is required to be hardened to a certain depth, a rotating body 10 having the above-described probe portion 12 is used. The surface hardening process may be efficiently performed using a rotating body having no 12.

In the method of the present invention, the lower surface of the rotating body 10 (that is, the lower surface of the probe section 12 and the rotating base section 11) is brought into contact with the surface 1f of the light metal semi-molten molded member 1, While rotating the member 10 at a predetermined rotation speed, the member 10 is made to enter the member surface portion 1f in the depth direction until the member reaches a predetermined depth. Due to the frictional heat generated at that time and the stirring action of the rotating body 10, the member surface portion 1f is brought into a non-melting plastic state, and the surface portion 1a in this plastic state is formed.
The (plastic portion) is cooled and solidified and hardened.

In particular, as for the solid phase portion having low hardness, the solid phase is divided in a non-molten state by the friction stir action of the rotating body 10 and the tissue is densified. It is possible to improve the surface hardness of a semi-molten molded member that could not obtain high hardness due to the mixture of phases.

A confirmation test was conducted to confirm the effect of improving the surface hardness of the semi-solid light metal member according to the method of the present invention. In this confirmation test, as a light metal which is a semi-solid molding material forming the light metal member 1 to be treated for the surface hardening treatment, a Mg alloy, particularly Mg-A containing 90% or more of Mg, is used.
1 alloy was used as a material, and this was injection-molded into a predetermined mold by a semi-solid injection molding method to prepare a test sample.
Table 1 shows the chemical composition of the Mg-Al alloy used in this test.

[0027]

[Table 1]

The semi-solid injection molding method is relatively clean (clean) in terms of working environment and higher in safety than the conventional casting method, and is also highly accurate and uniform in quality. It is known as a process by which light metal moldings can be obtained. Further, since the temperature of the molten metal is low, so-called "burrs" are not easily generated, which is suitable for high-speed and / or high-pressure injection, and is advantageous in improving productivity.
Furthermore, by injecting and filling the molten metal into the molding cavity in a semi-molten state, the molten metal in which the undissolved solid phase portion is mixed in the completely dissolved liquid phase portion is directly injected and filled, so that the flow is close to laminar flow. The gas is filled in a state, and the generation of gas defects due to the entrainment of the gas is relatively small.

Applying such semi-solid injection molding, using the Mg alloy material having the chemical composition shown in Table 1 above, the solid phase ratio is set to be variously different in a range of approximately 4% to 40% (specifically, Were set to approximately 4%, 25%, 30%, and 40%, respectively, to prepare test samples, and each sample was subjected to the surface hardening treatment by the method of the present invention described above. Note that M
In the case of a g-based alloy, the strength at a high temperature is generally lower than that of, for example, an Al-based alloy. Therefore, when the surface hardening method of the present invention is applied, processing at a higher speed is possible. Regarding the surface hardness of each sample, the hardness of the matrix and the solid phase before the curing treatment was measured, and the surface hardness after the curing treatment was measured to collect data. FIG. 3 shows the surface hardness measurement results before and after the treatment for each test sample.

As can be clearly understood from the measurement results shown in FIG. 3, before the treatment, the hardness of the solid phase is considerably low even if the matrix is somewhat hard. Accordingly, the surface hardness (average macro hardness) of the entire member remains at a low value between the matrix hardness and the solid phase hardness. In particular, the hardness of the matrix is substantially constant irrespective of the solid phase ratio, while the hardness of the solid phase is 25%
To the extent, the ratio rapidly decreases as the solid fraction increases.

The hardness difference between the matrix and the solid phase is small in a region where the solid phase ratio is extremely low, but becomes remarkably large when the solid phase ratio is gradually increased to about 10% or more. In particular, when the solid phase ratio is in the range up to about 25%, the hardness of the solid phase rapidly and remarkably decreases, so that the hardness difference between the matrix and the solid phase is very large. When the solid phase ratio is in the range of 25% or more, the change in hardness of the solid phase is relatively small.

As is apparent from the graph of FIG. 3, it was confirmed that the surface hardening treatment according to the method of the present invention reliably improved the surface hardness. That is, by performing the surface hardening treatment of the method of the present invention, the surface hardness of the semi-solid molded member is higher than the base hardness before the treatment irrespective of the solid fraction. Since the surface hardness after the treatment can be a high value in a narrow range close to substantially constant, the surface hardening treatment of the method of the present invention has a low solid phase hardness of approximately 10% before the treatment.
This is effective in the above region, and is particularly effective in the region where the solid phase ratio is 25% or more where the hardness of the solid phase before treatment is extremely low, and a high hardness improving effect is obtained.

As described above, according to the surface hardening treatment of the method of the present invention, a high effect can be obtained for improving the surface hardness of a semi-solid molded member having a solid phase ratio of about 10% or more. Insufficient hardness increases in a semi-solid molded member having a high solid phase ratio of 25% or more, and such a member is applied to machine parts and structural members having sliding parts by improving wear resistance. Will be able to do it. That is,
Without applying heat treatment such as T6 treatment, the surface hardness can be effectively increased and the wear resistance can be improved, and the applicable range of the use of the semi-solid molded member of light metal can be greatly expanded.

As described above, when the surface hardening treatment of the method of the present invention is performed, the effect of improving the hardness is obtained in a region having a high solid fraction of 25% or more where the hardness of the solid phase before treatment is extremely low. This solid phase ratio is too high,
Is exceeded, the fluidity of the material decreases (that is, the fluidity deteriorates), and it becomes difficult to manufacture members by injection molding or die-casting, and the practicality of manufacturing members is low. Become. Therefore, the solid phase ratio of the semi-solid molded member is preferably 60% or less.

As described above, the surface hardness of a semi-molten molded member which has not been able to obtain a high hardness as a whole due to the presence of a solid phase having a low hardness in the matrix of the tissue has been improved. As described above, the surface hardness 1f of the member (test sample) is brought into a non-melting plastic state by the friction stir action by the rotating body 10 and the surface portion 1a (plastic portion) in this plastic state is formed as described above. This is because the solid phase portion which is hardened by cooling and solidified, and in particular, has a low hardness, is divided in a non-molten state by the friction stir action of the rotating body 10 and the structure is densified.

FIGS. 5 and 6 are micrographs of the metal structure of the friction stir portion and the boundary portion between the portion and the substrate portion in the test sample after the surface hardening treatment obtained in the above confirmation test. A 30% test sample is shown as an example. As can be clearly understood from these photographs (especially from FIG. 6), in the substrate portion 1b, each solid phase (white portion in FIGS. 5 and 6) is dispersed and mixed in the matrix with a clear shape and size. In contrast, friction stir section 1a
In the (surface hardened portion), it was confirmed that the solid phase portion was divided into a dense structure.

Further, the hardness of the matrix and the solid phase before the surface hardening treatment and the macro hardness are measured, and the friction stir portion 1a (the surface hardened portion) after the surface hardening treatment is measured.
Was examined for variations in hardness. These hardness variations were measured using a test sample having a solid phase ratio of 30% as an example. The hardness of the matrix and the solid phase before the surface hardening treatment and the hardness of the macro were measured at three measurement points, respectively.
An average value was calculated for each hardness. Table 2 shows the measurement results.

[0038]

[Table 2]

As can be clearly seen from the measurement results in Table 2, before the surface hardening treatment, the difference between the hardness of the base portion and the hardness of the solid portion was very large (Hv 29 at the maximum, Hv 22 at the average).
The macro hardness shows a value closer to the hardness of the solid phase portion between them. That is, before the surface hardening treatment, even if the matrix is hard to some extent, the hardness of the solid phase is considerably low, and the surface hardness (macro hardness) of the entire member is low between the matrix hardness and the solid phase hardness. It was confirmed that the value remained.

Further, the friction stir section 1a after the surface hardening treatment
As shown in FIG. 4, the hardness of the (surface hardened portion) is defined as a starting point (measurement site 1) immediately near the boundary between the base portion 1 b not subjected to the surface hardening treatment and the hardened portion 1 a. 4 in the direction of the arrow in FIG. 4 at predetermined intervals (100 μm intervals) up to the point of the measurement site 15. Table 3 shows the measurement results.

[0041]

[Table 3]

As can be clearly seen from the measurement results in Table 3, the hardness of the friction stir portion 1a (the surface hardened portion) after the surface hardening treatment is determined in the vicinity of the boundary with the base material portion 1b (the measurement portion 1).
And 2), the variation is small (Hv1 at maximum).
3) In addition, the drop in the hardness value in the vicinity of the boundary is small, and even when such a vicinity is included, the variation is relatively small (Hv17 at the maximum). That is, it was confirmed that according to the surface hardening treatment of the method of the present invention, the surface hardness of the semi-solid molded member of the light metal can be increased stably (with less variation).

As described above, according to the surface hardening method according to the present embodiment, a semi-solid molding material of a Mg alloy (particularly, an Mg-Al alloy containing 90% by weight or more of Mg) as a light metal is used. The frictional heat generated when the rotating member 10 enters the substrate surface portion 1f while the rotating member 10 is in contact with the surface of the substrate and the stirring operation of the rotating member 10 is used as the base material 1f. In addition, a non-melting plastic state is generated in the light metal material in the vicinity thereof, and the surface portion 1a (plastic portion) in the plastic state is cooled and solidified and hardened, thereby increasing the hardness of the substrate surface portion 1a. In particular, the solid phase portion having a low hardness is cut off in a non-molten state by the friction stir action of the rotating body 10, the structure is densified, and the hardness of the member surface portion 1 a is increased. That is, the cured layer 1a can be formed on the surface portion 1f of the semi-solid molded member 1 without performing heat treatment.

In particular, regarding the semi-solid molded member 1 made of an Mg alloy whose solid phase ratio is 10% or more and whose surface hardness is remarkably insufficient,
Without heat treatment, the surface hardness is effectively increased and the wear resistance is improved. As a result, it becomes possible to apply the semi-solid molded member 1 made of Mg alloy to a mechanical part or a structural member having a sliding portion, and the application range can be greatly expanded.

In the above description, the light metal that is a semi-solid molding material forming the member to be subjected to the surface hardening treatment is described.
Using an Mg-Al alloy containing 90% by weight or more of Mg,
This was injection-molded into a predetermined molding die by a semi-solid injection molding method, but the present invention is not limited to such a case, and other types of Mg alloy as the light metal may be used. Further, other types of light metals such as an Al-based alloy can be used. In addition, the method of manufacturing the semi-solid molded member is not limited to the above-described semi-solid injection molding method, and for example, a casting method such as die casting can be used.

As described above, the present invention is not limited to the above-described embodiment, and it goes without saying that various improvements or design changes can be made without departing from the gist of the present invention.

[0047]

According to the method for hardening the surface of a semi-solid molded member according to the first invention of the present application, when the surface of a member formed of a semi-solid molded material of light metal is hardened, the surface of the member is hardened. Due to frictional heat generated when the rotating body enters the surface of the member while making contact with the rotating body and the stirring action of the rotating body,
A non-melting plastic state occurs in the light metal material on the surface of the member and in the vicinity thereof, and the surface portion (plastic portion) in the plastic state is cooled and solidified and hardened. In particular, the solid phase portion having a low hardness can be separated in a non-molten state by the friction stir action of the rotating body, and the structure can be densified to increase the hardness of the member surface portion. This makes it possible to effectively increase the surface hardness of a member formed of a semi-solid molding material of a light metal having a solid phase ratio of 10% or more and whose surface hardness is remarkably insufficient, without performing heat treatment, and thereby achieving abrasion resistance. Performance can be improved. As a result, the semi-solid molded material of light metal can be applied to mechanical parts and structural members having sliding parts.

According to the second aspect of the present invention, since the light metal is an Mg alloy, the same effect as in the first aspect can be obtained for an Mg alloy-based semi-molten molded material having a particularly remarkable surface hardness. Therefore, the range of application of the Mg alloy-based semi-solid molded material can be greatly expanded.

According to the third invention of the present application, the same effect as in the second invention is obtained when the semi-solid molding member is formed using a semi-solid molding material having a solid phase ratio of 25% or more. Can be played. In particular, the case where the solid phase is mixed in the matrix of the metal structure of the member has a particularly large influence on the hardness of the member (that is, the degree of insufficient hardness is particularly large) and the solid phase ratio is 25% or more. In particular, a large surface hardness improving effect can be obtained.

Further, according to the fourth invention of the present application,
Basically, the same effect as the second or third invention can be obtained. In particular, the solid fraction of the semi-solid molding material is set to 6
By setting the content to 0% or less, the fluidity of the semi-solid molding material can be secured (in other words, the fluidity of the molten metal can be secured), and the member can be favorably manufactured by injection molding or die casting. Sufficient practicality can be ensured for the production of the member.

Further, according to the fifth invention of the present application,
In particular, when a member is formed using a semi-solid molding material of an Mg-Al alloy containing 90% by weight or more of Mg,
The same effect as any one of the second to fourth inventions can be obtained. Usually, since the hardness decreases when the Mg content is large, the Mg content of the semi-solid molding material is set to 90% by weight or more, so that the Mg content is less than 90% by weight. The degree of effect due to surface hardening increases.

According to the sixth aspect of the present invention, a member formed of a semi-solid molding material of a light metal is used as a base material, and a rotating body is brought into contact with the surface of the base material to form a base member on the base material surface. Due to the frictional heat generated when entering and the stirring action of the rotating body,
A non-melting plastic state occurs in the base metal surface and in the vicinity of the light metal material, and the surface part (plastic part) in the plastic state is cooled and solidified and hardened, thereby increasing the hardness of the base material surface part. I have. In particular, the solid phase portion having a low hardness is divided in a non-molten state by the friction stir action of the rotating body, and the structure is densified, thereby increasing the hardness of the member surface portion. That is, the cured layer is formed on the surface of the semi-solid molded member without performing the heat treatment. In particular, for a member formed of a semi-solid molding material of light metal whose solidity ratio is 10% or more and whose surface hardness is remarkably insufficient, the surface hardness is effectively increased without heat treatment and the wear resistance is improved. improves. As a result, it is possible to apply the semi-solid molded material of light metal to mechanical parts and structural members having sliding parts.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a surface hardening target member and a main part of a friction stir processing apparatus for explaining a surface hardening method of a semi-solid molded member according to an embodiment of the present invention.

FIG. 2 is an explanatory cross-sectional view showing a main part of the surface hardening target member and a friction stir processing apparatus.

FIG. 3 is a graph showing a hardness measurement result of a test sample surface-hardened by the surface hardening method for a semi-solid molded member according to the embodiment.

FIG. 4 is an explanatory cross-sectional view of a relevant part of a test sample, showing measurement points for measurement data of the variation in hardness of a friction stir portion of the test sample.

FIG. 5 is a photomicrograph of a metal structure of a friction stir portion in a test sample surface-hardened by the surface hardening method for a semi-solid molded member according to the embodiment.

FIG. 6 is a micrograph of a metal structure of a boundary portion between a friction stir portion and a substrate portion in the test sample.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Semi-solid molding member 1a ... Friction stir part (surface hardened part) 1b ... Base part 10 ... Rotating body 11 ... Rotating base part 12 ... Probe part

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4E067 AA06 AC00 BG00 DA10 EA00

Claims (6)

[Claims] 1. A rotating body is brought into contact with a surface of a member formed of a semi-solid molding material of light metal having a solid phase ratio of 10% or more while being in contact with the surface of the member. A method for hardening a surface of a semi-molten molded member, wherein the method comprises stirring in a non-molten state. 2. The method according to claim 1, wherein the light metal is a Mg alloy. 3. The semi-solid molded member has a solid phase ratio of 25%.
The method for hardening a surface of a semi-solid molded member according to claim 2, wherein the method is formed using the semi-solid molded material. 4. The semi-solid molded member has a solid phase ratio of 60%.
The method for hardening a surface of a semi-solid molded member according to claim 2 or 3, wherein the semi-solid molded member is formed by one of an injection molding method and a die casting method using the following semi-solid molding material. . 5. The semi-solid molding material contains 90% by weight of Mg.
The method according to any one of claims 2 to 4, wherein the Mg-Al alloy contains the above. 6. A member formed of a semi-solid molding material of a light metal having a solid phase ratio of 10% or more is used as a base material, and is made to enter a base material surface portion while a rotating body is in contact with the surface of the base material. A surface-hardened member, wherein a hardened layer is formed on the surface of a semi-solid molded member by stirring the surface of the substrate in a non-molten state by the rotating body.