JP7033826B2 - How to join dissimilar metal materials - Google Patents

Description

The present invention relates to a method for joining dissimilar metal materials, particularly a method for joining an iron-based material and an aluminum material.

An engine such as an automobile is provided with an intake port and an exhaust port opened in a combustion chamber. These intake and exhaust ports are opened and closed by valves provided in the openings. Of the openings of each port, the portion where the valve is seated is usually provided with an annular valve seat made of a high-strength iron-based material.

The valve seat is often fixed to the cylinder head by press fitting. In this case, in order to secure the area of the press-fitting portion between the valve seat and the cylinder head, it is necessary to secure the height (axial dimension) of the valve seat to some extent. This limits the design of the cylinder head, especially the design of the intake port and the exhaust port, which may make it difficult to improve the intake / exhaust capacity.

Therefore, a method has been proposed that can be firmly joined to the cylinder head even when the height of the valve seat is reduced. For example, Patent Document 1 below discloses a technique in which a built-up layer is formed by irradiating a laser while supplying metal powder to an opening of a port, and a valve seat is formed by the built-up layer.

Further, Patent Document 2 below discloses a method in which a valve seat is formed of an iron-based sintered material and the valve seat is joined to a cylinder head made of an aluminum material by a resistance heat joining method. Specifically, by energizing between both members while pressing a plurality of members against each other, an oxide film or the like formed on the surfaces of both members is discharged from the interface of both members, and the base materials of both members are directly connected to each other. By bringing them into contact with each other, both members are firmly bonded.

Japanese Unexamined Patent Publication No. 2017-80756 Japanese Unexamined Patent Publication No. 9-239566

If the valve seat is formed by the overlay method using the laser beam shown in Patent Document 1, the height of the valve seat can be suppressed, but the manufacturing cost is high because the laser irradiation equipment or the like is required.

Further, the resistance heat bonding method shown in Patent Document 2 can firmly bond the same kind of materials, but it is not easy to firmly bond different materials. In particular, when an iron-based material and an aluminum material are bonded, it is very difficult to increase the bonding strength because a brittle Fe—Al compound layer is formed at these interfaces.

An object of the present invention is to firmly join a member made of an iron-based material and a member made of an aluminum material without using a press-fitting method or a laser overlay method.

According to the verification by the present inventors, when joining the first member made of an iron-based material and the second member made of an aluminum material, the first member is formed of an iron-based sintered material containing copper. It was clarified that both members are firmly bonded by applying a high current value between the two members while pressing the second member made of an aluminum material with a high pressing force.

This is considered to be due to the following reasons. By pressurizing and energizing both members as described above, a brittle Fe-Al compound layer is generated at the interface between the two members, but by increasing the pressing force and the amount of energization between the two members, the interface between the two members The Fe—Al compound layer is discharged from the material, and the base materials of both members come into direct contact with each other. By continuing to pressurize and energize in this state, at the interface between both members, between the copper contained in the base material (iron-based sintered material) of the first member and the base material (aluminum material) of the second member. Mutual diffusion occurs at the above, and a Cu—Al diffusion layer is formed at the interface between the two members. In this way, by discharging the brittle Fe-Al compound layer from the interface of both members and forming a Cu-Al diffusion layer at the interface, both members are firmly bonded to each other via the Cu-Al diffusion layer. .. That is, both members can be firmly joined by setting the pressing force and the current value between the two members so that the Cu—Al diffusion layer is generated at the interface between the two members.

Based on the above findings, the present invention is a method for joining a first member made of an iron-based sintered material containing copper and a second member made of an aluminum material. By energizing between both members while pressing against the second member, the Fe-Al compound layer formed at the interface between the two members is discharged from the interface, and a different type of Cu-Al diffusion layer is formed at the interface. A method for joining a metal material is provided.

When the first member and the second member are joined by the method as described above, the Fe—Al compound discharged from the interface between the two members is accumulated in the region adjacent to the interface. That is, it is a joining part formed by joining a first member made of an iron-based sintered material containing copper and a second member made of an aluminum material by the above method, and the first member and the above. A bonded part is obtained in which a Cu—Al diffusion layer is interposed at an interface with a second member and a Fe—Al compound is present in a region adjacent to the interface.

When the first member and the second member are pressurized and energized under the above conditions, the copper dispersed in the first member (iron-based sintered material) is carried along the energization path flowing through the first member. Move towards the interface of both members. As a result, the concentration of copper in the vicinity of the interface increases, and the copper and the second member (aluminum material) are mutually diffused to form a Cu—Al diffusion layer at the interface. Therefore, when copper is uniformly dispersed in the first member before being joined to the second member, the copper in the vicinity of the interface in the first member moves toward the interface by pressurized energization. Therefore, among the first members, the concentration of copper in the vicinity of the interface between the two members is lower than the concentration of copper in the other regions.

On the other hand, in the first member before joining to the second member, copper may be segregated so that the concentration of copper in the vicinity of the interface between the two members is relatively high. In this case, when both members are pressurized and energized, the amount of copper that moves toward the interface increases, and the concentration of copper at the interface is further increased, so that a Cu—Al diffusion layer is likely to be formed at the interface.

As described above, the Fe—Al compound layer is discharged from the interface between the first member made of an iron-based sintered material containing copper and the second member made of an aluminum material, and the Cu—Al diffusion layer is discharged at this interface. By generating the above, both members can be firmly joined without using a press-fitting method or a laser overlay method.

It is sectional drawing around the intake / exhaust port of the combustion chamber of an engine. It is an enlarged view near the valve seat of FIG. It is sectional drawing which shows the procedure of joining a valve seat to a cylinder head, and shows the state before the start of pushing. It is an enlarged view of the X part of FIG. It is sectional drawing which shows the procedure of joining a valve seat to a cylinder head, and shows the state in the process of pushing. It is an enlarged view of the Y part of FIG. It is sectional drawing which shows the procedure of joining a valve seat to a cylinder head, and shows the state which the pushing is completed. It is an enlarged view of the Z part of FIG. It is an enlarged sectional view which shows the joint part of a valve seat and a cylinder head. It is sectional drawing of the valve seat before joining to a cylinder head which concerns on another embodiment. It is sectional drawing of the valve seat before joining to a cylinder head which concerns on still another embodiment. It is a graph which shows the test condition (horizontal axis: pressing force per unit area, vertical axis: current density) of each test piece.

Embodiments of the present invention will be described with reference to the drawings. The present embodiment shows a case where a valve seat as a first member made of an iron-based material is joined to a cylinder head as a second member made of an aluminum material.

FIG. 1 shows a structure in the vicinity of the intake / exhaust port of the combustion chamber 3 of the engine. The cylinder head 2 is a cast product of an aluminum material (aluminum alloy). The cylinder head 2 is formed with an intake port 4 and an exhaust port 5 that are open to the combustion chamber 3. The openings of the ports 4 and 5 are opened and closed by the valve 6. The stem portion 6a of the valve 6 is inserted into the inner circumference of the cylindrical valve guide 7 attached to the cylinder head 2, and is reciprocated by a cam mechanism and a spring (not shown). An annular valve seat 1 is provided at the openings of the ports 4 and 5. When the umbrella portion 6b of the valve 6 is seated on the valve seat 1, the ports 4 and 5 are closed, and when the umbrella portion 6b of the valve 6 is separated from the valve seat 1, the ports 4 and 5 are opened.

The valve seat 1 is made of an iron-based sintered material containing copper. Specifically, the valve seat 1 is made of a sintered material containing 50% by mass or more of iron and 1 to 40% by mass of copper. If necessary, one or more of C, Ni, Co, Cr, Mo, V, W, Mn, Si, and S are added to the sintered material. In the valve seat 1, after the raw material powder containing copper powder and iron powder is uniformly mixed, the raw material powder is compression-molded with a mold to form a green compact, and the green powder is sintered at a predetermined temperature. It is formed by doing. Copper is uniformly dispersed throughout the valve seat 1 (valve seat 1 before joining to the cylinder head 2) formed in this way.

The valve seat 1 is formed in an annular shape. Specifically, as shown in an enlarged manner in FIG. 2, the inner circumference of the inner peripheral surface of the valve seat 1 to which the umbrella portion 6b of the valve 6 is attached is attached to the end of the port opening side (combustion chamber 3 side). A tapered surface 1a is provided. Further, an outer peripheral tapered surface 1b is provided at the end of the outer peripheral surface of the valve seat 1 on the back side of the port (the side away from the combustion chamber 3).

Hereinafter, the procedure for joining the valve seat 1 to the cylinder head 2 will be described with reference to FIGS. 3 to 9. In the present embodiment, the case where the valve seat 1 is joined to the opening of the intake port 4 (hereinafter, also simply referred to as “port 4”) will be described, but the procedure for joining the valve seat 1 to the exhaust port 5 is the same. Do it at.

First, as shown in FIG. 3, the cylinder head 2 is arranged so that the port 4 opens upward. A seat mounting portion 8 to which the valve seat 1 is mounted is provided at the opening of the port 4 of the cylinder head 2. In the state before joining, the inner diameter of the seat mounting portion 8 is smaller than the outer diameter of the valve seat 1. Specifically, the seat mounting portion 8 is provided between the cylindrical surface 8a having a diameter larger than the inner diameter of the port 4 and smaller than the outer diameter of the valve seat 1 and the cylindrical surface 8a and the inner peripheral surface of the port 4. It has a flat surface 8b and a chamfered portion 8c provided on the opening side (upper side in the drawing) of the cylindrical surface 8a. In the illustrated example, the stealing portion 8d is provided at the boundary between the cylindrical surface 8a and the flat surface 8b.

Then, the valve seat 1 is arranged in the seat mounting portion 8 of the cylinder head 2. At this time, since the inner diameter of the cylindrical surface 8a of the seat mounting portion 8 is smaller than the outer diameter of the valve seat 1 before joining, the valve seat 1 is not inserted into the inner circumference of the cylindrical surface 8a, and the seat mounting portion is not inserted. It is placed on the upper end of 8. In the illustrated example, the outer peripheral tapered surface 1b of the valve seat 1 is placed on the chamfered portion 8c provided at the upper end of the seat mounting portion 8.

FIG. 4 shows an enlarged interface between the valve seat 1 and the cylinder head 2 (contact portion between the outer peripheral tapered surface 1b of the valve seat 1 and the chamfered portion 8c of the seat mounting portion 8 of the cylinder head). As shown in the figure, coatings C1 and C2 made of oxide coatings, impurities, etc. are formed on the surfaces of the valve seat 1 and the cylinder head 2, respectively, and the respective base materials (iron-based sintered material, aluminum material) are formed with each other. Is not in direct contact.

Then, as shown in FIG. 5, the valve seat 1 is pushed downward by one electrode 10 and the other electrode (not shown) is brought into contact with the cylinder head 2, and in this state, one electrode 10 and the other electrode are brought into contact with each other. Energize during. In the illustrated example, the inner peripheral tapered surface 1a of the valve seat 1 is pushed downward by the tapered outer peripheral surface of the electrode 10. As a result, the valve seat 1 is strongly pressed against the cylinder head 2, and by energizing between the members 1 and 2 in this state, the interface P between the members 1 and 2, particularly the interface P under pressure from the electrode 10. That is, the interface P intersecting the pressurizing direction (vertical direction in FIG. 5) by the electrode 10, and in the present embodiment, the interface P between the outer peripheral tapered surface 1b of the valve seat 1 and the surface of the cylinder head 2 in contact with the outer peripheral tapered surface 1b is a resistance. It is heated by heat generation, softens, and plastically deforms. Specifically, the outer peripheral tapered surface 1b of the valve seat 1 crushes the chamfered portion 8c and the cylindrical surface 8a of the seat mounting portion 8 of the cylinder head 2, and the meat of the cylinder head 2 is plastically flowed. As a result, a tapered surface 8e that follows the outer peripheral tapered surface 1b of the valve seat 1 is formed on the seat mounting portion 8 of the cylinder head 2, and a raised portion 8f that is raised toward the inner diameter side due to the plastically fluidized meat below the tapered surface 8e. Is formed. At the same time, plastic deformation occurs on the outer peripheral tapered surface 1b of the valve seat 1, and the angle of the outer peripheral tapered surface 1b approaches the pressurizing direction (upper and lower direction in the figure) of the electrode 10.

At this time, the outer peripheral tapered surface 1b of the valve seat 1 is strongly pressed against the tapered surface 8e of the cylinder head 2, so that the coating films C1 and C2 intervening in these interfaces P are extruded from the interface P and both members. The base materials (iron-based sintered material and aluminum material) of 1 and 2 come into contact with each other. By continuing to energize between both members 1 and 2 in this state, an Fe—Al compound layer is formed at the interface P of both members 1 and 2, as shown in FIG. The Fe—Al compound layer is composed of, for example, one or more of FeAl, FeAl ₂ , and FeAl ₃ .

After that, by further energizing the valve seat 1 while pushing it downward, the valve seat 1 is seated on the flat surface 8b of the seat mounting portion 8 of the cylinder head 2 as shown in FIG. 7. At this time, the meat (raised portion 8f) of the cylinder head 2 that has flowed due to plastic deformation is housed in the stealing portion 8d previously provided in the seat mounting portion 8 of the cylinder head 2.

At this time, as shown in FIG. 6, if the Fe—Al compound layer is formed at the interface P of both members 1 and 2, the base material (iron-based sintered material) of the valve seat 1 and the mother material of the cylinder head 2 are formed. The material (aluminum material) is blocked by the Fe—Al compound layer. However, by pressurizing and energizing both members 1 and 2 at a high pressing force and a high current value, the Fe—Al compounded grain layer interposed at the interface P of both members 1 and 2 is discharged from the interface P. As a result, the base materials of both members 1 and 2 come into direct contact with each other, mutual diffusion occurs between the copper in the valve seat 1 and the base material (aluminum material) of the cylinder head 2, and Cu—Al diffusion occurs at the interface P. Layers are generated (see Figure 8). The Cu—Al diffusion layer is formed, for example, in a region of 50% or more of the area of the interface P. The Cu—Al diffusion layer is a Cu—Al compound produced by mutual diffusion of copper and aluminum, and is composed of, for example, CuAl and / or CuAl ₂ .

The Fe—Al compound discharged from the interface P of both members 1 and 2 exists in the region adjacent to the interface P. In the present embodiment, as shown in FIG. 9, a region adjacent to both sides of the tapered interface P in the generatrix direction, specifically, a cylindrical outer peripheral surface 1c of the valve seat 1 and a cylinder head 2 facing the outer peripheral surface 1c. The Fe—Al compound is present in the material between the inner peripheral surface of the surface and the material flowing into the stealing portion 8d.

When both members 1 and 2 are pressurized and energized as described above to discharge the Fe—Al compound from the interface P and generate the Cu—Al compound at the interface P, the copper dispersed in the valve seat 1 is generated. Along the path of the current flowing through the valve seat 1, the interface between the valve seat 1 and the cylinder head 2 (the outer peripheral tapered surface 1b of the valve seat 1 on which the pressure applied by the electrode 10 acts and the tapered surface 8e of the cylinder head 2 (Intersection) Moves toward P (see the dotted arrow in FIG. 9). In the present embodiment, since the copper is uniformly dispersed in the valve seat 1 before being joined to the cylinder head 2, the copper dispersed in the valve seat 1 moves toward the interface P as described above. As a result, the distribution of copper in the valve seat 1 becomes non-uniform. Specifically, as shown in FIG. 9, in the valve seat 1 after being joined to the cylinder head 2, the concentration of copper in the region Q near the interface P becomes lower than the concentration of copper in the other regions. (In FIG. 9, copper is represented by scattered dots). In the illustrated example, copper is scarcely present in the region Q.

As described above, the base materials of the valve seat 1 and the cylinder head 2 are at the interface P of both members 1 and 2 (in the present embodiment, the interface P between the outer peripheral tapered surface 1b of the valve seat 1 and the tapered surface 8e of the cylinder head 2). In the above, since the bonding is performed in a solid phase state via the Cu—Al diffusion layer without the intervention of the brittle Fe—Al compound layer, both members 1 and 2 can be firmly bonded. After that, if necessary, the valve seat 1 is machined to complete the joining between the valve seat 1 and the cylinder head 2. Ideally, there is no Fe—Al compound layer at the interface P, but there is no problem even if a small amount of the Fe—Al compound layer remains at the interface P.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the case where copper is uniformly dispersed in the valve seat 1 before joining is shown, but the present invention is not limited to this. For example, the copper in the valve seat 1 before joining may be segregated so that the concentration of copper in the vicinity of the outer peripheral tapered surface 1b forming the interface P with the cylinder head 2 is relatively high. As a result, the amount of copper that moves toward the interface P during pressurization and energization increases, the concentration of copper at the interface P increases, and the Cu—Al diffusion layer is likely to be formed at the interface P.

Specifically, for example, as shown in FIG. 10, the density of copper is increased only in the vicinity of the outer peripheral tapered surface 1b of the valve seat 1 before joining (indicated by dense scattering points), and the density of copper in other regions is increased. May be low (indicated by sparse dots). Alternatively, in the valve seat 1, the region where the current density is relatively high, specifically, as shown in FIG. 11, the outer peripheral tapered surface forming the interface P from the inner peripheral tapered surface 1a with which the electrode 10 abuts. The density of copper in the region along the shortest energization path to 1b may be increased (indicated by dense scattering points), and the density of copper in other regions may be decreased (indicated by sparse scattering points).

Further, the present invention shows a case where the first member (valve seat 1) made of an iron-based sintered material forms an annular shape and the first member is attached to the inner circumference of the second member (cylinder head 2). However, it is not limited to this. For example, the present invention may be applied when the first member made of an iron-based material is attached to the outer periphery of the second member made of an aluminum material. Further, the first member is not limited to the annular shape, and may have other shapes. Further, the present invention is not limited to joining the valve seat and the cylinder head, but can be applied regardless of the application as long as the iron-based sintered material and the aluminum material are joined.

The following tests were conducted in order to find appropriate conditions for the joining method of the present invention. Specifically, a plurality of test pieces are prepared by joining a first member made of an iron-based sintered material and a second member made of an aluminum material at different pressures and energization amounts, and each test is performed. The joint strength (removal strength) of the pieces was measured. The materials and shapes of the first member and the second member conform to the valve seat 1 and the cylinder head 2 (particularly the seat mounting portion 8) of the above embodiment. As the pressing force, the pressing force for pushing the first member (maximum pressing force during energization) is the pressurizing direction of the contact surface (interface P) between the first member and the second member to which the pressing force is applied. The value divided by the projected area (pressurization per unit area) was calculated. Further, as the energization amount, a value (current density) was calculated by dividing the maximum value of the current value flowing between the two members by the projected area of the contact surface (interface P) of both members in the pressurizing direction.

FIG. 12 is a graph showing the conditions (pressurized pressure and energized amount) of each test piece. Of these, the test conditions and test results of the test pieces shown in Example 1, Comparative Examples 1 and 2 are shown in Table 1 below.

Among the test pieces shown in the graph of FIG. 12, those shown in diamonds, that is, those having a current density of less than 2.9 A / mm ² or those having a pressing force of less than 370 MPa per unit area are joined. The strength was weak, specifically, the pull-out strength was 5 kN or less. For example, in Comparative Example 1, since the amount of energization was low, neither the Fe—Al compound layer nor the Cu—Al diffusion layer was formed at the interface between the two members. In Comparative Example 1, the interface was broken under a low load (3.97 kN) in the pull-out test. Further, in Comparative Example 2, although the energization amount was high, the pressing force was low, so that the Fe—Al compound layer at the interface between the two members was not discharged, and the Cu—Al diffusion layer was hardly formed. In Comparative Example 2, in the drawing test, the interface, particularly the Fe—Al compound layer, was broken under a low load (1.47 kN).

On the other hand, among the test pieces shown in the graph of FIG. 12, those shown in squares, that is, those having a current density of 2.9 A / mm ² or more and a pressing force of 370 MPa or more per unit area are used. The joint strength was strong, and specifically, the pull-out strength was 5 kN or more. In these Examples 1, it is presumed that the energization amount and the pressing force were sufficiently high, and a high heat amount (heat input amount) was supplied to the interface. Specifically, the Fe—Al compound layer was not formed at the interface between the two members of Example 1, and the Cu—Al diffusion layer was sufficiently formed. In Example 1, in the pull-out test, the interface was not broken, the base material (aluminum material) was broken, and the load at that time was 30 kN or more. From these results, it was confirmed that the bonding strength (pulling strength) of both members was significantly increased by forming the Cu—Al diffusion layer at the interface between the two members. Further, as the conditions for that, it was clarified that it is preferable that the current density is 2.9 A / mm ² or more and the pressing force per unit area is 370 MPa or more.

On the other hand, among the test pieces shown in the graph of FIG. 12, those shown by triangles, that is, those having a current density of more than 3.6 A / mm ² or a pressing force of more than 650 MPa per unit area are both members. Since the amount of current applied or the pressure applied between them is too large, there is a risk that the iron-based sintered material will be burnt, the aluminum material will be sagging, or the material will explode. Therefore, the energization amount and the pressing force are set so as not to cause the above-mentioned problems. Specifically, the energizing density is 3.6 A / mm ² or less, and the pressing force per unit area is 650 MPa or less. Is preferable.

1 Valve seat (first member)
2 Cylinder head (second member)
3 Combustion chamber 4 Intake port 5 Exhaust port 6 Valve 8 Seat mounting part 10 Electrodes C1, C2 Coating P Interface between the first member and the second member

Claims (2)

It is a method for joining a first member made of an iron-based sintered material containing copper and a second member made of an aluminum material.
By energizing between the two members while pressing the first member against the second member, the Fe—Al compound layer generated at the interface between the two members is discharged from the interface and Cu—Al is discharged to the interface. A method of joining dissimilar metal materials to form a diffusion layer. The method for joining a dissimilar metal material according to claim 1, wherein copper is uniformly dispersed in the first member before joining to the second member.

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