CN115473095B - Electric connector - Google Patents

Abstract

The present invention is an electrical connector, comprising a male connector and a female connector that can be plugged in, and an electrical connection device. The male connector comprises at least one aluminum wire harness and at least one male terminal, and the electrical connection device comprises a connection body, two bending structures are respectively provided at both ends of the connection body, and the two bending structures extend to the same side of the connection body, and the two bending structures are respectively connected to the aluminum wire harness and the male terminal, and the male terminal is inserted into the female connector. The present invention can reduce the spatial size of the connector, simplify the structure, reduce weight, and reduce cost.

Description

Electrical connector

Technical Field

The invention relates to the field of electrical technology automobile wiring harness, in particular to an electric connector.

Background Art

With the development of the new energy vehicle field, the proportion of high-voltage electrical connectors (generally referring to electrical connectors with a voltage greater than 500V) used in automobiles is increasing, and the requirements for the volume and reliability of connectors are also increasing. As the number of squares of wire harnesses increases, the size of high-voltage electrical connectors is also increasing. For large-square connectors, the flow of large currents causes the electromagnetic interference ability of the high-voltage wire harness itself to other components to become stronger and stronger. In order to avoid electromagnetic interference to other components, the current high-voltage electrical connector needs to add a shielding layer on the inside of the high-voltage electrical connector. Compared with unshielded electrical connectors, such high-voltage electrical connectors are more expensive, heavier, and larger in size, resulting in higher and higher manufacturing and processing costs for the wiring harness system and more and more complex processes. In addition, in some installation occasions, elbow electrical connectors (i.e., electrical connectors with an angle of 90°-180° between the axial direction of the wire harness and the length direction of the terminal at the equipment end) are often needed. However, the current elbow electrical connectors with large square aluminum wires (generally referring to connectors with a square number greater than 70 squares) occupy a large lateral space, are large in size, and have complex connections, large weight, and high costs.

Therefore, the inventor, relying on many years of experience and practice in related industries, proposes an electrical connector to overcome the defects of the prior art.

Summary of the invention

The object of the present invention is to provide an electrical connector which can reduce the space size of the connector, has a simpler structure, is light in weight and has a low cost.

The above-mentioned purpose of the present invention can be achieved by adopting the following technical solutions:

The present invention provides an electrical connector, comprising a male connector and a female connector that can be plugged in, and an electrical connection device; the male connector comprises at least one aluminum wire harness and at least one male terminal, the electrical connection device comprises a connection body, two bending structures are respectively provided at both ends of the connection body, the two bending structures extend to the same side of the connection body, the two bending structures are respectively connected to the aluminum wire harness and the male terminal, and the male terminal is inserted into the female connector.

In a preferred embodiment of the present invention, the electrical connection device is an integrally stamped plate-shaped structure.

In a preferred embodiment of the present invention, the bending structure and the aluminum wire harness are connected by friction welding.

In a preferred embodiment of the present invention, a protrusion that is recessed outward is provided on one of the bending structures.

In a preferred embodiment of the present invention, a plurality of embedding holes are provided on another bending structure.

In a preferred embodiment of the present invention, a guide plug-in portion whose thickness gradually decreases outward is formed at the end of the other bending structure.

In a preferred embodiment of the present invention, at least a portion of the connecting body is a flexible conductor.

In a preferred embodiment of the present invention, the flexible conductor is a multi-core cable or a braided cable or a flexible row of multiple layers of thin plates.

In a preferred embodiment of the present invention, the length direction of the male terminal is perpendicular to the axial direction of the aluminum wire harness, the connecting body and the two bending structures are both plate-like structures, and the plate surfaces of the two bending structures are perpendicular to each other and to the connecting body; the plate surface of one of the bending structures is perpendicular to the axial direction of the aluminum wire harness, and the plate surface of the other bending structure is parallel to the plate surface of the end of the male terminal connected to the bending structure.

In a preferred embodiment of the present invention, the distance between the axis of the aluminum wire harness and the outer surface of the connecting body is greater than the distance between the axis of the aluminum wire harness and the outer surface of another bending structure.

In a preferred embodiment of the present invention, the two bending structures extend in a direction parallel to the length of the male terminal.

In a preferred embodiment of the present invention, the male terminal includes a transition terminal and an equipment terminal, the first end of the transition terminal is plugged and fixed to the electrical connection device, and the second end of the transition terminal is plugged and fixed to the first end of the equipment terminal.

In a preferred embodiment of the present invention, a first slot and a second slot are respectively formed at the first end and the second end of the transition terminal, the electrical connection device is inserted in the first slot, and the first end of the device terminal is inserted in the second slot.

In a preferred embodiment of the present invention, the male connector further comprises a plug shell and an insulating inner shell, the electrical connection device and parts of the aluminum wiring harness are both inserted into the insulating inner shell, and the insulating inner shell is inserted and fixed in the plug shell.

In a preferred embodiment of the present invention, a plug insulating lining is further provided on the inner wall of the plug housing.

In a preferred embodiment of the present invention, a connector tail shell is connected to the rear end of the plug shell, a shielding locking ring is disposed on the outer sleeve of the insulating inner shell, and the shielding locking ring is in contact with the connector tail shell.

In a preferred embodiment of the present invention, the female socket includes a socket shell, the male terminal is inserted into the socket shell, and the plug shell and the socket shell are locked by a secondary locking device.

In a preferred embodiment of the present invention, a socket insulating lining is also provided on the inner wall of the socket shell.

In a preferred embodiment of the present invention, a coating is provided at the connection between the bending structure and the aluminum wire harness, and the coating is a copper-aluminum transition layer.

In a preferred embodiment of the present invention, the copper-aluminum transition layer contains no less than 6.5 wt % of copper-aluminum solid solution.

As described above, the electrical connector in the present invention utilizes an electrical connection device to realize the transfer between the aluminum wire harness and the male terminal, and the electrical connection device adopts a bending structure, which can be used for large-square aluminum wire connectors. It not only has a simple structure and is easy to process, but also can reduce the spatial size of the connector, reduce volume and weight, and reduce costs.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are intended only to illustrate and explain the present invention, and are not intended to limit the scope of the present invention.

FIG. 1 is a three-dimensional view of the electrical connector provided by the present invention.

Figure 2: A top view of Figure 1.

Figure 3 is a cross-sectional view along the A-A direction in Figure 2.

FIG. 4 is a structural diagram of the aluminum wire harness and the insulating inner shell provided by the present invention.

FIG. 5 is a structural diagram of the aluminum wire harness provided by the present invention in cooperation with the electrical connection device and the male terminal.

FIG. 6 is a structural diagram of the electrical connection device provided by the present invention.

FIG. 7 is a second structural diagram of the electrical connection device provided by the present invention.

FIG. 8 is a third structural diagram of the electrical connection device provided by the present invention.

FIG. 9 is a structural diagram of the transition terminal provided by the present invention.

Description of Figure Numbers:

1. Aluminum wiring harness;

2. Electrical connection device; 21. Connection body; 22. First bending structure; 221. Protrusion; 23. Second bending structure; 231. Embedding hole; 232. Guide plug-in portion;

3. Male terminal; 31. Transition terminal; 311. First slot; 312. Second slot; 32. Device terminal; 321. Second card slot;

4. Insulating inner shell; 41. First card slot;

5. Plug housing; 51. Plug insulation lining; 511. First clamping block; 52. Connector tail housing; 53. Shield locking ring;

6. Socket housing;

7. Secondary locking device.

DETAILED DESCRIPTION

In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described with reference to the accompanying drawings.

As shown in Figures 1 to 9, this embodiment provides an electrical connector, including a pluggable male head and a female socket and an electrical connection device 2. The male head includes at least one aluminum wire harness 1 and at least one male terminal 3, and the electrical connection device 2 includes a connection body 21, and two bending structures (i.e., a first bending structure 22 and a second bending structure 23) are respectively provided at both ends of the connection body 21, and the two bending structures extend to the same side of the connection body 21, and the two bending structures are respectively connected to the aluminum wire harness 1 (end) and the male terminal 3 (end), and the male terminal 3 is inserted into the female socket. Among them, the number of the electrical connection device 2, the aluminum wire harness 1 and the male terminal 3 is the same, and it is mainly suitable for elbow electrical connectors, that is, the angle between the length direction of the male terminal 3 and the axial direction of the aluminum wire harness 1 can be 90°-180°.

The electrical connector in this embodiment uses an electrical connection device 2 to achieve the transfer between the aluminum wire harness 1 and the male terminal 3, and the electrical connection device 2 adopts a bending structure, which can be used for large-square aluminum wire connectors. It not only has a simple structure and is easy to process, but also can reduce the spatial size of the connector, reduce the volume and weight, and reduce costs.

In a specific implementation, the electrical connection device 2 is an integrally stamped plate-shaped structure.

In this way, when used to connect the aluminum wire harness 1 and the male terminal 3, an integrated and bent electrical connection device 2 is used at the bending connection between the aluminum wire harness 1 and the male terminal 3, and there is no need for secondary bolt connection or crimping. The structure is simpler, the volume and weight are reduced, and the cost is reduced. Moreover, while ensuring a small size, the connection points of large-square aluminum wire terminals are reduced, thereby achieving a connection with a smaller contact resistance.

Preferably, the bending structure (specifically the first bending structure 22) is connected to the aluminum wire harness 1 by friction welding. Aluminum wire friction welding has better electrical conductivity, stronger mechanical connection performance, and can achieve the purpose of reducing cost and weight.

Generally, a protrusion 221 is provided on one of the bending structures (i.e., the first bending structure 22) that is concave outward (specifically, it is concave in the direction close to the aluminum wire harness 1). The specific shape of the protrusion 221 can be determined according to actual needs. For example, in this embodiment, referring to FIG. 5 and FIG. 6, the protrusion 221 is a round rod structure that is concave outward and is coaxial with the aluminum wire harness 1.

When installed in the connector, the protrusion 221 is connected to the aluminum wire harness 1 by friction welding. During processing, the rotating spindle of the friction welding device is inserted into the inner pit of the protrusion 221, and the aluminum wire harness 1 is clamped by the clamp of the friction welding device. During friction welding, the aluminum wire harness 1 remains stationary, and the first bending structure 22 rotates with the rotating spindle to achieve friction welding connection between the two. The protrusion 221 can be used to facilitate centering, ensure the concentricity of the electrical connection device 2 and the aluminum wire harness 1 at the connection, and ensure the connection appearance and connection quality.

Furthermore, a plurality of embedding holes 231 are provided on another bending structure (specifically, the second bending structure 23 ) to enhance the strength of the integral injection molding.

6 , a guide plug-in portion 232 whose thickness gradually decreases outward is formed at the end of another bending structure (ie, the second bending structure 23 ), which can facilitate plug-in cooperation with the male terminal 3 .

Furthermore, the connection body 21 is at least partially a flexible conductor, for example, the flexible conductor is a multi-core cable or a braided cable or a flexible row of multiple layers of thin plates. When the male terminal 3 vibrates, the connection body 21 can better absorb the vibration and reduce the vibration transmitted to the aluminum wire harness 1; at the same time, it has a better fault tolerance during assembly.

The specific bending angles of the above two bending structures are determined according to the angle between the length direction of the male terminal 3 in the elbow electrical connector used and the axial direction of the aluminum wire harness 1. For example, when applied to a 90° electrical connector, referring to Figures 5 and 6, the length direction of the male terminal 3 is perpendicular to the axial direction of the aluminum wire harness 1, the connecting body 21 and the two bending structures are both plate-like structures, and the plate surfaces of the two bending structures are perpendicular to each other and perpendicular to the connecting body 21; the plate surface of one of the bending structures (i.e., the first bending structure 22) is perpendicular to the axial direction of the aluminum wire harness 1, and the plate surface of the other bending structure (i.e., the second bending structure 23) is parallel to the plate surface of the end portion of the male terminal 3 connected to the bending structure.

The specific shapes of the first bending structure 22, the connecting body 21 and the second bending structure 23 can be determined as needed. For example, in this embodiment, the first bending structure 22 is a circular plate, the connecting body 21 is a right-angled triangular plate with a transition arc, and the length direction of the connecting body 21 extends along the axial direction of the aluminum wire harness 1, and the second bending structure 23 is a rectangular plate.

Due to the process requirements of stamping itself, the distance L between the axis of the aluminum wire harness 1 and the outer surface of the connecting body 21 must be greater than the distance T between the axis of the aluminum wire harness 1 and the outer surface of another bending structure (i.e., the second bending structure 23), as shown in Figures 6 to 8; and due to the friction welding process requirements of large-square friction welding terminals, the value of the distance L is relatively large and must be within a certain size range.

Further preferably, both of the two bending structures extend in a length direction parallel to the male terminal 3, which can reduce the space occupied by the terminal compared to the existing large-square friction welding terminal, and can ensure that the lateral dimension occupied by the electrical connection device 2 is small (the lateral dimension is perpendicular to the axis of the aluminum wire harness 1 and the dimension of the plate surface of the male terminal 3), which is convenient for reducing the lateral dimension of the connector; especially for multi-core terminals (that is, when the number of aluminum wire harnesses 1 is greater than or equal to two, each aluminum wire harness 1 is arranged in parallel), the lateral dimension is shortened more significantly; and the second bending structure 23 can also ensure that the contact area with the male terminal 3 meets the requirements of a large square number. The bending line formed between the second bending structure 23 and the connecting body 21 is arranged along the axial direction of the aluminum wire harness 1, and can be as close to the center line of the aluminum wire harness 1 as possible when meeting the requirements of the friction welding process, and the structure is more compact.

In an optional manner, an insulating layer is integrally molded and wrapped on the outer side of the electrical connection device 2. The insulating layer should avoid the connection position between the first bending structure 22 and the aluminum wire harness 1 and the connection position between the second bending structure 23 and the male terminal 3, that is, the insulating layer is not wrapped at the position where the electrical connection device 2 contacts the aluminum wire harness 1 and the male terminal 3, and the remaining positions of the electrical connection device 2 are wrapped with an insulating layer, which can play a role in insulation protection and prevent leakage. The above-mentioned multiple embedded holes 231 should be distributed on both sides of the first end of the male terminal 3, and the use of the embedded holes 231 can enhance the strength of the integral injection molding.

Preferably, the male terminal 3 includes a transition terminal 31 and an equipment terminal 32, the first end of the transition terminal 31 is plugged and fixed to the electrical connection device 2 (specifically the second bending structure 23), and the second end of the transition terminal 31 is plugged and fixed to the first end of the equipment terminal 32.

The transition terminal 31 and the device terminal 32 can be parallel to each other according to the plate surface shown in FIG. 5, or they can be arranged in other shapes and in other ways as needed. The plate surface of the second bending structure 23 should be parallel to the end plate surface of the male terminal 3, that is, parallel to the plate surface of the first end of the transition terminal 31, so as to facilitate the connection between the second bending structure 23 and the first end of the transition terminal 31, and at the same time facilitate the contact area between the two to meet the requirements of a large square number. The male terminal 3 is composed of a transition terminal 31 and a device terminal 32. When in use, the transition terminal 31 of different shapes, lengths and other structural forms can be connected and combined with the device terminal 32 (also called copper bus terminal) of different shapes (can also be bent) and lengths and other structural forms as needed, which is more flexible and diverse, making the connector more suitable for a variety of environments, meeting the diverse needs of the connector, and having stronger versatility.

In order to facilitate plug-in matching, referring to Figures 5 and 9, a first slot 311 and a second slot 312 are formed at the first end and the second end of the transition terminal 31, respectively. The electrical connection device 2 (specifically, the second bending structure 23) is inserted into the first slot 311, and the first end of the device-end terminal 32 is inserted into the second slot 312. The transition terminal 31 can be in the form of a single-piece terminal, or it can be composed of a plurality of sheet-shaped terminals stacked as shown in Figure 5, and then plugged with the device-end terminal 32.

Furthermore, the male plug further includes a plug shell 5 and an insulating inner shell 4, and the electrical connection device 2 and parts of the aluminum wire harness 1 are both inserted into the insulating inner shell 4, and the insulating inner shell 4 is inserted and fixed in the plug shell 5. The insulating inner shell 4 mainly serves to insulate and protect the electrical connection device 2 and the aluminum wire harness 1, and the corresponding ends of the aluminum wire harness 1 can extend out of the insulating inner shell 4.

In order to facilitate the fixation between the insulating inner shell 4 and the plug outer shell 5, a first clamping block 511 is protruded on the inner wall of the plug outer shell 5, and a first clamping groove 41 is provided on the outer wall of the insulating inner shell 4. The first clamping block 511 can be clamped in the first clamping groove 41. The plug outer shell 5 and the insulating inner shell 4 are positioned and locked by buckles, which can enhance the tensile strength of the connector.

In an optional manner, referring to FIG3 , a plug insulating liner 51 is further provided on the inner wall of the plug shell 5, and a first clamping block 511 is formed on the inner wall of the plug insulating liner 51. The plug insulating liner 51 is a glue-filled structure, which is filled between the plug shell 5 and the insulating inner shell 4. The plug insulating liner 51 can provide better protection for the electrical connection device 2 and the aluminum wire harness 1.

1 and 4, a connector tail shell 52 is connected to the rear end of the plug shell 5, and a shielding locking ring 53 is provided on the outer cover of the insulating inner shell 4. The shielding locking ring 53 contacts the connector tail shell 52 to realize an external shielding path. The shielding locking ring 53 can be integrally connected to the insulating inner shell 4 by injection molding.

Furthermore, the female socket includes a socket housing 6, the male terminal 3 is inserted into the socket housing 6, and the plug housing 5 and the socket housing 6 are locked by a secondary locking device 7. The specific structure of the secondary locking device 7 can adopt any existing method, and the present invention is not limited to this.

In order to facilitate the fixation of the male terminal 3 and the socket shell 6, a second clamping block is protruding on the inner wall of the socket shell 6, and a second clamping groove 321 is provided on the male terminal 3 (the second clamping groove 321 is specifically provided on the device terminal 32), and the second clamping block can be clamped in the second clamping groove 321.

In an optional manner, a socket insulation liner is further provided on the inner wall of the socket shell 6, and the second block is formed on the inner wall of the socket insulation liner. The socket insulation liner is a glue-filled structure filled in the socket shell 6, and the socket insulation liner can provide better protection for the male terminal 3.

In an optional manner, a coating is provided at the connection between the bending structure and the aluminum wire harness 1, and the coating is a copper-aluminum transition layer. The copper-aluminum transition layer is provided on the connection surface between the bending structure made of copper and the aluminum wire harness 1 made of aluminum. Under the action of heat and pressure, copper atoms and aluminum atoms mutually penetrate or combine to form a copper-aluminum transition layer, which not only avoids electrochemical corrosion between copper and aluminum, but also improves the electrical and mechanical properties of the copper-aluminum connection, thereby significantly improving the mechanical and electrical properties of the copper-aluminum composite terminal.

It should be noted that the copper-aluminum transition layer at least contains copper, aluminum, copper-aluminum solid solution and copper-aluminum compound. The copper-aluminum compound is one or more of Cu2Al, Cu3Al2, CuAl, and CuAl2.

In an optional manner, the copper-aluminum transition layer contains no less than 6.5wt% of copper-aluminum solid solution. When the copper-aluminum transition layer contains less than 6.5wt% of copper-aluminum solid solution, the other components in the copper-aluminum transition layer are greater than 93.5wt%. The copper-aluminum transition layer has a large proportion of copper and aluminum, which means that the copper-aluminum welding is not sufficient and the copper-aluminum elements are not fused into a copper-aluminum solid solution. The copper-aluminum transition layer has a large proportion of copper-aluminum compounds, and the electrical conductivity of the copper-aluminum compounds is very poor. The copper-aluminum compounds are also very brittle, and a high content will reduce the mechanical and electrical properties of the copper-aluminum composite terminal. Therefore, the copper-aluminum transition layer described in the present invention contains at least 6.5wt% of copper-aluminum solid solution.

In order to demonstrate the influence of different proportions of copper-aluminum solid solution in the copper-aluminum transition layer on the pull-out force and voltage drop between the bending structure and the aluminum wiring harness 1, the pull-out force, voltage drop and welding strength of the electrical connector with different proportions of copper-aluminum solid solution in the copper-aluminum transition layer were investigated. The results are shown in Table 1.

Table 1: Effect of the proportion of copper-aluminum solid solution in the copper-aluminum transition layer on the pull-out force and voltage drop of the electrical connector

It can be seen from Table 1 above that when the copper-aluminum solid solution contained in the copper-aluminum transition layer is less than 6.5wt%, the pull-out force between the bending structure and the aluminum wiring harness 1 is significantly reduced, while the voltage drop is significantly increased, and the mechanical and electrical performance requirements of the bending structure and the aluminum wiring harness 1 cannot be met. As the proportion of the copper-aluminum solid solution contained in the copper-aluminum transition layer gradually increases, the mechanical and electrical properties of the connection between the bending structure and the aluminum wiring harness 1 are gradually enhanced, so the inventors set that the copper-aluminum transition layer contains no less than 6.5wt% of the copper-aluminum solid solution.

The above are only exemplary embodiments of the present invention and are not intended to limit the scope of the present invention. Any equivalent changes and modifications made by any person skilled in the art without departing from the concept and principle of the present invention shall fall within the scope of protection of the present invention.

Claims (19)

1. An electrical connector, characterized in that it comprises a male connector and a female connector that can be plugged in and an electrical connection device; The male connector includes at least one aluminum wire harness and at least one male terminal, the electrical connection device includes a connection body, two bending structures are respectively provided at both ends of the connection body, the two bending structures extend to the same side of the connection body, the two bending structures are respectively connected to the aluminum wire harness and the male terminal, and the male terminal is inserted into the female seat; The length direction of the male terminal is perpendicular to the axial direction of the aluminum wire harness, the connecting body and the two bending structures are both plate-like structures, and the plate surfaces of the two bending structures are perpendicular to each other and to the connecting body; the plate surface of one of the bending structures is perpendicular to the axial direction of the aluminum wire harness, and the plate surface of the other bending structure is parallel to the plate surface of the end portion of the male terminal connected to the bending structure. 2. The electrical connector according to claim 1, wherein: The electrical connection device is an integrally stamped plate-shaped structure. 3. The electrical connector according to claim 1, wherein: The bending structure and the aluminum wire harness are connected by friction welding. 4. The electrical connector according to claim 1, wherein: A protrusion which is recessed outwards is provided on one of the bending structures. 5. The electrical connector according to claim 1, wherein: A plurality of embedding holes are provided on the other bending structure. 6. The electrical connector according to claim 1, wherein: A guide plug-in portion whose thickness gradually decreases outwards is formed at the end of the other bending structure. 7. The electrical connector according to claim 1, wherein: At least a part of the connecting body is a flexible conductor. 8. The electrical connector according to claim 7, wherein: The flexible conductor is a multi-core cable or a braided cable or a flexible cable formed by stacking multiple layers of thin plates. 9. The electrical connector according to claim 1, wherein: The distance between the axis of the aluminum wire harness and the outer surface of the connecting body is greater than the distance between the axis of the aluminum wire harness and the outer surface of another of the bending structures. 10. The electrical connector according to claim 9, wherein: The two bending structures both extend in a direction parallel to the length of the male terminal. 11. The electrical connector according to claim 1, wherein: The male terminal includes a transition terminal and an equipment terminal. The first end of the transition terminal is plugged and fixed to the electrical connection device, and the second end of the transition terminal is plugged and fixed to the first end of the equipment terminal. 12. The electrical connector according to claim 11, wherein: A first slot and a second slot are formed at the first end and the second end of the transition terminal, respectively. The electrical connection device is inserted into the first slot, and the first end of the device-end terminal is inserted into the second slot. 13. The electrical connector according to claim 1, wherein: The male connector further comprises a plug shell and an insulating inner shell, the electrical connection device and parts of the aluminum wiring harness are both inserted into the insulating inner shell, and the insulating inner shell is inserted and fixed in the plug shell. 14. The electrical connector according to claim 13, wherein: A plug insulating lining is also provided on the inner wall of the plug housing. 15. The electrical connector according to claim 13, wherein: A connector tail shell is connected to the rear end of the plug shell, a shielding locking ring is arranged on the outer sleeve of the insulating inner shell, and the shielding locking ring is in contact with the connector tail shell. 16. The electrical connector according to claim 13, wherein: The female socket comprises a socket shell, the male terminal is inserted into the socket shell, and the plug shell and the socket shell are locked by a secondary locking device. 17. The electrical connector according to claim 16, wherein: A socket insulating lining is also provided on the inner wall of the socket shell. 18. The electrical connector according to claim 1, wherein: A coating is provided at the connection between the bending structure and the aluminum wire harness, and the coating is a copper-aluminum transition layer. 19. The electrical connector according to claim 18, wherein: The copper-aluminum transition layer contains no less than 6.5 wt % of copper-aluminum solid solution.