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In order to realize the requirement of automobile lightweight, some new lightweight materials have been widely used in automobile body, engine and other parts. As an important part of the automobile, the Wire Harness accounts for 2% ~ 3% of the total mass of the whole vehicle. With the increase of the proportion of the automobile electrical system, the wiring harness, as an electrical connection system, becomes more and more complex, and its quality continues to increase. At present, all the wires used in automotive wiring loom are copper wires. In recent years, with the rising price of copper year after year, and in order to meet the requirements of lightweight automobiles, it is imperative to seek new methods and materials to replace copper wires. Compared with copper wire, aluminum wire has the advantages of light weight and low price. Therefore, aluminum wire is considered as one of the most suitable materials to realize the lightweight of automotive Wiring Harness.
Compared with copper wire, the density of aluminum wire is smaller, and the weight of aluminum wire is lighter under the same length, which is one of the trends of light weight development of wire harness. The density ratio of copper to aluminum is 10: 3, and the volume of 1t aluminum wire purchased is about 3.3t copper wire.
Global copper reserves are much smaller than aluminum, so the price of copper is higher than that of aluminum, and the price of copper is on the rise, while the price of aluminum is relatively low and fluctuates little. Automotive wiring harness uses a large amount of copper, and replacing copper with aluminum can effectively reduce the production cost in automotive wiring harness.
In view of the technical difficulties existing in the application of aluminum conductor in automotive wiring harness, these technical difficulties have been overcome continuously in recent years through continuous exploration by researchers, thus promoting the process of realizing the lightweight of automotive wiring harness.
As the most important function of conductor is to carry current, the conductivity of aluminum conductor is lower than that of copper conductor, which is the inherent characteristic of aluminum conductor. To achieve the same current-carrying capacity as copper conductor, the cross-sectional area of aluminum conductor must be increased. The current carrying capacity of aluminum conductor with the same cross section is 25% lower than that of copper conductor. When copper and aluminum wires have the same current carrying capacity, although the cross section of aluminum wire increases, its quality is still about 50% lower than that of copper wire.
In QC/T 29106 "Technical Conditions of Automobile Wire Harness", it is stipulated that the terminal should be firmly pressed with the wire, and should not be damaged or detached under the specified tension. However, the tensile strength of aluminum wire is low, which affects the pull-off force of terminal crimping. The most effective solution is to develop a brand-new aluminum alloy wire in order to restrain the decrease of conductivity of aluminum wire and improve its strength.
This brand-new aluminum alloy wire not only lightens the harness and ensures conductivity, but also makes the wire have excellent strength, processability and impact resistance.
It is easy for aluminum to form dense oxide layer in air, and it has strong insulation while protecting the inside from corrosion. For better electrical connection, it is necessary to destroy the oxide layer during terminal crimping. At this time, the key breakthrough is to improve the original groove-shaped pressing bar of the terminal crimping part into a "serrated" or "tapered bump" pressing bar. This structure can pierce the oxide layer on the surface of the aluminum conductor during crimping, and establish a good metal contact between the underlying metal aluminum and the terminal surface, thus realizing reliable connection. At the same time, the serrated or tapered bump pressing bar structure increases the crimping contact area and improves the terminal crimping pull-off force.
When copper terminals are crimped with aluminum wires, due to the potential difference between copper and aluminum, water vapor will appear at the junction, and when chemical medium is dissolved in the water vapor, electrochemical corrosion will be formed at the junction of copper and aluminum. The conditions of electrochemical corrosion in copper crimping are potential difference and electrolyte. At this time, the key breakthrough is to eliminate potential difference and seal and isolate electrolyte. The methods to eliminate the potential difference include the design of copper-aluminum transition terminal, etc. Electrolyte isolation methods include direct sealing isolation, intermediate sealing isolation, anti-corrosion treatment, etc.
Different metal materials have different standard electrode potentials. In order to make the potential difference between contacting metals zero, the contacting metals must be the same material.
To solve this problem, the copper-aluminum transition terminal developed includes a copper nose and an aluminum connecting tube. Using the copper-aluminum transition terminal to crimp aluminum wires eliminates the potential difference and avoids the electrochemical corrosion of copper and aluminum. For the terminal products with small wire diameter, the copper-aluminum transition terminal can't meet the diversified and complicated structural requirements of the products. Therefore, under the condition of keeping the existing structure of the terminal products with small wire diameter, the electrochemical corrosion of the crimping between the copper terminal and the aluminum wire can only be solved by isolating the electrolyte.
The electrochemical corrosion between copper and aluminum can be solved by anti-corrosion treatment after copper terminals are crimped with aluminum wires. The anti-corrosion treatment methods include resin molding and spraying. The resin molding method is that after the traditional copper terminal is crimped to the aluminum wire, an injection mold is used to seal the joint between the terminal crimping part and the aluminum wire with thermoplastic resin, so that the terminal crimping part and the aluminum wire are isolated from the outside. Anti-corrosion materials used in resin molding are: polyamide resin, polyethylene resin, polypropylene resin, polyolefin resin and other organic resins.
The spraying method is to use a special spraying device to spray the liquid or pasty anticorrosive agent on the exposed aluminum wire which is not covered by the terminal crimping part after the traditional copper terminal is crimped, so as to isolate the aluminum wire from the outside, prevent water and electrolyte from entering the contact between the copper terminal and the aluminum wire, and inhibit the electrochemical corrosion of copper and aluminum. The anti-corrosion materials used in the spraying method are: ① intermediate potential metal anti-corrosion film; ② photosensitive resin (ethoxylated phenyl acrylate, phenoxypolyethylene glycol acrylate, etc.); ③ Hydrophobic corrosion inhibitor (benzotriazole with hydrophobic group, etc.).
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