Why to use aluminum to instead coper in automotive wiring harness?

Cost reduction by 35% & weight reduction by 30%

The weight of the wiring harness has reached approximately 5% of the total vehicle weight. Along with the continuous advancement of automotive electrification and Intelligentization, the proportion is still gradually increasing. Therefore, cost reduction for wire harnesses has become an urgent task.

In automotive wiring harness, the resistivity of aluminum is 27.8, while that of copper is 17.24.

Due to the density of aluminum is 2.7 kg/m3 while that of copper is 8.89 kg/m3, aluminum wiring harness will still reduce weight by 30% than copper wiring harness even after increasing the diameter or corresponding cross-sectional area of the aluminum wire. 

Under the same substitution conditions, alternation from copper to aluminum will lead to wiring harness cost reduction by approximately 35%. 

Selection of aluminum-wire specifications 

It is necessary to have similar electrical conductivity, current-carrying capacity, and derating curves between copper and selected aluminum in case of equivalent replacing copper wiring harness by aluminum.

Figure is a specification comparison chart that can be considered as equivalent substitution between copper and aluminum.

Challenges faced

Galvanic corrosion

When there is water, carbon dioxide, and other impurities in the environment, an electrolyte is formed. Both electrolyte, copper terminals and aluminum wire constitutes a simple chemical battery.

Based on different chemical activities, in a chemical battery, aluminum is the negative electrode because it easily loses electrons, while copper is the positive electrode for the opposite reason. The chemical battery creates both an electromotive force of around 1.69V and tiny current between both electrodes. The continuous tiny current corrodes the aluminum wire slowly, which is known as Galvanic Corrosion.

Galvanic corrosion can cause loose contacts between copper terminal and aluminum wire, resulting in increased contact resistance.

While carrying working current, contact resistance will cause the temperature rise at the connection, thereby accelerating galvanic corrosion at the connection, ultimately leading to a further increase in contact resistance. This is a vicious cycle.

Creep deformation

coefficient of thermal expansion: Copper 0.0000165, Aluminum 0.0000236

Along with environmental temperature fluctuation, cavities will form in the copper-aluminum connection area gradually due to different thermal expansion coefficients of both metals.

Cavities caused by metal creep will not only reduce the electrical performance of connection area but also increase the contact resistance in the connection area. 

While carrying working current, contact resistance will cause the temperature rise at the connection area, thereby forming more creep cavities there, ultimately leading to a further increase in contact resistance. This is a vicious cycle also.

In the meantime, creep cavities will also lead to mechanical strength gradual decrease in the copper-aluminum connection area. In the case of vehicle vibrations, it is possible that severe creep cavities will lead to vehicle circuit break. 

Electrical performance decrease at the wire connection area

Aluminum metal reacts quickly with oxygen in the air to form Aluminum oxide (Al2O3) film on connection area.

The conductivity of pure Al2O3 at room temperature (300 K) is extremely low, typically in the range of 10^-13 to 10^-14 S/m. This makes Al2O3 an excellent electrical insulator.

While carrying working current, resistance of aluminum oxide will also cause the temperature rise at the connection area.

(A derating curve is used in engineering and electronics to indicate the maximum allowable operating conditions for components, such as temperature and current.)

Before aluminum wire harnesses are widely used in the automotive industry, above mentioned challenges related to copper terminals and aluminum wires harness need to be addressed first.

solutions

friction welding (for bimetallic terminals)

The bimetallic terminals are copper-aluminum transition wire terminal processed by friction welding. 

These terminals are constructed by welding two dissimilar metals, typically copper and aluminum, using a high-precision friction welding process. This ensures a secure, low-resistance connection, reducing the risk of overheating and enhancing overall electrical performance.

terminal crimping (for bimetallic terminals)

Terminal crimping ensures a secure and reliable electrical connection between wires and terminals. The crimping process creates a mechanical bond between the wire and terminal, preventing accidental disconnections due to vibrations, temperature changes, or other external factors. 

Different applications with different crimping shapes.

The aluminum end of the bimetallic terminal is connected to the aluminum wire through terminal square crimping process. 

ultrasonic welding (for copper terminals) 

Ultrasonic welding is an advanced terminal welding method. It uses high-frequency ultrasonic vibrations to create friction between materials, generating enough heat to bond them without additional solder or adhesives. This technique is particularly effective for joining thin materials, such as copper foil or aluminum sheets, to terminals.

Suffering high frequency vibration from ultrasound, any oxide layers or contaminants on the surfaces of aluminum monofilament will be thoroughly removed.

Both copper and aluminum belong to the face-centered cubic face (FCC) structure in metal crystal structures. 

Under sufficient pressure, the atoms of the two metal surfaces interlock (Atomic Swap), and a solid bond forms. Since there is no melting or heat involved, the bond is formed purely through atomic interactions at the interface.

Through ultrasonic welding technology, challenges such as galvanic corrosion, metal creep, and electrical performance at copper-aluminum connection area have been resolved completely.

Diffusion Welding (for bimetallic and/or copper terminals)

Diffusion Welding (DFW) is a solid-state welding method that involves placing tightly contacted weldments in a vacuum or protective atmosphere and maintaining them at a certain temperature and pressure for a period of time. This allows the atoms at the contact interface to diffuse into each other, achieving a reliable connection. 

Principles of Diffusion Welding

During diffusion welding, two or more weldments are tightly pressed together and placed in a vacuum or protective atmosphere. They are heated to a temperature below the parent material’s melting point and then pressure is applied. This shatters the oxide film on the surface and the microscopic protrusions on the surface undergo plastic deformation and high-temperature creep, achieving close contact.

This activates the diffusion between the atoms at the interface, achieving bonding in several small areas. After maintaining the temperature for a certain period of time, these areas further expand through atomic diffusion. When the entire connection interface forms a metallic bond, the diffusion welding process is completed. 

The resolution of above mentioned technical challenges has already led to the automotive industry increasingly replacing traditional copper wire harnesses by aluminum wire harnesses.

Why choose aluminum bus bar to replace aluminum wiring harness?

Challenges faced

Due to the higher resistivity of aluminum than copper, it is necessary to increase the diameter or cross-sectional area of the aluminum wires to meet both carrying capacity and resistance requirements of the vehicle circuit. 

However, due to the limited internal space of the whole vehicle, wiring harness layout has always been a challenge.

Subjected to increased diameter of the wire harness, the original layout of the wire harness might lead to interference with other components.

solutions

The aluminum bus bar uses a solid aluminum flat wire structure, and the layout is designed to fit the body more closely, thus the aluminum bus bar can effectively reduce the overall space occupation.

In addition, since the solid aluminum flat wire structure is easier to process than aluminum stranded wire, replacement from aluminum wiring harness to aluminum bus bar will lead to processing cost reduction. 

Why choose NORTHBRIDGES aluminum bus bar to replace aluminum wiring harness?

NORTHBRIDGES pioneered introducing EV high-voltage wiring harness industries.

Our high-voltage charging non-shielded aluminum bars and high-voltage charging shielded aluminum bars have been successfully used on many key projects in series production for both China local and European customers.

Our factory currently has 5 3-D bending machines, 10 ultrasonic welding machines, and 5 diffusion welding machines. The current production capacity of the factory can meet the annual demand of 1 million high-pressure aluminum bus bars from domestic and international customers.

An example of 800V electric vehicle, inside which our high-voltage aluminum bus bar is assembled. Our Engineers used the combination of high-voltage shield aluminum bus bar and powder-painted LBB solutions. It is a compact design which effectively saved space and cost of wiring harness while enhanced the electrical performance.