Both metals perform. We know that. Both copper and aluminium have been performing for years. Yet there are differences between the two, of course. Choosing between copper and aluminium busbars involves trade-offs regarding weight, manufacturability, accessibility and cost, and performance. Both copper and aluminium are used in electricity transmission because of their high conductivity-to-cost ratio, though aluminium’s lower density gives it a decisive advantage in weight-sensitive applications like overhead lines and EV busbars.
As an example, aluminium’s lower density enables favorable conductivity-to-weight ratios, and in many applications, this allows aluminium components to deliver equivalent conductance with reduced mass. And this can provide benefits in application design, transport efficiency and structural integration.
But let me get back to the importance of surface, and surface treatment, in electrical contacts.
1xxx and 6xxx aluminium alloys
Aluminium is not only aluminium. There are more than 500 aluminium alloy compositions – and those are only the registered compositions.
When it comes to electrical applications like busbars, tubular busbars, and conductors, the high purity 1xxx-series alloys offer excellent conductivity, light weight and good corrosion resistance. They are also widely used in heat exchangers due to their high thermal conductivity.
These alloys contain a minimum of 99% aluminum content by weight. Alloy 1050, for example, has a minimum purity of 99.5% while the electrical-grade 1370 alloy contains no less than 99.7% aluminium. Both can be extruded into profiles, rods, bars and tubes, and both offer good corrosion resistance and excellent forming, welding, brazing and finishing characteristics.
That said, while the high purity 1xxx-series alloys generally offer the highest electrical conductivity within the family of aluminium alloys, elements such as magnesium and silicon can be introduced to improve mechanical and electrical contact performance, improving important properties such as tensile/yield strengths, creep, fatigue, and stress relaxation.
These 6xxx-series alloys are therefore terrific candidates for applications where it is important to balance good electrical conductivity and mechanical performance. Typical applications include electrical-grade aluminium busbar products, power transmission systems and in transformer substations.
How surface treatment improves contact performance
As with copper, aluminium conductors naturally form a thin surface oxide layer when they are exposed to oxygen. While this oxide provides effective corrosion protection, it is highly insulating and it increases contact resistance at electrical interfaces – and can reduce system efficiency if not properly managed.
In demanding applications such as high-voltage connectors, reliable performance therefore depends on clean, stable, and durable contact surfaces. This is also true with regard to busbars for electric vehicles, which are flat metallic strips or bars – and in some installations, tubular conductors – used to conduct high electrical currents within an electric car.
Consequently, proper surface treatments are required to ensure minimum contact resistance and prevent overheating in joints and connections. They improve contact performance by:
- Lowering contact resistance. This ensures efficient current flow across joints.
- Preventing corrosion. This improves durability in humid, marine, or polluted environments.
- Improving joint stability. This reduces fretting, wear, and thermal cycling degradation.
- Extending service life. This minimizes maintenance and avoids downtime.
- Enabling dissimilar metal connections. This stabilizes aluminium-to-copper interfaces.
The most common treatments are nickel, tin, or silver plating, often with a zincate pre-treatment to ensure strong adhesion. Nickel plating is the recommended default for most aluminium busbar applications. Silver plating is the preferred treatment for high-temperature joints and switchgear.
Aluminium busbar surface treatments compared: tin, silver, nickel, and copper
Let us take a look at each of these treatments, starting with tin plating.
- Tin plating coats the aluminium contact surfaces with tin, often after a zincate and nickel pre-layer. This is a relatively simple process with a low cost, and it reduces galvanic corrosion while improving joint stability at elevated temperatures.
- Silver plating on aluminium busbars results in very high conductivity, and is suitable for high-temperature joints, most commonly for switchgear applications.
- Nickel plating consists of a sulfamate nickel layer, often added after a zincate pretreatment. Nickel plating provides stable contact resistance under vibration, humidity, and current cycling, and, among these three treatments, it offers the best balance of performance and cost.
A fourth treatment is copper coating, where a thin layer of copper is applied to the aluminium, either by cladding, electroplating or thermal spraying.
Copper coating maintains aluminium's low weight with improved electrical conductivity at surface level. It provides a stable copper-to-copper contact interface which reduces joint resistance. In addition, you get enhanced compatibility with copper connectors and busbars as well as an extra barrier against oxidation and fretting at the contact surface.
I hope you have a better understanding of the issue at hand, because at the end of the day, reliable performance depends on clean, stable, and durable contact surfaces.
