Aluminium busbar alloys: 1350 vs 6101-T6

What the two alloys are for

1350 is the electrical conductor grade of aluminium. It is essentially pure aluminium with a minimum aluminium content and a controlled impurity level, specified for conductivity. It is supplied in soft or strain-hardened tempers and is the default when the bar is mainly a current path.

6101 is a magnesium-silicon alloy in the 6xxx family. In the T6 temper it is solution treated and artificially aged, which raises its strength well above 1350. It is used where the bar has to carry mechanical load, span a gap without sagging or resist vibration, as well as carry current.

Conductivity and the section penalty

1350 is specified at a minimum conductivity of about 61 per cent IACS in the common electrical tempers. 6101-T6 is lower, typically around 55 per cent IACS, because the alloying elements that provide strength also scatter electrons. The exact value depends on the temper and the product, so the certificate is the reference.

That difference means a 6101-T6 bar needs more section than a 1350 bar for the same current and the same temperature rise. The extra section adds weight and cost, which partly offsets the reason for choosing the stronger alloy. The trade is worth it only when the mechanical requirement is real.

Strength, spans and vibration

1350 in the annealed condition is soft. It is easy to form and easy to damage, and it will sag under its own weight over a long unsupported span. In a short, well-supported link inside an enclosure, that is rarely a problem. In a long run between supports, or in a part that sees vibration, it can be.

6101-T6 has a yield strength several times that of annealed 1350. It holds its shape across a span, resists bending under fault current forces and keeps a joint face flatter when the bar is bolted. That is why it appears in busbar systems for vehicles, switchgear and equipment where the bar is also a structural member.

Vibration and fatigue are separate from static strength. A bar that carries alternating current in a magnetic field sees force cycles, and a bolted joint may see micro-movement. A stronger alloy helps, but the joint design and the support damping matter as much.

Bending and forming

1350 forms easily. It can be bent flatwise or edgewise to a relatively tight radius, and it tolerates the springback and hand adjustment that a prototype needs. Annealed 1350 is the most forgiving of the two for a formed busbar.

6101-T6 is much less forgiving. In the T6 condition it has limited ductility, and a tight bend will crack on the outside of the radius. The minimum bend radius is larger, and the bend line should be oriented across the extrusion direction where possible. A part that needs several tight bends is usually a poor fit for T6.

There are three ways round the problem. Design a larger bend radius and accept the space. Specify a softer temper, such as T4 or an annealed condition, form the part and then age it. Or form the bar in a press with a controlled radius and accept that some springback correction is needed. Each route adds cost or changes the strength, so the drawing should say which is intended.

Edgewise bending is harder than flatwise bending for both alloys because the neutral axis moves through the thickness. On 6101-T6, an edgewise bend at a tight radius is a common source of cracks. If the design needs one, check it with the supplier before the drawing is released.

Joining, welding and contact

Both alloys can be bolted, and both need a clean, flat joint face. Aluminium forms an oxide layer quickly, so joint preparation and the time between preparation and assembly matter. A joint that is prepared and left exposed will develop a resistive film.

Welding is easier on 1350. The pure grade welds well with the common aluminium processes, and the weld zone retains useful conductivity. 6101 is weldable but the heat of welding alters the temper near the weld, so the strength advantage is lost locally. If a welded joint is structural, the design should account for the softened zone.

Fault current and thermal cycling put the joint under repeated load. A bolted aluminium joint can relax over time, so the torque and the washer arrangement should be specified, and the joint should be checked at service intervals. A hard temper bar holds torque better than a soft one, which is another point in favour of 6101 where the joint is critical.

Weight, cost and availability

Aluminium is used on busbars mainly for weight. Its density is about a third of copper, so a bar of equivalent conductance is much lighter even though it is larger. Both alloys share that advantage, and the difference between them is in the section needed for conductivity and strength.

6101-T6 usually costs more per kilogram than 1350 because of the alloying and the heat treatment. It may also be less available in the exact flat bar size, which affects the minimum order and the lead time. For a large programme, the cost of the extra section needed for conductivity can outweigh the price difference per kilogram, so compare the finished part, not the metal price.

Choosing between them

Start with the mechanical requirement. If the bar is short, supported at close centres and mainly a conductor, 1350 is the simpler and cheaper choice. It forms easily, welds well and gives the best conductivity per unit of section.

If the bar spans a gap, carries a component, resists vibration or needs to hold a joint face flat under load, 6101-T6 is the better starting point. Accept the conductivity penalty, size the section for the current, and design the bends around the temper.

If the part needs both strength and tight bends, the answer is often a different temper rather than a different alloy. Forming in T4 and ageing to T6, or using a softer 6101 temper with a larger section, can satisfy both requirements. That route needs a supplier who can control the heat treatment and a drawing that says so.

What to put on the drawing

Name the alloy and the temper, with the standard that defines them. Add the conductivity minimum and the mechanical properties that matter, and ask for a mill certificate linked to the lot. If the part is formed after heat treatment, state the temper at the time of forming and the final temper.

Call out the bend radius and the bend direction relative to the extrusion. A note such as bend line across the extrusion direction, minimum inside radius stated, prevents a supplier from choosing a convenient orientation that cracks.

State the joint preparation, the plating or barrier at bimetallic contacts and the flatness of the joint face. Those details decide whether the bar works in service, and they are independent of the alloy.

• Alloy and temper, with the material standard
• Conductivity minimum and the certificate requirement
• Bend radius, bend direction and any forming temper
• Joint face flatness and surface preparation
• Plating, barrier or transition at bimetallic joints
• Support positions if the span is part of the design