How to solder aluminium

Aluminium is a trickier metal to solder than say copper or steel, and without the right technique it can become an incredibly frustrating exercise. But, with aluminium soldering fast becoming commonplace in vehicles and electronics manufacturing (not to mention its lower price) now is the time to learn the little nuances associated with bonding this lighter, conductive metal. The growing demand for lightweight, corrosion-resistant materials makes aluminium soldering an essential skill for professionals and hobbyists alike.

Based on our expertise, along with this article on aluminium soldering techniques we have provided this guide on soldering aluminium to give you some tips to help with your next metalwork project.

Clickmetal specialises in cutting aluminium down to your required size and can ship to anywhere in the UK mainland. Contact us today to learn more.

What is soldering aluminium?

Soldering is the process whereby a low melting point metal alloy (solder) is melted and applied to the joining metals to bond once the solder solidifies. It is a precise process that requires careful preparation and the right materials to create a durable and reliable joint.

Soldering is normally used for joining softer metals (like aluminium) to hold them together. The solder is heated to its melting point, turning the solder into a liquid for gluing or bonding the metals together. It’s commonly used in applications like repairing heat exchangers, electronics, and even intricate metalwork projects.

Which metals are used for soldering aluminium?

Soldering metals can be classified into three different groups based on their melting points:

Low temperature solders

Tin, lead, zinc and cadmium are low temperature solders that produce joints with the least corrosion resistance. The melting point of these solders range from 149°C to 260°C. These are often used for small, less critical applications.

Intermediate temperature solders

These solders melt at temperatures of between 260°C and 371°C. Intermediate temperature solders include tin or cadmium combined with zinc, along with small amounts of aluminium, copper, nickel, silver or lead. These provide a balance between strength and corrosion resistance, making them suitable for more demanding applications.

High temperature solders

These are typically zinc-based solders with melting points of between 371°C and 427°C. They contain 3 to 10 percent aluminium combined with small amounts of other metals such as copper, nickel, silver and iron. These high-zinc solders have the highest strength and provide the most corrosion resistance, making them ideal for heavy-duty applications like vehicle repairs or structural joints.

Tips with the aluminium soldering process

Soldering aluminium is somewhat more difficult than soldering other metals (especially if you’re soldering aluminium-to-aluminium) due to the heat required and the potential problems caused by aluminium oxide. Moreover, some aluminium series are easier to solder than others, and some are currently not possible to solder at all.

Here are some of our top tips to help you with the aluminium soldering process:

Preparatory work – cleaning, flux and pre-tinning

Before any soldering commences, we strongly advise cleaning your aluminium to get rid of any unwanted grease and oil. Use a degreasing agent to ensure a pristine surface.

As aluminium oxide (which all aluminium is coated in) cannot be soldered, it must be scraped off before soldering. We recommend using the right soldering flux to remove the oxide effectively. Flux types vary—acid flux is often preferred for aluminium due to its ability to penetrate the oxide layer, but always follow safety guidelines when using it.

For large joins or aluminium-to-steel metal soldering, pre-tinning can make a significant difference. Cover the material with a molten puddle of solder, then rub off the surface with a glass fibre brush or wooden stick to ensure optimal bonding.

Heating technique

When soldering aluminium, you will need a large-capacity heat source (like a soldering iron, hot air gun, or propane torch) to ensure the joint area is warmed to the correct soldering temperature. This can take up to ten minutes because of the high melting point of the solders typically used to join aluminium.

When the aluminium has been thoroughly prepared, use your heat source to warm up the joint area. Apply the solder quickly and evenly to the applicable areas for bonding. Keep in mind that soldering must be done very quickly before additional aluminium oxide forms as a result of the heat. If the metals do not bond, it’s likely that aluminium oxide has reformed. You will then need to brush and clean the aluminium before trying again.

Troubleshooting Common Issues

• Problem: Solder won’t stick to the aluminium.

  • Solution: Re-clean the surface and reapply flux.

• Problem: Joint is weak or brittle.

  • Solution: Check the type of solder and ensure proper heating.

• Problem: Overheating damages the aluminium.

  • Solution: Monitor the temperature closely and use heat-resistant tools.

Summary – general guidelines for soldering aluminium

If you are planning on a project which involves soldering aluminium, then we recommend you follow these guidelines:

1. Firstly, all metals should be cleaned to get rid of any grease and oil
2. You should then use an appropriate soldering flux to remove any oxide films that forms on the surface of the metals. Pre-tinning is also advised
3. Your proposed joint fit should be snug with a gap big enough for the solder
4. To achieve the best result when soldering, keep all metal stationary
5. Make sure you know the right amount of heat to apply – check the manufacturer’s instructions or check online

Clickmetal is specialist aluminium suppliers

Clickmetal is a leading UK supplier of aluminium and other nonferrous metals. We cut down all metal to size and supply nationwide to both the trade and to domestic customers.

Choose from our wide range of aluminium and stainless steel. Order online today for bespoke sizing and quick, nationwide delivery.

For more information, get in touch via our contact webpage or call us on 01794 526090.