Soldering is a common way to bond metal together. Aluminum can be soldered, but doing so can be much more difficult than with other metals. There are tips which can be applied to make soldering aluminum easier, including using the right blend of solder and removing aluminum oxide.

Professional mechanic soldering metal in workshop garage
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How to Solder Aluminum Together

What Is Soldering?

Soldering is a method of joining two bits of metal together. Any softer metal tends to be soldered to hold it together. Harder metals like steel and iron must be held together by welding. A soldering iron melts a type of metal called solder to 200 degrees. Once the metal becomes liquid, it can be used as a sort of glue to hold other metals in place. After removing the heat source, solder cools extremely quickly, forming a solid and holding the metals in place.

Which Metal Is Used For Soldering?

The metal used for soldering is colloquially called solder, but is made of a blend of different metals. In the past this was typically tin and lead, but lead-free options are far more commonly used today. These are made of a metal blends, usually containing a combination of tin, copper, silver, bismuth, zinc and silicon. Solder must have a low melting point and be quick to solidify. What's also key is that solder conducts electricity, which makes soldering an important aspect of creating circuits. Soldering can also be used to fix aesthetic breaks, like in jewelry.

How To Solder Aluminum

Soldering aluminum is notoriously difficult when compared to soldering other metals. This is particularly true when it comes to aluminum alloys. This is because all aluminum is coated in a layer of aluminum oxide, where the metal comes into contact with the atmosphere. Aluminum oxide cannot be soldered, so must be scraped off. Soldering must then be done very quickly, before more aluminum oxide forms. Aluminum also has a relatively low melting point of around 660 degrees, meaning you'll likely need a special soldering iron with a lower temperature.

Heat up your soldering iron. It can take around 10 minutes for it to reach the ideal temperature. It's a good idea to keep a damp sponge beside your iron in order to wipe off any excess solder and get the neatest finish. It's also recommended that you wear a safety mask, goggles and gloves whilst soldering.

You next need to remove the aluminum oxide from the aluminum. This can be done with a steel brush. Extremely oxidized aluminum may require more intensive sanding, or cleaning off with acetone. Apply the cleaning agent, called the flux, to prevent aluminum oxide from reforming as quickly.

You can then heat your solder until it becomes soft. The solder can then be applied to the aluminum. If it doesn't bond, the likely issue is that aluminum oxide has reformed and the piece needs to be brushed and cleaned again. The other issue may be that your aluminum is actually an aluminum alloy which cannot be soldered. If this is the case, you'll need to bond your metals using a ready bought aluminum adhesive.

Heat the areas you want to bond with your soldering iron. This prevents an easily cracked "cold join." Heat your solder, and using both the iron and the solder apply your solder to the areas you want to bond.

Once your solder is dry, which should take only a few seconds, you'll want to remove any remaining flux. If it's water based, it can be rinsed in water, but if it's resin based your piece will need to be cleaned in acetone.