Top tips for welding aluminium

Tips for Welding Aluminium

Aluminium is highly reactive with oxygen, causing a rust layer to form which stays attached to the surface of the metal rather than flaking off. This prevents oxygen from penetrating deeper into the metal. Aluminium also has a low melting point and is a good thermal conductor; it is the combination of these physical properties that makes the welding process more difficult than with other types of metal, however, it is possible and just takes practise.

Common issues encountered whilst welding aluminium include distortion and cracking caused by the quick dispersion of heat, this is called ‘blow through’ which is where the metal simply melts away under an over-powerful arc. Secondly, the oxidised layer has twice the melting point of the aluminium underneath so it will not melt during the welding process.

If you are keen to improve your welding skills read on for useful tips on how to successfully weld aluminium.

Safety When Welding Aluminium

Welding can give off hazardous fumes, you do not want to be breathing those in so make sure your surroundings are well ventilated, ensure you have the correct personal protective equipment (PPE) to protect you from burns, and that your work area is clear of clutter and fit for purpose.

Please see list of suggested welding equipment below

1. A welding mask, helmet, or goggles to protect your eyes. 
2. Gloves, gauntlets, and overalls to protect your skin from molten metal splashes. 
3. Leather shoes or boots to protect your feet from molten metal. 
4. Respirator for long periods spent welding.
5. Welding table to securely hold the piece while welding. 

Cleaning Aluminium Before Welding

As previously mentioned, aluminium can oxidise very quickly which forms as a white, powdery layer on the surface of the metal. This gives aluminium its corrosion resistance but interferes with the welding process, so this needs to be removed immediately before welding begins. We recommend using a stainless-steel wire brush as this leaves a clean surface.

The brush should be new and not used previously on steel. Brush the aluminium in a single direction so the oxide is not rubbed into the aluminium and clean any edges with a file. Make sure dust or filings left over from cutting are cleaned off because they can catch fire easily. Finally, if the metal and welding rods are greasy use a good degreaser to clean them.

Once the aluminium is clean and dry you can begin welding.

There are two main methods used for welding aluminium:

Metal Inert Gas (MIG) welding, and Tungsten Inert Gas (TIG) welding. Please see advice and tips for these methods below.

MIG Welding Advice

• When selecting electrode tips, make sure they are designed to be used with aluminium; these can be identified by being marked as ‘Al’
• Make sure your welding machine and wire-feed are correct for aluminium welding, you will need a Teflon liner and U-groove rollers.
• Make sure your MIG torch is in good condition and consider a larger torch if you are planning on welding a lot of aluminium. A smaller torch can be easily overloaded by the heat generated.
• Use a suitable welding rod for the grade and thickness of material you are welding.
• As with all welding, it is a good idea to clamp the joint to prevent any movement or distortion.
• It is best to hold your torch almost vertically and use a push movement rather than a pull meaning you weld into the shielding gas rather than away from it. This gives a much cleaner weld.
• Gas used for MIG welding aluminium is typically pure argon run at a gas-flow rate of around 14–16 LPM.

Tip: When welding thin aluminium, we recommend using a brass heat sink (which is a brass plate placed behind the work area) to help avoid ‘blow through’; brass has a higher melting point than aluminium it takes on most of the heat from the weld to enable you to slow down and produce a much neater weld. The build-up of aluminium is also reduced so there is less of the weld seam to file down if you are wanting a flat finish.

TIG Welding Advice

• TIG welding is the easiest method to use with aluminium.
• The main advice for TIG welding is to make sure you are using a suitable machine. You will need an AC/DC with sufficient power to weld the thickness of aluminium you are working with.
• Torch set-up is crucial so be sure the torch has a suitable duty cycle for the amperage. We recommend using heavy-duty TIG torches as the use of light-duty TIG torches on aluminium risks burning out the torch.
• When you begin welding, allow the weld puddle to pool a little before introducing the welding rod; this will reduce the risk of the rod sticking to the workpiece.
• Like MIG welding, be sure to match your TIG welding rod’s grade and thickness to the grade and thickness of the aluminium you are working with.
• Due to the reactivity of aluminium, try to learn how to use a foot pedal or a torch with a variable amperage control to help your welding to be more precise and controlled.

Tip: Remember to set your AC frequency and balance to suit the aluminium you are working with. This is usually around 80-120 Hz frequency and for the balance start with 30-35% for clean aluminium and slowly increase this for dirtier pieces.

To summarise…

For MIG and TIG welding aluminium, having the right machine is the tip of the iceberg. As with all hobbies and professions, welding aluminium gets better with well-chosen welding equipment, plenty of practice, and the application of helpful tips.

It is important to remember that it does not matter if you are a professional or amateur, listening to reliable advice and tips for your own level can make the world of difference.