A Complete Guide to Aluminum Welding
Aluminum presents some unique welding challenges you need to be aware of.
Aluminum’s high thermal conductivity and low melting point compared to steel require some differences in technique.
Below, we cover the basics of aluminum welding and tell you how to avoid some of the most common pitfalls.
Getting Prepped – Equipment
Before you even think about starting on aluminum welding, you’ll need to make sure you’ve got the right equipment.
We’re talking about two categories of equipment here. But they’re both as important as each other:
We’ll lead with this one because it’s not skippable.
To weld safely, you need a range of personal protective equipment. You should not begin welding without the equipment in place.
For starters, you need a welding mask and thick gloves. Ideally, the mask will have a darkening lens and should be rated at 10-13 shade. Your gloves should be fire-resistant.
Less obviously, you need a shirt with long sleeves to protect your arms against the ultraviolet radiation put out by the process. Also, ensure you aren’t wearing pants that can catch sparks and flammable material – avoid cuffs.
As always, you should have an appropriate fire extinguisher on hand.
For aluminum welding, you’ll need a TIG welder along with an appropriate shielding gas discussed below.
Choose an appropriate aluminum filler rod that matches the properties of your base material.
Getting Prepped – Cleaning
Cleaning is widely considered the number one factor in a successful aluminum weld. If you’re finding your welds aren’t strong enough, come back and reevaluate whether poor cleaning technique might be the cause.
Failing to properly complete cleaning operations before you start is likely to leave you with a bad weld.
Your enemy here is aluminum oxide. Aluminum reacts strongly with oxygen, so this substance forms over time on the surface of aluminum. As it melts at a higher temperature than aluminum itself, it interferes with the quality of the weld.
Along with aluminum oxide are the usual greases and dirt that can accumulate on the surface of a metal.
A stiff clean brush combined with a solvent should be enough to remove the aluminum oxide and other contaminants that might interfere with the join. If you use a degreaser, make sure it doesn’t contain hydrocarbons, as they’re one of the contaminants you’re looking to avoid.
It’s important the brush has only been used on aluminum. You don’t want to add contaminants while you’re in the act of cleaning!
You’ll also want to clean the filler rod at the same time. When both the aluminum and the filler rod are clean, you can start the weld.
Welding will become easier if you preheat the aluminum, and it can help prevent cracking. Particularly with thicker pieces, you also risk a weak bond without preheating.
Keep preheated temperatures below 320C. Keep a thermometer on hand to make sure the temperature stays under control at all times.
Preheating also has the advantage of removing moisture from the surface before you weld. Any hydro-contamination of the material’s surface should be removed by evaporation.
Now you’ve finally reached the welding process itself.
First off, be sure your material fits tightly together. Gaps will lead to weakness in the weld, so be thorough about ensuring a flush fit. Once satisfied, clamp the pieces tight.
This may involve some extra work on the materials themselves to ensure smooth weldable surfaces.
For your filler wire, you’ll want to use something with a similar melting point to your primary base material. Although you can get away with being in the ballpark, the closer you can get the melting points the easier the weld will be.
There are two shielding gasses commonly used for aluminum welding: argon and helium.
Argon provides a smoother arc than helium and is the most common shielding gas for aluminum welding. It results in a narrower, convex bead pattern.
Helium offers deeper penetration and a hotter arc.
It’s not uncommon to work with a mix – a ratio of around 75% helium to 25% argon will provide the benefits of each with few of the drawbacks.
As for the welding itself, you’ll want to run at high temperatures and move quickly. Aluminum has high thermal conductivity, so higher amperage and voltage settings are a must. With thinner base materials, you run the risk of burn through with lower travel speeds.
The arc length should be a rough match for the diameter of the electrode.
Aluminum welds benefit from a push rather than pull technique. Push the gun away from the weld puddle for a much cleaner weld free of contaminants.
The upside of aluminum’s high thermal conductivity is the rate at which cooling occurs. Welds will set much quicker than in steel, though the metal will deform more due to contraction as it cools.
Aluminum’s high thermal conductivity presents a few unique challenges.
Cracking causes most weld failures with aluminum welding. The high thermal conductivity results in rapid expansion during heating, which leads to significant contractions during cooling. This cooling action pulls at the new welds, cracking them.
Carefully choosing the right filler material will go a long way to preventing ‘hot’ cracking. This cracking occurs due to the fundamental chemistry involved, rather than due to stresses from cooling. There are selection guides available for choosing the right filler material, so follow AWS classifications for your selection.
Porosity is another contributor to a poor weld. Porosity describes the gas bubbles that form in a weld.
Those hydrocarbons we mentioned earlier? They’re one of the usual suspects when it comes to porosity issues.
If your weld is suffering from porosity, then you’ve either not been thorough enough in the cleaning process, or you’ve allowed the material to become damp. Condensation is a contributor here, so make sure the material has been allowed to sit at the temperature of the welding environment for a significant amount of time.
Keep this advice in mind and you should be able to master aluminum welding and avoid a flawed technique.