Aluminum and steel might look like they’d weld in much the same way. They don’t. Aluminum is lighter and resists rust, which is why it’s so common on trailers, fuel tanks, boats and food equipment, but it behaves very differently under a welding arc. Knowing why helps you understand what a good aluminum weld requires and why not every welder or shop does it well.
The oxide layer
Aluminum forms a thin, tough oxide layer on its surface almost immediately. That layer melts at a much higher temperature than the aluminum underneath it. If the oxide isn’t removed before welding, it can get trapped in the weld and weaken it. That’s why aluminum has to be cleaned carefully before welding, using a dedicated stainless steel brush or other suitable cleaning method rather than a tool that’s been used on other metals.
Heat behaves differently
Aluminum conducts heat far better than steel. Heat spreads quickly away from the weld, so more heat input is often needed to get started. But aluminum also melts at a lower temperature than steel and gives little warning before it sags or burns through. Controlling heat is a big part of the skill, especially on thin material.
It’s softer and moves more
Aluminum expands more when heated than steel does, so parts can distort as they heat and cool. Careful fit-up, clamping and welding sequence help keep the finished piece straight. Because aluminum is softer, it’s also easier to damage while handling and preparing.
Filler metal matters
Different aluminum alloys need different filler metals, and the wrong choice can cause cracking or a weaker joint. We cover this in more detail in our post on the difference between aluminum filler alloys.
Welding processes for aluminum
Aluminum is commonly welded with TIG (GTAW) or MIG (GMAW), and each has its place. TIG gives fine control and is often chosen for thin material and visible, precise welds. MIG is faster and suits longer runs and thicker material. Learn more in our guide to TIG (GTAW) welding.
| Steel | Aluminum | |
|---|---|---|
| Surface | Rust and scale | Tough oxide layer that must be removed |
| Heat | Stays near the weld | Spreads quickly, burns through easily |
| Distortion | Moderate | Higher; needs careful control |
| Filler | Matched to steel grade | Matched to the aluminum alloy |
Where aluminum welding is used
- Trailers, decks and ramps, see trailer welding repair
- Fuel tanks, see aluminum diesel fuel tank repair
- Custom aluminum fabrication for commercial and industrial customers
- Repairs to cracked or broken aluminum parts
Stainless steel has its own set of challenges, which we cover on our stainless steel welding page.
What to ask before you hire someone
- Does the shop regularly weld aluminum, or mostly steel?
- Which process will be used, and why?
- Will the aluminum be cleaned and prepared properly?
- Can they repair it on site, or does it need to come to the shop?
Talk to us about your aluminum project
Whether it’s a cracked part, a custom build or a repair, we can help. See our aluminum welding services in Calgary, our mobile welding repair, the Fabrication Pros homepage, or contact us for a free quote.
Contact us with any questions you may have.
