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You often hear aluminum in discussions about welding. That’s not surprising because aluminum is a commonly used industrial material. You will see this metal in workshops and fabrication shops. Welders, however, have to deal with a few issues when working with aluminum.
Why is aluminum challenging to weld?
- It has a low melting point. It melts at 650ºC, much lower than most industrial metals, like stainless steel, which melts at 1510ºC. That means you can easily burn holes on your aluminum sheets when you’re not careful
- It’s reactive. A lot of metals quickly react with oxygen, and aluminum is not an exception. In fact, it readily forms an oxide layer on its surface. Ironically, the oxide layer melts at 1370ºC, much higher than the melting point of pure aluminum itself. If you don’t get rid of this layer, you’ll have to start at a very high temperature and then watch your arc burn holes through your work piece.
- It absorbs hydrogen. The more you heat up aluminum, the more it takes in hydrogen. When it cools down, hydrogen gas forms bubbles that lead to porosity and material weakness.
Despite these factors, you can weld on aluminum. You just have to know the right techniques.
Preparing Aluminum
The right welding process distinguishes between a successful and a pointless weld. Because aluminum is likely to have impurities, preparing it is a key to a quality weld. Start by using acetone to remove oils and moisture from the surface. Then use a wire brush (preferably stainless steel) to eliminate surface oxides. Another way to remove the surface oxide film is to use a strong acid or alkaline. Rinse the surface. Make sure it’s dry before you start welding.
Ideally, you should clean your aluminum work piece only right before you weld it. Clean aluminum sheets or plates can be covered and kept in storage to avoid oxidation, but oxidation and contamination are inevitable. So cleaned aluminum pieces that are left in storage for several days should be prepped up again before welding.
Safety First!
Whenever you’re doing any type of welding, wear your safety gear. Aside from a helmet with the right lens shade, you need welding gloves, a welding shirt, and denim pants. Ensure that your work space has sufficient ventilation (1).
MIG vs TIG for Aluminum
The most common welding processes for aluminum are MIG and TIG. Let’s see the difference between the two.
MIG
Metal inert gas or gas metal arc welding is not the first choice for aluminum. MIG can easily melt aluminum. That means your weld puddle may be too hot for it and just burn a hole through what’s supposed to be a joint. For this reason, professionals don’t recommend welding on thin sheets of aluminum.
With aluminum, your MIG gun speed can’t be as slow as when you’re welding mild steel. You set your MIG machine on the same voltage as you would when welding mild steel, but you have to move twice as fast. This can feel weird when you’re doing it for the first time, but you’ll get used to it. Because you’re going to use a roll of aluminum wire, you’re better off using a spool gun than a MIG gun. Aluminum wire is softer than steel wire and can get tangled or stuck in the MIG gun liner. A spool gun eliminates this problem.
Another thing to get right is your gas mixture. Mild steel welding typically requires C25 gas, which is 25% carbon dioxide and 75% argon. For aluminum welding, you need to use pure argon gas. For aluminum plates thicker than 1/2 inch, you need to use 25-75% helium for deeper penetration.
Additional tips for MIG welding aluminum are pushing (not pulling) at a 10-15-degree angle, multi-pass welding for improved weld quality and appearance, and using a heat sink for heat absorption.
TIG
Tungsten inert gas welding is the preferred way of welding aluminum. Professional welders would choose a TIG machine over a MIG welder when they have to work with aluminum. With TIG, you need an equipment running on AC power and a pure argon supply. You don’t have to worry about mechanical wire feeding, because you will use a filler rod.
TIG Welding Tips
- Allow the arc to burn through the oxide film on the surface of aluminum and wait until a puddle forms. Touch the tip of the filler rod into the puddle. The tip of the rod melts in and becomes part of the bead. Don’t melt the filler in the arc.
- Your torch angle should be around 10-20 degrees from vertical, tilted away from your welding direction. That way, you’ll be pushing your way through and not pulling your arc along.
- Keep the arc as close to the metal without allowing the tip of the tungsten electrode to touch it.
- Make sure the aluminum work piece and the filler rod are clean before you start.
The Bottom Line
Welding aluminum is challenging not just for beginners but also for professionals. That’s because the properties of this metal require a different approach. The most preferred way to weld aluminum is TIG welding with special attention to your amperage, arc length, and torch angle. You can also do MIG, but when you’re not careful, you can easily burn holes through your aluminum plates. Then again, for both MIG and TIG processes, you need to clean your work piece before you start welding. Stick welding, on the other hand, is not recommended for aluminum.
Read our reviews to find the best welder to weld Aluminium.
