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What is Arc Rectification?


Everyone in the manufacturing and fabrication fields is familiar with the challenges posed by welding aluminum. One of those challenges is known as arc rectification; today I’ll be explaining what it is, whether you need to worry about it and what to do if you encounter it.

Welding aluminum is not as straightforward as working with stainless steel and other metals, but that doesn’t mean it can’t or shouldn’t be attempted. In fact, the ability to weld aluminum is part of what has made this amazing metal indispensable in nearly every modern industry.

Since it was first commercialized more than 100 years ago, aluminum has had a transformative effect on the way humans live their lives. From architecture to microelectronics, the prevalence (aluminum is the third most commonly found element in the Earth’s crust, following oxygen and silicon), flexibility and strength-to-weight ratio of aluminum have helped it become one of the most commonly used materials today.

An explanation of arc rectification

The phenomenon of arc rectification normally manifests itself as a fluttering in the arc of a gas tungsten arc welding (GTAW) machine. You’ll notice this flutter in both the look and sound of the arc, and this instability can prevent the arc from heating the metal enough to get a solid, consistent weld. If you haven’t experienced it before, it’s possible to force your welding equipment to rectify so that you can better understand what to look out for.

Take a one-inch thick piece of aluminum and set the AC power supply on your welder somewhere between 120 and 150 amps. Strike an arc and pass it along the surface of the aluminum; there’s no need to add filler wire. After you’ve moved about 4-5 inches along the metal, reverse back over the same area. You should see the arc begin to flutter.

The reason this is occurring is that the arc is acting as a rectifier, which means it is converting the alternating current (AC) of the power supply, which periodically reverses direction, into a direct current (DC), which flows in only one direction. In fact, the arc is partially removing the electrode-positive cycles of the AC, which happens as a result of the tungsten electrode being negative, and therefore emitting electrons. When the electrode becomes positive, that means electrons need to be emitted by the aluminum. Because electrons are more easily emitted by the tungsten than the aluminum, the reverse-polarity AC cycles are reduced or may be missing all together.

While newer GTAW power supplies may reduce the amount of rectification, even the most up to date ones can still rectify on occasion.

What can be done about arc rectification?

Just because there is some rectification doesn’t mean that it will result in weld defects. At the very least, it can be distracting to the welder, especially if they are relatively new to working with aluminum. In the worst cases, it can get difficult to add filler wire and you’ll end up with uneven welds that look bad and may even have integrity problems.

What can be done to prevent rectification? Before making any purchasing decisions, if you know you’ll be working with aluminum, find out how susceptible to rectification the power supply is. Your best bet is an inverter GTAW power supply, which is much less prone to rectifying. Square-wave power supplies have also gone a long way to eliminating rectification when compared to the older sine-wave power supplies.

If you have already invested in welding equipment you may not be able to purchase a new machine. In that case, you might need to do some troubleshooting. For example, if you’re experiencing a fluttering arc, it might be that your tungsten electrode is too small for welding process. If possible, switch to a larger size. Another problem could be that the manual balance control is not properly adjusted. Readjust to the negative position and see if that helps. Also, if you are using helium, it might be a good idea to reduce the percentage of helium.

Keep the following in mind when welding aluminum

Don’t forget, when it comes to welding aluminum, getting the right alloy is always important. Thankfully, it’s easy to estimate how an alloy will respond to welding based on what family or class it belongs to.

For example, the 1XXX family of alloys, the closest to pure aluminum, are considered easy to weld; as well as the 3XXX alloys, which have medium strength and are very formable. The 4XXX series, although easy to weld, are frequently used as filler material. Finally, the 5XXX series are also welding-friendly.

By contrast, 2XXX, 6XXX and 7XXX all have serious concerns when it comes to welding. There are some exceptions worth noting. The 2XXX alloys, because they are extremely strong, can be tough to weld; two exceptions being 2219 and 2519. The same is true of the 6XXX family, because they crack easily at high temperatures. If your welder uses the correct technique, it is possible to weld them. Finally, the 7XXX alloys often exhibit signs of cracking and corrosion when they’ve been welded, but there are three exceptions: 7003, 7005 and 7039 are all weldable with 5356 as filler.

Your Trusted Services Provider

Welding aluminum can be challenging even for experienced welders. To avoid the trial and error involved with learning a new technique, it’s always a smart idea to work with experts who can help eliminate a lot of the guesswork for you. At Clinton Aluminum, our goal is to help guide our clients through every step of the procurement process. That includes working with them to find the right material for the job.

Our sales professionals take pride in ensuring the success of our customers. While we can’t do the welding for you, we can make sure you have just the right material in the size and alloy that you need. To learn more about your aluminum options, contact one of our friendly and knowledgeable customer service representatives today.


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