What is Flux in Welding & What Does It Do?

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Arc welding flux consists of minerals, alloying materials, and chemical additives. Its primary purpose is to prevent harmful reactions of the molten metal and filler material with atmospheric gasses as an alternative to shielding gas. 

Manufacturers often apply or integrate the flux into a consumable electrode for ease of use. Simply weld, and as the electrode is consumed and fills the joint, the flux is applied at the same time.

No need to select, buy, handle, or apply the flux separately. For this reason, arc welders use the premanufactured flux/electrode combo for most welds.  But flux may need to be used in other ways for specialty applications.

Flux not only protects welds from reactive gasses in the atmosphere, but it also provides arc stability. This combination of features aids in creating strong, decent-looking welds with no need for shielding gas. 

However, many flux mixtures are used in arc welding, depending on the metal you are welding, and the flux can be employed using various techniques.

So, we assembled the relevant information in this article to present what flux is and the different ways it shows up in arc welding.

What Is Flux?

Flux is a complex composition made from both organic and inorganic materials. The different ingredients have specific uses, such as producing shielding gas or creating slag designed to work with specific applications.

For example:

  • Silica and lime – are often used as flux agents.
  • Titanium dioxide and iron powder – may be added to produce slag.
  • Ammonium chloride, resin acids, zinc chloride, hydrochloric acid, and borax – may be used in the mixture to enhance or impart certain properties.
  • Wood flour, limestone, and cellulose – may be used to generate gasses that shield the weld from atmospheric gasses. 

As you can see, serious chemistry is going on inside a flux mixture. The actual flux mixture depends on the metal being welded and the specific alloy of that metal. So, having the right flux for the weld you are performing is important. 

How Does Flux Work?

Flux “melts” into the weld pool where it rises to the top and creates slag. It simultaneously reacts with the heat and releases a shielding gas. So, the slag and gas formation protects the weld from the natural reactive gasses in the atmosphere. 

But slag formation also purifies the weld, which is definitely a good thing. But once the weld has hardened, you must remove the slag using a wire brush, chipping hammer, or an angle grinder.

The resulting slag when flux is used is why some welders will refer to any welding process that uses flux as “slag welding.”

What Arc Welding Processes Use Flux?

The procedures used to employ flux while arc welding can vary. But for the two most common types of flux use involve factory application of the flux to stick electrodes or a flux-cored wire.

A less common method involves casting the flux as a blanket over the arc, known as submerged arc welding. 

Let’s take a closer look at all three.


flux core welding process diagram

Flux-core uses a fluc-cored wire where the consumable electrode is a hollow wire with an interior core of flux.

With a metal outer “sleeve,” called a sheath, this flux-cored wire allows you to weld like MIG welding. The added benefit is you can weld without a gas bottle while still providing the simple, fast wire feed that allows you to achieve high production rates that stick welding cannot match.

flux core wire cross section
Cross section of flux-cored wire

Sometimes flux-cored welding is called gasless MIG, and it’s popular for applications like windy conditions where your shielding gas is rendered useless as it is blown away.

As we already mentioned, it’s similar to MIG welding, minus the gas tank. But it’s almost as easy to learn, which is why it’s popular. Also, in general, less slag is produced with flux-core wire than with stick welding. On the downside, the weld puddle isn’t as clear as stick welding. 

Read more: Flux Core vs. MIG Welding: Differences Compared

Stick Welding

stick welding process

Stick welding rods have a solid, consumable electrode at their center, with an external flux coating. The composition varies depending on what you are welding, so you must buy an electrode designed for the metal being welded. 

Once you get the right welding rod, you have a consumable electrode center that is a filler material. Plus, since the manufacturer applied the correct flux mixture at the factory to the outside of the electrode, you also get the right flux. 

Popular Stick Welding Electrode (E6010) used for general-purpose fabrication, construction, pipe welding, and shipbuilding

The flux melts at a lower temperature than the base metal and rises to the top of the molten weld. When cooled, the flux forms into what is called “slag.” Flux rising to the top facilitates the shielding gas and protective slag formation, which protects the hot joint. 

Stick welding is a classic process used in the shop or in the field, and the necessary equipment is not that expensive. These features make it another popular flux-based choice among welders.

Submerged Arc Welding

submerged arc welding example close up
Submerged Arc Welding example close up

While not as popular as the prior two flux uses just discussed, submerged arc welding is a fairly common practice. This method continuously feeds an electrode into the joint, just like flux-cored welding. But the major difference is how the flux is applied. It isn’t contained in or on the electrode. 

The flux used is a granular powder, and it is cast as a layer over the arc via a separate feed tube. Since the process is typically used when high volumes are necessary, this process is usually automated.


Is Flux Hard To Use?

Flux-core wire feed systems don’t feel as smooth as a regular MIG machine. However, after running a few beads, you’ll notice it isn’t much harder.

Shielded Metal Arc is tricky for many new welders. The electrodes have a lot to do with it. I’ve found welding rods with more flux easier to work with.  

Each rod is made for a different purpose, which is something to remember when choosing your electrode. 

Are Flux Welds Of Good Quality?

It can be harder to see your weld puddle when using flux-cored wire, potentially resulting in less pleasing welds. But with practice, you can make decent-looking welds.

Likewise, stick welding will produce ugly welds when done with insufficient skill. It can also make beautiful welds when done properly.
When you remove the slag, you will reveal the true character of your welds.

Can I Use Flux Indoors?

Using flux-core wire gives off more potentially toxic fumes than when using a normal MIG machine. The flux itself is designed to release gasses strong enough to shield molten metal. 

If you must weld indoors, be sure to keep the area as well-ventilated as possible.

Do Flux-Based Methods Make Strong Welds?

Yes, the welds can be of high strength. If proper care and attention are used, the welds will be as strong as any other welding method. Penetration is typically deeper when using flux, which helps provide added strength.

Are Flux-Based Techniques Easy Enough For A Hobbyist To Use?

Using flux-cored wire is a great way to learn the skill of welding. It’s a straightforward way to get the hang of a new skill.

Learning to stick weld depends on the electrode you’re using. If you’re doing flat, horizontal welds on heavy material, 7024 is your best friend. So, that’s a good place to start, then making the jump from 7024 to 7018 electrodes for vertical welds isn’t that large of a jump. 

Wrapping It Up

Flux-aided welds play an important role in the world of arc welding. The mixtures can be complex and vary, so you must ensure you have the right flux for the metal you are welding.

But if you stick or flux-cored weld, the flux is “preinstalled” for you as long as you get the right electrode/wire for the joint.

Since flux mixtures are designed to produce slag and gas, they protect the hot, molten metal instead of shielding gas. That means no gas bottle to lug around, and you are not tasked with correctly setting your gas flow rates. So, stick and flux-cored welding are popular with many welders who have learned the value of using flux-based methods.

Yes, you will not get the pretty stacked dimes of a TIG weld. But flux does provide strong, contaminate-free joints when done right, and with a little practice, you can make decent-looking joints.

Plus, since no gas is used, it also allows you to do things like weld in windy conditions. That’s something MIG welding struggles to do.

So, there are advantages to flux-aided arc welds, and it is well worth your time and effort to learn about and practice with methods that do use flux. You will be glad to have it at your disposal as part of your welding skills. 

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About Jeff Grill

Jeff Grill hails from Long Island, a 118 mile stretch of land that starts just off the coast of Manhattan and stretches deep into the Atlantic ocean. He has always been interested in welding from an early age and has the cuts and bruises to prove it as he set out to work with a variety of metals.

1 thought on “What is Flux in Welding & What Does It Do?”

  1. Love these articles I do training for new employees who do not have a lot
    of welding background these are down to earth easy to understand


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