Welding galvanized steel is infamous for poor weldability and the welder’s safety. But it’s a popular metal, and chances are you will weld it sooner or later.
This introductory article covers the basics of galvanized steel, as well as the many challenges and how to solve them. But let’s start with the short answer:
You can weld galvanized steel with your regular equipment and procedures if you remove the coating first. Otherwise, the coating makes welding harder because it creates additional fumes and many defects. To control these issues, you need to adapt your fume protection, equipment, and techniques.
Simple home or small workshop projects or repairs that will take static loads are easy to weld.
However, for heavy-duty projects with demanding service conditions, it’s necessary to remove the coating to get the safest welds.
After reading the rest of the guide, you will have answers to the following topics:
- What is galvanized steel
- The safety issues
- Why it’s hard to weld it – defects
- The best way to do it
- How to remove the coating
- How to weld it with the coating
- Joint modifications
- How suitable is each welding process (stick, MIG, FCAW, TIG, and oxyfuel)
- Welding tips for improved results
- Will it rust after welding and what to do about it
First, let’s see the basics of galvanized steel.
What is galvanized steel?
Galvanized steel is typical steel covered with zinc to acquire strong and long-lasting protection from rust. Galvanization is popular because it’s a cheap and effective method. The service life for most applications is around 50 years.
Most often, the steel under the coating steel is mild steel, which is the easiest metal to weld. However, according to the service conditions of the metal, you may have medium-carbon steel or other hard-to-weld metals. But that’s rare.
Galvanized steel doesn’t require painting or further maintenance, even if it’s lightly damaged. At the same time, it’s slightly more expensive than uncoated steel.
That makes it popular for large outdoor construction applications but also for fences, ladders, roofs, pipes, etc.
It’s also popular for sheet metal and small consumables such as car panels, nuts, screws, wires, etc.
One disadvantage of galvanized steel is that you must use it in applications that won’t exceed 392 °F (200 °C). After that, the heat-sensitive zinc coating will lose strength and start to erode. The steel underneath has much higher heat resistance.
How galvanization protects the steel?
Galvanization is “smart” because it protects the covered steel in two ways:
- The coating acts as a physical barrier between the steel and the environment. This way, the air’s oxygen, moisture, or other corrosion sources cannot contact the iron underneath it.
- Zinc can also protect slightly exposed steel. That’s because zinc absorbs the tiny electrochemical reactions that create rust. This is based on the galvanic corrosion process (Wikipedia) and works well up to 3/16″ (4.8 mm) of exposed metal.
What are the most common galvanization methods?
There are many ways to galvanize steel: hot dip, thermal spray, galvanneal, electrogalvanization, and cold galvanization.
Let’s look at the two most popular methods:
- The hot-dip method is the oldest and most widely used process, in which the steel is dipped in molten zinc. It creates a thick zinc coating suitable for large workpieces and harsh environments. As a result, the hot-dip method provides excellent rustproofing results, suitable even for marine applications.
- The electrogalvanizing method requires dipping the steel in a cold zinc solution. Then a low-voltage direct current (DC) adheres the zinc to the steel. It creates a thin and uniform coating and is considered more zinc-plated than galvanized. Electrogalvanizing is suitable for small or thin applications such as nails, screws, car panels, etc.
How to tell if your metal is galvanized?
It’s easy to tell hot-dipped galvanized steel by its external appearance. It has a matte-gray color and a characteristic crystallized pattern known as spangle. Furthermore, additional chromic acid treatments for enhanced corrosion resistance add a green-bluish iridescent look.
Electrogalvanized steel looks brighter and uniform. It is very smooth without spangle. However, if it has a thick, rough, and porous look without spangle, you have thermal spray galvanization.
Let’s see some other ways:
- Another way to tell galvanized steel is when you grind it. The sparks will be dull red, short, and in few numbers until you get through to the steel.
- When you tack weld it, you will notice right away a black residue with white borders next to the tack weld.
- You will also notice the characteristic white smoke even after a few tack welds.
- Finally, the sound when you weld over this coating is also characteristic.
Next, we’ll see what happens when you weld galvanized and why it has a bad reputation.
Why is it bad to weld galvanized steel?
Welding galvanized steel is bad practice because zinc has a low boiling point and generates additional white fumes.
Zinc has a boiling point of 1700 °F (930 °C). That’s far lower than the puddle at 3000 °F (1650 °C) or the arc at 10000 °F (5500 °C).
As a result, a large amount of zinc evaporates and combines with oxygen, resulting in dense white fumes.
Can welding galvanized steel make you sick?
If you inhale the fumes that arise when you weld galvanized steel, you may develop a temporary sickness known as metal fume fever. It’s also called zinc chills, zinc shakes, or galvanize poisoning.
Zinc fumes can quickly saturate a workshop that lacks ventilation. Even if you weld outside but forget to position your head away from the fumes, you will still inhale a large quantity.
Another problem is that hot-dipped galvanization may contain chromium or lead residues, especially if it’s old. For example, old galvanized fence posts that need repairing. These elements are more harmful than zinc.
The coating of electrogalvanized steel is almost pure zinc, without other toxic elements. As a result, these fumes are less harmful compared to the hot-dipped method.
Another thing to mention is that every time a welder gets metal fume fever, he becomes more sensitive. So the next time, an even lower fume amount can result in the same symptoms.
While metal fume fever is temporary, welding fumes can also create long-term side effects. For this, you should avoid overexposure every time you weld.
To avoid metal fume fever, you must avoid inhaling the dense zinc fumes:
- The best thing to do is remove the coating 1-3″ (25-75 mm) depending on the metal thickness. You must remove it on every surface close to the joint, not just on the side you want to weld.
- Use local ventilation. That’s a vacuum device with a capturing hood next to the fume source (the arc) that captures the fumes and drives them outside. This way, the fumes don’t escape into the workshop’s air. But it is expensive.
- Use mechanical ventilation that recycles the workshop’s air several times per hour.
- You also can weld outside.
- Always avoid the fumes’ path.
- Finally, wear a welding respirator for added protection.
Many welders recommend drinking milk because calcium can remove zinc from your body. But the truth is that there is no real evidence to verify that it actually works.
The rest of the article is about the weldability of this steel.
Why is it hard to weld galvanized steel?
Welding galvanized steel is hard because the coating creates defects by destabilizing the arc, restricting the puddle’s flow, and acting as a pollutant. The worse defects are zinc cracking, low penetration, and lack of fusion. The most frequent spatter and porosity.
The extent of defects depends on the coating’s thickness. The thicker the metal, the thicker the coating.
Furthermore, each galvanization method creates coatings with different thicknesses:
- Thermal sprayed, and hot-dipped steels have the thickest coatings.
- Galvannealed steel has a heat-treated hot-dipped coating that contains iron and is easier to weld.
- Electrogalvanized steel has a coating several times thinner than the previous methods.
- Cold galvanized steel also has a thin coating.
The most severe defect is zinc-penetration cracking. This crack happens when liquid zinc comes in contact and penetrates the weld metal and the heat-affected zone (HAZ). The HAZ is the area next to the bead.
For most common projects, the chances of zinc cracking are very low. But, it’s critical when you weld heavy-duty projects that will endure heavy loads.
High silicon content in the filler metal increases the cracking risk.
Other serious problems are reduced root penetration and lack of fusion. Zinc restricts the puddle’s fluidity, and it cannot penetrate deep into the joint’s root. Lack of fusion is when the filler metal sits on the base metal without fusing with it, most often at the bead’s sides (or toes).
Zinc vapors in the puddle may not escape to the atmosphere before it solidifies. This will cause porosity, a very common defect.
The zinc vapors also destabilize the arc, increasing the size and the number of spatter. Spatter will stick to the joint, resulting in a poor appearance. Spatter can also land on MIG or TIG torches, damaging them.
Zinc also increases the frequency of slag inclusions, if you use electrodes with flux material.
Finally, the coating will also interfere with the current flow through the metals. This will make the arc harder to start and less stable.
What is the best way to weld galvanized steel?
The best way to weld galvanized steel is to remove the protective zinc coating. This way, you avoid all the problems, either health issues or defects. Welding becomes easier, faster, cleaner, cheaper, and safer. Welding is going to damage the coating anyway, so it’s best to remove it yourself.
Even for simple metal fabrications, removing the coating is faster and costs less than removing spatter and smoke.
Even worse, if the defects are more than anticipated, you may have to remove the bead and reweld the joint.
When you weld heavy-duty projects or repairs, you always remove the coating to get the strongest joints. This way you ensure that no joint will fail and prevent injuries or costly damages.
Also, without the coating, you can use popular processes that cannot weld over galvanization. These are described later.
Removing the coating
However, removing the coating has its own issues. Because zinc is firmly attached to the steel, you need some aggressive ways to remove it:
- Grinding is the simplest and quickest removal method. It’s good enough for most jobs and procedures, but it always leaves zinc residue behind.
- You can use flame cleaning with an oxyfuel torch. This method doesn’t leave residues, but it generates a lot of fumes.
- You can also use sandblasting if you have large surfaces to clean. But it requires full-body protection except if you use a blasting cabinet.
- Finally, you can use acids, but most are very corrosive and release harmful vapors. Safe acidic products such as vinegar take a long time to remove the coating.
Depending on the removal method you use, the coating will pollute the air with dust, fumes, or vapors.
For this, it’s best to work outside, especially if you use flame cleaning or acids. Furthermore, keep your head away from dust or fumes. Finally, a quality respirator with N95 filters will protect you from most pollutants except acid vapors.
If you use strong acids which are not recommended, for example, muriatic acid, you need special gas cartridges to absorb chlorine vapors.
No matter the removal method, it’s best to remove the coating on every surface in and around the joint.
That’s because when the metals get hot enough, zinc will melt and vaporize even if the puddle is at a distance.
If you have a tee or lap joint, always remove the coating between the abutting surfaces.
Weldpundit has a detailed article on how to remove galvanized coatings.
Can you weld galvanized without removing the coating?
However, it’s not always possible to remove it. You can weld galvanized steel without removing the coating if you:
- Modify the joint design so that the liquid or gaseous zinc can escape.
- Select a process with a strong arc to vaporize the zinc inside or close to the puddle.
- Use welding consumables with strong cleaning action and low silicon content.
- Weld with techniques that burn the coating before it contacts the puddle.
Always remember that welding over zinc is not recommended for jobs with demanding service conditions, and always avoid inhaling the fumes.
How to prepare galvanized steel for welding?
Let’s start with what joint modifications you can make to get better results.
If you have a butt joint, you must set a 10-20% wider root opening and weld with a wider side-to-side movement. This way, you will achieve the same root penetration as with clean metal.
Even if you weld thin metal, try to avoid closed butt joints and leave a narrow gap so that zinc can escape.
Tee and lap joints are the most troublesome to weld because:
- Welding burns a larger surface area than the other joint types.
- Zinc cannot escape easily where the two metals touch. As a result, liquid zinc will penetrate the metals, and the zinc fumes will escape violently, passing through the puddle.
If the metals are thick, for instance, 1/4″ (6.4 mm), you can leave a small 1/32-1/16″ (0.8-1.6 mm) gap between the abutting areas.
On the other hand, outside corner joints create fewer problems because less galvanization is burned.
Galvanized steel is as easy to cut as the metal underneath. However, the hot-cutting processes, for example, oxyfuel cutting, will generate a lot of fumes.
Each welder type and consumables have significant differences. Let’s see how each one performs.
Can you stick weld galvanized steel?
Stick welding is not only capable of welding galvanized steel, but the best process for the job. The arc is aggressive and vaporizes the coating. Furthermore, stick rods have a flux covering that greatly reduces the defects. Finally, it’s portable and suitable for windy environments, since most galvanized steel is welded outdoors.
All stick rods create a strong arc and contain deoxidizing elements in their flux covering. But some rods are more suitable than others.
Stick welding has the advantage of cellulosic rods, such as the 6010 and the 6011. These have some strong advantages against the zinc covering:
- Using the same amperage, cellulosic rods create a 60-70% stronger arc compared to other rods. This helps to evaporate the zinc that’s close to or inside the puddle.
- Furthermore, they generate a large amount of shielding gases. This allows you to move the rod forth and back without letting the air contaminate the puddle. We call this whip and pause. This technique burns the zinc covering before the puddle arrives.
- Finally, they have the lowest silicon content, preventing the zinc cracking defect.
Rutile rods such as the 7014 or the 6013 are also suitable for galvanized steel because they have a low silicon content. But, they cannot reach the effectiveness of cellulosic rods.
Rutile rods are not designed for the whip and pause technique. However, you can slightly manipulate the rod forth and back to burn some of the zinc.
The 6013 is the best rod for thin galvanized sheet metal.
The basic or low-hydrogen rods such as the 7018 are heavy-duty rods, but they have some problems when welding galvanized steel:
- Their flux contains high amounts of silicon, increasing the zinc cracking risk. That’s critical since these rods are used for heavy-duty work.
- Because they generate low shielding gases, they need a short (one rod diameter) and steady arc length. Otherwise, you will have porosity even on clean metal.
- Their low gas coverage also prevents wide rod manipulation to burn the zinc.
While a 7018 rod isn’t suitable for welding directly over thick zinc coatings, you can use it for the additional passes of a multipass weld. That’s because it will weld over the previous bead and the burned galvanized coating. Using a cellulosic rod for the root pass is ideal.
For a simple project that will not take heavy stress, a 7018 rod can weld it without trouble. Porosity may be present but not so much to require rewelding.
Can you MIG weld galvanized steel?
MIG welding is popular but using it for galvanized steel is troublesome.
Most single-phase MIG machines create a low-heat arc that cannot weld galvanized steel with acceptable results. Furthermore, MIG wires don’t have flux material that could reduce the defects. Finally, you cannot MIG weld outside without surrounding the work with windscreens.
Even thin electrogalvanized coatings or zinc residue on the joint can create defects to a degree that will stop you from welding. The most common defect is excessive porosity not only on the bead’s surface but inside it as well.
Another troublesome situation is that spatter and smoke will cover the MIG torch. If spatter jams the contact tip, you will end up birdnesting the wire. Heavy spatter on the nozzle will make the gas flow irregularly.
Weldpundit already has a detailed article on MIG welding galvanized steel.
If you have a MIG welder, the best solution is to use a self-shielded flux-cored wire.
Can you weld galvanized steel with flux-cored wire?
You can successfully weld galvanized steel with flux-cored wires, such as the popular E71T-11. These wires generate a strong arc that can burn the zinc coating. Furthermore, the flux material has cleaning properties that prevent zinc defects. Finally, you can use them in windy environments.
The cored wires are similar to stick rods, but in the form of a long tubular wire filled with flux material. This way, they offer higher productivity and are easier to use.
Most flux-cored wires for low-amperage machines are self-shielded, meaning that they generate their own shielding gases. So you don’t need a gas cylinder, and you can use your MIG welder outside.
The E71T-11 is the most popular flux-cored wire and can weld galvanized steel with much better results than solid MIG wires. The flux inside the wire can decrease the zinc cracking risk and stabilize the arc, reducing spatter and porosity.
The E71T-14 flux-cored wire is designed for coated metals. It offers the best results for galvanized steel. However, it’s a single pass wire up to 3/16″ (4.8 mm) thick metal. It’s also harder to find and more expensive.
The main disadvantages of flux-cored wires are:
- They generate the most fumes.
- It’s hard to weld sheet metal, for instance, less than 1/8″ (3.2 mm).
- They are very expensive.
- There are no cored wires with cellulosic flux material.
You can use self-shielded wires with a typical MIG welder, but remember that they need DC- polarity to work properly, not DC+. They also require serrated rollers because they are soft and can deform easily.
There are also gas-shielded flux-cored wires that need external shielding gas, like MIG welding. One popular wire of this type is the E71T-1.
These wires are meant for high productivity. Most of them are available on large spools and need high-amperage machines.
Their performance on galvanized steel is not as good as self-shielded wires, but better than solid MIG wires.
Many manufacturers produce ExxT-G wires. These wires always have different characteristics. Many of them are specifically designed for galvanized steel. They can reduce many defects, especially porosity and spatter.
Can you TIG weld galvanized steel?
TIG welding galvanized steel is troublesome because the zinc vapors rapidly contaminate the tungsten electrode. This will make the arc erratic and create porosity and spatter. TIG needs perfectly clean metals to work properly.
If you only have zinc residues, and you want to proceed, here are some tips:
- Use a larger 70-degree torch angle and increase the gas flow by 50% or more. These will help to keep the zinc fumes away from the tungsten electrode.
- Using an ER70S-2 rod will also improve the results.
- Use standard gas cups and avoid expensive gas lenses.
Let’s see two alternatives when you have a TIG welder.
Most TIG machines can weld with stick rods that offer great results on thick galvanization.
To do this, you remove the TIG torch and replace it with a stick rod holder (stinger). Because most stick welding is done using DC+ polarity, switch the polarity because TIG uses DC- for the torch.
Another way to get good results with a TIG welder is to use braze welding rods, for instance, the silicon bronze rod (ERCuSi or SiB). These rods melt at low temperatures, so you can TIG weld thin galvanized steel with minimal coating damage.
But they are not suitable for critical welds because they cannot create welds as strong as steel rods. They are also more expensive.
Can you weld galvanized steel with oxyacetylene?
You can weld galvanized steel with oxyacetylene, but the slow traveling speed of this process will damage the coating to a high degree. Since you have this equipment, you can use the flame cleaning technique to remove the coating before welding and prevent many defects.
If you have thin metals, you can use a brazing rod and the proper flux material to braze them.
Welding tips for galvanized steel
Let’s see some tips for improved results when welding galvanized steel:
- Try to use the thickest electrode for the job. This way, you use higher amperage.
- If you have a multipass weld, use the fewer passes possible.
- Thick zinc coating will interfere with the workpiece (or grounding) clamp connection, especially with a MIG welder. Try to connect it to clean metal or connect it directly to the workpiece.
- Set the amperage a little higher (5%) than usual for improved arc stability and burn the zinc easier, especially when you weld fillet welds.
- Use a short arc length to reduce all zinc problems. A short arc length is essential if you weld vertically to prevent liquid zinc from running into the puddle.
- It’s very important to weld with a reduced traveling speed, depending on the coating thickness and process. Slow processes with a strong arc like stick welding need a 10-20% slower traveling speed. Faster ones like MIG need a 20-30% slower traveling speed. When you weld slower, the increased heat will burn the zinc coating easier, evaporate zinc in the puddle, and allow fumes to escape before the puddle solidifies.
- Use a torch manipulation technique that always points the arc in front of the puddle but not over it. See the following picture.
- Always fill the ending crater. If the crater is concave, the shrinkage forces may crack it, especially if there is zinc trapped inside.
Finally, let’s see what to do after welding.
Will galvanized steel rust after welding?
After welding, galvanized steel will rust if you use it in a damp or wet environment. That’s because you either removed the zinc coating or the welding heat destroyed it along the joint. To avoid rust, you must restore the steel’s corrosion resistance.
How to protect galvanized steel after welding?
You can protect damaged galvanization with zinc-rich paint. We call this cold galvanization. It offers strong rust protection and similar color. However, it’s not as strongly attached to the metal as real galvanization and can easily scratch off.
You clean the bead and the damaged area next to it with a wire brush or angle grinder. After that, you clean it again with a rag and apply zinc-rich paint or spray.
A more effective way to clean the affected area is abrasive blasting. This way, the paint adheres stronger to the metal.
If you want to paint over galvanization, you can use suitable paints that adhere to clean galvanized surfaces without flaking.
But ensure that you read their safety instructions first because their vapors are more harmful than typical paint.
When you want to weld galvanized steel, it’s best to remove the zinc coating 1-3″ from every surface around the joint. This way, you avoid additional fumes, cracking, porosity, and other defects that zinc creates.
If you cannot or don’t want to remove it, use extra care to avoid inhaling the additional fumes. Their high volume can cause metal fume fever.
To avoid most defects, use a process that creates an aggressive arc and consumables that combine with flux material.
Your best option is stick welding with E6010 or E6011 rods. If you have a MIG welder, use self-shielded flux-cored wires such as the E71T-11.
When welding, use a slower speed and a technique that always points the arc in front of the puddle. This way, most of the zinc burns before it enters the puddle. Also, use wider root gaps.
Finally, you want to restore the damaged steel, especially if it’s exposed to a wet environment.
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