The difference between normal steel and galvanized steel is the presence of the zinc layer that makes it rust-resistant.
Galvanized steel has many advantages over normal steel, and the major advantage is its resistance against rusting and corrosion. Due to this reason, it finds wide application in automobile, construction, and other industries. However, galvanized steel can be fabricated to its end product using multiple operations, including welding.
Welding galvanizing steel has complexity, which is exactly our discussion topic. Let us understand the complexity and see how experienced welders do the welding of galvanized steel.
Why this fuss about welding galvanized steel?
Welders worry about welding galvanized steel since the fumes produced during welding are toxic and dangerous to the welder’s health. You may think why the galvanizing cannot be done after fabrication. The reason is quite simple; it is easy to galvanize a steel sheet but difficult and uneconomical to galvanize a bulky fabricated item.
The melting point of the galvanized layer is very low compared to the steel beneath it. The galvanized layer burns off into vapor/fumes at welding temperature and mixes with the regular welding smoke. Two things happen during this process:
- The zinc content in the vapor reacts with the oxygen in the air and becomes zinc oxide. The zinc oxide is not highly toxic but can cause uneasiness.
- The real trouble comes from the 0.5% lead content in the zinc used for galvanization. The lead content in the vapor/smoke reacts with the oxygen in the air to form a lead oxide. This is highly toxic, and inhaling it can cause temporary health issues like headaches and nausea and long-term health issues like anemia, kidney problems, and carcinogens.
Safety measures are very important for the welder to avoid inhaling zinc oxide and lead oxide. The smoke color of galvanized metal welding is yellow-green.
Another issue with welding galvanized steel is maintaining its corrosion resistance after welding. The zinc coating on the welding location and surrounding is removed/burns away. To restore the corrosion resistance quality in and around the welded area, a galvanized spray or an equivalent paint may be used after thoroughly cleaning the area.
Can we weld galvanized steel?
Yes, you can weld galvanized steel, albeit following set standards and procedures. In the following paragraphs, we shall examine the welding of galvanized steel by using different welding processes like MIG welding, flux-cored arc welding, and stick welding.
The American Welding Society (AWS) standard 19.0 gives the specifications about welding galvanized steel. This standard advises preparing the zinc-coated metal for welding by grinding off the galvanized layer, 1 to 4 inches on either side of the welding line and both sides.
1. MIG weld galvanized steel
The MIG welding process uses an inert gas for shielding and can produce a clean weld for most metals. However, MIG welding is not advisable for welding galvanized steel.
The bare welding wire used in MIG welding does not contain sufficient scavenger material to deal with contamination like zinc. If you weld galvanized steel with MIG welding, it creates plenty of spatters, which can build up onto the nozzle and damage it. Also, the resulting weld bead will have porosity, inclusions, a low level of fusion, and other defects.
Even if you remove the zinc coating from the welding area before welding, the zinc coating in the adjoining region burn to create spatters and affects the welding quality.
However, you can change to the flux-cored wire and DC negative polarity and use your MIG to weld galvanized steel. The flux-cored wire contains sufficient scavengers and other components to deal with galvanized steel.
2. Weld galvanized steel with flux core
Self-shielding Flux Core Arc Welding (FCAW-S) is the preferred process for welding galvanized steel. The welder has the advantage of continuous filler wire and has both hands to work. It is always safe to grind off the galvanized zinc layer in the welding area. Welding the galvanized steel directly (without grinding off the zinc layer) releases toxic fumes/smoke, and never do it. Anyway, the galvanized zinc layer will burn off during welding, so why take the risk. Removing the galvanizing layer is the best option.
FCAW-S is more tolerant to contaminations on the metal, viz. rust, painting, galvanizing, etc. The scavengers present in the flux core bring all the surface contaminations into the surface, and the contaminations will either burn off or get trapped in the slag.
Do the welding of galvanized steel using FCAW-S in the following steps:
Step 1 – Select the location for welding, and the best location for welding galvanized steel is outdoor. If you have to do it indoors, ensure the location is well ventilated, and there is a fume extractor near the workpiece (if you do not have a fume extractor, you can place a fan to blow off the smoke away from you).
Step 2 – Wear your welder protective gear, including a high-quality respirator and a good quality auto-darkening welding helmet. Welding galvanized steel creates spatter and toxic fumes/smoke.
Step 3– Arrange the workpieces to be welded and tack weld. Grind off the zinc layer from the welding location (1 to 4 inches on either side of the welding line and on both sides) using a sander (180/220 grit) or a belt grinder, depending on the shape and size of the workpieces. Clean the workpieces with a dry cloth or brush.
Step 4 – If you are using your MIG welder, change the filler wire to flux-cored, change the welding polarity to DC negative, and other changes, if any. Select a recommended flux-cored wire for welding galvanized steel.
Step 5 – Weld the galvanized steel following the process of “pulling the weld pool forward,” This gives a better weld bead with minimum contamination. If the weld length is long, you can interrupt the welding to clean the spatter and slag. Use a chipping hammer and brush to remove the slag and clean the weld bead. The weld bead should be neat and clean without any bubbling around it.
Step 6 – Inspect the welding and, if necessary clean the weld bead by grinding and giving another welding run. Clean the weld bead and the spatters.
Step 7 – Use a galvanized spray or an equivalent corrosion-resistant paint containing zinc to create a protective coating on the weld bead and the surrounding area to restore its resistance to corrosion property.
Can you weld galvanized steel with a stick welder?
Yes, you can weld galvanized steel with a stick welder. The stick welder (SMAW shielded metal arc welding) uses a metal electrode coated with flux. You can select an electrode recommended for welding galvanized steel and do the welding of galvanized steel by following steps similar to welding with FCAW-S.
Do not forget to remove the galvanized coating in the welding area and wear your complete welding gear. Do the welding outdoor or in a well-ventilated area and use a fume extractor or fan to take the smoke away from you.
However, FCAW-S is the preferred process when you have more galvanized steel welding since the welder has more control over the welding than stick welding.
Galvanized steel is weldable only if you follow the set procedures and take additional precautions. It is essential to wear complete protective welding gear, including a high-quality respirator. Do not take the risk since zinc and lead poisoning can be dangerous to your health.