Weldfabulous Blog

Welding isn’t just about sparks flying or a steady hand — it’s about precision, chemistry, and selecting the right materials for the job. And one of the most critical components of any solid weld? The filler metal. 

Whether you're joining two pieces of mild steel or working with exotic alloys, filler metals play a starring role in determining the strength, durability, and overall integrity of your weld. 

For professionals and DIY welders alike, knowing which filler metal to use (and when to use it) can mean the difference between a beautiful, lasting weld and a failure that cracks under pressure. 

Let’s take a deep dive into the world of filler metals, breaking down the types, their uses, and the impact of using the wrong one.

What Are Filler Metals, & Why Do They Matter? 

Filler metals are the consumable materials melted during the welding process to help join two base metals together. Their chemical makeup and mechanical properties directly impact the performance of the final weld, including its strength, corrosion resistance, ductility, and toughness. 

For example: 

• In Shielded Metal Arc Welding (SMAW), the electrode itself is often the filler metal. 
• In Tungsten Inert Gas (TIG) welding, the filler rod is manually fed into the arc. 
• In Metal Inert Gas (MIG) welding, the continuously fed wire acts as both electrode and filler. 

The goal? Ensure the filler metal is compatible with the base metal and the welding process you’re using. Otherwise, you may compromise the entire weld.

Types of Filler Metals & When to Use Them 

1. Carbon Steel Filler Metals 

• Best For: Mild steel fabrication, structural steel, piping, and automotive repair. 
• Popular Choices: ER70S-6, E7018 

These are among the most commonly used filler metals due to the widespread use of carbon steel. ER70S-6, for example, contains deoxidizers like manganese and silicon that make it ideal for welding dirty or rusty steel, while E7018 is known for producing strong, low-hydrogen welds that are excellent for structural applications. 

Welders Tip: Use carbon steel fillers only when your base metal is carbon steel. Using them on stainless or aluminum can create brittle welds and severe cracking.

2. Stainless Steel Filler Metals 

• Best For: Food-grade equipment, marine applications, and high-corrosion environments. 
• Popular Choices: ER308L, ER309L, ER316L 

Stainless filler metals offer corrosion resistance and strength. ER308L is a go-to for welding 304 stainless, while ER309L is used when welding dissimilar metals (like stainless to mild steel). ER316L is perfect for more aggressive environments with exposure to chemicals. 

Caution: Using a carbon steel filler on stainless steel can introduce rust and destroy the corrosion resistance of your base metal.

3. Aluminum Filler Metals 

• Best For: Aerospace, automotive, HVAC, and marine fabrication. 
• Popular Choices: ER4045, ER5356 

Aluminum welds can be tricky. ER4045 is great for applications needing minimal cracking and excellent appearance, while ER5356 offers higher strength and better ductility for structural applications. 

Note: Match your filler to the base alloy. Improper combinations can lead to cracking, weak joints, and discoloration.

4. Nickel & Exotic Alloy Filler Metals 

• Best For: High-performance, high-heat, and high-corrosion environments (power plants, chemical refineries, aerospace). 
• Popular Choices: ERNiCr-3, ERNiFeCr-1 

These are used in critical welding applications where failure isn’t an option. For instance, ERNiCr-3 is often used with Inconel and other nickel alloys due to its excellent oxidation and heat resistance. 

Warning: Always consult specifications before welding exotic alloys, as there’s little room for error.

What Happens When You Use the Wrong Filler Metal? 

Using the wrong filler metal can cause a range of issues, including: 

• Cracking or embrittlement due to incompatible thermal expansion rates. 
• Corrosion from mismatched metals that degrade faster than intended. 
• Poor weld strength which jeopardizes safety and structural integrity. 
• Appearance issues, including porosity, spatter, or undercut. 

Let’s say you use a carbon steel filler to weld stainless steel tubing in a food processing plant. That weld will corrode quickly, risking contamination, health violations, and structural failure. Or, welding aluminum with a filler not designed for it might result in cracked beads and reduced weld strength.

Additional Considerations: Matching Filler Metal to Welding Process 

Different welding processes demand specific filler metal forms: 

• Stick (SMAW): Electrodes like E6011 or E7018. 
• MIG (GMAW): Wire spools like ER70S-6 or ER308L. 
• TIG (GTAW): Straight filler rods like ER5356 for aluminum or ER316L for stainless. 
• Flux-Cored (FCAW): Tubular wires filled with flux, used for heavy-duty or outdoor applications. 

Make sure your filler metal is compatible not only with your base metal, but also your process and welding environment (e.g., indoors vs. outdoors, clean vs. dirty metal, vertical vs. overhead welds).

Conclusion: Choose Wisely — Your Weld Depends on It 

Whether you're welding farm equipment, building a trailer, restoring a car, or fabricating stainless piping, the right filler metal makes all the difference. Strength, durability, corrosion resistance, and even appearance all hinge on using the correct consumables.

Filler Metal Questions? Weldfabulous Has You Covered 

At Weldfabulous, we carry a comprehensive selection of filler metals for every welding process, material, and application, from carbon steel rods to exotic alloy wires. Whether you're a seasoned pro or weekend welder, we make it easy to find exactly what you need to get the job done right. 

Call our team today at 507-494-5169 to explore our full inventory or speak with a welding expert. Your next great weld starts with Weldfabulous.