For general fabrication, ER70S-6 is widely regarded as the best all-round MIG wire for mild steel — it produces smooth welds, excellent penetration and reliable arc performance, and copes well with lightly oxidised steel. To choose correctly for your job, match the wire to the parent material, its thickness, the mechanical properties you need, the welding position and the shielding gas.
This guide covers how to choose MIG wire, what ER70S-6 is and how it compares to ER70S-3, which wires suit structural, automotive and galvanised steel, what diameter to use, and the difference between copper-coated and copper-free wire.
How do I choose the correct MIG wire?
Consider the parent material, thickness, mechanical properties, welding position and shielding gas. Mild steel applications typically use ER70S-6, while stainless steel and aluminium require dedicated filler wires designed for those materials.
Using the correct wire improves weld quality, productivity and compliance with recognised welding standards. (For stainless and aluminium, see stainless steel MIG wire and aluminium MIG welding.)
What is ER70S-6 MIG wire?
ER70S-6 is one of the world’s most widely used solid MIG wires for welding mild and low-alloy steels. It contains higher levels of manganese and silicon than ER70S-3, allowing it to tolerate light mill scale and surface contamination more effectively.
ER70S-6 offers excellent arc stability, smooth wire feeding and strong mechanical properties, making it suitable for structural steel, fabrication, automotive and general engineering applications.
ER70S-6 vs ER70S-3 — what’s the difference?
Both ER70S-6 and ER70S-3 are mild steel MIG wires, but ER70S-6 contains higher levels of deoxidisers, making it better suited to welding steel with light rust or mill scale. ER70S-3 performs well on clean steel but is less tolerant of surface contamination.
For most fabrication applications, ER70S-6 is the preferred choice because it provides more consistent weld quality and improved arc stability.
What is the best MIG wire for mild steel?
For general fabrication, ER70S-6 is widely regarded as the best all-round MIG wire for mild steel. It produces smooth welds, excellent penetration and reliable arc performance while coping well with lightly oxidised steel.
Available in a range of wire diameters and spool sizes, ER70S-6 is suitable for automotive repairs, fabrication, agricultural equipment and structural steel.
What is the best MIG wire for structural steel?
ER70S-6 is commonly used for structural steel because it offers excellent strength, weld quality and productivity. It performs well on steels such as S275 and S355 when used with the appropriate shielding gas and welding procedure.
For coded welding or specialist applications, always ensure the filler wire meets the required welding procedure specification (WPS) and relevant BS EN ISO standards. See MIG wire classifications and standards and Welding Standards & Compliance.
What is the best MIG wire for automotive repairs?
Automotive repairs often involve thin mild steel, galvanised steel and high-strength steels. ER70S-6 is commonly used for mild steel repairs because it offers stable arc characteristics and good weld appearance.
For galvanised components, remove the coating where possible and use suitable ventilation or fume extraction. Correct wire diameter and low heat input help minimise distortion.
What is the best MIG wire for galvanised steel?
ER70S-6 is widely used for welding galvanised steel after the zinc coating has been removed from the weld area. Removing the coating improves weld quality and reduces harmful zinc fumes.
Use appropriate fume extraction and PPE when welding galvanised materials — see Welding Safety. For heavily coated or specialist steels, seek technical guidance on filler metal selection.
What diameter MIG wire should I use?
Wire diameter depends on material thickness and welding current:
- 0.6 mm — ideal for thin sheet metal
- 0.8 mm — the most versatile size for general fabrication
- 1.0 mm — commonly used for thicker sections and higher deposition rates
Selecting the correct wire diameter improves penetration, weld appearance and productivity while reducing burn-through on thinner materials. In short, step down to 0.6 mm for thin sheet, stay on 0.8 mm for everyday fabrication, and move up to 1.0 mm for thicker steel and higher deposition. [VERIFY: source Q&A “0.6 mm vs 0.8 mm vs 1.0 mm MIG Wire” was supplied with no answer text — confirm any additional comparison detail SIF wishes to add.]
Copper-coated vs copper-free MIG wire
Copper-coated MIG wire provides good electrical conductivity and corrosion protection during storage. Copper-free wire reduces copper deposits inside the torch liner and can improve wire feeding in automated applications.
Both types can produce high-quality welds when manufactured to recognised standards. The best choice depends on your welding equipment, production environment and personal preference.
Get the right wire for your steel
Choosing the correct wire, diameter and finish has a direct impact on weld quality and productivity. Weldability SIF supplies ER70S-6 and a full range of steel MIG wires in multiple diameters and spool sizes — contact our technical team if you need help matching wire to your application, or see our guide to buying MIG wire.