GMAW on Carbon Steel and Transition to Aluminum Alloys

GMAW Transfer Modes: What They Are and Why They Matter

Gas Metal Arc Welding (GMAW) is the backbone of production welding in shipyards. Unlike a single fixed process, GMAW delivers weld metal in three distinct transfer modes, each created by a different combination of voltage, amperage, and wire-feed speed. Knowing which mode you are running — and why — is essential for meeting AWS D1.1, AWS D1.2, and ABS/USCG quality standards.

Short-circuit transfer occurs at lower voltage and wire-feed speed settings. The wire physically touches the puddle, shorts out, melts off, and repeats — roughly 20 to 200 times per second. The result is a characteristic crackling sound, low heat input, and a small, controllable puddle. Short-circuit is well suited to thin material and out-of-position work, but it is not acceptable for primary structural joints on most marine vessels under ABS rules because of the risk of cold lap and incomplete fusion in thicker sections.

Spray transfer uses higher voltage and wire-feed speed. The arc stays continuously open and propels tiny molten droplets axially into the puddle. The sound is a smooth hiss. Spray transfer produces deep penetration, a flat bead profile, and excellent mechanical properties — making it the preferred mode for flat and horizontal groove and fillet welds on thicker carbon steel structural members. It requires 100% argon or high-argon blended gas and is limited to flat and horizontal positions because the fluid puddle is hard to control overhead or vertically.

Pulsed spray transfer uses a power source that rapidly alternates between a high peak current (which detaches one droplet per pulse) and a low background current (which keeps the arc alive). The result is spray-quality metal transfer at average amperages low enough to weld out of position and on thinner material. Pulsed spray is increasingly specified in shipyards for aluminum and for code-quality steel welds in all positions.

Steel GMAW Setup

For carbon steel (A36 plate), the standard shielding gas is 75% Argon / 25% CO₂ (C25). This blend supports both short-circuit and spray transfer, controls spatter, and gives a good bead appearance. ER70S-6 is the most common solid wire for steel; its higher manganese and silicon content provides good deoxidation even on mill-scale surfaces. Drive rolls for steel are V-groove knurled type. Contact tips are sized to match the wire diameter (commonly 0.035 in. or 0.045 in.).

The Steel-to-Aluminum Changeover: Every Step Counts

Switching from steel to aluminum is not just swapping wire — it is a complete system changeover. Contamination is the primary enemy of aluminum welds; even a small amount of steel residue or moisture causes porosity or cracking.

Follow this sequence using the printed changeover checklist:

1. Power down and lock out the machine before opening the wire-feed cabinet.

2. Remove the steel wire spool and store it in a sealed container.

3. Swap the V-groove drive rolls for U-groove drive rolls sized for your aluminum wire. U-groove rolls grip the soft wire without deforming it.

4. Replace the steel gun liner with a clean Teflon or Nylon liner. Steel liners shave aluminum wire, creating metallic debris that causes feedability problems and contamination.

5. Install the correct aluminum contact tip — aluminum wire expands more than steel when heated, so aluminum-rated tips have a slightly larger bore.

6. Mount the ER5356 aluminum wire spool. Handle the spool with clean gloves only; skin oils contaminate aluminum.

7. Switch the shielding gas to 100% Argon. CO₂-containing blends are not used on aluminum because CO₂ causes porosity and the reactive chemistry attacks the aluminum oxide layer improperly.

8. Set voltage and wire-feed speed per the machine's aluminum schedule or the procedure specification, then verify with a digital multimeter.

9. Run a short test bead on scrap aluminum and inspect before production welding.

Welding 5083 Marine-Grade Aluminum

5083 aluminum is the dominant hull plate alloy in marine construction because of its excellent corrosion resistance in saltwater and its good strength-to-weight ratio. ER5356 filler is the standard wire matched to 5083 because it provides compatible strength and corrosion resistance.

Before welding, clean the aluminum plate with a dedicated stainless-steel wire brush (never use a brush that has touched steel) and wipe with acetone to remove the oxide layer and any oils. The aluminum oxide melts at roughly 3,700°F while the base metal melts near 1,200°F — failing to remove it causes inclusions.

In the flat position, run your gun at a push angle (gun angled 5–15° in the direction of travel). Push technique spreads the arc cleaning action ahead of the puddle, which helps break up residual oxide.

Visual Inspection to AWS D1.2

After welding, inspect each joint with a 10x hand-held magnifier against the AWS D1.2 visual acceptance criteria. Key discontinuities to check:

• Porosity: gas pockets visible at the surface. Any cluster or linear porosity exceeding code limits is a reject.
• Crater cracks: cracks at the weld stop point. Always fill craters by pausing before breaking the arc or using a crater-fill setting.
• Bead continuity: the weld must be full size along its entire length with no skips or undercut beyond allowable limits.

Safety

Aluminum welding produces ozone and metal fume. Ensure local exhaust ventilation is running before striking an arc. Wear clean leather gloves — contaminated gloves transfer oils to aluminum. Use a shade appropriate for your amperage (AWS recommends shade 10–12 for most GMAW amperages in this range; confirm for your specific setup). Compressed gas cylinders must be chained upright at all times. Follow your facility's lockout/tagout procedure every time you open the wire-feed cabinet.