White Metal Welding: Complete Guide to Aluminum and Pot Metal

I’ve spent 15 years welding everything from structural steel to exhaust pipes, but white metal welding still humbles me. You can have perfect technique and still end up with a porous, cracked mess if you don’t understand these finicky metals.

White metal welding is the process of joining zinc-based alloys (pot metal), aluminum, and magnesium using AC TIG welding with specialized techniques to overcome rapid oxidation, low melting points, and high thermal conductivity.

After repairing dozens of die-cast automotive parts and antique hardware, I’ve learned what actually works. This guide covers the exact process I use, including the safety measures that protect you from zinc fume fever.

What is White Metal?

White metal refers to a group of non-ferrous metals with distinct silvery appearances and low melting points. The term covers several alloys that behave differently than steel when welded.

The most common white metals you’ll encounter:

• Pot Metal (Zinc Die Cast): Zinc alloy with aluminum, copper, and magnesium. Melts around 700-800F. Prone to porosity and cracking.
• Aluminum: Pure aluminum (melting point 1220F) and alloys like 6061 (melting range 1080-1200F). The most weldable white metal when using AC TIG.
• Magnesium Alloys: Extremely lightweight, melting point around 1200F. Highly flammable – requires special precautions.
• Tin/Lead Alloys: Very low melting points (450-620F). Typically brazed or soldered rather than welded.

Metal Type	Melting Point	Weldability	Common Use
Pot Metal (Zinc)	700-800F	Difficult	Die cast automotive parts
Aluminum (6061)	1080-1200F	Good (with AC TIG)	Structural components
Magnesium	~1200F	Very Difficult	Aerospace, lightweight parts
Tin/Lead	450-620F	Brazing Required	Antique hardware

Why White Metal Welding is Difficult?

White metal welding frustrates even experienced steel welders. The rules you learned for steel don’t apply here.

The Four Main Challenges

1. Instant Oxidation: Aluminum and zinc form oxide layers within seconds of exposure to air. Aluminum oxide melts at 3722F – but aluminum melts at 1220F. You’re trying to weld through a layer that won’t melt until three times the base metal temperature.
2. Low Melting Points: Pot metal starts melting around 700F. You can accidentally melt the entire part before achieving proper weld penetration. I’ve watched repair holes grow larger as frustrated welders apply more heat.
3. Porosity from Outgassing: White metals trap gas during casting. When you apply heat, this gas expands and escapes through your weld pool, creating bubble-like voids. Zinc also boils at 1665F – lower than aluminum’s melting point – causing violent fuming and porosity.
4. High Thermal Conductivity: Aluminum conducts heat 5x faster than steel. Heat dissipates rapidly from your weld zone, requiring higher amperage but also making burn-through more likely on thin sections.

These challenges compound each other. Higher amperage to overcome conductivity leads to zinc boiling, which increases porosity. Lower amperage to prevent burn-through causes lack of fusion. The sweet spot exists but it’s narrow.

Critical Safety: Zinc Fume Hazards

This section could save your health. Most welding guides gloss over it, but zinc fumes are genuinely dangerous.

I learned this the hard way in 2026 while repairing a zinc die-cast grill body without adequate ventilation. That night I ran a 103-degree fever and sweated through three changes of sheets.

Required Safety Equipment

Equipment	Purpose	Minimum Rating
Respirator	Filter zinc oxide fumes	P100 cartridges
Ventilation	Remove fumes from breathing zone	150+ CFM fume extractor or outdoor welding
Gloves	Burn protection	Leather welding gloves
Eye Protection	UV and IR protection	Auto-darkening helmet shade 8-13

For quality protective gear, invest in equipment rated for metal fume exposure. Cheap particulate filters won’t capture zinc oxide nanoparticles effectively.

Equipment You Need for White Metal Welding

Let’s talk equipment. You can’t weld aluminum with a DC-only buzz box, and attempting pot metal repairs with the wrong setup guarantees frustration.

TIG Welder Requirements

AC TIG welding is the gold standard for white metals. You need alternating current because the electrode-positive (reverse polarity) half-cycle cleans away oxide, while the electrode-negative (straight polarity) half-cycle provides penetration and heat.

Minimum specs:

• AC output with balance control (not just AC/DC switch)
• High-frequency start for scratch-free ignition
• Amperage range: 5-200 amps for most white metal work
• Post-flow control: 3-5 seconds minimum to protect tungsten

I’ve used industrial robotic welding systems that make aluminum welding look effortless. For home shops, brands like Miller, Lincoln, and Everlast offer AC TIG units that handle white metals well. Expect to spend $800-1500 for a capable machine.

Torch and Tungsten Setup

A gas lens cup improves shielding gas coverage significantly. Standard cups produce turbulent flow; gas lenses create smooth, laminar flow that blankets the weld area more effectively. For white metals prone to oxidation, this matters.

Shielding Gas

100% argon is standard for white metal TIG welding. Pure argon provides:

• Better arc stability than helium blends
• Lower thermal conductivity – more focused heat
• Superior oxide cleaning action on AC balance
• Lower cost than argon-helium mixes

Flow rate: 12-18 CFH with gas lens, 15-20 CFH with standard cup. Too much gas creates turbulence that pulls in air and causes porosity. Too little leaves the weld pool unprotected.

Metal Preparation: The Make-or-Break Step

Preparation accounts for 80% of white metal welding success. I spent years fighting porosity until I learned to clean like a machinist, not like a welder.

The Three-Stage Cleaning Process

1. Mechanical Removal: Use a stainless steel brush dedicated to aluminum only. Brush aggressively to remove visible oxide and contaminants. Direction matters – brush parallel to the weld joint, not across it, to avoid embedding contaminants.
2. Solvent Degreasing: Wipe with acetone, lacquer thinner, or dedicated aluminum cleaner. Avoid brake cleaner – some formulations leave residues that become toxic when heated. Change rags frequently; you’re just spreading grease if the rag’s saturated.
3. Final Oxide Removal: If cleaning took more than 30 minutes, re-brush the joint area. Aluminum oxide reforms quickly. For critical repairs, clean immediately before welding – within 5 minutes max.

For cast parts with unknown history, I use a two-step chemical clean: acetone degrease followed by a quick wipe with dedicated aluminum prep solvent. This removes machining oils and casting release agents that vaporize and cause porosity.

Joint Design and Fit-up

White metals don’t forgive poor fit-up. Gaps cause burn-through; misalignment creates stress concentrations that crack during cooling.

For butt joints on material under 1/8″ thick: no bevel needed, just square edges and tight fit-up. For 1/8″ to 1/4″: single-V bevel with 60-75 degree included angle. Over 1/4″: double-V or U-joint prep to control heat input.

Tack welds are critical. Place tacks every 1-2 inches for longer joints. Let each tack cool completely before placing the next. This prevents warpage and maintains alignment during the final weld.

Step-by-Step TIG Welding Process

Now the actual welding process. Follow these steps in order and you’ll achieve consistent results.

Step 1: Machine Setup

Thickness	Amperage Range	Filler Rod Size	Tungsten Size
1/16″ (1.6mm)	30-50 amps	1/16″	1/16″
1/8″ (3.2mm)	50-80 amps	1/16″ to 3/32″	1/16″
3/16″ (4.8mm)	70-110 amps	3/32″	3/32″
1/4″ (6.4mm)	100-150 amps	1/8″	3/32″ to 1/8″
3/8″ (9.5mm)	140-200 amps	1/8″	1/8″

Recommended AC balance settings:

• Heavily oxidized aluminum: 60% EN / 40% EP (more cleaning)
• Standard aluminum: 70% EN / 30% EP (balanced)
• Clean, new aluminum: 75% EN / 25% EP (more penetration)
• Pot metal with zinc content: 65% EN / 35% EP (moderate cleaning)

Frequency setting: 80-120 Hz for most applications. Higher frequency narrows the arc cone for better control on thin material. Lower frequency widens the cone for faster fill on thicker sections.

Step 2: Establish the Weld Pool

Hold the torch at a 70-80 degree angle from horizontal. Tilt the torch slightly so the gas cup leads the tungsten – this pushes the weld pool forward and improves shielding.

Strike the arc on a separate copper block if your machine allows scratch-start. Otherwise, use high-frequency start directly over the joint. Hold the arc about 1/8″ from the workpiece.

Watch for the weld pool to form. On aluminum, you’ll see the oxide layer lift like a skin. This is the cleaning action working. Don’t add filler yet – establish a stable pool first.

Step 3: Add Filler Metal

Filler Rod Selection: 4043 vs 5356

Filler Alloy	Composition	Best For	Drawbacks
ER4043	5% Silicon	General purpose, 3000/6000 series, pot metal repairs	Lower strength, not anodize-friendly
ER5356	5% Magnesium	5000 series aluminum, higher strength applications	More cracking risk, higher amperage needed
ER4047	12% Silicon	High silicon castings, very fluid weld pool	Lower ductility, specialized use

For most white metal work, 4043 is your best bet. The silicon content improves wetting and reduces cracking. It flows well into pot metal’s irregular casting structure.

Feed technique: Dab the filler rod into the leading edge of the weld pool. Don’t just melt it into the center – that causes cold lap and lack of fusion. The rod should enter the puddle at about a 45-degree angle from the opposite side of the torch.

Step 4: Travel and Rhythm

Move the torch at a steady pace. Too slow and you overheat the metal; too fast and you lack penetration. On thin aluminum, I aim for about 2-3 inches per minute. Thicker material might be 4-6 inches per minute.

The “dab” rhythm: establish pool, dab filler, advance slightly, repeat. Most beginners add filler continuously. This cools the pool and causes lack of fusion. Intermittent dabbing keeps the pool hot and ensures proper mixing.

Stop technique: Back off the foot pedal slowly to ramp down amperage. Keep the gas flowing over the weld for 3-5 seconds after arc extinguishes. This protects the hot tungsten and the cooling weld from oxidation.

Alternative Welding Processes

AC TIG isn’t the only way to join white metals, though it’s usually the best. Let’s compare the alternatives.

Process	Difficulty	Best For	Equipment Cost	Weld Quality
AC TIG	High	Precision repairs, thin materials, all positions	$800-2500	Excellent
MIG with Spool Gun	Medium	Production work, thicker sections, flat position	$600-1800	Good
Oxy-Acetylene Brazing	Low	Non-structural repairs, low-stress joints	$200-500	Fair (not fusion weld)
Stick (SMAW)	Very High	Field repairs, dirty conditions (not recommended)	$300-800	Poor on white metals

MIG with Spool Gun

MIG welding aluminum requires a spool gun because soft aluminum wire bird-nests in a 10-foot gun liner. The spool mounts directly on the gun, feeding wire only 6-8 inches to the contact tip.

Advantages: Faster deposition than TIG, easier to learn, good for thicker sections. Disadvantages: Less precise control, cannot weld material thinner than 1/8″ effectively, wider heat-affected zone.

For DIY heat tools and light fabrication, MIG lacks the finesse of TIG. But for boat trailer repairs or ATV frame patches where appearance matters less, MIG gets the job done quickly.

Brazing for Non-Structural Repairs

Sometimes welding is overkill. Brazing uses a filler metal that melts below the base metal’s melting point, creating a mechanical bond without fusion.

Aluminum brazing rods melt around 700-800F – well below aluminum’s 1220F melting point. This allows repairs on thin pot metal that would dissolve under TIG heat.

I use brazing for: decorative trim repairs, low-stress brackets, and situations where I’d rather not risk burning through. The joint won’t have the strength of a fusion weld, but for many antique repairs, adequate is enough.

Troubleshooting Common Problems

Even with perfect preparation, problems happen. Here’s how to diagnose and fix the most common white metal welding issues.

Problem	Causes	Solutions
Porosity (bubbles in weld)	Trapped gas, zinc boiling, contamination, moisture	Clean thoroughly, reduce amperage, increase gas flow, preheat to 200F
Cracking in HAZ	Thermal stress, zinc content, rapid cooling	Preheat, slower travel, 4043 filler, peening while warm
Burn-through	Excessive heat, slow travel, thin material	Reduce amperage, increase travel speed, use copper backing bar
Lack of Fusion	Insufficient heat, oxide layer, wrong filler	Increase amperage, adjust AC balance, re-clean joint
Tungsten Contamination	Touching weld pool, dipping filler into tungsten	Hold tungsten closer to work, feed filler at leading edge
Dirty/Oxidized Appearance	Insufficient gas coverage, wrong AC balance	Increase gas flow, check for drafts, adjust AC balance

Repair vs. Replace Decision Guide

Sometimes welding a white metal part isn’t worth it. Use this decision framework:

I once spent 8 hours welding a pot metal transmission case only to have it crack again in a week. Some parts weren’t designed to be repaired. Know when to cut your losses.

Testing Your Weld

For non-critical repairs, visual inspection suffices. A good aluminum weld should have a uniform ripple pattern similar to a stack of coins. No craters, no excessive discoloration, and the weld should feather smoothly into the base metal.

For structural repairs, perform a bend test on a sample piece. The weld should bend to at least 90 degrees without cracking – preferably more like 120 degrees. If the sample cracks at the weld metal, your technique or filler choice needs adjustment.

Frequently Asked Questions

White metal welding rewards patience and preparation. Rush the cleaning and you’ll fight porosity. Rush the welding and you’ll burn through. Take your time, set up properly, and accept that some repairs might not be worth attempting. The best welders know when to walk away.