process guide
Aluminium Welding Guide
TIG and MIG techniques for welding aluminium; AC vs DC settings, amperage rules, filler wire selection, and how to avoid the most common defects.
Aluminium's oxide layer and high thermal conductivity make it a different beast to weld than steel, whichever process you're using. This guide covers both TIG and MIG welding of aluminium, AC vs DC settings, step-by-step technique for beginners, filler wire and equipment selection, and troubleshooting for the defects most likely to catch you out.
Should You Use AC or DC for TIG Welding Aluminium?
This guide covers TIG and MIG welding of aluminium specifically. For TIG welding fundamentals, how the process works, structural strength, and general safety, see our TIG Welding Guide.
AC (alternating current) is the industry standard for TIG welding aluminium, and for most jobs it’s the right choice. As the current alternates between positive and negative cycles, the positive cycle scrubs the surface, breaking up the oxide layer that would otherwise ruin fusion. The negative cycle handles weld penetration. Together, the two cycles produce the clean, high-quality welds TIG aluminium is known for, particularly on thin material.
DC (direct current) TIG can be used on aluminium, but only in specific circumstances. It becomes a practical option on thicker aluminium (generally 1/4" and above), and is suited to certain grades, including pure aluminium (1100), 6061, and 2219. With DC, the weld typically needs the joint bevelled, a root bead laid, and the weld completed in multiple passes to achieve proper penetration. Experienced welders sometimes prefer this route on heavy sections because it can be done in a single pass, saving time and filler material. DC should not be used on a thin aluminium sheet, as the high heat input can cause distortion and warping.
Why Aluminium Is Difficult to Weld
Aluminium is surrounded by an oxide layer that melts at a far higher temperature than the base metal underneath. Unless that layer is removed or broken up, you can’t achieve a sound weld; the base metal would liquefy and run before the oxide ever gave way. A steel wire brush can help loosen surface oxide, but AC current is what actually clears the weld pool during welding.
The second major challenge is heat input control. Aluminium’s high conductivity pulls heat away from the weld area quickly, so a lot of heat input is needed; but that heat has to be tightly controlled, or you risk the weld puddle running away or burning straight through the material. Keeping the arc length short helps concentrate heat in a smaller area, and a foot pedal lets the welder fine-tune current on the fly as the job progresses.
Equipment for AC TIG Welding Aluminium
You’ll need a power source capable of AC output, a torch, the correct tungsten electrode, compatible filler material, and the usual regulator, earth, and gas supply. Several manufacturers build TIG machines well-suited to aluminium AC work, including Miller, Fronius, and ESAB, all available as used and refurbished welding machines through Westermans.
Browse current AC/DC TIG welders in stock →
If you’re still deciding which machine to buy, our Which TIG Welder? Buying Guide covers AC/DC capability, brand comparisons, duty cycle, and other selection criteria in depth.
How to TIG Weld Aluminium: A Step-by-Step Guide for Beginners
If you’re new to aluminium TIG welding, getting your setup right before you strike an arc will save you a lot of frustration. Here’s the process from prep through to your first weld.
- Prepare the Material
- Clean the aluminium thoroughly, removing the oxide layer with a wire brush or similar.
- If you’re using an AC/DC TIG welder, set AC polarity. This keeps your weld free of oxidation as you go.
- Set the correct welding amperage for the material thickness (check your machine’s manual for specifics).
- Ball up the tungsten tip before you begin. - Control Heat and Amperage
Aluminium needs a large amount of heat to form a weld puddle in the first place, but once that puddle forms, you’ll usually want to reduce heat by up to half to avoid problems like cracking and porosity. A foot pedal is the easiest way to manage this live, letting you ease off once the puddle establishes. A shorter arc also helps keep heat concentrated and reduces the risk of a runaway puddle. - Set Your Amperage: A Rule of Thumb
A widely used starting point is 1 amp per 0.001 inch of material thickness. This rule applies up to around 1/4 inch; beyond that, the ratio reduces. Use AC current to keep the surface free of oxidation as you weld, and adjust the balance control to fine-tune cleaning versus penetration you’re getting from each half-cycle. Getting this balance right is one of the more important adjustments for avoiding oxidation in the weld pool. - Use the Right Equipment and Technique
- Use an AC/DC TIG welder with the correct aluminium-specific consumables fitted in the torch.
- Keep your torch angle close to 90°, or as near to vertical as possible; aluminium doesn’t forgive much tilt.
- Use a copper or brass wire brush for cleaning, never a steel brush, which will contaminate the aluminium with embedded steel particles.
- Watch the weld puddle rather than the tungsten; this is the technique most beginners need to consciously practise.
- Adding filler metal at the right moment gives the clean, shiny finish associated with good TIG welds, but only once your other settings are dialled in.
Common TIG Aluminium Mistakes and How to Avoid Them
| Mistake | What Happens | How to Avoid It |
| Wrong polarity/balance | Arc fails to break through the oxide layer | Double-check AC/DC settings and balance control before starting |
| Lack of fusion at the weld root | Improper, weak weld | Reduce arc length (distance from torch to weld area) |
| Craters at the end of a weld | Cracking | Don’t remove the filler rod or cut power too quickly at weld-end |
| Poor gas coverage | Weld contamination | Check gas type, flow rate, and all fittings for leaks |
| Too much amperage | Run-away weld pool, burn-through | Reduce amperage after arc strike, or increase travel speed |
It’s a process that rewards trial and error, changing one variable at a time, and the results will improve steadily with practice.
How to MIG Weld Aluminium
MIG welding offers a faster, more production-friendly route to joining aluminium than TIG, but it brings its own set of challenges: a low melting point, high thermal conductivity, and the same persistent oxide layer all make aluminium trickier to MIG weld than steel.
Equipment Selection
A MIG welder for aluminium needs a few specific features beyond a standard steel setup:
- Wire feeding: a push-pull gun or spool gun offers smoother, more reliable feeding than a standard feeder. Aluminium wire is soft and prone to tangling or “bird-nesting” otherwise.
- Liner: A Teflon liner reduces friction in the feed path and significantly cuts the risk of jams.
- Filler wire: must be aluminium, matched to the alloy you’re welding. The two most common choices are:
- ER4043 — suited to 3XXX and 6XXX series alloys (e.g. 3003, 6061, 6063); offers good fluidity, strong corrosion resistance, and a good colour match after anodising.
- ER5356 — suited to 5XXX series alloys (e.g. 5052, 5083); gives higher tensile strength and better crack resistance than 4043. - Nozzles and contact tips: use larger-bore versions designed for aluminium’s softer wire, to prevent clogging and maintain good gas flow.
- Drive rolls: use rolls specified for aluminium wire and size, not standard steel rolls.
Browse current MIG welders in stock →
If you’re choosing a new machine specifically for aluminium MIG work, our upcoming Best Aluminium MIG Welders Buying Guide (coming soon) will cover updated brand picks, duty cycle, and pulse capability in detail.
Pre-Weld Preparation
Removing oxidation and contaminants before you start is essential:
Shielding Gas
Pure argon, or an argon-helium mix, is the standard shielding gas for MIG welding aluminium. Both protect the weld pool from atmospheric contamination and help minimise defects. Whether pure argon or a mix is right for your job depends on material thickness and the parameters you’re running. Consult a welding reference chart or your gas supplier for the right ratio.
Technique
- Push vs pull: push the gun for thinner sections; pull for thicker material. Either way, angling the torch helps direct heat into the base metal and supports good arc stability.
- Back-stepping: moving the gun backwards briefly after laying a short section helps manage heat build-up and counter aluminium’s rapid heat dissipation.
- Pulse welding: alternating between high and low current reduces distortion and improves quality. Particularly useful on thin sections or where appearance matters.
- Weaving: a controlled side-to-side motion that distributes heat and widens the bead, useful on wider joints or where extra reinforcement is needed.
Troubleshooting Common MIG Aluminium Problems
Burn-through or warping: more likely on thin sections due to aluminium’s low melting point and high conductivity.
Fix: reduce heat input (voltage/wire feed speed), use a smaller-diameter filler wire, shorten arc length, or try tack/stitch welding to spread heat input.
Porosity: gas pockets in the weld.
Fix: keep the base metal and filler wire scrupulously clean, use high-purity shielding gas at the correct flow rate, and check gas nozzle positioning for full coverage.
Incomplete fusion or lack of penetration: a weakened joint.
Fix: increase heat input, confirm proper fit-up and joint prep, use a weaving technique, or preheat thicker sections.
Oxide formation and contamination: hinders fusion and causes defects.
Fix: clean thoroughly with a dedicated stainless steel wire brush (don’t cross-contaminate from other metals), use mechanical cleaning for stubborn oxide, and consider an aluminium-specific cleaning agent.
Wire feeding issues: bird-nesting or jamming the softer wire.
Fix: use a spool gun or push-pull system, check drive roll tension, and confirm the contact tip matches your wire diameter and is free of debris.
Joint fit-up and alignment problems: compromised strength.
Fix: use clamps or fixtures to hold parts securely, and bevel or groove thicker joints as needed.
Safety Considerations Specific to Aluminium
Beyond standard welding safety, keep in mind:
- Aluminium conducts electricity well, take care around electrostatic discharge and ground both yourself and the workpiece.
- High heat and sparks increase the risk of fire. Keep extinguishers nearby, clear flammable material from the work area, and use a fireproof blanket or welding curtain where items can’t be moved.
- Use proper fume extraction and standard PPE, and make sure you’re trained on both the process and the specific equipment you’re using. To learn more about fume extraction for welding, read our guide.
TIG vs MIG for Aluminium: Which Should You Use?
Both processes can produce strong, clean aluminium welds; the right choice depends on your priorities:
- TIG gives you the most control and the cleanest, most aesthetically refined welds, making it the preferred choice for thinner material, visible welds, and applications like aerospace, where precision matters most.
- MIG is faster and better suited to thicker material and higher-volume production work, where weld speed matters more than the finer control TIG offers.
Many fabricators use both, choosing process by job rather than committing to one across the board.
Aluminium for Other Processes
If plasma cutting aluminium, rather than welding it, is what brought you here, that’s covered in our separate Plasma Cutting Aluminium Guide, which deals with the cutting process rather than TIG/MIG joining covered here.
Frequently Asked Questions
Should you use AC or DC for TIG welding aluminium?
AC is the industry standard and the right choice for most aluminium TIG welding, especially on thinner material, because its positive cycle breaks up the oxide layer while the negative cycle provides penetration. DC TIG is viable on thicker aluminium (1/4" plus) and certain alloys like 1100, 6061, and 2219, but it isn’t suitable for thin sheet.
Why is aluminium harder to TIG weld than steel?
Aluminium is covered by an oxide layer that melts at a much higher temperature than the base metal, so it needs to be removed or broken up before a sound weld can form. Aluminium’s high thermal conductivity also quickly pulls heat away from the weld area, making heat control more demanding than with steel.
What amperage should I use for TIG welding aluminium?
A common starting rule of thumb is 1 amp per 0.001 inch of material thickness, reducing once the thickness goes beyond around 1/4 inch. Always check your machine’s manual and adjust based on the result you’re seeing in the weld pool.
What filler wire should I use for MIG welding aluminium?
ER4043 is the most widely used option, suited to 3XXX and 6XXX series alloys (3003, 6061, 6063), offering good fluidity and corrosion resistance. ER5356 suits 5XXX series alloys (5052, 5083) and gives higher tensile strength and better crack resistance. Match the wire to your base metal’s alloy.
Can I use a steel wire brush to clean aluminium before welding?
No, always use a dedicated copper, brass, or stainless steel brush kept exclusively for aluminium. A standard steel brush will contaminate the surface with embedded steel particles, leading to weld defects.
What’s the difference between TIG and MIG welding aluminium?
TIG offers more control and cleaner, more precise welds, making it the better choice for thin material and applications where weld appearance and precision matter most. MIG is faster and generally better suited to thicker sections and higher-volume work where production speed is the priority.
