4043 Aluminum Filler — What It Is and Why It Matters
4043 (ER4043) is the most commonly used aluminum filler metal for general-purpose welding. It contains approximately 5% silicon, which improves fluidity, reduces shrinkage cracking, and produces a weld with good corrosion resistance and a bright, clean appearance.
4043 is the default choice for welding 6061 aluminum — the most common structural alloy — and works well on 3003, 3004, and other non-heat-treatable alloys. It produces lower-strength deposits than 5356 but offers superior crack resistance and better feeding characteristics in MIG applications.
The companion alloy ER5356 (5% magnesium) provides higher strength deposits and is the choice when anodizing the finished weldment, as 4043 welds turn dark gray when anodized while 5356 matches more closely. Choosing between 4043 and 5356 depends on the base alloy, required strength, crack sensitivity, and finishing requirements.
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Frequently Asked Questions
Should I use 4043 or 5356 aluminum filler?
4043 for most general-purpose work, especially on 6061: better crack resistance, smoother feeding, cleaner appearance. 5356 when you need higher weld strength, when the part will be anodized (5356 anodizes with less discoloration), or when welding 5xxx-series base metals like 5052 and 5083.
Why does aluminum filler wire bird-nest?
Aluminum wire is much softer than steel wire and buckles easily in long cable runs. The wire deforms at the drive rolls or kinks in the liner rather than pushing smoothly to the contact tip. A spool gun (short feed path) or push-pull system (motor at both ends) solves this problem.