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Aluminum Filler Metals (4043 vs 5356 and others)

Most aluminum MIG and TIG work uses either 4043 (aluminum-silicon) or 5356 (aluminum-magnesium) filler. This sheet explains how the two families differ, when the less common alloys are used and why anodized parts need special care.

Ref WG-0106AWS A5.10

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Aluminum filler metals are classified in AWS A5.10 by alloy number, with ER for wire and rod (for example ER4043, ER5356). The 4xxx fillers are alloyed with silicon. Silicon makes the weld pool fluid and lowers crack sensitivity. The 5xxx fillers are alloyed with magnesium. Magnesium gives higher strength and better ductility. Choosing between them depends on the base alloy, strength needed, service temperature and whether the part will be anodized. See the aluminum filler selection chart for base metal combinations.

How to identify

Spools and tubes are labeled with the AWS class and diameter. 5356 wire is stiffer and feeds more easily through a push gun. 4043 wire is softer. After welding, 4043 welds often look smoother with a bright or slightly gray finish, and 5356 welds show more black soot near the bead.

Filler alloy families

Filler	Main alloy	Strengths	Limits
ER4043	About 5% silicon	Fluid puddle, good crack resistance, easy to use	Lower strength; gray after anodizing; not for high-magnesium 5xxx base metals
ER4047	About 12% silicon	Very fluid, low melting; good for brazing-type joints and thin parts	Low ductility
ER4943	Silicon with added magnesium	Higher strength than 4043 with similar welding behavior	Less widely stocked
ER5356	About 5% magnesium	Higher strength, better color match on anodized parts, feeds well	Not for sustained service above about 150°F (65°C)
ER5183	Magnesium with manganese	Higher strength for 5083 and 5456	Same elevated-temperature limit as 5356
ER5556	Magnesium with manganese	High strength for high-magnesium alloys	Same elevated-temperature limit
ER1100	Commercially pure	Pure aluminum and electrical parts	Low strength
ER2319	Copper	Some 2xxx alloys	Specialty item

Key points

4043 is the forgiving choice for 6061 and cast alloys when maximum strength is not needed.
5356 is the general choice where strength or anodize color matters.
High-magnesium fillers are not suited to sustained elevated temperature service. Use a 4xxx filler or the filler chart for parts that run hot.
Anodized welds made with 4043 turn dark gray. 5356 gives a closer match, but color is never exact.
Use a U-groove drive roll, a liner suited to aluminum and a spool gun or push-pull gun for soft wire.

Common mistakes

Using 4043 on 5xxx base metals with high magnesium content.
Using 5356 on parts that run hot in service.
Promising an exact color match after anodizing.
Feeding soft 4043 through a long steel liner and blaming the wire for birdnesting.

Governing standards: AWS A5.10 (bare aluminum and aluminum-alloy welding electrodes and rods); AWS D1.2 (structural welding code, aluminum). Filler maker selection charts.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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