Can 6061 aluminum be welded?
Yes, readily, by TIG or MIG with 4043 or 5356 filler. The catch is strength: the heat-affected zone of a T6 part drops to roughly annealed strength unless the weldment is re-heat-treated.
6061 is the most welded heat-treatable aluminum alloy. It TIG and MIG welds cleanly, resists hot cracking as long as the right filler is used, and is the alloy behind most aluminum frames, tanks, trailers and machine guards. The material itself is not the problem. The problem is what welding does to the T6 temper: the weld and about 12-25 mm (1/2-1") on each side of it see solution and over-aging temperatures, and the strength there falls from about 310 MPa (45 ksi) tensile to roughly 165-200 MPa (24-29 ksi), close to the annealed condition. AWS D1.2 and the Aluminum Design Manual design welded 6061 joints to that reduced figure.
Filler choice is the second decision. ER4043 (5% silicon) is the general-purpose filler: it flows well, resists cracking, and gives the fewest weld defects, but it anodizes dark grey against the parent metal and has lower strength and ductility. ER5356 (5% magnesium) is stronger, matches better after anodizing and is preferred for structural welds and for joints that will be anodized, but it must not be used where service temperatures exceed about 65 °C (150 °F), because the magnesium-rich weld becomes sensitised to stress corrosion. Never weld 6061 without filler: autogenous welds in 6061 hot-crack because the alloy sits right in the crack-sensitive composition range.
Three practical points. First, aluminum needs a clean surface: degrease, then remove the oxide with a dedicated stainless brush immediately before welding, or the weld will be porous. Second, preheat is not required and should stay below about 120 °C (250 °F) if used, because a long time at temperature widens the soft zone. Third, if the design needs T6 strength across the joint, weld in the T4 or O condition and re-solution-treat and age the whole weldment afterwards (T6 after welding), or place the weld where the load is low.
Welding for 6061 parts: where to send them
What to specify
- Weld process and filler: GTAW or GMAW with ER4043 or ER5356 per AWS A5.10; state which, because it affects colour after anodizing and service temperature
- Design allowable for the joint: state that the welded zone is taken at annealed strength, or call out post-weld solution treatment and aging (T6 after welding)
- Weld symbols, sizes and lengths per AWS A2.4; full penetration where the joint is loaded in fatigue
- Acceptance criteria: AWS D1.2 class, and any visual, dye-penetrant or radiographic inspection required
- Post-weld finishing: grind flush or leave as-welded, and whether the weldment will be anodized (use 5356 if so)
- Distortion control: welding sequence, fixturing or a stress-relief that is compatible with the temper
Pitfalls
- Designing to T6 numbers across a weld: the heat-affected zone is at roughly 60% of T6 strength and stays there
- Autogenous (no-filler) welds in 6061 crack; always add filler, even on tacks
- ER5356 on parts that run hot: above about 65 °C (150 °F) the weld metal becomes prone to stress-corrosion cracking; use 4043
- ER4043 on parts that will be anodized: the silicon-rich weld turns dark grey and stands out against the parent metal
- Porosity from hydrogen: oil, moisture, or an old oxide layer left on the joint; clean with a stainless brush right before welding
- Distortion: aluminum conducts heat fast and expands twice as much as steel; thin 6061 sheet pulls badly without fixturing
Frequently asked questions
- How much strength does 6061-T6 lose when welded?
- Roughly 35-45%. The heat-affected zone falls from about 310 MPa (45 ksi) tensile to around 165-200 MPa (24-29 ksi). Design codes use about 165 MPa (24 ksi) for welded 6061-T6 unless the weldment is re-heat-treated to T6 afterwards.
- Should I use 4043 or 5356 filler on 6061?
- 4043 for general fabrication, castings, and anything that runs above 65 °C (150 °F); it flows better and is more crack-resistant. 5356 for structural joints that need more strength and for parts that will be anodized, because it colour-matches.
- Can 6061 be TIG welded?
- Yes. AC TIG with a pure or lanthanated tungsten, argon shielding and ER4043 or ER5356 filler is the standard method for thin sections and cosmetic joints. MIG (spool gun or push-pull) is faster on plate above about 3 mm (1/8").
- Do I need to preheat 6061 before welding?
- Not for most sections. A light preheat to 65-120 °C (150-250 °F) helps on thick plate or castings, but keep it low and short: time at temperature widens the soft heat-affected zone and further over-ages T6 material.
