Aluminum Rocker Splice: Wire Birdnesting, Crater Cracks, and Steel Fastener Contact
An aluminum-intensive 2023 SUV needs a 2.0 mm 6061-T6 extrusion rocker section spliced to a 1.5 mm 5052-H32 inner panel. The shop uses a push-pull gun with a 10 m torch, 1.2 mm ER4043, 100% argon at 20 cfh, and a stainless-steel liner that has been in service for six months. The first welds show birdnesting at the gun, scattered porosity, black smut along the toe, crater cracks, and occasional burn-back to the contact tip. A steel bolt and washer are used temporarily to pull the panels together; the bolt contacts bare aluminum for two hours. The OEM procedure specifies 5356 wire for this joint and a 25 mm minimum edge distance.
1. Diagnose the wire-feeding and arc problems, and recommend corrections to the torch, liner, drive rolls, gas coverage, and cleaning.
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Birdnesting on a 10 m push-pull torch with a six-month-old stainless liner is a feeding problem, not a welding problem. Aluminum wire is soft and galling-prone; a stainless liner creates high drag, and the push and pull motors fight each other when the liner is dirty or kinked. Replace it with a Teflon or nylon liner dedicated to aluminum, use U-groove drive rolls with the minimum tension that still feeds, match push and pull motor speeds per the manufacturer, and shorten the torch if possible. Check the contact tip: aluminum wire expands, and a worn or undersized tip causes burn-back. The black smut and porosity point to poor cleaning and gas coverage: remove oxide with a dedicated stainless brush or carbide burr used only on aluminum, wipe with an aluminum-approved solvent, and set flow at 20–25 cfh with a gas lens and 12–15 mm standoff. Check for drafts that can strip shielding gas.
2. The OEM specifies 5356 wire, but the shop used 4043. Explain the difference for this joint and address the crater cracks.
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The OEM specification is not interchangeable with 4043. 5356 contains about 5% magnesium and gives higher tensile strength, better ductility and better crack resistance on 6xxx extrusions; 4043 is lower strength for some 6xxx welds and can be more crack-sensitive. Crater cracks are a technique issue: use the crater-fill or arc-off time, run onto a runoff tab, and do not break the arc on the joint. Porosity also follows from the feeding problem, because unstable wire feed changes arc length and can contaminate the wire. Set the machine to the OEM-approved synergic program for 5356 and the thickness, and weld scrap extrusion before touching the vehicle. Confirm the filler classification on the spool and record it, because using the wrong filler is a procedure nonconformance even if the weld looks acceptable.
3. Evaluate the two-hour steel bolt contact with bare aluminum and describe the dissimilar-metal and corrosion-control actions required before delivery.
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Remove the steel bolt and washer, inspect the aluminum under and around them for embedded iron, gouges and corrosion, and clean per the OEM. Two hours of dry contact is unlikely to cause deep galvanic damage, but steel fasteners in aluminum are a corrosion cell, especially with moisture and road salt; the OEM procedure should specify coated, isolated or aluminum-compatible fasteners and sealer. Use isolated fasteners or a barrier such as coating, sealer or an isolation washer as specified, never a steel wire brush on aluminum, and reapply the OEM corrosion protection after welding. Document the contact and the corrective action, because dissimilar-metal contact is a durability issue that may not appear until later. Also verify the 25 mm minimum edge distance before welding, since a short edge distance can cause blow-through and reduce joint strength.