Aluminum welding and repair

Aluminum welds well when it is clean and the heat is controlled, and it spoils quickly when it is not. This page is about the joint and the process. If you want to know how aluminum cuts and what grades are used, the aluminum material page covers that.

At a glance

• Oxide removed from the joint before welding
• Filler matched to the alloy family
• Heat managed to limit distortion and burn-through
• Repairs to cast and wrought aluminum parts
• Welding, all types, with machining in the same shop

The oxide skin and why cleaning comes first

Bare aluminum is covered by a thin oxide layer that melts at a much higher temperature than the metal underneath. If it is left in the joint, the weld pool cannot flow together cleanly and the weld ends up porous or weak.

So the joint is cleaned right before welding: degreased, then the oxide is brushed or cut away with tools used only on aluminum. Oil, paint and moisture trapped in a crack cause the same trouble, which is why a dirty repair on an old housing takes extra prep.

Heat goes somewhere else in aluminum

Aluminum carries heat away from the weld quickly, so it takes more heat to start a weld, and then the part holds that heat and can sag or burn through. Thin walls are the hardest case. The usual answers are tight fit-up, backing and clamps, and short, controlled welds that let the part cool.

Distortion is the other side of the same coin. On a machined housing, a weld that pulls the part out of flat can ruin a fit, so the plan often leaves extra material to machine after welding.

Filler depends on the alloy family

Aluminum is sold in families, and the filler wire has to suit the base metal. Common 6xxx wrought alloys and 5xxx alloys weld with different fillers, and some high-strength alloys are poor candidates for fusion welding at all. Cast aluminum often has porosity and trapped oil that make repairs more delicate.

If you know the alloy, say so. If you do not, a photo of the part, its use and any stamped markings give us a starting point, and we can look at the part before promising a repair.

Why cast aluminum parts crack and what to send

Cast aluminum parts usually crack at sharp corners, thin sections, mounting bosses and places that see vibration or impact. A repair that does not address the stress will crack again beside the weld.

For a quote, send the following and we will review it during shop hours at 4812 Longley Ln, Reno.

• Photos of the crack from two sides, with a ruler in the shot
• Whether the part is cast or machined from bar, if you know
• What the part does and what loads or heat it sees
• The machine or equipment it came from