Welding and Metal Fabrication in Yorba Linda

Because structural welding requires three things a field location cannot provide: the vehicle supported and unloaded so the weld is not made in a stressed member, cleanliness and environmental control so the weld is sound, and measurement before and after so you know the repair returned the structure to specification.

Welding a loaded frame member is the specific hazard. A trailer frame carrying its own weight and its cargo has stress in the metal, and adding a weld into a stressed member locks that stress into the repair. When the vehicle is unloaded later the geometry is wrong and the repair carries a permanent internal load it was never designed for.

Then there is the measurement. Structural work here is measured against factory dimensions before and after, and that record goes with the vehicle. That is not achievable with a portable welder in a parking lot, and any shop offering it should be treated with real caution.

Almost everything. Aluminum conducts heat several times faster than steel, so heat runs away from the joint and the surrounding material distorts before the weld pool establishes. It also has no colour change as it approaches melting, which means an inattentive welder discovers the temperature by watching the part collapse.

The oxide layer is the other problem. Aluminum forms an oxide skin instantly on exposure to air, and that oxide melts at a far higher temperature than the metal underneath. It has to be removed mechanically immediately before welding and kept out with shielding gas, or the weld traps oxide inclusions and is weak regardless of how it looks.

Then there is fatigue. Steel has a fatigue limit, a stress below which it will endure effectively unlimited cycles. Aluminum does not. Any aluminum structure that flexes will eventually crack, which is why aluminum trailer and rack design has to eliminate flex rather than simply be strong enough. It is also why aluminum frames are more often sectioned and replaced than pulled straight.

• High thermal conductivity causing distortion away from the joint
• No colour change warning as the material approaches melting
• Oxide layer that must be removed immediately before welding
• No fatigue limit, so flexing designs eventually crack
• Heat affected zone softening that reduces strength near the weld

By isolating them, because galvanic corrosion between dissimilar metals in the presence of moisture is not a possibility, it is a certainty given time. An aluminum bracket bolted directly to a steel frame with a steel fastener creates a cell, and the aluminum, being less noble, corrodes at the joint.

Recreational vehicles make this worse than most applications. They carry aluminum framing, steel chassis, stainless fasteners and fiberglass panels in the same assembly, they get wet, and coastal Southern California adds salt air to the equation.

The remedies are established and inexpensive at build time. Isolate the interface with a non conductive barrier, choose fasteners compatible with both metals, seal the joint so moisture cannot sit in it, and protect cut edges where the coating was broken. Doing this during fabrication costs minutes. Correcting it after five years costs a new bracket and a repair to whatever it was mounted on.