The Power Is In The Surface Plating

How hard the finish fights back against moisture, salt, and dissimilar-metal contact.

Plating adds material. On a threaded part that changes thread fit and the torque you feel going in.

What it costs, how many shops are qualified, and what the regulatory picture looks like in five years.

The long-running aerospace benchmark. A sacrificial coating — it corrodes first so the steel underneath stays intact. Excellent salt and marine resistance, naturally lubricious so it resists galling and gives repeatable torque-tension, conducts well for bonding and grounding, and plays nicely against aluminum. The catch: cadmium is toxic, regulatory pressure keeps tightening, and the list of qualified shops keeps shrinking. Still specified on plenty of defense and legacy airframe work.

The leading modern answer to the cadmium problem. It keeps the sacrificial behavior and delivers strong corrosion protection without the toxicity baggage. If a program is being designed today and someone asks what replaces cad, this is the first name on the list.

The gold iridescent parts. Zinc plating with a chromate conversion layer on top, and that top layer gives both the color and a real step up over plain zinc. Inexpensive and widely available. Earns its keep on commercial hardware, ground support equipment, tooling and interior fittings. Not the answer for salt spray or a flight-critical joint.

The bright, slightly blue-silver parts in the same family. Same zinc base, different conversion chemistry, cleaner cosmetic result, and generally a bit less corrosion protection than the yellow. Chosen when appearance matters or the gold look is not wanted.

A conversion coating rather than a plated-on layer, which is its whole advantage: it changes the surface instead of adding to it, so thread fit and torque are essentially untouched. Dark and low-glare, which matters in a cockpit. Cheap. Corrosion protection is mild and needs a supplementary oil or wax. Good for non-critical, controlled-environment hardware.

Strictly speaking not a coating at all. A chemical treatment for stainless that strips free iron off the surface and lets the chromium oxide film rebuild itself. Nothing is added, so no dimensional change and no effect on thread fit. Environmentally friendly and inexpensive. Works only on stainless, and adds no lubricity and no wear resistance.

For aluminum and titanium hardware. Like passivation it converts the surface, but unlike passivation it grows an oxide layer outward, so it does affect tolerances. Type II is the general-purpose, dyeable version. Type III hardcoat is the thicker, tougher one for wear surfaces. Plan for this: the anodic oxide is an insulator, so anodized hardware in a grounding or EMI path needs a deliberate answer.

Applied autocatalytically rather than by electric current, so it deposits at the same thickness everywhere — down in threads, into bores, and inside blind features where an electroplated finish goes thin or misses entirely. Hard, wear resistant and corrosion resistant. When geometry is complicated and coverage has to be uniform, this is the one.

A bonded PTFE or molybdenum disulfide film, and it is about friction rather than corrosion. It gives a predictable, repeatable coefficient of friction so torque actually correlates with clamp load, and it stops titanium and stainless from galling and seizing on assembly. Wide temperature range, nothing to migrate or contaminate. Frequently applied over another finish rather than instead of one.

The high-heat specialist. Anti-seize behavior at temperatures that would defeat almost anything else, plus excellent electrical conductivity. This is engine and exhaust-section hardware, and it pairs with the superalloys used out there.