Cadmium Application on Welds for Enhanced Corrosion Protection

If you’ve ever inspected a weld exposed to salty air, acidic fumes, or a marine environment, you know that corrosion doesn’t play fair. It starts slow, hidden beneath a layer of oxide, and before you know it, that perfect weld is under attack. One of the tools we have to fight back — often used today in critical sectors like aerospace and defense — is cadmium coating.

You might have heard of it. Perhaps you’ve seen it on fasteners or connectors with a distinct dull silver appearance. But what about welds? Can you cadmize a weld? Should you? The short answer is yes — and in some cases, it’s the most recommended solution.

Why Cadmium on Welds?

Welds are not just any surface. They’re heat affected, structurally complex, and often exposed to harsh conditions. And when they connect dissimilar metals, such as stainless steel to carbon steel, the risk of galvanic corrosion increases drastically. That’s where cadmium coating shines: It acts as a sacrificial layer, corroding first to protect the weld underneath.

Standards such as Society of Automotive Engineers (SAE International) Material Specification AMSQQP416, Plating, Cadmium (Electrodeposited), and American Society for Testing and Materials (ASTM) B766, Standard Specification for Electrodeposited Coatings of Cadmium, already permit cadmium coating on welded areas, provided it’s applied correctly. This isn’t a process to improvise. It requires proper preparation, precise application, and thorough postprocess inspection. However, when done well, it adds years to the structure’s life.

How’s It Applied?

There are three main ways to apply cadmium:

1. Electroplating: This is the most common method. A cadmium layer is deposited using an electrical current in a controlled bath. You can control thickness (usually 5–25 microns) and finish (as plated, clear chromate, or yellow chromate).
2. Diffusion Coating: Cadmium powder is applied, and the part is heated to 300°–450°C so the coating diffuses into the surface. This is ideal for hard-to-reach areas, such as weld roots or inside fillets.
3. Thermal Spraying: Molten cadmium is sprayed onto the surface. This technique is not as precise but valuable for repairs and large-scale applications.

Regardless of the method, one thing is non-negotiable: surface prep. A weld must be clean, dry, and free of slag or grease. This typically involves abrasive blasting (nonferrous), chemical degreasing, or a combination of both. Before coating, inspection is crucial. I always recommend checking with liquid penetrant (ASTM E165, Standard Practice for Liquid Penetrant Testing for General Industry) or radiography (ASTM E1742, Standard Practice for Radiographic Examination) to rule out cracks or porosity that might be hidden in the weld.

What Should You Inspect?

After cadmizing a weld, here’s what we look for:

• Visual: Is the coating uniform? Are there areas missing or signs of peeling?
• Thickness: Use eddy current testing (ASTM B499, Standard Test Method for Measurement of Coating Thicknesses by the Magnetic Method: Nonmagnetic Coatings on Magnetic Basis Metals) or magnetic pull-off testing (ASTM B530, Standard Test Method for Measurement of Coating Thicknesses by the Magnetic Method: Electrodeposited Nickel Coatings on Magnetic and Nonmagnetic Substrates) to verify that it meets the specification.
• Adhesion: If it doesn’t stick, it’s useless. Perform a cross-cut tape test (ASTM D3359, Standard Test Methods for Rating Adhesion by Tape Test) and ensure it holds.

For components in extreme environments, I prefer to take it a step further: salt spray testing (ASTM B117, Standard Practice for Operating Salt Spray [Fog] Apparatus) or even porosity analysis under a microscope can reveal the true durability of that coating.

Why It Still Matters

Cadmium has received a bad reputation due to its environmental concerns. As a result, it’s being replaced in some industries. However, in critical components — especially those where galvanic corrosion poses a serious risk — nothing protects like cadmium. It’s not just about resisting rust; it’s about maintaining the integrity of a weld that can’t be allowed to fail. Additionally, cadmium offers several benefits: It lubricates threads, resists mild wear, and conducts electricity effectively. That’s why you still see it in aircraft, military gear, and offshore structures.

In my years working as an inspector and instructor across industries and countries, I’ve learned this: A good weld isn’t enough. If you leave it unprotected in the wrong environment, you’re just giving corrosion a head start. Cadmium coating — when done correctly — adds that extra layer of defense that turns a vulnerable joint into a long-term asset.

Is cadmium on welds still worth considering? Absolutely. But like anything in our trade, it’s all about doing it right: Follow the standards, prepare the surface, inspect with care, and trust the science behind it.

And above all, remember what we protect today is what keeps structures safe tomorrow.

JORGE T. REYNA (contacto.jrsa@gmail.com) is owner of JRSA Engineering in Monterrey, Mexico. He is an AMPP Master Coatings Inspector, AMPP Senior Certified Coating Inspector, AMPP Protective Coating Specialist, ANST Level III, and AWS Senior Certified Welding Inspector.