What is the most durable type of metal plating?
“Durability” depends on the specific threat. For extreme wear resistance against abrasion and galling, hard chrome plating is often considered the most durable. For corrosion resistance in harsh chemical or marine environments, electroless nickel plating or thick cadmium plating (where specified) are top contenders. For a balance of good corrosion and wear resistance at a moderate cost, electroless nickel is a frequent choice. The “best” finish is always application-specific.
How does zinc plating prevent rust?
Zinc plating protects steel in two ways. First, it acts as a physical barrier, sealing the substrate from moisture and oxygen. Second, and more importantly, zinc is “sacrificial.” In the presence of an electrolyte (like water), zinc will corrode preferentially to steel. This electrochemical protection means that even if the coating is scratched, the surrounding zinc will continue to protect the exposed steel, preventing rust from forming.
What is the difference between plating and coating?
While the terms are sometimes used interchangeably, there’s a technical distinction. Plating typically refers to processes that deposit a distinct layer of metal (like zinc, nickel, or chrome) onto the substrate, often through an electrochemical (electroplating) or autocatalytic (electroless) reaction. Coating is a broader term that can include plating but also encompasses conversion coatings (like black oxide or phosphate) that chemically alter the surface of the base metal to create a new compound layer, as well organic coatings like paint or powder coat.
Why is passivation necessary for stainless steel?
Stainless steel resists rust due to a thin, invisible layer of chromium oxide on its surface. During machining or fabrication, iron particles can be smeared onto the surface, and the protective layer can be compromised. Passivation is a chemical bath (usually nitric or citric acid) that removes this free iron contamination and allows the chromium oxide layer to reform fully, uniformly, and more robustly, restoring and maximizing the material’s inherent corrosion resistance.
Can you plate an assembly, or must parts be disassembled?
It depends on the assembly and the process. For many plating processes, especially those requiring electrical conductivity like zinc or chrome plating, assembled parts can create “shadow” areas that don’t plate properly and can trap chemicals, leading to corrosion. It is almost always recommended to plate components individually before assembly. For some electroless processes or black oxide, plating simple assemblies might be possible, but it requires consultation with the finisher to avoid solution entrapment and ensure uniform coverage.
What is hydrogen embrittlement, and how is it addressed?
Hydrogen embrittlement is a condition where hydrogen atoms diffuse into the crystal structure of high-strength steel during acidic cleaning or electroplating processes, making the metal brittle and prone to sudden, catastrophic failure under stress. It is a critical concern for fasteners, springs, and critical aerospace components. It is addressed through a controlled thermal treatment called “baking,” performed within a few hours after plating. The baking process drives the hydrogen out of the metal, restoring its ductility and strength.
How do I choose between a clear and a colored (yellow, black) zinc finish?
The choice is based on both performance and aesthetics. Clear (blue-bright) zinc offers a basic silver-like appearance. Yellow chromate (hexavalent or trivalent) provides a higher level of corrosion resistance. Black chromate offers similar corrosion protection to yellow but with a distinctive black appearance for architectural or military specifications. Olive drab chromate is another option often specified for military hardware. Your finishing partner can guide you based on the required salt spray test hours and desired look.