Salt Spray
Salt spray is an accelerated corrosion test that evaluates how well a metal, coating, or plated CNC part resists rust and pitting under a controlled 5% sodium chloride fog at around 35°C, following standards such as ASTM B117 and ISO 9227. It is a comparative pass/fail durability screen, not a direct service-life predictor, with results recorded as time to first visible corrosion or coating breakdown.
On the shop floor, salt spray testing is used to validate the entire manufacturing chain for CNC-machined components, not just the final coating. Machined aluminum, steel, castings, and plated fasteners are run through the chamber to confirm that material choice, cutting-fluid compatibility, machining cleanliness, surface prep, coating thickness, and sealing all work together. For aluminum parts, corrosion resistance depends on upstream choices: low-corrosion cutting fluids, proper cleaning before anodizing, sufficient anodic thickness, and effective sealing are needed to reach 96 or more hours in the cabinet. Parts are exposed to a continuous 5% sodium chloride fog at 35°C, and results are compared against specification targets such as 24, 96, 240, 720, or over 1,000 hours, depending on the coating. The test is commonly required for marine hardware, automotive components, and coated systems such as zinc, zinc-nickel, electroless nickel, Dacromet, anodized aluminum, and stainless steel assemblies where corrosion performance is contractual.
What does a 96-hour salt spray pass actually mean?
It means the sample resisted visible corrosion for 96 hours under the specified chamber conditions; it does not mean 96 hours equals 96 hours of outdoor service.
Why do anodized aluminum parts sometimes fail early?
Failure often traces to inadequate cleaning, insufficient anodic thickness, poor sealing, or incompatible cutting fluids that leave corrosion-promoting residue on the part before anodizing.
Why do zinc-nickel parts outperform standard zinc in salt spray?
Standard zinc typically reaches 96 to 200 hours, while zinc-nickel can exceed 1,000 hours because the alloy provides improved barrier protection and more effective sacrificial corrosion performance.