How much corrosion resistance can anodized die-cast parts achieve in salt-spray tests?

Anodized Corrosion Resistance & Salt Spray Performance

The corrosion resistance of anodized die-cast parts in salt-spray (ASTM B117) tests is primarily determined by the thickness and sealing quality of the anodized layer. For standard Anodizing on aluminum die castings, a typical and widely accepted performance benchmark is to achieve 96 to 120 hours without the appearance of base material corrosion (white or red rust). This level of protection is suitable for many consumer electronics, interior components, and general industrial applications.

Factors Determining Salt Spray Performance

Several key factors directly influence the final result:

Anodize Layer Thickness: This is the most critical variable. A standard decorative anodize layer of 5-15µm will typically provide the 96-120 hours of protection. For harsher environments, such as automotive or marine applications, a hard anodizing or Arc Anodizing process is used to build a coating of 25-50µm or more. These thicker layers can reliably achieve 500 to 1000+ hours in salt-spray testing.

Sealing Quality: The porosity of the newly formed anodic layer must be sealed to prevent the entry of corrosive agents. Proper, high-quality sealing in hot water or with sealant additives is essential to meet the theoretical performance of the coating thickness.

Substrate Alloy: The base material has a significant impact on the uniformity and protective quality of the anodized coating. High-purity alloys are ideal for anodizing. While common die-casting alloys like A380 and ADC12 can be anodized, their high silicon content (7.5-9.5%) creates a silicon-phase network that interrupts the anodic layer, forming a darker, less uniform coating that can be more susceptible to pitting corrosion. For superior corrosion resistance, we recommend using a Die Cast Aluminum Alloy with lower silicon content, such as A360, whenever the casting process allows.

Achieving Higher Performance Standards

For projects demanding maximum corrosion resistance, a systems-engineering approach is necessary. This begins with die castings Design service that minimizes entrapping geometries and specifies the optimal alloy. Our die castings Engineering team then designs the Tool And Die to produce castings with a high-integrity skin, which is crucial for a consistent anodic film. Finally, specifying a thick, hard-coat anodize and validating the sealing process through cross-section analysis and salt-spray testing of samples is essential. This comprehensive approach is how we meet the stringent requirements for components used in automotive and other demanding sectors.