Corrosion Resistance & Coatings Flashcards

Which coating process involves immersing fasteners in molten zinc at approximately 840°F (449°C)?

Answer: Hot-dip galvanizing

Hot-dip galvanizing immerses fasteners in molten zinc at around 840°F to form a thick, alloyed zinc-iron coating.

Galvanic corrosion between two dissimilar metals is most severe when the metals are:

Answer: Far apart on the galvanic series

The greater the separation between two metals on the galvanic series, the higher the driving voltage and the more severe the galvanic corrosion.

Which type of corrosion occurs in the crevice between a fastener head and the mating surface due to oxygen depletion?

Answer: Crevice corrosion

Crevice corrosion initiates in confined spaces where oxygen is depleted, creating an aggressive local environment.

Dacromet coating is primarily used to avoid which problem associated with electroplated fasteners?

Answer: Hydrogen embrittlement

Dacromet is a water-based coating applied at low temperatures that eliminates the hydrogen embrittlement risk inherent in acid pickling and electroplating processes.

What is the purpose of a chromate conversion coating applied after zinc electroplating?

Answer: To passivate the zinc and extend corrosion resistance

Chromate conversion coatings passivate the zinc surface, sealing microscopic pores and significantly extending corrosion resistance.

ASTM B117 salt spray testing is used primarily to:

Answer: Compare relative corrosion resistance of coatings

The ASTM B117 salt spray (fog) test provides a standardized accelerated environment to compare the relative corrosion resistance of coated fasteners.

Which stainless steel series is most susceptible to intergranular corrosion after welding if not properly treated?

Answer: 300 series austenitic

300 series austenitic stainless steels sensitize in the 800–1500°F range during welding, causing chromium carbide precipitation and intergranular corrosion susceptibility.