Galvanic Corrosion of Al-7075-T6 and Steel-4340 Coupled to Brass QQ-B- 626,360 and Al-7075-T6 Coupled to Steel-4130 and Steel-4340: Exposure to Aqueous NaCl and Salt-Fog Environments
Technical rept. Jun-Dec 1985
NAVAL SURFACE WEAPONS CENTER SILVER SPRING MD
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For this investigation, laboratory studies on the corrosion behavior of four galvanic couples is discussed the four couples include A1-7075-T6 Brass QQ-B-626, 360, Al-7075-T6Steel-4340, Al-7075-T6Steel-4130, and Steel- 4340Brass QQ-B-626, 360. Test samples were exposed to aqueous 3.5 NaCl and to a salt-fog environment. A measurement of the galvanic current generated for each couple tested was used to determine the magnitude of galvanic interaction. Results indicated that the corrosion rate of Al-7075-T6 was significantly accelerated when galvanically coupled to brass or the steel samples. In addition, it was discovered that Steel-4130 and Steel 4340 corroded when coupled to Al-7075-T6, however, at a reduced rate when compared to the uncoupled steel samples. In contrast, brass samples revealed no signs of corrosion when coupled to either Al-7075-T6 or Steel-4340. For the Steel-4340Brass galvanic couple, it was found that the corrosion rate of Steel-4340 was significantly increased while the brass sample remained unaffected. In addition to the discussion of experimental results, a theoretical treatment relating galvanic currents to observed corrosion rates are presented for each of the four couples. Keywords Galvanic Corrosion, Polarization Resistance, Cathode, Anode, Salt-Fog, Cathodic Polarization, Zero-Impedance Ammeter, Galvanic current Density, Aluminum Alloys.
- Properties of Metals and Alloys
- Fabrication Metallurgy