Accession Number:

ADA627193

Title:

Galvanic Couple Current and Potential Distribution between a Mg Electrode and 2024-T351 under Droplets Analyzed by Microelectrode Arrays

Descriptive Note:

Journal article

Corporate Author:

NAVAL RESEARCH LAB STENNIS DETACHMENT STENNIS SPACE CENTER MS OCEANOGRAPHY DIV

Personal Author(s):

• King, A. D.
• Lee, Jason S.
• Scully, J. R.

Report Date:

2015-11-04

Pagination or Media Count:

14.0

Abstract:

The galvanic throwing power of bare and polymer coated Mg over a simulated bare AA2024 scribe was studied directly with diagnostic multi-electrode arrays, which enable the spatial distribution of cathodic current density to be elucidated. The galvanic current density over the AA2024-T351 coupled to Mg in various full immersion, thin layer, and droplet electrolyte geometries relevant to atmospheric field exposures was investigated during simulated atmospheric exposures. In these microelectrode studies, current and potential distributions extended somewhat more uniformly across a 5.75 mm long, simulated bare 2024-T351 scratch when the electrolyte layer was thick, continuous and more ionically conductive i.e., higher salt concentration in the absence of a polymer coating over the Mg. Current and potential distributions did not extend across simulated defects when the electrolyte became discontinuous or the ionic path became tortuous due to drying or the addition of a resistive polymer coating over the Mg. Additionally, galvanic protection is shown to intensify for short period of time during drying and re-wetting cycles at close distances between Mg and 2024-T351 rationalized to be caused by changing electrolyte conductivity, E-i behavior, and electrode area effects. The drying characteristics of individual salts were also shown to have an effect on the current and potential distribution as MgCl2 due to its low deliquescenceefflorescence point of approximately 35 RH at STP was shown to be less susceptible to drying at low RH, thus extending the time into the drying cycle where the galvanic couple was active compared to pure NaCl or ASTM Substitute Ocean Water.

Descriptors:

• *CORROSION INHIBITION
• *FINITE ELEMENT ANALYSIS
• *GALVANIC CORROSION
• *ORGANIC COATINGS
• *POLYMERS
• ALUMINUM ALLOYS
• CATHODIC PROTECTION
• COATINGS
• CONCENTRATION(CHEMISTRY)
• CURRENT DENSITY
• DEFECTS(MATERIALS)
• ELECTRICAL CONDUCTIVITY
• ELECTROCHEMISTRY
• ELECTRODES
• ELECTROLYTES
• MAGNESIUM
• SEA WATER
• SPATIAL DISTRIBUTION

Subject Categories:

• Physical Chemistry
• Coatings, Colorants and Finishes
• Properties of Metals and Alloys
• Electricity and Magnetism

Distribution Statement:

APPROVED FOR PUBLIC RELEASE