In-situ time-lapse SKPFM investigation of sensitized AA5083 aluminum alloy to understand localized corrosion

• Sensitized AA5083-H2 aluminum alloy was exposed to chloride-laden thin-film electrolyte at ambient temperature (20%–85% relative humidity) and the local Volta potential measured, in-situ and in real-time, using the Scanning Kelvin Probe Force Microscopy, with the intention to elucidate the earliest stage of localized corrosion. Positive Volta potentials vs alloy matrix were measured for magnesium silicides in ambient air, which, however, underwent a severe nobility loss during corrosion, causing their nobility to invert to active potentials (negative) relative to the alloy matrix. The reason for the nobility inversion was explained by the preferential dissolution of Mg2+, which resulted in an electropositive surface. Aluminides, both with and without silicon, were seen to form the main cathodes at all exposure conditions. The local alloy matrix next to closely-separated aluminides were seen to adopt the Volta potential of the neighbor aluminides, which, hence, resulted in local corrosion protection. The phenomenon of nobility adoption introduced in this work raises questions regarding the anode-to-cathode ratio, which was observed to change during corrosion, and the resulting impact to localized micro-galvanic corrosion. This work further demonstrates that it is necessary to measure the Volta potential during corrosion to reflect the true relationship between the Volta potential and corrosion potential or breakdown potential. © 2020 The Author(s). 

Subject headings

TEKNIK OCH TEKNOLOGIER  -- Kemiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Chemical Engineering (hsv//eng)

Keyword

Aluminum alloys

Aluminum chloride

Aluminum corrosion

Aluminum metallography

Atmospheric corrosion

Cathodes

Chlorine compounds

Corrosion protection

Electrolytes

Galvanic corrosion

Metallic matrix composites

Silicides

Active potentials

Breakdown potential

Corrosion potentials

Exposure conditions

Magnesium silicides

Preferential dissolution

Scanning Kelvin probe force microscopy

Thin film electrolytes

Localized corrosion

Publication and Content Type

ref (subject category)

art (subject category)