Abstract
A hyphenated optical-electrochemical technique and image analysis protocol is used to quantify global and local (intermetallic) corrosion process and kinetics. Our findings reveal an early stage (< 60 s) composition-dependent hierarchical local activation of all IMs that can be attributed to IM dealloying. This is followed by local trenching initiated at matrix locations adjacent to regions of the IMs previously dealloyed, which in turn develops into concentric trenching around the IMs. These stages have quantifiable activation times and kinetics. While dealloying kinetics are found to be strongly dependent on IM composition and slightly dependent on IM size in the case of the S-phases, trenching kinetics are IM composition and size independent.
Highlights
The lightweight aluminium alloy AA2024-T3 is a paramount mate rial in the aviation industry due to the good balance between mechanical properties and density [1]
Micro structural features, such as intermetallic (IM) second phase constituents (> 0.5 μm), were shown to play a major role in the initiation of local corrosion, which has been so far extensively explained through the model of micro-galvanic corrosion, i.e. local composition differences between the IM particles and the surrounding Al-rich matrix translate into local differences in Volta potential [10,11,12], making IMs appear as anodic or cathodic
We introduce the potential use of highlyresolved optical microscopy to study early stage local corrosion pro cesses in-situ at quasi real time of immersion
Summary
The lightweight aluminium alloy AA2024-T3 is a paramount mate rial in the aviation industry due to the good balance between mechanical properties and density [1]. High-spatial resolution microscopies like SEM and TEM, for example, allow to visualise micro-corrosion features in detail, but their experimental set-ups require high degrees of vacuum, thereby not being always compatible with the corrosive atmospher es/electrolytes to which the alloy is typically exposed In this way, the use of such techniques has mostly been limited to ex-situ analysis with the consequent loss of temporal resolution and out-of-equilibrium in formation, as the sample needs to be purposefully removed from the corrosive solution to perform the desired analysis. The high temporal and spatial accuracy of the optical measurements performed during immersion unveiled that all identified IMs (independently of their composition) locally behave as anodic in the first seconds to minutes of immersion, yet with composition-dependent kinetic differences
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call