Nondestructive analysis of pitting corrosion characteristics on EN AW-2024-T3 using 3D optical pattern profilometry

Abstract

High-strength age-hardenable aluminium alloys are susceptible to localised corrosion. It is vital to monitor the evolution of the corrosion depth in order to prevent a critical degradation of the mechanical properties. This study presents the application of 3D optical pattern profilometry for the analysis of the pitting corrosion behaviour of the aluminium alloy EN AW-2024-T3. Therefore, measurements were conducted using a 1 M NaCl solution at different exposure times. The measurements are compared to the results of optical microscopy investigations of metallographic specimens as well as laser scanning microscopy measurements. In immersion bath tests, the 3D pattern profilometry shows a high measurement accuracy of the pitting corrosion. Regarding the pit characteristics, corroded metal sheets exhibit an increase in the pit depth, volume and area with an increasing exposure time of up to 312 h and then decrease. Moreover, a higher increase in the width in rolling direction than perpendicular to it is noticeable.

An assessment of pitting corrosion in anodized aluminum alloys: It might not be what it seems

“…Despite this, OP presents some advantages for the evaluation of corrosion in Al alloys. For example, Schmidl et al [ 26 ] studied the formation of pits in the bare AA2024‐T3 Al alloy and showed that the undercuts on the left flank of the pits could not be measured by means of 3D pattern profilometry or laser scanning microscopy. Cross‐sectional analysis would be required to not omit certain regions in the pits.…”

“…It is important to point out that to analyze the depth and extension of the corrosive attack on Al alloys, different methodologies have been used and reported in the literature, such as optical microscopy (OM) and optical profilometry (OP) from the surface and analysis by OP and scanning electron microscopy (SEM) in metallographic cross-sections. However, some works have shown that the results obtained by OP can lead to misinterpretations, [18][19][20][21][22][23][24][25][26][27][28][29] once that, by this technique the calculation of the surface profile is carried out from the distortion of a regular shape light pattern projected on the surface. [26] Therefore, different results can be obtained depending on the condition of the surface such as accumulation of corrosion product or even depth limitation.…”

“…However, some works have shown that the results obtained by OP can lead to misinterpretations, [18][19][20][21][22][23][24][25][26][27][28][29] once that, by this technique the calculation of the surface profile is carried out from the distortion of a regular shape light pattern projected on the surface. [26] Therefore, different results can be obtained depending on the condition of the surface such as accumulation of corrosion product or even depth limitation.…”