E-Thesis 25 views
Fundamental Study of Filiform Corrosion on Novel Automotive Aluminium Alloys / SARAH ROWLAND
Swansea University Author: SARAH ROWLAND
DOI (Published version): 10.23889/SUThesis.67074
Abstract
The aim of this work was to obtain an improved understanding of filiform corrosion (FFC) on 6000 series alloys. Chapter 3 describes kinetic and mechanistic studies on AA6014 and AA6022 identifying two types of attack, “surface active” (SA-FFC) and “successive pitting” (SP-FFC) FFC. SA-FFC is superfi...
| Published: |
Swansea University, Wales, UK
2024
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| Institution: | Swansea University |
| Degree level: | Doctoral |
| Degree name: | EngD |
| Supervisor: | Williams, G.; Keil, P.; McMurray, H. N.; and Penny, D. J. |
| URI: | https://cronfa.swan.ac.uk/Record/cronfa67074 |
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| Abstract: |
The aim of this work was to obtain an improved understanding of filiform corrosion (FFC) on 6000 series alloys. Chapter 3 describes kinetic and mechanistic studies on AA6014 and AA6022 identifying two types of attack, “surface active” (SA-FFC) and “successive pitting” (SP-FFC) FFC. SA-FFC is superficial with a depth c.a. 1-2 μm and occurs when a near-surface deformed layer (NSDL) is present at the alloy surface.P-FFC is a form of intergranular attack which can penetrate to a greater depth of c.a.0-50 μm. SP-FFC only occurs when the NSDL is absent or has already dissolved. In Chapter 4 the effect of relative humidity and presence of a NSDL on the type and rate of FFC on AA6014 and AA6022 was investigated. In all cases 80%RH was found to produce the largest rate of corrosion and showed most clearly the 2 types of FFC. At RH < 80% successive pitting is the more dominant FFC. At RH > 80% surface active FFC is more dominant. Although not measured, it was also visually clear that samples with a NSDL show the filament width increasing as %RH increases, up until 80% RH, after which the individual filaments are difficult to discern because they all merge into one unified feature. Chapter 5 investigated the effect of thermal treatment and presence of a NSDL on the type and rate of FFC on AA6014 and AA6022. It was concluded that thermal treatment has negligible effect on surfaces without a NSDL. The effect of thermal treatment is more clearly seen on surfaces with a NSDL with both AA6014 and AA6022 showing the greatest corrosion rates and greatest potential difference at 140°C. The thermal treatment temperatures of 210°C to 250°C showed the greatest corrosion resistance, with the slowest corrosion rates and smallest potential difference.Chapter 6 investigated the effect of inhibitors and presence of a NSDL on the type and rate of FFC on AA6014 and AA6022. Three inhibitors were investigated, at a range of pigment volume fractions (PVF): hydrotalcite (HT), diethyldithiocarbamate (HT-DEDTC) and cationic benzotriazole (CBP). The general efficiency ranking order of the pigments used could be described as CBP > HT > HT-DEDTC. Finally, chapter 7 shows the preliminary work investigating the effect of mechanical deformation on FFC on AA6014 and AA6022. The preliminary work identified the defects on the bent samples for AA6014 and AA6022 show that the corrosion observed mirrors the flat samples without a NSDL present. There was no evidence of a corrosion pattern on the apex of the bend that mirrored the corrosion pattern observed on the flat sample when a NSDL is present. |
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| Item Description: |
A selection of content is redacted or is partially redacted from this thesis to protect sensitive and personal information. |
| Keywords: |
Corrosion, Cosmetic Corrosion, Aluminium, Aluminum, FFC, Filiform corrosion, Aluminium Alloys, Aluminum Alloys, Automotive Aluminium Alloys, Automotive Aluminum Alloys |
| College: |
Faculty of Science and Engineering |
| Funders: |
EPSRC, Coated2, European Social Fund, EU Funds : Investing in Wales |