Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.693018
Title: Investigation of microstructure and corrosion in Al-Cu and Al-Mg alloys with and without Li additions
Author: Carrick, David
ISNI:       0000 0004 5921 0774
Awarding Body: Loughborough University
Current Institution: Loughborough University
Date of Award: 2015
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Abstract:
The corrosion performance of Al-Cu and Al-Mg alloys with and without Li additions have been investigated. These include; AA2024-T3, AA2099-T8E77 (coarse and fine grain structure), AA5083-T351, spray formed Al-Mg-Li and spray formed Al-Mg-Li-Cu-Zn alloy. Atmospheric corrosion was investigated for up to 12 months of exposure in a rural-urban environment, prolonged immersion testing in 3.5 wt.% NaCl for up to 96 hr s and potentiodynamic polarisation in 3.5 wt.% NaCl were examined. This was to answer whether Li additions, spray forming and grain size impacted on the corrosion resistance. Atmospheric exposure showed Al2(CO3)3, NOx, SOx and NaCl compounds being deposited. Cathodic intermetallic compounds (Fe, Si, Mn and Cu rich) were shown to be associated with pitting corrosion, whereas anodic intermetallic compounds (Mg rich) offered sacrificial protection to the matrix. The Al-Cu alloys showed more corrosion compared to the Al-Mg alloys in all three corrosion investigations. The Al-Cu alloys showed pitting corrosion and intergranular corrosion, compared to primarily pitting corrosion on the Al-Mg alloys. AA2024-T3 developed a weakened, friable layer on the surface, consisting of a network of intergranular corrosion and numerous shallow pits. The Al-Cu-Li alloys also showed intergranular corrosion and pitting corrosion, but also developed selective grain dissolution, leading to extensive sub-surface cavities. This showed that Li additions in the Al-Cu alloys was detrimental and was primarily associated with the T type phases likely to be; T1 phase (Al2CuLi). Li additions in the Al-Mg alloys did not show any measurable improvement or reduction in corrosion resistance. Spray forming also did not appear to improve the corrosion resistance. Grain size in turn was shown to impact on corrosion resistance, with the general consensus being that finer grains offer increased corrosion resistances. Al-Cu alloys showed fine grain structures developed easy path propagation for intergranular corrosion, whereas fine grain structures on Al-Mg alloys promoted increased corrosion resistance.
Supervisor: Not available Sponsor: Loughborough Graduate Research School
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.693018  DOI: Not available
Keywords: Aluminium alloys ; Lithium ; Corrosion ; Potentiodynamic polarisation ; Immersion testing ; Atmospheric corrosion
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