Layered Double Hydroxide (LDH) Conversion Coatings for the Corrosion Protection of Aluminium Alloy 2024

The work carried out in this PhD focuses on the corrosion protection performance and characteristics of layered double hydroxide (LDH) conversion coating on AA2024.

LDH was explored both as a post- and pre-treatment for AA2024. As a post-treatment, it was tested as a sealing for a plasma electrolytic oxidation (PEO) coating on Al alloys. It was found that LDH growth is dependent on the final PEO morphology. In the case of unsuitable PEO coating, a new source of Al was used through a sol-gel treatment that covers the PEO with xerogel that is in turn exploited to produce the LDH coating. The results show a promising self-healing effect especially with the introduction of vanadate as a model corrosion inhibitor.

In the case of a pre-treatment, LDH was implemented on the very particular application of friction spot joining (FSpJ) of AA2024 with CF-PPS. The outcome of this study is that LDH can be used as an enhancer to adhesion bonding as well as improve the corrosion resistance of the Al alloy, but it is necessary to select the suitable inhibitor to be intercalated between the LDH layers.

Aside from the above investigated applications, the thesis was completed by studying the mechanism of LDH growth. It was possible for the first time to rely on synchrotron high performance XRD instrumentation to monitor in “live” the LDH film formation and growth. A combination of kinetic models as well as various laboratory methodologies were used to conclude the final mechanism of LDH formation on AA2024 and the influence of the Cu-rich intermetallic phases.

 

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