dc.contributor.advisor | Nisancioglu, Kemal | |
dc.contributor.advisor | Lunder, Otto | |
dc.contributor.advisor | Nordlien, Jan Halvor | |
dc.contributor.author | Stepanova, Mariia | |
dc.date.accessioned | 2018-01-18T15:34:45Z | |
dc.date.available | 2018-01-18T15:34:45Z | |
dc.date.issued | 2017 | |
dc.identifier.isbn | 978-82-326-2657-1 | |
dc.identifier.issn | 1503-8181 | |
dc.identifier.uri | http://hdl.handle.net/11250/2478244 | |
dc.description.abstract | Thin walled heat exchanger Al alloy tubes, with solid-solution Zn-rich surface, are widely used by the automotive industry and are considered by the heat, ventilation, air-conditioning and refrigeration market. This work investigates protection of Al surface with Zn-rich layers for improved corrosion resistance of Al tubes against pitting.
Zinc was applied on AlMn alloy extruded tubes by thermal-arc spraying. The tubes were subsequently subjected to heat treatment at various temperatures and durations to obtain solid-state AlZn alloy diffusion layer at the surface with varying thickness and Zn concentration profiles. Concentration depth profiles were obtained by glow discharge optical emission spectroscopy (GD-OES). Corrosion rate was determined by weight loss resulting from immersion for predetermined times in acidified artificial sea water solution of pH 3.
The as-sprayed Zn coating was found to be highly non-uniform which resulted in non-uniformity of the Zn-rich layers laterally and in depth. Thickness of Zn-rich layer increased with heat treatment time and temperature, while Zn concentration at the surface decreased. Zn-rich layers were found capable of protecting the AlMn alloy substrate against pitting at the expense of increased self-corrosion rate. SEM and EDS area analysis of corroded samples after immersion test showed that corrosion of Zn-rich layers was non-uniform due to non-uniformity of the layers themselves. Regions with higher Zn concentration, ρZn, corroded first and protected galvanically regions with lower ρZn. The well-known relationship between the corrosion potential of AlZn alloys and Zn concentration was extended over a wide concentration range using ρZn of corroded areas and related further to the corrosion rate in acidified synthetic seawater. The database thus developed is useful for optimizing the Zn-rich layer thickness and Zn concentration profile in the layer to minimize uniform corrosion, and therefore maximize service lifetime, without reducing the protection against pitting. | nb_NO |
dc.language.iso | eng | nb_NO |
dc.publisher | NTNU | nb_NO |
dc.relation.ispartofseries | Doctoral theses at NTNU;2017:294 | |
dc.title | Zinc-rich coatings for improved corrosion resistance of extruded aluminium heat-exchange tubing in acidified chloride solution | nb_NO |
dc.type | Doctoral thesis | nb_NO |
dc.subject.nsi | VDP::Technology: 500::Materials science and engineering: 520 | nb_NO |
dc.description.localcode | Digital fulltext not available | nb_NO |