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Improved organic coating delamination resistance using physical vapour deposited Zn-Mg layers on strip steel / REBECCA BOLTON

Swansea University Author: REBECCA BOLTON

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DOI (Published version): 10.23889/SUthesis.58629

Abstract

Physical vapour deposition (PVD) of zinc alloy coatings was investigated as a potential substitute process for commercially available hot dip galvanising (HDG) of strip steel. Therefore, zinc alloy coatings deposited by PVD were systematically compared with traditional sacrificial HDG zinc alloy coa...

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Published: Swansea 2021
Institution: Swansea University
Degree level: Doctoral
Degree name: EngD
Supervisor: Williams, G. ; Sullivan, J.
URI: https://cronfa.swan.ac.uk/Record/cronfa58629
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fullrecord <?xml version="1.0"?><rfc1807><datestamp>2021-11-12T13:07:08.3065264</datestamp><bib-version>v2</bib-version><id>58629</id><entry>2021-11-12</entry><title>Improved organic coating delamination resistance using physical vapour deposited Zn-Mg layers on strip steel</title><swanseaauthors><author><sid>4fa58e0865c744fd4ef71d86394c7f7d</sid><firstname>REBECCA</firstname><surname>BOLTON</surname><name>REBECCA BOLTON</name><active>true</active><ethesisStudent>false</ethesisStudent></author></swanseaauthors><date>2021-11-12</date><abstract>Physical vapour deposition (PVD) of zinc alloy coatings was investigated as a potential substitute process for commercially available hot dip galvanising (HDG) of strip steel. Therefore, zinc alloy coatings deposited by PVD were systematically compared with traditional sacrificial HDG zinc alloy coatings, in terms of bare metal corrosion resistance and resistance to corrosion-driven delamination of an organic overcoat, to establish the effects of magnesium content, microstructure and surface treatment. The effectiveness of modern corrosion inhibitor pigments, of known volume fraction, on HDG and PVD zinc coatings was also explored. All PVD coatings and commercially available HDG coatings were characterised using microscopy techniques and x-ray diffraction to identify the microstructure and phases present as a function of magnesium content. It was confirmed that the PVD coatings were significantly thinner than the HDG coatings. The pure zinc PVD coating was comprised of hexagonal microplates, whereas the HDG counterpart contained grains 5-10 time larger. The PVD coating containing 4 wt% magnesium exhibited a discrete structure, a binary system of zinc-rich and Mg2Zn11-rich phases, much finer than the HDG Zn-Mg-Al (ZMA) coating. The PVD coatings containing 10 wt% and 20 wt% magnesium were studied using transmission electron microscopy as they possessed nanostructures containing Mg2Zn11 and MgZn2 phases respectively. Open circuit potential (OCP) measurements in chloride-containing solution established that an increase in magnesium content in PVD coating resulted in a decrease in the initial immersion open circuit potential. Additionally, increased magnesium content in the PVD layers also correlated with an increase in corrosion resistance, as made evident by reduced Ecorr and Icorr values during potentiodynamic studies. Electrochemical impedance spectroscopy (EIS) comparative studies suggested an improvement in corrosion resistance exhibited by PVD0 compared to HDG, both zinc-only coatings, attributed to the finer and more compact surface morphology. Bare metal corrosion response for all coatings was studied using a novel augmentation of the scanning vibrating electrode technique (SVET), known as SVET-TLI (time-lapse imaging). The combination of electrochemical mapping and photographic imagery revealed a potential optimum magnesium content within the PVD coatings. PVD4 exhibited the lowest anodic current density over a 24 hour study compared to the HDG, ZMA and other PVD coatings. Furthermore, the characteristic black staining attributed to magnesium corrosion was observed on the magnesium-containing PVD coatings. However, on the PVD Zn-Mg coatings the staining was observed in the regions established as net cathodes, which is contrary to association of staining with magnesium dissolution which takes place in local anodes. Using the scanning vibrating kelvin probe (SKP) method, PVD4 was identified as the optimum magnesium composition as it was found to be resistant of both corrosion-driven cathodic delamination and anodic undermining. Cathodic delamination was observed on the zinc-only coatings, PVD0 and HDG, as well as PVD10 (although at a much slower rate). ZMA and PVD20, both MgZn2-containing systems, showed resistance to cathodic delamination and evidence of anodic undermining. Exploring several modern inhibitive pigments incorporated in the organic overcoat allowed the identification of a commercial pigment &#x201C;PAM&#x201D; to provide the greatest improvement in delamination resistance for the zinc-only metallic coatings.</abstract><type>E-Thesis</type><journal/><volume/><journalNumber/><paginationStart/><paginationEnd/><publisher/><placeOfPublication>Swansea</placeOfPublication><isbnPrint/><isbnElectronic/><issnPrint/><issnElectronic/><keywords>galvanising, physical vapour deposition, corrosion, electrochemistry, zinc, magnesium, SVET, SKP, delamination</keywords><publishedDay>12</publishedDay><publishedMonth>11</publishedMonth><publishedYear>2021</publishedYear><publishedDate>2021-11-12</publishedDate><doi>10.23889/SUthesis.58629</doi><url/><notes>A selection of third party content is redacted or is partially redacted from this thesis due to copyright restrictions.ORCiD identifier https://orcid.org/0000-0003-1183-2649</notes><college>COLLEGE NANME</college><CollegeCode>COLLEGE CODE</CollegeCode><institution>Swansea University</institution><supervisor>Williams, G. ; Sullivan, J.</supervisor><degreelevel>Doctoral</degreelevel><degreename>EngD</degreename><degreesponsorsfunders>Tata Steel, Engineering and Physical Sciences Research Council (EPSRC), European Social Fund, Coated2; Grant number: EGR0630-100</degreesponsorsfunders><apcterm/><lastEdited>2021-11-12T13:07:08.3065264</lastEdited><Created>2021-11-12T12:30:55.8446049</Created><path><level id="1">Faculty of Science and Engineering</level><level id="2">School of Engineering and Applied Sciences - Uncategorised</level></path><authors><author><firstname>REBECCA</firstname><surname>BOLTON</surname><order>1</order></author></authors><documents><document><filename>58629__21505__775e379dd4664a1da6c907e8cbdcb472.pdf</filename><originalFilename>Bolton_Rebecca_EngD_Thesis_Final_Redacted.pdf</originalFilename><uploaded>2021-11-12T13:00:50.7775913</uploaded><type>Output</type><contentLength>6103830</contentLength><contentType>application/pdf</contentType><version>Redacted version - open access</version><cronfaStatus>true</cronfaStatus><documentNotes>Copyright: The author, Rebecca Shuriea Bolton, 2021.</documentNotes><copyrightCorrect>true</copyrightCorrect><language>eng</language></document></documents><OutputDurs/></rfc1807>
spelling 2021-11-12T13:07:08.3065264 v2 58629 2021-11-12 Improved organic coating delamination resistance using physical vapour deposited Zn-Mg layers on strip steel 4fa58e0865c744fd4ef71d86394c7f7d REBECCA BOLTON REBECCA BOLTON true false 2021-11-12 Physical vapour deposition (PVD) of zinc alloy coatings was investigated as a potential substitute process for commercially available hot dip galvanising (HDG) of strip steel. Therefore, zinc alloy coatings deposited by PVD were systematically compared with traditional sacrificial HDG zinc alloy coatings, in terms of bare metal corrosion resistance and resistance to corrosion-driven delamination of an organic overcoat, to establish the effects of magnesium content, microstructure and surface treatment. The effectiveness of modern corrosion inhibitor pigments, of known volume fraction, on HDG and PVD zinc coatings was also explored. All PVD coatings and commercially available HDG coatings were characterised using microscopy techniques and x-ray diffraction to identify the microstructure and phases present as a function of magnesium content. It was confirmed that the PVD coatings were significantly thinner than the HDG coatings. The pure zinc PVD coating was comprised of hexagonal microplates, whereas the HDG counterpart contained grains 5-10 time larger. The PVD coating containing 4 wt% magnesium exhibited a discrete structure, a binary system of zinc-rich and Mg2Zn11-rich phases, much finer than the HDG Zn-Mg-Al (ZMA) coating. The PVD coatings containing 10 wt% and 20 wt% magnesium were studied using transmission electron microscopy as they possessed nanostructures containing Mg2Zn11 and MgZn2 phases respectively. Open circuit potential (OCP) measurements in chloride-containing solution established that an increase in magnesium content in PVD coating resulted in a decrease in the initial immersion open circuit potential. Additionally, increased magnesium content in the PVD layers also correlated with an increase in corrosion resistance, as made evident by reduced Ecorr and Icorr values during potentiodynamic studies. Electrochemical impedance spectroscopy (EIS) comparative studies suggested an improvement in corrosion resistance exhibited by PVD0 compared to HDG, both zinc-only coatings, attributed to the finer and more compact surface morphology. Bare metal corrosion response for all coatings was studied using a novel augmentation of the scanning vibrating electrode technique (SVET), known as SVET-TLI (time-lapse imaging). The combination of electrochemical mapping and photographic imagery revealed a potential optimum magnesium content within the PVD coatings. PVD4 exhibited the lowest anodic current density over a 24 hour study compared to the HDG, ZMA and other PVD coatings. Furthermore, the characteristic black staining attributed to magnesium corrosion was observed on the magnesium-containing PVD coatings. However, on the PVD Zn-Mg coatings the staining was observed in the regions established as net cathodes, which is contrary to association of staining with magnesium dissolution which takes place in local anodes. Using the scanning vibrating kelvin probe (SKP) method, PVD4 was identified as the optimum magnesium composition as it was found to be resistant of both corrosion-driven cathodic delamination and anodic undermining. Cathodic delamination was observed on the zinc-only coatings, PVD0 and HDG, as well as PVD10 (although at a much slower rate). ZMA and PVD20, both MgZn2-containing systems, showed resistance to cathodic delamination and evidence of anodic undermining. Exploring several modern inhibitive pigments incorporated in the organic overcoat allowed the identification of a commercial pigment “PAM” to provide the greatest improvement in delamination resistance for the zinc-only metallic coatings. E-Thesis Swansea galvanising, physical vapour deposition, corrosion, electrochemistry, zinc, magnesium, SVET, SKP, delamination 12 11 2021 2021-11-12 10.23889/SUthesis.58629 A selection of third party content is redacted or is partially redacted from this thesis due to copyright restrictions.ORCiD identifier https://orcid.org/0000-0003-1183-2649 COLLEGE NANME COLLEGE CODE Swansea University Williams, G. ; Sullivan, J. Doctoral EngD Tata Steel, Engineering and Physical Sciences Research Council (EPSRC), European Social Fund, Coated2; Grant number: EGR0630-100 2021-11-12T13:07:08.3065264 2021-11-12T12:30:55.8446049 Faculty of Science and Engineering School of Engineering and Applied Sciences - Uncategorised REBECCA BOLTON 1 58629__21505__775e379dd4664a1da6c907e8cbdcb472.pdf Bolton_Rebecca_EngD_Thesis_Final_Redacted.pdf 2021-11-12T13:00:50.7775913 Output 6103830 application/pdf Redacted version - open access true Copyright: The author, Rebecca Shuriea Bolton, 2021. true eng
title Improved organic coating delamination resistance using physical vapour deposited Zn-Mg layers on strip steel
spellingShingle Improved organic coating delamination resistance using physical vapour deposited Zn-Mg layers on strip steel
REBECCA BOLTON
title_short Improved organic coating delamination resistance using physical vapour deposited Zn-Mg layers on strip steel
title_full Improved organic coating delamination resistance using physical vapour deposited Zn-Mg layers on strip steel
title_fullStr Improved organic coating delamination resistance using physical vapour deposited Zn-Mg layers on strip steel
title_full_unstemmed Improved organic coating delamination resistance using physical vapour deposited Zn-Mg layers on strip steel
title_sort Improved organic coating delamination resistance using physical vapour deposited Zn-Mg layers on strip steel
author_id_str_mv 4fa58e0865c744fd4ef71d86394c7f7d
author_id_fullname_str_mv 4fa58e0865c744fd4ef71d86394c7f7d_***_REBECCA BOLTON
author REBECCA BOLTON
author2 REBECCA BOLTON
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publishDate 2021
institution Swansea University
doi_str_mv 10.23889/SUthesis.58629
college_str Faculty of Science and Engineering
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hierarchy_top_id facultyofscienceandengineering
hierarchy_top_title Faculty of Science and Engineering
hierarchy_parent_id facultyofscienceandengineering
hierarchy_parent_title Faculty of Science and Engineering
department_str School of Engineering and Applied Sciences - Uncategorised{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Engineering and Applied Sciences - Uncategorised
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description Physical vapour deposition (PVD) of zinc alloy coatings was investigated as a potential substitute process for commercially available hot dip galvanising (HDG) of strip steel. Therefore, zinc alloy coatings deposited by PVD were systematically compared with traditional sacrificial HDG zinc alloy coatings, in terms of bare metal corrosion resistance and resistance to corrosion-driven delamination of an organic overcoat, to establish the effects of magnesium content, microstructure and surface treatment. The effectiveness of modern corrosion inhibitor pigments, of known volume fraction, on HDG and PVD zinc coatings was also explored. All PVD coatings and commercially available HDG coatings were characterised using microscopy techniques and x-ray diffraction to identify the microstructure and phases present as a function of magnesium content. It was confirmed that the PVD coatings were significantly thinner than the HDG coatings. The pure zinc PVD coating was comprised of hexagonal microplates, whereas the HDG counterpart contained grains 5-10 time larger. The PVD coating containing 4 wt% magnesium exhibited a discrete structure, a binary system of zinc-rich and Mg2Zn11-rich phases, much finer than the HDG Zn-Mg-Al (ZMA) coating. The PVD coatings containing 10 wt% and 20 wt% magnesium were studied using transmission electron microscopy as they possessed nanostructures containing Mg2Zn11 and MgZn2 phases respectively. Open circuit potential (OCP) measurements in chloride-containing solution established that an increase in magnesium content in PVD coating resulted in a decrease in the initial immersion open circuit potential. Additionally, increased magnesium content in the PVD layers also correlated with an increase in corrosion resistance, as made evident by reduced Ecorr and Icorr values during potentiodynamic studies. Electrochemical impedance spectroscopy (EIS) comparative studies suggested an improvement in corrosion resistance exhibited by PVD0 compared to HDG, both zinc-only coatings, attributed to the finer and more compact surface morphology. Bare metal corrosion response for all coatings was studied using a novel augmentation of the scanning vibrating electrode technique (SVET), known as SVET-TLI (time-lapse imaging). The combination of electrochemical mapping and photographic imagery revealed a potential optimum magnesium content within the PVD coatings. PVD4 exhibited the lowest anodic current density over a 24 hour study compared to the HDG, ZMA and other PVD coatings. Furthermore, the characteristic black staining attributed to magnesium corrosion was observed on the magnesium-containing PVD coatings. However, on the PVD Zn-Mg coatings the staining was observed in the regions established as net cathodes, which is contrary to association of staining with magnesium dissolution which takes place in local anodes. Using the scanning vibrating kelvin probe (SKP) method, PVD4 was identified as the optimum magnesium composition as it was found to be resistant of both corrosion-driven cathodic delamination and anodic undermining. Cathodic delamination was observed on the zinc-only coatings, PVD0 and HDG, as well as PVD10 (although at a much slower rate). ZMA and PVD20, both MgZn2-containing systems, showed resistance to cathodic delamination and evidence of anodic undermining. Exploring several modern inhibitive pigments incorporated in the organic overcoat allowed the identification of a commercial pigment “PAM” to provide the greatest improvement in delamination resistance for the zinc-only metallic coatings.
published_date 2021-11-12T04:15:18Z
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score 11.014358

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