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Development of Zn-Al-Mg Alloys for Galvanising Applications / DANIEL BRITTON

Swansea University Author: DANIEL BRITTON

  • E-Thesis under embargo until: 28th April 2030

DOI (Published version): 10.23889/SUThesis.69817

Abstract

The use of Zn-Al-Mg coatings as an alternative to traditional zinc galvanising gives the benefitof increased corrosion protection and post-coating manufacturing improvements. However,samples taken from TATA Steel’s galvanising line in Llanwern, South Wales, show that thecomplex Zn-Al-Mg microstructu...

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Published: Swansea University, Wales, UK 2025
Institution: Swansea University
Degree level: Doctoral
Degree name: EngD
Supervisor: Penney, D., and Challinor, C.
URI: https://cronfa.swan.ac.uk/Record/cronfa69817
first_indexed 2025-06-26T10:09:52Z
last_indexed 2025-06-27T09:32:32Z
id cronfa69817
recordtype RisThesis
fullrecord <?xml version="1.0"?><rfc1807><datestamp>2025-06-26T11:49:37.0721238</datestamp><bib-version>v2</bib-version><id>69817</id><entry>2025-06-26</entry><title>Development of Zn-Al-Mg Alloys for Galvanising Applications</title><swanseaauthors><author><sid>bc2281a43b1971692a161d79925b68ee</sid><firstname>DANIEL</firstname><surname>BRITTON</surname><name>DANIEL BRITTON</name><active>true</active><ethesisStudent>false</ethesisStudent></author></swanseaauthors><date>2025-06-26</date><abstract>The use of Zn-Al-Mg coatings as an alternative to traditional zinc galvanising gives the benefitof increased corrosion protection and post-coating manufacturing improvements. However,samples taken from TATA Steel&#x2019;s galvanising line in Llanwern, South Wales, show that thecomplex Zn-Al-Mg microstructure and precise manufacturing process make consistent coatingsvery difficult to produce. The research presented here will analyse many of the parametersinvolved in galvanising, with the aim of gaining a better understanding of how they affectZn-Al-Mg coatings.The first research chapter of this thesis investigates the effect of varied coating weight on themicrostructure and subsequent electrochemical properties of Zn-Al-Mg coatings. The surfaceof lower coating weight samples (80 g&#xB7;m-2) displayed a much finer microstructure compared to thicker coatings (310 g&#xB7;m-2), with primary Zn dendrite size showing a decrease of 68 %. Surfacearea percentage of the dendrites was also a lot higher in the thinner coating weight, at 70.1 %compared to 50 %. Whilst these differences did not appear to influence the performance of cut-edge corrosion, surface scanning vibrating electrode technique testing showed a substantialincrease in metal loss in lower-weight samples over a 24-hour period. This was consistent withresults from linear polarisation resistance and open circuit potential tests, which indicated anincrease in both negative potential and corrosion rate, respectively.The effect of post-coating cooling rates on Zn-Al-Mg coatings was investigated in chapter 4.Faster cooling rates (ranging from 5 K&#xB7;s-1 to 35 K&#xB7;s-1) were shown to provide improvedcorrosion resistance due to a change in microstructure. Specifically, cooling at a slower rate(5 K&#xB7;s-1) resulted in an overall rise of eutectic phase at the sample surface compared to faster cooled samples (35 K&#xB7;s-1), from 60.89% to 76.97%, respectively. This exposed a greater number of MgZn2 intermetallics which were rapidly attacked by anodic dissolution upon exposure toNaCl solution during accelerated corrosion tests.The effect of varying Zn-Al-Mg composition is presented in chapter 5. Al and Mg additions toZn alloy coatings was investigated by systematically raising the wt.% of each element. Drasticchanges in microstructure were observed, with a 72 % reduction in primary Zn volume whenboth additions were raised from 1 wt.% to 3 wt.%. Similarly, eutectic phase increased from22 % to 94 % volume, resulting in substantial changes to electrochemical behaviour. The workshowed that increasing Al whilst keeping Mg at a lower level gave the best results, caused byan increased coating potential and decreased corrosion kinetics.Previous research has shown that microcracks can occur in Zn-Al-Mg coatings when strain isapplied, simulating the effect of body panel forming and bending. Whilst additions of Ge havebeen investigated recently as a way of increasing coating formability and solving this issue, Geis very expensive and not commercially viable for use in industry. As Sb additions have longbeen used in traditional zinc to increase bath fluidity, its use in Zn-Al-Mg coatings was testedin chapter 6. It was proposed that the additions would help to improve coating surface finish,thereby making Zn-Al-Mg coatings more formable and attractive for automotive customers.Use of microscopy and other unique characterisation techniques found additions of 0.45 and0.83 wt. % Sb caused a reduction in binary eutectic volume, decreasing from 13.8 % in standardZn-Al-Mg alloy, to 5.0 % and 4.4 % in these two novel Sb-addition alloys, respectively.Furthermore, an addition of 1.80 wt. % Sb was found to remove the binary eutectic completely.Hardness testing confirmed the hypothesis that removal of the binary eutectic leads to anincrease in formability, showing a reduction of 14 %. Extensive electrochemical testing showedfavourable corrosion protection properties. The formation of Mg3Sb2 intermetallics, which wereshown to be cathodic with respect to the matrix, resulted in a 43 % drop in corrosion rate for samples with additions of 1.8 wt. % Sb, despite a 15 mV increase in alloy potential. Both anodicand cathodic deactivation were shown to be responsible for the behaviour seen during corrosion.Finally, annex A details the challenges in commissioning and running Swansea University&#x2019;shot dip simulator, which was used for much of the research within this thesis. Several casestudies are included which detail the problems caused by zinc dust and complex pneumaticsystems, as well as research that couldn&#x2019;t be completed due to limitations of the simulator.Recommendations and adaptions the manufacturer could implement to improve the HDS arealso noted.A thorough account of all the research conducted in requirement of this Doctorate is thereforepresented here. It is the hope of the author that the results gained throughout this research canbe learned from, if not incorporated by industry in its attempt to continuously improve theperformance of their products and reduce their impact on the environment.</abstract><type>E-Thesis</type><journal/><volume/><journalNumber/><paginationStart/><paginationEnd/><publisher/><placeOfPublication>Swansea University, Wales, UK</placeOfPublication><isbnPrint/><isbnElectronic/><issnPrint/><issnElectronic/><keywords>Galvanising, Zn-Al-Mg coatings, Automotive</keywords><publishedDay>28</publishedDay><publishedMonth>4</publishedMonth><publishedYear>2025</publishedYear><publishedDate>2025-04-28</publishedDate><doi>10.23889/SUThesis.69817</doi><url/><notes>A selection of content is redacted or is partially redacted from this thesis to protect sensitive and personal information.</notes><college>COLLEGE NANME</college><CollegeCode>COLLEGE CODE</CollegeCode><institution>Swansea University</institution><supervisor>Penney, D., and Challinor, C.</supervisor><degreelevel>Doctoral</degreelevel><degreename>EngD</degreename><degreesponsorsfunders>TATA Steel, EPSRC</degreesponsorsfunders><apcterm/><funders>TATA Steel, EPSRC</funders><projectreference/><lastEdited>2025-06-26T11:49:37.0721238</lastEdited><Created>2025-06-26T10:54:08.4012534</Created><path><level id="1">Faculty of Science and Engineering</level><level id="2">School of Engineering and Applied Sciences - Materials Science and Engineering</level></path><authors><author><firstname>DANIEL</firstname><surname>BRITTON</surname><order>1</order></author></authors><documents><document><filename>Under embargo</filename><originalFilename>Under embargo</originalFilename><uploaded>2025-06-26T11:06:43.8199774</uploaded><type>Output</type><contentLength>16478005</contentLength><contentType>application/pdf</contentType><version>E-Thesis</version><cronfaStatus>true</cronfaStatus><embargoDate>2030-04-28T00:00:00.0000000</embargoDate><documentNotes>Copyright: The author, Daniel Alexander Britton, 2024</documentNotes><copyrightCorrect>true</copyrightCorrect><language>eng</language></document></documents><OutputDurs/></rfc1807>
spelling 2025-06-26T11:49:37.0721238 v2 69817 2025-06-26 Development of Zn-Al-Mg Alloys for Galvanising Applications bc2281a43b1971692a161d79925b68ee DANIEL BRITTON DANIEL BRITTON true false 2025-06-26 The use of Zn-Al-Mg coatings as an alternative to traditional zinc galvanising gives the benefitof increased corrosion protection and post-coating manufacturing improvements. However,samples taken from TATA Steel’s galvanising line in Llanwern, South Wales, show that thecomplex Zn-Al-Mg microstructure and precise manufacturing process make consistent coatingsvery difficult to produce. The research presented here will analyse many of the parametersinvolved in galvanising, with the aim of gaining a better understanding of how they affectZn-Al-Mg coatings.The first research chapter of this thesis investigates the effect of varied coating weight on themicrostructure and subsequent electrochemical properties of Zn-Al-Mg coatings. The surfaceof lower coating weight samples (80 g·m-2) displayed a much finer microstructure compared to thicker coatings (310 g·m-2), with primary Zn dendrite size showing a decrease of 68 %. Surfacearea percentage of the dendrites was also a lot higher in the thinner coating weight, at 70.1 %compared to 50 %. Whilst these differences did not appear to influence the performance of cut-edge corrosion, surface scanning vibrating electrode technique testing showed a substantialincrease in metal loss in lower-weight samples over a 24-hour period. This was consistent withresults from linear polarisation resistance and open circuit potential tests, which indicated anincrease in both negative potential and corrosion rate, respectively.The effect of post-coating cooling rates on Zn-Al-Mg coatings was investigated in chapter 4.Faster cooling rates (ranging from 5 K·s-1 to 35 K·s-1) were shown to provide improvedcorrosion resistance due to a change in microstructure. Specifically, cooling at a slower rate(5 K·s-1) resulted in an overall rise of eutectic phase at the sample surface compared to faster cooled samples (35 K·s-1), from 60.89% to 76.97%, respectively. This exposed a greater number of MgZn2 intermetallics which were rapidly attacked by anodic dissolution upon exposure toNaCl solution during accelerated corrosion tests.The effect of varying Zn-Al-Mg composition is presented in chapter 5. Al and Mg additions toZn alloy coatings was investigated by systematically raising the wt.% of each element. Drasticchanges in microstructure were observed, with a 72 % reduction in primary Zn volume whenboth additions were raised from 1 wt.% to 3 wt.%. Similarly, eutectic phase increased from22 % to 94 % volume, resulting in substantial changes to electrochemical behaviour. The workshowed that increasing Al whilst keeping Mg at a lower level gave the best results, caused byan increased coating potential and decreased corrosion kinetics.Previous research has shown that microcracks can occur in Zn-Al-Mg coatings when strain isapplied, simulating the effect of body panel forming and bending. Whilst additions of Ge havebeen investigated recently as a way of increasing coating formability and solving this issue, Geis very expensive and not commercially viable for use in industry. As Sb additions have longbeen used in traditional zinc to increase bath fluidity, its use in Zn-Al-Mg coatings was testedin chapter 6. It was proposed that the additions would help to improve coating surface finish,thereby making Zn-Al-Mg coatings more formable and attractive for automotive customers.Use of microscopy and other unique characterisation techniques found additions of 0.45 and0.83 wt. % Sb caused a reduction in binary eutectic volume, decreasing from 13.8 % in standardZn-Al-Mg alloy, to 5.0 % and 4.4 % in these two novel Sb-addition alloys, respectively.Furthermore, an addition of 1.80 wt. % Sb was found to remove the binary eutectic completely.Hardness testing confirmed the hypothesis that removal of the binary eutectic leads to anincrease in formability, showing a reduction of 14 %. Extensive electrochemical testing showedfavourable corrosion protection properties. The formation of Mg3Sb2 intermetallics, which wereshown to be cathodic with respect to the matrix, resulted in a 43 % drop in corrosion rate for samples with additions of 1.8 wt. % Sb, despite a 15 mV increase in alloy potential. Both anodicand cathodic deactivation were shown to be responsible for the behaviour seen during corrosion.Finally, annex A details the challenges in commissioning and running Swansea University’shot dip simulator, which was used for much of the research within this thesis. Several casestudies are included which detail the problems caused by zinc dust and complex pneumaticsystems, as well as research that couldn’t be completed due to limitations of the simulator.Recommendations and adaptions the manufacturer could implement to improve the HDS arealso noted.A thorough account of all the research conducted in requirement of this Doctorate is thereforepresented here. It is the hope of the author that the results gained throughout this research canbe learned from, if not incorporated by industry in its attempt to continuously improve theperformance of their products and reduce their impact on the environment. E-Thesis Swansea University, Wales, UK Galvanising, Zn-Al-Mg coatings, Automotive 28 4 2025 2025-04-28 10.23889/SUThesis.69817 A selection of content is redacted or is partially redacted from this thesis to protect sensitive and personal information. COLLEGE NANME COLLEGE CODE Swansea University Penney, D., and Challinor, C. Doctoral EngD TATA Steel, EPSRC TATA Steel, EPSRC 2025-06-26T11:49:37.0721238 2025-06-26T10:54:08.4012534 Faculty of Science and Engineering School of Engineering and Applied Sciences - Materials Science and Engineering DANIEL BRITTON 1 Under embargo Under embargo 2025-06-26T11:06:43.8199774 Output 16478005 application/pdf E-Thesis true 2030-04-28T00:00:00.0000000 Copyright: The author, Daniel Alexander Britton, 2024 true eng
title Development of Zn-Al-Mg Alloys for Galvanising Applications
spellingShingle Development of Zn-Al-Mg Alloys for Galvanising Applications
DANIEL BRITTON
title_short Development of Zn-Al-Mg Alloys for Galvanising Applications
title_full Development of Zn-Al-Mg Alloys for Galvanising Applications
title_fullStr Development of Zn-Al-Mg Alloys for Galvanising Applications
title_full_unstemmed Development of Zn-Al-Mg Alloys for Galvanising Applications
title_sort Development of Zn-Al-Mg Alloys for Galvanising Applications
author_id_str_mv bc2281a43b1971692a161d79925b68ee
author_id_fullname_str_mv bc2281a43b1971692a161d79925b68ee_***_DANIEL BRITTON
author DANIEL BRITTON
author2 DANIEL BRITTON
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institution Swansea University
doi_str_mv 10.23889/SUThesis.69817
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hierarchy_top_title Faculty of Science and Engineering
hierarchy_parent_id facultyofscienceandengineering
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department_str School of Engineering and Applied Sciences - Materials Science and Engineering{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Engineering and Applied Sciences - Materials Science and Engineering
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description The use of Zn-Al-Mg coatings as an alternative to traditional zinc galvanising gives the benefitof increased corrosion protection and post-coating manufacturing improvements. However,samples taken from TATA Steel’s galvanising line in Llanwern, South Wales, show that thecomplex Zn-Al-Mg microstructure and precise manufacturing process make consistent coatingsvery difficult to produce. The research presented here will analyse many of the parametersinvolved in galvanising, with the aim of gaining a better understanding of how they affectZn-Al-Mg coatings.The first research chapter of this thesis investigates the effect of varied coating weight on themicrostructure and subsequent electrochemical properties of Zn-Al-Mg coatings. The surfaceof lower coating weight samples (80 g·m-2) displayed a much finer microstructure compared to thicker coatings (310 g·m-2), with primary Zn dendrite size showing a decrease of 68 %. Surfacearea percentage of the dendrites was also a lot higher in the thinner coating weight, at 70.1 %compared to 50 %. Whilst these differences did not appear to influence the performance of cut-edge corrosion, surface scanning vibrating electrode technique testing showed a substantialincrease in metal loss in lower-weight samples over a 24-hour period. This was consistent withresults from linear polarisation resistance and open circuit potential tests, which indicated anincrease in both negative potential and corrosion rate, respectively.The effect of post-coating cooling rates on Zn-Al-Mg coatings was investigated in chapter 4.Faster cooling rates (ranging from 5 K·s-1 to 35 K·s-1) were shown to provide improvedcorrosion resistance due to a change in microstructure. Specifically, cooling at a slower rate(5 K·s-1) resulted in an overall rise of eutectic phase at the sample surface compared to faster cooled samples (35 K·s-1), from 60.89% to 76.97%, respectively. This exposed a greater number of MgZn2 intermetallics which were rapidly attacked by anodic dissolution upon exposure toNaCl solution during accelerated corrosion tests.The effect of varying Zn-Al-Mg composition is presented in chapter 5. Al and Mg additions toZn alloy coatings was investigated by systematically raising the wt.% of each element. Drasticchanges in microstructure were observed, with a 72 % reduction in primary Zn volume whenboth additions were raised from 1 wt.% to 3 wt.%. Similarly, eutectic phase increased from22 % to 94 % volume, resulting in substantial changes to electrochemical behaviour. The workshowed that increasing Al whilst keeping Mg at a lower level gave the best results, caused byan increased coating potential and decreased corrosion kinetics.Previous research has shown that microcracks can occur in Zn-Al-Mg coatings when strain isapplied, simulating the effect of body panel forming and bending. Whilst additions of Ge havebeen investigated recently as a way of increasing coating formability and solving this issue, Geis very expensive and not commercially viable for use in industry. As Sb additions have longbeen used in traditional zinc to increase bath fluidity, its use in Zn-Al-Mg coatings was testedin chapter 6. It was proposed that the additions would help to improve coating surface finish,thereby making Zn-Al-Mg coatings more formable and attractive for automotive customers.Use of microscopy and other unique characterisation techniques found additions of 0.45 and0.83 wt. % Sb caused a reduction in binary eutectic volume, decreasing from 13.8 % in standardZn-Al-Mg alloy, to 5.0 % and 4.4 % in these two novel Sb-addition alloys, respectively.Furthermore, an addition of 1.80 wt. % Sb was found to remove the binary eutectic completely.Hardness testing confirmed the hypothesis that removal of the binary eutectic leads to anincrease in formability, showing a reduction of 14 %. Extensive electrochemical testing showedfavourable corrosion protection properties. The formation of Mg3Sb2 intermetallics, which wereshown to be cathodic with respect to the matrix, resulted in a 43 % drop in corrosion rate for samples with additions of 1.8 wt. % Sb, despite a 15 mV increase in alloy potential. Both anodicand cathodic deactivation were shown to be responsible for the behaviour seen during corrosion.Finally, annex A details the challenges in commissioning and running Swansea University’shot dip simulator, which was used for much of the research within this thesis. Several casestudies are included which detail the problems caused by zinc dust and complex pneumaticsystems, as well as research that couldn’t be completed due to limitations of the simulator.Recommendations and adaptions the manufacturer could implement to improve the HDS arealso noted.A thorough account of all the research conducted in requirement of this Doctorate is thereforepresented here. It is the hope of the author that the results gained throughout this research canbe learned from, if not incorporated by industry in its attempt to continuously improve theperformance of their products and reduce their impact on the environment.
published_date 2025-04-28T05:27:57Z
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score 11.089572

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