{"title":"Electrochemical Evaluation of Al-5 wt% Zn Metal Rich Primer for Protection of Al-Zn-Mg-Cu Alloy in NaCl","authors":"A. Korjenic, L. Blohm, A. Druschitz, J. R. Scully","doi":"10.5006/4424","DOIUrl":null,"url":null,"abstract":"\n An intact and X-scribed Al-5wt%Zn rich primer (AlRP) without pretreatment or topcoat was evaluated for its ability to suppress potential dependent intergranular corrosion (IGC) and intergranular stress corrosion cracking (IGC-SCC) of peak aged AA7075A-T651 in NaCl salt fog and full immersion. The ability of the primer to provide sacrificial anode-based cathodic prevention of peak aged AA7075-T651 substrate was evaluated both under the primer coating and at scratches. The AlRP evaluated consisted of an epoxy-based resin embedded with spherical Al-5wt%Zn pigment particles. Performance was evaluated under full immersion in 0.6 M NaCl solution and compared to ASTM B-117 salt spray exposure using two approaches. These consisted of the University of Virginia (UVa) cycle test on intact coatings and the full immersion galvanic couple testing on simulated scratched panels created when intact coatings form bimetal couples with bare AA7075-T651. Focus was placed on the ability of the AlRP to achieve a targeted intermediate galvanic couple potential near a “prevention” potential which suppresses stress corrosion crack growth, intermetallic particle corrosion as well as intergranular corrosion. The long term (24-hour) open circuit potential (OCP) of AlRP coated AA7075-T651 in 0.6 M NaCl indicated that the AlRP provided less than 100mV of cathodic potential shift of the intact coating from its OCP. Electrochemical cycle testing conducted at −0.95 VSCE demonstrates that the AlRP did not enable sacrificial anode-based cathodic protection as the coupled potential remained at the corrosion potential of bare AA7075-T651. Furthermore, the current observed throughout galvanic corrosion experiments coupling of AlRP:AA7075-T651 indicated the AlRP coating was a cathode in the bimetal galvanic couple. ASTM B117 salt spray exposure of the AlRP revealed oxidation of the AA 7075-T651 substrate below the primer detected as a continually growing oxygen signal at the primer-substrate interface that did not arrest corrosion over the exposure period.","PeriodicalId":10717,"journal":{"name":"Corrosion","volume":null,"pages":null},"PeriodicalIF":1.1000,"publicationDate":"2024-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Corrosion","FirstCategoryId":"88","ListUrlMain":"https://doi.org/10.5006/4424","RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"MATERIALS SCIENCE, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
Abstract
An intact and X-scribed Al-5wt%Zn rich primer (AlRP) without pretreatment or topcoat was evaluated for its ability to suppress potential dependent intergranular corrosion (IGC) and intergranular stress corrosion cracking (IGC-SCC) of peak aged AA7075A-T651 in NaCl salt fog and full immersion. The ability of the primer to provide sacrificial anode-based cathodic prevention of peak aged AA7075-T651 substrate was evaluated both under the primer coating and at scratches. The AlRP evaluated consisted of an epoxy-based resin embedded with spherical Al-5wt%Zn pigment particles. Performance was evaluated under full immersion in 0.6 M NaCl solution and compared to ASTM B-117 salt spray exposure using two approaches. These consisted of the University of Virginia (UVa) cycle test on intact coatings and the full immersion galvanic couple testing on simulated scratched panels created when intact coatings form bimetal couples with bare AA7075-T651. Focus was placed on the ability of the AlRP to achieve a targeted intermediate galvanic couple potential near a “prevention” potential which suppresses stress corrosion crack growth, intermetallic particle corrosion as well as intergranular corrosion. The long term (24-hour) open circuit potential (OCP) of AlRP coated AA7075-T651 in 0.6 M NaCl indicated that the AlRP provided less than 100mV of cathodic potential shift of the intact coating from its OCP. Electrochemical cycle testing conducted at −0.95 VSCE demonstrates that the AlRP did not enable sacrificial anode-based cathodic protection as the coupled potential remained at the corrosion potential of bare AA7075-T651. Furthermore, the current observed throughout galvanic corrosion experiments coupling of AlRP:AA7075-T651 indicated the AlRP coating was a cathode in the bimetal galvanic couple. ASTM B117 salt spray exposure of the AlRP revealed oxidation of the AA 7075-T651 substrate below the primer detected as a continually growing oxygen signal at the primer-substrate interface that did not arrest corrosion over the exposure period.
期刊介绍:
CORROSION is the premier research journal featuring peer-reviewed technical articles from the world’s top researchers and provides a permanent record of progress in the science and technology of corrosion prevention and control. The scope of the journal includes the latest developments in areas of corrosion metallurgy, mechanisms, predictors, cracking (sulfide stress, stress corrosion, hydrogen-induced), passivation, and CO2 corrosion.
70+ years and over 7,100 peer-reviewed articles with advances in corrosion science and engineering have been published in CORROSION. The journal publishes seven article types – original articles, invited critical reviews, technical notes, corrosion communications fast-tracked for rapid publication, special research topic issues, research letters of yearly annual conference student poster sessions, and scientific investigations of field corrosion processes. CORROSION, the Journal of Science and Engineering, serves as an important communication platform for academics, researchers, technical libraries, and universities.
Articles considered for CORROSION should have significant permanent value and should accomplish at least one of the following objectives:
• Contribute awareness of corrosion phenomena,
• Advance understanding of fundamental process, and/or
• Further the knowledge of techniques and practices used to reduce corrosion.