The use of multiple electrochemical techniques to characterize Mg-rich primers for Al alloys

Bierwagen, Gordon P.; Battocchi, Dante; Simões, A.M.; Stamness, Anthony; Tallman, Dennis E.

doi:10.1016/j.porgcoat.2007.01.022

Cited by 84 publications

(71 citation statements)

References 23 publications

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“…120,122 The oxides/hydroxides of the active metal particles (with an approximate size of 30-40 µm 122 ) could also serve to provide long-term protection to the underlying metal substrate as reported by Bierwangen et al Indeed, the Mg-rich primer system was reported to provide protection after a 3000 h Prohesion exposure and up to 6000 h under ASTM B117 salt spray testing when a top coat was applied. 120 However, the "self-corrosion" of active metal particles within the primer itself has proven to be a major drawback of metal-rich primer systems. The high solubility of some of the Zn or Mg salts could also result in high osmotic pressure within the primer, causing blistering of such coatings.…”

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confidence: 83%

“…116,118,119 In the case of Zn rich primers, the cathodic protection range is estimated to be at or below~−0.78 V SCE for steel. 120,121 On the other hand, in the case of Mg-rich primers, the corrosion potential of the underlying metal (such as an Al alloy~−0.64 V SCE in 3% NaCl) could also be maintained well below its pitting potential during contact with Mg-rich particles in the primer (~−0.93 V SCE in 3%NaCl). 120,122 The oxides/hydroxides of the active metal particles (with an approximate size of 30-40 µm 122 ) could also serve to provide long-term protection to the underlying metal substrate as reported by Bierwangen et al Indeed, the Mg-rich primer system was reported to provide protection after a 3000 h Prohesion exposure and up to 6000 h under ASTM B117 salt spray testing when a top coat was applied.…”

mentioning

confidence: 99%

“…As reported by Bierwangen et al, only Mg-rich coated AA2024-T3 showing OCPs <−0.90 V SCE showed cathodic protection and the requirement for sacrificial protection is for the metal rich coating to be more electrochemically active than the substrate. 120 …”

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confidence: 99%

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Chromate replacement: what does the future hold?

Gharbi

Thomas

Smith³

et al. 2018

npj Mater Degrad

175

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The ubiquitous use of chromium and its derivatives as corrosion preventative compounds accelerated rapidly after the second industrial revolution, with such compounds now integral to modern society. However, the detrimental impact of chromium compounds on the environment and human health has prompted the need to revisit the majority of current industrial corrosion protection measures. This review retraces the origins of chromium replacement motivations, introducing the various legislative actions aimed at diminishing the use of chromium compounds, and critically reviews alternative corrosion preventative technologies developed in the recent decades to now. The review, herein, is intended for a broad audience in order to provide a concise update to an increasingly timely issue.

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confidence: 83%

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confidence: 99%

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Chromate replacement: what does the future hold?

Gharbi

Thomas

Smith³

et al. 2018

npj Mater Degrad

175

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“…The second is a trivalent chromium based pretreatment (TCP) SurTec 650, supplied by SurTec. This coating is a fluozirconate-based conversion coating with an enrichment in Cr 3+ compounds such as Cr 2 O 3 and Cr(OH) 3 and a dry film thickness of 0.4 μm. The third pretreatment is anodization with hexavalent chromium sealing (ACS) with a dry film thickness of 8.9 μm.…”

Section: Methodsmentioning

confidence: 99%

Performance of a Magnesium-Rich Primer on Pretreated AA2024-T351 in Full Immersion: a Galvanic Throwing Power Investigation Using a Scanning Vibrating Electrode Technique

Kannan

Glover

McMurray

et al. 2018

J. Electrochem. Soc.

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The scanning vibrating electrode technique (SVET) was employed to examine the effect of 'galvanic throwing power' and the distance over which a Mg-rich primer (MgRP) provided sacrificial anode-based cathodic protection to AA2024-T351. Three systems were investigated in full immersion conditions where the same MgRP was used with three different pretreatments: Non-film forming (NFF), trivalent chromium pretreatment (TCP) and anodization with a chromate seal (ACS). Experiments were conducted with two coating/defect area ratios and three parameters were monitored: 1) the maximum peak height of local anodes, inferring the location and intensity of pits, 2) the current density profile at the coating/defect interface (CDI) region and 3) total integrated anodic and cathodic current density values of defined areas in the defect region moving progressively away from the CDI. The NFF-based system was shown to provide the superior galvanic throwing power and a quasi-steady-state galvanic current distribution was detected in the defect region adjacent to the CDI indicating enhanced cathodic activity in response to the MgRP. High resistance between the MgRP and the substrate, due to the thickness of the pretreatment layer, appeared to mediate galvanic interactions in the case of TCP and ACS-based systems.

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“…OCP and potentiodynamic polarization plots provide an idea of the extent of the cathodic protection versus time during service. An OCP below ~−0.9 V (SCE) for Al 2024 T provides an indication of the cathodic protection provided by Mg-rich primers [45]. Figure 4 provides a visual summary of the cathodic protection offered by Mg-rich primer to Al alloy AA2024 T3.…”

Section: Open Circuit Potential and Potentiodynamic Dynamic Polarizatmentioning

confidence: 99%

Magnesium-Based Sacrificial Anode Cathodic Protection Coatings (Mg-Rich Primers) for Aluminum Alloys

Pathak

Mendon

Blanton

et al. 2012

Metals

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Abstract:Magnesium is electrochemically the most active metal employed in common structural alloys of iron and aluminum. Mg is widely used as a sacrificial anode to provide cathodic protection of underground and undersea metallic structures, ships, submarines, bridges, decks, aircraft and ground transportation systems. Following the same principle of utilizing Mg characteristics in engineering advantages in a decade-long successful R&D effort, Mg powder is now employed in organic coatings (termed as Mg-rich primers) as a sacrificial anode pigment to protect aerospace grade aluminum alloys against corrosion. Mg-rich primers have performed very well on aluminum alloys when compared against the current chromate standard, but the carcinogenic chromate-based coatings/pretreatments are being widely used by the Department of Defense (DoD) to protect its infrastructure and fleets against corrosion damage. Factors such as reactivity of Mg particles in the coating matrix during exposure to aggressive corrosion environments, interaction of atmospheric gases with Mg particles and the impact of Mg dissolution, increases in pH and hydrogen gas liberation at coating-metal interface, and primer adhesion need to be considered for further development of Mg-rich primer technology.

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The use of multiple electrochemical techniques to characterize Mg-rich primers for Al alloys

Cited by 84 publications

References 23 publications

Chromate replacement: what does the future hold?

Chromate replacement: what does the future hold?

Performance of a Magnesium-Rich Primer on Pretreated AA2024-T351 in Full Immersion: a Galvanic Throwing Power Investigation Using a Scanning Vibrating Electrode Technique

Magnesium-Based Sacrificial Anode Cathodic Protection Coatings (Mg-Rich Primers) for Aluminum Alloys

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