Dante Battocchi

Use of Magnesium Alloys as Pigments in Magnesium-Rich Primers for Protecting Aluminum Alloys

Abstract As an alternative to toxic chromate coating, Mg-rich primers have been designed to protect Al alloys (in particular AA2024-T3 [UNSA92024]) and developed in analogy to Zn-rich primers for s...

Modeling of Electrochemical Impedance Data of a Magnesium-Rich Primer

The application of Mg-rich primers MRPs for the protection of aluminum structures represents an attractive alternate to the environmentally unfriendly Cr-rich primers that are presently used. The protective modes of MRPs are similar to those of Zn-rich primers ZRPs on steel and include cathodic protection driven by the more active Mg particles compared to the Al substrate and a barrier-type protection due to the insulation of the substrate from the environment. Interpretation of ZRP electrochemical impedance spectroscopy EIS data has been accomplished using a transmission-line model that accounted for the contact impedance between the zinc particles, the impedance associated with the zinc dissolution, and the percolation resistance of the coating. EIS experiments results are presented here for an MRP on a gold substrate under immersion in dilute Harrison’s solution. The data were analyzed using the measurement model technique to determine the consistency with respect to Kramer–Kronig relationships. The transmission-line model was used to analyze the data to demonstrate their applicability for analyzing the protection afforded by the MRP. Gold was used as a noble substrate and to promote that the electromotive degradation of the MRP as the mixed potential of an MPR/gold system was more positive than that of an MRP/Al system.

Real-Time Monitoring of a United States Air Force Topcoat/Mg-Rich Primer System in ASTM B117 Exposure by Embedded Electrodes

Abstract The protection of metallic structures by organic coatings has traditionally been as a barrier, reducing the transport of water, ions, and oxygen from the environment to the substrate. Orga...

Hydrogen Evolution and Early Blistering from Magnesium-Rich Primers on AA2024-T3

Early blistering was observed on topcoated magnesium-rich primers (MgRPs) over AA2024-T3 substrate under constant immersion or constant salt spray tests. Hydrogen evolution and the cause of early b...

Inhibitors for prolonging corrosion protection of Mg-rich primer on Al alloy 2024-T3

This research investigated the possibility of adding inhibitors into magnesium-rich primer (MgRP) to prolong the corrosion protection time of MgRP on Al alloy 2024-T3. Three inhibitors: sodium benzoate (SB), sodium dodecylbenzenesulfonate (SDBS), and 8-hydroxyquinoline (HQ), were tested and added into MgRPs separately. Potentiodynamic scans on pellet electrodes confirmed that the inhibitors reduced Mg corrosion rate. The coating systems with and without inhibitors were compared through electrochemical tests, hydrogen volume measurement, accelerated weathering tests, and adhesion tests. It was observed that the addition of SB, SDBS, and HQ into MgRPs could prolong cathodic protection time and improved barrier properties of MgRPs, without compromising adhesion strength.

The Use of AC-DC-AC Methods in Assessing Corrosion Resistance Performance of Coating Systems for Magnesium Alloys

The potential utility of AC-DC-AC electrochemical methods in comparative measures of corrosion-resisting coating system performance for magnesium alloys under consideration for the USAMP “Magnesium Front End Research and Development” project was previously shown in this forum [1]. Additional studies of this approach using statistically-designed experiments have been conducted with focus on alloy types, pretreatment, topcoat material and topcoat thickness as the variables. Additionally, sample coupons made for these designed experiments were also subjected to a typical automotive cyclic corrosion test cycle (SAE J2334) as well as ASTM B117 for comparison of relative performance. Results of these studies are presented along with advantages and limitations of the proposed methodology.

Characterization of Coatings on Steel Self-Piercing Rivets for Use with Magnesium Alloys

Incorporation of magnesium alloys in self-pierce rivet (SPR) joints poses several unique challenges among which are the creation of spurious galvanic cells and aggravated corrosion of adjacent magnesium when coated steel rivets are employed. This work firstly reviews efforts on development of coatings to steel fasteners for the diminution of galvanic corrosion when used with magnesium alloys. Secondly, approaches, based on several electrochemical methods, for the measurement of the galvanic-limiting effect of a number of commercially-available coatings to hardened 10B37 steel self-piercing rivets inserted into alloy couples incorporating several grades of magnesium are reported. Electrochemical impedance spectroscopy (EIS), zero-resistance ammeter (ZRA), corrosion potential and potential-mapping visualization methods (e.g. scanning vibrating electrode technique — SVET) are illustrated for the several rivet coatings considered.

Embedded Reference Electrode for Potential-Monitoring of Cathodic Protective Systems

Micron-scale silver (Ag) wires were chemically oxidized in 0.05M FeCl3 solution to form Ag/AgCl reference electrodes. The wire electrodes were embedded between a topcoat and metal-rich primer-a sacrificial coating-to monitor the corrosion protection by its open circuit potential (OCP). A metal-rich system equipped with an embedded reference electrode (ERE) would allow in-situ measurement of the OCP; this indicates the level of protection afforded by the coating to the substrate and aims to eliminate the standard, less-accurate practice of scheduled maintenance. Measurement of the metal-rich primer/substrate OCP versus the ERE, and also versus a saturated calomel electrode (SCE), were the key experimental techniques to verify the concepts validity. Also, potentiodynamic experiments were utilized to mimic imposed-potential cathodic protection systems; the potential versus ERE, recorded with an additional potentiostat, responded favorably. This study shows the feasibility of a Ag/AgCl ERE for use in cathodic protective systems by effectively relaying OCP information. Further experiments using electrochemical impedance spectroscopy (EIS) and in-situ OCP measurements in a salt spray chamber strengthen this conclusion. This methodology allows the possibility of upgrading the monitoring and control systems currently used for imposed cathodic protection as well as the in-situ observation of corrosion protection levels for metal-rich sacrificial coatings.