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Predicting Atmospheric Galvanic Corrosion Of Aluminum Alloy By Combining Electrochemical Techniques And Accelerated Laboratory Corrosion Tests

Predicting Atmospheric Galvanic Corrosion of Aluminum using Accelerated Laboratory Electrochemical Experiments
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Aluminum (Al) alloys are the most common non-ferrous metals used (approximately 25 million tons per year) and the second most commonly used metal alloy after steel1. Some of the properties of Al alloys that attribute to their worldwide use include lightness, thermal conductivity, electrical conductivity, suitability for surface treatments, and corrosion resistance. Al alloys are also combined with other metals/materials to achieve desired properties for specific applications. Al alloys can be joined to other materials with ease to enhance their combined properties with the following techniques: welding, bolting, riveting, clinching, adhesive bonding, and brazing1. 

Product Number: 51322-18163-SG
Author: Raghu Srinivasan, Toomas Kollo, Matt Cullin
Publication Date: 2022
Industry: Corrosion Monitoring and Control
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Aluminum (Al) alloys are the most commonly used non-ferrous metals (approximately 25 million tons per year) for various technical applications and the second most commonly used metal alloy after steel. Al alloys are also combined with other metals/materials to get specific desirable properties for particular applications. However, a system of dissimilar materials can lead to potential corrosion problems such as galvanic and/or crevice corrosion. In this work, atmospheric galvanic corrosion of aluminum (Al) alloy was predicted by combining electrochemical techniques and accelerated laboratory corrosion tests. Three different galvanic couples were analyzed where 6061-T6 Al alloy (UNS A96061) was coupled with a passivating metal (304 stainless steel or UNS S30400), noble metal (copper or UNS C11000) and a conductive polymer matrix composite (PMC) reinforced with carbon fiber. The galvanic current flowing between the anode and cathode was measured using the zero-resistance ammeter (ZRA) technique in the humidity-chamber setup. Electrolytes with varying amounts of chloride contents were used to imitate different atmospheric conditions. An equation based on Faraday’s law was developed to calculate the corrosion rate in grams per meter square per day (gmd) by relating the time of wetness (TOW) from the field exposure to the galvanic current measured from the accelerated laboratory experiments. The total exposure time was divided into wet periods (Twet) and dry periods (Tdry). Cyclic corrosion test chamber following a modified GM9540P cycle and outdoor exposure experiments are planned for the future.  

Aluminum (Al) alloys are the most commonly used non-ferrous metals (approximately 25 million tons per year) for various technical applications and the second most commonly used metal alloy after steel. Al alloys are also combined with other metals/materials to get specific desirable properties for particular applications. However, a system of dissimilar materials can lead to potential corrosion problems such as galvanic and/or crevice corrosion. In this work, atmospheric galvanic corrosion of aluminum (Al) alloy was predicted by combining electrochemical techniques and accelerated laboratory corrosion tests. Three different galvanic couples were analyzed where 6061-T6 Al alloy (UNS A96061) was coupled with a passivating metal (304 stainless steel or UNS S30400), noble metal (copper or UNS C11000) and a conductive polymer matrix composite (PMC) reinforced with carbon fiber. The galvanic current flowing between the anode and cathode was measured using the zero-resistance ammeter (ZRA) technique in the humidity-chamber setup. Electrolytes with varying amounts of chloride contents were used to imitate different atmospheric conditions. An equation based on Faraday’s law was developed to calculate the corrosion rate in grams per meter square per day (gmd) by relating the time of wetness (TOW) from the field exposure to the galvanic current measured from the accelerated laboratory experiments. The total exposure time was divided into wet periods (Twet) and dry periods (Tdry). Cyclic corrosion test chamber following a modified GM9540P cycle and outdoor exposure experiments are planned for the future.  

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Product Number: 51322-17536-SG
Author: Takahiro Osuki, Yuhei Suzuki, Shinnosuke Kurihara, Toshihide Ono, Masaki Ueyama
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Various austenitic stainless steels such as UNS S30409, S31609, S32109 and 34709 are widely used in complex refinery or chemical plants at temperature ranges between 550°C and 950°C. However, Stress Relaxation Cracking (SRC) in welded joints or cold deformed parts has been a serious problem during fabrication or operation. Several researches were conducted to construct SRC test methods. This included the evaluation of SRC susceptibilities among various austenitic stainless steels and to determine SRC mechanism within TNO Science and Industry or JIP1-4. It was concluded that SRC was caused by the accommodation of strain due to both carbide/nitride precipitation hardening inhibiting dislocation movement and the formation of precipitation free zone along the M23C6 carbide at grain boundary during stress relaxation process of welding residual stresses at temperatures between 550°C and 750°C.
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Product Number: 51322-17589-SG
Author: Luca Casanova, MariaPia Pedeferri, Gianluigi A. Botton, Marco Ormellese
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Refinement Of Citric Acid Passivation Methods And Comparison To Traditional Nitric Acid Based Chemistries

Product Number: 51322-17628-SG
Author: David G. Enos, Derek Wichhart
Publication Date: 2022
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Traditional solutions for the chemical passivation of stainless steel are nitric acid based, with the addition of sodium dichromate as an inhibitor for precipitation hardened and free machining stainless steels. These passivation chemistries are difficult to handle from an environmental health and safety point of view, particularly the dichromate inhibited versions. Citric acid passivation has been pursued as a replacement for both nitric acid and inhibited nitric acid based chemistries for many years, and has been incorporated into consensus specifications such as ASTM A967 and SAE AMS2700.
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