Microstructure Evolution in the Near-Surface Region During Homogenization of a Twin-Roll Cast AlFeMnSi Alloy

The corrosion behaviour of silanated AA2198‐T851 alloy substrates with and with no manufacturing‐process induced near‐surface deformed layer (MPI‐NSDL) has been investigated. Two methods (alkaline etching + desmutting and mechanical polishing) were employed in removing the MPI‐NSDL. Silanization was performed using 2‐bis‐triethoxysilylethane. Electrochemical impedance spectroscopy (EIS), salt spray test, and microscopy techniques were employed in the investigation of the corrosion behaviours. The studies revealed that polishing appeared to be the best silanating pre‐treatment (compared with degreasing and etching + desmutting) for the new generation AA2198‐T851 Al‐Cu‐Li alloy, and this was reflected in the EIS spectra. The etched + desmutted and the degreased surface with MPI‐NSDL did not respond well to silanization and presented more pitting sites per square millimeter. However, the severity of corrosion per pit was more on the polished sample compared with the other two. Also, the corrosion mechanisms were different for the three cases.

Section: Introductionsupporting

confidence: 57%

Section: Introductionmentioning

confidence: 99%

The effect of surface pretreatment on the corrosion behaviour of silanated AA2198‐T851 Al‐Cu‐Li alloy

Donatus

Klumpp

Mogili

et al. 2018

“…Given that SLC sites are associated with more HE compared with other corrosion sites on the surfaces of Al alloys, the polished surface generated most intense sites of evolution hydrogen compared with the as‐received surface of the alloy. The as‐received surface of a rolled Al alloy is characterized by the presence of the NSDL that was induced by the rolling process during the production of the alloy . This NSDL, in the case of the investigated alloy, is composed of Mg‐rich bands (as typified by the results in Figure ) and an oxide layer that is far thicker than the one present on a polished surface of the alloy.…”

Section: Resultsmentioning

confidence: 92%

The local electrochemical behavior of the AA2098‐T351 and surface preparation effects investigated by scanning electrochemical microscopy

Silva

Milagre

Oliveira

et al. 2019

In this work, scanning electrochemical microscopy (SECM) measurements were employed to characterize the electrochemical activities on polished and as-received surfaces of the 2098-T351 aluminum alloy (AA2098-T351). The effects of the near surface deformed layer (NSDL) and its removal by polishing on the electrochemical activities of the alloy surface were evaluated and compared by the use of different modes of SECM. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) were also employed to characterize the morphology of the surfaces. The surface chemistry was analyzed by X-ray photoelectron spectroscopy (XPS). The surface generation/tip collection (SG/TC) and competition modes of the SECM were used to study hydrogen gas (H 2 ) evolution and oxygen reduction reactions, respectively. H 2 evolution and oxygen reduction were more pronounced on the polished surfaces. The feedback mode of SECM was adopted to characterize the electrochemical activity of the polished surface that was previously corroded by immersion in a chloride-containing solution, in order to investigate the influence of the products formed on the active/passive domains. The precorroded surface and as-received surfaces revealed lower electrochemical activities compared with the polished surface showing that either the NSDL or corrosion products largely decreased the local electrochemical activities at the AA2098-T351 surfaces. KEYWORDS aluminum alloy, localized corrosion, SECM, surface finishing condition 1 | INTRODUCTION Aluminum alloys are commonly used in automotive and aerospace applications because of their good mechanical properties and low density.There is an increase in the demand for materials that exhibit a combination of high specific strength and corrosion resistance for industrial applications. 1,2 In order to meet this demand, new generation aluminum-lithium (Al-Li) alloys with properties superior to those of the conventionally used Al alloys are being developed for use as structural components in aircraft. [3][4][5] The AA2098 Al-Cu-Li alloy was developed as a substitute for AA2024 and AA2219. The AA2098 alloy presents low density, high mechanical resistance, high toughness, high-temperature resistance, weldability, and good response to natural aging. These properties are achieved by a carefully tailoring its chemical composition, whose main alloying elements are Cu, Li, Mg, Ag, and Zr. The addition of lithium improves the mechanical properties of the Al alloy in that for every 1 wt% of Li added to aluminum, the density of the alloy is reduced by 3%, and the Young's modulus is increased by almost 6%. 5-7 However, this element increases the susceptibility of the alloy to localized

“…Severe localized corrosion in Al‐Cu‐Li alloys has been associated with hexagonal T1 phase (Al 2 CuLi), which is preferentially located in regions of high dislocation density 3–14 . This leads to severe localized corrosion 13,15,16 . According to literature, 17,18 T1 phase is initially anodic relatively to the matrix, but due to the high reactivity of lithium, its selective dissolution from T1 phase leads to its copper enrichment, polarity reversal, and, in turn, the dissolution of the surrounding matrix 16 .…”

Section: Introductionmentioning

confidence: 99%

Corrosion protection of the AA2198‐T8 alloy by environmentally friendly organic‐inorganic sol‐gel coating based on bis‐1,2‐(triethoxysilyl) ethane

Klumpp

Donatus

Silva

et al. 2020

In this work, a surface coating composed of organic‐inorganic hybrid sol‐gel based on bis‐1,2‐(triethoxysilyl) (BTSE) ethane was applied on AA2198‐T8 samples, and its effect on corrosion resistance was investigated and compared with that of a chromate layer formed in a solution with hexavalent chromium ions. The corrosion resistance of BTSE coated samples was evaluated by immersion tests in sodium chloride solution (0.005 mol/L NaCl) and monitored by global electrochemical techniques such as electrochemical impedance spectroscopy (EIS) and local electrochemical techniques such as scanning vibrating electrode technique (SVET) and scanning electrochemical microscopy (SECM). The formed coating layers were characterized by X‐ray photoelectron spectroscopy (XPS). The results pointed out that the BTSE is an effective alternative coating for corrosion protection of new generation Al‐Cu‐Li alloys and could replace chromates obtained in toxic and carcinogenic CrVI containing solutions leading to improved corrosion protection.