Influence of the Anodizing Time on the Microstructure and Immersion Stability of Tartaric-Sulfuric Acid Anodized Aluminum Alloys

Abstract

Tartaric-sulfuric acid anodizing (TSA) has been selected by the aerospace industry to replace Cr(VI)-based anodizing treatments of aluminum alloys. Modification of the bath composition can result in the necessity to revise the process conditions, including the time necessary to obtain the desired properties of the anodized layer. This study focuses on the microstructure and immersion stability of the pilot scale anodized AA2024 aluminum alloy, with anodizing times of 25 min and 45 min. The layer structure was characterized by scanning electron microscopy (SEM) and glow discharge optical emission spectrometry (GD-OES). The electrochemical impedance spectroscopy (EIS) was used to evaluate the corrosion resistance and immersion stability of the samples in 0.01 M NaCl solution. The density of pores formed in the 45 min anodized samples was higher which correlated with higher impedance modulus at equivalent immersion time and higher thickness of the oxide layer. Contact angle measurements demonstrated better wettability of the 45 min anodized sample. The results suggest that 45 min anodizing offers higher corrosion resistance and better initial adhesion with subsequent post-treatment such as sealing or painting.

Innovative Applications of Cerium Oxide-Based Materials in Civil Engineering, Automation, and Energy Sectors

“…The topology of the anodic aluminum oxide (AAO) layers depends on various factors during layer formation, including: (i) nature and concentration of the contact electrolyte [143]; (ii) applied current density or formation voltage [128,144]; (iii) composition of the to-be-anodized aluminum alloy [145][146][147][148][149] and its structure [150]; (iv) temperature [151]; (v) duration [55,152]; (vi) presence of additives [153], including Ce(IV) species [154], and of course, (vii) preliminary surface treatment [155][156][157]. Additionally, it should be mentioned that anodization at rather high voltages alters the process mechanism, converting it to plasma electrolytic oxidation (PEO).…”

Incorporation of Anions into Anodic Alumina—A New Track in Cr(VI) Anodizing Substitution?

“…On the one hand, the immersion tests indicated better corrosion performance of samples anodized at 7 V. On the other hand, neutral salt spray testing and electrochemical impedance spectroscopy indicated better corrosion performance of the oxide coatings grown at 14 V [ 16 ]. Interesting results were delivered by Raffin et al [ 18 ]. They anodized AA 2024 T3 and AA 7075 T6/AA 7175 T6 in 40 g/L H 2 SO 4 + 80 g/L C 4 H 4 O 6 at 14 V for 25 or 45 min [ 18 ].…”

Abrasive Wear Resistance and Tribological Characteristics of Pulsed Hard Anodized Layers on Aluminum Alloy 1011 in Tribocontact with Steel and Ceramics in Various Lubricants

“…The magnitudes and durations of voltage changes between electrodes and pulses with high and low current densities in the process of PHAL synthesis are shown in Figure 1. To select anodizing modes, the results of other studies were analyzed and taken into account [57,58]. 51] and slow (at the frequency of their change < 0.1 Hz) [38,43,[52][53][54].…”

“…The magnitudes and durations of voltage changes between electrodes and pulses with high and low current densities in the process of PHAL synthesis are shown in Figure 1. To select anodizing modes, the results of other studies were analyzed and taken into account [57,58]. The electrolyte temperature in the synthesis process of PHAL was maintained with an accuracy of ±1 °С at the levels of −5, 0, +5, and +10 °С.…”