Characterization of non‐Cr‐based deoxidizers on Al alloy 7475‐T7651

Abstract

Al alloy 7475-T7651 were investigated. Several analytical methods were employed, including SEM, AES, transmission electron microscopy (TEM), electron energy-loss spectroscopy (EELS) and glow discharge optical emission spectrometry (GDOES), to study the effects on the surface of this alloy after each treatment compared with the as-received and alkaline-cleaned alloy surfaces. The untreated alloy was found to have a thick oxide of 200-320 nm, consisting mainly of MgO. Alkaline cleaning results in an etching effect that thins the oxide and also deposits a thin silicate layer on the surface. In the case of the deoxidizers, there is significant removal of the native oxide of the alloy by the NaBrO 3 /HNO 3 deoxidizer. There is also evidence of intermetallic attack on the alloy. The (NH 4 ) 4 Ce(SO 4 ) 4 /H 2 SO 4 deoxidizer, which is a low-etch-rate deoxidizer, resulted in a slight thinning of the oxide. However, the effect was not significantly greater than with alkaline cleaning alone. The most effective deoxidizer in reducing the oxide thickness of the alloy is Fe(III)/HF/HNO 3 , in which the etch rate was sufficiently high to remove completely the native oxide. In this case, equilibrium between oxide removal and the formation of new oxides on the alloy surface was achieved.

Influence of the alloy microstructure and surface state on the protective properties of trivalent chromium coatings grown on a 2024 aluminium alloy

“…The scalloped surface is characteristic of a severe chemical attack of the aluminium matrix. In the literature, such a significant dissolution operates in acidic desmutting bath, as shown by Toh et al [18]. In this study, this severe chemical attack in the degreasing bath was consistent with the pH of the degreasing solution (pH = 9) and the relative in stability of aluminium oxide at this pH.…”

“…the nature of the IMCs present on the surface before the pre-treatrnents and the evolution of their distribution due to their reactivity in the pre-treatrnent baths. Considering that (i) the IMC dissolution can lead to copper redistribu tion (ii) incomplete dissolution of the IMC can leave significant loca lized quantities of copper [16,18,41] and (iii) copper can have a sig nificant impact on the conversion process [42--44], the arnount of electroactive copper remaining on the surface was a major pararneter considering the surface properties; it was determined by CV experi ments for al! the samples.…”

“…They attributed the decrease of the anticorrosion proper ties to the roughness generated by the desmutting process, and more precisely, to the nucleation and growth of pits with increasing depth over the time of desmutting in Turco Liquid Smut-Go NC. Toh et al have studied different desmutting solutions on aluminium alloy 7475-T7651; they have shown important differences in the morphology and oxide roughness at the alloy surface [18]. Others works have shown a huge influence of the substrate microstructure on the surface reactivity during the pre-treatments and as a consequence on the anti-corrosion properties of the coatings [19][20][21][22].…”

Modificaciones de la microestructura y la capa pasiva de la aleación 2024-T3 Al-Cu durante una limpieza química empleada en la industria aeroespacial

“…5(b) muestran que el contenido en cobre es constante antes y después del decapado ácido con Smut Go. Este resultado discrepa con el notable aumento de cobre observado por diversos autores (Toh et al, 2004;Viroulaud et al, 2017) que fue atribuido a la disolución de cobre tanto de las fases Al(Cu, Mg) como de la matriz y su posterior redeposición en la superficie del metal.…”

Coatings for corrosion prevention based on rare earths

“…97 The objective of these cleaning processes is to render the surface in a reproducible state after processing, regardless of the source of material, and there are standard processes for chromate conversion coating or anodizing of aerospace alloys. 6,182,183 The process steps remove surface grease and oils, surface oxides and surface intermetallic particles. In particular they aim to produce a surface with the minimal amount of Cu, although Cu build-up is inevitable even for low-Cu containing alloys.…”