Anodic Coating Characteristics of Different Aluminum Alloys for Spacecraft Materials Applications

Abstract

Anodic oxide coatings on aluminum alloys are used for space environment applications. These provide specific thermo-optical properties to spacecraft surface. Fragments of these coatings lead to generate the contamination in satellites and affect the mission lifetime. The current work concerns studying of the anodic processes applied on aluminum and different groups of aluminum alloys as Al7075, Al2024 and Al6061. Experimental procedures are performed using sulfuric acid at different values of current density (1 -2 A/dm 2 ). The influence of the parameters of anodic film formation on the coating characteristics and layer thickness of aluminum alloys has been investigated. Reflectance and optical properties of the anodized aluminum alloy coatings are determined and found to be dependent on the alloying elements. Changes in anodic coating weight and film thickness of aluminium alloys with the process parameters as current density, temperature, time duration, acid concentration, and sealing system have been studied. Moreover, morphology and surface structure of the considered samples are carried out in attempt to understand the physical characteristics. The obtained results are compared and briefly outlined.

Citric Acid as an Alternative to Sulfuric Acid for the Hard-Anodizing of AA6061

“…The low magnitude orders indicate that Type III hard anodizing can be carried out with citric acid solutions as the main component and effectively provide corrosion protection better than the substrate without anodizing treatment. This type of behavior has also been found in 7075 aluminum alloys anodized with other systems and is mainly attributed to the barrier effect generated by anodizing [64].…”

Plasma Electrolytic Oxidation Coatings on Aluminum Alloys: Microstructures, Properties, and Applications

“…According to studies conducted by El-Hameed et.al, a reduction in oxide film thickness (weight loss) was observed during the sealing process [45] (Table 2). i = current density, v =cell voltage, t = duration of anodizing, T = temperature of electrolyte, NA = not known To prevent reduction of the film thickness and reduce hygroscopicity, the porous oxide layer could be impregnated with organic or inorganic dyes before sealing, and this could also serve as a way of coloring the anodized piece [30,41,45]. There are several researches works on anodic oxidation of aluminum and aluminum alloys, some examples of recent research work are shown in Table 2.…”

“…Generally, the oxide coatings formed via AO process is porous in nature with only a few micrometers in thickness and has limited elasticity and high hygroscopicity which exhibits some improvement in the corrosion and wear resistance [41][42][43][44][45][46]. For aerospace applications that requires high level of corrosion protection, sealing is required after anodizing in order to reduce surface cracking and block penetration of corrosive species [33,42].…”

“…for about 15 to 30 min or in hot nickel sulphate solution (5-10g/L, ~90°C) for about 20 to 30 min, hot nickel acetate (5g/L, 90°C) for 30 min, and cold nickel acetate (5 g/L, 25°C) for 30 min [33,[42][43][44][45].…”

“…The effect of hot water, hot nickel acetate and cold nickel acetate sealing on corrosion performance of anodized aluminum coupons and foils was investigated by Hu et al [42], it was found that hot nickel acetate showed the best corrosion performance as shown in becomes hydrated to form aluminum mono-hydroxide or boehmite (equation 6) which fills the pores and seals the surface in order to prevent environmental attack and reduces corrosion [33,43,45].…”