Abstract
Cerium-based conversion coatings were deposited on as-cast aluminum alloy 380 substrates by a spontaneous immersion process. In this study, the effects of rinsing temperature prior to immersion in the coating deposition solution were studied with respect to the surface morphology, electrochemical response, and corrosion resistance of the coatings. Panels rinsed at25°Cprior to coating had large cracks and holes in the coating. In contrast, panels rinsed at100°Cprior to coating had a uniform coating morphology with fewer, smaller cracks. Electrochemical testing revealed that coatings deposited on substrates rinsed at100°Chad higher impedance (~80 kΩ·cm2) and lower corrosion current (~0.34 μA/cm2) compared to coatings deposited on substrates rinsed at25°C, which had 10 kΩ·cm2impedance and 2.7 μA/cm2corrosion current. Finally, ASTM B117 salt spray testing showed that rinsing at100°Cprior to coating resulted in cerium-based conversion coatings that could resist the formation of salt tails for at least 8 days.
Highlights
Aluminum cast alloys are widely used in the automotive and aerospace industries where innovative, lightweight materials and product forms are needed to improve performance [1]
Analysis of surface morphology (Figures 1(a) and 1(b)) and chemistry of the substrate after pretreatment revealed that intermetallic particles containing Fe and Si were dissolved by the alkaline or acid pretreatments
No discernible differences in surface morphology were observed for panels that had been rinsed with water at room temperature or 100◦C
Summary
Aluminum cast alloys are widely used in the automotive and aerospace industries where innovative, lightweight materials and product forms are needed to improve performance [1]. Common aluminum casting alloys contain alloying additives that affect the mechanical properties, fluidity, and corrosion resistance [2]. Chromate conversion coatings are used for corrosion protection for a wide variety of aluminum alloy components [4]. Environmentally benign alternatives to chromates have been extensively investigated [8]. Potential replacements for chromate conversion coatings include anodized coatings [9], rare-earth-based inhibitors in conversion coatings [10], and sol-gel coatings [11]. Hinton et al were the first to investigate cerium-based conversion coatings (CeCCs) as an environmentally benign alternative to chromate conversion coatings [12, 13]
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