• Yoon, Yuhchae
• Buchheit, Rudolph

Abstract

The dissolution rate and Cu surface enrichment of sputter-deposited Al_2CuMg thin films exposed to 0.5 M NaCl solutions and chromate conversion coating solutions has been characterized. Dissolution rates were measured using an electrochemical quartz crystal microbalance, and Cu surface enrichment was characterized by energy-dispersive spectroscopy (EDS). Surface morphology and Volta potential were characterized by scanning probe microscopy. In 0.5 M NaCl solutions, Al_2CuMg dissolves rapidly by dealloying, forming a passivating Cu-rich surface layer. Upon layer breakdown a dissolution rate of about 0.08 µg/cm2 s was observed. In chromate conversion coating baths, Al_2CuMg demonstrated a net mass loss rate, which included mass loss from dissolution and mass gain from film formation. Cu surface enrichment was not detected after conversion coating. By comparison, pure Al thin films exhibited a net mass gain under similar conditions. Al_2CuMg samples that were first chromate conversion coated and then exposed to 0.5 M NaCl solution exhibited low dissolution rates, 0.001 µg/cm2 s, suggesting that the film formed in the conversion bath was somewhat protective. EDS showed that Cu enrichment occurred on conversion-coated Al_2CuMg during exposure to 0.5 M NaCl, indicating that conversion coatings on Al_2CuMg cannot completely suppress Cu surface enrichment, Cu redistribution, and deposition corrosion phenomena.

Topics

• Deposition
• surface
• corrosion
• phase
• thin film
• forming
• Energy-dispersive X-ray spectroscopy
• scanning probe microscopy