En'am Alsrayheen, PhD Candidate.

DEPARTMENT OF CHEMISTRY

CHEMISTRY 601/603

FINAL PhD PRESENTATION

SPEAKER:            Enam A. Alsrayheen, PhD Candidate.

DATE:                     Tuesday Dec 13, 2011.

TIME:                      3:00 pm.

PLACE:                  ST 147

TITLE:                    Characterization and Optimization of Oxide Films Formed on Al-Cu Alloys

ABSTRACT:           

The Al-Cu alloy AA2219 (~6.3 wt.% Cu) is of great interest for use in aerospace applications, primarily due its high strength to weight ratio. However, AA2219 suffers from poor corrosion resistance in chloride-containing solutions because of the presence of Al₂Cu intermetallics, which are cathodic to the Al-rich matrix. An AC/DC spark anodization method was used to deposit an oxide film on the Al–Cu alloy AA2219. The oxide films were formed in an alkaline silicate solution at constant current densities, showing three main stages of growth. The barrier Al oxide film growth occurring in Stage I, the onset of porous layer growth commencing in Stage II (arcing stage), and the deposition of a rough, thick, and porous Si-rich layer in Stage III (sparking stage).  While the current efficiency is the lowest in Stage III, this is when the most rapid rate of oxide film growth occurs and when the most corrosion resistance is imparted onto the alloy.  Under all of the anodizing conditions used in this work, the oxide film passivity in neutral solutions is at least 1000 times greater, and the corrosion resistance at least 100 times greater, than what is seen for bare AA2219. The oxide film thickness, porosity, and corrosion resistance have been improved by optimizing the applied current density, time of anodizing, AC/DC ratio, and anodizing solution composition. It was also discovered that SiO₂ nanoparticles can be easily infiltrated into the porous oxide film, also forming a thick silica over-layer, resulting in a dramatic improvement in the passivity and corrosion resistance of the oxide layer on AA2219.