Tuesday, 3 October 2017
Prince George's Exhibit Hall D/E (Gaylord National Resort and Convention Center)
Three AA6063T5 alloy samples were investigated: as received, trimmed and polished mechanically and chemically treated. The mechanical treatment was performed using sandpaper SiC of sizes 320 to 4000 and the chemical was performed using an aqueous solution containing a mixture of hydroxide, sulfate and sodium chloride. All samples were physically characterized by X-ray diffractometry (XRD), hardness measurements, scanning electron microscopy (SEM) and optical microscopy (OM), and by open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. The SEM images showed that the presence of intermetallic particles on the alloy surface decreases after the chemical treatment compared to the mechanical treatment. The EIS results showed that the chemical treatment offers higher resistance to corrosion than those submitted to the other treatments, because the alkaline attack used dissolved most precipitates containing Fe or Cu, elements responsible for cathodic sites. Washing with HNO3 through which the chemically treated sample passed probably reinforced the oxide layer, making the surface of the alloy more resistant to attack by chloride.