Corrosion protection of Al5086 and sensitized Al5086 using a titanate based conversion coating

Chromate conversion coatings have been widely used in the materials industry, particularly on aluminum, to provide corrosion protection. Due to their toxicity and harmful environmental effects, replacement coatings have been sought. An alternative process to chromate conversion coatings using the titanate ion was developed and tested on 5086-H32 aluminum alloy and sensitized 5086-H32 aluminum alloy. Electrochemical impedance spectroscopy (EIS) was employed to quantify the performance of the coating, while scanning electron microscopy (SEM) along with energy X-ray dispersive spectroscopy (EDS) were used to examine the surface and surface composition of the samples. Auger electron spectroscopy (AES) was used to determine the coating composition as a function of depth. The titanate conversion coating provided good corrosion protection on 5086-H32 samples, based on impedance data. SEM micrographs revealed light and dark areas on the surface on the coating, while AES determined that the light area was predominantly magnesium and the dark area mostly aluminum oxide. For sensitized samples, the titanate coating provided increased corrosion protection on samples sensitized at or below 100°C for less than two weeks. Samples with a higher degree of sensitization exhibited a greater increase in pitting failure and did not exhibit adequate corrosion protection