Various factors such as film porosity, stress, type of underlayer, and the presence of an overcoat were found to affect the corrosion resistance of CoCr and CoCrTa thin-film magnetic disks exposed to high-humidity, corrosive environments. It was found that corrosion products form preferentially along the polishing and texture lines of the NiP substrate. Relieving internal stresses in the disk layers using a low-temperature annealing process improved the corrosion resistance of these Co alloy films. Additionally, eliminating the carbon overcoat allowed the formation of an oxide layer which was more protective in chlorine-containing environments.