Residual Stresses of Aluminum Alloy Blank Disk for Hard Disk Drive

Memory disks for a hard disk drives are required to achieve higher recording densities. To achieve this, there is a demand for thinner aluminum alloy blank disks. As the thickness of the blank disk becomes thinner, the stiffness of the blank disk decreases and its flatness deteriorates. To achieve excellent flatness, it is necessary to know the residual stress in the blank disk. For this reason, we developed a technique for measuring the residual stress in blank disks. In this study, we measured the diffraction spots of coarse grains using a double exposure method, completed the image processing procedure, and established a method for measuring the residual stress in the blank disks. When the residual stresses in the blank disks were measured using this method, it was found that the tensile residual stress was generated on the outside of the blank disk with press-annealing. This suggests that a slightly larger compressive force was applied to the outside of the blank disk under press-annealing. Furthermore, the residual stress was divided into compressive and tensile residual stresses on the front and back of the blank disks, respectively.