Embodiments of the present invention provide a magnetic disk drive with an enclosure that prevents the low-density gas from leaking out owing to reduction of shrinkage cavities near tapped holes. According to one embodiment of the present invention, an aluminum alloy is forced into the region of the base in which the tapped hole is to be made, by squeezing in the final stage of die casting to form the base. This procedure increases the density of aluminum alloy above 2.7 g/cm3, and the densified aluminum alloy in the region for tapped holes, is free of shrinkage cavities that can cause gas leakage.