Abstract: An example thin substrate built-in hard disk drive includes a magnetic disk in a disk shape having a through-hole at the center, a spindle motor inserted into the through-hole of the magnetic disk and co-rotatably supporting the magnetic disk, and a base plate made of an aluminum alloy and supporting the spindle motor. The base plate has a metallographic structure in which a perimeter of a second phase particle having a longest diameter of 10 ?m or more is 3 mm/mm2 or more, and the number of second phase particles having a longest diameter of 500 ?m or more is 0 particles/mm2.

Abstract: A balance adjustment method for a rotor includes an imbalance acquisition step of acquiring imbalance position and amount of the rotor after a first balance correction step of correcting balance of the rotor by cutting a compressor wheel side, an excision target section determination step of determining, based on the imbalance position and amount of the rotor, an excision target range including an imbalance correction position of the turbine wheel and a removal amount in the excision target range, and a second balance correction step of correcting the balance of the rotor by repeatedly irradiating the excision target range determined in the excision target section determination step with laser light from a laser marker device to remove by the removal amount from the turbine wheel.

Abstract: A balance adjustment method for a rotor includes an imbalance acquisition step of acquiring imbalance position and amount of the rotor after a first balance correction step of correcting balance of the rotor by cutting a compressor wheel side, an excision target section determination step of determining, based on the imbalance position and amount of the rotor, an excision target range including an imbalance correction position of the turbine wheel and a removal amount in the excision target range, and a second balance correction step of correcting the balance of the rotor by repeatedly irradiating the excision target range determined in the excision target section determination step with laser light from a laser marker device to remove by the removal amount from the turbine wheel.