A concentric electrode is provided. The concentric electrode includes a cylindrical base and a tip disposed on the cylindrical base. The cylindrical base extends axially along an axis of rotation, and the cylindrical base includes a conductive metal. The tip includes a concentric surface extending axially from the cylindrical base and defined by an outer shoulder having an outside diameter and an inner shoulder having an inside diameter. The tip is configured to provide an electrical current to a steel workpiece and purge a coating from at least a portion of the steel workpiece.

A plurality of aluminum materials overlapped with each other are sandwiched between electrodes for spot welding. After main energization to form a nugget between the aluminum materials sandwiched between the electrodes, pulsation energization in which energization and stop of the energization are repeated a plurality of times is performed. A current value in the pulsation energization is set to be greater than a current value of the main energization, the energization and stop of the energization are repeated at least three times in the pulsation energization, and an energization stop period is increased from a first half of the pulsation energization to a second half of the pulsation energization.

A welding method and a welding apparatus using the same control heat emission amounts of interfaces of a welding subject to be similar by adjusting cross-sectional areas of two welding tips arranged on both outer facing surfaces of a panel type welding subject, superimposed in multi-layers, to simultaneously form a nugget diameter.