Abstract: 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.

Abstract: A resistance spot welded joint of an aluminum material is obtained by joining a stack of a plurality of aluminum materials by spot welding. A nugget formed by the spot welding includes a solidified part of the aluminum materials and a shell having a different solidification structure from the solidified part. The shell is formed annularly in a cross-section of the nugget in a stacking direction of the aluminum materials. The solidified part and the shell are alternately arranged from an outer edge of the nugget toward a nugget central part.

Abstract: A resistance welder controller is disclosed, which controls a resistance welder for welding workpieces clamped between two electrodes with Joule heat generated by passing a welding current between the electrodes. The controller includes a preliminary current passing device for passing preliminary current between the electrodes until the workpieces and the electrodes become intimate with one another, a regular current passing device for passing regular current between the electrodes for welding the workpieces, a current control device for controlling the welding current according to the rate of expansion of the workpieces or the rate of increase of the resistance of the workpieces, and a current passing ending device for ending the welding current at or after an instant when the rate of expansion of the workpieces or the rate of increase of the resistance of the workpieces has become substantially zero.