A method for manufacturing a liquid-cooling jacket, in which a jacket body provided with a bottom portion and a peripheral wall portion rising from a peripheral edge of the bottom portion, and a sealing body to seal an opening portion of the jacket body are friction stir welded,
- wherein the jacket body is made of a material harder than the sealing body,
- wherein a rotary tool used for friction stirring is provided with a shoulder portion and a stirring pin hanging down from a center of a bottom face of the shoulder portion, and
- wherein an outer circumferential face of the stirring pin is inclined to have a smaller diameter with increasing distance toward a tip thereof,
- the method comprising:
- a preparation process in which a peripheral wall stepped portion having a step bottom face and a step side face is formed along an inner peripheral edge of the peripheral wall portion, the step side face obliquely rising from the step bottom face toward the opening portion to spread, and the sealing body is formed to have a thickness larger than a height dimension of the step side face of the peripheral wall stepped portion;
- a placing process in which by placing the sealing body on the jacket body, a first butted portion is formed to have a gap between the step side face of the peripheral wall stepped portion and an outer peripheral side face of the sealing body, and a second butted portion is formed so that the step bottom face overlaps with a back face of the sealing body;
- a primary joining process in which a coarse portion is formed in the vicinity of the step side face with a plasticized region, formed at a moving trace of the rotary tool, in a length direction of the plasticized region while the rotary tool is being moved one round along the first butted portion to perform friction stirring in a state that the tip of the stirring pin of the rotary tool being rotated is inserted to the same depth as or deeper than the step bottom face and the bottom face of the shoulder portion is in contact with the sealing body and the stirring pin is in contact with at least an upper portion of the jacket body, wherein the coarse portion is a region in which a plastically fluidized material has not been sufficiently stirred and a density of the plastically fluidized material is coarser than other regions of the plasticized region, and the coarse portion and a width of 100 μm or more and 400 μm or less;
- and
- an inspection process in which a passed position of the stirring pin is specified by performing, after the primary joining process, a flaw detection using an ultrasonic flaw detection device to detect the coarse portion.