Method for manufacturing joined body

A method for manufacturing a joined body, in which a first metal member and a second metal member are joined together by friction stirring,

• wherein the first metal member is made of a first aluminum alloy, and the second metal member is made of a second aluminum alloy, the first aluminum alloy having a higher hardness than the second aluminum alloy, and
• wherein a rotary tool used in the friction stirring has a stirring pin,
• the method comprising the steps of:
• a butting process to form a butted portion by butting a side face of the first metal member and a side face of the second metal member, and
• a primary joining process to perform friction stirring to the butted portion by moving the stirring pin of the rotary tool at a predetermined depth along a set moving track that is set on an inner side relative to the side face of the second metal member in a state that the stirring pin of the rotary tool being rotated is inserted into the second metal member and that an outer circumferential face of the stirring pin is slightly in contact with the first metal member,
• wherein in the primary joining process, an ending position is set on the first metal member at an outer side relative to the set moving track, and a leaving section is provided, in which after friction stir welding is performed to the butted portion, the rotary tool is moved toward the ending position and is made to leave the first metal member at the ending position,
• wherein in the primary joining process, the friction stirring is performed to the butted portion while the stirring pin is rotated at a predetermined rotational speed, and
• wherein the rotary tool is made to leave the first metal member in the leaving section when the rotary tool is moved to the ending position while gradually decreasing a rotational speed of the stirring pin from the predetermined rotational speed.