Joining method and structure of metal members

A joining method of metal members, in which a first metal member and a second metal member, which have different coefficient of thermal expansion from one another, are overlapped and joined, the joining method comprising:

• a first step of forming a plurality of first joint portions, the first joint portions being formed by a frictional joining at a plurality of frictional joint areas of the overlapped first and second metal members, the frictional joining comprising pressing of a rotating tool under rotation against the first metal member for generating a frictional heat, softening of the first metal member with the frictional heat generated for making a plastic flow state at the first metal member, and joining of the overlapped first and second metal members in a solid state;
• and
• a second step of forming a second joint portion, the second joint portion being formed by a mechanical joining at a joint area of the overlapped first and second metal members that is located between said frictional joint areas.

A joining structure of metal members, in which a first metal member and a second metal member, which have different coefficient of thermal expansion from one another, are overlapped and joined, the joining structure comprising:

• a plurality of first joint portions, the first joint portions being formed by a frictional joining at a frictional joint area of the overlapped first and second metal members, the frictional joining comprising pressing of a rotating tool under rotation against the first metal member for generating a frictional heat, softening of the first metal member with the frictional heat generated for making a plastic flow state at the first metal member, and joining of the overlapped first and second metal members in a solid state;
• and
• a second joint portion, the second joint portion being formed by a mechanical joining at a joint area of the overlapped first and second metal members that is located at an end portion of said frictional joint area.

A joining structure of metal members, in which a first metal member and a second metal member, which have different coefficient of thermal expansion from one another, are overlapped and joined, the joining structure comprising:

• a plurality of first joint portions, the first joint portions being formed by a frictional joining at a plurality of frictional joint areas of the overlapped first and second metal members, the frictional joining comprising pressing of a rotating tool under rotation against the first metal member for generating a frictional heat, softening of the first metal member with the frictional heat generated for making a plastic flow state at the first metal member, and joining of the overlapped first and second metal members in a solid state;
• and
• a second joint portion, the second joint portion being formed by a mechanical joining at a joint area of the overlapped first and second metal members that is located between said frictional joint areas.