Patent ID: 8740042

Claim:
A method of friction-welding to join a first member and a second member together, the first member being made of an aluminum alloy material and having a uniform cross-section portion in a cylindrical shape with a pipe-wall thickness “t” ranging from 2 to 5 mm and a length equal to or more than (6 mm+t/2), and the second member being made of an aluminum alloy material and having a uniform cross-section portion in a cylindrical shape with the same cross-section as the first member and a length equal to or more than (6 mm+t/2), the method of friction-welding comprising the steps of: (a) a friction process of butting the uniform cross-section portion of the first member with the uniform cross-section portion of the second member and applying a friction pressure to the first and the second members while the first and the second members are rotating relatively to each other, and (b) an upset process of applying an upset pressure greater than the friction pressure, wherein a friction upset length is set to be a length within t to 2×t, wherein the pressure between the first and the second members rises to the upset pressure within 0.5 seconds after the relative rotation starts to stop, and wherein a portion corresponding to each of the uniform cross-section portions of the first member and the second member has a length as long as or longer than 5 mm after the friction-welding is finished.