Critical for the use of aluminum alloys for engine pistons are strength and durability behind customers demand high power and low fuel consumption to protect environment. In general, there are many case of generating cracks in a top part of the piston by thermal load of combustion during car driving. As a countermeasure, AC8A casting aluminum on a top part of the piston partially substitutes with A6061 wrought aluminum which is more strengthen than the ACS A. This paper deals with the joint characteristics of friction welded joint between the A6061 solid cylinder and the AC8A casting pipe. If the joint was made by a conventional friction welding machine, it was clarified that the friction welding of A6061 solid cylinder and ACS A casting pipe was difficult because the travelling phenomenon of the weld interface was cause by the combination of the shapes of the friction welding specimens. To prevent braking deformation until rotation stop, the joint was made by a continuous drive friction welding machine that has an electromagnetic clutch. In addition, the joining strength improved through the joining cross section of both specimens are the same shape of pipe by digging out the surface of the A6061 cylinder. As a result, the joining could be successfully achieved and that had the joint efficiency of 80 - 97% when the joint was made with a friction pressure of 25MPa, a friction time of 0.7s, and a forge pressure of 75MPa and post-weld heat treatment with the T6 of AC8A.
