Friction welding of 6061 aluminum alloy was carried out in order to examine the relationship between deformation heat input in the upset stage, upset burn-off length and joint performance. The joint performance was evaluated by tensile testing and fatigue testing. Stabilized tensile strength was obtained when the deformation heat input in the upset stage and the upset burn-off length exceeded 200 J/s and 4 mm, respectively. Weld condition at the weld interface and the width of softened area affected fatigue strength more than tensile strength. On the other hand, when the weld condition at the weld interface is good and the softened area is narrow, and when the weld condition at the weld interface is somewhat poor in spite of the wide softened area, fatigue strength decreases. The fatigue limit obtained by the fatigue testing reveals that, when the deformation heat input in the upset stage and the upset burn-off length exceed a certain value, sound joints can be produced.
Friction welding is used in many fields because the procedure is relatively simple and it is possible to weld dissimilar materials. However, there are still unresolved issues in this method, such as the difficulty in setting the appropriate welding conditions for some materials, and the variance of optimum welding conditions between friction welding machines. Recently, the authors began research to examine the evaluation of joint strength by analyzing heat input. In friction welding of 5056 aluminum alloy, the authors previously examined the relationship between joint strength and heat input (friction heat input, deformation heat input and total heat input, in the friction stage, the upset stage and the total stage), and revealed that the joint strength could be evaluated by the deformation heat input in the upset stage (Ochi, Sawai, Yamamoto, Ogawa, Tsujino and Suga, 2000).