Mechanical characterization of spot friction stir welded joints in aluminum alloys by combined experimental/numerical approaches: Part II: Macromechanical studies

This is part II of a two part paper summarizing material characteristics of Spot Friction Stir Welded (SFW) lap joints in aluminum alloy 6111 at the macromechanical and micromechanical levels. In this paper, modal vibration testing and static flexure testing at the macromechanical level combined with numerical finite element models have been used to indirectly determine the elastic moduli of the base metal and weld zone. It was observed that the modal frequencies (and the corresponding apparent stiffness) of the joint oscillate at low amplitudes with increasing processing time. For each vibration mode, the amplitude of the oscillation in the frequency vs. processing time is only a few percent of the mean frequency, while the corresponding lap shear strength increases monotonically by a factor of about 8 as the processing time increases. Comparison of predicted modal frequencies and static load–displacement response of SFW joints with the corresponding measured responses seem to indicate that the weld zone is not as stiff as the base metal. Parametric studies to determine the effect of weld zone measurements on the modal frequencies have been carried out using finite element models.