MACRO/MICRO MECHANICAL LEVEL CHARACTERIZATION OF SPOT FRICTION WELDED LAP JOINTS IN 6111 ALUMINUM ALLOY USING COMBINED EXPERIMENTAL/NUMERICAL APPROACHES

摘要

Modal vibration testing and static flexure testing at the macromechanical level combined with numerical finite element (FE) models have been used to indirectly determine the elastic moduli of 6111 aluminum alloy base metal and spot friction welded (SFW) joints which have been formed at different processing times. It was observed that the frequency (and the corresponding apparent stiffness) of the joint oscillates at low amplitudes as processing time increases. For each vibration mode, the amplitude of the oscillation in the frequency vs. processing time is only a few percent of the mean frequency with 99% confidence level, while the corresponding lap shear strength increases monotonically by a factor of about 8 as the processing time increases. Due to the scatter in the damping data it is difficult to detect any significant trends. Comparison of predicted modal frequencies and static load-displacement response of SFW joints at the macromechanical level with the corresponding measured responses seems to indicate that the weld zone is not as stiff as the base metal, but more detailed micromechanical analysis is required before definite conclusions can be drawn. In addition, studies of microstructural characteristics and Vickers microhardness distributions across the weld zone for the SFW samples reveals the formation of a partial metallurgical bond in the direction of flow, which is governed by the tool used, whereas the hardness distribution in the weld zone depends on the processing time.