Microstructure and mechanical properties of dissimilar friction stir welds of AA2014 and AA7075

This work investigates the effect of process parameters on microstructure, mechanical properties, and fracture behavior of friction stir welded high-strength aluminum alloys AA2014-T6 and AA7075-T6. Optical micrograph, tensile property, and hardness profile of each weld were determined for analysis, and the tensile fracture surfaces were studied by scanning electron microscope. Welds microstructure were heterogeneous and displayed structures comprising of both base metals and the onion rings were seen in all welds except for the lowest heat input weld. Grains in the weld nugget zone were more refined on the retreating side than the other side. Asymmetric hardness profile had a distinct softened zone on each side whose location and softening extent varied with the processing parameters. Welding speed had a more significant effect on tensile strength than rotary speed and, drastically decreased the same. Faster welding speed formed microscopic defects and changed the appearance of fractured surfaces from flat to zigzag. The welds underwent ductile and mixed-mode tensile failure on the advancing side. Attainment of optimum combination of process parameters is imperative to yield defect-free stronger dissimilar welds