Microstructural Evolution and Mechanical Properties of Friction Stir Welded Dissimilar AA2014-T6 and AA7075-T6 Aluminum Alloy Joints

The dissimilar AA2014-T6 and AA7075-T6 aluminum alloy butt joints were made by friction stir welding with different process parameters. Friction stir welding is an efficient technique to join dissimilar aluminum alloys when compared to other traditional techniques. This paper aims to address the effect of various parameters, in particular the welding speed and shoulder diameter to pin diameter ratio (D/d ratio) on microstructures and mechanical properties of the joints. Six joints were made using two different welding speeds and three different D/d ratios without altering the tool rotational speed and the axial load. The results showed that the D/d ratio greatly influences the mechanical properties of the joints. Plastic deformation and recrystallization during the weld process resulted in the formation of distinct zones which could be identified by their respective microstructures. X-ray diffraction analysis was carried out to predict the formation of the precipitates which influences the properties of the joints. Fractographic images collected with a scanning electron microscope for establishing D/d ratio of 3, for two different welding speeds, were discussed. The dissimilar joints fabricated with the tool rotational speed 1200 RPM, welding speed 20 mm/min, axial load 8 kN, and D/d ratio of 3 yielded the higher tensile strength and hardness.