In addition to the constant demand to reduce emissions and transport costs at the expense of cargo weight, lightweight materials with good mechanical properties are increasingly used in industry. High-strength aluminium alloys are one of them, but it is impossible to successfully join them with conventional fusion welding processes, especially in the case of joining dissimilar alloys. From this point of view, the process of friction stir welding (FSW) is extremely promising as it enables a quality welded joint without defects even in the case of joining these materials. In the final part, we cut samples from FSW joint made of dissimilar aluminum alloys of the 2017A-T451 and 7075-T651 series and prepared them accordingly for further measurements and analyzes. We then performed detailed microhardness measurements in the longitudinal direction of the weld in several lines. At the same time, from the point of view of studying the influence of the tool and heat input, we performed measurements at different depths below the top surface of the welded joint. Then we macroscopically examined the samples and made microscopic measurements of the transition areas of the welded joint and places where the microhardness extremes were measured. Then we attempted to appropriately relate the microhardness profiles to the microstructural characteristics of the FSW joint.
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