Fractography analysis of AW-7020 alloy joints welded by FSW

Technology development of Friction Stir Welding (FSW) method for joining AW-7020 aluminum alloy elements was described. Two kinds of tools were used during research: with a regular pin and with a „TRI-FLUTE” pin. Tools were with different dimensions and the following parameters changed mandrel’s rotary speed Vn [rev/min], welding speed Vz [mm/min], angle of tool deflection αz [o]. The thickness of the joining sheets was g = 12 mm. The sheets were one side milled to a thickness of 10 mm in the contact portion. Samples were tested by Charpy impact strength according to PN-EN ISO 148-1:2010. After these tests, the samples were analysed by means of fractographic examination. The tests were made with using a scanning electron microscope (SEM) Philips XL-30. The analysis has shown that there is the influence of the joining parameters and chosen tools for the possibility of occurrence welding defects in joints. Welding defects detected in the structure of joints after impact studies were: incomplete fusion, separations dissection, and cracks. During the development of friction stir welding technology, the best results, in terms of structure homogeneity and the absence of welding defects, were achieved for the tool with TRI-FLUTE pin and joining parameters: Vn = 450 rev/min, Vz = 180 mm/min, αz = 88.5 °.