Quality index for friction stir welds in 7050 aluminum plates

• Published in: Materials & design 2022-10, Vol.222, p.111052, Article 111052
• Main Authors: Garcia Ruano, Shirley Alexandra, dos Santos Junior, Auteliano Antunes
• Format: Article
• Language: English
• Subjects: Aluminum alloy; Friction stir welding; Non-destructive testing; Quality index; Residual stress; Ultrasonic method
• ISSN: 0264-1275; 1873-4197
• DOI: 10.1016/j.matdes.2022.111052

[Display omitted] •A quality index QI-FSW based on residual stresses is proposed and can identify the best set of welding parameters.•FSW joints at 400 mm/min showed the worst quality and at 200 mm/min, the best.•Maximum equivalent residual stress (ERS) was 250 MPa, 50% of AA7050 Yield Strength.•Plates welded with same parameters show residual stress distributions with M shapes.•Maximum stress between 149 MPa and 356 MPa were found close to the weld center. AA7050-T7451 is a heat-treating aluminum alloy with high mechanical strength, ideal for producing lightweight structural components. Common types of welding lead to structural changes in the material that could decrease their mechanical properties affecting the fatigue life of the joints; however, a solid-state process known as friction stir welding (FSW) have been increasingly used as an alternative solution to reduce these severe effects. This work attempts to study the FSW behavior over 7050-T7451 aluminum alloys through the characterization of the resulting residual stresses and propose a manufacturing quality index based on their magnitude and distribution. An ultrasonic method employing longitudinal critically refracted (LCR) waves was used to determine the longitudinal residual stresses at different distances from the centerline in plates welded with different parameters.The resulting stress distribution is consistent with the literature review, presenting maximum values around 200 MPa at the center of the weld. A quality index was calculated through the average of all stresses in that region. It was found that higher residual stresses are produced with higher traverse and rotational speed (400 mm/min and 908 RPM). Therefore, to improve the process regarding the level of residual stresses, it is recommended to use lower welding tool velocities.