Quality index for friction stir welds in 7050 aluminum plates

Abstract

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.

Keywords

• Non-destructive testing
• Quality index
• Residual stress
• Ultrasonic method
• Friction stir welding
• Aluminum alloy