EFFECT OF THERMO-MECHANICAL TREATMENT ON MECHANICAL AND FATIGUE BEHAVIOR OF AA 2024

Abstract

The aluminum alloy 2024 is extensively used in the aerospace, civil, and automobile industries. This alloy finds extensive applications in the wings, fuselage, and aircraft stringers. In these applications, the components are produced by metal joining techniques such as riveting, bolting, and conventional welding. All these techniques decrease mechanical efficiency by adding extra weight and high weld residual stresses. To overcome these issues, friction stir welding has been widely used nowadays. Further, components experienced complex mechanical loading during their service consisting of very high-to-low amplitude loading. This typical loading creates the mean stress effect on the service life. Thus, the combined effect of mean stress and weld residual stresses needs to be addressed for the safe and reliable life of the components. In this study, friction stir welding is performed on the aluminum alloy 2024-T3, followed by post-weld heat treatment at different aged conditions: 190 °C for 10 hrs and 200 °C for 10 hrs. The welding results in the microstructural inhomogeneity and thermal gradient across the weld cross-section. The microstructural features are explored through an optical microscope and electron back-scattered diffraction techniques. The weld residual stresses are measured by X-ray diffraction technique. The post-weld heat treatment results in the re-precipitation of the precipitates, specifically in the thermo-mechanically affected zone and weld nugget zone, however, no significant abnormal grain growth has been observed in the weld nugget zone. A significant improvement in the ductility and the hardness of the welded joint has been observed after post-weld heat treatment at 200 ◦C-10 hrs. This increase in hardness across the weld cross-section is devoted to the uniform distribution of hardening precipitates after heat treatment.