RSM-Assisted Dynamic Mechanical Analysis and Thermo-Mechanical Stability of Dissimilar AA5083–AA6061 Friction Stir Welded Joints

This study presents a comprehensive thermo-mechanical and viscoelastic characterization of dissimilar AA5083-AA6061 friction stir welded (FSW) joints through dynamic mechanical analysis (DMA) integrated with response surface methodology (RSM). Three key process parameters tool rotational speed (900–1500 rpm), welding traverse speed (30-90 mm·min⁻¹), and axial force (4-8 kN) were systematically varied using a statistically designed experimental framework to establish correlations between heat input, microstructural evolution, and temperature-dependent mechanical stability. DMA tests conducted up to 450 °C provided storage modulus (E′), loss modulus (E″), damping factor (tan δ), complex modulus (E*), dynamic viscosity (η), stiffness-loss slope (S), and characteristic transition temperature (T*). Experimental results showed significant sensitivity of viscoelastic behavior to welding conditions. Storage modulus varied from 14.41 to 26.13 GPa, loss modulus from 3.50 to 5.66 GPa, and tan δ from 0.143 to 0.393, while dynamic viscosity ranged between 5.57×10⁸ and 9.00×10⁸ Pa·s. Tensile strength values reached up to 202 MPa with elongation ≈11%, confirming sound joint integrity under optimized heat input. Regression modeling indicated that rotational speed and axial force were the most influential factors, with significant AC interactions governing stiffness and damping responses. The developed quadratic and 2FI models demonstrated strong predictive capability (R² up to 0.96, Adeq. Precision > 16). Multi-objective desirability optimization identified an optimal parameter combination of 900 rpm, 30 mm·min⁻¹, and 4 kN, yielding E′ ≈ 23.22 GPa, E″ ≈ 3.69 GPa, tan δ ≈ 0.132, E* ≈ 23.41 GPa, η ≈ 5.88×10⁸ Pa·s, S ≈ 0.161, and T* ≈ 312 °C with a maximum desirability of 0.729. The proposed RSM–DMA framework provides a predictive tool for tailoring thermo-mechanical stability of dissimilar aluminum FSW joints for elevated-temperature and vibration-sensitive structural applications. The stiffness-loss slope (S) ranged from 0.1212–0.1931 GPa °C⁻¹, while the characteristic transition temperature varied between 282–337 °C, indicating stable thermo-mechanical performance under varying conditions. Furthermore, statistical analysis confirmed that rotational speed and axial force are the dominant parameters controlling viscoelastic response.