Friction Stir Welding Process and Cryogenic Mechanical Properties of 2219 Aluminum Alloy Thick Welded Blanks

To prepare reliable thick aluminum alloy tailor welded blanks for cryogenic forming, 2219 aluminum alloy friction tailor welded blanks that has the thickness of 12 mm were selected as the research object in our study. Vickers hardness tests were employed to clarify the property distribution across the weld cross-section. Room temperature uniaxial tensile tests have been used to reveal through- thickness deformation behavior under tensile loading. The mechanical tests at room and cryogenic temperatures were employed to investigate the effects of welding parameters of the friction tailor welded blanks on the mechanical properties, and evaluate the cryogenic formability of the welded blanks. Results show that the single-sided FSW specimens exhibit decreased hardness values from the top to the bottom surface, causing more severe deformation in bottom region and macroscopic bending under tension stress condition. In contrast, the double-sided FSW specimens exhibit a more uniform hardness distribution across the weld cross-section, resulting in nearly symmetric deformation and no significant bending. Lower welding speeds combined with higher rotational speeds significantly improved the ductility of the tailor welded blanks. The optimal welding parameters are identified as 200 mm/min and 800 rpm, showing a 321.1 MPa tensile strength and a 22.2% elongation, at room temperature after water quenching and solution treatment. These values increase to 385.5 MPa and 33.5% at liquid nitrogen temperature, showing a more than 20% enhancement in strength and around 50% enhancement in ductility, indicating excellent formability. This study offers a reliable material and process basis for the integrally forming of ultra-large components.