High temperature deformation behavior of friction stir welded 2024-T4 aluminum alloy sheets

The deformation behavior was characterized using uniaxial tensile and free bulging testing. Digital Image Correlation (DIC) system was used to probe the full strain fields during the whole bulging process. Thickness distribution of the friction stir welded (FSW) sheet was analyzed and compared with the base metal. The flow stress of FSW joint was lower than that of base metal at the temperature of 400 °C and initial strain rate of 0.001 s−1. The ultimate tensile strength of FSW joint was about 70% of the base metal. The deformation was concentrated in the nugget zone of the weld during both uniaxial tensile tests and free bulging tests at high temperature, exhibiting significant inhomogeneous deformation characteristic. The bulging height of FSW sheet was only 50% of the base metal. The directions of major strains of weld zone and adjacent base material in the FSW sheet were vertical to each other during bulging tests. Such an incompatible deformation behavior resulted in the poor formability of FSW sheet compared with base metal.