Characterization of material flow in friction stir-assisted incremental forming with synchronous bonding of dissimilar sheet metals

Material flow is evaluated to investigate the mechanism of pin-less friction stir-assisted incremental forming with synchronous bonding (FS-ISF&SB) process in a macro and micro scope. Dissimilar metal sheets AA5052-H32 and DC05 are incrementally formed with synchronously bonding by this novel process. Analytical mechanical models combined with microscopic image reveal that materials experience severe but different flow modes during the process. To make clear the underlying forming mechanism, the fabricated part is divided into three zones: wall flow zone (WFZ), rotation flow zone (RFZ), and bump structure flow zone (BSFZ). Bonding may even appear at Fe-Al interface to produce Fe-Al intermetallic compound in WFZ and RFZ, which depends on uncoordinated deformation controlled by mechanical force coupled with heat. Contributed to the torque transfer applied by forming tool, obvious wall side deflection in WFZ and grain refinement at the near surface area in RFZ are observed. Based on the simulation characterization, thermal effect is considered to build force frame on the deformation element for making semi-quantitative investigation of softening effect on BSFZ. This work prompts a better understanding of the underlying mechanism of this process and establishing the process window for potential industrial applications.