Deformation mechanism of ZK61 magnesium alloy cylindrical parts with longitudinal inner ribs during hot backward flow forming

Thin-walled cylindrical parts with longitudinal inner ribs (CPLIRs) made of magnesium alloys are one of the most promising lightweight components. Flow forming is an effective technology to realize the integrated manufacturing of thin-walled CPLIRs. However, due to the complicated material flow and narrow temperature window, defects like insufficient filling at the rib groove and concavity of the back of rib occur easily during hot backward flow forming (HBFF) of ZK61 alloy thin-walled CPLIRs. The isothermal uniaxial compression test was proposed as the physical simulation test of the HBFF of thin-walled CPLIRs, and a novel method for analyzing the formability of hot spin-forming was proposed on the basis of the combination of 3D hot processing maps (HPMs) and finite element (FE) simulation. The process experiment and FE simulation integrated with 3D HPMs were conducted to investigate the deformation characteristic and material flow, and formation mechanism of defects was revealed. Further, the influence of process parameters on the power dissipation efficiency of spun workpiece was discussed. The results show that safe deformation of the alloy is concentrated at a narrow region with high temperature and low strain rate; the large tangential flow at the cylindrical wall and radial flow at the inner rib contributed to the filling of rib groove; unsaturated inner rib and concavity of the outer wall at the back of rib are typical defects; the ZK61 alloy CPLIRs exhibits good formability under reasonable process parameters, which is beneficial for obtaining qualified forming quality and uniform recrystallized microstructure.