Prediction of microstructure evolution of ZK61 alloy during hot spinning by internal state variable model

An internal state variable (ISV) model was established according to the experimental results of hot plane strain compression (PSC) to predict the microstructure evolution during hot spinning of ZK61 alloy. The effects of the internal variables were considered in this ISV model, and the parameters were optimized by genetic algorithm. After validation, the ISV model was used to simulate the evolution of grain size (GS) and dynamic recrystallization (DRX) fraction during hot spinning via Abaqus and its subroutine Vumat. By comparing the simulated results with the experimental results, the application of the ISV model was proven to be reliable. Meanwhile, the strength of the thin-walled spun ZK61 tube increased from 303 to 334 MPa due to grain refinement by DRX and texture strengthening. Besides, some ultrafine grains (0.5 μm) that played an important role in mechanical properties were formed due to the proliferation, movement, and entanglement of dislocations during the spinning process.