Influence of Isothermal Precision Forming on Crystal Phases, Recrystallization Behavior and Mechanical Properties of Profiled Thin-Walled Forgings with High Ribs

In this paper, a profiled thin-walled forging with high ribs were fabricated by isothermal precision forming process, which dramatically reduced the die forging force and improved the forming efficiency. The results show that compared with conventional hot forming, the continuous high temperature environment of the isothermal forming process enhanced the diffusion ability of the crystal phase particles and eliminated the uneven distribution. The uniform temperature field facilitated the uniform nucleation of continuous dynamic recrystallization (CDRX) process and promoted the dispersive precipitation of spherical precipitated phases. Nucleation by second phases stimulated recrystallization results in a higher dynamic recrystallization (DRX) nucleation rate. The strong dynamic recovery (DRV) and DRX in isothermal forming process annihilated abundant dislocations and reduced the driving force of static recrystallization (SRX) in solution process. The dispersion distribution of crystal phases provided a favorable position for the homogeneous nucleation of SRX process. Meanwhile, the spherical precipitating phases pinned the grain boundaries and hindered the grain boundary migration, which inhibited continuous static recrystallization (CSRX) and obtained a uniform ultrafine grain structure with an average grain diameter of 14 μm. Compared with the conventional hot-formed forgings, the yield strength of the top frame, skin, stiffening rib and bottom frame of the isothermal formed forgings was increased from 385 MPa, 387 MPa, 389 MPa and 388 MPa to 410 MPa, 442 MPa, 451 MPa and 448 MPa, respectively, increased by 6.5%, 14.2%, 16.0% and 15.5%, respectively.

Graphical Abstract