Microstructure Characteristics and Hardening Mechanisms of the Thin-Walled Cylindrical ZK61 Parts with Transverse Inner Rib Fabricated by Rolling-Spinning

The filling defects of the ZK61 alloy thin-walled cylindrical part with transverse inner ribs were easy to occur by direct hot spinning, which could be attributed to the hindering effect of mold and low filling force in the radial direction. To improve the filling defects, the rolling-spinning method was proposed and made great progress. Since the non-uniformity of plastic deformation and the non-simultaneous filling of material into the rib, the microstructure in different areas of the rib presented significant differences that the grain refinement effect and dynamic recrystallization fraction gradually increased with the distance closer to the wall region. The microstructure differences led to performance differences in the rib that the Vickers hardness gradually increased when the distance became closer to the wall region. After evaluating the contributions of different hardening mechanisms, the second-phase precipitation hardening mechanism, solid solution elemental hardening and dislocation density hardening mechanisms were the main hardening mechanisms.