Evolution of the microstructure, texture and mechanical properties of ZK60 alloy during processing by rotating shear extrusion

Abstract

In this work, we use a kind of punch with a shear structure by combining torsion and backward extrusion (BE) to produce a ZK60 alloy cylinder part by rotating shear extrusion (RSE) at 643 K. This process can introduce a torsional shear component on the basis of backward extrusion by changing the direction of plastic flow and increasing the shear deformation amount to make it easier for the material at the bottom of the punch to flow to the barrel wall. Compared with BE, RSE can obviously refine grains and effectively improve the problems of a small deformation amount and insufficient flow of the material at the bottom of the back extrusion punch. The relevant microstructure evolutions of different parts of formed cylinder parts are investigated, and the results show that the proportions of dynamic recrystallization (DRX) in the inner and the middle wall of the lower half region of RSE processed part increase obviously (by 49% and 21.7%, respectively) and that the size of fine grain is ~2–4 µm; further, that of the bottom of the barrel increases by 44.6%. The deformation mechanisms of rotating shear are mainly continuous DRX (CDRX) accompanied by discontinuous DRX (DDRX) in the early stage, and with the progress of deformation, DDRX plays a leading role. The (0001) plane in the BE processed part is basically parallel to the transverse direction (TD), while the (0001) plane in the RSE part is deflected to the extrusion direction (ED) and at an angle of 30°−45° to the TD, and the texture strength is obviously weakened. A comparison of the variation in ∆Hv(%) along the TD of the barrel wall of the two extruded parts shows that RSE can generate a larger deformation amount and wider deformation effect range under the same extrusion ratio, effectively improving the microhardness of the ZK60 alloy. The ultimate strength (UTS), yield strength (YS), and elongation (EL) of alloy are ~313 MPa, ~279 MPa, ~12.1% after the RSE process, respectively. And the strength and ductility of the alloy can be improved by the RSE process.