Effects of extrusion speed on the microstructure and mechanical properties of ZK60 alloys with and without 1wt% cerium addition

The effects of extrusion speed on the microstructure and tensile properties of the ZK60 and ZK60-1Ce alloys were investigated by performing indirect extrusion at three ram speeds (0.3, 1.0 and 3.0. mm/s). All of the extruded alloys showed a bimodal microstructure consisting of equiaxed fine recrystallized (DRXed) grains and elongated coarse unDRXed grains. With increasing extrusion speed, the exit temperature increased due to deformation heating, resulting in a larger grain and a higher DRXed fraction. The yield and ultimate tensile strengths and elongation at RT decreased with an increase of extrusion speed. The ZK60-1Ce alloys exhibited a finer grain size, a higher DRXed fraction, and weaker texture intensity than the ZK60 alloys at the same extrusion speed due to the inhibition of grain growth by the pinning effect and the promotion of DRX by particle-stimulated nucleation. The yield and ultimate tensile strengths at room and elevated temperatures were increased by the addition of Ce, while elongation was decreased due to cracking at the Mg-Zn-Ce particles.