Hot shear deformation constitutive analysis of fine-grained ZK60 Mg alloy sheet fabricated via dual equal channel lateral extrusion and sheet extrusion
(1. Mechanical Engineering Department, Hamedan University of Technology, Hamedan, Iran;
2. School of Metallurgical and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran)
2. School of Metallurgical and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran)
Abstract: Dual equal channel lateral extrusion (DECLE) process with various passes followed by sheet extrusion process was performed to produce fine-grained ZK60 alloy sheets. The coarse grain structure of the annealed sample after applying sheet extrusion (size: 68 μm) changed to fine grains of 6.0 and 5.2 μm after 3 and 5 passes of DECLE and following extrusion. The hot shear deformation behavior of samples was studied by developing constitutive equations based on shear punch test (SPT) results. SPT was carried out in the temperature range of 200-300 °C and strain rate range of 0.003-0.33 s–1. The activation energy of 125-139 kJ/mol and the stress exponent of 3.5-4.2 were calculated for all conditions, which indicated that dislocation creep, controlled by dislocation climb and solute drag mechanism, acted as the main hot deformation mechanism. It was concluded that material constants of n and Q are dependent on the microstructural factors such as grain size and second phase particle fraction, and the relationship of which was anticipated using a 3D surface curve. Moreover, the similar strong basal texture of extruded sheets gave rise to the same deformation mechanisms during SPT and similar n and Q values for ZK60 alloy.
Key words: ZK60 Mg alloy; constitutive equation; extrusion; hot deformation; shear punch test; metal forming