Spiral equal channel angular extrusion (Sp-ECAE) as a modified ECAE process

Abstract

This research includes efforts to introduce a new severe plastic deformation (SPD) technique, entitled spiral equal channel angular extrusion (Sp-ECAE). In this operation, spiral grooves are provided in the inlet channel of equal channel angular extrusion (ECAE) process. Therefore, a cylindrical specimen twists about its centerline and experiences shear strain prior to the lateral extrusion in ECAE processing. Forming load required for lateral extrusion is much more than that for filling spiral grooves. Thus, the material follows such spiral paths throughout the process. In fact, the Sp-ECAE is modified based on axisymmetric forward spiral extrusion (AFSE) and the ECAE operations. The Sp-ECAE was experimentally conducted on AZ80 magnesium alloy at 200°C and with a ram velocity of 5mm/min. Then, both mechanical and microstructural improvements of the alloy were measured. Findings revealed considerable increase in the strength of alloy. The yield stress and the ultimate tensile strength were increased from 90 and 144MPa to 160 and 247MPa, respectively, denoting a 70% improvement compared to the as-cast state. The ductility was also increased from 2.65 to 3.18%. Moreover, the Sp-ECAE was capable of homogenizing and improving the microhardness from 76.5 to 108.5HV. Studies showed that more than 60% of the total increase in the microhardness was attained after the spiral region which indicates the effective role of this section of Sp-ECAE in improving the mechanical properties of AZ80. The average grain size was also decreased from 48 to 17μm, showing 64% refinement in comparison with the as-cast condition. Comparing such improvements with those achievable via ECAE and AFSE processes, shows significant efficiency of the Sp-ECAE process. Therefore, this process can be considered as an effective, novel SPD process.