Multi-objective optimisation of a novel expansion equal-channel angular spiral extrusion using response surface methodology

Based on the traditional equal channel angular extrusion (ECAE), this paper develops a novel composite for severe plastic deformation, namely expansion equal-channel angular spiral extrusion (Exp-ECASE). We conduct multi-objective optimisation using the response surface method to utilise the maximum effective strain and the minimum strain uniformity coefficient as the optimisation objectives. The variables in this optimisation include the diameter of the expansion channel, the length of the transition channel, and the length of the spiral channel. Moreover, variance analysis is performed on the established model, and its reliability is verified by simulation and experiment. During deformation, the billet was first upset in the expansion channel, breaking and refining coarse grains, with the average hardness rising from 81.8HV to 108.1HV. It was sheared when passing through the die corner, and the hardness increased to 122.8HV. Entering the spiral torsion channel, it underwent intense plastic deformation, and the hardness further rose to 130.3HV, a 59.3% increase.