The microstructural homogeneity, hardness and tensile strength of aluminium alloy 5083, with and without copper shielding (CS), processed by equal-channel angular extrusion (ECAE) are investigated in this work. The two opposite longitudinal faces of the rectangular billets are shielded with copper sheets of various thicknesses (1·0, 1·5, 2·0 and 2·5 mm) and ECAE’d at room temperature in route A (no rotation of billet) up to four times. The required extrusion load is drastically reduced due to the smaller coefficient of friction between the CS and channels of the steel die. The shielded copper reduces the effect of the dead metal zone and microcracks and improves strain uniformity in the extruded alloy. The hardness and tensile strength of the extruded alloy with CS are increased extensively due to newly formed submicron-sized grains in the homogeneous structure. Also, the ductility of ECAE’d alloy with CS is higher compared to that of the alloy extruded without shielding. It is noticed that the increase in the thickness of CS does not have a noteworthy effect on the structural and mechanical behaviour of the extruded alloy.

The microstructural evolution and mechanical behaviour of semicircular AA 5083 billets subjected to equal channel angular extrusion (ECAE), without and with copper casing (CC), are investigated in this work. The semicircular billets, circumferentially covered with and without CC, are extruded up to three passes in route A at room temperature. Even the coarse grain structure of the initial material is significantly refined, the microcracks and the structural defects were observed in the billets extruded without CC due to non-uniform strain distribution. The use of CC on the circumference of the semicircular billets reduces the dead zone effect on the structural homogeneity and minimises the formation of microcracks on the outer periphery of the extruded material. The uniform distribution of the effective strain imposed on the billets ECAE’d with CC enhances the development of equi-axed ultrafine grains at low pressing loads. The newly formed ultrafine grains with a size of few hundreds of nanometres significantly increase the mechanical properties of the ECAE’d AA 5083 with the CC. The obtained results were in good agreement with the earlier reports in which ECAE was carried with back pressure arrangement.