This paper reports on a crucial role of the morphology of intermetallic Al11RE3 phase and Al/Al11RE3 interphase (where RE - Rare Earth) surface area, before plastic deformation, on the electrical and mechanical properties and the thermostability of aluminium alloys. Cast Al-4.5 (Ce + La) alloy samples, processed with and without spheroidization treatment (ST), were subjected to high pressure torsion (HPT) at room temperature (RT) followed by annealing at 230 degrees C, 280 degrees C and 400 degrees C for 1 h. It is demonstrated, that the changes of initial alloy structure (particles shape/size) and the decrease of interphase surface area affect the distribution of intermetallic particles after HPT, the distribution of ultrafine grains and the dislocation density, as well as the formation of a supersaturated solid solution of Ce and La in aluminium. The optimal combination of strength (ultimate tensile stress (sigma(UTS)) 430 MPa) and conductivity (55.9% International Annealed Copper Standard, IACS) was obtained after ST, HPT and an annealing temperature of 230 degrees C. (C) 2019 Elsevier B.V. All rights reserved.