Processing of an as-cast Al-7.5 wt%Y eutectic alloy by rolling and annealing to improve the tradeoff between strength and electrical conductivity

Abstract

This paper describes insights from an experimental investigation into tailoring microstructure of an Al–Y eutectic alloy to improve its trade-off between strength and electrical conductivity via casting, cold rolling, and annealing. Mechanical testing, ex-situ microscopy, and in-situ synchrotron X-ray diffraction were employed to characterize microstructural evolution as well as strengthening and conduction mechanisms. The as-rolled alloy exhibited substantially improved strength and electrical conductivity compared to the as-cast alloy. The rolling deformation induced a lamellar structure in the alloy consisting of coarse primary α-Al grains organized into fibers floating within ultrafine eutectic matrix of α-Al grains and β-Al3Y particles. Subsequent annealing at 280 °C for 1-h caused partial recrystallization of the primary α-Al phase, while annealing at 400 °C for 1 h cause both α-Al and β-Al3Y phases to undergo recrystallization with coarsening of α-Al but reduction in size of β-Al3Y. Interestingly, stacking faults were observed to be thermally stable during the annealing processing contributing to the heat resistance of the alloy. Relative to the cold-rolled state, the alloy after annealing at 280 °C for 1 h retained a tensile strength of 90 % with improved ductility and electrical conductivity. Furthermore, the alloy after annealing at 400 °C for 1 h lost some strength but electrical conductivity further increased. The effects of cold rolling on the lamellar-structure creation and subsequent annealing on the microstructural changes and resulting strength and electrical conductivity of the alloy are discussed in this paper.