Microstructure design to achieve optimal strength, thermal stability, and electrical conductivity of Al-7.5wt.%Y alloy

Abstract

Aluminum-rare earth (Al-RE) alloys are being increasingly evaluated as new generation heat resistant conductor materials owing to their superior thermal stability, which is attributed primarily to the limited solubility of RE elements in the Al matrix and resulting RE-containing eutectic intermetallic compounds formed in their microstructure. This paper describes the main results from an experimental investigation into tailoring the contrasting strength-electrical conductivity characteristics of an Al–Y eutectic alloy by manipulating several microstructural features using multi-passes cold drawing and annealing processes. High strength of the alloy was achieved not only owing to substantial grain refinement, high dislocation density, and β-Al3Y intermetallic phases but also by forming stacking faults and inducing <111> fiber texture via cold drawing. The alloy was found to preserve fine grains in its annealed state, which is attributed to the β-Al3Y intermetallic phases at grain boundaries stimulating nucleation but also preventing grain growth. Moreover, <111> fiber texture and some stacking faults remained stable during annealing, while the β-Al3Y intermetallic phases spheroidized. As a result, the alloy exhibited extraordinary thermal stability with some loss of strength originating mainly from the reduction in dislocation density upon annealing. Importantly, the novel Al–Y wires exhibit superior heat resistance over the commercial Al–Zr wires. Finally, electrical conductivity of the Al–Y wires improved with annealing, which is primarily due to the release of interfacial energy accompanying spheroidization of β-Al3Y phases and underlying decrease in interfacial scattering at β-Al3Y/α-Al interfaces.