Microstructure, mechanical and conductive properties of Al–4La–6Ce-xCo alloys: Optimal Co addition for balanced performance

This study investigates the effects of cobalt (Co) content (0-2.0 wt.%) on the solidification behavior, microstructure, mechanical properties, and conductive properties of an Al-4La-6Ce alloy with a La-to-Ce ratio designed to mimic that of typical mischmetal. The results show that Co addition significantly refines the alloy's microstructure: the primary α-Al transforms from coarse cellular grains into fine dendrites, while the eutectic structure transforms from a lamellar binary eutectic (α-Al + Al 11 (La,Ce) 3 ) into a ternary eutectic (α-Al + Al 11 (La,Ce) 3 + Al 9 Co 2 ) and a granular structure. Increasing Co content enhances the room-temperature tensile strength of the alloy from 140.6 MPa to 173.1 MPa, but degrades its plasticity. The electrical conductivity exhibits a non-monotonic variation with increasing Co content, showing a rebound at 1.0 wt.% Co due to the morphological transition of the eutectic structure from lamellar to granular. Overall, the Al-4La-6Ce-1.0Co alloy offers the best balance of ultimate tensile strength (≈ 164.3 MPa), plasticity (elongation ≈ 7.3%), electrical conductivity (≈ 26.6 MS/m), and thermal conductivity (≈ 170 W/(m·K)), which demonstrates its promising potential as a structural material for high-performance thermal management systems.