Crystallization inhibition and microstructure refinement of Al-5Fe alloys by addition of rare earth elements.

Hypereutectic Al-Fe alloys are extremely brittle owing to the formation of coarse Fe-rich intermetallics in the Al matrix. In this study, a Ce-rich rare-earth (RE) mixture was introduced to modify an Al-5Fe binary alloy, and the crystallization, microstructure, and mechanical properties of the alloy were investigated. The experimental results indicated that the RE addition decreased the temperature of the primary Al 3 Fe phase, enhanced the temperature of the eutectic transformation, and disturbed the normal crystallization process of eutectic α-Al crystals by decreasing the intrinsic growth along the preferential close-packed (111) Al plane and promoting the growths depending on the sub-closed (200) Al plane. Furthermore, RE addition refined the primary Al 3 Fe phases and formed Al-Ce eutectics in the as-cast state of the alloy. Fine nodules and rods of the Al 4 Ce and AlCe phases containing La elements were produced through homogeneous annealing via the decomposition of the Al-Ce eutectics and precipitation of REs from the RE-enriched area. Rolling further broke up the coarser primary Al 3 Fe phases into short rods and particles and caused the Al-Ce and Al-Fe phases to become uniformly distributed in the Al matrix. A mixed cleavage and dimple fracture was produced by RE modification, annealing, and rolling. The optimized amount of added RE mixture for improving the microstructure and mechanical properties of the alloy was 0.9 wt%. • RE addition decreased the primary temperature of Al 3 Fe phase. • RE addition inhibited intrinsic growth of eutectic α-Al along (111) plane. • RE addition promoted the growth of eutectic α-Al along sub-closed (200) plane. • RE addition refined primary Al 3 Fe phases and formed Al-Ce eutectics. • 0.9 wt% RE was optimized for improving microstructure and mechanical properties. [ABSTRACT FROM AUTHOR]