Managing both high strength and thermal conductivity of a laser powder bed fused Al–2.5Fe binary alloy: Effect of annealing on microstructure

Abstract

Abstract The microstructure of Al–2.5Fe (wt%) binary alloy samples additively manufactured by laser powder bed fusion (L-PBF) was systematically characterized, and its change due to subsequent annealing at 300 °C and 500 °C was examined. The as-fabricated samples featured homogeneous distribution of numerous fine particles of the metastable Al6Fe phase in the solidification microstructure where melt pools formed, and a relatively coarsened cellular structure was observed around the boundaries between the melt pools formed at different locations (melt pool boundaries). After the annealing at 300 °C, a slight growth of the nano-sized Al6Fe phase occurred, and coarsened plate-like θ-Al13Fe4 phases were locally formed in the cellular structure at melt pool boundaries. Annealing at 500 °C induced a pronounced transformation of the metastable Al6Fe phase to the stable θ-Al13Fe4 phase in the microstructure where melt pools formed, although no significant change in the microstructure of the α-Al matrix was detected. The thermal conductivity and tensile properties of as-fabricated and subsequently annealed specimens were measured. The as-fabricated specimens exhibited a high tensile strength of ~320 MPa and a thermal conductivity of ~150 W m−1 K−1. Annealing at 300 °C improved the thermal conductivity to ~185 W m−1 K−1 without a loss of tensile strength, whereas annealing at 500 °C significantly decreased the tensile strength. These results are utilized to discuss a balance between mechanical properties and thermal conductivity, which provided novel insights for managing both high strength and thermal conductivity of L-PBF-built Al–Fe binary alloys by controlling microstructure.