Microstructure, mechanical properties and thermal conductivity of Al-1.2Fe alloy fabricated by laser-directed energy deposition

Abstract

The Al-1.2Fe (wt%) alloy was fabricated using the laser-directed energy deposition (L-DED) process at various combinations of laser power and scanning speed, followed by laser rescanning (LR) and heat treatment at 873 K for 24 h. The microstructure, mechanical properties, and thermal conductivity were investigated to evaluate the suitability of Al-1.2Fe alloy fabricated by L-DED as heat dissipation material. The results show that the L-DED samples exhibited a multilayered microstructure with coarse columnar structures. The bead thickness was reduced in the LR samples compared to the L-DED samples, but the microstructure remained similar. Heat treatment altered the microstructure, forming spherical and plate-like precipitates of Al₆Fe and Al₁₃Fe₄. A great number of nano-scale Al₆Fe particles predominated in the L-DED sample, while a small number of micro-scale Al₁₃Fe₄ particles were found in the heat-treated sample. All samples exhibited elongated α-Al grains along the build direction (BD). The grain size decreased in the order of the L-DED, LR and heat-treated samples. The LR process had negligible effects on hardness and tensile properties. On the other hand, the heat treatment reduced both hardness and tensile properties. The thermal conductivity was slightly improved by the LR process and significantly increased to approximately 30 W/m∙K after the heat treatment. Across all fabrication types (N, R, and H), increases in laser power and scanning speed led to improvements in the tensile properties and thermal conductivity. Additionally, there was clear anisotropy in tensile properties and thermal conductivity. The tensile properties were superior in the horizontal direction along the BD compared to the vertical direction, while the thermal conductivity was higher in vertical direction than in the horizontal direction. The anisotropy in these properties is believed to be primarily caused by the elongated grains along the BD.