Microstructure and high-temperature tensile properties of a near-eutectic Al-2Fe-2Cr-1Mn-0.7Zr (wt.%) alloy designed for additive manufacturing

This study introduces a novel Al-2Fe-2Cr-1Mn-0.7Zr (wt.%) alloy designed for high-temperature applications. The design strategy leverages the alloy's near-eutectic composition to create a printable alloy with refined eutectic intermetallic reinforcements and to take advantage of the supersaturation of slow-diffusing elements (Mn, Zr, and Cr). The as-printed microstructure shows a homogeneous grain structure with coarse columnar grains. The distribution, nature, size and morphology of the intermetallic dispersoids is heterogeneous at the melt pool scale. Coarse facetted Cr-rich precipitates are only found near the melt pool boundaries while the melt pool interiors consist of a refined eutectic structure (interparticle spacing ∼200 nm) with elongated, Fe-rich intermetallics (∼10% in area fraction). The composition of the solid solution is also heterogeneous with higher supersaturations in Mn, Zr, and Cr in the melt pool interiors than at the melt pool boundaries. The high-temperature tensile properties of the as-printed material are evaluated from 100 to 350°C and over four orders of magnitude in strain rate. This alloy shows a very limited decrease in yield strength between 100 and 300°C, nearly no strain rate sensitivity, and maintains a reasonable ductility (elongation to failure ≥5%) despite a reduction in ductility at low strain rate. The role of the refined eutectic structure to confine dislocation motion and mitigate dynamic recovery is emphasized. The role of supersaturation in climb-restricting solutes such as Fe, Mn and Zr is highlighted. A mechanism to rationalize the drop in ductility at elevated temperature and low strain rate is proposed.