Assessing microstructure, morphology, and mechanical properties of Al-2Fe-1Ni alloy through correlational characterization analysis

Abstract

One approach to addressing the growing demand for Al alloys in an environmentally sustainable manner is through recycling. However, the primary challenge involves mitigating the loss of mechanical properties and expanding the application range of scrap-containing alloys, primarily due to the formation of deleterious Fe-rich intermetallic phases. To tackle this issue, various methodologies have been explored, ranging from the less efficient dilution of scrap in primary Al to the use of elements such as Ni that modify these harmful phases, combined with control of solidification thermal parameters. Despite the potential of this approach, there is a notable gap in the literature regarding the formation kinetics of Fe-rich intermetallics under varying thermal conditions and the addition of Ni in Fe-rich Al alloys. This study investigates the Al-2Fe-1Ni alloy solidified at cooling rates of 0.5 K/s and 10.5 K/s using optical microscopy, SEM, XRD, EBSD, XCT, and tensile tests. The findings demonstrate the effectiveness of Ni in suppressing the formation of the primary Al₁₃Fe₄ intermetallic phase and promoting microstructures predominantly composed of eutectic cells containing Al + Al₉FeNi. The Al₉FeNi fibers within the eutectic cells exhibited morphological variations, with the central segments being more refined and orderly compared to the coarser and less aligned peripheric segments. Furthermore, the microstructural refinement induced by increasing the cooling rate during solidification (from approximately 1 K/s to 8 K/s) resulted in enhanced yield strength (from 88 MPa to 125 MPa) and tensile strength (from 116 MPa to 138 MPa), while maintaining ductility, as evidenced by a consistent fracture strain of approximately 25 %.