Synergistic effect of Fe, Ni, and Er on microstructural stability and high-temperature performance of Al-Cu-Mg alloys

This study demonstrates that microalloying with Fe, Ni, and Er establishes a permanent microstructural framework that significantly mitigates high-temperature softening. To establish the optimal thermal processing route for the co-modified alloys, homogenization treatments were evaluated at 490 °C for holding times of 4, 6, and 8 h, while the subsequent artificial aging kinetics were closely monitored over varying durations at 180 °C. Implementing the optimized heat-treatment route, consisting of a homogenization stage at 490 °C for 6 h followed by artificial peak aging (T6) at 180 °C for 8 h, successfully promoted the formation of a thermally stable microstructural skeleton. Phase transformations and microstructural evolution were characterized using differential scanning calorimetry (DSC), optical microscopy (OM), and scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX). The mechanical behavior was evaluated using Vickers hardness testing and RT- and elevated-temperature compression testing. Mechanical properties evaluations showed that, at RT, the Fe-/Ni-modified alloy attained the highest compressive yield strength of 353 MPa, reflecting a 15.7% enhancement over the reference alloy (305 MPa), attributed to precipitation hardening within the α-Al matrix. Conversely, the Fe-/Ni-Er-modified alloy exhibited remarkable ductility, with a fracture strain of 0.78. Most notably, at 250 °C, the Fe-/Ni-Er-modified alloy maintained an ultimate compressive strength of 320 MPa, achieving a high strength retention rate of approximately 60.4% compared to its RT performance. This elevated thermal stability is attributed to the formation of a highly interconnected, rigid intermetallic framework comprising thermally stable Al₉FeNi (T-phase) and Er-rich phases, which acts as a permanent load-bearing framework that effectively prevents macro-scale thermal softening and structural degradation of the α-Al matrix at elevated temperatures.