Design, microstructure and thermal stability of a novel heat-resistant Al-Fe-Ni alloy manufactured by selective laser melting

Selective laser melting (SLM) technology is promising to fabricate complex-shaped metal components, especially light-weight aluminum (Al) alloy. Facing the grow requirement of thermal stability for applications in aviation and aerospace at high temperatures, the poor thermal stability of Al alloy needs to be improved. Thus, in this study, we developed a novel heat-resistant eutectic Al-Fe-Ni alloy which is suitable for the SLM process. Firstly, the composition of Al-1.75Fe-1.25Ni (wt%) alloy was designed and confirmed through the calculation of hot crack susceptibility index |dT/d(fs0.5)| and the analysis of the as-cast microstructure. Then, the designed alloy was fabricated using the optimized SLM processing parameters. Finally, the effects of heat treatment on microstructure evolution and phase stability during thermal exposure were investigated. Results show that the SLMed alloy is consisted of α-Al and cellular eutectic Al9FeNi phases. The fine grain structure and nano-sized Al9FeNi phase of the SLMed sample result in high hardness which is more than twice higher than that of the as-cast sample. During long-term thermal exposure at 300 °C, the fine grain structure and cellular eutectic phase remain almost unchanged, and thus, the hardness of the alloy can be kept stable. When the exposure temperature further increased, the fine grains gradually grew up and the cellular Al9FeNi phases were gradually collapsed and coarsened. Heat treatment at such high temperature (above 400 °C) resulted in microstructure coarsening and formation of large-sized rod-like or spherical phases, which significantly degraded the hardness. The novel heat-resistant Al-Fe-Ni alloy together with the alloy composition design method provides new insight into light-weight and complex-shaped components produced by the SLM process for high-temperature applications.