Investigation of Solid‐Solution Phase Formation in AlCuNiSi Medium Entropy Alloys and its Effect on Microstructural, Thermal, and Microhardness Properties

Medium‐entropy alloys (MEAs) are increasingly being used in various fields, including the electrical industry, robotics, and automotive sectors, due to their high strength and electrical conductivity. This study focuses on the synthesis of equiatomic AlCuNiSi MEAs using mechanical alloying. The X‐ray diffraction results indicate formation of AlNi and Al 2 Cu intermetallic phases after 50 h of mechanical alloying. Extending milling time to 100 h results in the formation of body‐centered cubic, face‐centered cubic, and Si‐rich solid solution phases. With increasing milling time from 50 to 140 h, the crystallite size decreases, while lattice strain, dislocation density, and grain boundary fraction increase. Scanning electron microscope analyses reveal that the increased milling time leads to a decrease in particle size due to agglomeration, welding, and fragmentation. Differential thermal analysis indicate the formation of endothermic peaks in the temperature range of 750–800 °C, marking the intermetallic or solid‐solution phase transformations. The maximum microhardness value is 381.15 ± 5 HV in a specimen sintered at 650 °C and milled for 140 h. A novel finding is that in equiatomic AlCuNiSi MEA, the Si element forms a Si‐rich solid‐solution phase after 100 h milling, and it does not form any intermetallic phases with other constituent elements even after 140 h of milling.