Microstructure evolution and mechanical properties of electron beam welded AlCoCrFeNi2.1 eutectic high-entropy alloy/304 stainless steel joints

The AlCoCrFeNi_2.1 eutectic high-entropy alloy has emerged as a promising candidate for advanced structural applications due to its exceptional strength and thermal stability. In contrast, 304 stainless steel is widely employed in industrial settings owing to its low cost, excellent corrosion resistance, and superior processability. In this study, dissimilar welding of AlCoCrFeNi_2.1 and 304 stainless steel was successfully performed using electron beam welding, and the influence of various welding parameters on joint microstructure and mechanical properties was systematically investigated. Microstructural analysis revealed that under moderate heat input conditions, second-phase particles precipitated within the weld, with Cr-rich nanoparticles embedded inside them, ultimately forming a dual-phase structure comprising FCC and B2 phases. In contrast, at high or low heat inputs, the weld region primarily exhibited a single-phase disordered FCC solid solution, with no second-phase formation. Mechanical testing showed that the joint produced under low heat input achieved a maximum tensile strength of 687 MPa, corresponding to 91 % of the 304SS base metal, along with a post-fracture elongation of 21.5 %. The enhanced strength is primarily attributed to grain refinement, Al-induced crystalline defects, and the triaxial stress constraint effect arising from the narrow nail-shaped weld geometry. These findings provide critical insights for the design of high-quality weld joints between AlCoCrFeNi_2.1and Fe-based structural materials.