Strengthening electron beam welded joints of AlCoCrFeNi_2.1 eutectic high entropy alloy and 304 stainless steel via constructing cellular heterogeneous dual-phase microstructure

Electron beam welding of AlCoCrFeNi_2.1 eutectic high entropy alloy and 304 stainless steel was studied. The application of this dissimilar joint was limited by its susceptibility to softening and low strength. Alloying of the joint was conducted using Al layers of varying thicknesses, and the optimally alloyed joint was subsequently subjected to post-weld heat treatment. When the alloying layers were 150 μm and 100 μm, the weld zone exhibited a B2 phase dominated matrix, resulting in joint embrittlement. Reducing the alloying layer thickness to 50 μm resulted in a significant enhancement of the joint strength, reaching 724 MPa. The cellular heterogeneous dual-phase microstructure was obtained in the weld zone, where the softer FCC phase provided ductility while the harder BCC phase contributed strength. The resulting hardened weld produced high strength joints that consistently fractured in the 304 stainless steel base metal. Subsequent heat treatment at 650 °C for 2 h was performed on the joint alloyed with the 50 μm interlayer. The BCC phase underwent coarsening and an ordering transformation, resulting in the formation of the B2 phase. The maximum width of the B2 phase reached approximately 4 μm, representing a 100 % increase. This growth resulted in enhanced second phase strengthening, contributing to joint strength of 761 MPa.