On the investigation of the microstructure and mechanical properties of the AlCoCrFeNi2.1/304 heterogeneous gas tungsten arc welded joint

Abstract

High entropy alloys have demonstrated significant use potential in the field of petrochemical and nuclear energy equipment. However, the investigation on the heterogeneous joining of the AlCoCrFeNi_2.1 and stainless steel is still lacking, and a sound match between strength and ductility is highly pursued. This study aims to perform the welding examination of the AlCoCrFeNi_2.1 HEA and commercial 304 stainless steel using the gas tungsten arc approach. A free-imperfection welded joint was obtained, with obvious columnar grains in the FZ. The thermodynamic calculation results, using the obtained results from energy dispersive spectroscopy, revealed that a redundant σ phase emerges in the fusion zone, while the XRD pattern exhibits a phase composition of FCC + BCC in the FZ. This difference is attributed to the rapid cooling rate during the welding process. The average grain size of the FZ near 304 stainless steel and AlCoCrFeNi_2.1 HEA is 38.18 μm and 9.90 μm, suggesting a difference in the thermal conductivity of two base metals. The FZ/AlCoCrFeNi_2.1 side exhibits obvious brass, cube, S, and α-fiber, with the texture strength being strongest in Brass and Cube, whereas the FZ/304 side displays a much smaller texture strength. The tensile strength of the AlCoCrFeNi_2.1/304 welded joints is ∼1022 MPa and ∼27 %, respectively, demonstrating that a great match between strength and ductility is realized. The micro-hardness test results suggested a valley hardness happens in the FZ, within the range of 150∼180 HV_0.2, which is consistent with the final fracture zone, indicating a stress concentration occurs in the FZ.