## 1 Introduction
Co-Cr-Fe-Ni HEAs have been built using a single face-centered cubic (FCC) solid solution. Elemental components have a noticeable influence on their structure and performance; the Cr and Fe elements, in particular, have an apparent effect on structural stability and the equilibrium lattice constant. In addition, the Ni components have a noticeable impact on rigidity. According to the Pugh ratios, Cr and Ni addition may enhance ductility, but Co and Fe addition may lower it. Therefore, the structural stability and stiffness of Co-Cr-Fe-Ni HEAs are enhanced by increasing Co and Fe concentrations or reducing Cr and Ni contents. The structural stability and mechanical characteristics of Co-Cr-Fe-Ni HEAs may be attributed to the strength of the metallic bonding and covalent bonding, which is influenced by the element content variation [29]. In previous studies, the mechanical properties of the weldments have been related only to the thickness of the IMC layer, and the weld interface area among the stainless steel and aluminum has not been considered. Mechanical strength should evolve linearly with the bonding area. However, the continuous IMC layer generated at the weld surface prevents the linear trend from being observed. A thickness of the IMC layer up to 8 \(\upmu\)m would result in sound Fe-Al joints [30; 31; 32]. Although utilizing shallow energy in the welding process to restrict IMC layer formation has a favorable impact, this method also results in the formation of a narrow bonding area with lower weld strength [33; 34]. In dissimilar metal welding, the sluggish kinetic diffusion property is exploited to prevent the blending of adjacent layers. For example, using powdered HEAs as a filler metal leads to the effective joining of aluminum and austenitic stainless steel in butt configuration [35]. Nevertheless,using HEAs as filler metals in the laser welding of dissimilar metals, such as aluminum and steel, has been little explored. Since none of the standard filler metal compositions meet the stricter requirements of HEAs, further investigations into the competence of such alloys to perform as fillers are worthwhile, and focus has shifted in this direction. In the following, we use the Pickering and Jones convention [36; 37] and label HEAs to reflect the atomic number of the elements. However, there are non-equiatomic configurations with more predominant elements in the composition over others; this results in the renaming of selected alloys. The elements are rearranged from how they were provided in their initial form. For the welding of dissimilar alloys, such as hyper-duplex stainless steel and aluminum alloy, vanadium and niobium are frequently utilized as corresponding layers that have a substantial repressive influence upon the generation of Fe-Al IMCs. The welding stress can lessen the exceptional ductility of copper, and the coefficient of diffusion of Ni and Fe is much greater than that of Al and Fe. Supplementing Ni can interfere with the formation of IMCs formed by the combination of Fe and Al. According to HEA theory, the atomic radius of Cu, Ni, Mn, and Co are identical. Therefore, they can produce a solid solution with ease. This research presents a laser welding technique for hyper-duplex stainless steel (UNS S33207) and aluminum alloy (AA6061) using Fe\({}_{5}\)Co\({}_{20}\)Ni\({}_{20}\)Mn\({}_{35}\)Cu\({}_{20}\) HEAs. Fe-Al IMCs are predicted to be repressed using HEAs fillers in Fe/Al lap joint configuration and to limit the melting of parent metal on the hyper duplex stainless-steel side. To date, this type of laser welding has been rarely performed.