Effects of a cladding zone in the steel groove on microstructure evolution of dissimilar metal laser welded of aluminum to steel

Abstract Welding dissimilar metals of aluminum (Al) alloy to steel is an effective strategy for achieving lightweight designs in transportation vehicles. However, metallurgical reactions between Al and steel are prone to promoting the formation of Fe-Al intermetallic compounds (IMCs), which are detrimental to the formability and mechanical properties of Al/steel welded joints. In this study, dissimilar metal joining of Al alloy (AA) 6061 to 304 stainless steel (SS) was performed using a NiMnCu 2 filler metal. A cladding layer was applied to the steel groove using the same filler metal and welding parameters. The effects of the cladding zone (CZ) on the microstructural evolution of the weld metal were investigated. It was found that the NiMnCu 2 filler metal could successfully join AA 6061 and 304 SS. Between the weld zone (WZ) and the AA 6061 base metal (BM), a mixed zone (MZ) was observed. The width of the MZ in Joint-CW (∼13 μm) was narrower than that in Joint-BW (22–29 μm). Both types of weld metals preliminarily met the formation criteria for high-entropy alloys (HEAs) based on elemental content and mixing entropy values. Consequently, the dominant phase formed in the weld metal exhibited a face-centered cubic (FCC) structure. Although the addition of a CZ in the steel groove caused a crack in the weld seam near the CZ, it reduced the width of the MZ on the AA 6061 side and effectively decreased the iron (Fe) content and hardness in the weld seam of the Al/steel joints.