Enhancement mechanism of wetting and spreading during mesh-assisted laser–metal inert gas hybrid welding–brazing of steel/aluminum

Abstract

This paper proposes the insertion of a stainless-steel mesh interlayer to enhance the laser–metal inert gas (MIG) welding–brazing process of aluminum (Al) to steel. The mesh improves the spreading behavior and overall properties of the steel/Al overlap joints. The impacts of the mesh on the spreading dynamics of molten Al and on the microstructural characteristics and mechanical properties of the resultant joints are investigated. Under capillary forces, the mesh aids the spreading of molten aluminum on the steel surface. Moreover, the mesh dissolves into the molten pool, elevating the iron (Fe) content, intensifying the interfacial reactions, and leading to the formation of intermetallic compound (IMC) particles within the weld. The intensified interfacial reactions drive the wetting and spreading of the molten Al. The IMC particles function as additional nucleation sites, refining the grain structure of the weld. The mesh improves the average tensile shear strength of the joints from 308 to 368 N/mm (an improvement of 19.5 %) and shifts the fracture area from the interface or weld seam to the heat-affected zone. In summary, the mesh enhances the mechanical properties of the joints by increasing the spreading width, refining the weld grains, and forming IMC as a secondary phase for reinforcement.