Microstructure and mechanical properties of laser welding-brazed aluminum alloy to steel with CuSi3 filler metal

Laser welding-brazing of 6061 aluminum alloy to galvanized steel with CuSi3 filler metal was investigated by full-factor experiments. The surface appearances, microstructures and mechanical properties of joints were studied in detail by optical microscope, scanning electron microscope (SEM), EDX analysis and tensile tests. The results indicated that steel-aluminum dissimilar metal lap joint was successfully realized by laser welding-brazing with CuSi3 filler wire, and the joint showed good appearance. The lap joint presented three feature areas:the interface at the side of steel, weld center and the copper solder wire/aluminum transition area at the side of aluminum. Further studies had shown that the copper solder wire/aluminum transition region composed of Cu₉Al₄ and CuAl₂.presented four different morphologies:ribbon, large skeleton-like, small skeleton-like mixed with small amounts of lamellar and dendritic. The hardness of copper solder wire/aluminum transition zone is much higher than that of the adjacent zone, which was up to 9.97 GPa at the coarse skeletal zone. The tensile fracture was in the coarse skeletal zone and the fracture appeared brittle fracture.