Role of zinc coating on joint properties in impact spot welded Al 6111 aluminum alloy to galvanized high-strength low-alloy steel

This study investigates the influence of Zinc (Zn) coating on the mechanical properties of impact spot welded joints between Aluminum (Al) 6111 alloy and galvanized high-strength low-alloy (HSLA) 340 steel using vaporizing foil actuator welding (VFAW). The Zn coating significantly impacts the weld interface, leading to a heterogeneous structure with regions of retained Zn and trapped jetted material. These regions inhibit direct contact between Al and steel, preventing effective metallurgical bonding and reducing joint strength by 60 % compared to uncoated steel. While the Zn coating impedes bond formation in some areas, near-complete Zn removal in other zones promotes localized ductile tearing and partial bonding, slightly mitigating the overall negative effect. Additionally, a brazing effect outside the weld zone, resulting from the jetting and solidification of Zn and Al-Zn, provides some strength to the joint. The findings highlight the complex role of Zn coating in VFAW, demonstrating that a continuous Zn layer at the weld interface is more detrimental to joint performance than discrete and thin intermetallic compounds.