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

• Al-Zn coated steel weld interface in VFAW shows heterogeneous regions with retained Zn coating and trapped jetted material. • Retained Zn coating hinders direct Al-steel contact, leading to a lack of metallurgical bonding. • Near-complete Zn removal in some regions of the weld zone promotes localized ductile tearing, improving joint performance. • Brazing effect outside the weld zone from Zn-Al jetting adds some strength to the joint. • A continuous Zn layer at the weld interface is more detrimental to joint performance than discrete intermetallic compounds. 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.