자동차 차체용 변태유기소성강의 기계적 특성에 미치는 접합방법의 영향

Abstract

Advanced High Strength Steel(AHSS), such as Dual Phase(DP) steel and Transformation Induced Plasticity(TRIP) Steel, was developed to improve a fuel efficiency and a safety for passengers. The automobile industry required development of new bonding method because AHSS has poor weldability. Weld-bond was developed and is being used on automotive assembly line. Weld-bond was carried out by adhesive bonding followed resistance spot welding. In this study, 1180 TRIP steel of 1.2mm thickness were prepared by resistance spot welding, adhesive bonding and Weld-bond processes. Tensile shear properties and fatigue properties of the joints were evaluated and were analyzed by tensile shear test and fatigue test. Nugget diameters of resistance spot welding and nugget diameter of Weld-bond were produced with 4.0mm, 5.0mm, 6.0mm and 7.0mm, respectively, when tensile shear test performed. Tensile shear strength of resistance spot welding is increased as the nugget diameter increases. The failure mode of 4.0mm and 5.0mm are interfacial fracture and plug fracture respectively and tear fracture is occurred over 6.0mm nugget diameter while tensile shear test is performed. Tensile shear strength of adhesive bonding is higher than resistance spot welding. The failure mode of adhesive bonding is cohesive fracture because the thickness of adhesive layer is very thin. Tensile shear strength of Weld-bond is increased as the nugget diameter increases. The failure mode of adhesive layer of Weld-bond is similar to that of adhesive bonding and the failure mode of weld nugget of Weld-bond is similar to that of resistance spot welding.

Nugget diameter of resistance spot welding was produced with 6.0mm and nugget diameter of Weld-bond were produced with 4.0mm and 6.0mm respectively when fatigue test performed. The endurance limit of adhesive bonding is much higher than resistance spot welding but lower than 4.0mm nugget diameter of Weld-bond. The endurance limit of adhesive bonding is similar to that of 6.0mm nugget diameter of Weld-bond.