The automotive manufactures increase their use of lightweight materials to improve fuel economy and energy usage has a significant influence on the choice of developing materials. To meet this requirements manufacturers are replacing individual body parts with lightweight metals, for these the process treating and painting surfaces is changing. The pre-coated steels are newly developed to avoid the conventional complex and non-environmental painting process in the body-in-white car manufacturing. The development of new joining techniques is critically needed for pre-coated steel sheets, which are electrically non-conductive materials. In the present study, dissimilar combination of pre-coated steel and galvanized steel sheets were joined by the self-piercing rivet, adhesive bonding and hybrid joining techniques. The tensile shear test and free falling high speed crash test were conducted to evaluate the mechanical properties of the joints. The highest tensile peak load with large deformation was observed for the hybrid joining process which has attained 48% higher than the self-piercing rivet. Moreover, the hybrid and adhesive joints were observed better strain energy compared to self-piercing rivet. The fractography analyses were revealed that the mixed mode of cohesive and interfacial fracture for both the hybrid and adhesive bonding joints.
In dissimilar overlap joints that are welded using gas metal arc welding, the shape of the weld bead changes due to changes in welding variables such as current, voltage, speed, and teaching position. The bead shape is a major factor that influences the evaluation of the tensile strength. Thus, it is crucial to control the shape of the bead and produce a bead with an optimal shape. In particular, in the case of a dissimilar combination with a thickness ratio of 4:1, it is difficult to weld all the joint surfaces of the upper plates. The presence of such a non-jointed area can change the tensile strength according to the bonded area. It is expected that a particular value of the critical jointed area satisfies the tensile strength constraints. In this study, various bead shapes were fabricated according to the welding parameters of dissimilar combinations with a thickness ratio of 4:1, and the corresponding tensile properties were evaluated. In addition, regression analysis was used to investigate the correlation between the bead shape and tensile strength.
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