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Due to the high thermal diffusivity and metallurgical sensitivity, the proper welding processes of the aluminum are required. The Laser beam welding and friction stir welding processes have been focused as the appropriated welding processes for aluminum. The heat treated 6xxx series and 7xxx series aluminum sheet were welded by the laser beam welding and friction stir welding processes. Also, the effects of heat input through the welding parameters were investigated. The tensile strength of weldments was evaluated respectively and compared by the processes and heat input level. The insignificant tensile strength differences were found for the 6xxx series by the welding processes. However, the friction stir welded 7xxx series weldments were shown 82~89% joint efficiency while laser beam welded weldment were shown 48~58%. Overall, the effect of heat input level was not revealed in this experiment range. The degradations in hardness of weldments tended to be in proportion to the joint efficiency loss.

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.

Friction spot welding is a kind of solid state welding process which can prevent welding defects observed in fusion welding processes. Friction stir welding inherently utilizes a rotating tool and a keyhole is formed after retreat of the tool like a welding crater. In this paper, two kinds of keyhole refilling techniques (1-step and 2-step processes) were introduced. 1-step refilling methods employed specially designed welding tools. The pin and shoulder (or sleeve) can be separately driven to stir the base material and refill the keyhole. In the 2-step refilling methods, friction stir and resistance spot processes were suggested as a successive process and optionally filler metal was supplied. Resistance spot process is more economical process than friction stir welding, and the keyhole was refilled without melting by selecting proper parameters.