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Research work was aimed at the welding of thin sheets using high power CO2 laser. Process parameters, evaluation of the weld by micro, macro and mechanical are briefly given. Characteristics of the laser welding are described. Optimal proces parameters which are power, weld speed, gas flow, focal point, gap distance, were used. Microstructural evaluation by light microscope and transmission electron (TEM) microscope for substructural analysis was employed. Therefore general weld imperfections were observed and laser weld evaluation was made with EN ISO 13919-1. Mechanical performance of welded sheets was done by uniaxial tensile test, Erichsen test, and microhardness test. Uniaxial tensile test was employed transverse-weld oriented to the tensile direction and longitudinal-weld oriented to the tensile direction. Results were compared with base metal properties. Maximum tensile strength was obtained from the longitudinal-weld with reduced ductility. In transverse-weld direction fracture was far from the weld. Microhardness test was applied to the cross section of the welded sheets. Maximum hardness was obtained from the weld fusion zone (FZ) where hardness was increasing from HAZ to weld FZ center. Therefore hardness results were verified by empirical equations, which are proposed by various authors. Erichsen test was employed for the ductility evaluations of the welded sheets whereby two types of defect were observed from the Erichsen test. The First one was observed in the weakest sheet (lowest gauge or lowest strength). It occurs when the major strain direction is perpendicular to the weld seam. The second one occurred across the weld by the higher strength and lower elongation of the weld while major strain direction was parallel to the weld seam. Process parameters, microstructural and substructural analyses were compared with mechanical performance of the welded sheets. As a result the laser welded thin sheets were evaluated in many aspects.
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