Continuous advancements in the electrification of the whole automotive industry rely heavily on the use of lightweight materials. Due to the overall requirements for mass reduction that such rapid development imposes, lightweight materials such as aluminum play a major role in the optimization and development of powertrain components and vehicles while at the same time ensuring the structural integrity of the system. In the introduction of this thesis a short overview of the four most common fatigue assessment methods is given which includes the description of the approaches based on nominal stress, structural hot spot stress, and effective notch stress as well as the crack propagation analysis. In the continuation of the thesis the focus will be on the fatigue assessment of weld seams joining extruded aluminum profiles with the use of modern-day fatigue assessment tools. A closer look will be given into the notch stress-based method behind FEMFAT Weld analysis tool and its benefits for the weld seam fatigue investigations. The fatigue assessment method for welded components proposed by FEMFAT Weld will be validated on an example of welded aluminum profiles from the literature before final experimental investigations begin. In the main focus of the work will be the high cycle fatigue testing of two different weld seams, I-seam butt weld and corner fillet weld, both made of extruded aluminum profiles. Along with the high cycle fatigue testing, additional microscopic measurements of the weld geometry and hardness will be performed. The results of such investigations will be used to conduct a thorough investigation of FEMFAT Weld in order to understand the notch stress methods that are being used and apply them in the desired way. The final results of fatigue assessment with the use of FEMFAT Weld analysis tool will be compared to the results from high cycle fatigue tests and certain conclusion will be drawn. In the end the work from this thesis will represent a detailed overview of FEMFAT Weld assessment tool and clear instructions on how to customize it to specific needs in respect to weld fatigue assessment.