Solid-state welding of light alloy components. The thesis is about new solid-state welding process called Friction Stir Welding. The first part consists of a brief explanation of how it works, what are the main properties of the tool used and what are the parameters needed to be set in order to get a good welded joint. Then, after a deep research into literature, reading books and various papers, the design of some welding tools with a special pin and shoulder and them own proper adapter has been performed in order to be able to weld Aluminium Alloys sheets with different thickness (1.5 mm and 2.5 mm) and arranged so that butt and lap joint could be obtained.