Influence of Friction Stir Weld Parameters on the Corrosion Susceptibility of EN AW-7075 Weld Seam and Heat-Affected Zone

Friction stir welding enables joining of high-strength, lightweight aluminum alloys, e.g., EN-AW-7075, below the melting point by induced plastic deformation. Therefore, heat transfer into the adjacent regions beneath the weld seam is significantly reduced as compared to fusion welding processes such as laser beam welding. However, specific zones along the weld seam area are susceptible to localized corrosion due to grain growth and the precipitation of intermetallic phases. Thus, several approaches toward lowering the corrosion susceptibility of the heat-affected zone are presented. Special interest is given to increasing the plastic deformation by the use of novel multipin welding tools that eventually facilitate reduced heat input during welding as a result of substantially lower tool revolutions. The corrosion behavior is tested by means of full material immersion tests and electrochemical measurements which provide insight into the corrosion kinetics. Using pre- and postmortem microstructural analysis, the mechanisms influencing the initiation of corrosion can be identified. Supported by in-operando temperature measurements, the varied welding parameters and their interrelationships to corrosion resistance can be derived. Furthermore, recommendations on optimal welding parameters to obtain enhanced corrosion resistance can be deduced.