Realization of Ultrasound Enhanced Friction Stir Welded Al/Mg- and Al/Steel-Joints: Process and Robustness, Mechanical and Corrosion Properties

Abstract

As an innovative hybrid joining process ultrasound enhanced friction stir welding (USE-FSW) was successfully applied on Al/Mg-joints and offers a beneficial impact on the resulting microstructure and mechanical properties. Whereas in conventional FSW of Al to Mg continuous band-shaped intermetallic layers of Al₃Mg₂ and Mg₁₇Al₁₂ are always present, the formation of these layers can be influenced positively by the ultrasound energy that is transferred into the stirred zone in USE-FSW. In this case, the intermetallic phases are spread over the complete nugget zone. Consequently, the tensile strength increases about 25% and the fatigue strength rises by up to 3.5 times. Based on this USE-FSW was investigated with regard to possible advantages for Al/steel-hybrid-joints. Preliminary investigations have shown significant differences in the microstructure of ultrasound enhanced and non-ultrasound enhanced EN AW-6061/DC04-joints. While conventional FSW led to hooks and larger particles of steel in the aluminum, USE-FSW-joints show remarkably smaller and more homogenous distributed steel particles in the nugget. Beside mechanical investigations, non-destructive examinations and corrosion tests were carried out.