Microstructure and Properties of AA 2195 T8 Material and Friction Stir Welds

Abstract

The study shows the main properties of AA2195 in relation to the microstructure developing in the friction stir weld process, which were comprehensively investigated in the ESA Technology and Research Programme Damage Tolerance of Cryogenic Pressure Vessels (TRP T401-02 MC). Friction Stir Welding (FSW) on 5 mm sheets of AA2195 in T8 condition was performed and process parameters were optimized. Non-destructive Inspection (NDI) methods were used to detect potential defects and metallographic investigations were applied in order to detect their origin. The properties on the friction stir joints were determined and the influence of temperature down to 20 K is shown. Particular attention is given to the microstructure and the fracture characteristics of the friction stir welds and base material. Optical and scanning electron microscopy investigations are used to determine the failure mode. Additionally, the influence of temperature is discussed on the basis of samples fractured at RT, 77 K, 20 K and 4 K. The metallographic analysis of NDI results of friction stir welds indicates that a thorough process control can avoid the main large defects in FS welds. High strength FSW joints of AA2195 can be achieved with promising toughness down to cryogenic temperatures. The potential for the application in future launcher systems is discussed with respect to potential future serial production