The Fatigue Behaviour of Friction Stir Welded Aluminium Joints

The friction stir welding (FSW) technology enables the production of high-strength joints of light weight metal sheets. In this paper, the fatigue properties of AA5454-FSW-joints will be discussed. High-resolution plastic strain amplitude, temperature and electrical resistance measurements were performed to describe and evaluate the fatigue behaviour in detail. The plastic strain amplitude determined in mechanical stress-strain hysteresis measurements is qualified to describe the proceeding fatigue damage. Additionally, the change in temperature caused by plastic deformation work and measured with thermocouples fixed on the specimen surface allows a precise fatigue assessment. The electrical resistance measurements are directly related to the fatigue-induced defect structure and density in the welding zone. The fatigue behaviour of the welding zone, which corresponds to the specimen gauge length, is characterized by pronounced cyclic hardening leading to a plastic strain amplitude nearby zero. Additionally, results of microscopic investigations of the welding zone are presented for a microstructure-related interpretation of the fatigue properties.