Fatigue Crack initiation Mechanism of Aluminium Alloy Welded Joint In Gigacycle Fatigue

摘要

Ultrasonic fatigue test was performed on 5052 aluminium alloy welded joint to investigate the very high cycle fatigue properties and the fatigue crack initiation mechanisms with the help of microhardness tester and scanning electron microscope (SEM). The results showed that the hardness of fusion zone was higher that base metal and heat affected zone, which led to the embrittlement of welded zone. Fusion zone became the weakest part of welded joint under cyclical loading. Fatigue crack usually initiated from the pores beneath the surface from the SEM observation of fracture surface. The influence of pores on the fatigue crack initiation was analyzed to figure out the deterioration of fatigue strength for welded joint as compared with base metal.