Fatigue strength improvement by ultrasonic impact treatment of highly stressed spokes of cast aluminium wheels

This paper reports on the application of the ultrasonic impact treatment on spokes of cast aluminium (AlSi11Mg) wheel spiders and its influence under spectrum loading. After preliminary investigations with specimens removed from the spokes for the adjustment of the treatment parameters, fatigue tests, measurement of residual stresses and metallographic analyses of untreated and treated spokes were performed. The mechanical impacts of the UIT effected a significant change of the microstructure, porosity and hardness. The application of the ultrasonic impact treatment introduced plastic deformations and consequently compressive residual stresses at the surface. The fatigue strength increased significantly compared to the untreated spokes under constant and variable amplitude bending loading. The UIT-technology promises a high potential for improving of the structural durability and safety and the saving of material in the production of cast aluminium wheels.