M. Thomä, G. Wagner, B. Straß, B. Wolter, S. Benfer, W. Fürbeth
Chapter Friction Stir Welding and Processing X, Part of the series The Minerals, Metals & Materials Series, S. 23-32
Ultrasound Enhanced Friction Stir Welding (USE-FSW) is an innovative hybrid method for solid-state joining. This process resulted in remarkably positive findings in the successful realization of hybrid aluminum/magnesium joints as well as in first investigations on the microstructure of aluminum/steel joints due to the parallel and synchronous transmission of power ultrasound into one of the joining partners. The present work investigates the impact of additional power ultrasound on the mechanical properties of AA6061/SAE1006-joints by comparing FSW and USE-FSW. Therefore, light microscopy, as well as scanning electron microscopy, was carried out for examining the microstructure of the joints. Furthermore, mechanical tests on the microhardness of the weld zone of the joints as well as tensile and first fatigue tests were examined. The investigations proved an influence of the power ultrasound by a change in the morphology of the nugget. It showed to be more cleared up and also contains a thinner intermetallic phase of FeAl3 at the interface aluminum to steel. Furthermore, an increase in the tensile strength of the joints of about 15% could be observed. First stepwise load increase tests resulted in slightly different stress levels for the estimated fatigue limit.