On the influence of corrosion and manufacturing on the very high cycle fatigue behavior of aluminum bronzes

For high performance propulsion systems in medium and large ships, the demand for light and safe propellers is crucial. Nevertheless, those heavy propellers made of aluminum bronze are highly subjected to mechanical and corrosion induced loads due to sea water and have to withstand up to 5·108 load cycles during usage. While guidelines like DNV offer methods for a synthetic life-time assessment of propellers under corrosion, these methods do not imply present material developments, and local changes in the microstructure. Within the research project "Bross" the Mecklenburger Metallguss GmbH and the Fraunhofer Institute for Structural Durability and System Reliability LBF worked on the development of aluminum bronze alloys and a corresponding fatigue design concept for ship propellers. Based on different cast samples the high-cycle and very high-cycle fatigue behavior of copper aluminum alloys was investigated. The fatigue investigations were conducted stress-based under ambient air and sea water. It could be shown that the influence of sea water leads to a reduction in fatigue strength. In this paper, the fatigue strength with regards to corrosion is presented. It is shown that the corrosive effect of sea water is the driving force to fatigue strength reduction.