Influence of Corrosive Conditions on the Mechanical Performance of Flow Drill Screw Joints between Light Metals

Kurzfassung

The major research project Next Generation Car (NGC) concentrates the expertise of the German Aerospace Center (DLR) in ground based traffic for a sustained and safe mobility of tomorrow. A tool for the automatic selection of joining technologies for multi material design (MMD) is being developed within the NGC project. A particular function of this tool is to consider the increased demand MMD structures place on corrosion resistance. In this paper, the influence of corrosive conditions on the mechanical performance of Flow Drill Screw (FDS) joints is investigated in greater detail. Different combinations of light metals such as high strength/stainless steel, aluminium and magnesium alloys served as the test material. The joint strength, under quasi-static and cyclic loading, of FDS joints was measured before and after six weeks of corrosion climate change testing. Furthermore metallographic sections of the samples were compared in order to evaluate the stage of surface, galvanic and crevice corrosion. To classify the effect of progressing corrosion on the mechanical properties of FDS joints the following factors are taken into account: corrosion resistance of the materials, joining parameters, geometry of the joint, as well as corrosion protection by coating. For all material combinations there is an apparent change in both the fatigue strength and the failure behaviour after corrosion testing. These results confirm that environmental conditions have a significant impact on the structural durability of MMD structures during the lifetime of a vehicle.