For the implementation of lightweight concepts, multi-material concepts are increasingly being used in the modern vehicle bodies. Joining ultra-high-strength steels with aluminum poses a particular challenge for the joining technology. Self-piercing riveting is an important technology for this. The rivets may reach tensile strengths up to 2000 MPa, which means they are capable to connect even high strength steels safely. However, due to the high strengths resulting from the presence of martensitic microstructure, the self-piercing rivets have an in-creased potential for hydrogen-assisted cold cracking (HACC).
As part of a research project funded from the Federal Ministry of Education and Research (BMBF) in Germany, specimens are to be accumulated with hydrogen by using cathodic hydrogen charging. These specimens are then subjected to a mechanical test under constant load. The measurement of the diffusible hydrogen content and its diffusion rate is carried out by thermal desorption analysis (TDA) using a quadrupole mass spectrometer. The project’s objective is to determine the critical load of the specimen as a function of the hydrogen concentration profile in the component. The hydrogen distribution in the specimen is calculated and adjusted using diffusion equations. The concentration profile is set by a controlled variation of the parameters for the electrolytic charging as well as a modulation of the desorption time. In addition, this should be supported using diffusion laws trough a comparison of the diffusion coefficient, average hydrogen concentration and the hydrogen concentration at the edges of the specimen during electrolytic charging.