Materials for Lightweight Construction

The susceptibility of high-strength aluminium alloys to intercrystalline corrosion still represents a great challenge in the development of these classes of materials. Intergranular corrosion; a form of corrosion in which the grain boundaries are preferentially dissolved and, owing to its deep penetration, can represent considerable safety risks, is considered as a potential initiator and promoter of stress corrosion cracking. On superposing the corrosive attack with mechanical stresses, SCC can lead to catastrophic component failure in high-strength aluminium alloys - in particular in Al-Zn-Mg-(Cu) alloys.

In the KKS (department for Corrosion and Corrosion Protection), intergranular corrosion and SCC are primarily investigated on precipitation-hardened wrought alloys and the corrosion mechanisms are correlated with the microstructural attributes. The grain boundaries and matrix precipitates, the dislocation density and structure, texture, stress state and other material parameters which are specifically set by means of forming and manufacturing processes as well as by heat treatment are the focus of the investigations.

As a light-weight, engineering metal, magnesium and its alloys are very important for light-weight constructions. At the same time, it is also necessary to further optimise the comparably low corrosion resistance of magnesium alloys in order to further exploit this material group’s enormous potential for light-weight constructions.  The research in the department of corrosion and corrosion protection concentrates on the microstructural optimisation of material properties by identifying the corrosion mechanisms at the micron and nano scales. Here, on the one hand process-led optimising is performed by means of conventional manufacturing methods (hot-rolling, extrusion, sand, die and pressure casting) and unconventional processes (thixomoulding, continuous roll-casting, and special casting technologies) and on the other hand, by means of alloy development.

Hybrid structures and components which are composed of different materials and thus combine the individual strengths of various material systems together in order to obtain the maximum performance for minimal weight. An essential, safety relevant challenge consists of reducing the susceptibility of hybrid components to corrosion, which are dependent on the employed material combinations’ propensity to contact corrosion.  By means of innovative coating systems, which can be applied either during or after the hybrid structure’s manufacture, the KKS hastens the optimisation of these new types of components for applications in modern, light-weight structures.

Advanced high-strength steels are highly susceptible to hydrogen-induced stress corrosion cracking (SCC), also known as hydrogen embrittlement (HE), which limits their application in many fields. During manufacture processes and in service, hydrogen atoms can easily dissolve into high-strength steels, locate at interstitial lattice sites and become trapped to various degrees at material defects. Upon application of stresses, hydrogens present in steels can cause a deterioration of mechanical properties leading to severe failures.

At the chair of corrosion and corrosion protection, the effects of hydrogen on the mechanical properties of high-strength materials are investigated considering microstructures, hydrogen content and material stress states. The hydrogen uptake, diffusion and trapping in materials as well as fracture behaviors are focuses of the research.