Increasing requirements for energy saving and emission reduction provide a favorable framework for the extended use of magnesium (Mg) alloys for lightweight design. During application, Mg components are subjected to a variety of corrosive and mechanical loads, while the deformability of the hexagonal lattice is limited by the number of slip systems and the lack of cross-slipping. In contrast to dislocation motion, twinning is only possible when deformation occurs in tensile direction perpendicular to the basal plane or in compressive direction parallel to the basal plane. In extruded Mg profiles, this influences the macroscopic material properties due to pronounced textures. Furthermore, the comparatively low corrosion resistance of Mg alloys is still one of the major obstacles preventing their widespread use in corrosive applications. The characterization of the corrosion behavior as well as the previously described texture represents an important basis for alloy development and the production of optimized pre-products to exploit the potential of Mg alloys.
The study aims to investigate the microstructural and corrosive properties of extruded Magnesium-Zinc alloys (Mg-2Zn, Mg-1Zn) with varying contents of Yttrium (Y) and Calcium (Ca). For a time-efficient screening of alloy compositions, cast and homogenized samples were characterized in terms of microstructure (SEM, EDX) and corrosion properties (potentiodynamic polarization). On this basis, promising alloys were selected for subsequent extrusion with varying process parameters. The samples were evaluated for microstructural details, in particular, texture by EBSD and corrosion properties by a combined approach of immersion tests and corrosion morphology investigation. Instrumentation of the immersion tests using a eudiometer and intermittent electrochemical impedance spectroscopy allowed conclusions to be drawn about the time-dependent corrosion rate, passivation and pitting tendencies. For both alloy classes (Y and Ca), a strong dependence on the alloy composition and extrusion parameters was found. It was possible to reduce the corrosion rate by a factor of 5 (Mg-2Zn) or 6 (Mg-1Zn) compared to the initial condition by the appropriate addition of alloying elements.