Description
Due to its low density, magnesium and its alloys exhibit a high potential to reduce weight in the automotive industry. However, the use of magnesium is often limited by the low corrosion resistance. The scope of the present work is to characterize the corrosive load that derives from hygroscopic Ca2+-containing de-icing salt additives (e.g. CaCl2) by using an electrolyte with and without the addition of Ca2+. The influence of these two electrolytes on the magnesium alloy AM50 was characterized by means of electrochemistry, hydrogen evolution measurements and gravimetric analyses under conditions of galvanic corrosion, immersion and atmospheric corrosion. Surface analysis techniques proved that the deposition of CaCO3 during the corrosion process significantly influences the corrosion mechanisms and it was shown that the addition of Ca2+ to the electrolyte does not increase the corrosive load in general. Furthermore, commercially available corrosion protection systems for magnesium alloys were characterized by means of surface analytical tools and electrochemistry. Within the present work a new and innovative anticorrosive primer is introduced which takes advantage of the interaction of blood with magnesium implants by using simulated body fluids and cell culture mediums (e.g. DMEM). The contact of magnesium surfaces with DMEM triggers the deposition of carbonated calcium phosphates which exhibit a high compactness, a good adhesion to the substrate and a high charge transfer resistance. Electrochemical investigations proved the presence of a distinct passive behavior on a technical wrought magnesium alloy (AZ31) under anodic polarization which has the potential to reduce the anodic dissolution by up to a factor of 1000 compared to selected commercially available conversion coatings. This was accompanied by no significant filiform corrosion at scratches and at stone chip defects after several weeks of INKA-Test.
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