CORROSION AND MECHANICAL PROPERTIES OF BIODEGRADABLE Zn-BASED AND Mg-BASED ALLOYS

Zn and Mg based alloys are promising materials for medical implants because the mechanical characteristics of their alloys are close to human bone and zinc and magnesium are relatively non-toxic. In addition, magnesium is well-known for providing optimum corrosion rates under specific conditions. Therefore, in this paper, the corrosion behaviour of these alloys is compared to that of biodegradable materials. Alloys were prepared by casting without protective atmosphere. The microstructure of prepared alloys was observed by light and scanning electron microscopy (SEM). The mechanical properties of the investigated alloys were determined by Vickers hardness measurements at ambient temperature. The corrosion rates of alloy samples were measured by their exposure in a solution with similar characteristics to the body fluid. Corrosion rates were calculated of the decrease weight of the exposed samples per exposure time. Corrosion products on the surface were analysed using X-ray diffraction analysis. The surface of each alloy after the exposure test was documented by scanning electron microscope (SEM). Due to the heterogeneity of structure of magnesium alloys it is possible to observe micro-galvanic cells with the surrounding matrix in the phase structure. Therefore, homogenization of the structure of magnesium alloys was performed and subsequently the same exposure test of obtained alloys was carried out. It was found that the homogenization treatment led to a decrease of corrosion rates. Magnesium alloys in the as-cast condition and after homogenization treatment have higher corrosion rates than zinc-based alloys.