Structure and mechanical properties of an Mg-Zn-Zr alloy subjected to the high-pressure torsion extrusion

Magnesium is the lightest structural metal with ρ = 1,74g/cm³. Its alloys are used in the automotive sector as well as in the aircraft industry. Another area of application of magnesium alloys is the medical field where it is used in stents and implants (fig.1). Magnesium is characterized in this field by its good biocompatibility and mechanical properties that are close to those of human bone [2,3]. The low corrosion resistance that magnesium exhibits can be used here. If properly controlled, implants made of magnesium alloys can become bioresorbable, which means that they will dilute in the body after they have served their purpose [2,3]. Influences on the corrosion resistance can be alloy additions, the manufacturing route, and the microstructure [4]. Severe Plastic Deformation (SPD) processes [5] are one set of manufacturing processes that can be used to increase the ductility and the strength of magnesium alloys and influence the microstructure drastically.
In the current project, the magnesium alloy ZK30 is deformed by High Pressure Torsion Extrusion (HPTE, cf. fig.2) [6] under different conditions to develop a fine granular microstructure. The fatigue strength and the corrosion behaviour of the specimens created in this process are subsequently tested. For this purpose, quasi-static and cyclic three-point bending tests are used with and without superimposed corrosion. NaCl and phosphate-buffered saline (PBS) serve as electrolytes in the tests with corrosion. Where PBS is used as it mimics human bodily fluids better than NaCl. The results are expected to give first indications whether the magnesium alloy ZK30 deformed by the corresponding HPTE routes can be a promising material for bioresorbable implants.

Literatures:

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[2] M.P. Staiger, A.M. Pietak, J. Huadmai, G. Dias, Magnesium and its alloys as orthopedic biomaterials: A review, Biomaterials 27 (2006), pp. 1728-17334, doi.org/10.1016/j.biomaterials.2005.10.003

[3] Y. Chen, Z. Xu, C. Smith, J. Sankar, Recent advances on the development of magnesium alloys for biodegradable implants, Acta Biomaterialia 10 (2014), pp. 4561-4573, dx.doi.org/10.1016/j.actbio.2014.07.005

[4] C. op’t Hoog, N. Birbilis, M.-X. Zhang, Y. Estrin, Surface grain size effects on the corrosion of magnesium, Key Eng. Mat. 384 (2008), pp 229-240, doi.org/10.4028/www.scientific.net/KEM.384.229

[5] A. Vinogradov, Effect of severe plastic deformation on tensile and fatigue properties of fine-grained magnesium alloy ZK60, J. Mater. Res. 32 (2014), pp. 4362-4374, doi.org/10.1557/jmr.2017.268

[6] Y. Ivanisenko, R. Kulagin, V. Fedorov, A. Mazilkin, T. Scherer, B. Baretzky, H. Hahn, High Pressure Torsion Extrusion as a new severe plastic deformation process, Mater. Sci. Eng. 644 (2016), pp. 247-256, doi.org/10.1016/j.msea.2016.04.008

Contact person:

M. Sc. Stella Diederichs