Ultra-fine grained degradable magnesium for biomedical applications

Properties of commercially available purity magnesium and wrought ZM21 Mg alloy were investigated in view of their biodegradable applications. In particular, the opportunities offered by grain size refinement down to the ultra-fine scale achieved by equal channel angular pressing (ECAP) and warm extrusion were discussed and material properties were analyzed. Results show that the grain refinement will lead to a significant improvement in compression strength. The tension strength of the coarse grained alloy is always significantly higher than that measured in compression due to the sharp texture of the starting wrought alloy. ECAP also causes an attenuation of the above texture effects, promoting marked changes in plastic flow behavior. The corrosion behavior of the investigated materials are affected by a combination of microstructural effects such as chemistry, grain size and the extent of lattice distortion inherited from previous processing stages. ECAP leads to refinement of grain size and to increased lattice defect density which apparently produce counterbalancing effects on corrosion performance. The improved dispersion of second-phase particles brings positive effects on development of pitting.