Mechanical properties and corrosion behaviors of Mg-4Zn-0.2Mn-0.2Ca alloy after long term in vitro degradation

An extruded Mg-4Zn-0.2Mn-0.2Ca alloy was developed as potential biodegradable bone-plate due to its excellent biocompatibility. Long term in vitro immersion in Hank's solution and bending test were used to evaluate the degradability and the mechanical integrity of the alloy. The results revealed that the degradation rate of the bone-plate increased in the first 7 days and then decreased with the prolonged immersion time before it finally reached a steady stage (about 0.84 mm/a) after immersion for 90 days. The bending strength after immersion for 60 days was 67.6 MPa, indicating that the bone-plate could support certain mechanical load after long term degradation. The formation of corrosion pits after degradation stemmed from the separation of the continuously distributed second phases from Mg matrix under the action of micro-galvanic couples. As a result, the mechanical performance of Mg-4Zn-0.2Mn-0.2Ca alloy was aggravated owing to the corrosion holes on its surface.