| The magnesium (Mg) alloys are characterized by low specific density, appropriatemechanical properties and good biocompatibility. However, the most importantembarrassments are the poor corrosion properties, lack of anti-corrosion technology andthe corrosion mechanism analysis in the application of Mg biomaterials.In the present work, the improved zone solidification casting method, backwardextrusion technology and alloying elements are employed to improve the corrosionproperties of Magnesium (Mg) based alloys. The alloying elements are Zinc (Zn), Calcium(Ca) and Dysprosium (Dy). The identify methods are microstructures, includingmetallography and corrosion morphology; corrosion tests, including open circuit potential(OCP), electrochemical impendence spectroscopy (EIS) and polarization curves (LP);corrosion products detections, including X-Ray diffraction and energy spectrum.According to the experiment results, backward extrusion is contributed to therefinement and homogenization of structure and corrosion resistance. Alloying element ofCa acts as grain refiner and purifying agent in Mg-Zn alloys, which can be attributed tothe enhancement of corrosion resistant. As the addition of Ca is more than0.8wt.%, theextra Ca element tends to generate micro-galvanic couples. Consequently, the protectivefilm on the alloy surface tends to be broken, and the improvement of the corrosionresistance decreases. Dy element in Mg alloys can accelerate the formation of Long-periodStacking Ordered (LPSO) structure. Under different heat-treatment condition, there can betwo kinds of LPSO phase exist in Mg-Dy-Zn alloy, which is18R-type or14H-type LPSO.As the results of OCP, EIS, LP and corrosion morphology, the as-cast alloys containing14H type LPSO exhibits more corrosion resistance due to the uniformed and compactprotective film on the surface compared to the heat-treated alloys containing18R typeLPSO. |
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