Mechanical and Corrosion Properties of Mg-Based Alloys with Gd Addition

Magnesium alloys with rare earth metals are very attractive materials for medical application because of satisfactory mechanical properties. Nevertheless, low corrosion resistance is an obstacle in the use of Mg alloys as resorbable orthopedic implants. The paper presents results of mechanical and corrosion properties of MgCa5-xZn1Gdx (x = 1, 2, and 3 wt. %) alloys. Based on the microscopic observations it was stated that the studied alloys show a dendritic microstructure with interdendritic solute rich regions. The phase analysis reveals an occurrence of α-Mg and Mg₂Ca, Ca₂Mg₆Zn₃ phases that are thermodynamic predictions, and stated Mg₂₆Zn₅₉Gd₇ phases in MgCa5-xZn1Gdx (x = 1, 2, and 3 wt. %) alloys. The Mg₂₆Zn₅₉Gd₇ phases are visible as lamellar precipitations along interdendritic regions. It was confirmed that an increase of Gd content from 1 to 3 wt. % improves ultimate tensile (R_m; from 74 to 89 MPa) and compressive strength (R_c; from 184 to 221 MPa). Moreover, the studied alloys are active in Ringer's solution. They are characterized by an increase of corrosion potential (E_corr) of about 150 mV in comparison with values of open circuit potential (E_OCP). The best electrochemical parameters (e.g., corrosion current density, i_corr, polarization resistance, R_p, and E_corr) were obtained for the MgCa3Zn1Gd2 alloy.