Effects of cooling rate on the biocorrosion, microstructure and mechanical properties of biomedical Mg-2Zn-0.5Sr-0.3Ca alloy

Abstract Effects of cooling rate on microstructure, biocorrosion behavior and mechanical properties of Mg-2Zn-0.5Sr-0.3Ca alloy prepared by water-cooling copper mold casting (material I) and steel mold casting (material II) were investigated by microstructure analysis, tensile studies, microhardness testing, electrochemical measurements and immersion test in SBF solution (simulated body fluid). Microstructural studies show that both materials are composed of α-Mg, Mg 17 Sr 2 and Ca 2 Mg 6 Zn 3 phases. The higher cooling rate in material I results in the finer grain size and well-distributed second phases. Material I shows the enhanced UTS (159 ± 4 MPa) and YS (70 ± 3 MPa). Moreover, fracture elongation of material I improves from about 8.9% to 16.3%. However, material II shows less corrosion current density (1.95 ± 0.12 µA·cm − 2 ) and better corrosion resistance. The higher fraction of secondary phases, together with the discontinuity of grain boundaries leading to more galvanic cells in material I, may help the propagation of galvanic corrosion. Larger impedance is obtained for material I which changing trend is well in accordance with the polarization curves and bode phase angles.