چكيده به لاتين
In this study, the Mg-2Zn-0.5Sr-0.3Ca alloy was cast using several molds, including a water-cooled copper mold (with a diameter of 10 mm), a steel mold (with a diameter of 40 mm), and a stepped mold with step thicknesses of 6, 12, and 18 mm. The alloy was subsequently homogenized at 400°C for 12 hours. The objective of this research was to investigate the effect of increased cooling rates, achieved by varying the mold type and size, on the microstructure, corrosion behavior, and mechanical properties of this alloy for biomedical applications. The samples in this study included castings in the copper mold (CM), castings in the steel mold (SM), homogenized samples (CMH and SMH), and samples from the stepped mold (StH1, StH2, and StH3). The surface microstructure of the samples was examined using optical microscopy (OM), scanning electron microscopy (SEM), and field emission scanning electron microscopy (FESEM). X-ray diffraction (XRD) analysis, electrochemical corrosion tests, immersion tests, uniaxial tensile testing, and microhardness measurements were also conducted to assess the properties of the samples. XRD results revealed that the microstructure of the samples consisted of α-Mg, Ca2Mg6Zn3, and Mg17Sr2 phases. According to energy-dispersive X-ray spectroscopy (EDS), the Ca2Mg6Zn3 and Mg17Sr2 phases were secondary phases located primarily at grain boundaries and as spherical precipitates. Microstructural analysis showed that the CMH sample had an average grain size of approximately 37 μm, while the SMH sample had a grain size of 95 μm. The stepped mold samples exhibited grain sizes of 53.7 μm, 79.8 μm, and 97.7 μm for StH1, StH2, and StH3, respectively. Corrosion behavior was evaluated using electrochemical corrosion tests in simulated body fluid (SBF), revealing that the increased cooling rate in the CMH sample led to a higher corrosion current density (4.45 µA/cm²) compared to the SMH sample (1.95 µA/cm²). Polarization results for the stepped mold samples indicated that StH1 had the highest corrosion current. Impedance test results also demonstrated higher corrosion resistance in the SMH sample. Immersion tests in SBF showed that the increased cooling rate promoted faster formation of corrosion products on the surface of the CMH sample, which slowed the corrosion process. However, over longer exposure times, the SMH sample exhibited lower corrosion rates due to fewer galvanic corrosion sites. Mechanical property tests, including hardness and uniaxial tensile tests, indicated that the finer grain size and increased precipitation in the CMH sample resulted in higher hardness. The stress-strain curve from the tensile test showed that increasing the cooling rate led to an increase in yield strength from 59 MPa to 70 MPa and in ultimate tensile strength from 128 MPa to 159 MPa.
