Desenvolvimento microestrutural, resistências mecânica e à corrosão de ligas Mg-Si e Mg-Si-Zn para aplicações biomédicas

Abstract

The absorbable alloys, especially those based on Mg, have stood out in biomedical applications due to the possibility of eliminating the need for implant removal surgeries. In the scope of this PhD study, Mg-0.6%Si, Mg-1.3%Si, Mg-1.7%Si, Mg-0.6%Si-2%Zn, and Mg-0.6%Si-3%Zn alloys were examined using the directional solidification technique. This technique allowed for a wide range of cooling rates, enabling a comprehensive evaluation of microstructural characteristics and tensile mechanical properties. Additionally, the corrosion behavior of two microstructural conditions (𝜆2 of 11 and 41 μm) of the Mg-0.6%Si-2%Zn alloy in SBF (simulated body fluid) for 7 days was analyzed. In general terms, microstructures composed of Mg-rich dendrites and eutectic microconstituent (Mg+Mg2Si) were observed in Mg-0.6%Si, Mg-0.6%Si-2%Zn, and Mg-0.6%Si-3%Zn alloys. In ternary alloys, structures composed of the eutectic microconstituent Mg+MgZn were also identified for low cooling rates (below 0.48°C/s for the 2%Zn alloy and 0.44°C/s for the 3%Zn alloy). In the case of the Mg-1.3%Si alloy, predominantly a eutectic cellular microstructure (Mg+Mg2Si) was observed, while the Mg-1.7%Si alloy exhibited a typical structure of hypereutectic alloys in the Mg-Si system. The Mg-0.6%Si alloy showed a higher tensile strength limit compared to the Mg-1.7%Si alloy, due to the increase in the Mg2Si fraction with increasing Si, an effective phase in stress concentration. On the other hand, the Mg-1.3%Si alloy, composed of the eutectic microconstituent, revealed a clear dependence between tensile strength limit and cell spacing, being the worst among the three binary alloys. In the case of ternary alloys, the higher the Zn content, the higher the mechanical strength. Corrosion analysis allowed evaluating the electrochemical characteristics throughout the transient regime and the apparent stabilization during the immersion period. The results obtained in the analysis of the Mg-0.6%Si-2%Zn alloy indicate that the electrochemical response is little influenced by dendritic spacing.