Research On Mg-Ca Alloys And Their Corrosion Behavior In Simulated Body Fluids

The attentions are recently focused on the study of new medical magnesium alloys. Calcium, being an essential element in human body, can be applied in medical magnesium alloys as an alloying element.The microstructure and corrosion morphology of Mg-Ca (0.5-1.5% Ca) alloys were observed by means of an optical microscope and scanning electron microscope. The tensile propertiesof the alloys and the influence of their content of calcium microstructure, heating treatment and the extruded microstructue on them were investigated. The immersion tests to get weight loss and gas evolution as well as potentiodynamic electrochemical technique were employed to study corrosion behavior of the above alloys and influence of temperature and anions such as Cl^-,SO₄^2-,CO₃^2-,PO₄^3- and glucose as well on corrosion. Energy dispersive spectrum (EDS), X-ray diffraction analysis (XRD) were used to characterize the structure and composition of the alloys and its corrosion products.The results showed that for the as-cast Mg-0.5Ca, Mg-1.0Ca and Mg-1.5Ca alloys, the grain size decreases, the hardness increased, and elongation to failure decreased with increasing the Ca contents, but the tensile strength and yield strength of Mg-0.5Ca alloy are highest among the three alloys. when. The mechanical property was improved by heat treatment, particularly the solution treatment. Grains in the microstructure refined and the hardness, tensile strength and yield strength increased through an extrusion process.The corrosion rate of as-cast Mg-Ca alloys in Hank's solution decreases in the order: MX3>MX1>MX2. The corrosion resistance was enhanced by heat treatment, specially the solution heat treatment. The corrosion rate was greatly decreased after the extrusion. For instance, the corrosion rate of Mg-1.5Ca alloy slowed down one order of magnitude. The corrosion resistance of the extruded alloys decreases in following order: MX2>MX1>MX3. The corrosion types of the cast and extruded alloys are pitting corrosion and filiform corrosion as well as intergranular corrosion. Pitting corrosion and filiform corrosion occurred after solution treatment and ageing treatment.CO₃^2- PO₄^3- and glucose can slightly inhibit the corrosion of Mg-Ca alloys in Hank's solutions. The corrosion products (Ca, Mg)CO₃ and Ca₂Mg(PO₄)₂·2H₂O formed on the surfaces of samples increase the corrosion resistance of Mg-Ca alloys. Whereas, the anion Cl^- reduced the corrosion resistance of the calcium containing alloys in Hank's solutions. and trace of SO₄^2- ions had insignificant impact on corrosion rate.