Research On Properties And Controlling The Degradation Rate Of Mg-Zn-Sr-Ca Alloys

Magnesium alloy is a light weight metal with mechanical properties similar to natural bone, moreover magnesium is playing an important role in biological systems of human. But the corrosion resistance of magnesium alloy is poor, it limits the using of magnesium alloy as implant material for load-bearing. Therefore how to control the degradation rate ofmagnesium alloys and improve the biological activity have become a hot researchtopic in recent years.Mg-Ca alloy was investigated for biomedical application due to the biological function of Ca in the human body.In this paper, we developed theMg-2.67%Zn-0.99%Sr-0.34%Ca, Mg-2.87%Zn-1.25%Sr-0.62%Ca alloys by squeezing casting and extrusion technology. The coatings formed on the magnesium alloy were characterized by XRD, and the morphology of sample surfaces were observed by SEM. The samples were subsequently immersed in the simulated body fluid (SBF) for the degradation test. The results are summarized as follows:(1) DevelopedMg-2.67%Zn-0.99%Sr-0.34%Ca alloy and Mg-2.87%Zn-1.25%Sr-0.62%Ca alloy have good properties, whose tensile strength are275MPa,275MPa;yield strength are210MPa,230MPa;elasticmodulus are50.11Gpa,42.57Gpa;elongation rate maximum are16.00%,11.60%;compression strength are460.33MPa,452.37MPa;dimensional hardness are58.02,55.83; density are1.767g-cm"3,1.771g-cm"3.(2) The coatings on the surface of Mg-2.67%Zn-0.99%Sr-0.34%Ca and Mg-2.87%Zn-1.25%Sr-0.62%Ca alloys were produced using biomimetic technique. The uniform and compact coatings are mainly composed of Ca10(PO4)6(OH)2(abbreviated to be HA) by X-ray diffraction.(3) The corrosion potential Ecorr of Mg-2.67%Zn-0.99%Sr-0.34%Ca alloy and its HA coating sample were-1.70V and-1.63V, respectively. While the corrosion current densities of them were2.91×10-4A·cm-2,2.26×10-5A·cm-2, and the corrosion resistance of them were 85Ω,205Ω. And the corrosion potential Ecorr of Mg-2.87%Zn-1.25%Sr-0.62%Ca alloy and its HA coating sample were-1.70V and-1.53V, respectively. While the corrosion current densities of them were1.43×10-4A·cm-2,4.61×10-5A·cm-2, and the corrosion resistance of them were83Ω,135Ω; Electrochemical results clearly show corrosion resistance of the alloy with coating is higher than that of the alloy without coating.(4) Hydrogen evolution of the Mg-2.67%Zn-0.99%Sr-0.34%Ca alloy without coating and the alloy with coating after15days of immersion in SBF were318ml,172ml respectively. While hydrogen evolution of the Mg-2.87%Zn-1.25%Sr-0.62%Ca alloy without coating and the alloy with coating after15days of immersion in SBF were472ml,179ml respectively. The hydrogen evolution reaction rates of the samples with HA coating were much lower than Mg-Zn-Sr-Ca alloy without coaying(5)Weight loss of the Mg-2.67%Zn-0.99%Sr-0.34%Ca alloy without coating and the alloy with coating after21days of immersion in SBF weight loss were11.28%,6.35%; while the weight loss of the Mg-2.87%Zn-1.25%Sr-0.62%Ca alloy without coating and the alloy with coating were19.58%,12.44%. The coating also make the weight loss of the Mg-Zn-Sr-Ca alloy was reduced. HA coating on both alloys can improve electrochemical corrosion resistance and resistance to general corrosion in SBF solution.