Investigation On Microstructure, Mechanical Properties And Corrosion Resistant Performance Of Mg-Mn-Ca Alloys

At present, many researches have been taken on the magnesium alloys that are applied inthe field of engineering, the application technology is already relatively mature. Although thepoor corrosion resistance of magnesium alloys limits its application in some areas, but in thefield of biodegradable materials magnesium alloy has a very big advantage. Magnesiumalloys have good mechanical properties, but it is easy to corrosion, and its elastic modulus isvery close to humanbodybone tissue’ modulus. So magnesium alloy is a potential degradablebone implants metal materials for bone surgery. But the corrosion rate of magnesium alloy istoo fast that make its application in the field of medical biological greatly circumscribed. Sothe purpose of this research is to study the corrosion behavior of magnesium alloy under thesimulated conditions of human body fluids (SBF solution) in vitro, to find the magnesiumalloy with lower corrosion rate which can be accepted by human body.The Mg-2Mn-xCa(x=0.81.01.2wt%) alloys were prepared by metal mold castingmethod. Then the alloys were subjected to heat treatment. The microstructure, phaseconstituents, component distribution and mechanical properties were investigated by means ofoptical microscope, X-ray diffraction (XRD) analysis, scanning electron microscope(S EM)and universal mechanical tensile testing machine. The corrosion behavior of magnesium alloyin the S BF solution in vitro were researched by testing the hydrogen gas production curve andthe corrosion polarization curve getting from the electrochemical workstation.The results showed that, with the increase of calcium content, the grain size of the as-castalloy and solid solution state alloy are tapering, but after solid solution treatment the grainbecome bigger than the as-cast alloy. The as-cast alloy is mainly composed of α-Mg matrix,reticular eutectic Mg2Ca phase formed along the grain boundary and granulate β-Mnprecipitated phase distributed on the α-Mg matrix. Through the solid solution treatment, theeutectic Mg2Ca phase have been dissolved in the Mg matrix, the grain boundary became thin and uniform, the simple substance β-Mn precipitated phase became long and thin strip orsmaller granularity aging precipitated phase distributed on the α-Mg matrix. The mechanicaltensile testing results showed that, the tensile strength of the as-cast alloy and solid solutionstate alloy increase with the calcium content, while the ductility decrease with the calciumcontent. After the solid solution treatment, the tensile strength and du ctility of the alloys ishigher than the as-cast alloys.The hydrogen gas production curve results showed that, after immerse in the SBFsolution for more than56hours, we found that the hydrogen evolution rate of1.0Ca(T4) alloyis the lowest, and after solution treatment the hydrogen evolution rate of the same componentsample has been obviously decreased. F rom the polarization curve we can get that, neither theas-cast nor the solution treated state alloys, the corrosion potential of the1.0Ca(T4) alloy isthe highest, in other words the1.0Ca(T4) alloy has the best corrosion resistant ability. Thecorrosion potential of the1.0Ca(T4) alloy is higher than the1.0Ca as-cast alloy. With theincrease of calcium content, the corrosion current density is decreasing, the solution treatedalloy’ corrosion current density is lower than the as-cast alloy, that1.0Ca(T4) alloy’ corrosionrate is the lowest. The testing results of the alloys’ corrosion current density is in line with thehydrogen evolution test, during the alloys researched in this paper,the Mg-2Mn-1.0Ca alloyboth in the as-cast state and the solution treated state have the lowest corrosion rate. And aftersolid solution aging treatment, the alloy corrosion resistance is significantly better than theas-cast alloy. This is mainly due to that after solid solution treatment, the precipitated phasedistributing on the grain boundary have dissolved in the α-Mg matrix, which improved thegrain boundary corrosion resistant performance of the alloy, and also the alloy corrosionresistant performance is overall improved. Therefore the1.0Ca alloy’s corrosion rate is thelowest and the corrosion resistant property is the best.