| As the population ages and the number of fractures caused by various accidents increase gradually,the proportion of people who need to repair damaged bones is increasing year by year.Bone plate?internal fixation?is one of the most effective methods to treat fractures?fractures,open fractures,comminuted fractures?.Its material properties,mechanical properties and biocompatibility are the main factors affecting the safety and effectiveness of surgery.The mechanical properties of commonly used bone plate materials?such as titanium alloy,stainless steel,cobalt-based alloy,etc.?are quite different from that of human bone,and toxic substances will be released.Therefore,there will be a"stress shielding effect"and toxic side effects.With the further exploration of medical metal materials by researchers from various countries,magnesium alloy has similar mechanical properties to human bone.Moreover,it has unique characteristics of biocompatibility and degradability.It expects to replace the traditional medical metal materials and become the preferred degradable metal materials in the field of medical implant materials.At the same time,the corrosion rate of magnesium alloy is difficult to match the healing rate of human bone,and the mechanical properties need to be improved,which limits its full application.Because of this,magnesium calcium zinc alloy with different composition content was prepared by powder metallurgy method.The aim is to change the mechanical properties and corrosion resistance of the alloy by adding appropriate alloying elements to meet the needs of medical implant materials.In this paper,five magnesium alloy materials with different calcium and zinc contents?mass fractions:Mg-0.4%Ca-0.5%Zn,Mg-0.8%Ca-1.0%Zn,Mg-1.2%Ca-1.5%Zn,Mg-1.6%Ca-2.0%Zn,Mg-2.0%Ca-2.5%Zn?were prepared by powder metallurgy method.The microstructure and mechanical properties of the prepared magnesium calcium zinc alloys were tested and analyzed.EDS component test,XRD phase composition analysis and metallography microstructure observation.These three methods used to observe the internal structure of magnesium,calcium and zinc alloy powder metallurgy.Furthermore,it found that the internal structure was uniform and dense,and the sintering effect was good.The mechanical properties of magnesium calcium zinc alloy were measured by Vickers hardness test,quasi-static compression test and tensile test.The best mechanical properties of alloy?,Vickers hardness is 132.27 HV,tensile strength of 231.71 MPa.The corrosion resistance and abrasion resistance of magnesium calcium zinc alloy were tested.The magnesium alloy sample was placed in Hanks simulated body fluid for immersion corrosion test.The weight loss rate of the alloy was calculated,and the micromorphology of the corroded surface was observed by using the deep field microscope.The electrochemistry test of magnesium,calcium and zinc alloy samples was carried out by electrochemical workstation.The corrosion solution is Hanks simulate body fluids.The corrosion resistance of magnesium alloy was further observed by comparing the corrosion potential and self-corrosion current density of five kinds of magnesium calcium zinc alloys.The friction and wear test of magnesium calcium zinc alloys were carried out by Rtec friction and wear testing machine.Then the worn surface was scanned with a white light interferometer to observe the 3D microstructure of the worn surface of the alloy sample.It is concluded that Alloy IV has the best corrosion and wear resistance,with a self-corrosion potential of-0.931V,a self-corrosion current of 2.477×10-4A·cm-2,and a wear rate of 0.036%.Then milling experiments were carried out to analyze the effect of different cutting parameters on the roughness and residual stress of the machined surface.Three factor and four-level orthogonal milling experiments were carried out on magnesium alloy samples with different cutting speeds,feed per tooth and cutting depth.It found that the critical degree of cutting factors affecting surface roughness is in order:feed per tooth,radial cutting depth,cutting speed.The cutting speed,feed per tooth and radial cutting depth are the essential factors that influence the residual stress on the machined surface.The mathematical prediction models are established,and the model formulas are verified by experiments. |
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