Study On The Magnesium Matrix Composites Reinforced By Biodegradable Ca-P Ceramic Particles

Magnesium and its alloy have potential to be bone repair devices, stents,hemostatic clip and other biodegradable implant materials due to its light weight,appropriate mechanical property, biological safety and degradable property. However,magnesium and its alloy exhibited a high corrosion rate in the physiological environment containing Cl-, thus lead to the rapid loss of mechanical strength,quickly increase of p H value and the mass release of hydrogen.therefore, above problems are the main obstacles of magnesium alloy application in clinical. To slove this key problem, Ca-P bio-ceramic particles were used to be refinement in magnesium matrix composite in this paper, which can refine grain size, enhance corrosion resistance and mechanical properties.In this paper, pure Mg with different grain size was prepared by controlling the cooling rate and Mg-30%Ca alloys were prepared by the vacuum smelting to research effect of grain size and β-phase on corrosion behavior. The high shear melting technology was used for preparing 1HA/Mg-3Zn-0.2Ca composites and1β-TCP/Mg-3Zn-0.2Ca composites which were characterized by optical microscope(OM), scanning electron microscope(SEM), transmission electron microscope(TEM)and X-ray diffraction analysis(XRD). The corrosion mechanism of the composites were studied by electrochemical test. And the influence of reinforcement addition on the hot deformation behavior of Mg-Zn-Zr alloys was studied by the hot compression experiment. The as-cast composites were deformed by equal channel angle extrusion(ECAE), and the effect of ECAE to microstructure, texture, and electrochemical behavior was researched. The main conclusions are as follows:1. Grain refinement can increase the corrosion sensibility of magnesium matrix materials.The magnesium matrix materials which have high density of grain boundaries can produce passivated layer that has a stronger effect during the immersion test.2. To the Mg-30wt%Ca alloys, Mg2 Ca phase was preferentially corroded as the anode in the matrix, which was different with other β-phase. The immersion test(90days) of Mg-30%Ca alloys showed that some non-degradable corrosion products which were considered as encapsulation structure have appeared in the later stage of the degradation.3. Comparing to the HA-addition, the β-TCP-addition can more effectively refine grain, due to a smaller mismatch. The HA or β-TCP-addition can enhance passivation ability for magnesium alloys, which increase their corrosion resistance.4. The deformation mechanism for Mg-3Zn-0.8Zr alloys is chiefly dislocation-control climb when the deformation temperature is low than 573 k. The deformation mechanism partly transform to grain boundary slip when the temperature is higher than 623 K, which can be inhibited by HA-addition. The HA-addition also can enhance the peak stress during the hot compress, due to inhibition for the dislocation motion or grain refinement.5. The grain and agglomerate size of 1HA/Mg-3Zn-0.2Ca can be refined by ECAE, and The ED plane parallel to the {002} during ECAE, which can increase the corrosion resistance of Mg-based materials,due to the highest binding energy.