| Biomedical Mg sheet reinforced poly lactic acid (PLA)-matrix composites combine the advantages of Mg and PLA. Besides complete degradation and good mechanical properties, the mechanical performance and degradation behavior of the composites can be controlled. In addition, acid-base neutralization process can also occur in the degradation micro-environment. These make the composites have wide application prospect in the field of implanted device in bone fixation. Interface feature and the bonding condition are the key facts that effect the properties of composite material, especially for the implanted materials, interfacial structure not only effect the mechanical properties but also effect the degradation behavior and mechanical property retention of the composite. Therefore, the interface types, structure feature, bonding condition of PLA/Mg composite between different components, and the effects on the performance are the key issues in material research, which have great theoretical and practical significance on optimizing preparation process of composite, evaluating the in vivo degradation behavior and predicting the service life.This paper using the surface-treating technologies of chemical conversion, anodic oxidation and micro-arc oxidation on the surface of magnesium alloy, and the morphology and structure of the oxidation layer after different surface treatments by the technologies of SEM/EDS, XRD and so on. And then PLA/Mg composite was prepared by hot pressing process, the interface bonding feature and strengthening mechanism between the original sheet and the sheets after surface treatments were studied. The mechanical properties of the composite material after different surface treatments were studied by tensile, bending and shear tests. In addition, the in-vitro immersion experiment was performed in SBF to evaluate and analyze the degradation behavior. The main conclusions are as followed:The surface film with different morphology, micro-structure and properties was prepared by chemical conversion, anodic oxidation and micro-arc oxidation respectively, which could improve the performance of interface bonding between PLA and Magnesium alloy. The average shear strength of the bi-materials interface was improved over 300%, and the fracture located in PLA. And the two kinds of anodic oxidation made the shear strength increased 70%, the main damage occurred on the oxidation film.The main bonding force are internal friction force, intermolecular force and mechanical interlocking force. The strengthening mechanism of the anodic oxidation and MAO is the mechanical interlocking because the PLA mounted in the porous structure of MAO coating, and the strengthening of chemical conversion is mainly due to the intermolecular force from wetting adsorption and electrostatic adsorption between PLA and conversion film containing fluorine.The mechanical properties of the composite material decreased with the extended immersion time. The cracks on PLA surface, the degradation of PLA, the corrosion of oxidation film on Magnesium alloy sheet surface and the decrease of interface bonding force mainly leaded to the decrease of the bending properties after immersion. Through the result of weight loss, viscosity-average molecular weight, the pH change, the rule of H2 release and the analysis of corrosion morphology, it was found that both the PLA and surface film protected the matrix Magnesium alloy effectively, only the slight corrosion occurred on the Magnesium sheet, and the reducing interface bonding force was the main reason that resulted in the failure of the composite material. |
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