BACKGROUND: As a metal internal fixation material, magnesium alloy has more unique advantages, such as biodegradability and elastic modulus. The elastic modulus of magnesium alloy is similar to the compact bone,which is enough to avoid stress-shelter effect. However, biological activity represents bonding ability with the bone in the body for fracture fixation materials, which is of great significance for studies on new kinds of magnesium alloys.OBJECTIVE: To observe the microstructure of Mg-Zn-Gd alloys and to analyze the corrosion products on the material surface after immersed in simulation body fluid.METHODS: The Mg-Zn-Gd alloys were manufactured by the method of fusion casting. Scanning electron microscope with spectrometer was applied to observe microstructure and distribution of precipitated phase and corrosion products of Mg-Zn-Gd alloys in simulated body fluid.RESULTS AND CONCLUSION: The Mg-Zn-Gd alloy was composed of α-Mg solid solution containing Gd and Zn elements and eutectic structure. The eutectic structure was almost feathery, oval-shaped, herringbone-shaped and strip-shaped along the grain boundary. The main ingredients of eutectic structure included Mg, Zn and Gd elements.Deposition layer was composed of O, Mg, Ca and P elements on the surface of Mg-Zn-Gd alloy after 72 hours soak in Hank's solution. X-ray diffraction analysis showed that film layer contained Mg(OH)2 phase, which promoted calcium salt deposition and reduced the corrosion rate. So Mg-Zn-Gd alloy can obtain better biological activity.

BACKGROUND:Magnesium al oy as a fracture fixation material has mechanical properties similar to the bone, good biocompatibility and biodegradability, but its rapid degradation rate in body fluids becomes a clinical bottleneck. Therefore, the use of surface treatments to improve its corrosion resistance is important.
OBJECTIVE:To use magnetron sputtering technology and alkali heat treatment technology in the preparation of coating characterized as both corrosion resistance and biological activity.
METHODS:First, we prepared Mg-Zn-Mn al oy using the smelting technology, and prepared a dense coating on the al oy surface by the magnetron sputtering technique. Then, we processed the coating surface using an alkaline solution, and studied the corrosion behavior of the coating by use of simulated body fluid experiments. We speculated the biological activity of the coating by measuring the content of calcium and phosphorus from the surface products.
RESULTS AND CONCLUSION:We prepared the coating, which had both corrosion resistance and biological activity, on the surface of magnesium al oy by use of magnetron sputtering and alkali heat treatment technology. After soaking in the simulated body fluid for 24 hours and 168 hours, the deposition of the coating surface contained Ca, P products. Ca/P ratios were 1.54 and 2.11, respectively, closed to the bone-phosphate Ca/P ratio. The coating surface formed 5-10μm pitting after 24 hours of immersion, and the pitting grew up with the immersion time. The pitting was enlarged to 100-800μm after 168 hours.