Microstructure and modification of Nd and Zn trace elements in a Mg-Zn-Y-Nd vascular alloy stent

Xueli LU; Xinliang YAO; Yanming LI

ABSTRACT

BACKGROUND:

With the continuous development of materials science, magnesium alloy vascular stent materials have become a hot research. Because of the mechanical properties and biocompatibility of commercial magnesium alloy, it is difficult to meet the requirements of vascular stents. Therefore, effective measures to improve the sten's surface properties and comprehensive performance become the focus of research.

OBJECTIVE:

To study the histology and surface modification of vascular stents in rapidly solidified Mg-Zn-Y-Nd alloy.

Methods:

The low-zinc Mg-2Zn-0.2Y alloy with good mechanical properties and corrosion resistance was selected as the basic material, and Nd and Zn elements were added to refine the alloy stents. After the microstructure of the stent was extruded, the surface modification of the stent was completed and the comprehensive properties of the alloy were improved. The new magnesium alloy for the stent was obtained and the stent surface was modified. The metallographic microstructure, scanning electron microscopy and radiological analysis were used to study the microstructure and mechanical properties of the prepared stents. The mechanical properties of the stents were investigated by hardness and tensile tests.RESULTS AND

CONCLUSION:

(1) Metallographic microstructure results showed that when Y elements were not added, the second phase of the magnesium alloy was rod-shaped, and there were a few granules embedded in the matrix. After addition of 0.5% Y elements, in the second phase of the magnesium alloy stent, the shafts were significantly reduced in number, and granules were increased in number and evenly distributed in the body. After the addition of 1% Y,the second phase number increased, a large number of dendrites were visible in the grains, and discontinuous rods existed in the second phase. After the addition of 1.5% Y, the second phase was rod-shaped, with mixture of large and local dendrites in the alloy. (2) X-ray diffraction test

results:

Mn-Zn-0.5Nd alloy and Mn-Zn-1.0Nd alloy contained the same phases (Mg4Zn7 and (Nd, Y) 2Zn17 phase). When the concentration of Nd increased to 1%, the new MgZn2 phase appeared in the alloy. (3) SEM & EDS test results of modified magnesium alloy showed that after magnesium alloy modification, the second phase contained Zn, Nd and Y elements, and their contents were very close. EDS analysis showed that after the addition of Zr elements, the level of Zn elements in the lamellar second phase decreased significantly, and the level of Nd and Y elements increased, indicating a more stable performance. (4) Micro-hardness test results showed that with the increasing of the content of magnesium alloy, the alloy microhardness increased. (5)Tensile test results showed that the tensile strength and yield strength of the Mg-Zn-Y-0.5Nd-Zr stent were significantly higher than those of Mg-Zn-Y-0.5Nd, Mg-Zn-Y-1.0Nd,Mg-Zn-Y-1.0Nd-Zr stents (P < 0.05); and the elongation at break of Mg-Zn-Y-0.5Nd-Zr and Mg-Zn-Y-1.0Nd-Zr stents was significantly higher than that of Mg-Zn-Y-1.0Nd and Mg-Zn-Y-0.5Nd stents (P < 0.05). To conclude, with Mg-2Zn-0.2Y as core materials, the material modification could be completed by the addition of Nd and Zn elements, and the surface modification could be implemented by extruding and refining the stent microstructure. The modified material has excellent properties.