Chunxiang Xu

The effect of extrusion on the microstructure, mechanical property, corrosion behavior, and in vitro biocompatibility of as-cast Mg-1.5Zn-1.2Y-0.1Sr (wt.%) alloy was investigated via tensile tests, electrochemical methods, immersion tests, methylthiazolyl diphenyltetrazolium bromide (MTT), and analytical techniques. Results showed that the as-cast and as-extruded Mg-1.5Zn-1.2Y-0.1Sr alloys comprised an α-Mg matrix and Mg₃Y₂Zn₃ phase (W-phase). In the as-cast alloy, the W-phase was mainly distributed at the grain boundaries, with a small amount of W-phase in the grains. After hot extrusion, the W-phase was broken down into small particles that were dispersed in the alloy, and the grains were refined considerably. The as-extruded alloy exhibited appropriate mechanical properties that were attributed to refinement strengthening, dispersion strengthening, dislocation strengthening, and precipitation strengthening. The as-cast and as-extruded alloys exhibited galvanic corrosion between the W-phase and α-Mg matrix as the main corrosion mechanism. The coarse W-phase directly caused the poor corrosion resistance of the as-cast alloy. The as-extruded alloy obtained via hydrogen evolution and mass loss had corrosion rates of less than 0.5 mm/year. MTT, high-content screening (HCS) analysis, and cell adhesion tests revealed that the as-extruded alloy can improve L929 cell viability and has great potential in the field of biomedical biodegradable implant materials.

The effect of Sr on the microstructure of Mg–Zn–Zr alloys was investigated by means of scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. An immersion experiment and electrochemical experiment were designed to study the effect of Sr on the corrosion performance of the alloys. The results show that the addition of Sr promotes the formation of Mg₁₇Sr₂ phase in the alloy, and this stripe phase appears at the alloy grain boundaries. With the increase in Sr content, a network structure is formed at the grain boundary, creating a corrosion barrier to prevent further corrosion of the alloy. The study found that Mg-4Zn-0.4Zr-1.0Sr alloy has the best corrosion performance.

The effect of Al microalloying on microstructure and corrosion behaviors of as‐cast Mg–6Zn–8.16Y–2.02Mn is investigated. Microstructural characterization reveals that Al addition can refine grain and lead to the formation of Al(Y, Zn) phase. When a 0.3 wt% Al is added, the alloy exhibits the lowest weight loss rate of 0.99 mm/Y and displays relatively uniform corrosion morphology. However, alloys with more Al addition present localized corrosion on the surface. It results from more W phase (Mg₃Zn₃Y₂) and a little long‐period stacking order (LPSO) phase along the grain boundary. Electrochemical tests are also used to rationalize the corrosion behaviors observed in weight loss. In conclusion, the decrease in corrosion rate is due to grain refinement, optimal quantification of Al(Y, Zn) with short‐rod shape and LPSO phase.

The previous study conducted on the as-cast Mg-2Y-1Zn-0.6Zr alloy showed that the tensile strength, yield strength and elongation of the as-cast alloy were 245 MPa, 135 MPa and 14.4%, respectively. In order to further explore the potential of the material, the hot extrusion process of variable temperature (250 °C, 300 °C and 350 °C) was carried out on the basis of the as-cast alloy. After hot extrusion, the mechanical properties of the material have been greatly improved compared with as-cast alloy. The tensile strength, yield strength and elongation of the extruded alloy reached 327 MPa, 322 MPa and 24.9%, respectively. The reason for the significant improvement of material properties is mainly due to the dynamic recrystallization during thermal processing, which greatly fines the grains of as-cast alloy. Moreover, the experimental results shown that the corrosion performance of the alloy after hot extrusion at 300 °C is also optimal.

Herein, as‐cast Mg–2Y–Zn–0.4Zr–0.3Sr alloy's solution treatment at 500 °C in the range of 10–35 h, and then cooled in 80° warm water, is used to investigate its dynamic corrosion behavior and surface morphology using a dynamic stimulating human environment device. Based on the result of corrosion behavior and microstructure, the alloy is mainly composed of α‐Mg and W‐phase (Mg₃Zn₃Y₂) in Mg–2Y–Zn–0.4Zr–0.3Sr alloy. With the increase in solution time, the corrosion resistance is prompted due to the uniform microstructure and second phase dissolved into the matrix. The corrosion resistance of Mg–2Y–Zn–0.4Zr–0.3Sr alloy is increased by enhancing solution time before 25 h due to the uniformly distributed second phases and microstructure, which can alleviate the galvanic corrosion. However, increasing solution time exceeding 25 h reduces the corrosion resistance of the alloy due to coarse grains. Furthermore, twinning, which appears in grains interior after solution treatment, has a positive influence on corrosion resistance. Therefore, the good corrosion resistance of solution‐treated Mg–2Y–Zn–0.4Zr–0.3Sr alloy makes it excellent for biomaterial applications.