In this study, Mg-8Sn-2Zn-2Al (TZA822) alloys with varying Mg₂Sn contents prior to extrusion were obtained by different pre-treatments (without and with T4), and the strengthening response related to micro and nano-size Mg₂Sn precipitates in the extruded TZA822 alloys was reported. The results showed that the morphology of nano-size Mg₂Sn precipitates exhibits a significant change in basal plane from rod-like to spherical, owing to the decrement in the fraction of micro-size particles before extrusion. Meanwhile, the spherical Mg₂Sn precipitates provided a much stronger strengthening effect than did the rod-like ones, which was ascribed to uniform dispersion and refinement of spherical precipitates to effectively hinder basal dislocation slip. As a consequence, the extruded TZA822 alloy with T4 showed a higher tensile yield strength (TYS) of 245 MPa, ultimate tensile strength (UTS) of 320 MPa and elongation (EL) of 26.5%, as well as a lower degree of yield asymmetry than their counterpart without T4. Detailed reasons for the strengthening effect were given and analyzed.

Magnesium (Mg) alloys have received increasing interest in the past two decades as biomaterials due to their excellent biological compatibility. However, the corrosion resistance of Mg alloys is relativity low which limits their usage in degradable implant applications, and controlling the corrosion resistance is the key to solving this problem. This review discusses the relative corrosion mechanisms, including pitting, filiform, high temperature, stress corrosion, etc., of Mg alloys. Various approaches like purification (Fe, Ni, Cu, etc.), micro-alloying (adding Zn, Mn, Ca, RE elements, and so on), grain refinement (severe plastic deformation, SPD, etc.), and surface modifications (various coating methods) to control corrosion and biological performance are summarized. Moreover, the in vivo implantations of Mg alloy vascular stents and the issues that have emerged based on the reports in recent years are introduced. It is recommended that corrosion mechanisms should be further investigated as there is no method that can remove all the impurities and a new purification approach needs to be developed. The concentration of micro-alloy elements should be carefully controlled to avoid superfluous compounds. Developing new continuous SPD methods to achieve fine-grained Mg alloys with a large size scale is necessary. The development of a multifunctional coating could also be considered in controlling the Mg degradation rate. Moreover, the research trends and challenges in the future of Mg biomaterials are proposed.

An I-phase containing Mg-8Sn-6Zn-2Al (wt %; TZA862) alloy was fabricated and subjected to different number of passes of equal channel angular pressing (ECAP) processing at 300 °C. The results showed that the alloys exhibited a bimodal microstructure, which consisted of fine dynamically recrystallized (DRX) grains and coarse non-DRX grains. When increasing the number of ECAP passes from 2 to 6, the fraction of DRX grains and the dispersed second phase particles subsequently increase. However, the fraction and particles then decrease once the number of ECAP passes increases to 8. After 6 ECAP passes, remarkable grain refinement was achieved and increasing the number of passes to 8 cannot further refine the microstructure. Furthermore, the alloys having undergone ECAP exhibited a strong ED-tilted texture, the intensity of which increased with an increase in the number of ECAP passes. The ultimate tensile strength (UTS; 338 MPa) and elongation (El.; 14.2%) of the alloy processed with 6 ECAP passes were considerably higher compared to those of the other materials that had undergone ECAP. These significant enhancements were attributed to extensive grain boundary strengthening, precipitation strengthening and a higher work-hardening capacity.

Employing a suitable crystal structure can significantly modify the electrochemical performances of materials. Herein, hydrogenated TiO2 nanotube arrays with orientation and different rutile/anatase ratio were fabricated via anodisation, high-temperature annealing and electrochemical hydrogenation. The crystal structure was determined by TEM and X-ray diffraction pattern refinement of whole powder pattern fitting. Combined with the model of anatase to rutile transformation and the characterisation of crystal structure, the effect of phase transition on the super capacitive properties of oriented hydrogenated TiO2 nanotube arrays was discussed. The results suggested that the anatase grains were characterised by orientation in direction with plate crystallite and stacking vertically to the substrate resulting in excellent properties of electron/ion transport within hydrogenated TiO2 nanotube arrays. In addition, the specific capacitance of oriented hydrogenated TiO2 could be further improved from 20.86 to 24.99 mF cm−2 by the partial rutile/anatase transformation due to the comprehensive effects of lattice disorders and rutile, while the good rate performance and cyclic stability also retained.