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In recent years, more attention to unique and complex structures, such as nature-inspired and porous structures for medical applications, has been strongly developed. Open-cell porous metal-based ones display more benefits than rigid ones since they facilitate the transformation of load between the bone and the implants and avoid the phenomenon of stress shielding and bone resorption. By being biodegradable and non-toxic, as well as having lower density and mechanical properties close to those of natural bone, Mg and its alloys are considered promising materials for porous scaffolds. However, a high corrosion rate is the main drawback of Mg alloys. The porosity of porous structures can also worsen it as it enhances the surface area exposed to the corrosive solution and negatively impacts the performance of porous structures, that these issues have not been addressed in detail so far. Since fabrication methods of Mg-based scaffolds can significantly affect the porosity-related properties (e.g., porosity percentage, type, size, and geometry) and, consequently, scaffolds' mechanical behavior and corrosion resistance, this paper reviews and compares the fabrication methods of porous structures and how they affect the resultant properties. However, among different methods, due to the expansion of additive manufacturing as a novel and exciting manufacturing technique, the paper's central focus is on using additive manufacturing in biomedical applications, discussing its advantages over other techniques. The effect of geometrical parameters on mechanical properties and corrosion rate, which strongly affects bio-application, are also given. Moreover, different strategies are briefly introduced for tailoring the high corrosion rate of Mg and its alloys, such as alloying elements and coatings. However, there is still less information regarding the additive manufacturing of porous Mg scaffolds and the optimum way of controlling the corrosion rate of Mg-based parts. [ABSTRACT FROM AUTHOR]

Layered double hydroxide (LDH) films have attracted extensive attention in Mg alloy anti-corrosion due to their unique physical barrier function and ion exchange performance. However, most of the LDH films on Mg alloy have problems of harsh preparation conditions, poor anti-corrosion stability, and poor adhesion. In this paper, a typical Li–Al-alanine (Ala) LDH film has been successfully prepared on AZ91D Mg alloy surface under milder conditions using multi-arc ion plating and in-situ dipping for the first time. Then an improved vacuum impregnation further modified the Li–Al-Ala LDH film in an ethanol solution of stearic acid (SA) to improve its protective stability. The potentiodynamic polarization curves and electrochemical impedance spectra (EIS) showed that the Li–Al-Ala LDH/SA film's corrosion resistance is more than three orders of magnitude higher than that of the blank Mg alloy in 3.5 wt% NaCl, showing a highly increased corrosion resistance. The long-term immersion experiments found that the surface structure and corrosion resistance of the Li–Al-Ala LDH/SA film did not change much after immersion in 3.5 wt% NaCl for 432 h. The bonding force between the film and the Mg alloy substrate can reach grade 0 based on the standard from International Standardization Organization (ISO). And the hydrophobicity of the film can remain stable with the water contact angle (WCA) being steady at about 140° after a certain distance of external abrasion, showing excellent mechanical wear resistance. The study provides a new milder approach to fabricating superhydrophobic LDH films with durable anti-corrosion resistance, good adhesion, and mechanical stability on Mg alloy surface. [ABSTRACT FROM AUTHOR]

Various electrochemical techniques were used to study the corrosion behaviour of the CNT-reinforced NiAl alloys under NaCl and Na2SO4 environments. The potentiodynamic polarization curves revealed activation Tafel behaviour when the NiAl alloy specimens were immersed in NaCl solution while passivation followed by slight development of transpassivation resulted under Na2SO4 environment. The reinforcement of pure NiAl alloy with up to 1.0 wt.% CNT increased the corrosion rate from 0.10 to 0.63 mm/yr under NaCl environment, while under Na2SO4 environment, the corrosion rate increased from 0.04 to 0.12 mm/yr. The observed increase in corrosion rate with an increase in CNT reinforcement (under both NaCl and Na2SO4 environments) suggested that the reinforcement of NiAl alloys with CNT reduced the corrosion resistance of NiAl. The X-ray diffraction analysis revealed that the corrosion products consisted of oxides including Al2O3 under NaCl environment, while scanning electron microscope analysis showed a porous passive layer on the surface of the alloy specimens immersed in Na2SO4 solution. [ABSTRACT FROM AUTHOR]

The present study aims to collect data, compare results and assess techniques used for improving corrosion resistance and mechanical properties of biodegradable Mg alloys for fixation elements and orthopedic applications. A general description of biomaterials used for orthopedic implants is performed, including non-bioabsorbable materials. Different methods for reducing the corrosion rate in Mg alloys are researched, and the efficiencies are assessed. After evaluating different techniques, surface modification is found to be the most promising technique to reduce the corrosion rate with an efficiency of 85%. Regarding the Mg alloying agents, Zn is considered as the best candidate to improve the corrosion response and biocompatibility of the Mg. [ABSTRACT FROM AUTHOR]

Many engineering structural parts, such as internal gear pumps, worked in high-salt and high-temperature environments. The material (40Cr) of the parts in the pump failed due to severe wear and corrosion. To improve the wear resistance and corrosion resistance of 40Cr, the FeCoNiCrMox (x = 0, 0.3, 0.6, 0.9, 1.2) HEAs coatings were deposited on the surface of 40Cr by laser cladding technology, and the phase structure, microstructure and hardness of the coatings were investigated. In addition, friction and wear tests, electrochemical tests and neutral salt spray tests were conducted to investigate the effect of Mo content on the wear resistance and corrosion resistance of the coatings. The results showed that the phase structure of the FeCoNiCrMo0 coating was the FCC phase, and the phase of the FeCoNiCrMox (x = 0.3, 0.6, 0.9, 1.2) coatings were composed of the FCC phase and σ phase. The Mo element was enriched in interdendrite. With the increasing content of Mo elements, solid solution strengthening, fine grain strengthening, and second phase strengthening occurred in the coatings, which led to the increased hardness and wear resistance of the coatings. The FeCoNiCrMo1.2 coating had the best wear resistance. In the 3.5%NaCl solution, the corrosion resistance of the coatings was better than that of the substrate. With the increase of Mo content, the corrosion potential of the coatings drifted positively, the corrosion current density decreased, and the corrosion resistance increased. However, with excessive Mo element content, the σ phase will precipitate, leading to galvanic coupling corrosion of the coatings and reducing the corrosion resistance. Because the FeCoNiCrMo0.9 coating had the highest corrosion potential and the lowest corrosion current density. Therefore, it had the best corrosion resistance. The neutral salt spray test result also showed that the corrosion resistance of the FeCoNiCrMo0.9 coating was the best. [ABSTRACT FROM AUTHOR]

The intergranular corrosion (IGC) resistance of age-hardening Al–Mg–Si–Cu alloys is closely related to the precipitation behavior adjacent to grain boundaries. In this study, we proposed to regulate the interaction of solute atoms and solute partitioning of Zn-containing Al–Mg–xSi–Cu alloys by introducing dislocations, which can synergistically decorate the intergranular and intragranular precipitation behavior. Consequently, the continuity of grain boundary precipitates and width of solute-depleted precipitate-free zones are inhibited accompanied with high number density or coarse precipitate in the matrix. As a result, the IGC resistance is greatly improved without strength and ductility loss, and the related mechanism has been proposed. [ABSTRACT FROM AUTHOR]